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A Comparison of Material Quantities Estimates to Onsite Material Use for Bridge Infrastructure Projects
by
Bolaji Akinola Olanrewaju
A thesis submitted in conformity with the requirements for the degree of Master of Applied Science
Graduate Department of Civil and Mineral Engineering University of Toronto
© Copyright by Bolaji Akinola Olanrewaju (2020)
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A Comparison of Material Quantities for Highway Bridge Projects:
Detailed Design Stage vs Construction Stage
Bolaji Akinola Olanrewaju
Master of Applied Science
Department of Civil and Mineral Engineering
University of Toronto
2020
Abstract
Material estimates play a crucial role in predicting project cost, project duration, and embodied
CO2e emissions for construction projects. Several factors that occur during the implementation
stage introduce discrepancies in material quantity estimates, which misinform critical decisions
that affect project delivery. There is, however, a limited understanding of the variability in material
estimates for construction projects, and its impacts on other estimating processes. This thesis
compares construction stage quantities to detailed design estimates for eighteen Canadian-based
bridges to quantify the variability in material quantities and to determine the driving factors.
Results show a 3%-85%, 8%-23%, 5%-19%, and 11%-17% increase in concrete, rebar, structural
steel, and asphalt quantities between estimates and onsite use. The results of this thesis inform our
understanding of design estimates and their interpretation. Adjusting for the discrepancy between
estimates and onsite measurements and targeting the driving factors will reduce environmental
impacts, minimize cost overruns and limit delays.
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Acknowledgements
First, I am incredibly grateful to my supervisors, Professor Shoshanna Saxe and Professor Daman
Panesar for the opportunity to pursue my Master’s degree, and for their guidance, kindness,
patience and encouragement throughout my graduate study. Thank you!
I am also thankful to my research sponsors, EllisDon, Looby, WSP, BASP, NSERC, and the
Ontario Centres of Excellence. My special gratitude to Jonathan Waltr, Jon Vallieres and the
Looby staff for their time and commitment to this research, which has been very much appreciated.
My research team, The InfraGHG Group, thank you all for the continued support. Special thanks
to our project manager Mel Duhamel for efforts in obtaining the data used for this study, and for
handling correspondence with our industry partners.
I am most thankful to my parents, siblings, my uncle, aunt and cousins in the US for their love,
constant encouragement and support. Finally, I thank my friends for all their support and
memories.
Glory to God!
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Table of Contents
Acknowledgements ........................................................................................................................ iii
Table of Contents ........................................................................................................................... iv
List of Tables ................................................................................................................................. vi
List of Figures ............................................................................................................................... vii
Introduction .................................................................................................................................1
1.1 Background ..........................................................................................................................1
1.2 Research Objectives and Contributions ...............................................................................4
1.3 Outline of the Thesis ............................................................................................................5
Literature Review ........................................................................................................................7
2.1 The Need for Material Quantity Estimates in the Construction Industry ............................7
2.2 Factors Driving Uncertainty and Variability in Estimates .................................................10
2.3 Knowledge Gap .................................................................................................................12
Methods .....................................................................................................................................14
3.1 Data Source and Description .............................................................................................14
3.2 Estimating Material Quantities for the Design and Construction Stages ..........................18
3.2.1 Conceptual Design Stage .......................................................................................18
3.2.2 Preliminary Design Stage ......................................................................................19
3.2.3 Detailed Design Stage ............................................................................................19
3.2.4 Construction Stage .................................................................................................21
3.3 Comparison of Material Quantities between the Design and Construction Stages ...........22
3.3.1 Comparison of Detailed Design Estimates to Construction Stage Material Use ...22
3.3.2 Comparison of Material Quantities between the Four Main Stages of a Bridge
Project ....................................................................................................................23
Discussion of Findings ..............................................................................................................24
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4.1 Comparison of Material Quantities Between the Detailed Design Stage and
Construction Stage .............................................................................................................24
4.1.1 Comparison of Concrete Quantities .......................................................................24
4.1.2 Comparison of Reinforcing Steel (Rebar) Quantities ............................................36
4.1.3 Comparison of Structural Steel Quantities ............................................................37
4.1.4 Comparison of Asphalt Quantities .........................................................................38
4.2 Comparison of Material Quantities across the Four Main Design and Construction
Stages .................................................................................................................................39
4.2.1 Evolution of Concrete Quantities...........................................................................39
4.2.2 Evolution of Reinforcing Steel (Rebar) Quantities ................................................42
4.2.3 Evolution of Structural Steel Quantities ................................................................43
4.2.4 Comparison of Results with GHG Results Available in Literature .......................45
Conclusions ...............................................................................................................................46
5.1 Recommendations for the Construction Industry ..............................................................48
Limitations and Future Research ..............................................................................................50
References ......................................................................................................................................51
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List of Tables
Table 2-1: The role of material quantity estimates of project stakeholders .................................... 8
Table 2-2: The four main stages of a bridge project ....................................................................... 9
Table 2-3: Causes of variability in estimates for specific case studies ......................................... 11
Table 2-4: Most important factors driving variability in the construction projects ...................... 11
Table 3-1: Composition of the highway bridge case studies regarding bridge span and width,
bridge type, completion status, delivery method, and availability of data ................................... 15
Table 3-2: Design and construction documents obtained from the contractors and their level of
completion..................................................................................................................................... 17
Table 3-3: Mass per unit length value of each girder type ........................................................... 20
Table 4-1: The construction stages of the In-progress bridge case studies................................... 27
Table 4-2: Factors driving additional onsite concrete use ............................................................ 32
Table 4-3: Factors responsible for additional mass concrete use ................................................. 33
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List of Figures
Figure 1-1: Percentage of bridges in need of rehabilitation or replacement ................................... 2
Figure 3-1: Structural components of a typical bridge ................................................................. 23
Figure 4-1: Comparison of concrete quantities between the detailed design stage and the
construction stage of the completed case studies .......................................................................... 25
Figure 4-2: Comparison of concrete quantities between the detailed design stage and the
construction stage for the In-progress bridge case studies............................................................ 26
Figure 4-3: Completed Projects - Comparison of substructure concrete quantities between the
detailed design stage and the construction stage........................................................................... 29
Figure 4-4: Completed Projects - Comparison of superstructure concrete quantities between the
detailed design stage and the construction stage........................................................................... 29
Figure 4-5: In-Progress Projects: Comparison of substructure concrete quantities between the
detailed design stage and the construction stage........................................................................... 30
Figure 4-6: Change in substructure and superstructure concrete quantities between the detailed
design stage and the construction stage ........................................................................................ 30
Figure 4-7: Contribution of factors driving additional onsite concrete use to total substructure
concrete increase ........................................................................................................................... 33
Figure 4-8: Contribution of factors to additional onsite concrete use .......................................... 35
Figure 4-9: Comparison of reinforcing steel quantities between the detailed design stage and
construction stage.......................................................................................................................... 36
Figure 4-10: Comparison of structural steel between the detailed design stage and construction
stage .............................................................................................................................................. 38
Figure 4-11: Comparison of asphalt between the detailed design stage and construction stage .. 39
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Figure 4-12: Evolution of Concrete Quantities for B4 ................................................................. 40
Figure 4-13: Evolution of Concrete Quantities for the Substructure of B8 .................................. 41
Figure 4-14: Evolution of Reinforcing Steel Quantities for B8 .................................................... 43
Figure 4-15: Evolution of Structural Steel Quantities for B8 ...................................................... 44
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Introduction
This thesis investigates the material quantity differences between onsite material use and estimates
to quantify the uncertainty in material quantity estimates for bridge infrastructure projects in
Canada.
1.1 Background
Bridges are critical components in Canada's transportation network. They are essential for
personal mobility, connect regions and communities, and are vital to Canada's economic
productivity (Transport Canada, 2019). There are over 80,000 highway bridges in Canada, and
on average, 11 million commuters travel over some of Canada's busiest bridges annually
(Government of Canada, 2017). However, over 40% of highway bridges in Canada were built
more than fifty years ago and are nearing the end of their service life (National Research Council
Canada, 2015; Canadian Infrastructure Report Card, 2019). A significant number of these
bridges are structurally deficient, i.e., their structural components are defective due to damage or
deterioration, with about 10,000 highway bridges needing urgent rehabilitation or replacement
(Palu and Mahmoud, 2019).
Figure 1-1 displays the aggregated percentage of Canadian bridges approaching the end of their
service life and requiring immediate attention (Statistics Canada, 2016). Thus, it is expected that
many of these bridges will need to be restored or replaced to meet current and future traffic
demands, as well as to sustain trade networks which accounts for more than 60% of Canada's total
revenue (The Canadian Chamber of Commerce, 2017; Fenn et al., 2019).
In addition to the fact that infrastructure is ageing and warrants repair or replacement, several
economic and environmental indicators suggest there will be a significant boom in bridge
construction activities over the next 30 - 50 years (National Research Council Canada, 2015;
Ministry, 2017; Steer Group, 2019). The most prominent factor is increasing traffic volumes
(Jackson, 2019). The projected increase in Canada's population by about 50% (from 37.1 million
inhabitants to 55.2 million inhabitants) from 2018 to 2068 will intensify the need to improve
regional connectivity and expand current transportation infrastructure network (The Canadian
Chamber of Commerce, 2017; Infrastructure Canada, 2018; Statistics Canada, 2019).
