Group 1 Final Thesis report
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Transcript of Group 1 Final Thesis report
ANALYSIS AND DESIGN
TA: ENG. OMAR, ENG
Amira Saleh 900100346
Fady Aziz 900114681
Fredy Vector 900114776
Haia Bediwy 900114810
Nada Abdellatif 900115019
CENG: 4980
SENIOR PROJECT 1
ANALYSIS AND DESIGN OF PEARL GARDENS HOTEL
SUPERVISED BY:
DR. EZZAT FAHMY
DR. SAFWAN KHEDR
DR. EZZELDIN SAYED-AHMED
DR. WAEL HASSAN
TA: ENG. OMAR, ENG ZAHRA, ENG. AHMED ABDELHAMID, ENG JASSER
1
PEARL GARDENS HOTEL
2
Abstract
The building that was chosen to be structurally designed was the Pearl Project. There are
different forms of high-rise buildings; all defined depending on their heights. A skyscraper is
used to describe buildings that are higher than 150m, such as that of the Pearl Project, which
reaches up to 187.67m in height. The objective of the work to be done is to accommodate
between design of the building due to gravity loads as well as lateral loading. In addition to that,
the design is to target the most economical solution as well as saving space by designing on the
smallest possible dimensions of structural elements.
3
Table of Contents
Abstract ......................................................................................................................................................... 2
Table of Contents .......................................................................................................................................... 3
List of Figures ................................................................................................................................................ 5
Introduction .................................................................................................................................................. 8
Project Description........................................................................................................................................ 9
Sections ................................................................................................................................................... 11
Scope ........................................................................................................................................................... 12
Deliverables................................................................................................................................................. 13
Methodology ............................................................................................................................................... 14
Initial TimeLine .................................................................................................................................... 15
Challenges ................................................................................................................................................... 15
Preliminary Design ...................................................................................................................................... 16
Loads ....................................................................................................................................................... 16
Slabs ........................................................................................................................................................ 16
Benefits ............................................................................................................................................... 17
Columns .................................................................................................................................................. 19
Modelling of the building ............................................................................................................................ 21
Selection of the Gravitational Slab System ................................................................................................. 23
Elliptical Plan floors from 6th till 34th: ...................................................................................................... 23
ETABS Model: .............................................................................................................................................. 30
Seismic Analysis: ..................................................................................................................................... 30
Wind Analysis: ......................................................................................................................................... 36
System Selection: .................................................................................................................................... 37
Diaphragm Condition: ............................................................................................................................. 42
Remedial Measurements: ....................................................................................................................... 45
Modal Analysis: ....................................................................................................................................... 46
Swimming Pool System: .............................................................................................................................. 48
Shear Walls and Cores Analysis and Design: ............................................................................................... 49
4
Columns Design:...................................................................................................................................... 51
P-Δ effect: ............................................................................................................................................ 52
Torsion Check on Vertical Elements: .................................................................................................. 52
Stairs Design: ........................................................................................................................................... 53
Raft Design: ............................................................................................................................................. 54
Recommendations in Analysis of High Rise Buildings ................................................................................. 58
Aerodynamics Analysis ............................................................................................................................... 58
Differences in Etabs and GID .............................................................................................................. 62
Geotechnical Analysis, Constructions Stages and Foundation Design ....................................................... 63
Detailing ........................................................................................................................................................ 1
Columns .................................................................................................................................................... 1
Slab Reinforcement ................................................................................................................................... 2
Shear Walls ............................................................................................................................................... 7
Stairs: ........................................................................................................................................................ 7
References .................................................................................................................................................... 9
5
List of Figures
Figure 1 ......................................................................................................................................................... 9
Figure 2 ....................................................................................................................................................... 10
Figure 3 ....................................................................................................................................................... 11
Figure 4 ....................................................................................................................................................... 12
Figure 5 ....................................................................................................................................................... 16
Figure 6 ....................................................................................................................................................... 17
Figure 7 ....................................................................................................................................................... 19
Figure 8 ....................................................................................................................................................... 24
9 .................................................................................................................................................................. 24
10 ................................................................................................................................................................ 25
Figure 11 ..................................................................................................................................................... 26
Figure 12 ..................................................................................................................................................... 26
Figure 13 ..................................................................................................................................................... 27
