Q3 of 3 [30 marks] As an engineer working for a forensic engineering consultancy, you are tasked with evaluating the critical collapse mode of a factory building subjected to an accidental explosion event. The main framework of the building is idealised as a series of equally spaced steel portal frames ABCD as shown in Figure Q3. The explosion load is represented by quasi-static uniformly distributed loading of 5kN/m as indicated in Figure Q3 acting on vertical member AB. In addition to this, there is a static load of 30 kN acting on member BC as indicated. Assume local buckling of the frame section is not a critical mode of failure. The plastic moment capacity of the members AB (4m long), BC (5m long) and CD (6m long) is Mp, 3Mp, and 2Mp, respectively. The frame is fixed to its base at A and pinned at D. a) First determine up to 5 potential collapse mechanisms for the portal frame. Consider beam, sway and combined beam-sway modes. Draw a sketch of each of these clearly showing the location of the plastic hinges and determine the value of Mp (in kNm) for each of the mechanisms. b) Determine the critical collapse mechanism and corresponding value of Mp. [25 marks] [5 marks] B 3m 30 kN 5 kN/m Mp 4m 3Mp A Figure Q3 2m-> C 6m 2Mp D .