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

Defining structural robustness under seismic and simultaneous actions:an application to precast RC buildings

The increasing complexity of urban systems is making robustness a crucial requirement for structural design. The paper deals with the concept of robustness of civil structures against extreme events. After a brief literature survey, a novel point of view to robustness assessment is proposed, fitting the most accepted robustness definition. The proposed approach is discussed and compared with other methodologies for quantifying structural robustness. Thus, the methodology is developed and applied to an existing precast industrial building case study, assumed to be prone to seismic and wind hazards. In particular, the case study is assumed to be located in Emilia, Italy, where a significant earthquake occurred in 2012, causing relevant damage to gravity load designed industrial buildings. Three structural options are discussed, namely a simple supported beam–column connection (gravity load designed solution) and two pinned connections (seismic designed solution), where only one of them satisfies the current structural code requirements. The results are discussed in terms of robustness quantification, by means of a robustness matrix. The authors envisage that this approach can be effectively adopted for portfolios of existing structures, to prioritize retrofitting interventions, aimed at maximizing the overall risk mitigation with limited economic resources. © 2015 Springer Science+Business Media Dordrech

Analytical versus observational fragilities::the case of Pettino (L’Aquila) damage data database

A damage data database of 131 reinforced concrete (RC) buildings, collected after 2009 L’Aquila (Italy) earthquake, is employed for the evaluation of observational fragility curves. The specific interpretation of damage data allowed carrying out fragility curves for slight, moderate, and heavy damage, (i.e., DS1, DS2, and DS3), defined according to EMS 98 macroseismic scale. Observational fragility curves are then employed for the calibration of FAST analytical methodology. FAST method is a spectral based approach, meant for the estimate of fragility curves of infilled RC buildings up to DS3, evaluated, again, according to EMS98. Kullback–Leibler divergence is employed to check the matching between analytical and observational fragilities. FAST input variables can vary in quite large ranges and the calibration provides a valuable suggestion for the application of the method in other cases in which field damage data are not available. Results showed that optimizing values, for the input variables calibrated, are in good agreement with typical values assumed in literature. Analytical results showed a very satisfactory agreement with observational data for DS2 and DS3, while systematical underestimation was found for the case of DS1

Seismic Risk Mitigation for a Portfolio of Reinforced Concrete Frame Buildings through Optimal Allocation of a Limited Budget

The mitigation of seismic risk for a population of vulnerable civil critical structures (e.g., hospitals, schools, and bridges) is a crucial issue for many governments of earthquake-prone regions. Furthermore, owing to the global economic crisis, limited financial resources make full seismic rehabilitation of entire building stocks challenging. Therefore, a critical decision has to be made on the following key question: what is the most advantageous way of spending the available budget while treating each building in a portfolio differently, by giving it a different level of structural improvement to reduce the overall risk of the portfolio of buildings as much as possible? Herein, a decision-making tool is proposed to address this high-social-impact issue. Starting with a limited amount of information, which is gathered through expeditious surveys on existing buildings, and by involving uncertainties, the overall risk is evaluated from the fragility analysis of each structure. This is conducted via simplified pushover analyses by considering the local seismic hazard. Then, an optimization is performed for each building of the portfolio to select a relevant structural intervention from four alternatives (no intervention, partial retrofit, full retrofit, and demolition and reconstruction), based on both the overall risk reduction and the amount of financial resources. Procedures for quick estimation of fragility curves and installation costs are also discussed as part of the proposed approach. Finally, a practical application is presented with reference to a simulated case study consisting of 46 reinforced concrete school buildings located in Campania, Italy

Simplified Modeling of Rectangular Concrete Cross-Sections Confined by External FRP Wrapping

The goal of this research project is to model the effect of confinement by means of fiber reinforced polymer (FRP) externally bonded wrapping, hence to provide a simplified closed form solution to determine directly the ultimate confined concrete strength. Common cross-section shapes for reinforced concrete (RC) columns are considered herein, namely square and rectangular. The simplified model is derived from a more refined iterative confinement model proposed by the same authors to evaluate the entire stress-strain relationship of confined concrete. Based on a detailed analysis of the stress state through Mohr's circle, a simplified closed form solution is proposed to account for the non-uniformly confined concrete performance exhibited in non-axisymmetric sections. The non-uniform confining stress field exhibited in such cross-sections is explicitly considered by means of the mean value integral of the pointwise variable stress state over the cross-section. The key aspect of the proposed methodology is the evaluation of the effective equivalent pressure to be inserted in any triaxial confinement model, to account for the peculiarities of square and rectangular cross-sections. Experimental data, available in the literature and representative of a wide stock of applications, were compared to the results of the theoretical simplified model to validate the proposed approach, and satisfactory results were found

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

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

Eurocode-based seismic assessment of modern heritage RC structures:The case of the <i>Tower of the Nations</i> in Naples (Italy)

Given the interest earned recently by modern heritage structures, seismic assessment criteria of Eurocode 8 for ordinary reinforced concrete structures are applied to a modern heritage RC building. This case study, the Tower of the Nations in Naples, was designed at the end of 1930s. Modal dynamic identification, in situ inspections and testing provided the necessary knowledge of the structure in terms of geometry, structural details, and material properties. Two nonlinear models of the structure are built up in both the hypotheses of accounting and not accounting for tuff infills’ stiffness and strength contribution. Lumped plasticity model for reinforced concrete elements and equivalent strut macro-models for tuff and concrete infills are employed. Seismic assessment through nonlinear dynamic analyses is carried out for both limit states of Significant Damage and Damage Limitation. Assessment of bare and infilled models emphasizes a lower demand in terms of maximum interstorey drift of the infilled model with respect to the bare model, for both limit states considered. Record-to-record variability for the sets of seven records becomes larger if infills strength and stiffness contribution is taken into account. Outcome of the assessment is not affected by infills, i.e. the structure can be considered safe (according to EC8 provisions) for both limit states, and in both modeling hypotheses. On the other hand, the ratio demand over capacity, for both the limit states considered, is strictly influenced by infills’ contribution. Assessment tools provided for ordinary RC structures can be addressed to modern heritage buildings as shown in this case study, even if specific care is necessary for nonlinear structural modeling in case of non-conventional structural elements and non-conventional structural materials (e.g., tuff infills in lieu of clay hollow brick infills)

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