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Figure 1-1: Percentage of bridges in need of rehabilitation or replacement
% of bridges in need of rehabilitation or replacement
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Other factors indicating significant bridge construction work in the future include further
deterioration of existing bridge infrastructure due to climatic conditions (freezing and thawing,
and chloride exposure), and the influences of future climate change impacts (e.g. floods, frequent
heatwaves, and excessive rainfall) on the safety and performance of existing bridges (Wright et
al., 2012; Public Sector Digest, 2015; Palu, 2019). Also, the lack of routine bridge maintenance
due to inadequate funding and considerable bridge maintenance backlogs further exacerbate
deterioration, resulting in the need to replace the bridges in the future (Ministry of Transportation
Ontario, 2009).
The rehabilitation and replacement of existing bridges, as well as the construction of new bridges
due to the expansion of the current infrastructure network, have the potential for significant
environmental and financial impacts through the use of materials and fuel in construction. The
construction industry, of which the bridge industry is a part of, consumes 50% of global resources
annually (OECD, 2019). It also contributes to the depletion of commonly used construction
materials (Graham, 2017). For example, the shortage of sand and gravel used for the erection of
roads and bridges has been attributed to the increasing rate of construction and urbanization
(Graham, 2017; Beiser, 2019; Brown, 2019). Also, the production processes of the most widely
used bridge construction materials, i.e., concrete, steel, and asphalt, contribute to between 12% -
15% of global anthropogenic CO2 emissions (European Commission, 2016; Lehne and Preston,
2018), and account for 75% - 85% of the total embodied energy of bridges (Du, Safi and Pettersson,
2014; Krantz et al., 2015). Additionally, the bridge construction industry generates a significant
amount of construction waste. In 2016, asphalt and concrete from roads and bridges were
responsible for about 45% of the total construction and demolition debris generated in the U.S.
(U.S. Environmental Protection Agency, 2019).
Furthermore, bridge projects can cause substantial financial strains on federal and provincial
resources, as well as on taxpayer's money (Palu and Mahmoud, 2019). They often experience cost
overruns, with the actual cost being about 34% higher than cost estimates (Flyvbjerg, Holm and
Buhl, 2007; Antoniou, Konstantinidis and Aretoulis, 2016; Dimitriou, Marinelli and Fragkakis,
2018).
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For these reasons, it is encouraged that future bridge projects are designed and constructed in ways
which mitigate their resource consumption, waste generation, financial impacts, and
environmental impacts.
1.2 Research Objectives and Contributions
A first step to mitigating the impacts of bridge construction is to understand material use within
the construction industry. Material quantity estimates are essential in the construction industry
(Antoniou et al., 2018). They are necessary for predicting project cost, labour and equipment
requirements, project duration, and in informing embodied greenhouse gas (GHG) assessments
(Garemo, Matzinger and Robert, 2015; ProEst, 2018; Kiper, 2020). However, several factors that
occur during the construction stage, including design changes due to owners request and differing
site conditions, introduce uncertainty in material quantity estimates (Alaryan, Elshahat and
Dawood, 2014; Desai, Pitroda and Bhavasar, 2015; Albtoosh and Haron, 2017). The uncertainty
in material estimates introduces variability in subsequent estimation processes, which limit efforts
to minimize the aforementioned impacts of the bridge construction industry, and negatively impact
decision making that affect project delivery (Alnuaimi et al., 2010; Choudhry et al., 2017).
Quantifying the variability in material quantity estimates, and understanding the driving factors
can initiate better and comprehensive mitigating solutions to ensure bridge projects are delivered
on-time and under-budget while limiting their environmental impacts. Several authors have
conducted studies to explore the factors causing discrepancies in construction projects across
several countries Asia and Europe (Arain, Assaf and Pheng, 2004; Keane, Sertyesilisik and Ross,
2010; Khoso et al., 2019). There is, however, a limited understanding of the variability in material
quantities estimates for construction projects. Additionally, there is limited research investigating
the factors driving the variability for construction projects across North America.
This thesis compares material quantity estimates at the detailed design stage to onsite material use,
i.e., construction stage material quantities, for eighteen bridge projects. Secondly, this thesis
identifies bridge components and factors responsible for changes in material quantities within the
case studies considered. The bridge construction materials assessed in this thesis are concrete,
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reinforcing steel (rebar), structural steel, and asphalt. These materials were the focus of this thesis
because they are the most widely used bridge construction materials, and also because they
contribute significantly to the cost and environmental impacts of bridge construction (Collings,
2006; Hammervold, Reenaas and Brattebø, 2013; Wang et al., 2015). All eighteen case studies
are located in Canada and are subject to the same bridge code. The case studies comprise nine
prestressed concrete girder bridges, two reinforced concrete bridges, two steel girder bridges, one
post-tensioned concrete bridge, and four structural steel bridges. Eleven of these case studies are
highways crossing over water bodies, while the remaining cross over existing roadways. Seven
of the case studies are recently completed projects as of July 20th 2020, and were constructed in
the last five years. The remaining eleven are ongoing construction projects that are at varying
levels of completion, ranging from superstructure construction to asphalt paving and are all
expected to be completed by early 2021.
Furthermore, using a subset of the case studies where more data was available, this thesis conducts
a preliminary investigation to compare material quantities across the four main bridge design and
construction stages. These stages include the conceptual design stage, the preliminary design stage,
the detailed design stage, and the construction stage. The continuous material quantities
assessment between the four design and construction stages is an attempt at determining the
material quantity impacts of bridges with design and construction development.
The results of this thesis provide information that will inform and facilitate better decision-making
in an uncertain space, to impact the delivery of construction projects positively. The results also
provide information to facilitate the development of other accurate decision support tools
including, cost estimation models, embodied GHG estimation models, and waste generation
models.
1.3 Outline of the Thesis
This thesis is divided into six chapters. Following the introduction in Chapter 1, Chapter 2
identifies existing practices for estimating bridge material quantities in the industry, the factors
driving variability in material quantity estimates and addresses the research gaps. Chapter 3
describes a comprehensive method for analyzing the material quantities between the detailed
design stage and construction stage in this thesis. Also, it describes the process of obtaining
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material quantities for the subset of case studies investigating the evolution of material quantities
across design and construction stages. This chapter also highlights the available data and sources
of supplementary information used in this work. Chapter 4 discusses the findings of the study.
Chapter 5 includes the conclusions and addresses recommendations for the construction industry,
and lastly, Chapter 6 presents research limitations and future work.
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Literature Review
Based on existing literature, this section highlights the need for material quantities estimates, the
factors driving discrepancies in material quantities between the design and construction stages,
and lastly, addresses research gaps.
2.1 The Need for Material Quantity Estimates in the Construction Industry
The estimation of material quantities in the construction industry dates back to the early 19th
century (Canadian Institute of Quantity Surveyors, 2017). During this time, estimations, otherwise
known as quantity takeoffs (QTO)), were done manually by project stakeholders, using
specifications from design drawings to determine the appropriate amount of materials needed by
a project (Popescu, Phaobunjong and Ovararin, 2003; Finch, 2016). The stakeholders responsible
for this process are expected to have a thorough understanding of the construction drawings and
design specifications to produce accurate material quantity estimates (Ramos, 2017). However, in
the mid-2000s, the Architectural-Engineering-Construction (AEC) industry experienced a
significant shift from traditional manual estimations to using several automated takeoff programs
including Autodesk Revit QTO, ProEst, and Navisworks (Azhar, Khalfan and Maqsood, 2012;
ProEst, 2018; Liu, Lu and Peh, 2019). The increasing use of such programs has improved the
efficiency of the estimation process, and reduced estimation errors observed in the manual method
(Golaszewska and Salamak, 2017; Merz, 2019).
Material estimates are vital in the construction industry. They have different levels of importance
to stakeholders involved in a project, i.e., project owner, designers, contractors, and
subcontractors, as summarized in Table 2-1. Estimates vary across the design and construction
stages of bridge projects, which ranges from the conceptual design stage, preliminary design stage,
detailed design stage, to the construction stage, as shown in Table 2-2. They become more accurate
with project development due to the availability of more information (García de Soto, Adey and
Fernando, 2014; Naneva et al., 2020).
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Table 2-1: The role of material quantity estimates of project stakeholders
Source: (Durana, 1999; Watt, 2014; Garemo, Matzinger and Robert, 2015; Marinelli et al.,
2015; Jeong and Gransberg, 2016; Antoniou et al., 2018; Dimitriou, Marinelli and Fragkakis,
2018; ProEst, 2018; QTO Estimating, 2018; Kiper, 2020)
Stakeholder Role of Material Quantity Estimates
Project Owner Provides a holistic view of the project requirements
To effectively allocate a budget within the general financing of the project
Acts as a decision-making tool for determining if the project should be modified, executed
as planned, or abandoned
Provides vital information regarding the construction materials required
Guides the client when choosing the best contractor
Designer Assess the environmental impacts of the bridge design and to ensure bridge designs meet
regulatory requirements relating to greenhouse gas (GHG) emissions
In providing forecasts of construction costs in the pre-planning phases of the design stage
Ensuring that project requirements are met, and design solutions are cost-effective.
Informs the type of contract
Contractor Helps in estimating labour requirements
Informs actual onsite material-use
Develop project milestones
Assists in determining equipment rental costs
Ensures sufficient profit margin
Monitoring and tracking project success
Guides the contractor when agreeing to contractual terms
Guides project bidders when submitting bid proposals
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Table 2-2: The four main stages of a bridge project
Source : (Ma, Chen and He, 2009; Chen and Lian, 2014; Alberta Transportation, 2016; Arjun, 2016; U.S. Department of Transportation, 2016; MEC Bridge Design Engineers,
2017; Multnomah County, 2017; Tang, 2017)
Stage Description
1 Conceptual Design Stage Description of project problem and project objectives Preparation of concept plans
Development of bridge design alternatives
Available information includes bridge width and length, number and types of spans, and material types.
