Reinforcement topology optimization with multiple diameter options and its application in RC planar member design

Conventional reinforcement design approaches for reinforced concrete (RC) planar members are often inefficient and heavily reliant on empirical practices. To address these limitations, this study proposes a reinforcement topology optimization technique with multiple diameter options. Based on the Bi-directional Evolutionary Structural Optimization (BESO) algorithm, the method uses rebar element groups—defined as sets of rebar elements aligned along the same line—as the basic optimization unit, with unified diameter adjustment for all elements within each group. Nonlinear finite-element analysis validates the performance of the optimized design through comparison with the Strut-and-Tie Model (STM) design. Results show that the proposed technique not only maintains a high level of optimization performance but also generates more practical reinforcement layouts compared to the multi-level rebar element diameter optimization method. Moreover, it achieves a 5.9% reduction in rebar consumption, an 8.3% increase in ultimate load-bearing capacity, and improved ductility characterized by a flexural failure mode. This technique provides an efficient and intelligent design solution for RC members, yielding a rational and code-referenced layout that, after standard detailing checks, can be developed into a construction-ready design.