Creep and Shrinkage of Columns in Tall Buildings

Creep and Shrinkage of Columns in Tall Buildings

Creep and Shrinkage of Columns in Tall BuildingsA MS Thesis Presentation by Oluwatobi Babarinde

Supervisors/ Committee Members:Professor David CorrProfessor Gianluca Cusatis2/11/2016

McCormick Northwestern EngineeringCan we get started?

Hello everybody, thank you for coming. my name is Oluwatobi Babarinde andToday I will be making a presentation on

I will be talking about -the concepts of creep and shrinkage in concrete-how we model these concepts-I used the models in estimating creep and shrinkage deformations of a column I will be willing to take your questions during and after the presentation1

2/11/20162

McCormick Northwestern EngineeringPresentation Outline32/11/2016

McCormick Northwestern Engineering

3

BackgroundConcrete in all its various types is the most used material in the construction industry all over the world.The consumption of cement gives an indication of the consumption of concrete. World cement consumption grew an estimated 4.6 percent in 2014 from 4.0 billion metric tons in 2013 to 4.3 billion metric tons. Consumption is expected to grow 2.2 percent in 2015, 3.7 percent in 2016, and remain near 4 percent growth during 2017-2018 according to PCA.Concrete is widely used because:it is very durable to waterit has significantly better resistance to fire and cyclic loading it can be easily formed into whatever structural shape is desired and it is relatively cheapHowever, the durability and serviceability of concrete is a major concern nowadays. We want stronger concrete that lasts longer.

2/11/20164

McCormick Northwestern EngineeringMotivation:

Concrete is without argument, the most used construction material. Cement consumption gives an indication of concrete consumption.

Durability, serviceability are two common concerns for concrete nowadays. We are pushing the limits on the service life of structures to at least 100 years.

Therefore, we are looking into ways of making concrete stronger, and last longer.This is where creep and shrinkage studies come in.

Creep and shrinkage deformations of concrete are easily overlooked, but play significant roles in the durability of concrete.Leads to crackingreduces lifedeterioration.

So we need to understand concrete, especially, its creep and shrinkage.4

Composition of ConcreteConcrete is popularly defined as a mixture of hydraulic cement, aggregates, and water, with or without admixtures, fibers, or other cementitious materials. That is, concrete is a heterogeneous material or a composite. The following are the basic components of concreteCement:The typical compounds that compose Ordinary Portland Cement are Tricalcium Silicate - C3S (50%), which is responsible for strength and is the most dominant constituent of cement, followed by Dicalcium Silicate C2S (18%), Tricalcium aluminate (C3A), Tetracalcium aluminoferrite, with Calcium Sulfate Dihydrate the has the least quantity at 6%.2/11/20165

McCormick Northwestern EngineeringThis study looks and concrete in terms of 2 broad views-the hygral, thermal and chemical processes -How these processes translate to creep and shrinkage behaviors.But first, a brief comment on concrete.5

Hydration Reaction of CementCalcium silicates consisting of tricalcium silicate and dicalcium silicate react with water to form hydrated cement paste. The two calcium silicates induce very similar hydration reactions2C3S + 11H C3S2H8 + 3CH2C2S + 9H C3S2H8 (C-S-H) + CH

2/11/20166

McCormick Northwestern EngineeringWhen mixed with water concrete undergoes a hydration reaction.

This is an exothermic reaction and Fig 1 shows the heat evolution comprising of 5 stages

Tricalcium Silicate, C3S, is responsible for the early age strength., Dicalcium Silicate C2S,. Tricalcium Aluminate C3A, similarly contributes to early age strength development, but only slightly. It is responsible more notably for releasing large amounts of heat during the first few days of hydration

All these are important in formulating a model to capture the behavior of concrete.6

Composition of ConcreteAggregatesHydrated cement paste in concrete acts a binder whereas it is the aggregates that form the matrix. Aggregates are considered fine comprises those that pass through sieve No. 4 (1/4) while those retained are referred to as coarse aggregates.. 60 75% by volume (70-85% by mass), hence it can be expected that its properties should dominate the overall concrete properties.AdmixturesConcrete has greatly changed since its discovery due to changes in the constituents of cement used today and the various admixtures available to give concrete the desired properties. Admixtures are chemicals used to alter the concrete properties such as the set time, strength, workability and heat generated during hydration of cement. Some of admixtures are air-entraining, retarding, hydration controlling, while some are water-reducing and Alkali-Silica Reaction (ASR) inhibiting2/11/20167