2 Preliminary Design Stage Involves the selection of the best design scheme from the proposed design alternatives
Ascertains the feasibility of the selected bridge concept
Modifications in the stage include: optimization of bridge girders, alteration of girder spacings
3 Detailed Design Stage Involves finalizing all the bridge design details
Design documents are sufficient for the construction of bridge components
Available information includes dimensions and locations of structural members, connections with other members, quantities of rebar.
4 Construction Stage Involves installation of the bridge components using detailed design documents
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However, in construction, very rarely do onsite material quantities align with estimates (Flyvbjerg,
Holm and Buhl, 2007; Cantarelli et al., 2012; Garemo, Matzinger and Robert, 2015). Overrun is a
common occurrence in large infrastructure projects including bridges, and is described as the
difference between the predicted and actual material use (Love et al., 2014; Garemo, Matzinger
and Robert, 2015; Mckinsey & Company, 2015; Institute of Civil Engineers, 2019). Occasionally,
it is caused by the project manager or estimator incorrectly measuring the quantity from the project
drawings and specifications (Netscher, 2015). However, in most cases, it is caused by change
orders initiated at the construction stage either due to client requests, design complexity, change
in project scope or unforeseen site conditions (Chan and Kumaraswamy, 1997; Hameed Memon,
Abdul Rahman and Faris Abul Hasan, 2014; Wang et al., 2015). These factors introduce
uncertainty and variability in material quantity estimates, especially in the design stage, which
causes a ripple effect that propagates to downstream estimating processes, including project cost,
project duration, and embodied GHG assessments (Assaf and Al-Hejji, 2006; Assaf, Hassanain
and Abdallah, 2017; Choudhry et al., 2017).
2.2 Factors Driving Uncertainty and Variability in Estimates
There are a plethora of studies that have been conducted to explore the potential reasons and
causative factors driving uncertainty and variability in estimates in the construction industry (Chan
and Kumaraswamy, 1997; Assbeihat and Sweis, 2015; Jibrin, Muhammad and Labaran, 2020).
Some of these studies highlighted factors specific to a particular case study such as a classroom
building (Alnuaimi et al., 2010), healthcare facility (Keane, Sertyesilisik and Ross, 2010), a road
project, and water transmission project (Alnuaimi et al., 2010), as shown in Table 2-3. Others
explored factors that were particular to project types, i.e. residential projects, transportation
infrastructure, building projects, or general factors for all forms of construction projects, as
outlined in Table 2-4.
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Table 2-3: Causes of variability in estimates for specific case studies
Table 2-4: Most important factors driving variability in the construction projects
Authors
Geographical area Case study
Lack of Coordination between
stakeholders
Errors and omissions in design
documents Differing Site
conditions Change in
project scope Changes due to owners request
(Alnuaimi et al., 2010) Oman Road project x x
(Keane et al., 2010) England Healthcare facility x x x
(Alnuaimi et al., 2010) Oman Water transmission project x x x
(Alnuaimi et al., 2010) Oman Classroom buildings x x
(Alnuaimi et al., 2010) Oman Breakwaters for a seaport x
Authors Geographical
area Structure types
Lack of Coordination
between stakeholders
Insufficient drawing details
Errors and omissions in design
documents Design
complexity
Differing site
conditions
Inadequate contractor experience
Change in project Scope
Weather conditions
Changes due to
owner's request
Lack of contractor
involvement in the design
(Chan and Kumaraswamy, 1997) Hong Kong General x x x x x x x
(Fisk, 1997) U.S.A. Buildings x x x x x x
(Arain et al., 2004) Saudi Arabia Buildings x x x x x x x x
(Wu et al., 2005) Taiwan Transport x x x x x x x x
(Alnuaimi et al., 2010) Oman General x x x
(Keane et al., 2010) England General x x x
(Pourrostam et al., 2011) Malaysia General x x
(Alaryan et al., 2014) Kuwait General x x x x x
(Hameed Memon et al., 2014) Malaysia General x x x x x
(Assbeihat and Sweis, 2015) Jordan General x x ` x
(Desai et al., 2015) India General x x x x x
(Perkins, 2016) U.S.A. General x x x x
(Staiti et al., 2016) Palestine General x x x x x x x x
(Albtoosh and Haron, 2017) Jordan General x x x x x
(Choudhry et al., 2017) Pakistan General x x x x x
(Ali Kamal Balbaa et al., 2019) Egypt General x x x x x x x x x
(Khoso et al., 2019) Pakistan General x x x x x x
(Mohammad and Hamzah, 2019) Malaysia Residential x x x x x
(Tran and Do, 2019) Vietman General x x x x x
(Jibrin et al., 2020 Nigeria General x x x
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Table 2-3 and Table 2-4 show that the most common factors driving variability in the construction
industry and uncertainty in estimates are changes due to owners request, insufficient drawing
details, errors and omissions in design documents, differing site conditions, and change in project
scope.
These two tables suggest the sources of uncertainty and variability in quantity estimates have been
well explored in literature and well understood. However, despite the knowledge that has been
accumulated, little work has been done to investigate and quantify the discrepancies between
onsite material use and estimates due to these driving factors. Additionally, as observed in Table
2-3 and Table 2-4, minimal research studies have investigated the factors driving discrepancies
between design and construction stages for construction projects in North America.
To the authors' knowledge, only two studies in the literature compare detailed design material
quantity estimates to onsite use, i.e., the construction stage, to understand the differences in
material quantities between the two stages. Tang, Cass and Mukherjee, 2013 compared as-planned
estimates and as-built data for a highway reconstruction project in Michigan, U.S.A, and the
authors found a 6% discrepancy in non-reinforced concrete quantities. Similarly, the research
study by Nahangi et al., under review, compared preconstruction estimates obtained from a
Navisworks (a building information modelling software) model, to onsite material-use for a bridge
renewal project in Ontario, Canada. The authors observed a 63%, 31%, and a 171% increase in
concrete, structural steel, and asphalt quantities, respectively. Although very informative, the
limitation of these two studies is that their analyses are based on a single case study, and as a result,
cannot be generalized for other infrastructure types.
2.3 Knowledge Gap
This thesis contributes to the existing literature in two main areas: (1) the discrepancies between
design and construction concerning materials, and (2) factors driving variability in construction
projects. This paper compares the material quantity estimates generated during the tendering stage,
i.e., detailed design stage, to actual onsite material use for bridge construction projects. This thesis
improves on existing studies that have compared onsite material use to estimates by conducting
assessments on eighteen bridge case studies that are all based in Canada. Also, this thesis augments
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our knowledge on the variability and causes of discrepancies in material quantities for construction
projects across North America which is currently limited.
This thesis increases our understanding of the influence of material variability and uncertainty on
subsequent estimation processes that occur during the preconstruction stages of bridge projects.
Additionally, it provides information that can inform the type of adjustments that need to be
incorporated into future estimates to mitigate impacts of inaccurate forecasts before they become
consequences. The results of this thesis will also inform the uncertainty of the decisions made
regarding the projects relating to the material quantities, to allow stakeholders make better
decisions under uncertainty.
Furthermore, using a subset of the case studies where more data was available, this thesis conducts
a preliminary investigation to compare material quantities across the conceptual design stage, the
preliminary design stage, the detailed design stage, and the construction stage. This thesis will
improve our understanding of how design and construction development impacts the material
quantities of bridge construction projects.
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Methods
This chapter describes an empirical approach to estimate the material quantities of eighteen
Canada-based highway bridges at the detailed design stage and construction stage. Concrete,
reinforcing steel (rebar), structural steel, and asphalt are the four construction materials studied in
this thesis. This is because they are the most widely used bridge construction materials, and they
contribute significantly to the cost and environmental impacts of bridge construction (Collings,
2006; Marinelli et al., 2015; Wang et al., 2015; Antoniou et al., 2018; Penadés-Plà et al., 2018).
3.1 Data Source and Description
Eighteen highway bridge case studies are examined in this thesis. All bridges are located within
Canada and are subjected to the same bridge code. The bridge spans and widths of the case studies
range from 29 – 194 m, and 11 – 19 m, respectively. The bridge case studies are composed of nine
prestressed concrete girder bridges, two reinforced concrete bridges, two steel girder bridges, one
post-tensioned concrete bridge, and four structural steel bridges. Eleven of these case studies are
highways crossing over water bodies, while the remaining cross over existing roadways. Also, the
case studies include thirteen highway projects that were executed using a design-bid-build project
delivery method, and five highway projects implemented using the design-build project delivery
method. None of the case studies is named to protect anonymity; instead, they are referred to with
bridge ID such as B1, B2…B15b, as detailed in Table 3-1.
All eighteen bridges are new constructions and are clustered into three categories: The first
category comprises seven bridge projects that were completed between 2015 and 2019. The second
category includes two ongoing bridge case studies (B6a and B13a), where all the concrete
construction work has been finalized and are at the asphalt paving stage as of July 1st 2020. The
third category comprises nine case studies (B3a, B3b, B6b, B8, B10, B11, B13b, B14a, B14b),
where some of the structural components are still under construction. The substructures of these
nine case studies have been constructed as of July 1st 2020. However, their superstructures are at
varying levels of completion, ranging from deck construction to the construction of the barrier
walls. For this study, the nine bridge projects in the first two categories are grouped as the
completed bridge projects, while the nine case studies in the third category are labelled as in-
progress bridge projects.
