Beam shear
Beam shear
(OP)
Does anyone know why you can neglect the shear in concrete and wood beams that occurs up to a distance "d"(depth of member) from the face of the support but you cannot do this with steel beams?
When was the last time you drove down the highway without seeing a commercial truck hauling goods?
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RE: Beam shear
In wood, it is similar but more affected by the horizontal shear reaction to the load as it comes near the support.
The above is fairly non-technical - you might want to re-visit some concrete or wood textbooks to get a total grasp of the effect.
RE: Beam shear
RE: Beam shear
To calculate the shear at the end of the span instead of at a distance "d" from the support is easier and does not penalize the design.
For deep plate girders, where the shear may control, AISC allows to use the "tension field action" that follows more closely the actual behavior of the shear stresses near the supports and at the point of application of concentrated loads.
The latest ACI 318 now allows to use, as an alternative, the equivalent method for concrete, the "Strut-and-Tie Model", to design for shear in deep beams, pile caps, and other similar concrete elements.
RE: Beam shear
Hence one way to look to your statement is that a check can be set at lower levels of solicitation that satisfies the requirements wanted of design.
RE: Beam shear
This is explained very well (with diagrams) in ACI Clause R11.1.3.1.
In normal situations, a flexure shear crack will start in the top surface at the critical section for shear and extend diagonally to the support face at the bottom of the member. At points closer to the suport, the angle of the compression strut will rise and the shear capacity will increase faster than the uniform load shear will increase.
So, for uniform loading and correctly aligned supports, it is permissable to design for a critical section at d from the column face and assume that the design between the column face and the critical section requires the same reinforcement as at the critical section.
If heavy loads are applied between the support face and the critical section, then the shear must be checked at the support face (fig R11.1.3.1 (f)), also if there is no diagonal compression into the support. This shear check will be similar to a Deep Beam shear design and failure would be by direct shear rather than flexure shear as would occur at points outside the critical section.
In steel design, I presume you are checking for direct shear all of the time, rather than flexure shear as you ar in concrete design, as a direct shear failure can occur at any cross-section, so you need to check it at the support face and all points between.
British, Eurocode2 and Australian codes all allow for increased shear capacity in the region from 2d to the support face (this assumes a 30degree compression strut rather than the 45degree compression strut implied by the critical section being located at d from the support), but do require a check at the support face for non-uniform loads in the region of the support.