Figure 14 ..................................................................................................................................................... 29
Figure 15 ..................................................................................................................................................... 30
Figure 16 ..................................................................................................................................................... 33
Figure 17 ..................................................................................................................................................... 33
Figure 18 ..................................................................................................................................................... 34
Figure 19 ..................................................................................................................................................... 38
Figure 20 ..................................................................................................................................................... 38
Figure 21 ..................................................................................................................................................... 39
Figure 22 ..................................................................................................................................................... 39
Figure 23 ..................................................................................................................................................... 39
6
Figure 24 ..................................................................................................................................................... 40
Figure 25 ..................................................................................................................................................... 40
Figure 26 ..................................................................................................................................................... 40
Figure 27 ..................................................................................................................................................... 41
Figure 28 ..................................................................................................................................................... 42
Figure 29 ..................................................................................................................................................... 42
Figure 30 ..................................................................................................................................................... 44
Figure 31 ..................................................................................................................................................... 44
Figure 32 ..................................................................................................................................................... 47
Figure 33 ..................................................................................................................................................... 48
Figure 34 ..................................................................................................................................................... 49
Figure 35 ..................................................................................................................................................... 49
Figure 36 ..................................................................................................................................................... 50
Figure 37 ..................................................................................................................................................... 50
Figure 38 ..................................................................................................................................................... 51
Figure 39 ..................................................................................................................................................... 54
Figure 40 ..................................................................................................................................................... 54
1 - Soil Parameters ...................................................................................................................................... 63
Table 1* ....................................................................................................................................................... 18
Table 2 ......................................................................................................................................................... 20
Table 3 ......................................................................................................................................................... 21
Table 4 ......................................................................................................................................................... 23
Table 5 ......................................................................................................................................................... 28
7
Table 6 ......................................................................................................................................................... 31
Table 7 ......................................................................................................................................................... 31
Table 8 ......................................................................................................................................................... 32
8
Introduction
High-rise buildings started to emerge in the States during the last 19th century in urban
areas, due to the fact that an increase in land prices and great population densities created a large
demand for buildings that were rising vertically, rather than those spreading horizontally, and in
turn occupying lower areas of expensive land. High-rise buildings were made practicable by the
use of steel structural frames and glass exterior sheathing. By the mid-20th century, high-rise
buildings had become a standard feature of the architectural landscape in most countries in the
world.
High-rise buildings sometimes require foundations that can withstand and support very
heavy gravity loads. These foundation systems usually consist of concrete piers, piles or caissons
that are sunk into the ground. Beds of solid rock are the most desirable base, but ways have been
found to distribute loads evenly even on relatively soft ground. The most important factor in the
design of high-rise buildings, however, is the building’s need to withstand the lateral forces
imposed by winds and potential earthquakes. Most high-rises have frames made of steel or steel
and concrete. Their frames are constructed of columns and beams. Cross-bracing or shear walls
may be used to provide a structural frame with greater lateral rigidity in order to withstand wind
stresses. Even more stable frames use closely spaced columns at the building’s perimeter, or they
use the bundled-tube system, in which a number of framing tubes are bundled together to form
exceptionally rigid columns.
Project Description
United Arab Emirates, Dubai
5 Star, Luxury Hotel
AL-KHAWAJAH Engineering Consultancy
United Arab Emirates, Dubai
KHAWAJAH Engineering Consultancy
Figure 1
9
10
Figure 2
11
Sections
Figure 3
12
Figure 4
Scope
● Propose a Structural System.
● Load Identification
● Identify Construction Method for excavation
● Structural Analysis due to gravity and lateral loads (Earthquake and Wind)
● Design of the superstructure components.
13
● Analysis and design of the substructure and foundation.
● Producing drawings up to the design development stage.
Deliverables
● Valid Construction Method
● Adequate System for Lateral Loads
● Calculation Sheets
Load definition
Structural Analysis
Design Calculations for Superstructure and Substructure
● Design Development (up to 60%) drawings.
14
Methodology
● Gravity, wind and earthquake loads from ASCE 7-10.
● Preliminary sizing of structural members (slabs, beams, columns).
● Structural modelling and analysis using SAP2000, SAFE and ETABS 2015.
● Geotechnical and basement analysis using Geo5.
● Structural and Geotechnical design following ACI 318-14.
● Structural drawings and detailing using AutoCAD.
15
Initial TimeLine
Challenges
Designing the 4-storey basement.
Total of 19.58 m below the ground level
Considering uplift pressure of the water in the soil on depth of foundation
Large Spans & Restrictions due to deflection.
Swimming pool (mass irregularity).
Using new codes of practice.
Using new programs for analysis.
High likelihood for analytical torsion on top floors.
16
Preliminary Design
Loads
Below is the table of load combinations as per the ACI
Figure 5
- Live Loads are reduced by around 30% in combinations with earthquakes.
Slabs
We need to choose a system for the slabs that will not be a problem to the architecture
design as it is a hotel building and architecture features is a major requirement. Choosing our
system to be a Flat Slab System for various reasons. It is one of the systems that provide the most
flexible arrangements for services distribution as services do not have to divert around structural
elements.
17
Figure 6
Benefits
1) Construction
Construction of flat slabs is one of the quickest methods available. Lead times are very short
as this is one of the most common forms of construction. And this will be very efficient as a
critical activity to the project. Flat slabs are considered to be faster and more economic than
other forms of construction, as partition heads do not need to be cut around down stand beams or
ribs.
