09-08-2012, 03:29 PM
plastic analysis
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2.5 Plastic analysis
In plastic analysis and design of a structure, the ultimate load of the
structure as a whole is regarded as the design criterion. The term plastic has
occurred due to the fact that the ultimate load is found from the strength of steel
in the plastic range. This method is rapid and provides a rational approach for the
analysis of the structure. It also provides striking economy as regards the weight
of steel since the sections required by this method are smaller in size than those
required by the method of elastic analysis. Plastic analysis and design has its
main application in the analysis and design of statically indeterminate framed
structures.
2.5.1 Basics of plastic analysis
Plastic analysis is based on the idealization of the stress-strain curve as
elastic-perfectly-plastic. It is further assumed that the width-thickness ratio of
plate elements is small so that local buckling does not occur- in other words the
sections will classify as plastic. With these assumptions, it can be said that the
section will reach its plastic moment capacity and then undergo considerable
rotation at this moment. With these assumptions, we will now look at the
behaviour of a beam up to collapse.
Consider a simply supported beam subjected to a point load W at midspan.
as shown in Fig. 2.14(a). The elastic bending moment at the ends is w