Increasing Panel Ductility to Improve Blast Response

BLAST RESISTANT CONCRETE WALL PANELS

Patrick Trasborg, Ph.D. Student – Lehigh University Pierluigi Olmati, Ph.D. Student – Sapienza Università di Roma Clay Naito, Ph.D., P.E. – Lehigh University

NSF PD 08-1637

2012 Critical Infrastructure Symposium

Overview

What is precast concrete and a sandwich panel?

How do we design blast resistant reinforced concrete components?

Can we design wall panels the same way?

How can we improve a wall panel’s blast performance?

2

Precast Concrete

Parking Structures / Office Buildings / Residential / Manufacturing

Precast Concrete Construction • Cost Effective • Energy Efficient • High Quality • Rapid Construction

3

Sandwich Panel

Exterior Wythe with Architectural Features

Insulation Foam – XPS, EPS, PIMA

Interior Wythe with Wall-to-Structure Connections

Shear Ties to Connect Interior and Exterior Wythes 4

Overview

How do we design blast resistant reinforced concrete components?

5

Blast Design of Concrete Components

6

Far-field Detonation

Known Threat

Blast Design of Concrete Components

7

Differential Equation of Motion

Approximated as a single degree of freedom (SDOF)

Solve an “equivalent” SDOF system

Development of Resistance Function

8

Idealized RC Resistance Function

Plastic Hinge Formation

Correlating Panel Response to Damage

9

Defined in terms of:

Support rotation,

Displacement Ductility,

Dyield

Dultimate q

D

yield

ultimate

D

D

D

fCSpan

1tanqCurrent Response

Limits for Structural Members

Correlating Panel Response to Damage

10

Defined in terms of:

• Support Rotation, θ

• Displacement Ductility, μ

Overview

Can we design wall panels the same way?

11

Sandwich Wall Resistance Function

12

Uniform Static Load Tests

Resistance Function

Sandwich Wall Resistance Function

13

Resistance Function

Superficial Moderate Heavy Hazardous Blowout

Current RC Limits μ ≤ 1.0 θ ≤ 2.0º 2.0º < θ ≤ 5.0º 5.0º < θ ≤ 10.0º θ > 10.0º

Observed RC Limits μ ≤ 1.0 θ ≤ 3.1º 3.1º < θ ≤ 5.7º 5.7º < θ ≤ 7.6 θ > 7.6

0

1

2

3

4

5

6

7

0 2 4 6 8

Resi

stan

ce [

psi

]

Support Rotation [deg.]

UFC Estimate (M1)

Measured (M1/PSC2)

Measured (M3/TS2)

UFC Estimate (M3)

Unconservative Estimate of Performance

Overview

How can we improve a wall panel’s blast performance?

14

Locally Unbonding Reinforcement

15

Teflon Tubing

Locally Unbonding Reinforcement

16

0

2

4

6

8

10

12

14

16

0 5 10 15 20

Res

ista

nce

[psi

]

Support Rotation [deg]

UFCUnbond Average

Bar Fracture

Near Elastic-Perfectly Plastic Behavior

Locally Unbonding Reinforcement

17

0

2

4

6

8

10

12

14

0 5 10 15 20 25

Res

ista

nce

[psi

]

Support Rotation [deg]

Control7.5" Unbond15" Unbond22.5" Unbond

Heavy Damage Threshold

Hazardous Damage Threshold

Blowout Threshold

Average Values

Numerical Modeling

18

Discrete Crack Model

Beam Element Model

Numerical Modeling

19

Resistance Function

Rebar Stress Distribution

Conclusion

20

Standard Approach Leads to Unconservative Design

0

1

2

3

4

5

6

7

0 2 4 6 8

Res

ista

nce

[p

si]

Support Rotation [deg.]

UFC Estimate (M1)

Measured (M1/PSC2)

Measured (M3/TS2)

UFC Estimate (M3)

Elastic-Hardening-Softening

Elastic-Perfectly Plastic

Superficial Moderate Heavy Hazardous Blowout

q q q q q

Current Limits 1.0 - - 2º - 5º - 10º - >10º

Observed Limits 1.0 - - 3.1º - 5.7º - 7.6º - >7.6º

Conclusion

21

0

2

4

6

8

10

12

14

0 5 10 15 20 25

Res

ista

nce

[psi

]

Support Rotation [deg]

Control7.5" Unbond15" Unbond22.5" Unbond

Locally unbonding longitudinal reinforcement may:

»Increase panel ductility

»More closely match elastic-plastic behavior

0

2

4

6

8

10

12

14

16

0 5 10 15 20

Res

ista

nce

[psi

]

Support Rotation [deg]

UFCUnbond Average

Conclusions

22

Analytical Model

Resistance Function

Clarification Questions?

23

Patrick Trasborg, EIT

pat310@lehigh.edu

Clay Naito, Ph.D., P.E.

cjn3@lehigh.edu

2012 Critical Infrastructure Symposium

This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1030812. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

References

(1) PCI Committee on Precast Sandwich Wall Panels, “State-of-the-Art of Precast/Prestressed Sandwich Wall Panels”, PCI Journal: Vol 2, No 2, March 1997

(2) PCI Blast Resistance and Structural Integrity Committee, “Blast-Resistant Design of Precast/Prestressed Concrete Components”, PCI Report, July 2010

(3) Department of Defense, “Structures to Resist the Effects of Accidental Explosions”, UFC 3-340-02, 2008, p. 1106

(4) U.S. Army Corps of Engineers, “Single Degree of Freedom Structural Response Limits for Antiterrorism Design”, Protective Design Center Technical Report PDC-TR 06-08 – Rev 1, 2008

(5) Air Force Research Laboratory, “Analytical Assessment of the Blast Resistance of Precast, Prestressed Concrete Components”, AFRL-ML-TY-TP-2007-4529 Interim Report, April 2007

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