Page 371 - Design of Reinforced Masonry Structures
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6.22                       CHAPTER SIX








































         FIGURE 6.20  Concrete masonry bond patterns for structural tests [6.18].


           Figure 6.21 shows the relative strengths of wall panels of different bond patterns using
         8-in.-high units laid in running bond as the standard. It can be observed that there is no
         marked decrease in compressive strength of panels of different bond patterns. Units laid in
         vertical stack bond or diagonal bond generally exhibited 75 percent of the strength obtained
         from the running bond pattern. The reduction in strength of the vertical stack running bond
         can be attributed to the decrease in the net block area in compression. In vertical stack bond,

         the end walls and the web of the unit are so oriented with respect to the applied load that
         they do not contribute to the compressive strength of the panel. When blocks are laid in
         horizontal position, the end walls and the middle wall (i.e., the web) of the masonry units
         are parallel to the applied load, and they contribute to the strength of the wall panel.
           With regard to the flexural strength of the walls spanning vertically, tests showed that
         failure from transverse loading occurred as bond failure between block and the mortar.
         Horizontal stack bond construction was 30 percent stronger in vertical span flexure, whereas
         the walls with units laid in diagonal position were 50 percent stronger. The latter higher
         strength is attributed to the fact that more mortar bond area is included in the “saw-tooth”
         line across the width of the panel. As for the flexural strength of the horizontally span-
         ning wall panels, tests indicated that the relative strength of the stack bond walls is about
         30 percent of the strength of the walls in running bond construction.
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