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

A Semi-Active Control Technique through MR Fluid Dampers for Seismic Protection of Single-Story RC Precast Buildings

The work proposes an innovative solution for the reduction of seismic effects on precast reinforced concrete (RC) structures. It is a semi-active control system based on the use of magnetorheological dampers. The special base restraint is remotely and automatically controlled according to a control algorithm, which modifies the dissipative capability of the structure as a function of an instantaneous dynamic response. The aim is that of reducing the base bending moment demand without a significant increase in the top displacement response. A procedure for the optimal calibration of the parameters involved in the control logic is also proposed. Non-linear modelling of a case-study structure has been performed in the OpenSees environment, also involving the specific detailing of a novel variable base restraint. Non-linear time history analyses against natural earthquakes allowed testing of the optimization procedure for the control algorithm parameters, finally the capability of the proposed technology to mitigate seismic risk of new or existing one-story precast RC structures is highlighted

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

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

Modelling of the beam-to-column dowel connection for a single-story RC precast building

As widely known, connections performance under seismic loads can significantly affect the structural response of RC precast buildings. Within the scientific community, an increasing number of studies has been carried out on this topic, in the light of the recent earthquake aftermaths all over Europe. Indeed, connections turned out to be the weakest part of the precast structures and their failure often provoked the global collapse of the whole building. The present study aims at assessing the seismic behavior of a single-story RC precast building in terms of global collapse implementing two different model of the beam-to-column connection, a simplified and a refined one. A lumped plasticity approach is used to simulate the structural nonlinear behavior at the column base. In order to assess the refined connection model, a preliminary scheme with an isolated single dowel is validated by comparing the pushover outcomes with experimental results from literature. Nonlinear static and dynamic analyses are performed on two models of a 3D single-story RC precast building, one implementing the simple beam-to-column connection model, the other one implementing the refined mode. The comparison clearly shows that the differences are negligible if the global collapse limit state is considered

Out-of-plane seismic performance of plasterboard partition walls via quasi-static tests

Internal partitions, as many nonstructural components, should be subjected to a careful and rational seismic design, as is done for structural elements. A quasi-static test campaign aimed at the evaluation of the out-of-plane seismic performance of Siniat plasterboard internal partitions with steel studs was conducted according to FEMA 461 testing protocol. Four tall, i.e. 5 m high, specimens were selected from the range of internal partitions developed in Europe by Siniat, a leading supplier of plasterboard components in Europe. Under the specified testing protocol, a significant nonlinear pinched behaviour of the tested specimen was observed. The pinched behaviour was caused by the damage in the screwed connections, whose cyclic behaviour was strongly degrading. Both stiffness and strength of the specimens are significantly influenced by the board typology and the amount of screwed connections. Finally, it was concluded that Eurocodes significantly underestimate the resisting bending moment of the tested specimens