2) Procurement
Because this is one of the most common forms of construction, all CONSTRUCT members
and many other concrete frame contractors can undertake this work.
3) Cost, whole life cost, value
Flat slabs are particularly appropriate for areas where tops of partitions need to be sealed to
the slab soffit for acoustic or fire reasons.
18
Slab thickness came out to be 30 cm, according to the ACI states that slab thickness of
the slab is L/30* and since our largest span is 9 m. the slab thickness 30cm is taken from floors 6
to 34 only and not including the podium. Each slab is checked for deflection through SAP 2000
to check the accepted deflection.
Table 1*
19
Figure 7
Columns
We started by taking the Architecture drawings and at each column suggested by the architect
we took the tributary areas and through excel equations to get the Ultimate the loads on each column.
According to the ACI the column dimensions should not be less than 30cm.
The ratio between the dimensions should be at least 0.4. The procedure of preliminary
sizing process is:
1- Locate column service area.
2- Multiply ultimate gravitational area loads by service area to get column’s axial load.
3- Assume As/Ag of 1%, determining column section area (Ag).
4- Multiply that area by 1.3 to account for lateral loads’ effect.
For Axial and account for eccentricity.
20
Table 2
The table above is used in modelling of members to be cracked sections under flexure and axial
loads. In checking serviceability, factors are permitted to be multiplied by 1.4.
Initial table of the column sizes as per the tributary area (preliminary sizing of columns)
Modelling of the building
We will be modelling our project using SAP2000, ETABS & SAFE14. Each software
will result in special cases, the table below illustrates the differences and common features of the
software’s.
All the softwares will analysis our building and as well will give us the deformation of
the model, while only safe and etabs can give us the area steel required to cover the moment.
will be able to get the punching values at the columns by
Each software results in same and different results depending on the way it is modelled.
Software Specialties
SAP
2000
- Irregular Shapes
Regular Contouring
Control of mesh
Table 3
ling of the building
We will be modelling our project using SAP2000, ETABS & SAFE14. Each software
will result in special cases, the table below illustrates the differences and common features of the
All the softwares will analysis our building and as well will give us the deformation of
the model, while only safe and etabs can give us the area steel required to cover the moment.
will be able to get the punching values at the columns by modelling the project on SAFE.
Each software results in same and different results depending on the way it is modelled.
Comparison
Irregular Shapes -
Regular Contouring -
Control of mesh
- Same +ve moments as
SAFE
- Different –ve Moment as
21
We will be modelling our project using SAP2000, ETABS & SAFE14. Each software
will result in special cases, the table below illustrates the differences and common features of the
All the softwares will analysis our building and as well will give us the deformation of
the model, while only safe and etabs can give us the area steel required to cover the moment. We
the project on SAFE.
Each software results in same and different results depending on the way it is modelled.
ve Moment as
22
- Locating Column as Point
hinges
- Manual Meshing
SAFE
SAFE 14 - Checking Punching to
Manual calculations
- Locating column as
section area
- Self Meshing
- Same +ve moments as
SAP
- Different –ve moment as
SAP; more accurate in
accounting for their
stiffness connection.
Due to discontinuity of nodes in
the shells
ETABS - 3D modelling, for transfer
floors modelling
- l3D modelling lateral
loads
- Self Meshing
-Accurate results for Lateral
Loads.
23
Table 4
Selection of the Gravitational Slab System
Elliptical Plan floors from 6th till 34th:
- To maintain the view of the slab clear and to cover the large spans, a flat slab
acting as a rigid diaphragm is selected for the slab system. There are no edge
beams because slab edge is not ending at column faces, there are cantilever parts.
- By having the largest span of 9 meters and following ACI 318-14, the slab depth
is selected to be (hSlab = L/30 = 9000/30 = 300 mm). (i.e: the yielding tensile
stress of main reinforcing steel is 400 MPa which is approximately equivalent to
60,000 psi).
- To test the system’s capacity for flexure, immediate deflection and long-term
deflection, a model has been constructed on SAP2000 for typical floor from 6th to
13th.
24
9
Moments Results (M11):
Figure 8
25
10
- Slabs are also modeled using SAFE to account for columns stiffness giving more
accurate results for moments and deformation.
- Moments in M1-1 and M2-2 are obtained from analysis to choose an adequate
reinforcement mesh layer. Moment capacity with the chosen reinforcement mesh
is calculated to locate the areas that require additional bottom reinforcement for
positive moment and area that require additional top reinforcement for negative
moment.
- Punching Check is also check manually and through SAFE.
26
Figure 11
Section Capacity Ratio for Punching Shear
Figure 12
- Punching is also check for all planted columns
27
Figure 13
- Here is our excel sheet used for slabs’ flexure design:
28
Table 5
- “True” means section is safe against flexure and “False” means the section still
needs additional reinforcement.
