Shear Lug Design

Normally, frictional resistance and the shear capacity of the anchors used in a foundation adequately resist column base shear forces. In some cases, however, the engineer may find the shear force too great and may be required to transfer the excess shear force to the foundation by another means such as shear lugs. If the total factored shear loads are transmitted through fiiction plus shear lugs, the anchors need not be designed for shear, but the eccentricity induced by the couple of the applied shear and the shear lug resultant force should be taken into account when designing the anchor for tension. 

The applied shear load used to design the shear lug should be computed as follows ... 

Design the weld between the plate shear lug and the base plate considering the shear and moment calculated is step 3. 

See Appendix A, Example 3 for an example of the design of a pipe shear lug. 

Steel embedded plates are often used to transfer loads from structural members to concrete structures or foundations. Such plates are often cast-in-place for constructability and to provide a smooth surface for attachment. These plates are attached to the concrete with welded anchors, which typically consist of headed studs, headed anchors, weldable rebar, or shear lugs they can be designed to resist applied tension, shear, and moment. Welding should be compatible with the anchor type. 

The guidelines for designing welded anchors for embedded plates presented herein are based on ACI 318 Appendix D, and the user should refer to that document for details not included herein. Shear lugs on embedded plates are similar to those discussed in 3.7 except without grout, and will not be discussed further. 

Design a shear lug pipe section for a 19-in. square base plate, subject to a factored axial dead load of 25 kips, a factored axial live load of 50 kips, and a factored horizontal shear load of 55 kips. The base plate and shear lug have Fy = 36 ksi and the concrete has a strength, f c = 4 ksi. The contact plane between the grout and base plate... 

Anchorage - A structural assembly designed to transmit all components of the design force from a structure or equipment to the foundation it consists of a combination of anchors, shear lugs, concrete, and reinforcement. 

Shear Lug - A short element of the anchorage used to transmit the portion of the shear component of the design force that exceeds the frictional resistance from the structure or equipment to the foundation it consists of plate(s) or a structural member (such as a wide flange shapes, square structural tubes, or pipes). 

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