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Q3. A simply supported steel beam 8 metres long has a hollow box section as shown in Figure Q3(a). (a) If the second moment of area of the square box cross-section, shown in Figure Q3(a), about the x-x axis is 1196 cm+ and the maximum allowable stress in tension and compression is 165 N/mm²; calculate: (i) The moment of resistance of the section. [5 marks] (ii) The maximum uniformly distributed load that this beam can carry. [5 marks] = = (b) If the existing steel beam is strengthened by the addition of two steel plates as shown in Figure Q3(b), calculate: (i) The maximum uniformly distributed load that the beam can carry. [8 marks] The minimum central length over which the additional plates are required. (ii) [7 marks] 120 mm 5 mm 150 mm 150 mm -X X Х 5 mm 120 mm 150 mm (a) (b) (Figure not to scale) Figure Q3