Fatigue crack growth analysis of welded bridge details

The paper investigates the fatigue crack growth in typical bridge weldments by means of numerical analysis. The extended finite element (XFEM) method is coupled with the low-cycle fatigue (LCF) approach in ABAQUS, and parametric analyses are carried out in order to assess the influence of the main sample/testing features on the fatigue life of the investigated structures. The numerical results are found to be robust and reliable by performing comparisons with past experimental data and regulation design correlations

Acoustic emission entropy: An innovative approach for structural health monitoring of fracture‐critical metallic components subjected to fatigue loading

The paper presents an innovative approach for structural health monitoring of metallic components under fatigue crack phenomena. The methodology is based on the evaluation of the information entropy of the acoustic emission (AE) data. AE testing of fatigue crack growth (FCG) is performed on metallic components is performed within an extremely noisy testing environment. Basic AE data analysis is demonstrated to be inefficient with regard to the specific testing conditions. AE entropy is proven to be a reliable damage‐sensitive feature for real‐time assessment despite both significant noise disturbance and complexity/randomness of the acoustic phenomena. This was also confirmed for (time‐)discontinuous monitoring processes over random‐based data detections. An innovative monitoring protocol is finally developed according to the experimental evidence also considering the recommendations of the current monitoring. The protocol is found to be promising for structural health monitoring of metallic fracture‐critical components of structures under fatigue

Performance of precast buildings during Emilia-Romagna earthquakes: a case study

On May 2012 two earthquakes occurred in Emilia-Romagna region (Italy) causing several damages to existing industrial precast structures. These damages were mainly due to inadequate connection systems and the main recorded failures were the loss of support of structural elements due to the sliding of friction connections. This paper aims at justifying some of these damages by investigating the response of a real industrial building, located in Mirandola (Modena, Italy) and seriously damaged after the second main shock. In this structure the main damages were significant rotations at the columns base and relative displacements in both beam-to-column and roof-to-beam connections. Nonlinear dynamic analyses are performed in the OpenSees program with the accelerograms of the second event and the experienced damage in the structure is justified. The defined frictional element is able to simulate the behavior of both beam-to-column and roof-to-beam connections. Moreover, the nonlinear dynamic analyses demonstrate the damage in the precast columns

Code formula for the fundamental period of RC precast buildings

Recent seismic events in Europe, as L’Aquila earthquake (2009) and Emilia earthquake (2012), seriously hit the precast concrete structures. Among the others, one of the most widespread damage is the collapse of the cladding panels system. The high vulnerability of precast panels connections motivate the need of an extended study on the behavior of precast panels and on their interaction with the structure. The first step of this study must be the investigation of the dynamic behavior (in particular, the vibration periods) of one-story precast structures with and without cladding panels. In this paper a parametric study is performed in order to evaluate the first period of one-story precast buildings, without and with the cladding system. In particular, the aim of the work is to compare the results of the model with cladding panels to the dynamic properties of the bare model, in order to evaluate the cladding system influence on the stiffness and on the first period of this structural typology. Moreover, the results are compared with the code relationships that predict the first period of structures in linear static analysis

Fatigue crack growth in metallic components: numerical modelling and analytical solution

The paper presents innovative approaches for the simulation of fatigue crack growth (FCG) in metallic compact tension (CT) specimens using finite element (FE) analysis and analytical solution. FE analysis is performed in ABAQUS using the extended finite element method (XFEM) coupled with the direct cyclic low-cycle fatigue (LCF) approach. Novel methods are developed for the computation of the numerical crack growth by processing the analysis outputs. The numerical modelling is validated by considering past experimental data. The analytical solution for the fatigue life evaluation is formally reviewed, and novel fatigue damage descriptors are defined. The influence of the main sample/testing features on numerical and analytical fatigue life is extensively assessed by a parametric study. The discrepancy between the numerical and analytical estimations of the fatigue life of the components is investigated and correlated to the features of the testing/modelling. A statistical-based correction factor is finally proposed in order to enhance the analytical solution

