Masonry Structural design

Example of Strength Design of a Two-Wythe Panel Wall Using Hollow Units, Face-Shell Bedding Only

Check the design of a two-wythe panel wall in which the outer wythe is modular clay units and the inner wythe is 8-in. CMU with face-shell bedding. The wall has the panel wall of the example of Sec. 5.1.5, assuming face-shell bedding only (mortar on the face shells of the units only). The wall has a wind load w of 20 lb/ft2, and uses PCL mortar, Type N. The panel wall will be designed as unreinforced masonry, assuming that the vertical strips of the inner wythe resist 100 percent of the out-of-plane load. The design is therefore identical to the example of Sec. 5.1.5. The critical stresses will occur on the bed joint, which is the horizontal plane through the masonry where the section modulus is minimum. This idealized horizontal cross section is shown in Fig. 5.7.

The calculated flexural tensile stress, 37.9 lb/in.2, exceeds the modulus of rupture normal to bed joints for hollow units and Type N PCL mortar (48 lb/in.2), reduced by the strength-reduction factor of 0.6 (28.8 lb/in.2). If the mortar is changed to Type S (modulus of rupture 63 lb/in.2), the design will be satisfactory. Addition of the outer wythe does not change the design of the panel wall.

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