Limit state STR

Limit state STR, dealing with rupture or excessive deformation, is defined as:

Internal failure or excessive deformation of the structure ... where the strength of construction materials ... governs. [en 1990 §6.4.1(1)P(b)]

To prevent limit state STR from occurring, design effects of actions Ed must be less than or equal to the corresponding design resistance Rd, i.e.:

as illustrated in Figure 2.8.

Design effecl 7 / VSfifV X. / Design of actions /-►< _ „ ><-/ resistance

Figure 2.8. Verification of limit state STR

Returning to the example of Figure 2.7, the bending moments induced in the motorway gantry under its self-weight are shown in Figure 2.9. If the maximum design bending moment in the structure is MEd = 500 kNm and the minimum design bending resistance of the cross-section is MRd = 600 kNm, then limit state STR is avoided, since:

In this book, we define the 'utilization factor' for the STR limit state as the ratio of the effect of actions to its corresponding resistance:

ASTR R j d

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 fail, the structure is less reliable than required by the Eurocodes. For the motorway gantry of Figure 2.9:

A MEd 500kNm

Figure 2.9. Bending moments acting in the motorway gantry of Figure 2.7
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