The paper explores multi-domain strategies in order to reduce time costs as well as mitigate memory problems for simulations of the non linear behaviour of reinforced concrete structures under seismic loading. The multi-scale time approach proposed by COMBESCURE AND GRAVOUIL [2001,2002,2003] enables to divide the computation domain in several subdomains connected by interfaces and to choose for each subdomain the best appropriate time-integrator amongst the Newmark family (α and β time integration scheme parameters) with a suitable time-step. Each subdomain is first solved independently (free solution) and the global solution is then computed by taking into account the link relations on the interfaces (link corrections added to previous free solutions). The subdomain coupling is achieved by prescribing continuity of velocities on interfaces enabling the stability of the algorithm as proved by the authors for all following cases of coupling time-integration schemes: implicit/implicit, explicit/implicit, explicit/explicit. This work is here focused on coupling implicit schemes (mean acceleration scheme) with different time-steps depending on subdomains. First we present the multi-domain strategy for a structure decomposed in two subdomains: a linear implicit subdomain with a large time step is coupled with a non linear subdomain with a fine time step. The flowchart of the subdomain strategy is given. The subdomain strategy is applied to two structures modelled with multi-fibre Timoshenko beam elements: a reinforced concrete column and a simplified three-story one bay building designed according to older construction code without earthquake provisions. Energy dissipation at subdomain interfaces is scrutinised in order to assess the effect of the size of the large time-step as well as the ratio between the two time steps.