- Deformation is also checked on slabs.
29
Figure 14
- In some case our limit for deflection was L/480 under immediate live loads as
slabs are connected to non-structural curtain walls.
- We also checked long term deformation by taking into consideration the creep
effect on concrete under dead and sustainable live loads; creep effect under dead
loads could be decreased using Cambering technique. The creep factor is
influenced by the time factor and compression steel in the section.
30
ETABS Model:
Figure 15
- Dealing with structure dynamics and lateral loads on the structure, we have
modeled the structure on ETABS, performed seismic and wind analysis in
addition to selecting the adequate system.
Seismic Analysis:
- Special Reinforced Concrete Shear Walls system is adequate for SDC B and C for
no limit (NL) for the building height. The system is limited to buildings of height
160 ft (50m) for SDC D and it is not permitted to be used for SDC E and F. Our
building is more than 160 meters height using Special shear walls so SDC C is
acceptable at most.
31
Table 6
Table 7
- In this case, SDS cannot exceed 0.5 and SD1 cannot exceed 0.2 to remain in SDC C.
- Here are the data input for Special Shear Walls: ASCE 7 and other model building codes
acknowledge that structures will be loaded beyond their elastic range during seismic
events. Damping and ductile yielding make it unnecessary to design for the full inelastic
design force, so the code divides the seismic response by the R-factor to get a lower
elastic design force or base shear. Higher R-factors represent more ductile systems and,
therefore, yield a lower seismic design force. Deflections are multiplied by the Deflection
32
Amplification Factor (Cd) to obtain the expected inelastic deflections. Similarly, the
System Overstrength Factor (Ωo) is an amplification factor that is applied to the elastic
design forces to estimate the building can exist safely in Dubai, but we have assigned
seismic data for higher ground acceleration within the acceptable limit and SDC the
maximum expected force that will develop.
- The building can exist safely in Dubai, but we have assigned seismic data for higher
ground acceleration within the acceptable limit and SDC C to have seismic design.
- Here is the response spectrum for the selected seismic records to locate the acceleration
of the structure for each mode according to the mode’s period.
Table 8
- To maintain SDC C to maintain the adequacy of using Special Shear Walls system
maximum seismic record can be used is: Ss=0.31 and S1=0.14.
-
- Here is the Response Spectrum:
33
Figure 16
- Here is our ETABS data input following the response spectrum:
Figure 17
It is included that SDS and SD1 are within the limit of Seismic Design Category (C).
- Our project is residential and SDC is C so the importance factor is (1.0) which is case
2. For that, the allowable interstory drift is 0.025 following ASCE 7-10.
0
0.05
0.1
0.15
0.2
0.25
0.3
0 1 2 3 4 5 6 7
From (0) to (To)
From (To) to (Ts)
From (Ts) to (TL)
34
Figure 18
- Here is all seismic data input:
35
- Here is the seismic output with the base shear coefficient and the elastic base shear
acting on the structure. Load case (EQx) means 100% earthquake force on X-
direction and 30% in Y-direction; and vice versa with (EQy).
36
Wind Analysis:
- Following ASCE 7-10 specifically chapter 6, our project exists in urban area and is
satisfying surface roughness and exposure condition of B.
- Structure is considered to be flexible if the natural frequency is less than 1 Hz. In our
case, the fundamental period 6.233 second showing the natural frequency of (wn =
2π/6.233 = 1.008 Hz). So the natural frequency is just on the edge of being flexible to
rigid structure; as a result, wind gust factor is calculated twice; one for being flexible
and one for being rigid. As a result, the maximum gust effect factor is taken to be 1.
Four wind load cases are assigned; (X-direction), (Y-direction), -(X-direction), -(Y-
direction).
37
- Here is also our data input for topographic (Kzt) and directional (Kd) factors in
addition to the wind speed.
System Selection:
- After assigning the lateral loads on the structure, major problems appeared in the
system:
1- The top 3 floors are only supported laterally on 3 walls and almost supported
partially in Y-direction so they are very soft stories. Also, these walls are carrying
huge shear forces at these floors.
38
Figure 19
2- The center of rigidity is very far from the center of mass which is inducing high
torsional stresses on these walls.
3- The drift is also deemed unsafe where it is more than the allowable. The drift was
0.015529*Deflection Amplificator (5) = 0.076145
Figure 20
39
Figure 22 Figure 21
- We have been thinking to replace some columns to be shear walls without any
violation for the architectural drawings. As a result, 10 columns are changed to be
shear walls and they are located within the center of mass so they are controlling drift
and reducing the distance between center of mass (CM) and center of rigidity (CR).
Before Adjustments After Adjustments
- The limitation in increasing the stiffness, the period decreases which matches higher
ground acceleration since we are in “displacement sensitive” zone in response
spectrum.
