Profitability versus safety of high-rise office buildings

The paper applies a computer-based method involving evolutionary search, Pareto optimization, and color filtering to investigate the tradeoff between the life-cycle profitability of high-rise commercial office buildings and their load-path safety against progressive collapse under abnormal loading. The study was motivated by the progressive-collapse failure of the twin towers of the World Trade Center in New York on September 11, 2001. The assessment of life-cycle profitability is based on annual lease rates for office space that reflect the amounts of natural window lighting and open floor area that a building has. The assessment of load-path safety against progressive collapse is based on the degree of force redundancy that the structural system of a building has. For a particular office building project, a multi-criteria genetic algorithm is applied to find a relatively large number of cost-revenue Pareto designs that together form an optimal tradeoff surface in the 3D-space of capital cost, operating cost, and income revenue. Computer color filtering of the cost-revenue tradeoff surface is employed to highlight the relative profitability and safety of the different building designs. It is shown that designs with the most profit potential and those with the most safety potential correspond to buildings that also are the least safe and the least profitable, respectively. Finally, several good compromise building designs having profit and safety potentials that are both reasonable are identified from among a small number of profit-safety Pareto designs. The paper concludes with some general discussion and remarks concerning the design of buildings to withstand or delay progressive collapse under abnormal loading.