Simplified assessment of seismic performance for RC building classes towards preliminary applications of SISMABONUS incentive at the community scale

This paper applies a simplified approach for the attribution of seismic risk classes SRC to infilled reinforced concrete RC archetype buildings representative of existing gravity load designed GLD building typologies in Italy and investigates on the effect of possible local retrofit interventions to reduce SRC. The evaluation is based on simplified modeling of lateral seismic behavior and on the estimate of the peak ground acceleration PGA corresponding to attainment of building capacity at increasing damage limit states. The SRC is attributed as the minimum between two classes, depending on safety level (percentage of new building standard %NBS) and on expected annual loss EAL. It is shown that, due to brittle failures induced by local infill-frame interaction and consequent low seismic capacity at life safety limit state, the lower (worst) SRC is generally attained for the considered building typologies, independently from the seismic hazard at the site. The application of local retrofit interventions allows ameliorating the SRC and it is found that the most probable SRC for retrofitted building typology depends on the seismic hazard at the sitelower SRC are obtained for zones of higher hazard. Application to RC building typologies in the town of Pompei, near Naples, and cost benefit analysis CBA is performed to investigate on the convenience of alternative retrofit strategies towards risk reduction at the community level

POST-EARTHQUAKE ASSESSMENT OF DAMAGED NON-DUCTILE BUILDINGS: DETAILED EVALUATION FOR RATIONAL REPARABILITY DECISIONS

Non-ductile reinforced concrete frame structures represent a large portion of the existing building stock all over the world; the lacking of important reinforcement details on such constructions render them vulnerable and a significant source of hazard to life in future earthquakes as well as a of economic losses during moderate to severe seismic ground motions. Ideally, effective risk mitigation may be obtained with structural retrofit or by building demolition and replacement. However, economic and social constraints impair abrupt application of those solutions, requiring the study of alternative policies to encourage owners of more vulnerable structures to undertake risk assessment and mitigation. One important aspect in debate on risk mitigation is the treatment of buildings damaged by earthquakes and their possible reparability; different solutions may be adopted in order to make cities safer and more resilient to earthquakes. Building reparability strongly depends on the expected future performance of damaged building and the required repair costs. After earthquakes, the exhaustive assessment of the costs requires detailed on site surveys to establish the damage level, amount of needed interventions to restore the building in all its structural and nonstructural components and the computation of related costs. On the other hand, analytical prediction of damage level due to earthquakes could help significantly to forecast expected costs; also, applying performance-based earthquake engineering methods can contribute significantly to this scope and further allow the sound evaluation of safety variation due to damage, in addition to costs. The main objective of this research is to explore and test different methods and tools for the assessment of buildings reparability taking into account both the expected safety variation and costs. In particular, two main level of analyses for the assessment of damaged buildings are explored, namely detailed analysis based on non-linear time-histories, that is finalized to accurate estimation of expected safety variation for mainshocks corresponding to increasing return period and related repair costs, and pushover based ones, that allows simplified, practice oriented, assessment of variation of the residual capacity and performance loss due to assigned earthquakes

Building retrofit prior to damaging earthquakes: reduction of residual capacity and repair costs

When a seismic event occurs, damage may accumulate in a building affecting its capacity to withstand future earthquakes. This study investigates, by means of a detailed case study, the advantages related to the application of structural retrofit prior of earthquake events in terms of structural safety variation due to damage. The response of an existing non -ductile RC frame in Califor nia is simulated using a refined finite element model that properly accounts for possible brittle failures of structural members. Furthermore, the actual structural capacity is evaluated accounting for typical collapse modes that can affect the behavior of non -ductile buildings. Different retrofit strategies have been adopted and damaging earthquake scenarios considered. The future seismic performances of retrofitted structure before damage are compared with the case in which no mitigation strategies have b een adopted showing the advantages of different categories of intervention for different earthquake scenarios

Simplified approach for building inventory and seismic damage assessment at the territorial scale: An application for a town in southern Italy

