8/12/2019 Poster Sadegh

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Investigation of Damage in Reinforced Concrete Shear Walls

Under Flexural Bending in ChileJasmin Sadegh, REU student | Tufts University , Medford, MA | jasmin.sadegh@gmail.com

Christopher Hilson, PhD Candidate and John Wallace, Ph.D., P.E., M. ASCE | University of California, LA, Los Angeles, CA

Overview of Project Phase I: Drift Analysis

Phase II-A: Buckling Failure of Steel Reinforcement

Phase II-B: Testing

Buildings in Chile

(built in early 2000s)Buildings in the US

6-8in thick RC shear walls

Hoop spacing every 8

inches

8+in thick RC shear walls

Hoop spacing every 4-6

inches

Figure 2. Background

(2-A) The building code in Chile, NCh433.Of96, adopted US

building code ACI 318-95, but did not require SBEs.

Observations and analysis of wall damage after the 2010 Mw

8.8 earthquake in Chile show that the walls were not compliant

with current ACI 318 11 and is a possible explanation for poor

performance. Results of this study will potentially yield

revisions to the US and Chilean codes.

Figure 4. Steps for Assessing Acceptable Moment at Anticipated

Roof Drift Demand from 2010 Earthquake in Chile

(4-A) The building response spectrum from the 2010 earthquake was usedto estimate roof drift. If the shear wall achieved this drift under imposed

monotonic loading, then drift was not cause of failure. This process used

displacement-based design methods to determine anticipated drift ratio.

Figure 3. Axial Load, WallShape, and Plastic Hinge

Impacts on Behavior

(3-A)Taller buildings have higher

axial loads that tend to increase

strength but decrease ductility.

(3-B) Flanged wall configurations

experience different strain

values, and have a different

moment - curvature under cyclic

loading than typical rectangular

walls.

(3-C) In elastic region of a

moment - curvature diagram,

structural analysis determines

relationship from curvature to

drift. Past 1st yield, plastic hinge

model is used to relate curvature

and drift.

Figure 5. Comparison of Moment-Curvature Diagrams for Varying Wall Configurations [assessed in steps 1, 2, 3](5-A) Wall geometry, reinforcement spacing, and axial load were inputted into Biax1996 and outputted moment-curvature plots for

five major shear walls. The first yield point was important for finding the beginning of the inelastic portion. The neutral axis depth at

a compressive strain of 0.003 is important for special boundary element trigger check. (5-A.1) The steep slope in the elastic portion

of this moment curvature graph shows that wall E8-E is stiff due to its long length (increased moment of inertia) and large axial

load demand (P/Ag*fc). (5-A.2) This graph for T-shaped wall E11-I shows the moment-curvature when the web is in compression.

Acknowledgments

Rodriguez,M., Botero, J., Villa, J. (1999). Cyclic Stress-StrainBehavior of Reinforcing Steel Including Effect of Buckling J.Struct. Engrg.,ASCE, 605-612.

Wallace, J. W. (2011) "February 27, 2010 Chile earthquake: Preliminaryobservations on structural performance and implications f or

U.S. building codes and standards," Proc. ASCE StructuresCongress, Las Vegas.

This project was generously funded by NIST towards ATC 94Task order 21. Thanks to ATC and CUREE, NEHRP, and FEMA foradditional support. This research was possible with funding fromACEEC-1005054 and CMMI-0927178.Special acknowledgement toJohn Wallace and particularly Chris Hilson for his patience and support.

1. Total Seismic Load on

critical section= (200psf)Dead Load + (40psf)Live

load+ Column and Wallload + load factors

The utility of the 2010 earthquake in Chile is

proposed

The results will impact the requirements of

SBE in ACI 318-11

Preliminary analysis must ensure the

concrete did not fail before achieving

anticipated drift demand using

displacement-based design

Secondary analysis must examine steelbuckling as an issue

Steps 1-3 of Phase I was completed for

major walls in the Emerald building

2. Use typical floor plan with shearwalls to determine wall geometry

4. Convert to Moment-Drift Graph andobserve if curve reaches drift capacity

Site specific response

spectrum;

4-A

6-A

6-A.2 Using Moment vs. Drift Ratiograph, identify varying driftpercentages and the respective ep*

For s/db ratios less than ~8.0

6-A.3 Hoop spacing and range ofpossible ep* values indicating bar

buckling (Rodriguez 1999)

Figure 6. Method for Determining

Expected Strains at Failure using

%Drift

(6-A) Steps for Determining Buckling:

(6-A.2) Calculate bar strain, ep*,

(defined in 6-A.1) at a % drift based on

Moment-Drift graphs

(6-A.3) See if ep* of reinforcement

meets or exceeds range of ep*expected at the s/db (Rodriguez 1999).

Incrementally increase drift ratio and

repeat process until steel buckles or

drift demand met

Figure 7. Method for Finding p*

for Reinforcement Restrained by Concrete

(7-A) Supplementing the Rodriguez test, this

test will identify the expected ep* values for

reinforcement in concrete rather than just

exposed steel. (7-B) Four specimens with

varying detailing as per ACI 318 S21.9.6.5 forwith fixed-fixed boundary conditions and

minimal cover. The construction and testing

will begin in Fall 2012. (7-C) Incrementally

increasing strain values will be applied until

steel failure.

bw

2.5bw

7-A 7-B

Estimated curve for

reinforcement steel restrainedin concrete

Figure 1. Investigating Wall Damage in Chile to Improve

ACI 318-11

(1-A) With the widespread failures observed in boundary

zones of Chilean walls, would they have required special

boundary elements (SBE) according to ACI 318-11? With

such a large spacing, could bar buckling have been an issue?

Phase I: Assess concrete crushing failure at large drift

demands Phase II: Assess failure of steel from tensile yielding

2-A Wall Shape P/Ag*f'c

1st Yield

Curvature, Web

Compr. (1/in)

c @ Compr.

Strain= 0.003c/lw

E8-E rectangular 0.271 0.0000148 120 0.426

E11-Grectangular

with small flange0.229 0.0000205 83.2 0.276

E11-IT

with small flange0.089 -0.0000174 73.9 0.365

E11-K T 0.189 -0.0000276 116.7 0.647

E11-L L 0.214 -0.0000235 89.1 0.473

5-A

6-A.1

ep* = eo ep(Rodriguez 1999)

5-A.2

3-A

3-C

3-B

1140

y

y w

w

hh

Typical Moment-

Curvature Diagram

3. Wall configuration and axial load yielda moment curvature using Biax1996

Typical Moment-.

Drift Ratio Diagrampyp

py

w

y

w

l

lhh

)(

)(

-400,000

-350,000

-300,000

-250,000

-200,000

-150,000

-100,000

-50,000

0

50,000

100,000-0.00008-0.00007-0.00006-0.00005-0.00004-0.00003-0.00002-0.000010.00000

Moment(kip-in)

Curvature(1/in)

M-C E11-I WEB COMP

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

0.00000 0.00001 0.00002 0.00003 0.00004 0.00005 0.00006 0.00007 0.00008

Moment(kip-in)

Curvature(1/in)

M-C E.8-E WEB COMP

For Further InformationFor further information, please contact: Jasmin Sadegh, Chris Hilson(chilson14@gmail.com), or John Wallace (wallacej@ucla.edu)

1-A

Centro Mayor- Concepcion

5-A.1

-0.003

0.002

0.007

0.012

0.017

0.022

0.027

0.032

1 2 3 4 5 6 7 8 9 10 11

Strain(in./

in.)

Phase IIB-Test Protocol7-C

Summary

Key Literature