Abstract

Several approaches are investigated to model interior reinforced concrete waffle-flat-plate-column connections. A model is proposed that provides very good results with reasonable low computational cost. The proposed model is validated with the experimental results obtained on a 3/5 scale specimen, subjected to quasi-static in cyclic loads up to collapse. To this end, the non-linear advanced theory of reinforced concrete is applied on a three-dimensional finite element model and non-linear analysis are conducted. Both fiber and layer elements are used for the one-dimensional and bi-dimensional components respectively. The main results of the simulation were: (i) the capacity curve obtained through out a push-over analysis with displacement control, (ii) the hysteretic curves of the slab, and (iii) the crack patterns. A very good agreement is found between numerical and experimental results.

Abstract

This work presents the results of quasi-static non-linear analyses of two masonry buildings using, for the discretization of walls, a macro-element that combines the bending and the in-plane shear responses. The macro-element uses the force-based beam- column element equipped with cross sections discretized in fibers, where the behavior of each fiber is described by uniaxial constitutive models. To describe the shear response of the structural element, the macro-element embeds a shear hinge at mid-span, with a phenomenological non-linear constitutive model calibrated on experimental data. The analyzed buildings are two tangibles examples of un-reinforced and reinforced masonry of the Italian Heritage. The un-reinforced masonry building is a strategic building monitored by the O.S.S., partially damaged by the seismic events in Center Italy in 2016. The reinforced masonry building, a three-storey residential structure, is subject of evaluations carried out in the ReLuis RINTC project, designed as per D.M. 2018.

Abstract

If the stress intensity at a certain point of a structure made of ductile materials reaches the yield point, the structure does not necessarily fail or deform excessively. Instead, stress redistribution could take place and some further load increments could be supported. Thus, the actual load-carrying capacity of a structure is generally higher than the elastic limit and this overstrength can be exploited for a cost-effective design. However, during their operational life, structures are subjected to variable loads, whose law of variability in time is often unknown. Instead, it is usually possible to have a good estimate of the variability range in terms of maximum and minimum load amplitude. Within this context, shakedown analysis is able to provide a reliable safety factor against plastic collapse, loss in functionality due to excessive deformations (ratcheting) or collapse due to low cycle fatigue (plastic shakedown). This work presents an efficient fiber analysis for evaluating the shakedown safety factor of 3D frames under multiple load combinations. Mixed beam elements are employed for an accurate discretization of the structures. A continuation method, similar to an incremental elasto-plastic analysis, is used at structural level. It evaluates a fictitious equilibrium path made of a sequence of safe states with a converging non-decreasing load factor. Each point of the path is obtained by finding kinematic variables corresponding to self-equilibrated stresses satisfying Melan's condition for the current load factor to be safe. The stress admissible domain is defined at fiber level as a function of the load factor using the maximum and minimum effect due to all loads. An iterative state determination provides finite element stresses corresponding to assigned kinematic variables and load factor. The overall analysis differs from previous proposals for two novelty points. Firstly, a direct application of the Newton method is possible, without any need for constrained optimization solvers. Moreover, dimension and complexity of the load domain does not affect the computational cost of the nonlinear analysis. Numerical tests highlight an accurate estimate of the safety factor using a small number of fibers and an efficient solution also for large buildings.