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Lateral support and skin reinforcement for reinforced beam

The buckling of the unsupported beam with any dimension even narrow and deep is a rare occurrence. If the beam subjected to appreciable lateral torsion. ACI code [10.4.1] stating that lateral support is not required to placed closer than 50 times b, where b is the least width of compression face or flange.however, it must be considered in determining the maximum spacing for lateral support.

Skin Reinforcement for Deep Beams
ACI code [10.6.7] stating that skin reinforcement shall be added for beams with depth h is 400 mm or more, the purpose of this reinforcement is to control cracks in the upper part of the tension zone, this reinforcement will be distributed in both vertical faces of the beam within a distance of h/2 from the tension zone as shown in figure 1,
Figure 1

spacing between skin reinforcement shall be according to ACI code [10.6.4], 

S=380(280/fs)-2.5Cc and not greater than S=300*(280/fs)


fs is the calculated closest to the tension face at service load shall be computed based
on the unfactored moment. It shall be permitted to take fs as 2/3fy.
Cc is the least distance from the surface of skin reinforcement or prestressing reinforcement to the side face.

skin reinforcement may be used to calculate the beam flexural strength if the correct strains for the additional reinforcement related to the neutral axis are used to calculate bar stresses. ACI doesn't state any amount of skin reinforcement, it is only stating that additional reinforcement shall be added in the vertical faces of tension zone to prevent excessive cracking. skin reinforcement doesn't have to exceed the half of bending tensile reinforcement


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