[BS] A106.2 Existing Unreinforced Masonry
The facing and backing wythes of multiple-wythe walls shall be bonded so that not less than 10 percent of the exposed face area is composed of solid headers extending not less than 4 inches (102 mm) into the backing wythes. The clear distance between adjacent header courses shall not exceed 24 inches (610 mm) vertically or horizontally. Where backing consists of two or more wythes, the headers shall extend not less than 4 inches (102 mm) into the most distant wythe, or the backing wythes shall be bonded together with separate headers for which the area and spacing conform to the foregoing. Wythes of walls not meeting these requirements shall be considered to be veneer, and shall not be included in the effective thickness used in calculating the height-to-thickness ratio and the shear capacity strength of the wall.
Exception: Where SD1 is 0.3 g or less, veneer wythes anchored and made composite with backup masonry are permitted to be used for calculation of the effective thickness.
Mortar shear test values, vto, shall be obtained by one of the following:
- ASTM C1531.
- For masonry walls that have high shear strength mortar, or where in-place testing is not practical because of crushing or other failure mode of the masonry, alternative procedures for testing shall be used in accordance with Section A188.8.131.52.
The tensile-splitting strength of existing masonry, fsp, or the prism strength of existing masonry, f'm, is permitted to be determined in accordance with ASTM C496 and calculated by the following equation:
The minimum number of tests per masonry class shall be determined as follows:
- At each of both the first and top stories, not less than two tests per wall or line of wall elements providing a common line of resistance to seismic forces.
- At each of all other stories, not less than one test per wall or line of wall elements providing a common line of resistance to seismic forces.
- In any case, not less than one test per 1,500 square feet (139.4 m2) of wall surface and not less than a total of eight tests.
- (Equation A1-2)
- Individual unreinforced masonry walls with more than 50 percent of mortar test values, vto, less than 30 pounds per square inch (207 kPa) shall be pointed prior to and retested.
- The lower bound mortar shear strength, vtL, is defined as the mean minus one standard deviation of the mortar shear test values, vto.
- Unreinforced masonry with mortar shear strength, vtL, less than 30 pounds per square inch (207 kPa) shall be pointed and retested or shall have its structural function replaced, and shall be anchored to supporting elements in accordance with Sections A106.2.1 and A113.8. When existing mortar in any wythe is pointed to increase its shear strength and is retested, the condition of the mortar in the adjacent bed joints of the inner wythe or wythes and the opposite outer wythe shall be examined for extent of deterioration. The shear strength of any wall class shall be not greater than that of the weakest wythe of that class.
- The minimum average value of tensile-splitting strength, fsp, as calculated by Equation A1-1 shall be 50 pounds per square inch (344.7 kPa).
- Individual unreinforced masonry walls with average tensile-splitting strength of less than 50 pounds per square inch (344.7 kPa) shall be pointed and retested.
- The lower-bound mortar strength fspL is defined as the mean minus one standard deviation P D+L of the tensile-splitting test values fsp.
Deteriorated mortar joints in unreinforced masonry walls shall be pointed in accordance with the following requirements:
- Joint preparation. Deteriorated mortar shall be cut out by means of a toothing chisel or nonimpact power tool until sound mortar is reached, to a depth not less than 3/4 inch (19.1 mm) or twice the thickness of the joint, whichever is less, but not greater than 2 inches (50 mm). Care shall be taken not to damage the masonry edges. After cutting is complete, all loose material shall be removed with a brush, or air or water stream.
- Mortar preparation. The mortar mix shall be proportioned as required by the construction specifications and manufacturer's approved instructions.
- Packing. The joint into which the mortar is to be packed shall be dampened but without free-standing water. The mortar shall be tightly packed into the joint in layers not exceeding 1/4 inch (6.4 mm) deep until it is filled; then it shall be tooled to a smooth surface to match the original profile.