- After these adjustments, the top 3 floors are no longer soft and drift is safe.
Figure 23
40
Figure 26 Figure 25
- Drift = 0.004235*Deflection Amplificator = 0.0212.
Lateral Loads on the structure:
- Lateral Wind Loads on stories diaphragms from X-direction in step number 2:
Figure 24
Story Shear from Seismic Loads on the Structure
EQx EQy
41
Drift due to Earthquake (EQx):
Figure 27
Drift = 0.004235*Deflection Amplificator = 0.0212
Earthquake Drift Criticality = 0.0212/0.025 = 0.848
- Drift due to Wind (Windx):
42
Figure 28
Wind’s Drift Criticality = 0.000747/0.0025= 0.3
Earthquake is governing as its drift is more critical than wind.
Diaphragm Condition:
Figure 29
- Slab Diaphragm is considered to be rigid if (Max/Avg) diaphragm drift is less than 2
or if the void area is 50% greater than the total area. Rigid diaphragm is not likely to
43
get deformed and it is capable of transferring stresses to its vertical support. Flexible
diaphragm is considered to be simply supported on its vertical elements.
- In our model, we have assumed rigid diaphragm to be checked after running the
model.
- From the analysis results, our assumption is valid.
- Seismic Moments on slabs from ETABS are very small as slabs are modeled as rigid
diaphragms. So slabs are exported from ETABS to SAFE with all loads cases to
account for moments acting on the slabs from seismic loads.
44
Figure 30
Moment M1-1 from ETABS for EQx
Story 12th
Figure 31
M1-1 from SAFE for EQx in accounting for cumulative deformation and seismic
moments on Slabs
Story 12th
- To check the match between ETABS and SAFE in transferring loads cases, moments
and stresses on the slabs from vertical loads are checked to be similar in both
softwares.
45
Remedial Measurements:
- In case of structure irregularities, ASCE 7-10 is permitting remedial actions to
account for irregularities based on Seismic Design Category. Types of irregularities
are:
1- Torsional Irregularities that took place in upper 3 floors(Horizontal Irregularity)
2- Mass Irregularity due to swimming pool (Vertical Irregularity)
3- Stiffness Irregularity between podium and basement floors (Vertical Irregularity)
Example for types of Torsional Irregularity
- The remedial actions depend on the type of irregularity and the SDC of the structure.
- List of Remedial Measurements:
46
Modal Analysis:
- Modal Analysis has been performed to get the modal shapes of the structure under
free vibration; there is a specific period for each modal shape. Under each mode, the
building undergoes specific ground acceleration and modes are combined together
using (CQC); not Square Root of Summation of Squares (SRSS) since the difference
between the participation in most cases is less than 10%. The target is to reach 90%
of modal participation so we have performed analysis for 90 modes.
47
Figure 32
- 69 modes are enough to be used in the analysis after reaching 90% percent
participation.
- Ritz Modal analysis is used over Eigen analysis as Ritz-vector analysis seeks to find
modes that are excited by a particular loading. Ritz vectors can provide a better basis
than do Eigenvectors when used for response analysis that are based on modal
superposition. Eigen Modal is not really efficient for High Rise Buildings due to the
huge number of DOFs which requires much more modal shapes to reach participation
of 90%.
- 2nd and 3rd modal shapes are torsional which may lead to critical condition in case of
structure free vibration. As a result, the structure system is adjusted to minimize this
problem especially the torsional stresses in free vibration.
48
Swimming Pool System:
- A large swimming pool exists in the 4th floor in the podium with an average depth of
2 meters inducing area loads of 15kN/m2 over the pool’s area. In addition, there is the
problem of large span of 16 meters; as a result, flexure and deflection are very
critical. That area in the 3rd floor is “Plant and Equipment Room”, so our goal is to
make it functional for the equipment; not to be open for the people comfort. We
thought of Planted Columns to support the swimming pool system.
Figure 33
- The Criteria of placing the columns and their orientation was:
1- Span of 5 meters to maintain the space for equipment
2- Minimizing the unbalanced moments transferred to columns to reduce the
likelihood of Punching Shear.
3- Considering the load path to efficiently locate the columns orientation.
4- Controlling one-way slab shear to be fully controlled and resisted by concrete.
System for Slabs Large Spans:
49
- All Podium floors except the second floor are having a areas of large spans of 16
meters; having one slab of thickness 30 cm is deemed unsafe against deflection, and
having one slab of 60 cm is deemed uneconomic for the other areas. As a result, it is
decided to design a slab of thickness 60 cm only for the area that needs it. The thick
slab’s borders are targeted to have minimal stresses on them, so a model has been
made to locate the inflection points.
Figure 34
- Moving with the line of inflection points, the cutting line has been located.
