units meet the requirements of ASTM C 90 (ref.masonry is laid in running bond using Type M or S mortar, and.the backfill is granular and soil conditions in the area are non-expansive,.the length of foundation walls between perpendicular masonry walls or pilasters is a maximum of 3 times the foundation wall height,.tops of foundation walls are laterally supported prior to backfilling,.backfill is drained to remove ground water away from foundation walls,.terrain surrounding the foundation wall is graded to drain surface water away from foundation walls,.Table 1 may be used for foundation walls up to 8 feet (2.4 m) high under the following conditions (ref. Table 1 lists the allowable backfill heights for 8, 10 and 12-inch (203, 254 and 305 mm) concrete masonry foundation walls. Empirical design is often used to design concrete masonry foundation walls due to its simplicity and history of successful performance. The empirical design method uses historical experience to proportion and size masonry elements. Vertical load effects are not included in the tables and design example presented in this TEK (references 2 and 3 include vertical load effects). Further, if the wall spans horizontally, vertical compression does not offset the flexural tension. In low-rise construction, these vertical loads are typically small in relation to the compressive strength of concrete masonry. When foundations span vertically, this vertical compression counteracts flexural tension, increasing the wall’s resistance to flexure. For design, foundation walls are typically assumed to act as simple vertical beams laterally supported at the top and bottom.įoundation walls also provide support for the structure above, transferring vertical loads to the footing. The maximum force on the wall depends on the total wall height, soil backfill height, wall support conditions, soil type, and the existence of any soil surcharges. This lateral soil load is expressed as an equivalent fluid pressure, with units of pounds per square foot per foot of depth (kPa/m). For design, the load is traditionally assumed to increase linearly with depth resulting in a triangular load distribution. Soil imparts a lateral load on foundation walls.
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