Advanced analysis of hybrid steel and concrete frames: Part 2: Refined plastic hinge and advanced analysis

Robust geometric and material nonlinear analysis of buildings under ultimate loads is a key to success of advanced analysis, performance-based seismic design and progressive collapse analysis. This is the second part of two companion papers about the advanced analysis of hybrid steel and concrete frames allowing for various effects such as initial imperfections, gradual cracking effect and geometrical and material nonlinearities. Besides the use of Pointwise-Equilibrium-Polynomial (PEP) element allowing for initial imperfections and the P-Δ-δ effects by one element per member, the plastic hinge approach is refined for modelling of material yielding. In order to assess the sectional strength, the cross-section analysis technique described in the companion paper is utilized in this paper for analysis of steel reinforced concrete (RC) and steel-concrete composite (SCC) sections. Cracking in concrete component, which has significant influence on structural deformation and internal force distribution, is considered by using the Branson's model combined with the concrete cracking fracture surface. The distinct feature of the proposed method is that it integrates the accurate cross-sectional analysis technique to the refined lumped plasticity approach such that a feasible and reliable solution can be obtained. Members with previous experimental results and a portal frame are studied and compared for validation of the proposed method.