Seismic risk assessment of residential buildings by the Heuristic vulnerability model: influence of fragility curve models and inventory scale

Typological-observational methods still constitute one of the most commonly applied tools for evaluation of the seismic risk and vulnerability of the existing building stock. Their efficiency is mainly related to the effectiveness of the procedure for deriving fragility curves, and the reliability and completeness of the database that describes the building stock. This paper presents a comparison between the vulnerability and damage distribution assessment provided by fragility curves used in the Macroseismic and Heuristic methods, and a comparison of exposure evaluation methodologies according to two different approaches, namely a compartment- and a building-scale survey. An application to the case study of the residential building stock in the historic center of Alcamo, a town of 45,000 inhabitants in Western Sicily (Italy), shows the major reduction in fragility provided by recalibration of the masonry buildings’ ductility values that characterize the Heuristic method. Moreover, the efficiency of the compartment scale survey approach, based on the CARTIS typological-structural characterization method of ordinary buildings in urban areas, is underlined

Tecniche di analisi statica non lineare multimodale per strutture intelaiate

Viene presentata una panoramica delle pi\uf9 efficienti tecniche di analisi statica non lineare, evidenziando i progressi fatti nella formulazione di procedure con profili di carico adattivi multimodali, finalizzati alla valutazione della risposta di strutture a comportamento fortemente non lineare. Vengono poi presentate le diverse procedure che consentono di analizzare il comportamento di strutture irregolari in altezza o con grandi periodi di vibrare, nella quale la risposta \ue8 fortemente influenzata dai modi superiori. In quest\u2019ambito viene evidenziato il ruolo della procedura Modal Pushover Analysis, che risulta fra le pi\uf9 efficienti nel riprodurre il comportamento di strutture fortemente irregolari in pianta e in elevazione a comportamento debolmente non lineare. Viene ripresa una tecnica di combinazione dei contributi modali mediante la CQC, implementata attraverso l\u2019impiego di coefficienti di correlazione non lineari per sistemi isteretici. Un esempio numerico nel quale la tecnica viene applicata per la prima volta a sistemi spaziali irregolari in pianta ne mostra l\u2019efficacia in questo campo

Shear Strength Degradation due to Flexural Ductility Demand in R.C. Elements

A proposal is formulated that allows to evaluate the residual shear strength of reinforced concrete columns and beams for an assigned flexural ductility demand by limiting the range of the deviation angle between the inclinations of the yield \uf071 and the crack lines. In order to take into account the degradation due to cyclic loads, the reduction of the range of the deviation angle is related to the value of cinematic ductilit

Push-Over Analysis of RC Frame with Corroded Rebar

As known, the Italian building heritage largely consists of reinforced concrete frames designed before the '80s, which are, in many cases, built in the absence of specific anti-seismic criteria. Moreover, many of them, today, are characterized by bad structural conditions. Moreover, the problem of the structural conditions of the existing buildings, and their residual strength capacity, is often linked to the deterioration induced by the corrosive phenomena, which end up having a big impact on steel rebar mechanical properties. In this work, in order to investigate the influence of corrosion-damage on seismic response of existing reinforced concrete structures, a study has been carried out by analysing the non-linear behaviour of a reinforced concrete frame. The strength deterioration and reduction of the cross-section of steel rebar have been investigated and taken into account in the numerical analysis. This work shows the way in which the corrosion levels affected the push-over response, and the numerical results have been deeply analysed

Comparison of fully non-stationary artificial accelerogram generation methods in reproducing seismicity at a given site

Seismic input modelling is a crucial step when Non-Linear Time-History Analyses (NLTHAs) are performed, the seismic response of structures being highly responsive to the input employed. When natural accelerograms able to represent local seismicity are not available, the use of generated accelerograms is an efficient solution for input modelling. The aim of the present paper is to compare four methods for generating fully non-stationary artificial accelerograms on the basis of a target spectrum, identified using seven recorded accelerograms registered in the neighbourhood of the construction site during a single event, assumed as target accelerograms. For each method, seven accelerograms are generated and used to carry out NLTHAs on three RC structures, having irregular mass and stiffness distributions. The generation methods are evaluated in terms of both input modelling and seismic response of three RC structures. The results point out that maximum interstorey drift ratios are well reproduced only by generation methods based on spectrum-compatible criterion, while energy contained by the target set is only simulated by methods based on records of natural signals. Moreover, none of the method here investigated is able to reproduce the hysteretic energy dissipated by the structures subjected to the target accelerograms, in terms of both total amount and cumulative trend over the duration

A Review of Current Research on the Use of Geopolymer Recycled Aggregate Concrete for Structural Members