McCormick Northwestern EngineeringAgg are the largest constituents of concrete7

Microstructure of Concrete: The Interfacial Transition Zone (ITZ)On the macroscopic level, concrete can be seen to have 2 components: the hydrated cement paste and the aggregates. However, on the microscopic level, an additional phase is further identified called the Interfacial Transition Zone (ITZ), which explains so many behaviors of concrete including creep and shrinkage. The ITZ exists between the aggregates and the hcp as shown in Figure 2.2/11/20168

Figure 2: Diagrammatic Representation of the ITZ Source: Mindess, Young, & Darwin (2002)

McCormick Northwestern EngineeringConcrete and the Hygro-Thermo-Chemical (HTC) Model

2/11/20169Di Luzio, G., & Cusatis, G. (2009). Hygro-thermo-chemical modeling of high performance concrete. I: Theory. Cement and Concrete Composites, 31(5), 301308.

McCormick Northwestern EngineeringThe model simulates moisture transport and heat transfer in HPC by taking into account explicitly the coupled effect of cement hydration, SF pozzolanic reaction, and silicate polymerization

Water can be found in concrete in various phases [1113] thatcan be classified as follows: (a) capillary water, (b) water vapor, (c)adsorbed water, and (d) non-evaporable (chemically bound) water

9

Concrete and the Hygro-Thermo-Chemical (HTC) Model

2/11/2016Di Luzio, G., & Cusatis, G. (2009). Hygro-thermo-chemical modeling of high performance concrete. I: Theory. Cement and Concrete Composites, 31(5), 301308. 10

McCormick Northwestern EngineeringConcrete and the Hygro-Thermo-Chemical (HTC) Model

2/11/2016Di Luzio, G., & Cusatis, G. (2009b). Hygro-thermo-chemical modeling of high performance concrete. I: Theory. Cement and Concrete Composites, 31(5), 301308. 11

McCormick Northwestern Engineeringaxis-symmetric setting

11

Solidification Microprestress Microplane (SMM) Model for Creep and ShrinkageDefinition of Terms:Shrinkage Basic shrinkageDrying shrinkagePlastic shrinkageSwellingCreep strainBasic creepDrying creep2/11/201612

Figure 2 Showing the Relationship between Derived and Measure Strain Values Source: (ACI, 2005)

McCormick Northwestern EngineeringDefinition of Terms:Shrinkage: is the strain measured on a load-free concrete sample. Basic shrinkage: which is caused by water loss due to the hydration of cement.Drying shrinkage: here, the strain is due to moisture loss to the atmosphere due to relative humidity of the concrete samples environment been less than 100%.Plastic shrinkage: refers to the shrinkage concrete experiences before it sets into a non-fluid state.Swelling: is the expansion of concrete due to the reduction of capillary forces when immersed in waterCreep strain: This is the strain concrete experiences even though the stress level remains constant. It consists of:Basic creep: which is the type of creep occurring without water content loss i.e. in a sealed sample.Drying creep: as the name implies, is the creep strain accompanying moisture loss in a concrete specimen.

12

Factors Affecting Creep and ShrinkageSome of the factors considered to affect creep and shrinkage are :Mix proportion and Concrete Contents: Aggregate content Aggregate sizes, Water content and Elastic Modulus of AggregateProperties of cementAdmixtures Environmental Factors: Relative humidity, Cyclic humidity, TemperatureEffects of Design and Construction Practices: Curing , Heat and steam curing, Size and shape of member,Load and loading age

2/11/2016(Baant, Hauggaard, Baweja, & Ulm, 1997; Di Luzio & Cusatis, 2013; P. K. Mehta & Monteiro, 2013; Mindess et al., 2002)13Mechanisms of Creep and Shrinkage:The water molecule layers attached to the lining of the pores of the hydrated portland cement (hpc) gel, also known as adsorbed water, acts as a lubricant that helps sliding and shear of cement paste during creep or shrinkage.Consolidation due to the seepage of the adsorbed water Delayed elasticity due to hcp acting as a restraint to the elastic deformation of the aggregatesMicrocracking occurring in the transition zone in concrete, andMechanical deformation

