You have been appointed as the structural engineer to design an 80-storey structure. The structure has a square external footprint of 50m by 50m and a square central core of lift shaft of 10m by 10m. The storey height is 4.5m. All floors have the same structure, constructed of unpropped composite beams of 20m in length and 2.5m in regular spacing that span between the central core and and the external loadbearing walls. The composite beam consists of a UB610x229x101 steel section (cross-sectional area = 129cm, second moment of area= 75780cm, overall height=602.6mm) and a 130mm thick profiled concrete slab with a trough depth of 60mm on the top. The composite beam is simply supported and there are sufficient shear connectors in the composite beam to achieve full shear connection. The steel grade is S355 with a yield stress of 355MPa and a Young's modulus of 205GPa. C60 concrete is used with a cube strength of 60 MPa and a Young's modulus of 40GPa. The characteristic permanent and variable actions (dead and live loads) on the floor are 3.5kN/m and 5kN/m respectively. The characteristic wind load is 1kN/m. The partial safety factors for unfavourable permanent and variable actions are 1.35 and 1.5 respectively. The combination factor is 0.6 for all variable actions. (a) Check whether the composite beams have sufficient bending moment resistance. [20%] (b) For such a long span composite beam, deflection limit is likely to govern. Check whether the steel section of the composite beam should be increased so that the maximum deflection of the composite beam under combined permanent and variable actions does not exceed a deflection limit of span/250. Do not redesign the beam. [30%] (c) Determine the lateral load to be applied on a floor, considering both scenarios of imposed load leading and wind load leading. The structure has an inter-storey lateral stiffness K=n*40,000kN/m where n is the number of storeys above the floor. [50%]