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Table 3-1: Composition of the highway bridge case studies regarding bridge span and width, bridge type, completion status, delivery
method, and availability of data
Available Data
Bridge ID
Bridge Span (m)
Bridge Width (m)
Bridge Type Highway Type Status Delivery Method
C P D Con
B1 29.0 13.0 Prestressed Girder Bridge River Crossing Completed DBB x x
B2 33.0 12.4 Prestressed Girder Bridge River Crossing Completed DBB x x
B3a 28.0 14.0 Reinforced Concrete Bridge Roadway Crossing Incomplete DBB x x
B3b 37.5 14.0 Reinforced Concrete Bridge Roadway Crossing Incomplete DBB x x
B4 43.4 12.4 Prestressed Girder Bridge River Crossing Completed DB x x x x
B5 44.0 13.0 Steel Girder Bridge River Crossing Completed DB x x
B6a 46.5 18.5 Prestressed Girder Bridge Roadway Crossing Incomplete DBB x x
B6b 46.5 18.5 Prestressed Girder Bridge Roadway Crossing Incomplete DBB x x
B7 46.5 12.3 Prestressed Girder Bridge River Crossing Completed DB x x
B8 52.1 10.7 Prestressed Girder Bridge River Crossing Incomplete DB x x x x
B9 88.0 11.0 Prestressed Girder Bridge Roadway Crossing Completed DBB x x
B10 98.8 12.1 Prestressed Girder Bridge Roadway Crossing Incomplete DBB x x
B11 112.0 12.1 Post-Tensioned Concrete Bridge Roadway Crossing Incomplete DBB x x
B12 118.0 12.3 Steel Girder Bridge River Crossing Completed DB x x
B13a 150.0 14.0 Steel Bridge River Crossing Incomplete DBB x x
B13b 150.0 14.0 Steel Bridge River Crossing Incomplete DBB x x
B14a 194.0 14.3 Steel Bridge River Crossing Incomplete DBB x x
B14b 209.0 14.3 Steel Bridge River Crossing Incomplete DBB x x
C – Conceptual Design Stage, P – Preliminary Stage, D – Detailed Design Stage, and Con – Construction Stage
16
Lastly, the case studies include four sets of twin bridges (B3a and B3b, B6a and B6b, B14a and
B14b, and B15a and B15b), that represent the northbound and southbound bridge lanes of four
separate case studies.
Design and construction documents for all eighteen case studies were obtained from the general
contractor. For thirteen of the case studies (B1, B2, B3a, B3b, B6a, B6b, B9, B10, B11, B13a,
B13b, B14a, B14b), an external consultant (bridge designer) hired by the project owner designed
the bridges, while the contractor merely executed the project using the prepared design documents.
For the remainder of the case studies, the contractor was responsible for both the design and
construction stages. Table 3-2 gives a comprehensive summary of all the design and construction
documents used in this study. The database of documentation includes:
Preliminary Design Reports: These reports document the early stages of design and
constructability. It makes a full acknowledgement of existing conditions and constraints,
establishes alternatives and comparatives studies between bridge alternatives for selection. It also
serves as the basis for plans and specifications for the final design and construction contracts.
Structural Drawings: These were provided by the general contractor, and comprise a set of plans
and details on how the bridge is going to be built.
Estimator's Bills of Quantities (BOQ): These are documents stating estimated quantities of work
to be performed. The estimators prepared them during the bidding and tendering stages of the DBB
projects, and the detailed design stage of the DB projects.
Concrete and Asphalt Delivery Packages: These documents are concrete and asphalt delivery
invoices provided by material suppliers upon delivery.
Bills of Lading and Steel Mill Certificates: Bills of lading documents are a detailed list comprising
the types and quantities of materials delivered. Steel mill certificates are documents that provide
the chemical and physical composition of the structural steel sections. These documents, which
both contain steel quantities, were supplied by the material suppliers and were handed over to the
general contractor upon delivery.
17
Table 3-2: Design and construction documents obtained from the contractors and their level of completion
● - Available and complete, ◓ - Available but Incomplete, ○ – Not Available, N/A – Not Applicable
N/A indicates that the material or document did not apply to the case study under consideration
Detailed Design Stage Data Construction Stage Data
BOQ
Bridge ID
Prelim. Design Report
Struc. Drwgs Asphalt Concrete Rebar
Struc. steel
Project Schedule (Asphalt
Quantities)
Precast girder
erection files
Struc. steel erection
files
Concrete placement packages +
Concrete Delivery invoices
Asphalt delivery invoices
Bills of Lading (rebar)
Mill certificates (structural
steel)
1 B1 ○ ● ● ● ● ● ○ ● N/A ● ● ◓ ○
2 B2 ○ ● ○ ○ ○ ● ○ ● N/A ● ○ ○ ○
3 B3a ○ ● ○ ● ● N/A ● N/A N/A ● ○ ◓ ○
4 B3b ○ ● ○ ● ● N/A ● N/A N/A ● ○ ◓ N/A
5 B4 ● ● ● ○ ○ N/A ○ ● N/A ● ◓ ○ N/A
6 B5 ○ ● ○ ○ ○ ○ ○ N/A ● ● ● ◓ ●
7 B6a ○ ● ○ ● ● N/A ● ● N/A ● ○ ◓ N/A
8 B6b ○ ● ○ ● ● N/A ● ● N/A ● ○ ◓ N/A
9 B7 ○ ● ● ● ● N/A ○ ● N/A ● ● ● N/A
10 B8 ● ● ● ● ● ○ ○ ● ○ ● ○ ○ ●
11 B9 ○ ● ○ ● ● ● ○ ● ● ● ● ● ●
12 B10 ○ ● ○ ● ● N/A ● ● N/A ● ○ ◓ N/A
13 B11 ○ ● ○ ● ● N/A ● N/A N/A ● ○ ◓ N/A
14 B12 ○ ● ● ● ● ● ○ N/A ● ● ● ● ●
15 B13a ○ ● ○ ● ● ○ ● N/A ● ● ○ ◓ ●
16 B13b ○ ● ○ ● ● ○ ● N/A ● ● ○ ◓ ●
17 B14a ○ ● ○ ● ● ○ ● N/A ● ● ○ ◓ ●
18 B14b ○ ● ○ ● ● ○ ● N/A ● ● ○ ◓ ●
18
Project Schedules: These are documents that describe the project activities, milestones, and
deliverables. They were generated during the bidding stages of the DBB projects, and the detailed
design stage of the DB projects by the scheduler.
Concrete Placement Packages: These documents are prepared by the site superintendent and
indicate the quantities of poured concrete.
Erection Procedure Plans: These are documents produced by the designers and contractors
during the preconstruction stage detailing the assembly of structural components on a
construction site.
Canadian Precast and Prestressed Concrete (CPCI) Manual: A document covering the design,
manufacture and installation of precast and prestressed concrete(Canadian Precast/Prestressed
Concrete Institute, 2017). It contains general design information of precast and prestressed
girders that are made in Canada.
Canadian Institute of Steel Construction (CISC) Steel Manual: A handbook for structural steel
design in Canada containing physical properties of currently available structural steel sections.
3.2 Estimating Material Quantities for the Design and Construction Stages
For this thesis, the design and construction stages of bridges are divided into four stages. These
stages include the conceptual stage, the preliminary stage, the detailed design stage, and the
construction stage. This section gives a detailed description of how material quantities were
calculated for each stage.
3.2.1 Conceptual Design Stage
The conceptual design stage is where the project is defined, and multiple bridge design alternatives
are explored (Morcous et al., 2001). Data for this stage was obtained from preliminary structural
design reports which were prepared by the bridge designers and provided by the contractor.
19
As illustrated in , this report was available for two bridge case studies, B4 and B8 (both DB
projects). The preliminary structural design reports provided ten bridge design alternatives B4,
and five for B8, with each alternative accompanied by concrete, reinforcing steel (rebar), and
structural steel quantity estimates. The analysis resulted in a range of concrete and steel quantities,
with the highest and lowest representing the design alternative with the most and least concrete
and steel quantities, respectively.
3.2.2 Preliminary Design Stage
The preliminary stage involves the selection of the best bridge design among the proposed
alternatives (Tang, 2017). The quantities of this design stage comprise concrete and steel quantity
estimates (i.e. rebar and structural steel) of the selected bridge design for B4 and B8. Reinforcing
steel, structural steel and concrete quantity estimates were available for B8. However, the chosen
design for B4 was a single-span concrete box girder which required zero structural steel quantities.
Thus, the steel quantities for B4 comprised of just the estimated rebar quantities.
3.2.3 Detailed Design Stage
In this design stage, a detailed analysis of the selected design is conducted to finalize all the
essential details of the bridge structure needed for tendering and construction (Wang et al., 2015).
For this thesis, the material quantities in this design stage were primarily obtained from the
estimator's bills of quantities (BOQ), as shown in Table 3-2. For bridge projects with missing BOQ
estimates, other data sources like the structural drawings and project schedules were used in
supplementing missing information, which is further explained below.
3.2.3.1 Asphalt
The primary data source for the asphalt quantities was the estimator's BOQs. The estimators BOQs
were produced just before construction using the detailed design documents. Asphalt quantities
for thirteen case studies were unavailable, as shown in Table 3-2 The unavailable asphalt data for
ten of the thirteen bridge case studies (B3a, B3b, B6a, B6b, B10, B11, B13a, B13b, B14a, and
B14b) were obtained from the project schedules also created during the bidding process. Each
project schedule had the estimated weight of asphalt quantities needed to pave the bridge deck.
For project schedules without asphalt quantities, they were estimated by multiplying the bridge
20
deck area by the proposed asphalt thickness using dimensions obtained from the structural
drawings. The calculated volume was then multiplied by the density of asphalt to obtain the asphalt
mass in megagrams (Mg). This method was validated by comparing asphalt quantities calculated
from the structural drawings, with asphalt quantity estimates obtained from the project schedules,
for case studies where both data were available. The quantities were within 5% of each other.
