The net concrete cross-sectional area of most concrete masonry units ranges from 50 to 70, depending on unit width, face-shell and web thicknesses, and core configuration.

Two-Way (Punching) Shear When a footing fails by two-way (punching) shear, the failure occurs at an angle approximately 30 degrees to the column or pier, as shown in Figure.2.

The footing width should project a minimum of 2 inches from both faces of the wall (to allow for a minimum construction tolerance but not greater than the footing thickness.Engineering specifications generally require reinforcement of concrete or masonry foundation walls because of somewhat arbitrary limits on minimum steel-to-concrete ratios, even for plain concrete walls.In residential construction, nominal 8-inch-thick concrete masonry units are readily available.The required width or area of a spread footing is determined by dividing the building load on the footing by the soil-bearing capacity from Table.2 or Table.3, as shown below.The following steps are required to determine the amount of reinforcement required in a typical residential concrete foundation wall to resist combined flexure and axial loads: calculate axial and lateral loads; verify that the non-sway condition applies; calculate slenderness; calculate the moment magnifier; and plot.Accelerators may also increase the early strength of concrete; and air-entrainers used for concrete that will be exposed to freeze-thaw conditions and de-icing salts.Members Only, members Site Registration.A residential designer using concrete and masonry materials must have a basic understanding of such materials, as well as an appreciation of variations in the materials composition and structural properties.The fundamental assumptions, derivation of formulas, and design procedures are similar to those developed for strength-based design for concrete except that the material properties of masonry are substituted for those of concrete.Moment Magnifier liar game the final stage indowebster Method The moment magnifier method is an approximation method allowed in ACI31810.10 for concrete walls with a slenderness ratio less than or equal to 100.Flexure in a concrete footing is checked by computing the moment created by the soil-bearing forces acting over the cantilevered area of the footing that extends from the critical flexure plane to the edge of the footing (hatched area in Figure.2).In rare and peculiar instances where bearing compressive forces on the concrete are extreme and approach or exceed the specified concrete compressive strength, ACI-31810.17 and ACI-31812.3 should be consulted for appropriate design guidance.Calculation of lintel deflection should use unfactored loads and the effective section properties EcIe of the assumed concrete section; refer to ACI-3 to calculate the effective moment of inertia Ie of the section.The design equations used later in this section are based on ACI-318 and principles of engineering mechanics as described below.The designer may elect to design the wall as either a reinforced or a plain concrete wall.Low-slump concrete is molded and cured to produce strong blocks or units.