Tension Stiffening Behavior of Reinforced Masonry

Abstract

The tensile behavior of reinforced concrete and clay unit masonry was studied by conducting a series of 33 direct tension tests on instrumented specimens. The effect of the steel reinforcement ratio was the principal variable considered. Reinforcing steel bars varied from no. 4 to no. 11 bars, while masonry unit widths varied from 90 to 290 mm. The measured tensile stress-strain curve permitted determination of the decrease in the tension stiffening behavior as a function of the cracking strain. All specimens were strained to levels far in excess of those permitted by design codes without suffering tensile bar failure. Initial behavior was governed by elastic properties. After cracking, a rapid decrease in effective stiffness was observed with the stiffness reducing to that of the reinforcing steel at a strain of approximately four times the cracking strain. This observation is significantly different from that reported for reinforced concrete. Examination of the stress-strain curve after yield showed a very strong influence of the reinforcing ratio on the shape of the stress-strain curve with lower steel ratios resulting in decreased ductility.