McCormick Northwestern EngineeringSolidification Microprestress Microplane (SMM) Model for Creep and ShrinkagePrediction Models:ACI ModelCEB ModelGL2000B3/B4 ModelSSM Mechanisms:Aging of concreteShort term chemical agingLong term aging due to non-chemical aging

Drying creep effect: due to the Pickett effect. This is due to:Microcracking or due to strain-softening damage. Mechanism in the nanostructure related to the microprestressTransitional thermal creep: This is due to heating or cooling of concrete. The governing mechanisms are:Microcracking due to thermal effectsNanoscale mechanisms related to the microprestress

2/11/2016(Baant, Cusatis, & Cedolin, 2004) 14

McCormick Northwestern EngineeringSolidification-Microprestress-Microplane (SSM) Theory:Development of the solidification theory ~Bazant and Prasannan1989a,b! showed that the chemical aging ~mechanism 1a! canbe separated from the viscoelastic constitutive model if thatmodel is formulated not for concrete but for the solidifyingconstituentthe hardened cement gel

Aging of concreteShort term chemical aging due to the formation of new hydration products in a stress-free state on the wall of the capillary poresLong term aging due to non-chemical aging but due to relaxation of the microprestressDrying creep effect: due to the Pickett effect, the total strain during drying creep is lesser than the sum of the basic creep and drying shrinkage. This is due to:Microcracking or due to strain-softening damage. This is an apparent effect occurring in a companion sample and not the drying creep specimen itselfMechanism in the nanostructure related to the rate of shear slip and restoration of bonds. This is affected by the microprestress.Transitional thermal creep: This is due to heating or cooling of concrete. The governing mechanisms are:Microcracking due to thermal effectsNanoscale mechanisms related to the microprestress

14

Solidification Microprestress Microplane (SMM) Model for Creep and Shrinkage

2/11/201615Di Luzio & Cusatis, (2013) and Baant, Cusatis, & Cedolin, 2004)

McCormick Northwestern Engineering15

Solidification Microprestress Microplane (SMM) Model for Creep and Shrinkage2/11/2016Di Luzio & Cusatis, (2013) and Baant, Cusatis, & Cedolin, 2004) 16

McCormick Northwestern EngineeringSolidification Microprestress Microplane (SMM) Model for Creep and Shrinkage2/11/2016Di Luzio & Cusatis, (2013) Bazant, Caner, Carol, Adley, & Akers, (2000); Caner & Baant, (2000).17

McCormick Northwestern Engineering17

Purpose:To understand how different parts of the complete simulation interplayHTC Modeling of the column is modeledMesh Information: 32 triangle elements, 25 nodes The analysis was performed over a time period of 192 hours (8 days)

2/11/201618

Rudimentary AnalysisColumn Segment Modeled and Mesh Used

McCormick Northwestern EngineeringNo BCs and Self-heating18

Rudimentary AnalysisHTC Simulation Results2/11/2016

19

McCormick Northwestern Engineering center of the column (node 25) and exterior corner (node 1)19

Rudimentary AnalysisBarycentric Interpolation:Consider a point P with a triangle, with x1, x2 and x3 as the humidity or temperature values at the vertices as in the figure. The Barycentric coordinates are: Portion of red= A1/A=1Portion of green= A2/A=2Portion of blue= A3/A=3Value at P:(A1x1+A2x2+A3x3)/A

2/11/2016

20

This concept was used in matching the result of the HTC model to the Abaqus mesh

McCormick Northwestern EngineeringThe implementation basically involved checking if the coordinates of a node from the Abaqus mesh fell within a triangular element of the HTC mesh, and if it does, the areas and ratio of areas are found and used to interpolate the nodal values of the vertices of the element to the node in question. The interpolation program reads the INTERP.DAT file and the coordinates of the Abaqus mesh and outputs DIFOUT.fil.