3.2.3.2 Concrete
Concrete volume quantities of structural components were in most cases provided in the estimator's
BOQ, as displayed in Table 3-2. For case studies where BOQ records were not available, the
concrete volume of each bridge component was estimated using dimensions in the structural
drawings. Similarly, in determining the weight of the prestressed girders, the total girder length
obtained from the estimators BOQs or structural drawings was multiplied by the section's mass
per unit length ratio of each girder type, as shown in Table 3-3. For girder types with unavailable
mass per unit length ratios, the weight of the prestressed girder was estimated using the dimensions
available in the structural drawings.
Table 3-3: Mass per unit length value of each girder type
Bridge ID Type of Girder Girder code Mass per unit length
(kg/m)*
B1 Box Girder B900 Not Available
B2 Box Girder B800 Not Available
B4 Box Girder B1000 Not Available
B6a I-girder CPCI 1900 1,380
B6b I-girder CPCI 1900 1,380
B7 Box Girder B1000 Not Available
B8 Box Girder B700 Not Available
B9 I-girder NU 1600 1,322
B10 I-girder CPCI 1900 1,380
* Mass length ratio from (Canadian Precast/Prestressed Concrete Institute, 2017)
21
3.2.3.3 Steel
3.2.3.3.1 Reinforcing Steel (Rebar)
Rebar quantities were for the most part obtained from the BOQs, as shown in Table 3-2. Bridge
case studies with no rebar data in the BOQs, i.e. B2, B4, and B5, were excluded from the rebar
comparison analysis.
3.2.3.3.2 Structural Steel
Structural steel quantities comprise of the structural steel piles for the bridge foundations in B9;
structural steel girders in B5 and B12; and structural steel frames that make up the four steel
bridges (B13a, B13b, B14a, and B14b). Steel pile quantities were estimated by multiplying the
total pile length obtained from the BOQs, by the corresponding mass per unit length ratio of each
pile type available in the Canadian Institute of Steel Construction Manual. Structural steel girder
quantities and steel frame quantities were extracted from erection procedure plans provided by the
contractor, as displayed in Table 3-2.
Structural steel data was aggregated by the contractor for two sets of twin bridges that represent
northbound and southbound lanes of the same project (B14a and B14b, and B15a and B15b).
Consequently, in each case, the twin bridges were treated as one case study just for the structural
steel comparison analysis
3.2.4 Construction Stage
Onsite material quantities were obtained from a combination of documents delivered to the
construction site by construction material suppliers, and documents used by the contractor in
tracking material delivery, as illustrated in Table 3-2. These documents include asphalt and
concrete delivery invoices, concrete placement packages, steel mill certificates, and bills of lading.
For all the bridge case studies, it is assumed that all the materials delivered to the construction site
were used for construction.
Asphalt quantities were extracted and collated from asphalt delivery tickets. Ready-mix concrete
quantities were aggregated from concrete delivery tickets and concrete placement packages.
Prestressed girder concrete quantities were obtained from shop drawings provided by the suppliers;
22
rebar and structural steel quantities were obtained from bills of lading and mill certificates
provided by the steel suppliers. Only B7, B9, and B12 had a complete set of rebar bills of lading
documents, as shown in Table 3-2. Others either had incomplete or missing rebar data. For this
reason, the rebar analysis for the construction stage was only conducted for B7, B9, and B12 where
sufficient data was available to facilitate comparison between detailed design and construction
stages.
Also, construction sequence documents, minutes from site meetings, change order documents,
project coordinator's notes, and site engineer's records were obtained to verify that stipulated
material quantities correspond with the amounts listed out in the bills of lading, concrete delivery
packages, and asphalt delivery packages.
3.3 Comparison of Material Quantities between the Design and Construction Stages
3.3.1 Comparison of Detailed Design Estimates to Construction Stage Material Use
Following the analyses, a comparison of concrete, rebar, structural steel, and asphalt quantities
was conducted between the detailed design stage and construction stage for the completed and in-
progress case studies. This comparison aims to assess the changes in material quantities between
these two stages.
Also, for the nine completed projects (seven fully completed bridge projects and two ongoing
projects with finalized concrete work), a comparison of concrete quantities between onsite material
use and detailed design estimates was conducted for the two major structural components, i.e., the
substructures and superstructures. For the nine in-progress projects, a comparison of concrete
quantities between the detailed design and construction stage was conducted just for the
substructures.
The substructure is the portion of the bridge below ground that supports the superstructure. It
consists of the pier, pier footings, wingwalls, abutments, mass concrete, and tremie concrete, as
shown in Figure 3-1. The tremie concrete is concrete that is placed below water level to tie
23
different structural elements together. The American Concrete Institute defines mass concrete as
'any volume of concrete with dimensions large enough to require that measures be taken to cope
with the generation of heat from the hydration of cement and attendant volume change to minimize
cracking'. In contrast, the superstructure is the portion of the bridge above the substructure. It
comprises the deck slab, bridge girders, and barrier walls.
* Substructure includes mass concrete and tremie concrete which are not shown in figure
Figure 3-1: Structural components of a typical bridge
3.3.2 Comparison of Material Quantities between the Four Main Stages of
a Bridge Project
A comparison of concrete, rebar and structural steel quantities between the four design and
construction stages (conceptual design stage, preliminary design stage, detailed design stage, and
construction stage) were conducted for the two case studies with sufficient data for all four stages.
24
Discussion of Findings
The results of the material quantity analyses are presented in this chapter based on material type
and level of completion. Firstly, the comparison of concrete quantities for the completed and in-
progress bridges between the detailed design stage and construction stage are presented. Secondly,
the comparison of concrete quantities between the detailed design stage and construction stage of
the superstructure and substructure are presented. Subsequently, the comparison of rebar,
structural steel and asphalt quantities of the completed bridges between the detailed design stage
and construction stage are introduced. Lastly, the evolution of concrete, rebar, and structural steel
quantities across the conceptual, preliminary, detailed design and construction stages for the two
bridge case studies with sufficient data (B4 and B8) are introduced.
4.1 Comparison of Material Quantities Between the Detailed Design Stage and Construction Stage
4.1.1 Comparison of Concrete Quantities
4.1.1.1 Completed Bridge Projects
The completed bridge projects comprise seven fully completed bridges and two ongoing bridge
projects where concrete construction work has been finalized and are currently being asphalt paved
(B6a and B13a) as of July 1st 2020. These include six prestressed concrete girder bridges (B1, B2,
B4, B6a, B7, and B9), two steel girder bridges (B5 and B12), and one steel bridge, B13a.
Figure 4-1 shows the comparison of concrete quantities between the detailed design stage and
construction stage for the completed bridge case studies bridges. Overall, more concrete quantities
were used in the construction stage than predicted in the detailed design stage. The additional
concrete use range from 3% to 85%, with a mean of 21%. B7 experienced the most noticeable
25
change in concrete quantities between the two stages, which was due to the construction of a new
concrete wall not included in the detailed design estimates.
Figure 4-1: Comparison of concrete quantities between the detailed design stage and the
construction stage of the completed case studies
0
500
1000
1500
2000
2500
3000
3500
B1 B2 B4 B5 B6a B7 B9 B12 B13a
Co
ncr
ete
Qu
anti
ties
(M
g)
Detailed Design
Construction
26
4.1.1.2 In-Progress Bridge Projects
The in-progress bridge projects comprise two reinforced concrete bridges (B3a and B3b), three
prestressed girder bridges (B6b, B8, and B10), one post-tensioned concrete bridge (B11), and three
steel bridges (B13b, B14a and B14b). These bridges are at varying levels of completion, as
illustrated in Table 4-1. The aggregated concrete quantities of the completed structural
components, which were obtained from onsite delivery documents were compared with concrete
estimates of the respective components.
Figure 4-2 illustrates that compared to the detailed design concrete estimates, there was generally
more concrete use in the construction stage. The increase in concrete quantities ranges from 7% to
71%, with a mean of 27%. Further investigation into the design and construction documents
indicated that the substructure was the major contributor to the additional concrete use.
Figure 4-2: Comparison of concrete quantities between the detailed design stage and the
construction stage for the In-progress bridge case studies
0
500
1000
1500
2000
2500
3000
3500
4000
4500
B3a B3b B6b B8 B10 B11 B13b B14a B14b
Co
ncr
ete
Qu
anti
ties
(M
g)
Detailed Design
Construction
27
Table 4-1: The construction stages of the In-progress bridge case studies
Bridge ID Construction Stage Structural components yet to
be constructed
Projection of Total Concrete Use
(Mg)
Estimated Concrete Quantities for
Completed Segments (Mg)
Concrete Used to Date
(Mg)
B3a Removal of bridge deck formwork barrier walls 1227 1181 1697
B3b Bridge deck curing approach slabs, barrier walls 1783 1627 1745
B6b Construction of bridge deck approach slabs, barrier walls 1688 1486 1744
B8 Erection of parapet wall formwork Parapet walls 1574 1415 1568
B10 Erection of prestressed girders deck, barrier walls, approach slabs 2320 1161 1582
B11 Erection of Approach Slab Formwork approach slabs 3782 3677 4235
B13b Erection of Structural frames deck, barrier walls, approach slabs 2843 1237 1546
B14a Erection of Bridge Deck Formwork deck, barrier walls, approach slabs 2878 859 1469
B14b Erection of Structural frames deck, barrier walls, approach slabs 4222 1505 1736
28
B14a had the most substantial concrete quantity increase of 71% from 859 Mg to 1469 Mg, as
shown in Figure 4-2 and Table 4-1. This considerable increase is attributed to additional concrete
deliveries being made for the construction of the mass concrete structure, which was not initially
accounted for in the estimator's BOQ.