Figure 35
Shear Walls and Cores Analysis and Design:
- Checking the nominal shear and torsion are less than the maximum allowable
specified by ACI.
- Checking the maximum acting axial load from “Envelope” load combination to locate
the plastic centriod and getting the dimensions of Boundary Element.
50
- Determining the type of boundary element (Special, Ordinary, no ties)
- Interaction Diagram has been developed to first estimate the reinforcement needed.
Figure 36
- Exporting results from all load combinations from ETABS to CSICOL to check steel
reinforcement and capacity ratio.
Figure 37
Example for One Core Wall in CSICOL
-2000
-1500
-1000
-500
0
500
1000
1500
2000
2500
-5000 0 5000 10000 15000 20000 25000
Mue 1%
Mue 2%
Mue 3%
Mue 4%
51
- Confining ties for the boundary elements are checked.
- Transverse Horizontal reinforcement is calculated and checked to be above minimum.
Columns Design:
- Following the same procedure of walls regarding:
1- Nominal Shear and Torsion Check.
2- Using interaction diagram to estimate the required reinforcement.
3- CSICOL Modeling to check the selected reinforcement for flexure under all load
combinations.
4- Design for Shear.
Figure 38
Column Analysis using CSICOL
52
P-Δ effect:
- Slenderness or “P-delta” effect is considered in designing vertical elements as it
induces higher moment values.
Torsion Check on Vertical Elements:
- Even after adjusting the lateral structure system, the center of mass and the center of
rigidity for the diaphragm slab are still not close adequately. So, it is important to
check torsion on vertical elements. Torsion is taking place due to accidental torsion
with eccentricity of 0.05 in addition to analytical torsion due to the distance between
center of mass and center of rigidity.
53
All units in lb and in
- If the nominal torsional torque is less than quarter the cracking torsion, no torsion
reinforcement needed for the section.
Stairs Design:
- The project contained two different types of stairs; Slab Stairs and Helical Stairs. For
more accurate and economic analysis, stairs are first modeled using SAP 2000 on
hinges boundary condition, and then we could identify the load reaction for each
hinge for load cases and ultimate combination. Moving to ETABS, we could identify
the deformation at the locations of supports for the same load case. Moving back to
SAP 2000 Model, springs are assigned for the slab’s boundary conditions where the
stiffness used is the reaction force divided by the deformation for the same load case.
Iterations have been made in order to reach same deformation under the same load
case so the stair and the support are acting dependently as one unit.
54
Figure 39
Helical Stairs Modeling using SAP2000
Figure 40
Slab Stairs Modeling using SAP2000
Raft Design:
- All loads in the base are exported from ETABS to SAFE to model the raft. The area
of raft is limited with the boundaries of diaphragm walls. However, the raft is not
fixed to the diaphragms to avoid structure collapse in case of Raft’s settlement so they
have to behave independently.
55
- In modeling, soil properties (Modulus of Sub grade) have been assigned according to
the soil report.
- For Raft, settlement is more critical than soil bearing capacity and the maximum
allowable settlement is 50 mm under working loads condition.
- After Multiple iterations to adjust settlement, bearing capacity and avoid tension on
edges, the final thickness of the raft is 2.5 meters.
Settlement under working Loads
56
Soil Pressure Table in kN/m2
- Balanced-Failure reinforcement percentage has been calculated.
- The reinforcement percentage is limited between the minimum (0.2%) and balanced
reinforcement percentage.
- For flexure resistance for “Envelope” load case, we are using 3 layers top and 3 layers
bottom each of reinforcement web 10φ25/m. However, this reinforcement is not
enough for some areas requiring additional steel.
- For the blue shaded parts, additional of 10φ25/m.
57
- Shrinkage reinforcement is needed to be 5 layers of 10φ12/m. Although Raft is not
exposed to temperature frequently, but concrete pouring takes place in stages to
minimize the strain of concrete.
- Punching Check gives positive results where there is no likelihood for columns
punching the raft.
58
Recommendations in Analysis of High Rise Buildings
- Slabs are not preferred to be modeled independently using 2D model using hinges as
elastic shortening of columns shall be considered especially for the top floors.
- Slabs are not preferred to be designed under gravitation loads only as seismic loads
induce additional moments on the slab. Further, the system might get changed after
assigned lateral loads.
- Using Ritz Modal Analysis rather than Eigen Modal Analysis since the latter requires
much more modal shapes to achieve 90% modal participation factor due to the huge
number of degrees of freedom.
Aerodynamics Analysis
Using the GID software, which will analysis the pressure, exposed to the Slab edge of our
project.
What is GID? GID is a universal, adaptive and user-friendly pre and postprocessor for
numerical simulations in science and engineering. It has been designed to cover all the common
needs in the numerical simulations field from pre to post-processing: geometrical modelling,
effective definition of analysis data, meshing, data transfer to analysis software, as well as the
visualization of numerical results.
