Masonry Wall Design

The program performs the design of a tall slender reinforced masonry wall when subjected to a vertical load per unit length and a horizontal load per unit area perpendicular to its plane, as per either UBC '97, IBC '03 or IBC '06.

The ultimate moment, computed by taking into account the P-Delta effect, is compared to the nominal moment times the appropriate phi factor. The service load deflection is compared to the allowable deflection. The axial stresses are also checked against the allowable limits.

The following assumptions are made:

a) The strain in reinforcing steel and masonry is directly proportional to the distance from the neutral axis.The maximum strain at the extreme masonry compression fiber is 0.003 in/in.
b) The elasto-plastic stress-strain relationship is used for the reinforcing steel.
c) The tensile strength of masonry is neglected in flexural calculations for nominal and ultimate strength. However, it is considered in calculating deflections for the uncracked and cracked section.
d) Under factored loads, masonry stress distribution is considered rectangular and uniform, with a maximum value of either 0.80 or 0.85 f'm, depending on the design code selected.

Input Data

The input data required by the program includes the wall dimensions, the reinforcing bar size and spacing, the materials' properties, and the applied loads. In addition, it is necessary to specify if the wall is supported only at the base, and whether itis solid grouted. Figure to the right shows schematically the required input data.

The program uses the maximum lateral load for the wind loading given as data and the seismic loading computed with the specified seismic factor. Masonry type is concrete hollow block of normal weight (115 pcf) and the thicknesses available are 6, 8, 10, 12, 14 and 16 inches. Bar spacing must be in multiple of 8 inches and are located either at the blocks' mid-depth or at the outer edge.

Example

Determine the adequacy of a 6" concrete block wall that is 21'-6" between horizontal supports, as shown in the figure to the left. Grout only the reinforced cells. Try bars #5 @ 16". Perform design per IBC '03. Seismic acc. Sds is 0.36. Wind pressure is 15 psf.

Output

When the input data is entered, the program automatically performs the calculations and shows the analysis results. The output consists basically of four messages indicating the adequacy of the design in amount of reinforcement, axial capacity, bending capacity, and deflections. Figure above shows the template related to this module, with the example problem.