ABSTRACT
101Shear is fundamental to how bending members resist load. It holds the outer layers together, causing them to act as one. This chapter will focus on how we size lintels for shear stress. Chapter 7 covers shear wall design to resist wind and seismic forces.
Let’s take a moment and conceptually understand the fundamentals of shear behavior. You are likely familiar with the action scissors make when cutting paper or fabric. The blades are perpendicular to the material, going in opposite directions. This creates a tearing of the material like that shown in Figure 5.1. In beam shear, the action is similar, but the movement of material is parallel to the length of the beam. The top portion moves relative to the bottom, illustrated in Figure 5.2.
Shear strength is fundamentally tied to bending strength and stiffness. If we take a stack of paper and lay it across two supports, it sags (Figure 5.3a), unable to carry even its own load. If we glue each strip of paper together, we get a beam with enough strength and stiffness to carry a reasonable load, as shown in Figure 5.3b. And so, it is with masonry beams. The lengthwise fibers provide bending strength, but it is the material in the middle that holds them together.
