ABSTRACT

When a beam is subjected to a vertical load, each unit element transfers the shear through a shear couple (the vertical forces shown in Figure 28.1) that must be counteracted by a counteracting couple (the horizontal forces shown) in order for the unit to remain stable. These forces cause planes of compression and planes of tension. When shear forces cause diagonal tension greater than the tensile strength of the concrete, shear cracks appear. Because shear is usually greatest at the support, shear cracks most often occur at the bottom of the beam near the edge of a support and work diagonally upwards and toward the center of the beam. Tension and compression planes caused by shear https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203583159/43b499e8-36af-4c2c-ba25-59ab9f62f21b/content/Page241-01_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>

Vc = amount of shear force unreinforced concrete can resist

Vc = 2λ(√f′c)bwd

λ = weight modification factor (1.0 for normal weight concrete)

bw = web thickness = b for rectangular sections