Furthermore, the analyses show that at their current stages of construction, B3a, B6b, and B11
have consumed 38%, 29% and 8%, respectively, more concrete than the total concrete estimates
for the entire project. As illustrated in Table 4-1, B3a and B11 are missing one structural
component each to reach completed status, while the approach slabs and barrier walls are still
expected to be built for B6b.
4.1.1.3 Comparison of Concrete Quantities Between the Detailed Design Stage and Construction Stage of the Substructure and Superstructure
A comparison of concrete quantities between the detailed design stage and construction stage of
the substructure and superstructure was conducted to investigate the components responsible for
additional concrete use. The substructure consists of the pier, pier footings, wingwalls, abutments,
mass concrete, and tremie concrete, as shown in Figure 3-1. The superstructure comprises the deck
slab, bridge girders, and barrier walls.
Figure 4-3 and Figure 4-4 display the comparison of concrete estimates to actual onsite use for the
substructure and superstructure, respectively, for the nine completed bridge case studies. The
substructure is seen to have consumed significantly more concrete quantities compared to the
superstructure. B1 is the only exception, and the reason for this was due to 30% less concrete being
used for the substructure tremie pour. The mean of the additional onsite concrete use for the
substructure and superstructure across the nine completed bridges are 56% and 5%, respectively,
as illustrated in Figure 4-6.
29
Figure 4-3: Completed Projects - Comparison of substructure concrete quantities between
the detailed design stage and the construction stage
Figure 4-4: Completed Projects - Comparison of superstructure concrete quantities
between the detailed design stage and the construction stage
0
500
1000
1500
2000
2500
B1 B2 B4 B5 B6a B7 B9 B12 B13a
Co
ncr
ete
Qu
anti
ties
(M
g)Detailed Design
Construction
0
200
400
600
800
1000
1200
1400
1600
1800
B1 B2 B4 B5 B6a B7 B9 B12 B13a
Co
ncr
ete
Qu
anti
ties
(M
g)
Detailed Design
Construction
30
Figure 4-5: In-Progress Projects: Comparison of substructure concrete quantities between
the detailed design stage and the construction stage
Figure 4-6: Change in substructure and superstructure concrete quantities between the
detailed design stage and the construction stage
0
200
400
600
800
1000
1200
1400
1600
1800
2000
B3a B3b B6b B8 B10 B11 B13b B14a B14b
Co
ncr
ete
Qu
anti
ties
(M
g)
Detailed Design
Construction
31
The substructure concrete quantities between the detailed design stage and construction stage of
the nine in-progress bridge projects were also compared to investigate additional concrete use.
Although these bridges are incomplete, all the structural components of the substructure have been
constructed, thus allowing for comparison with the concrete estimates from the detailed design
stage.
Figure 4-5 displays the changes in the substructure concrete quantities for the in-progress bridge
projects. On average, the substructure of the in-progress bridges consumed approximately 44%
more concrete quantities in the construction stage, as shown in Figure 4-6.
4.1.1.4 Factors Driving Additional Concrete Use
Across the case studies, five main factors were responsible for the additional concrete quantities
used in the construction of the substructure. They include:
1) Mass concrete for substructure construction: Mass concrete refers to large quantities of concrete
used for filling voids, for example, excavated trenches. It also comprises significant volumes of
concrete with dimensions large enough to require that measures be taken to cope with the
generation of heat from the hydration of the cement and attendant volume change to minimize
cracking (American Concrete Institute, 2016). Structural components with a member thickness of
about 900mm or more are often identified as mass concrete (Alper and Jijina, 2018).
Additional mass concrete was ordered in the construction stage for 10 of the case studies, B3a,
B6a, B6b, B7, B10, B12, B13a, B13b, B14a, and B14b as reported in Table 4-2. According to the
project coordinator's notes and change order documents, the additional mass concrete orders were
used to rectify rock overbreaks during excavation for B3a, B6b, B10, B13a, and B13b, as observed
in Table 4-3. Other reasons driving additional mass concrete quantities in the construction stage
include, more concrete quantities being used to raise the elevation of mass concrete in B14b to the
height of the abutment footing, and omission of mass concrete quantities in the estimators' BOQ
for B14a as shown in Table 4-3. No information on the reasons behind further mass concrete use
was available for B6a, B7, and B12, as observed in Table 4-3.
32
Table 4-2: Factors driving additional onsite concrete use
Bridge ID Mass
concrete
Unexpected
Retaining
Wall
Mudsills/
Levelling
Pads
Unshrinkable
Fill
Concrete in
Footings
Concrete in
Wingwalls and
Abutment
B2 x
B3a x x x x x
B3b x x
B4 x x
B5 x
B6a x x x x
B6b x x
B7 x x
B8 x
B9 x x
B10 x x x
B11 x x x
B12 x x
B13a x x x x
B13b x x x
B14a x x x
B14b x x
33
Table 4-3: Factors responsible for additional mass concrete use
Bridge ID Factors Driving the Increase in Mass Concrete
1 B3a Overbreak
2 B6a Not available
3 B6b Overbreak
4 B7 Not available
5 B10 Overbreak, Reinforce ground in areas where loose rock was found
6 B12 Not available
7 B13a Overbreak, Reinforce ground in areas where loose rock was found
8 B13b Overbreak
9 B14a Omitted in tendering BOQ
10 B14b To increase the elevation of mass concrete to abutment footing level
Figure 4-7: Contribution of factors driving additional onsite concrete use to total
substructure concrete increase
34
The mass concrete had a 6% - 96% contribution to the total concrete increase of the substructure
for the case studies affected, as illustrated in Figure 4-7.
2) Use of mudsills and levelling pads- Temporary structures known as mudsills and levelling pads
were built in B3a, B3b, B6a, B9, B11, and B13a, as shown in Table 4-2, to distribute loads from
the falsework to the supporting ground evenly. The mudsills and levelling pads contributed
between 2% - 88% of the total substructure concrete increase, as illustrated in Figure 4-7
3) Retaining wall – Unexpected retaining walls were introduced in the construction stage for B3a
and B7, as displayed in Table 4-2: Factors driving additional onsite concrete use. This had a 69%
and 86% contribution to the total increase in substructure concrete quantities between the detailed
design and construction stages for B3a and B7, respectively. Also, the contractors carried out
repair work on the retaining walls of B7, as observed in the concrete placement packages, which
accounted for an additional 10% concrete increase.
4) Unshrinkable fill – Bridge B9 ordered more concrete quantities in the construction stage in the
form of unshrinkable fill during the installation of the corrugated steel pipe (CSP) for the integral
abutments. Integral abutments are abutments that allow the substructure and superstructure to
move together to accommodate the required translation and rotation, i.e. no need for bridge
expansion joints and bearings (White, 2007). According to the instruction notices to contractors
prepared by the client, the unshrinkable fill was used as backfill and to provide lateral support for
CSP. The decision to use the unshrinkable fill was backfill was made in the construction stage,
and represented approximately 58% of the additional concrete use in the substructure of B9.
5) Concrete use in the footings, wingwalls, and abutment – Additional concrete use was observed
in the construction of footings, wingwalls, and abutment, as illustrated in Table 4-2. Ten bridge
case studies consumed more concrete in the construction of the footings, while the construction
stage of fifteen bridge case studies consumed more concrete quantities in the construction of the
wingwalls and abutments, as observed in Table 4-2: Factors driving additional onsite concrete
useTable 4-2. The additional concrete use in the footings, and for the combined wingwalls and
abutment had a 6% - 77% and 4% - 100% contribution to the additional concrete use in the
substructure of these bridges as illustrated in Figure 4-7. No information on the reasons behind
further concrete use in these structural members was available.
35
Figure 4-8: Contribution of factors to additional onsite concrete use
-200
0
200
400
600
800
1000
1200
1400
B1 B2 B3a B3b B4 B5 B6a B6b B7 B8 B9 B10 B11 B12 B13a B13b B14a B14b
Co
ntr
ibu
tio
n t
o A
dd
itio
nal
Co
ncr
ete
Use
(M
g)
Unshrinkable fill
Wingwalls and Abutments
Footings
Retaining Walls
Mudsills and Levelling Pads
Mass Concrete
36
Figure 4-8: Contribution of factors to additional onsite concrete use summarizes the contribution
of the factors mentioned above to the additional concrete quantities observed in the substructure.
The negative concrete quantities observed for B3b, B7 and B12 indicate lower concrete quantities
compared to estimates were used onsite. However, the savings in concrete quantities for these three
case studies were marginal compared to the overall quantities of additional concrete used onsite.
Also, Figure 4-8 shows that mass concrete, additional concrete use in footings, wingwalls, and
abutments were the most common for all eighteen bridge case studies, and are the major factors
responsible for the variability in concrete quantities for the highway bridges considered.
4.1.2 Comparison of Reinforcing Steel (Rebar) Quantities
Detailed design stage rebar estimates of the three bridge case studies considered were obtained
from the estimator's BOQ. For the construction stage, rebar quantities were obtained from QA/QC
documents, i.e., bills of lading documents. B7 and B12 were constructed under the same contract;
as a result, the provided QA/QC documents were the combined bills of lading for these two
bridges. For this reason, these two bridges were treated as one case study. Figure 4-9 shows the
comparison between the BOQ estimates and the onsite quantities of reinforcing steel for B9 and
the combined B7 and B12 case studies.
