Explicit/implicit multi-time step co-computations for blast analyses on a reinforced concrete frame structure

Abstract

The paper explores the coupling between finite element codes based on implicit and explicit time integration schemes. An external coupling software has been developed based on the multi-time subdomain coupling algorithm, labelled as the GC method in the literature, allowing coupling of any time integration schemes from the Newmark family with the appropriate time step dependent on the features of the subdomain. Explicit/implicit multi-time step co-computations have been carried out for predicting the response of a reinforced concrete frame structure under a blast loading striking its front face. The well known SPEAR structure, pseudo-dynamically tested at the ELSA laboratory, in Ispra, Italy, has been adopted as a testing structure for blast analyses. The structure has been modelled with multi-fibre elements, whose steel and concrete fibres composing the beam and column section, have cyclic and non-linear behaviours. Anticipating that non-linear phenomena will essentially occur in the slender columns of the SPEAR frame structure, a mesh partitioning has been considered, composed of two subdomains: a first subdomain, with linear material behaviour, gathering beam elements handled by an implicit time integration scheme with a large time step and a second subdomain, with non-linear material behaviour, handled by an explicit time integration scheme with a fine time step. Results from co-computations with time step ratio up to 1000 have been checked with respect to full explicit computations. Despite the number of interface nodes involved into the subdomain partitioning, the explicit/implicit multi-time step co-computations provide very accurate global and local response parameters in terms of maximum inter-storey drifts, maximum mid-height column drifts or extreme strains in concrete and reinforcement, while reducing by 60% the computation time.