20

Rudimentary AnalysisAbaqus Temperature, Humidity and Aging Input Files :Input files contain Record Keys used for different purposes ranging from specifying the version of the software to specifying nodal values. To illustrate the notation used in Record Keys, consider the following:*I 19I 41921A6.11-3I is used to specify an integer, D and A are for floating point and alphabet respectively. The above statement is for a record label 9 (from I 19), for a record key 1921 (from I 41921) used to specify Abaqus release details, which in this case is 6.11-3 (from A6.11-3). The other record keys used in our case are:1921 Abaqus release details2000 Increment start record1911 Output request definition201 Output variable identifier2001 Increment end recordMATLAB Scripts were used to generate the input files

2/11/2016MATLAB Script credits Erol Lale21

McCormick Northwestern EngineeringRudimentary AnalysisAbaqus Model:A two C3D8R element mesh as shown in Figure

Also, further simulations were performed for HTC modeling that had BCs and Abaqus model with and without steel components2/11/201622

McCormick Northwestern EngineeringColumn Modeling and ResultsProblem Statement:Deflection data have been collect on points as shown in Figure 16 starting from the sixth level at 3 and 28 days age with additional data collected on level 6 and 7 at 60 and 90 days age The columns of interest are highlighted in red because they are closest to the effect of the cantilever slab on level 5 and 6 especially level 5. The level 5 column is of more interest because of its cross section and because it is about 50ft (15m) in length, which is about five floor levels.

2/11/201623

McCormick Northwestern EngineeringColumn Modeling and ResultsL5 column has the steel cruciform and 12 #11 rebars L6 column does not have the cruciform but has 24 #11 rebars Both columns were constructed with 10,000psi concrete.2/11/201624Level 6 Column

Level 5 ColumnLevel 6 Column

McCormick Northwestern EngineeringColumn Modeling and Results

2/11/201625

Illustration of ProblemSymmetry Boundary Conditions


25

Column Modeling and Results2/11/201626Environmental Conditions of Columns

McCormick Northwestern EngineeringWhile level 5 spans the whole 147 days of data beginning on 1/8/2014, level 6 starts 47 days afterwards26

Column Modeling and Results2/11/201627Results of HTC modeling of Columns

McCormick Northwestern EngineeringColumn Modeling and Results2/11/201628Results of HTC modeling of Columns




30

Column Modeling and Results2/11/201631Load and Loading HistoryTributary Area - 712.89ft2

McCormick Northwestern EngineeringColumn Modeling and Results2/11/201632Abaqus ModelThe procedure for the analysis follows as such:Job was created and submitted. However, the analysis was terminated before full execution because the reason for the job was to write the models input fil (.inp) and also to create the part files.The part files are required for heat, aging and humidity files. Therefore, the part file (.prt) from step (i) above was replicated for each of the three inputs and named accordingly.

Next, a copy of the job input file created from step (i) was modified to read the temperature, aging and humidity files.Finally, a job was created from the modified input file from step (iii) above. The directory of the subroutine that evaluates the creep and shrinkage deformation according to the microprestress-solidification theory was also specified.Job was submitted and completed for each of the columns.

McCormick Northwestern EngineeringColumn Modeling and Results2/11/201633Abaqus Model

McCormick Northwestern EngineeringColumn Modeling and Results2/11/201634

McCormick Northwestern EngineeringConclusionThe results validate the ability of the models to capture processes of the hydration of cement, and the creep and shrinkage of concrete. This is powerful, because it adds to the array of tools available to the engineer for the design of concrete members to predict and monitor the progression of creep and shrinkage of such members.It is therefore recommended that: First, the HTC model currently accounts for the effect of silica fume on the hydration reaction, however there are other supplementary cementitious materials (SCMs) such as fly-ash and slag used high performance concrete (HPC). It is therefore worth incorporating such into the existing framework.A unification of all the programs used in the modelling will be a worthwhile endeavor. This unification would go a long way in helping to make this process transcend the research usage and encourage integration into structural design2/11/201635

McCormick Northwestern EngineeringThank you !Questions?2/11/201636


Creep and Shrinkage of Columns in Tall Buildings

Documents

Transcript of Creep and Shrinkage of Columns in Tall Buildings