13TU.Bouw

2013 Structural SynergyLong-Term Capacity of Concrete Structures

PhD candidate: Reza Sarkhosh

E-mail: Rsarkhosh@me.com

Promoter: Prof. J.C. Walraven

E-mail: J.C.Walraven@tudelft.nl

Department: Structural Engineering, Concrete Structures

Origanization: TU Delft

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Long-term Capacity of Concrete Structures?

• Motivation

• Planning

• Outcome

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Main Questions regarding this research:

• What is the behaviour of concrete structures under long-term loading?

• What happens to a cracked concrete member?

• Are our old concrete structures as safe as we think?

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• Aug 2004: The $21.3 million MLK Drive Bridge opens to traffic. Bridge carries about Aug 2004: The $21.3 million MLK Drive Bridge opens to traffic. Bridge carries about 4,500 vehicles a day.4,500 vehicles a day.

• Mar 2009: Shear cracks in concrete bridge beams found during INDOT inspection.Mar 2009: Shear cracks in concrete bridge beams found during INDOT inspection.• April 2010: A research team is hired by INDOT to inspect the bridge. Early findings April 2010: A research team is hired by INDOT to inspect the bridge. Early findings

lead INDOT to restrict traffic on bridge to cars only. lead INDOT to restrict traffic on bridge to cars only. • May 2010: INDOT closes Martin Luther King Drive Bridge indefinitely. May 2010: INDOT closes Martin Luther King Drive Bridge indefinitely. • July 2010: Inspectors say 3 more bridges all built by the same firm in same time-frame July 2010: Inspectors say 3 more bridges all built by the same firm in same time-frame

as MLK Bridge — are safe.as MLK Bridge — are safe.• Jan 2011: Further inspections find MLK Bridge is too damaged to be repaired. INDOT Jan 2011: Further inspections find MLK Bridge is too damaged to be repaired. INDOT

decides bridge will be demolished and rebuilt.decides bridge will be demolished and rebuilt.• Feb 2012: Demolition begins. Feb 2012: Demolition begins. Superior Construction Company, its designer and its Superior Construction Company, its designer and its

primary material supplier have agreed to pay INDOT a total of $1.35 million.primary material supplier have agreed to pay INDOT a total of $1.35 million.• Oct 2012: The new bridge opened to traffic.Oct 2012: The new bridge opened to traffic.

Appearance of Shear cracks after 5 years in Martin Luther King Drive Bridge, Indianapolis

Karl Zimmerman, Ph.D., P.E.

Former Assistant Professor of Civil

Engineering,Valparaiso University,

Indiana

Shear failure!

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Aims of the research

• To investigate the sustained long-term loading effect in concrete beams without shear reinforcement.

• To Investigate the behavior of a cracked beam in Time.

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Experiments:

6 short-term static tests:fcm = 38,1 MPa

Pultimate,mean = 184,7 kN (COV = 4,6%)

3 Ф 20 *

Load

Support Support

300 1200 mm 3001200 mm

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Long-Term Sustained Loading TestsTest setup and measuring devices

Roller Support Roller

Support

Load CellLoading plate

Measuring Grid

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Crack length under long-term loading

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Crack Width under long-term loading

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Conclusions

• Under sustained loading equal to 87% ~ 95% of the static strength no significant sustained loading effect is observed;

• Crack width and length are monitored periodically:• slight propagation of shear cracks is observed and found to be

more pronounced in the first six months of loading;

• Crack width increases in the first week of loading, but afterwards

the cracks stabilize and become dormant;

• most of the new cracks that appeared on the surface of the

beams are likely shrinkage cracks.

• During long-term loading tests, no failure observed!

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Thanks for your attention!The old and new East Spans of the SF-Oakland Bay Bridge The old and new East Spans of the SF-Oakland Bay Bridge stand side-by-side, bathed in a sunset glow. Photo by Karl stand side-by-side, bathed in a sunset glow. Photo by Karl Nielsen.Nielsen.