First, assuming that the beam contains no Openings, design the longitudinal reinforcement. if the beam is subject to a sagging moment. the main reinforcement, AG will be at the bottom. The top reinforcement will be lighter than the bottom reinforcement and the same amount is usually continued throughout the length of the beam, including the opening region. Thus, the top reinforcement in the compression chord is known. Use the same amount and arrangement at its bottom as additional reinforcement required to restore the strength and avoid brittle failure of the beam due to the provision of openings.Step 2: Determine the shear force carried by the compression chord Since the amount and arrangement of longitudinal reinforcement in the compression chord are known, and as the axial force acting on it is given by Eq. (10), the moment capacity of the section may be estimated in the usual manner. Because of symmetry, the capacity in positive and negative bending will be numerically the same. Therefore, from the free-body diagram of Fig. ll(c), the amount of shear force that can be transmitted through the compression chord at ultimate may be obtained as
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