Figure 4-9: Comparison of reinforcing steel quantities between the detailed design stage
and construction stage
0
50
100
150
200
250
B9 B7 + B12
Rei
nfo
rcin
g St
eel Q
uan
titi
es (
Mg)
Detailed Design
Construction
37
B9 experienced a 23% increase in rebar quantities from 79 to 97 Mg. Also, an 8% increase in the
combined rebar quantities for B7 and B12 was observed between the detailed design stage and
construction stage, thus resulting in a total mean increase of 16% for the three case studies.
4.1.3 Comparison of Structural Steel Quantities
Figure 4-10 displays the structural steel comparison between the detailed design stage and
construction stage for seven bridge case studies (B5, B9, B12, B13a, B13b, B14a, and B14b).
Estimates for the detailed design stage were obtained either from the estimator's BOQ (B5 and B9)
or from the structural steel erection procedure documents (B5, B12, B13a, B13b, B14a, B14b).
For the construction stage, quantities were obtained from bills of lading documents and mill
certificates. Structural steel data was aggregated by the contractor for two sets of twin bridges that
represent northbound and southbound lanes of the same project (B13a and B13b, and B14a and
B14b). Consequently, in each case, they were treated as one case study. Figure 4-10 displays the
sum of the structural steel quantities of the twin bridges for the detailed design stage and
construction stage.
As observed in Figure 4-10, the construction stage structural steel quantities are higher than the
detailed design estimates for all the case studies. The increase in structural steel use range from
5% – 19%, with a mean of 11%. However, due to insufficient data, it was not possible to
determine the driving factors responsible for the additional structural steel quantities in the
construction stages of these case studies.
38
* B7 has zero structural steel but is included in the figure to maintain consistency with rebar quantities figure and
asphalt quantities figure
Figure 4-10: Comparison of structural steel between the detailed design stage and
construction stage
4.1.4 Comparison of Asphalt Quantities
Figure 4-11 displays the increase in asphalt quantities from the detailed design stage to the
construction stage for four bridge case studies (B1, B5, and B7 and B12). As observed for the other
construction materials, the asphalt quantities consumed in the construction stage are higher than
the estimated amounts in the detailed design stage. The changes in asphalt quantities range from
11% to 17%, with a mean of approximately 15%. The discrepancy in asphalt quantities indicates
a larger area of roadway paving than what was provided in the structural drawings, and the
estimators BOQ. For example, in B5, an existing road leading to the bridge was paved in the
construction stage which resulted in additional asphalt use. The decision to pave the existing road
was made during the construction stage, resulting in more asphalt quantity use in the construction
stage.
0
500
1000
1500
2000
2500
3000
B5 B9 B7 + B12 B13a + B13b B14a + B14b
Stru
ctu
ral S
tee
l Qu
anti
ties
(M
g)
Detailed Design
Construction
39
Figure 4-11: Comparison of asphalt between the detailed design stage and construction stage
4.2 Comparison of Material Quantities across the Four Main Design and Construction Stages
4.2.1 Evolution of Concrete Quantities
Figure 4-12 and Figure 4-13 illustrate the comparison of concrete quantities across the four design
and construction development stages, i.e., the conceptual design stage, the preliminary design
stage, the detailed design stage and the construction stage, for two bridge case studies (B4 and B8).
These two case studies were the only bridge case studies with sufficient concrete quantity data for
the four design and construction stages considered.
The conceptual stage for B4 comprises concrete quantities of ten design alternatives. The mean of
the concrete quantities for the ten design alternatives (1426 Mg) is plotted, as shown in Figure
4-12.
11740
13012
0
200
400
600
800
1000
1200
1400
1600
1800
B1 B5 B7 + B12
Asp
ahlt
Qu
anti
ties
(M
g)
12000
13000
14000
11000
40
The error bar represents the design alternatives that consume the most and least concrete quantities,
i.e. the most concrete-intensive and least concrete-intensive alternative designs considered. The
preliminary stage is composed of the aggregated concrete quantities of the selected bridge design
(936 Mg); 34% less than the mean value of the preceding stage. The selected design was the eighth-
most concrete-intensive and consumed 52% less concrete compared to the conceptual estimate for
the most concrete-intensive design alternative. As shown in Figure 4-12, the concrete quantities at
the detailed design stage experienced a 6% decrease from the preliminary design stage. The
decrease in material quantities is attributed to the reduction in width and span of the bridge by 150
mm and 2600 mm, respectively.
Figure 4-12: Evolution of Concrete Quantities for B4
Dash line represents the concrete quantities at the conceptual design stage, which is the mean of the concrete
quantities of 10 design alternatives
The error bar represents the most concrete-intensive and least concrete-intensive design alternatives
0
500
1000
1500
2000
Conceptual Design Preliminary Design Detailed Design Construction
Co
ncr
ete
Qu
anti
ties
(M
g)
Design and Construction Stages
41
Conversely, there was an 18% increase in concrete quantities from the detailed design stage to the
construction stage. The 18% increase was due to additional onsite concrete use for the bridge
abutments, wingwalls, and parapet wall.
B8 experienced a different concrete quantity evolution to B4, as shown in Figure 4-13. The
substructure of B8 was completed at the time this thesis was written (July 2020), but the
superstructure remains under construction. Thus, a comparison of concrete quantities between the
four design and construction stages was conducted for just the substructure, as illustrated in Figure
4-13.
Dash line represents the concrete quantities at the conceptual design stage, which is the mean of the concrete
quantities of 5 design alternatives
The error bar represents the most concrete-intensive and least concrete-intensive design alternatives
Figure 4-13: Evolution of Concrete Quantities for the Substructure of B8
0
200
400
600
800
Conceptual Design Preliminary Design Detailed Design Construction
Sub
stru
ctu
re C
on
cret
e Q
uan
titi
es (
Mg)
Stages of Design and Construction Development
42
The conceptual stage comprises the concrete quantity estimates of five substructure design
alternatives, the mean of which is 346 Mg. At the preliminary stage, the design consultant selected
the most concrete-intensive design alternative, with a total concrete weight of 1275 Mg. According
to the preliminary design report, this design was chosen because of lower future maintenance costs
and constructability benefits. The substructure concrete estimate at the preliminary design stage
was 480 Mg, a 39% increase from the conceptual stage mean. At the detailed design stage, there
was a 16% increase in the substructure concrete quantities from the preliminary stage. This
increase was due to more concrete quantities assigned to the abutment and wingwalls after the
completion of the detailed design analysis. The final onsite concrete use (i.e. for construction stage)
for the substructure was 709 Mg; 28% higher than the detailed design stage. This increase was
due to additional concrete use in the construction of the piers, pier caps, abutment and wingwalls.
4.2.2 Evolution of Reinforcing Steel (Rebar) Quantities
Figure 4-14 illustrates the comparison of rebar quantities across the conceptual design stage, the
preliminary design stage, and the detailed design stage of B8. The construction stage rebar data
was incomplete due to ongoing construction as at the time this thesis was written (July 2020).
The conceptual stage comprises rebar quantities of five design alternatives. The rebar quantity
estimates for each design alternative was 25 Mg, resulting in a mean of 25 Mg. The preliminary
stage rebar estimates were of the selected bridge design, which was 25 Mg. After the detailed
design analysis was carried out, the resulting rebar quantity estimates at the detailed design stage
increased by 104% to 51 Mg. As of July 1st 2020, 47 Mg of rebar quantities had been ordered to
the construction site of B8, and it is expected that more rebar quantities will be needed to construct
missing structural components (the parapet walls).
43
Dash line represents the rebar quantities at the conceptual design stage, which is the mean of the rebar quantities of
5 design alternatives
Figure 4-14: Evolution of Reinforcing Steel Quantities for B8
4.2.3 Evolution of Structural Steel Quantities
B8 was the only case study with complete structural steel data for all four design and construction
stages. The structural steel data are composed of structural steel piles that make up the bridge
foundations. The conceptual stage of B8 comprises structural steel quantities of five design
alternatives, with an average of 91Mg, as illustrated in Figure 4-15. The error bar represents the
design alternatives that consume the most and least structural steel quantities. The preliminary
stage is composed of the structural steel estimates of the selected bridge design (77 Mg). At the
detailed design stage, there was a 137% increase in structural steel quantities from the preliminary
stage.
0
10
20
30
40
50
60
Conceptual Design Preliminary Design Detailed Design Construction
Rei
nfo
rcin
g St
eel Q
uan
titi
es (
Mg)
44
Dash line represents the rebar quantities at the conceptual design stage, which is the mean of the structural steel
quantities of 5 design alternatives
The error bar represents the most structural steel intensive and least structural steel intensive design alternatives
Figure 4-15: Evolution of Structural Steel Quantities for B8
Additional steel piles required to support the modular bridge introduced in the detailed design
stage was the reason for the increase in structural steel quantities. The modular bridge serves as a
temporary detour and aims to reduce traffic disruptions for road users during the construction of
B9. Also, there was a 98% increase in structural steel quantities from the detailed design stage to
the construction stage. However, there was no readily available information to ascertain the reason
for this increase.
0
50
100
150
200
250
300
350
400
Conceptual Design Preliminary Design Detailed Design Construction
Stru
ctu
ral S
tee
l Qu
anti
tes
(Mg)
Design and Construction Stages
45
4.2.4 Comparison of Results with GHG Results Available in Literature
The results of the material quantities trend for bridges across the four design and construction
stages considered were compared to results available in literature for buildings. Cavalliere et al.,
2018 conducted a study to assess the embodied greenhouse gas (GHG) emissions impact of
buildings with design and construction development. The results of their research showed a
declining trend in embodied GHG emissions for buildings, across the design and construction
stages. Their study also suggests that for buildings, the construction stage contributes a lesser
embodied GHG impact than the detailed design stage, which is contrary to the results obtained in
this thesis.
