Reinforced concrete pads

Where the pad foundations require reinforcement the following checks should be carried out to ensure:

■ Sufficient reinforcement to resist bending moments.

■ Punching shear strength.

■ Beam shear strength.

The moments and shear forces should be assessed using the STR combination:

However, there may be economies to made from using Expressions (6.10a) or (6.10b) from the Eurocode.

The critical bending moments for design of bottom reinforcement are located at the column faces. Both beam shear and punching shear should then be checked at the locations shown in Figure 3. For punching shear the ground reaction within the perimeter may be deducted from the column load (Expression (6.48), Eurocode 2—1—1s). It is not usual for a pad foundation to contain shear reinforcement, therefore it is only necessary to ensure that the concrete shear stress capacity without shear reinforcement (vRd,c - see Table 6) is greater than applied shear stress (vEd = VEd/(bd)).

If the basic shear stress is exceeded, the designer may increase the depth of the base. Alternatively, the amount of main reinforcement could be increased or, less desirably, shear links could be provided. (See Chapter 4, originally published as Beams8 for an explanation of how to design shear reinforcement.)

L = width of base

L = width of base

SLS pressure distributions

ULS pressure distribution or

ing using EQU " actions and iination 2 properties.

Design foundation (structural design) using the worst of Combinations 1 and 2 (ULS) for actions and geotechnical material properties.

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