Demands Placed on Steel Frameworks of Tall Buildings Having Reinforced Concrete or Massive Wood Horizontal Slabs

This paper presents the relative demands that alternative floor and roof slab constructions place on the steel frameworks of relatively tall composite construction buildings. Slab types examined were standard steel and reinforced concrete (SRC) composite plates and prefabricated massive wood plates constructed from cross-laminated timber (X-Lam). Case studies for six-storey and 24-storey buildings addressed how the stresses and deflections of the steel framing members are influenced by the choice of slab type for load combinations associated with gravity forces, and lateral forces generated as a result of wind or seismic actions. It is shown that using X-Lam slabs places much lower stress demands on steel frameworks because the self-weight of the slabs is only about one-third of the weight of mechanically equivalent SRC slabs. Maximum lateral drifts for buildings with X-Lam slabs under earthquake and wind loads are predicted to be in the order of half to two-thirds of those for similar buildings with SRC slabs, with the greatest reductions being for the 24-storey building. Therefore, use of X-Lam slabs opens up the possibility of either reducing the amount of steel in tall buildings or improving the performances of systems without increasing the steel content. As constructability and fire performance are key issues for large buildings, how to make construction joints that permit rapid assembly of systems is discussed and fire protection strategies are outlined.