The main idea behind the analysis is to find weather the shape of the building is suitable
for the wind in the area of the project.
Analysis:
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- Evaluate the wind action over structure
- Wind forces and pressures acting on a building structure
Importance, determination of airflow patterns around the building for interference effect among
adjacent building may alter the velocity filed in the surrounding.
Wind @ x direction velocity Streamline
Presssure @ x direction Pressure stream line
Kn/m
Pressure
n velocity Streamline
Pressure stream line Ranging Pressure 656 Kn/m to
Suction
Suction
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Ranging Pressure 656 Kn/m to -585
The drag force wind in the x direction is per meter height in order to get the force for the floor
with a height of 3.5m = 12.25 *3.5
Rotated the building in the other direction to see the effect of the wind in the other
surface.
Wind @ Y direction Velocity
The drag force wind in the x direction is per meter height in order to get the force for the floor
with a height of 3.5m = 12.25 *3.5
Rotated the building in the other direction to see the effect of the wind in the other
Velocity streamline
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The drag force wind in the x direction is per meter height in order to get the force for the floor
Rotated the building in the other direction to see the effect of the wind in the other
Pressure @ Y direction
Pressure stream line
Ranging Pressure 1310 Kn/m to
Differences in Etabs and GID
In the comparison of the drag forces between the GID and etabs we found
slight differences between the force. In the GID software, we import the slab edge without any
Ranging Pressure 1310 Kn/m to -3400 Kn/m
In the comparison of the drag forces between the GID and etabs we found
differences between the force. In the GID software, we import the slab edge without any
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In the comparison of the drag forces between the GID and etabs we found out, we have
differences between the force. In the GID software, we import the slab edge without any
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41 - Soil Parameters
voids, columns or shear walls while in etabs the slab is modelled with Structure Interaction and the
Direction Factors, and the structure system.
Geotechnical Analysis, Constructions Stages and Foundation Design
We started off by analyzing and assessing the soil report in details to be able to determine the
type of soil we have and hence come up with initial proposals for our foundation and
construction stages.
Our soil type was general weak rock and since it was more convenient, we used the conversion
of rock parameters to soil parameters to perform our analysis and design. The following table
shows the soil profile with its shear parameters:
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We first started off by determining the maximum depth to which the excavation can be carried out
without bracing/support. This was done by obtaining the active lateral earth pressure acting on the
soil profile as shown:
It is estimated that only about depths 3 to 6 m would be stable, while the rest of the soil would
fail. This would be inapplicable to having an open-cut excavation. Since we also have a
basement depth of 19.5 m under the ground we settled for an installation of a reinforced concrete
diaphragm wall that will support the soil as we excavate deep in the soil for more than 20 m. The
diaphragm wall will also be of advantage because it will act as the basement wall at the same
time. Stresses on the diaphragm as a basement wall were also taken into consideration using the
ETABS program. A raft foundation was chosen to be the most suitable foundation type for our
soil because of it being a weak rock and because we already have a deep basement. We have a
ground water table at 13m under the ground which we’ll have to dewater or place a jet plug to
decrease it to at least 22 m under the ground. We initially settled for the use of a jet plug to avoid
any settlement in the soil that will affect the surrounding building foundations.
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Our initial step was to be able to settle for proper construction stages. Many trials were
performed on the Geo5 program (sheeting check) to be able to determine an initial proposal of
construction stages and hence we verify each construction stage. Our initial Proposal was as
follows:
- Diaphragm wall of 2m thickness and 26 m depth.
- Excavation of 22m depth.
- Decreasing water level from 13 m to 21 m under the ground
We later on edited this initial proposal to a thickness of 1 m since a 2 m thick diaphragm wall
would be hard to construct in weak rock with a high chance of caving in. Excavation depth was
increased to 25 m deep underground to account for any increase in the raft depth. Also, depth of
the diaphragm wall was increased to 33 m to try to overcome any uplift pressure that will result
from decreasing the water level from 13 m to 25 m underground. Four Anchors will be placed at
different stages of the construction stages to limit the displacement of the diaphragm wall to less
than 2 cm to avoid any effect it may have on the superstructure of the high rise building. The
anchor specifications were obtained from Strand Anchor Systems with a cross sectional area of
12880 mm^2, placed at an angle of 15 degrees to the horizontal line, has a length of 10.5m and
anchor spacing of 4m:
- First Anchor at 8 m deep
- Second Anchor at 10 m deep
- Third Anchor at 18 m deep
- Fourth Anchor at 20 m deep
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Then we came up with the following ten final construction stages and checked the stability of the
diaphragm wall at each stage, the maximum moment, shear and displacement at each stage, the
internal stability of each anchor at each stage and finally the overall slope stability at each stage:
1st Stage: 8 m deep excavation
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2nd Stage: 1st Anchor
68
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3rd Stage: 10 m deep excavation
70
71
4th Stage: 2nd anchor
72
5th Stage: Placement of Jet Plug
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74
75
6th Stage: 18m deep Excavation
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7th Stage: 3rd anchor
77
78
8th Stage: 20 m deep excavation
79
80
9th
Stage: 4th anchor
81
82
10th Stage: 25 m deep excavation
83
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As seen previously, each stage is stable in terms of internal anchor stability and overall slope
stability. Also the maximum stresses and displacement the diaphragm wall is subjected to are:
- Maximum Moment of 763 KNm/m
- Maximum Shear Force of 531 KN/m
- Maximum Displacement of 1.34 cm
Since we initially settled for an installation of a jet plug at 25 m depth under the ground, we had
to calculate the uplift pressure resulting from this decrease. The uplift pressure was calculated
manually by drawing a flow net and obtaining the uplift pressure at the most critical point at the
end of the diaphragm wall and then checking how much of the soil can overcome the uplift
pressure and final determining the depth of jet plug we need to help overcome it. This is a picture
of the flow net hand drawn along with the calculations performed:
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Hence these calculations allowed us to settle for a jet plug thickness of 1.5 m deep.
