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

Abstract

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.