TMS Journal July 2000 45 A reinforced masonry shear wall subjected to in-plane lateral and axial loads behaves as a two-dimensional con- tinuum in a state of plane stress. In a grouted masonry shear wall with longitudinal steel reinforcement, bond be- tween masonry and steel enables effective transfer of forces between the longitudinal steel rebars and adjoining ma- sonry through shear stresses, commonly known as bond stresses, acting at the surface of the rebar. The load-resist- ing mechanism of the wall can be explained using the tradi- tional analogy of a parallel chord pin-jointed truss [Park et al. (1975), Collins et al. (1991)] shown in Figure 1(a). Force in the longitudinal tension chord of a parallel chord truss changes at the discrete pin-joints due to forces entering the joints from the diagonal compression struts. Analo- gously, in a two-dimensional reinforced masonry wall con- tinuum, forces in the longitudinal rebars change continu- ously from point to point along the rebar length due to the diagonal compression field in the masonry [Figure 1(a)]. Intraction of In-Plane Shear and Flexure in Masonry Walls with Unbonded Longitudinal Reinforcement Alok Madan 1 , Andrei M. Reinhorn 2 and John B. Mander 3 The change in the longitudinal steel tensile force, which also equals the change in the longitudinal component of masonry compressive force, produces change in the inter- nal resisting moment (couple) required for balancing the external shear force. This mode of shear resistance, termed as ‘beam action’ [Figure 1(a)], is viable only in the presence of bond stresses. In an ungrouted masonry shear wall with longitudinal (ver- tical) steel reinforcement, forces in the longitudinal reinforc- ing bars cannot change along the length because of the com- plete absence of bonding between the reinforcing steel and adjacent masonry. As a result, ‘beam action’ is replaced by an alternative mechanism known as the ‘arch action’ after devel- opment of a flexural crack at the base. In arch action, external shear is resisted by an inclined internal compression field in the masonry [Figure 1(b)]. The change in internal resisting couple along the height, required for the shear resistance, is Figure 1—Shear Resisting Mechanism of a Masonry Wall – Bonded vs. Unbonded Reinforcement 1 Assistant Professor, Department of Civil Engineering, Indian Institute of Technology, New Delhi, India 2 Professor and Chairman, Department of Civil Engineer- ing, State University of New York, Buffalo, NY 14260 3 Associate Professor, Department of Civil Engineering, State University of New York, Buffalo, NY 14260 V C 4 C 3 C 2 C 1 T 1 T 2 T 3 T 4 Bonded Rebars V T C θ jd Unbonded Rebars End Anchorage x Inclined Masonry Compression Field V C C T V T = = U V W ⇒ = sin / cos tan θ θ θ V dM dx C T jd V dT jd dx jd dT dx T d jd dx = = ⋅ U V | W | ⇒ = ⋅ = ⋅ + ⋅ b g bg Perfect Beam Action Perfect Arch Action