This document summarizes a PhD research project studying the long-term capacity of concrete structures. The research aims to investigate the behavior of concrete beams without shear reinforcement under sustained long-term loading, and how cracks in beams change over time. Experiments included short-term static tests and long-term sustained loading tests where crack length, width, and propagation were monitored periodically. The research found that under loads up to 95% of the static strength, no significant effects were observed over time. Crack width increased initially but then stabilized, and crack length saw slight propagation especially in the first six months, with most new cracks being shrinkage cracks. No failures occurred during long-term loading testing.

1. 13TU.Bouw
2013 Structural Synergy
Long-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

2. 23TU.Bouw
Long-term Capacity of
Concrete Structures?
• Motivation
• Planning
• Outcome

3. 33TU.Bouw
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?

4. 43TU.Bouw
• Aug 2004: The $21.3 million MLK Drive Bridge opens to traffic. Bridge carries aboutAug 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 findingsApril 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-frameJuly 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. INDOTJan 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 itsSuperior 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!

5. 53TU.Bouw
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.

6. 63TU.Bouw
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

7. 73TU.Bouw
Long-Term Sustained Loading Tests
Test setup and measuring devices
Roller
Support
Roller
Support
Load CellLoading plate
Measuring
Grid 

8. 83TU.Bouw
Crack length under long-term loading

9. 93TU.Bouw
Crack Width under long-term loading

10. 103TU.Bouw
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!

11. 113TU.Bouw
Thanks for your attention!
The old and new East Spans of the SF-Oakland Bay BridgeThe old and new East Spans of the SF-Oakland Bay Bridge
stand side-by-side, bathed in a sunset glow. Photo by Karlstand side-by-side, bathed in a sunset glow. Photo by Karl
Nielsen.Nielsen.