Lateral load design of masonry walls and their behavior
There are three types’ failure modes that define seismic behavior of structural masonry walls when subjected to in-plane seismic loads. The mechanism depends on the geometry of the wall (height/ width ratio) and quality of materials, and the type of load transfer.
It is a typical mode of failure of masonry wall subjected to seismic loads, and it takes place where the principal tensile stresses, developed in the wall under a combination of vertical and horizontal loads exceeds the tensile strength of masonry.
flexural mode of failure (flexural compression). With the improved shear resistance and high moment/shear ratio, crushing of compresses zones at the ends of the wall usually take place,
The diaphragms are classified into three groups of relative flexibilities: rigid, flexible, and semi rigid.
It is assumed to tribute the horizontal forces to the vertical resisting elements in direct proportion to the relative rigidities of those elements. This premise stems from the fact that under a symmetrical loading, the rigid diaphragm, which in it self does not deform appreciably will cause each vertical element to deflect the same amount. Rigid diaphragms are capable of transferring lateral and torsional forces to the walls. Rigid diaphragm
It may be likened to a series spans extending between very rigid supports, (i.e. vertical resisting elements). It is assumed here that the relative stiffness of these non yielding supports is very great compared to that of the diaphragm, which therefore deflects as a beam. This beam, having no appreciable continuity across the supports, thus develops no negative moment over them which would affect the distribution of lateral load Flexible diaphragm:
These exhibits significant deflection under load, and also have sufficient stiffness to distribute a portion of their load to the vertical elements in direct proportion to the rigidities of those elements. Semi rigid diaphragm
Horizontal forces at any floor or roof level may be transferred to the foundation through the strength and rigidity of the side walls, called as shear walls. The design strength of shear walls is often governed by flexure. However, in low walls, the governing design criterion may be shear, Masonry shear walls can be described not only in terms of types of masonry used , but also as load- bearing , non load bearing , reinforced or unreinforced, solid or perforated rectangular or flanged and cantilevered or coupled. Vertical stability elements
Δ f Deflection of walls due to bending and shear deformations Rigidity of the pier = R f = P Ph/2 Ph/2 P P Moment Shear
Effect of aspect ratio on deflection due to shear Aspect ratio h/L Percentage deflection due to shear Cantilever wall Fixed end wall 0.25 92 98 1 43 75 2 16 43 4 5 16 8 1 4.5
1 For squat walls (h/L < 0.25), rigidities based on shear deformations are reasonably accurate. 2 For (0.25<h/L<4) intermediate cantilever walls both deflections components should be include ‘d’ in the calculation of relative rigidities. For high (h/L) the effect of shear deformation is very small and rigidity based on flexural stiffness is reasonably accurate.
SEISMIC RESISTANCE OF RAT-TRAP BOND WALL AND FILLER SLAB SYSTEM
Experimental setup EXPERIMENTAL SET - UP 2 2 5 2 3 0 1 5 0 2 3 0 9 2 0 2 3 0 1 5 0 2 3 0 6 6 0 1 5 0 2 3 0 # # # # # # # # # # O n e l a y e r b r i c k o n e d g e 1 5 M B 3 0 0 1 5 M B 3 0 0 1 5 M B 3 0 0 1 6 2 5 9 7 4 8 3 1 0 1 . 2 6 5 . 9 7 1 0 8 4 . 3 WALL UNDER TEST ELEVATION END VIEW 1. STRAILS 2. DEFORMAIONS 3. LOADS 4. FAILURE PATTERN
Specimen Details S.No. Name Load (N) Moment (N mm) Failure Between 1 450M1 650 292500 Brick and Concrete surface at the bottom level 2 450M2 18431 310500 Brick and Concrete surface at the bottom level 3 340M3 1440 597600 II and III level Bricks 4 340M4 6143 601750 II and III level Bricks 5 450M5 4733 647400 I and II level Bricks 6 450M6 7973 9337500 I and II level Bricks 7 340M7 90000 0 Vertical cracks on all four sides