This depth was to our advantage because we were able to then maximize the depth of
our raft as we please but while keeping our bearing capacity and settlement limits. We
choose a raft depth of 2.5 m and performed the allowable bearing capacity
calculations for rock to determine the allowable bearing capacity for the raft
foundation. Nevertheless, we were more concerned with settlement issues than
bearing capacity issues since rafts undergo local shear failure and our analysis
obtained a settlement of 48 mm which is less than the allowable of 50 mm. The
following page shows the calculations performed to determine the bearing capacity of
the raft foundation:
Detailing
Columns
The reinforcement of the columns was determined according to design calculations.
Some of the columns were safe with little reinforcement, however the
was increased to satisfy the minimum code limitations (
required steel in each of the columns, the bars were arranged in the columns
maintaining the symmetrical requirement, and ensuring that the spacing between bar
and stirrups do not exceed 150 and 300 mm respectively, by placing stirrups every
two bars (ensuring that the maximum spacing between each bar is less than 150 mm).
The reinforcement of the columns was determined according to design calculations.
Some of the columns were safe with little reinforcement, however the reinforcement
was increased to satisfy the minimum code limitations ( = 0.01). Upon finding the
required steel in each of the columns, the bars were arranged in the columns
maintaining the symmetrical requirement, and ensuring that the spacing between bar
and stirrups do not exceed 150 and 300 mm respectively, by placing stirrups every
two bars (ensuring that the maximum spacing between each bar is less than 150 mm).
1
The reinforcement of the columns was determined according to design calculations.
reinforcement
= 0.01). Upon finding the
required steel in each of the columns, the bars were arranged in the columns
maintaining the symmetrical requirement, and ensuring that the spacing between bars
and stirrups do not exceed 150 and 300 mm respectively, by placing stirrups every
two bars (ensuring that the maximum spacing between each bar is less than 150 mm).
2
Elevation for a Typical C38 Column
Slab Reinforcement
Reinforcement for the slabs was determined through the moment analysis done by
SAFE. For each floor two plans were drawn, one to show the top reinforcement, and
one to show the bottom reinforcement of the slab. Each of these plans showed the
moments coming from both directions on each slab (M11 and M22). A mesh was
unified across the entire slabs for each the top and bottom, and additional steel was
added in areas that required more reinforcement where the additional steel
reinforcement varied from slab to slab, depending on the moments acting on it.
3
First Floor Bottom Mesh
Unified Mesh for Entire Slab
4
First Floor Top Mesh
M11 Reinforcement
M22 Reinforcement
5
14th to 24th Typical Plan Top Mesh
Areas showing additional moment, requiring extra reinforcement
6
32nd Floor Bottom Mesh
32nd Floor Top Mesh
7
Shear Walls
This is the detailing of one of the shear walls based on NIST for reference, showing
special boundary element, which are used in areas that have high compression from
both moment and axial.
Shear Wall Reinforcement
Stairs:
Since this is a slab type staircase, the main reinforcement is placed at the bottom, and
the secondary reinforcement is placed parallel on top of it. The stirrups are placed
perpendicularly over the two layers, holding then together in place.
8
Stairs Reinforcement
9
References - Codes Used: - American Concrete Institute 315-99 - American Concrete Institute 318-14 - American Society of Civil Engineers 7-10 - National Institute of Standards and Technology
- Articles/Books Used: - Strand Anchor Systems for Permanent and Temporary Rock and Soil Anchors.
(2011, February). Retrieved April, 2016, from http://www.contechsystems.com/cts-cd/Strand/Catalogue.pdf
- Taranath, B. (n.d.). Structural analysis and design of tall buildings.