This document summarizes research on the effect of sustained loading on the shear capacity of concrete beams. The research involved testing concrete beams under both short-term static loading and long-term sustained loading up to 38 months. The results showed that for sustained loading between 87-95% of the static strength, no significant reduction in capacity was observed over time. Crack width and length increased initially but then stabilized, with most new cracks likely due to shrinkage rather than sustained loading effects.

1. Assessment, Upgrading and Refurbishment of Infrastructures
IABSE Conference, Rotterdam, May 6 - 8, 2013
Shear Capacity of Concrete Beams
under Sustained Loading
R. Sarkhosh, PhD Researcher, TU Delft
J.C. Walraven, Professor, TU Delft
J.A. den Uijl, Associate Professor, TU Delft
C.R. Braam, Associate Professor, TU Delft
Delft University of Technology, the Netherlands

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TABLE OF CONTENTS
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
 Introduction
 Aim of research
 Experiments on concrete beams
 Short-term static loading
 Long-term sustained loading
 Conclusions and outlook

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INTRODUCTION
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
Millions of concrete structures in the world…
Q: What happens to concrete under loading in ages?
A known phenomenon is creep/relaxation…
… which is time dependent strain under applied stress
Q: What is the effect on concrete beams?
Appearance of flexural and shear cracks
Propagation of existing cracks

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SHEAR!
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
• Aug 2004: The $21.3 million MLK Drive Bridge opens to traffic. Bridge carries about
4,500 vehicles a day.
• 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
lead INDOT to restrict traffic on bridge to cars only.
• 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 as MLK Bridge — are safe.
• Jan 2011: Further inspections find MLK Bridge is too damaged to be repaired.
INDOT decides bridge will be demolished and rebuilt.
• Feb 2012: Demolition begins. Superior Construction Company, its designer and its
primary material supplier have agreed to pay INDOT a total of $1.35 million.
• 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

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SUSTAINED LOADING EFFECT?
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
Sustained loading tests on plain concrete
By: Zhang, Phillips and Green , 1998
Formulation of sustained
loading effect in EC-2
c
ck
cccd
f
f
γ
α=
c
ctk
ctctd
f
f
γ
α=
For concrete in compression
For concrete in tension
Values for αcc and αct are mostly chosen between 0,8 and 1,0

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AIMS OF THE RESEARCH
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
• To investigate the sustained loading effect in
concrete beams without shear reinforcement.
• To Investigate the behavior of a cracked beam in
Time.

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TEST SCHEME
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
Group fcm,cube [MPa] Type of test Pmax, mean [kN] Load ratio Sustained loading duration
1 30.3 6 short-term 184.7 (COV = 4.6%) - -
2 32.1 3 short-term
3 long-term
188.9 (COV = 3.2%)
-
-
0.87
-
3 months
3 47.0 3 short-term
3 long-term
204.9 (COV = 1.4%)
-
-
0.95
-
38 months
4 42.0 3 short-term
3 long-term
194.7 (COV = 4.9%)
-
-
0.95
-
12 months
5 44.2 3 short-term
3 long-term
203.2 (COV = 3.1%)
-
-
0.89
-
14 months
6 73.4 3 short-term
3 long-term
250.1 (COV = 2.7%)
-
-
0.90
-
24 months
7 78.0 3 short-term
3 long-term
229.9 (COV = 6.7%)
-
-
0.92
-
18 months

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TEST RESULTS: BEAMS GROUP 1
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
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
Short-term static loading

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LONG-TERM SUSTAINED LOADING
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
Test setup and measuring devices
Roller
Support Roller
Support
Load CellLoading plate
Measuring
Grid 

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DEVELOPMENT OF CRACK LENGTH
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology

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DEVELOPMENT OF CRACK WIDTH
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology

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FAILURE IN EARLY AGES
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
Fracture of two specimens shortly after application of
sustained loading
In these cases, however, the
sustained load was beyond the 95%
confidence interval of the short-term
shear capacity.

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CONCLUSIONS
Shear Capacity of Concrete Beams under Sustained Loading
R. Sarkhosh, PhD Researcher, Delft University of Technology
• 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;
•the crack width increase 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.