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The introduction of new regulations for seismic assessment of structures established stricter performance requirements for existing buildings. In order to account for the poor seismic behaviour of such buildings, recent seismic codes, namely Eurocode 8 (EC8), introduce a number of prescriptions regarding issues such as analysis type, load distribution, accidental eccentricity, etc. At the same time, these codes give room for engineering judgment to be used with reference to the definition of structural and non-structural elements such as slabs or infill walls, and obviously leave the modelling assumptions, such as Finite Elements typology, meshing, mass modelling, etc. to the analyst decision. As such, four existing RC buildings, representative of traditional Mediterranean construction, considering different modelling assumptions, were subjected to an extensive number of nonlinear static analyses. The interpretation of possible deviations in the results will hopefully provide indications on the relative importance of each modelling parameter or decision. N/A

The application of Nonlinear Static Procedures (NSPs) to assess the seismic vulnerability of existing structures has become widely accepted and extensively used in the literature as well as in engineering practice. Nevertheless, their success in predicting the response of irregular buildings is not yet fully verified. The main goal of the present study is to evaluate the capability and accuracy of some of the existing nonlinear static procedures (N2 and ACSM, in this case) to estimate the seismic performance of irregular structures. In order to accomplish this objective, four existing buildings, irregular in plan and elevation, were subjected to an extensive number of nonlinear static and dynamic analyses. The comparisons, focused on both global and local response parameters provide first indications on the reliability of static procedures to estimate the actual response of irregular RC buildings. N/A

Problemi di modellazione per l’analisi sismica delle strutture esistenti Molti edifici in c.a. del patrimonio edilizio esistente sono stati progettati per i soli carichi verticali, presentando un’inadeguata resistenza ai carichi laterali e scarsi dettagli costruttivi. Inoltre, il concetto di regolarità in pianta e in elevazione, tipico di una buona progettazione sismica, spesso è stato trascurato. Per valutare il comportamento sismico di tali edifici, alcune recenti normative in materia sismica - quali l’EC8 e le NTC08 - hanno introdotto diverse prescrizioni sulle tipologie di analisi, le distribuzioni di carico, l’eccentricità accidentale, ecc., lasciando, però, ai progettisti piena autonomia a proposito delle strategie di modellazione (es. impalcati, tamponamenti verticali, tipologia di elementi finiti, masse, ecc.). L’obiettivo del presente lavoro è quello di stimare, tramite l’esecuzione di analisi non-lineari (statiche e dinamiche) per un edificio reale, l’influenza di tali strategie nella valutazione sismica delle strutture, al fine di fornire indicazioni sull’importanza di ogni scelta progettuale. N/A

Many existing RC structures worldwide were designed for gravity loads only, with inadequate lateral load resistance, lateral stiffness and poor detailing of the reinforcement. Moreover, the concept of regularity both in plan and elevation that characterise a good conceptual design was, in most cases, not taken into account. The introduction in Europe of the regulations for seismic assessment of existing structures imposed stricter performance requirements for building structures. In order to take into account the poor seismic behaviour of such buildings, recent seismic codes – namely EC8 and NTC08, introduce a number of prescriptions regarding issues such as analysis type, load distribution, accidental eccentricity, etc. At the same time, these codes give room for engineering judgment to be used with reference to the definition of structural and non-structural elements such as slabs or infill walls, and obviously leave it up to the analyst decisions regarding Finite Elements typology, meshing, mass modelling, etc. The main goal of this work is thus to provide an extensive and wide evaluation on the influence of each of the abovementioned parameter on the seismic assessment of structures. For this purpose, nonlinear static analysis, as well as nonlinear dynamic analysis are performed on a real building that has also been experimentally tested in the past. The results will hopefully provide indications on the relative importance of each modelling parameter or decision. N/A

Nonstructural elements (NEs) are generally defined as elements typically housed within buildings/facilities that are not part of the structural system. Nonstructural elements are often classified as architectural elements, mechanical/electrical/hydraulic systems, and building contents. Nonstructural elements are often associated with critical seismic risk, due to their high vulnerability and exposure to seismic actions, especially for critical facilities such as hospitals and nuclear plant facilities. Accordingly, the combination of major exposure and vulnerability makes NEs extremely critical in terms of seismic risk even for low to moderate seismicity. The paper reviews and evaluates the main international testing approaches and protocols for the seismic assessment of NEs by means of experimental methods, which are referred to for seismic qualification. Existing test protocols are technically analyzed considering quasi-static, single-floor dynamic, and multi-floor dynamic procedures, supplying technical and operative guidance for their implementation, according to the latest advances in the field. The study proposes novel perspectives and a unified approach for the seismic assessment and qualification of NEs. The technical recommendations lay the groundwork for a more robust and standardized testing and qualification framework. In particular, the provided data might represent the first step for developing code and regulation criteria for the experimental seismic assessment and qualification of NEs.

