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Unformatted text preview: Lecture 24  Design of Two Lecture 24  Design of Two Way Floor Slab System Way Floor Slab System August 4, 2003 CVEN 444 Lecture Goals Lecture Goals Shear Strength of Slabs Shear Example Direct Design Method Shear Strength of Slabs Shear Strength of Slabs In twoway floor systems, the slab must have adequate thickness to resist both bending moments and shear forces at critical section. There are three cases to look at for shear. Twoway Slabs supported on beams TwoWay Slabs without beams Shear Reinforcement in twoway slabs without beams. 1. 2. 3. Shear Strength of Slabs Shear Strength of Slabs Twoway slabs supported on beams The critical location is found at d distance from the column, where The supporting beams are stiff and are capable of transmitting floor loads to the columns. ( 29 bd f V 2 c c φ φ = Shear Strength of Slabs Shear Strength of Slabs The shear force is calculated using the triangular and trapezoidal areas. If no shear reinforcement is provided, the shear force at a distance d from the beam must equal where, ( 29 bd f V V 2 c c ud φ φ ≤ ≤  = d l w V 2 2 u ud Shear Strength of Slabs Shear Strength of Slabs There are two types of shear that need to be addressed TwoWay Slabs without beams Oneway shear or beam shear at distance d from the column Twoway or punch out shear which occurs along a truncated cone. 1. 2. Shear Strength of Slabs Shear Strength of Slabs Oneway shear or beam shear at distance d from the column Twoway or punch out shear which occurs along a truncated cone. 1. 2. Shear Strength of Slabs Shear Strength of Slabs Oneway shear considers critical section a distance d from the column and the slab is considered as a wide beam spanning between supports. ( 29 bd f V V 2 c c ud φ φ = ≤ Shear Strength of Slabs Shear Strength of Slabs Twoway shear fails along a a truncated cone or pyramid around the column. The critical section is located d/2 from the column face, column capital, or drop panel. Shear Strength of Slabs Shear Strength of Slabs If shear reinforcement is not provided, the shear strength of concrete is the smaller of: perimeter of the critical section ratio of long side of column to short side b o = β c = ( 29 d b f d b f V o c o c c c 4 4 2 φ β φ φ ≤ + = Shear Strength of Slabs Shear Strength of Slabs If shear reinforcement is not provided, the shear strength of concrete is the smaller of: α s is 40 for interior columns, 30 for edge columns, and 20 for corner columns....
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