A numerical procedure for the plastic collapse load evaluation of welded beam-to-column steel connections

The restoration or the seismic upgrading of existing buildings is often pursued with the adoption or insertion of steel components. This design choice is, as known, very useful to improve the strength capabilities of the original parts of the building and, in seismic zones, to create parts able to absorb and/or to dissipate the energy of the earthquake actions. However, when dealing with masonry constructions, a conflict in the adoptable design methodologies arises. From one side, steel members, steel frames or steel connections are configured and designed with sophisticated design codes based on a complete and experimented knowledge of the post elastic behaviour of this material. Step-by-step procedures, in statics or in dynamics, able to reproduce the steel sub-system response up to collapse are normally offered by all the commercial codes. From the other side, masonry components or masonry organisms do not possess a precise and reliable behaviour specially in the post elastic phase. The constitutive assumptions and the adopted models for masonry structures are often inappropriate because the real behaviour is often related to circumstances which depends not only on the material but also on the constructive techniques. In this context, simplified methods of analysis such as direct methods, [1], can result more effective and reliable. One of the most popular is, with no doubt, limit analysis that, renouncing to a detailed description of the post elastic behaviour of a structure, focuses on a different goal, namely the prediction of the ultimate load the structure can bear. Thinking to a structural system made by steel and masonry members, limit analysis should be able to predict a limit load of plastic collapse for steel members and of rupture for masonry ones. Limit analysis in a real engineering practical context should also be performed numerically, i.e. based on a finite element friendly procedure. The present work belongs to the above outlined research line and, as a first step of the study, presents a limit analysis FE-based numerical procedure applied to steel connections oriented to masonry building restoration actions. The method is here applied to welded beam-to-column connections to predict their plastic collapse load. Two different numerical techniques, based on the static and kinematic approach of limit analysis respectively, are simultaneously applied to detect eventually the plastic collapse limit load of the analysed connection. The procedure and the related numerical findings are validated by comparison with experimental outputs on real scale prototypes, [2]. [1] P. Fuschi, A.A. Pisano, D. Weichert (Eds). Direct Methods for Limit and Shakedown Analysis of Structures – Advanced Computational Algorithms and Material Modelling, Springer, International Publishing Switzerland, 2015. [2] A. Castiglioni, R. Pucinotti, Failure criteria and cumulative damage models for steel components under cyclic loading, Journal of Constructional Steel Research, 65, (4), 2009, pp. 751-765.