Old precast buildings are often characterized by poor detailing that may hamper the structural performance, particularly in the case of earthquakes. This is essentially related to: (i) a limited past knowledge of seismic design and behaviour, also reflected in past building codes; (ii) the evolution of seismic zonation of the Italian territory. The aim of this work is to assess the probabilistic seismic vulnerability with respect to the usability preventing damage and global collapse performance levels of four existing single-story precast buildings designed in accordance with past Italian building codes from 1960s to 1990s in three sites with increasing seismic hazard.

The damage observed during past earthquakes repeatedly showed the vulnerability of non-structural elements and their importance in the functionality of critical facilities, such as hospitals. Performance-based seismic design (PBSD) implies the harmonization of performances between structural and non-structural elements. To this aim, performance parameters for non-structural elements need to be evaluated through experimental and numerical studies. Among the multitude of non-structural typologies, the seismic performance of piping systems is of paramount importance in order to guarantee the immediate post-event functionality of critical facilities. Few research studies available in the literature have attempted to evaluate the performance parameters required to enable PBSD of piping systems and more specifically of suspended piping restraint installations. This paper summarizes the results of an experimental and numerical research project dealing with the evaluation of the seismic behaviour of suspended piping restraint installations. Four typologies of suspended trapeze piping restraint subassemblies with channel and rod bracing systems were tested under monotonic and cyclic loading to determine their hysteretic responses and failure modes. The results of the subassembly tests were used to calibrate simplified nonlinear numerical models useful to assess the seismic response of full-scale suspended piping layouts subjected to floor acceleration time-histories

Robustness of reinforced concrete (RC) structures is an ongoing challenging research topic in the engineering community. During an extreme event, the loss of vertical load-bearing elements can activate large-deformation resisting mechanisms such as membrane and catenary actions in beams and floor slabs of cast-in-situ RC buildings to resist gravity loads. However, few studies have been conducted for precast concrete (PC) buildings, especially focused on the capacity of such structures to withstand column loss scenarios, which mainly relies on connection strength. Additional resistance resource and alternate load paths could be reached via tying systems. In this paper, the progressive collapse resistance of a PC frame building is analyzed by means of nonlinear dynamic finite element analyses focusing on the fundamental roles played by beam-to-column connection strength and tying reinforcement. A simplified modelling approach is illustrated in order to investigate the response of such a structural typology to a number of sudden column-removal scenarios. The relative simplicity of the modelling technique is considered useful for engineering practice, providing new input for further research in this field.

Seismic performance-based design approach is currently implemented in modern building codes. Design requirements and provisions ensure an adequate structural performance under different intensity levels of seismic action. However, the probability of attainment of a performance level is implicitly considered in the code design approach (provisions and requirements); for instance, the minimum requirements in concrete structures cannot be simply correlated to the probability of collapse of the building as well as to its overall structural response. The aim of this work is to assess the vulnerability with respect to the collapse limit state of industrial single-story RC precast buildings designed according to the current Italian seismic code. The comparison between the Italian code and the Eurocodes is provided throughout the paper. A parametric study is performed by investigating the safety against the collapse of 40 RC single-story precast structures. Multi-stripe analyses are performed by non-linear dynamic analyses at 10 intensity levels. The fragility of the structures is defined by means of the incremental N2 method, which has been demonstrated to be a suitable method for evaluating the collapse capacity of single-story precast buildings. The results demonstrate that the buildings are safe against the collapse mainly because of the structural overstrength with respect to seismic actions. The modelling assumptions are also validated in order to demonstrate the negligible influence of the cracking on the collapse as well as the importance of the geometrical nonlinearities for precast buildings.

This research represents an attempt to combine good convergence properties of recursive quadratic programming methods with the benefits of mid-range approximations, initially developed in the field of structural optimization. In this paper, an optimization method based on Arora and coworkers PLBA (Pshenichny– Lim– Belegundu– Arora) algorithm is proposed in which, during the line search phase, cost and constraint functions are substituted by their two-point approximations using the Generalized Convex Approximation formulae of Chickermane and Gea. The results showed that the proposed optimization method preserves the reliability and accuracy of the recursive quadratic programming method while it might simultaneously reduce the computational effort for some problems. Therefore, the proposed optimization method may be taken as potentially suitable for general design optimization purposes.