Example of Strength Design of Reinforced Clay Masonry Shear Wall

Consider the masonry shear wall shown in Fig. 6.26.

Design the wall. Unfactored in-plane lateral loads at each floor level are due to earthquake, and are shown in Fig. 6.27, along with the corresponding shear and moment diagrams.

Assume an 8-in. nominal clay masonry wall, grouted solid, with Type S PCL mortar. The total plan length of the wall is 24 ft (288 in.), and its thickness is 7.5 in. Assume an effective depth d of 285 in.

Unfactored axial loads on the wall are given in the table below.

Shear design is satisfactory so far, even without shear reinforcement.
Code Sec. will be checked later.
Now check flexural capacity using a spreadsheet-generated momentaxial force interaction diagram. Try #5 bars @ 4 ft. Neglecting slenderness effects, the diagram is shown in Fig. 6.28.

At a factored axial load of 0.9 D, or 0.9 × 360 kips = 324 kips, the design flexural capacity of this wall is about 4000 ft-kips, and the design is satisfactory for flexure.

We have designed the wall for the calculated design shear, which is normally sufficient. Now suppose that the wall is a special reinforced masonry shear wall (required in areas of high seismic risk), so that the capacity design requirements of Code Sec. apply. First try to meet the capacity design provisions of that section. At an axial load of 324 kips, the nominal flexural capacity of this wall is the design flexural capacity of 4000 ft-kips, divided by the strength reduction factor of 0.9, or 4444 ft-kips. The ratio of this nominal flexural capacity to the factored design moment is 4444 divided by 3000, or 1.48. Including the additional factor of 1.25, that gives a ratio of 1.85.


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