Evaluation of tension stiffening and moment-curvature of high performance reinforced concrete beams under sustained load

Kawa Taha Abualwafa Ahmed

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

E-mail: kawaa54@yahoo.com. 

Original: 08.07.2015; Revised: 14.12.2015; Accepted: 28.01.2015; Published online: 20.06.2016

DOI Link: 

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. 

KEYWORDS

Sustained Load, High performance reinforced concrete, Eurocode2, MC 90, Tension

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