Vtm

where fc' is the compressive strength of concrete, A1 is the area of the base plate, and A2 is the area of the concrete pedestal that is geometrically similar to and concentric with the loaded area, A1 < A2 < 4A1.

From Equation 4.118, it can be seen that the bearing capacity increases when the concrete area is greater than the plate area. This accounts for the beneficial effect of confinement. The upper limit of the bearing strength is obtained when A2 = 4A1. Presumably, the concrete area in excess of 4A1 is not effective in resisting the load transferred through the base plate.

Setting the column factored load, Pu, equal to the bearing capacity of the concrete pedestal, f cPp, and solving for A1 from Equation 4.118, we have

Beam splices

Column splices

Column splices

Bolted

FIGURE 4.28 Bolted and welded beam and column splices.

Bolted

Bolted

Welded

Bolted

FIGURE 4.28 Bolted and welded beam and column splices.

Welded

Use shims as required

Erection pin hole (optional)

Welded

Erection pin hole (optional)

The length, N, and width, B, of the plate should be established so that N x B > A1. For an efficient design, the length can be determined from the equation

where 0.95d and 0.80bf define the so-called effective load bearing area shown cross-hatched in Figure 4.29a. Once N is obtained, B can be solved from the equation

Both N and B should be rounded up to the nearest full inches.

The required plate thickness, freq>d, is to be determined from the limit state of yield line formation along the most severely stressed sections. A yield line develops when the cross-section moment capacity is equal to its plastic moment capacity. Depending on the size of the column relative to the plate and the magnitude of the factored axial load, yield lines can form in various patterns on the plate. Figure 4.29 shows three models of plate failure in axially loaded plates. If the plate is large compared to the column, yield lines are assumed to form around the perimeter of the effective load bearing area (the cross-hatched area) as shown in Figure 4.29a. If the plate is small and the column factored load is light, yield lines are assumed to form around the inner perimeter of the I-shaped area as shown in Figure 4.29b. If the plate is small and the column factored load is heavy, yield lines are assumed to form around the inner edge of the

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