Fabio Ferrario

Non-linear analysis of the low-cycle fracture behaviour of isolated Tee stub connections

Abstract The present work deals with the numerical analysis of the low-cycle fracture behaviour of isolated Tee stub connections with partial fillet welds. The overall objective of the research is to assess the seismic performance of bolted partial strength beam-to-column joints under seismic loading; but first, the complexity of these joints is approached after understanding the behaviour of more simple geometries which govern the response. In fact, the study focuses on the low-cycle fracture behaviour of Tee stub connections that are elemental components of extended end plate connections with partial fillet welds. First, the general experimental program dealing with bolted end plate joints and component parts is presented. The program comprises sets of constant and variable displacement amplitude cyclic tests both on complete specimens and on components. Test results have shown good performance of bolted extended end plate moment joints under cyclic loading as well as that of fillet welds that represent an economic solution for thin and moderate extended end plates. Then, the connection material is characterized from a microstructural and fracture mechanics standpoint. Successively, detailed three-dimensional non-linear finite element analyses are carried out in order to tune model material parameters; whilst two-dimensional inelastic analyses are performed in a monotonic and cyclic loading regime to validate connection finite element models. Lastly, a parametric study is conducted in order to define details able to reduce loading-induced toughness demands. Analyses have inferred that fracture driving force demands, quantified in terms of crack tip opening displacements, are reduced by using fillet welds matching the end plate material, by limiting welding-induced residual stresses and by increasing the yield-to-ultimate strength ratio compatibly with plastic analysis requirements.

Seismic-Induced Fire Analysis of Steel-Concrete Composite Beam-to-Column Joints: Welded Solutions

A multi-objective design methodology dealing with seismic-induced fire on steel-concrete composite moment resisting frames endowed with concrete filled tubes (CFT) full strength joints is presented in this paper. In order to achieve these goals analytical and FE simulations including thermal analyses were carried out to design the proposed joints: this was followed by experimental tests under monotonic and cyclic loadings. Preliminary, seismic and fire analyses provided valuable information on the performance of moment resisting frames endowed with the chosen joint typology. A total of six specimens was designed and subjected to lateral loads. The specimens were subassemblages of interior beam-to-column joints connected by means of welded connections. Relevant experimental results are presented and commented. Furthermore, since the scope of the project was to promote joint typologies able to survive a seismic-induced fire, specimens were damaged by imposing monotonic loads equivalent to damage induced by seismic excitations, before being subjected to fire loadings. Thus, valuable information was obtained about the endurance of the proposed joint typology.

A Multi‐Objective Advanced Design Methodology of Composite Beam‐to‐Column Joints Subjected to Seismic and Fire Loads

A multi‐objective advanced design methodology dealing with seismic actions followed by fire on steel‐concrete composite full strength joints with concrete filled tubes is proposed in this paper. The specimens were designed in detail in order to exhibit a suitable fire behaviour after a severe earthquake. The major aspects of the cyclic behaviour of composite joints are presented and commented upon. The data obtained from monotonic and cyclic experimental tests have been used to calibrate a model of the joint in order to perform seismic simulations on several moment resisting frames. A hysteretic law was used to take into account the seismic degradation of the joints. Finally, fire tests were conducted with the objective to evaluate fire resistance of the connection already damaged by an earthquake. The experimental activity together with FE simulation demonstrated the adequacy of the advanced design methodology.