The assemblage of a building inventory is necessary for the evaluation of seismic impact scenarios at the territorial scale. Building inventory, representing the distribution of building vulnerability classes at the territorial scale, could be performed at different levels of detail, depending on the size of the building stock, the territorial unit of analysis and on the adopted vulnerability model. Census-based data are usually employed as primary source for building inventory. A recent advancement towards compilation of regional scale inventories is provided by the interview-based Cartis approach, implemented in Italy within “Territorial themes” Reluis project, financed by the Italian Civil Protection Department. This paper proposes a first comparison of the results in terms of building inventory and the subsequent impact assessment that are obtained using Census (CE) and Cartis-based (CA) data for a town in southern Italy; a probabilistic framework for inventory is applied. Different vulnerability models are adopted and results compared. Moreover, a simple procedure that combines the informative levels present in the two approaches is proposed, allowing a mixed-type inventory from Census and Cartis data (CC) to be used for seismic impact assessment. Results of the application show that the inventory and related damage distribution changes as a function of the method adopted and in relation to the parameters considered for building classification in the vulnerability model. Comparing the impact in terms of a mean value of damage over the entire municipality, d m , calculated for various seismic intensities and starting from CE, CA and CC inventory, it is seen that the CC inventory is generally more conservative with respect to CA and CE for all the vulnerability methods, and a maximum scatter of approximately 45% in terms of d m is obtained for the considered application with one of the vulnerability methods

Stick model for as-built and retrofitted infilled RC frames

The Stick model is a MDOF system composed of masses lumped at the story level, connected in series by nonlinear shear link elements suitably calibrated to simulate the interstory inelastic behavior. The model has been demonstrated to predict with sufficient accuracy the dynamic response of existing masonry-infilled RC structures in terms of damage concentration and evolution under specific ground motion records. Previous works proposed interstory backbones calibrated on the response of refined MDOF finite element models representative of gravity-load designed buildings. In this work, with the aim of extending the applicability of the Stick model to different building typologies, a simplified procedure is proposed to generate interstory backbones for the Stick model simulating the behavior of existing masonry-infilled RC structures in as-built and retrofitted configurations. The procedure allows generating Stick models accounting for different levels of design (gravity load, obsolete seismic codes), age of construction, number of storeys and in-plan shape and dimensions. Relevant features characterizing existing buildings are accounted for, explicitly simulating typical failure modes of non-conforming RC elements, brittle failures induced by local frame-infill interaction phenomena, and introducing typical building-level collapse modes for existing buildings. The proposed procedure is extended to account for the possible implementation of retrofit intervention at the building level to both increase the structural capacity and the stiffness of the building. The proposed procedure can be employed to generate typological Stick models to be adopted in large-scale loss assessment studies, also evidencing the beneficial effect of possible retrofit interventions

Calibration of a Simplified Model for Dynamic Response Assessment of Infilled RC Buildings

The prediction of the engineering demand parameters, such as interstorey drifts and peak floor accelerations due to a seismic event, represents a necessary stage for the assessment of direct economic losses in existing buildings. Generally, performing non-linear dynamic analyses on highly refined finite element models would be the most effective method for the estimation of such parameters. However, these procedures require a level of detail that is not employable on the large scale because of the required computational effort. This work presents a simplified model, that can be adopted for the rapid evaluation of the engineering demand parameters in infilled frames subject to seismic actions. The proposed simplified model consists of a system of masses concentrated at each storey, connected by means of non-linear elements that properly describe the interstorey behavior. The procedure adopted to construct the simplified model of a multi-span multi-storey frame is described in detail. The interstorey non-linear envelope is defined by properly assembling the envelope of individual members under the simplifying hypothesis that rotation at the end of the columns are restrained. The hysteretic behavior of non-linear elements is calibrated for each storey based on the response of a 3D building modeled adopting a refined finite element model, and using the results of non-linear cyclic pushover analysis. The calibration is performed by adopting a multi-objective optimization procedure that involves the use of a Genetic Algorithm. The results of the proposed model are compared with those obtained by finite element analysis of a reference building for different intensities. The proposed model can be easily applied to carry out simplified numerical analyses useful for the assessment of direct economic losses at the large scale

Assessing building reparability after damaging earthquakes with a sustainable performance based approach

Building reparability after an earthquake is a cent ral issue for a sustainable engineering. Effective policies concerning building reparability should account for building Initial Performance (IP) before an earthq uake and of Performance Loss (PL) due to seismic damage, proper ly accounting of repair/strengthening costs. This p aper presents a pushover based procedure for evaluating IP and PL and demonstrates its usability by means o f a case study for an RC building. Moreover, preliminary estimatio n of damage-dependent reparation costs for the case study building shows the possibility of associating PL th resholds to reparability limit states