Section A108 Design Strengths

The unreinforced masonry shear strength, v_m, shall be determined for each masonry class from one of the following equations:

1. The unreinforced masonry shear strength, v_m, shall be determined by Equation A1-4 when the mortar shear strength has been determined by Section A106.3.3.1.  
   
   
   
   
   
   The mortar shear strength values, v_t, shall be determined in accordance with Section A106.3.3.
2. The unreinforced masonry shear, v_m, shall be determined by Equation A1-5 when tensile-splitting strength has been determined in accordance with Section A 106.3.3.2, Item 1 or 2.
   
   
   
3. When f'_m has been estimated by categorization of the units and mortar in accordance with Section 2105.1 of the International Building Code, the unreinforced masonry shear strength, v_m, shall not exceed 200 pounds per square inch (1380 kPa) or the lesser of the following:
   
   
   
   
   
   For SI: 1 psi = 6.895 kPa
   
   where:
   
   

   v	=	62.5 psi (430 kPa) for running bond masonry not grouted solid.
   v	=	100 psi (690 kPa) for running bond masonry grouted solid.
   v	=	25 psi (170 kPa) for stack bond grouted solid.

Where any increase in dead plus live compression stress occurs, the compression stress in unreinforced masonry shall not exceed 300 pounds per square inch (2070 kPa).

Unreinforced masonry shall be assumed to have no tensile capacity.

The resistance values of the existing anchors shall be the average of the tension tests of existing anchors having the same wall thickness and joist orientation.

For existing foundations, new total dead loads may be increased over the existing dead load by 25 percent. New total dead load plus live load plus seismic forces may be increased over the existing dead load plus live load by 50 percent. Higher values may be justified only in conjunction with a geotechnical investigation.