From sequentially linear analysis to incremental sequentially linear analysis

Robust algorithms for solving the non-linear equations of structures of quasi-brittle materials

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Abstract

It is difficult to accurately predict the strength of masonry and concrete structures. The most widely used method for simulating their behaviour is finite element analysis with the Newton-Raphson method and arch length control. However, the Newton-Raphson method can diverge and not produce a result, for example in bifurcations or during snap-back. In order to enhance the robustness of solving non-linear problems, a new method – called incremental sequentially linear analysis (ISLA) – is proposed. The method is based on a combination of the Newton-Raphson method and a total approach called sequentially linear analysis.

In ISLA, local damage is induced by reducing the material secant stiffness of the element that fails a unity check. The load is applied in force increments or displacement increments, which are adjusted to trace the complete structural response.

It has been showed that ISLA can handle non-proportional loading, geometrically non-linear analysis and transient analysis. The robustness of ISLA has been demonstrated in four examples: a concrete beam with both prestress and vertical load; out-of-plane bending of a masonry wall with overburden; a differential settlement test on a pre-loaded masonry façade and a 3D pushover analysis of a masonry house.