Structural optimization of modular high-rise buildings

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The demand for high-rise building has been
increasing over the past decades which has induced new developments such as
modular construction. Modular construction has advantages in terms increased
speed, safer construction and less construction waste. Applying modular
construction in high-rise however brings about great complexities for the
structural design of the building. Therefore, a design aid is created which
generates a structural model from any arbitrary shape and uses structural
optimization techniques to explore a range of designs for the early design
stage. Existing optimization techniques have been
studied, including Cross-Section (CS-) optimization (size) and BESO (topology).
CS-optimization adapts the size of each member, considering utilization and
displacement conditions whereas BESO removes or adds elements from the model
based on stress level and Target Ratio (TR). Performing the methods
successively further decreases the structural weight at certain TR. Generally,
weight increases as more elements are removed. By developing the two-way coupled
ESO<>CS-optimization method, elements are removed by lowest strain energy
density, while the cross-sections of the remaining members are updated in each
iteration, thus coupling ESO (topology) and CS-optimization (size). This
results in a logical load path and additional weight reduction especially in
the braced frame structures loaded by lateral loads when displacement is
governing. In multiple load case design, the removal of elements is somewhat
hard to interpret, however the method consistently results in the lowest
structural weight for the considered cases. In order to create a modular structural design,
boundary conditions are assumed by standardizing column and beam dimensions and
considering multiple realistic load cases (wind+vertical load). By transforming
arbitrary shapes into structural models and optimizing these, a range of
solutions for the structural design is presented in which the number of
elements and the structural weight are generally negatively related. For the
considered rectangular buildings, the results are more efficient than core or
outrigger structures and almost as efficient as mega frame structures, with the
added benefit that it can be applied to any shape. Exploration of these
solutions is a useful contribution to the early design stage of modular
high-rise buildings, while the coupled ESO<>CS-optimization method could
also be useful in other optimization problems.