Geopolymer cement (GPC) is a sustainable alternative to ordinary Portland cement (OPC) that considerably cuts the emission of carbon dioxide linked to the building of concrete structures. Over the last few decades, while a large number of papers have been written concerning the use of GPC with natural aggregates and OPC with recycled aggregates, few papers have been devoted to investigating the use of Geopolymer Recycled Aggregate Concrete (GRAC) in structural members. Most of them show more interest in the mechanical strength of the material, rather than the structural behavior of RC members. This review critically compiles the present and past research on the behavior of structural members cast with different types and compositions of GRAC. The focus is on the few research studies investigating the structural behavior of GRAC elements, with an analysis of the load-bearing capacity, the load-deflection mechanism, shear behavior, tensile and flexural strength, and ductility of GRAC structural members. This review aims to indicate the research and experimental tests needed in the future for characterizing the behavior of structural members made up of GRAC

Seismic Vulnerability of Segmental Bridges with Drop-In Span by Pushover Analysis

Featured Application When evaluating the seismic vulnerability by means of non-linear static analysis of bridges characterized by the presence of drop-in spans, attention must be paid to the choice of the force distribution, which must be able to excite the structure in such a way as to represent the oscillations of all its parts and the possible phase deviation angle.Abstract Insight into the application of pushover analysis to prestressed concrete segmental bridges built in the 1950s-1970s by cantilevering with medium-large span length is provided. Seismic assessment must be carried out considering the whole structural response and, in particular, the task of tall piers, bearings, and drop-in spans with Gerber saddles, which are likely to be subjected to girder pounding and/or unseating. In this paper, the assessment of seismic vulnerability is initially performed by linear modal dynamic analysis; then, the efficiency in assessing the seismic response of different methods of pushover analyses is compared, assuming as a benchmark the results of non-linear time history analysis. The outcomes show that, for the bridge with the drop-in span, criteria for selecting the load pattern considered in pushover analysis, the reliable modeling of the bearings, and tall piers play a dominant role in the assessment of the seismic vulnerability, particularly in longitudinal motion

Low-Damage Friction Connections in Hybrid Joints of Frames of Reinforced-Concrete Buildings

Seismic-resilient buildings are increasingly designed following low-damage and free-from-damage design strategies that aim to protect the structure’s primary load-bearing systems under ultimate-level seismic loads. With this scope, damping devices are located in accessible and easy-to-inspect sites within the main structural frames where the damage concentrates, allowing the primary structure to remain mostly undamaged or easily repairable after a severe earthquake. This paper analyses the effects of friction-damping devices in structural joints of RC buildings endowed with hybrid steel-trussed concrete beams (HSTCBs) and standard RC columns. The study proposes innovative solutions to be adopted into RC moment-resisting frames (MRFs) at beam-to-column connections (BCCs) and column-base connections (CBCs). The cyclic behaviour of the joint is analysed through 3D finite element models, while pushover and non-linear time history analyses are performed on simple two-storey and two-span MRFs endowed with the proposed devices. The main results show that the BCC endowed with curved slotted holes and Perfobond connectors is the most effective in preventing the damage that might occur in beam, column, and joint, and it is adequate to guarantee good dissipative properties. For CBCs, the results showed that the re-centering system with friction pads is the most effective in containing the peak and residual drifts, preventing the plasticization of the column base

Innovative connections for steel-concrete-trussed beams: a patented solution

The most recent design strategies welcome the adoption of innovative techniques for seismic energy input mitigation, aiming to achieve high dissipation capacity, prevent the structure from collapse and ensure the serviceability of the construction. Friction damper devices have been widely adopted in framed steel structures for decades, while their introduction in different structural types is still under investigation. This paper presents the outcomes of innovative research supported by the industry and conducted on beam-to-column connections of RC structures in which the beams are Hybrid Steel-Trussed Concrete Beams (HSTCBs) and the columns are classical RC pillars. An innovative solution, recently patented, has been found for the mitigation of the effects of seismic cyclic actions on small-sized beam-column joints, typically characterised by a large amount of longitudinal reinforcement due to the small effective depth of the beam. This paper collects the main featuring steps of the innovative research, which has led to the patented solution. The calculation procedure for designing the proposed connection is shown, and the validation through 3D finite element modelling is described. For the structural analysis of the joint, several monotonic and cyclic simulations have been carried out with the scope of investigating different design moment values. The finite element results proved that the patented solution is effective in preventing beam, column and joint from damage and it is suitable for exhibiting adequate dissipative capacity ensured by a flexural behaviour dominated by wide and stable hysteresis loops