Evaluation of tension stiffening and momentcurvature of high performance reinforced concrete beams under sustained load.

Volume 18 , Issue 2 , February 2016 , Pages 139-154

Authors

¹ Faculty of Civil Engineering -Sulaimani University, Bakrajo Street, Sulaimaniyah

In this paper, the effects of creep and shrinkage on the deflection and cracking of

reinforced high performance concrete beams subjected to sustained load type in bending

are investigated. Mid-span deflections, cracking and surface strain profiles were

monitored over a 90 day period so that to verify the structural response of HPRC (high

performance reinforced concrete) beams. Using the results obtained from the

experiments, the effect on tension stiffening was examined. Four concrete strengths 52,

95, 96 and 100 MPa were included as a major experimental parameter. The results

showed that as higher strength concrete was employed, not only cracks along the

reinforcement more extensive, but also the transverse crack spacing became smaller.

Thereby, the effective tensile stiffness of the high-performance concrete specimens at

the stabilized cracking stage was much smaller than those of normal-strength concrete

specimens. This observation is contrary to the current design provisions, and the

reduction in the tension stiffening effect by employment of high-performance concrete

is much greater than that would be expected. Measured surface strains in both the

tension and compression zones of beams of HPC subjected to sustained load were

considerably higher than the normal strength concrete beam. This was thought to be

primarily due to the effects of creep in the compression zone and a higher degree of

cracking within the tension zone. The progressive long-term increase in deflection is

shown to be a result of strain development primarily in the compression zone. The

sustained load is shown to affect the section stiffness most significantly within the early

stages of loading. Using experimental results, the validity of Eurocode 2 (EC2) is

examined.

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