Example 375

Plastic bending moment capacity of a nonuniformly heated steel beam

An example is given in Table 37.7 to illustrate this method. Input information for this example are shown in Figure 37.11.

As can be seen, the plastic bending moment capacity method requires many calculations. Hence, the only benefit of using this more elaborate method is to explore possible benefits of nonuniform temperature distribution in the cross-section of a beam, particularly to justify the use of unprotected steelwork.

Instead of using the plastic bending moment method, Eurocode 3 also gives an alternative method that is much simpler to use. In this simple method, the plastic bending moment capacity of a beam is given by

where Mp is the plastic bending moment capacity of the cross-section at ambient temperature; ky,T is the retention factor for the effective yield strength of steel at the maximum temperature in the lower flange. Thus, ky,TMp gives the reduced plastic bending moment capacity of the cross-section at a uniform temperature T. The modification factor k1 is used to account for nonuniform temperature distribution in the cross-section and k1 = 0.7. For the above example, ky>rMp = 137.5 kN m. Using Equation 37.20 gives a value of 196.5 kNm, which is close to that obtained using the more time-consuming plastic bending moment capacity method.

TABLE 37.7 An Example of Using the Bending Moment Capacity Method
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