compressive stress is greater than the bending tensile stress; the entire cross section remains in compression

and the section properties will be based upon what is termed the "uncracked section". This condition occurs

when the virtual eccentricity, ev, is less than or equal to 1/6 of the thickness, t, of the member. ev is defined

as the ratio of the moment, M, to the axial load, P. Figure 9-3 shows the uncracked section with three loading

conditions where ev is less than or equal to t/6. When the flexural tensile stresses exceed the axial

compressive stresses (ev exceeds t/6) and the edge of the compressive stress block is at or outside the location

of the reinforcing steel, the stress distribution is as shown in figure 9-4a. This condition, where the section

is cracked but the reinforcing steel is not in tension, is not a consideration when the unity equation (equation

9-8) is used for design of combined stresses. It is, however, a point used in the development of the interaction

diagram for a masonry pilaster or column. When the flexural tensile stresses exceed the axial compressive

stresses, a portion of the cross section is cracked and the design cross sectional properties are based upon

a reinforced masonry "cracked section" as shown in figure 9-4(b). Since it is assumed that the masonry will

not resist tension, the reinforcement must resist all tensile forces. The design will be governed by the

compressive stresses (axial and flexural) developed within the masonry section or by the flexural tensile

stresses developed in the reinforcement. The combined loading effects will be considered in the design by

using the basic unity interaction equation given later in this chapter.

conditions of the members (beams, girders, trusses, etc.) supported by the masonry column or pilaster. If

these members are not restrained against rotation, the resulting reaction will tend to move toward the edge

of the support, increasing the eccentricity of the reaction. When a beam supported on a bearing plate is

subject to rotation under loading, the vertical resultant reaction will be assumed at the third point of the

bearing plate, as shown in figure 9-5(a). When a supported member displays very little rotation, due to its

stiffness or continuity with other supported members, the load will be more uniformly distributed over the

length of the plate, and the resulting reaction may be assumed to act at the center of the bearing plate, as

shown in figure 9-5(b).

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