Influence of cladding panels on dynamic behaviour of one-storey precast building

Recent Italian seismic events, as L’Aquila earthquake (2009) and Emilia earthquake (2012), demonstrated the deficiency of the actual design approach of the cladding panels system in precast buildings. Collapse of these precast panels is observed due to the connection system failure. Although cladding panels are designed as non-structural elements according to the actual code approach, i.e. no interaction with the structure is considered, a seismic excitations could make the panels collaborating with the resistant system. In this paper the influence of vertical cladding panels on seismic behavior of one-story precast concrete buildings is investigated. A parametric study is carried out to judge the influence of the cladding presence on the dynamic characteristics of precast structures. At this purpose, modal analyses are performed on both bare and infilled models. The parametric study shows a high influence of the panels on the first period of the structure, as well as the inadequacy of the code relationships for the evaluation of the natural period for such typology of structure. More suitable relations are proposed in order to evaluate the seismic demand of one story precast buildings both in the case of bare and infilled system

Influence of infill panels on the seismic behaviour of a r/c frame designed according to modern buildings codes

It has been broadly shown that presence of infill panels as closing elements of R/C frame buildings has a significant influence on global structural behaviour. Nevertheless, infill elements are not usually considered in the modelling process during the design phase. The present work investigates the effect of infill masonry walls on the dynamic characteristics of a R/C MRF building, designed according to a modern seismic building code, and on its seismic performance at different levels of seismic intensity. An analytical investigation is carried out through eigenvalue analysis on both bare and infilled structure, in order to calibrate the elastic properties of the concrete and infills according to in situ tests; nonlinear static analyses are also performed to characterize the inelastic behaviour. The infill system considerably affects the behaviour of the examined structure, in agreement with earlier studies related to very simple and usually ¿unrealistic¿ structures. This result becomes more reliable due to the consistency between the results of the eigenvalue analysis and the experimental dynamic data

Seismic behavior of beam-to-column dowel connections: numerical analysis vs experimental test

The high vulnerability of precast structures during seismic events is mainly related to the poor performance of the connection systems, among which the beam-to-column connections. The dowel typology is largely used in Europe and a detailed study is required in order to understand its seismic response. The behavior of dowel beam-to-column connections is influenced by a lot of parameters and it can be analyzed through numerical analyses. In this work a FEM model of a typical dowel connection is provided; it is validated by experimental evidences and it is used for several parametric analyses in order to investigate the influence of different parameters on the connection behavior in terms of strength and failure mechanism

Inelastic seismic shear in multi-storey cantilever columns

Seismic shear magnification in the columns of multi-storey precast structures entering far into inelastic domain is addressed in the paper. Such structures consist of an assemblage of cantilever columns connected with ties. Considering analogy with cantilever walls, it has been expected that during inelastic response the actual shear forces in multi-storey cantilever columns could be considerably higher than the forces foreseen by traditional equivalent elastic analytical procedures (equivalent lateral force or modal spectrum). A parametric study of a set of realistic three-storey structures/columns was performed. These structures were designed according to Eurocodes and shear forces were determined by the equivalent elastic (modal spectrum) analysis. Average values of the shear forces obtained by the inelastic response analysis were compared to those of the traditional (modal spectrum) procedure. They were also compared to magnified shear forces predicted using the shear magnification factor ε suggested in Eurocode 8 for RC ductile walls. In parallel, modelling issues related to the inelastic response analysis of multi-storey cantilever columns were also discussed. Very large seismic force magnifications (up to 3 times and more) were observed. Therefore it is essential to account for this phenomenon in the seismic (capacity) design of cantilever columns in multi-storey precast buildings. It was demonstrated that for this purpose the expression given in Eurocode 8 to account for seismic shear magnification in ductile cantilever walls could be used with some minor modifications

Seismic performance of single-story precast 1 buildings: Effect of cladding panels

In reinforced concrete industrial precast structures one of the most common seismic damage is the collapse of the cladding panels because of the failure of the panel-to-structure connections. This damage is caused by the interaction between the panels and the structures, which is usually neglected in the design approach. The present study aims at investigating this interaction. Nonlinear dynamic analyses are performed on several structural models in order to take into account both the panel-to-structure interaction and the roof diaphragm. According to the analyses results, if the current European single-story precast buildings stock is considered, panels stiffness significantly influences the overall structural behavior under seismic actions and the failure of the connections occurs at very low intensity values. The progressive collapse of the panels is also simulated in order to evaluate the redistribution of seismic demand in the columns during the earthquake. In the final part, fragility curves are evaluated in order to generalize the dynamic analyses results