Structural analysis under variable loads (Structure 3)

MODULAR PROGRAMME COURSEWORK ASSESSMENT SPECIFICATION

When dealing with variable (live) loads the internal forces or reactions that a structure generates will vary according to a probability distribution. In order to determine the design value of a live load, we multiply the characteristic load by a partial safety factor, leading to a design live load value, which represents a worst case scenario associated with that load. However, when multiple loads interact together it might not be evident if applied partial safety factors should amplify or minimise each individual load. A probabilistic analysis has then to be performed, so as to determine how the internal forces or reactions will vary, and determine the output values of these distributions which have a small probability, on an absolute basis, of being exceeded. A workflow of this process is shown in Fig. 1.

Figure 1: Diagram of probabilistic analysis for a supported beam subjected to two variable uniformly distributed loads (UDL). At the centre, three bending moment diagrams illustrate the variability which can be expected due to the UDL distributions. The histograms represent the distributions of the bending moments at one support and one mid-span of the beam, and the vertical dashed lines are the  corresponding threshold output values.

Structure 3: Vertical reaction at 3 and bending moment at 6 towards 5

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