ABSTRACT
However if only conditions 1 and 2 are satisfied, then there may not be enough plastic regions to cause collapse. In such a case the ultimate load capacity calculated will be equal to or less than the true collapse load. It is therefore called a lower bound to the true collapse load. In the case of steel structures, the yield stress and cross-sectional properties will define the plastic resistance capacity. However, in the case of reinforced and prestressed concrete structures, if the yield criterion is known then for a given state of stress, the necessary reinforcement can be calculated in order to cause yielding. If the calculated reinforcement properly matches the stress state, then all parts of the structure yield and the structure will satisfy the collapse condition. However, practical restrictions prevent the exact matching between the reinforcement provided and the corresponding state of stress, resulting in a solution which will give a collapse load larger than the applied load. In other words, the resulting solution will be a lower bound solution. Designs based on lower bound approach have proved to be a very powerful approach and have become very popular.
