Deep Beam Flexure and Shear Design

A presentation on

Flexural & Shear Design of Deep Beam

Presented by Pragya N R P Roy (P (Peter) t ) Structural Engineer

Contents • What is Deep Beam • Behavior of Deep Beam • Flexural Design of Deep Beam • Shear Design g of Deep p Beam • Examples p

What is Deep Beam • Large depth/thickness ratio • And shear span depth ratio less than 2.5 for concentrated load and less than 5.0 for distributed load. • Where the shear span is the clear span of the beam for distributed load

Application • • • • •

Pile Cap Cap. Bridge Girder. W ll slabs Wall l b under d vertical ti l lloads. d Floors slabs under horizontal loads. Some shear walls.

Behavior of Deep beam • Two-Dimensional Action. • Plane Section Do Not Remain Plane, in the deep beam design. • The strain distribution is no longer linear. • The shear deformation cannot be neglected as in the ordinary beam. • The stress distribution is not linear even in the elastic stage. • At the ultimate limit state the shape of concrete compressive i stress bl block k iis not parabolic b li shape h again.

Behavior of Deep beam • The distribution of tensile stress at bottom fiber is constant over the span. • Tensile stress in the bottom fiber at support and at mid span is almost the same. • The tension reinforcement must be extended to the end of support. • The Th maximum i ttensile il stress t att th the b bottom tt fiber is far exceed the magnitude of compressive i stress. t

Design Criteria for flexure in deep Beams Simply Supported beams:

• The ACI code does not specify a simplified g pprocedure design • ACI procedure for flexural analysis and design of deep beams follows rigorous non linear approach • The simplified provisions presented in this section are based on the recommendations of the Euro Euro-International International Concrete Committee (CEB).

Design Criteria for flexure in deep Beams • A schematic stress distribution in a homogeneous deep beam having a span/depth ratio Ln/h = 1.0 10 • It was experimentally observed that the moment lever arm does not change significantly even after initial cracking

Design Criteria for flexure in deep Beams Nominal Resisting Moment, Mn = Asfy (moment arm jd) The reinforcement area ‘As’ for flexure is As = Mu/φfyjd ≥ 3√fc 3√fcӘ bd/fy ≥ 200bd/fy The lever arm as recommended by CEB j 0.2(l+2h) jd= 0 2( 2 ) for f 1 ≤ l/h