Multiplying the concrete quantities in Figure 4-12 and Figure 4-13 by an Ontario-specific
embodied GHG intensity factor obtained from (Nahangi et al., under review) will reveal that the
embodied GHG emissions of the construction stage for bridges are higher than that of the detailed
design stage. The difference in the relationship between detailed design stage impacts and
construction stage impacts for buildings and bridges initiates the question on whether the material
estimation procedures for buildings produce more accurate estimates than that of bridges.
Alternatively, it could also indicate that for buildings, there are fewer design changes that impact
material quantities in the construction stage than there are for bridges.
However, it is important to note that the results of the study conducted by Cavalliere et al., 2018
were based on fifteen low-rise Swiss residential buildings; thus, the embodied GHG trend for high-
rise and commercial buildings might be very different. Also, the construction stage data were not
actual onsite data but rather material quantities obtained from BIM models. Thus, based on existing
literature, there is a high possibility that those values do not reflect actual onsite use (Nahangi et
al., under review). Unfortunately, there are not enough research studies that compare detailed
design estimates to that of onsite material use. Neither are there enough studies that compare the
evolution of material quantities to fully understand how material quantities, and their associated
impacts vary across design and construction stages for multiple building and infrastructure types.
46
Conclusions
This thesis explored two main objectives: (1) it quantified the variability in material quantity
estimates for eighteen bridge infrastructure projects in Canada and, (2) it identified the factors
driving the differences in quantities.
The first part of the thesis investigated the differences in concrete, reinforcing steel (rebar),
structural steel, and asphalt quantities between the detailed design stage and construction stage
using data obtained from Canadian-based bridge projects. The findings revealed that compared to
estimates, substantially more construction materials are used in the construction stages of bridge
projects. For the completed bridge projects, which comprises seven fully completed bridges and
two ongoing projects where concrete work has been finalized, between 3% - 85% more concrete
quantities were used onsite compared to estimates. Similarly, for in-progress projects, where
concrete construction work is ongoing, between 7% to 71% more concrete quantities were
consumed onsite when compared with estimates.
The substructure was identified as the major contributor to additional concrete use in the
construction stage of the eighteen case studies, which is indicative of its influence on the variability
in material quantity estimates. When compared to their respective detailed design concrete
estimates, the substructure of the completed and in-progress bridge projects consumed, on average,
56% and 44% more concrete quantities, respectively. Upon further investigation, five main factors
were revealed to be responsible for the additional concrete use in the substructure:
a. Rock overbreak during excavation and the improvement the underlying ground conditions
b. The construction of temporary structures known as mudsills and levelling pads in the
construction stage
c. The introduction of unexpected structural components (retaining walls)
d. Extra concrete quantities to serve as backfill and provide lateral support for the CSP during
the installation of the integral abutment
e. Increased concrete use in the construction of footings, wingwalls and abutment.
Also, the observed change in rebar, structural steel, and asphalt quantities range between 8% -
23%, 5% - 19%, and 11% - 17%, respectively.
47
The substantial increase in concrete, rebar, structural steel, and asphalt quantities observed in this
thesis provides empirical evidence which reinforces the general view that there are often
discrepancies between design and construction architectural and structural details, and material
quantities. It is also worth noting that the onsite concrete quantities analyzed in this thesis are not
inclusive of rejected concrete batches that did not meet the design specification. Including these
quantities in the analysis would mean a higher average increase in concrete quantities from the
detailed design stage to the construction stage for the competed and incomplete projects,
respectively.
This thesis is beneficial to project owners, consultant, and contractors as it quantifies the variability
in material quantity estimates and emphasizes some of the reasons responsible for additional
material quantities in the construction stage of bridge projects. It identifies the areas upon which
impact mitigation efforts need to be intensified. Also, it empowers the stakeholders involved with
the necessary information needed to put in place necessary preventive measures to reduce cost
overruns, project delays, and environmental impacts, as well as to increase productivity on the
construction site. For example, although cost contingencies are commonly used in practice to
minimize the impacts of cost overruns due to excess material use onsite, it appears that these
contingencies are inadequate in protecting against increases in project cost and project schedule.
The results of this thesis will inform the uncertainty of the decisions made regarding the project
costs, and allow for the provision of appropriate cost buffers that should be incorporated into the
project cost. The same applies to improve the reliability of the environmental impact assessments
during the pre-construction stage, thus allowing for better decisions to be made under uncertainty.
Additionally, the findings of this study demonstrate that adequate geotechnical risk management
and extensive geotechnical investigations are fundamental to mitigating the impacts of the
variability in material quantity estimates for bridge infrastructure projects.
The second part of this thesis compared material quantities across four main design and
construction stages, i.e., the conceptual design stage, preliminary design stage, detailed design
stage, and construction stage, for a subset of the bridge projects. This comparison was conducted
to determine the material quantity impacts of bridges with design and construction development.
The results of the analysis revealed that the evolution of concrete quantities is influenced by
decisions made across the four design and construction stages. The concrete quantities at the
48
preliminary stage and detailed design stage will either decrease or increase from their respective
preceding stage depending on the decisions and modifications made to the bridge design. However,
based on current industry practices, the concrete quantities at the construction stage of bridge
projects will always be higher in comparison to the detailed design stage.
The results of the rebar analysis suggest an increase in rebar quantities between the preliminary
stage and the detailed design stage. However, due to limited data, it was not possible to determine
the variation in rebar quantities between the detailed design stage and construction stage. Also, the
results indicated that the change in structural steel quantities between the conceptual stage and the
preliminary stage is dependent on design decisions made between these two stages. However, an
increasing trend in structural steel quantities was observed between the preliminary stage, the
detailed design stage, and the construction stage.
Understanding the material quantities evolution allows for stakeholders to initiate new practices
in the conceptual design stage that minimize the occurrence of future design changes responsible
for increases in material quantities. The report published in the Engineering and Physical Sciences
Research Council by Sun et al., 2004 states that more than a third of clients are displeased with
the contractor's ability to keep to quoted price estimates and project timeline. Understanding the
trend in material quantities across will allow for designers and contractors to delineate the project’s
needs and requirements, with an increased level of reliability, to improve the client's satisfaction.
Additionally, the trend in material quantities across the design and construction stages observed
for past bridge projects can be leveraged for early stage decision making of new projects to mitigate
the resource consumption, waste generation, financial impacts, and environmental impacts of the
bridge construction industry.
5.1 Recommendations for the Construction Industry
The authors propose the following recommendations for the construction industry to minimize
variability in material quantity estimates, which should contribute to mitigating the adverse
impacts associated with bridge construction.
A more extensive ground investigation should be conducted before construction to have a better
understanding of the site conditions. Being cognizant of the underlying ground conditions will
49
reduce the occurrence of change orders due to unforeseen ground conditions, which ultimately
influences the variability of material estimates. Also, contractors should adopt methods that either
eliminate overbreak or keep it to a minimum. If the preferred method of excavation is the drilling
and blasting method, then the specific charge and the maximum charge per delay should be
carefully selected to reduce blast-induced damage to surrounding work, either in the form of
overbreak or damaged zone or both. The specific charge is a measure of the explosive mass
required to break a unit volume or a unit mass of the rock, while the maximum charge per delay is
the maximum quantity of explosive charge detonated on one interval within a blast (Adhikari,
2000; Singh and Verma, 2010). Verma et al., 2016 highlighted that depending on the rock mass
quality, a specific charge greater than 2.5 kg/m3 and a maximum charge per delay exceeding the
25-30 range may yield at least a 20% overbreak.
Alternatively, if overbreak cannot be avoided, then adequate allowance for overbreak during
excavation should be incorporated in the concrete and steel preconstruction estimates. Also, it is
good practice for stakeholders to carefully check and scrutinize quantities in design drawings and
estimators BOQs in the design and tendering stages to detect omissions. Recognizing omissions
before the start of construction can limit cost overruns, project delays, and also improve the
reliability of the environmental impacts assessments. Also, it can help prevent the contractors from
being held liable for additional costs due to the omissions.
Furthermore, the project stakeholders responsible for estimating material quantities should also
include quantities of materials that are not included in the drawings but are needed to facilitate the
construction process, e.g. temporary structures. Finally, more collaboration between academia and
industry is encouraged, and more proprietary data from several firms in the construction industry,
including design and engineering firms, and contractors should be made available for researchers
to facilitate more research in this domain.
50
Limitations and Future Research
The findings of this thesis are based on case studies that come from one contractor. Thus, the
inherent biases of the construction methods adopted by the contractor limit the generalization of
the thesis outcomes for the construction industry in Canada. Despite this limitation, this thesis still
offers insight into the importance of understanding the variability in material quantity estimates.
However, further research is needed to validate the results of the material quantity changes
between the detailed design stage and construction stage, especially for rebar, structural steel, and
asphalt, where limited data was available. Also, more studies should be conducted to fully
understand the evolution of material quantities across the design and construction stages of
bridges.
Further research is required to compare the changes in material quantities between the detailed
design stage and construction stage of the design-bid-build project delivery system, with the less
fragmented design-bid project delivery method. The delivery method has a considerable influence
on the organization, documentation, and flow of the projects. Hence it would be interesting to
investigate how the intricacies of the two different project management methods impact the
material quantity changes between the detailed design stage and construction stage, and across the
four design and construction stages.
Furthermore, further research on the influence of construction methods, code of practice,
geographical location (cold and tropical locations), and weather factors on the evolution of
material quantities across the design and construction stages can be conducted to investigate if the
results will be consistent with the material quantities trend provided in this thesis.
51
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