Seismic Interaction of Flexural Ductility and Shear...

Seismic Interaction of Flexural

Ductility and Shear Capacity

Presented by: Rachel Howser, REU Student

Graduate Mentor: A. Laskar

Faculty Mentor: Dr. Y. L. Mo

Sponsored by the National Science Foundation

Contents

• Introduction

• Computer Modeling System

• Parametric Studies

• Determination of Ductility and Shear Capacity

• Previous Shear Strength Models

• Analysis of Accuracy of Previous Models

• Proposed Models

• Analysis of Accuracy of Proposed Models

• Conclusions

Introduction

• Not only applicable in US or Taiwan

• Research has worldwide implications

http://research.education.purdue.edu/challenge/hypermedia/04_05/Bill_Combs/New_Madrid/history.htm

Computer Modeling System

Cyclic Softened Membrane Model

(CSMM)

• UH preformed significant amount of research

to predict shear behavior

• Most recent model proposed by Mansour and

Hsu in 2005, CSMM

• Accurately predicts cyclic shear behavior

“Simulation for Reinforced Concrete

Structures” (SRCS)

• CSMM was implemented into a finite

element framework, OpenSees

• A non-linear finite element computer

program, SRCS, was developed by Zhong

and Mo in 2005

SRCS Accuracy and Parametric

Studies• Accuracy of program proven by comparing real data to predicted outcomes

• Accuracy allowed that series of tests be completed using SRCS instead of experimental results to develop relationship

• Preferred over experimenting because of cost and time constraints

Specimen PI2

-500 -400 -300 -200 -100 0 100 200 300 400 500

Displacement(mm)

Force(KN)

Analysis

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Seismic Loading

Specimen PI2

-90 -70 -50 -30 -10 10 30 50 70 90

Displacement(mm)

Force(KN)

Envelope Curve

Determination of Ductility

and Shear Capacity

Determination of Deflection at First

Yield• Determine 75% of the

maximum force and

corresponding

deflection

0 10 20 30 40 50 60 70 80

Deflection (mm)

Force (kN)

D @ 75%

Yield• Determine 75% of the

maximum force and

corresponding

deflection

• Draw a line through this

point and the origin

Yield• Determine 75% of the maximum force and corresponding deflection

• Draw a line through this point and the origin

• Find the deflection along this line that corresponds with the maximum force

0 10 20 30 40 50 60 70 80

Deflection (mm)

Force (kN)

D @ 75%

Determination of Deflection at

Ultimate Point• Determine 80% of the

maximum force and

corresponding

deflection along the

descending branch of

the curve

0 10 20 30 40 50 60 70 80

Deflection (mm)

Force (kN)

D @ ultimate

Flexural Ductility and Shear Strength

• Ductility is assumed to

be the ratio of the

deflection at the

ultimate point to the

deflection at the first

yield point

• The shear strength was

assumed to be 80% of

the maximum strength

0 10 20 30 40 50 60 70 80

Deflection (mm)

Force (kN) Data

D @ 75%

D @ ultimate

D @ yield

Flexural Ductility and Shear Strength

• Each envelope curve represents one point on Ductility vs. Shear plot

• More than 200 points obtained for study

• Points connected to represent relation-ships determined in parametric studies

Previous Models

• Previously defined models analyzed for this study were proposed by the following institutions:

– American Concrete Institute (ACI)

– California Department of Transportation (Caltrans)

– University of California San Diego (UCSD)

– University of Southern California (USC)

– University of California Berkeley (UCB)

Previous Models

• Applicable shear strength models plotted with actual shear strength

• No model is accurate for all given points

• Accuracy measured by taking the actual shear strength divided by the shear strength proposed by the model

