H. Bischoff ¹ , D. Moxon²

1. Professor,
2. Graduate Student Department of Civil Engineering, University of New Brunswick, P.O. Box 4400, Fredericton, NB, Canada E3B 5A3 E-Mail: BISCHOFF@UNB.CA

ABSTRACT

When designing reinforced masonry for strength, the contribution of tension in the masonry is typically neglected and the tensile forces are assumed to be resisted by the steel reinforcement. Although the masonry does not resist tension at a crack, it is still able to carry tension between the cracks through transfer of bond forces between the reinforcement and masonry. This effect is called tension stiffening, and it affects the deformation and stiffness of reinforced masonry elements where part of the element is under tension, such as beams or walls subjected to bending.

This paper describes the results of an experimental programme to investigate tension stiffening of reinforced masonry members under axial load. Half-block specimens six courses high are reinforced with either a single 15M or 20M bar and subjected to uniaxial tension. The load-deformation response of each member is compared with the bare steel response to observe the effects of tension stiffening for reinforced masonry under direct tension. Results are then used to determine the average tensile stress carried by the masonry after cracking (and before yielding of the reinforcing steel), which is compared with the average tensile strength of cracked concrete. This effectively provides a material model for cracked masonry, which can be useful for nonlinear analysis of reinforced masonry structures as well as for assessing serviceability requirements after cracking related to member stiffness, deformation and crack control. Analysis of the test data indicates that tension stiffening in masonry may be comparable to concrete, but results are affected by shrinkage and more work is required to validate this behaviour.

Key words: reinforced masonry, shrinkage, tension stiffening

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