Limit state EQU

Limit state EQU, dealing with static equilibrium, is defined as:

Loss of static equilibrium of the structure... considered as a rigid body, where minor variations in the [actions or their distribution]... are significant, and the strengths of... materials ... are generally not governing.

Limit state EQU does not occur when the destabilizing design effects of actions Ed,dst are less than or equal to the stabilizing design effects Ed,stb:

as illustrated in Figure 2.6.

as illustrated in Figure 2.6.

Figure 2.6. Verification of limit state EQU

For example, consider a motorway gantry (see Figure 2.7) subjected to a design horizontal wind load Pd = 250kN acting at a height h = 7.5m above the base of the gantry. The design destabilizing (i.e. overturning) moment about the toe of the structure MEd,dst is given by:

If the design self-weight of the gantry is Wd = 1600kN and its base width B = 2.5m, then the design stabilizing (i.e. restoring) moment about the toe

MEd,stb is:

M„, iU = W, x - = 1600kN x -— = 2000kNm Ed, stb d 2 2

M„, iU = W, x - = 1600kN x -— = 2000kNm Ed, stb d 2 2

Motorway Gantry Wind Actions
Figure 2.7. Motorway gantry subject to wind load

Limit state EQU is therefore avoided (in the direction of the wind), since:

Mr , , . = 1875kNm < M„, = 2000kNm Ed, dst Ed, stb

In this book, we define the 'utilization factor' for the EQU limit state as the ratio of the destabilizing and stabilizing effects:

For a structure to satisfy design requirements, it must have a utilization factor less than or equal to 100%. If A exceeds 100%, although it may not necessarily lose equilibrium, the structure is less reliable than required by the Eurocodes. For the motorway gantry of Figure 2.7:

. MEd, dst 1875kNm

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Responses

  • amanda
    What is "EQU" eurocode?
    7 years ago

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