UCBACI

Actual Data

Caltrans

Accuracy of Previous Models

Normal Strength Concrete

High Strength ConcreteACI Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

Caltrans Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

UCSD Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

USC Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

UCB Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

Proposed Models

• Normal Strength Concrete Model

• High Strength Concrete Model

• Universal Model

Normal Strength Concrete Model

spcn VVVV ++=

• Vn=nominal shear strength

• Vc=nominal shear strength provided by the concrete

• Vp=nominal shear strength provided by the axial load

• Vs=nominal shear strength provided by the shear

reinforcement

Concrete Contribution to Shear

ecc AfkV '=

• Vc=nominal shear strength provided by the concrete, N

• k=influence factor for flexural ductility

• fc’=specified compressive strength of the concrete, MPa

• Ae=80% of the cross-sectional area, mm2

Determination of Influence Factor for

Flexural DuctilityTypical Ductility vs. Shear Capacity

0 1 2 3 4 5 6 7

Ductility

Increased

Stirrup

Increased

Longitudinal

Steel Ratio

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

Flexural Ductility

3.5144

• q=upper limit of flexural ductility beyond which the

shear capacity remains constant

• ρt=stirrup ratio, decimal

0 1 2 3 4 5 6 7

Ductility

Flexural Ductility

8.224213300 2

++−=

r tt ρρ

• r=flexural ductility at which rate of decrease of shear

capacity with flexural ductility changes

Flexural Ductility

025.0095.053.0

12.053.0

−−=

• µ=flexural ductility

• r=flexural ductility at which rate of decrease of shear capacity with flexural ductility changes

• q=upper limit of flexural ductility beyond which the shear capacity remains constant

Typical Ductility vs. Shear Capacity

0 1 2 3 4 5 6 7

Ductility

Axial Load Contribution to Shear

• Vp=nominal shear strength provided by the axial load, N

• D=the overall section depth, mm

• c=the depth of the compression zone, mm

• a=the ratio of the moment to the shear at the critical section, mm

• P=the factored axial load normal to the cross section occurring simultaneously with the factored shear force at the section, N

Steel Contribution to Shear

( ) θρρρ cot)(2.11153300 23 cdfbV yhwttts −+−=

• Vs=nominal shear strength provided by the steel, N

• bw=width of the web, mm

• fyh=yield strength of the transverse steel, MPa

• d=distance from the extreme tension fiber to the centroid of the longitudinal tension reinforcement, mm

• c=depth of the compression block, mm

• θ=angle of principal shear crack to column axis, can be assumed to be 30 degrees

θρ cot)( cdfbV yhwts −=

Other Models

Normal Strength Concrete

Proposed Model Accuracy Based on Ductility

0.00 1.00 2.00 3.00 4.00 5.00 6.00

Ductility

V/V (proposed)

High Strength Concrete Model

spcn VVVV ++=

reinforcement

ecc AfkV '=

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

0 1 2 3 4 5 6 7

Ductility

Flexural Ductility

+−= 6144ρ

≥for

0 1 2 3 4 5 6 7

Ductility

Flexural Ductility

2.335 += tr ρ

• r=flexural ductility at which rate of decrease of shear

capacity with flexural ductility changes

Flexural Ductility

025.0095.053.0

12.053.0

−−=

0 1 2 3 4 5 6 7

Ductility

High Strength ConcreteACI Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

Caltrans Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

Proposed Model Accuracy Based on Ductility

0 1 2 3 4 5 6 7 8 9 10

Ductility

V/V (proposed)

Universal Model

spcn VVVV ++=

reinforcement

ecc AfkV '=

Flexural Ductility

++−= 3.403.0144 'ρ

• r=flexural ductility at which rate of decrease of shear capacitywith flexural ductility changes

≥for

Flexural Ductility

8.3011.035 ' +−= ct fr ρ

Flexural Ductility

025.0095.053.0

12.053.0

−−=

0 1 2 3 4 5 6 7

Ductility

High Strength ConcreteCaltrans Accuracy Based on Ductility

0 1 2 3 4 5 6 7

Ductility

V/V (predicted)

0 1 2 3 4 5 6 7

Ductility

V/V (predicted)

0 1 2 3 4 5 6 7

Ductility

V/V (predicted)

ACI Accuracy Based on Ductility

0 1 2 3 4 5 6 7

Ductility

V/V (predicted)

0 1 2 3 4 5 6 7

Ductility

V/V (predicted)

Accuracy

0 1 2 3 4 5 6 7

Ductility

V/V (predicted)

Conclusions

1. SRCS is capable of accurately predicting the nonlinear behavior of reinforced concrete structures subjected to various loading situations.

2. There are several models available that predict the relationship between flexural ductility and shear strength; however, the accuracy of these models is doubtful due to either over- or under-estimations. Hence, they cannot be used in practice.

3. The proposed models can accurately predict the relationship between flexural ductility and shear strength.

Questions?

Seismic Interaction of Flexural Ductility and Shear...

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