Rehabilitation of RC buildings from the late 19th - early 20th centuries - methodological discussion

Reinforced concrete (RC) constructions from the late 19th - early 20th centuries present new challenges associatedto their conservation and repair. The specificities involved in the conservation/rehabilitation of historicaland heritage RC constructions require a special approach that must account for several restrictions. Suchrestrictions are related to the safeguarding of the heritages cultural value, significance and authenticity thathave to be weighed against safety and durability requirements, as well as against duration and budget constraintsof the intervention. For the case of late 19th - early 20th centuries RC constructions, such issues aremore complex since materials have evolved and construction techniques of that era cannot be replicated.Some issues that are raised when dealing with the conservation/rehabilitation of these constructions are addressedherein based on a case study. A methodological approach for the conservation of these constructionsis discussed, highlighting challenges that need to be addressed

Material strength safety factors for the seismic safety assessment of existing RC buildings

New material safety factors (CFmat) are proposed to characterize material strength in existing buildings.These safety factors are developed in order to be compatible with seismic safety assessment proceduresdefined by current standards such as Eurocode 8 Part 3. The general theory behind the development ofthe CFmat safety factors considers the uncertainty associated to the number of surveyed structuralelements and the inherent variability of the material strength under analysis. The CFmat safety factorsare developed using a finite population approach where the material properties in a building are discretizedby considering one value per element. The proposed theory is used to define specific CFmat valuesand survey plans for the concrete compressive strength and for the reinforcing steel yield strength

Seismic fragility analysis of RC frames with masonry infills

Given the evidence provided by past earthquakes and experimental tests carried out since the mid-1950s, the contribution of the infill wall on the global response of the RC structures cannot be ignored. Therefore, the seismic vulnerability of this type of buildings needs to be assessed by considering the effect of the infill wall to determine their level of safety and, therefore, to identify their possible strengthening needs. This paper addresses the seismic fragility assessment of several reinforced concrete (RC) frames with different infill panel configurations and number of storeys. The selected structures involve fully infilled and partially infilled RC frames, as well as RC frames with an open ground floor, with four and eight storeys, whose behaviour was compared to that of the corresponding bare frames. The behaviour of the infill panel was simulated by a single strut model with properties that were calibrated using experimental data. Each structure was analysed using nonlinear dynamic analysis considering fifty real ground motion records that were scaled to several intensities. Structural performance was measured using maximum interstorey drifts over the height of the structure and fragility curves were then computed based on the demand distributions for several limit states. The fragility curves that were obtained show distinctive evolutions reflecting the different behaviour of the selected structures due to their infill configuration

An indicator for the economic loss in value of damaged cultural heritage properties

Disaster risk management (DRM) initiatives recognize the importance of cultural heritage and emphasise the need to assess the impact of hazards on the built cultural heritage. These impacts are connected to one of the challenges for the DRM sector related to the need to integrate non-monetized losses (such as those related to cultural heritage) into loss estimation procedures to obtain a sound quantification of disaster impacts. Quantifying loss in value of a cultural heritage asset introduces a high level of subjectivity due to the difficulty in estimating losses across the multiple types of values it embodies as a result of a certain amount of physical damage to the asset. To address this issue, the paper presents an indicator to estimate economic losses that represent the loss in value of cultural heritage properties due to damage caused by hazardous events. The indicator estimates loss in value of cultural heritage properties as a function of the (physical) damage they suffered and of the estimated economic impact that cultural heritage has in a country. This indicator does not reflect the true value of economic losses but establishes a standardized measure of potential economic losses comparable across countries

Proposals to account for the angle of seismic incidence when applying the PEER-PBEE methodology

The paper discusses the overall effect of the angle of seismic incidence during the seismic safety assessment of reinforced concrete buildings employing state-of-the-art methods of analysis, and provides proposals on how to account for this effect. Particularly, the Performance Based Earthquake Engineering (PBEE) methodology developed by the Pacific Earthquake Engineering Research (PEER) Centre is applied to six reinforced concrete buildings and the effect of the angle of seismic incidence is evaluated in all relevant stages of the procedure. The PEER-PBEE methodology provides a general framework for the probabilistic assessment of the seismic performance of individual buildings, it comprises four stages of analyses, and yields results that are of interest both for practitioner engineers and stakeholders. The angle of seismic incidence is involved in the second stage of the framework, which includes the structural analysis of the building, and primarily affects the resulting engineering demand parameters. Subsequently, the propagation of the effect of the angle of seismic incidence is also examined in the following two stages of the framework, which involve the damage and the loss analysis of the building. Different metrics of building performance are analysed in each stage of the framework, including two engineering demand parameters (in the structural analysis stage), the probability of collapse (in the damage analysis stage) and the expected annual loss of the building (in the loss analysis stage). Proposals to account for the angle of seismic incidence are provided based both on results obtained for each individual stage of the framework, as well as on the overall assessment procedure

Avaliação da segurança sísmica de edifícios de betão armado com base em perdas: um passeio no parque ou um pesadelo?

O presente artigo analisa uma formulação analítica para a avaliação do desempenhosísmico de edifícios de betão armado, seguindo um procedimento direto com formatosemelhante ao dos regulamentos atuais. A metodologia proposta considera um conjuntode estado limites formulados em termos de custos de reparação total, incluindo o efeitoda probabilidade de demolição do edifício sem colapso e a probabilidade de colapso. Ametodologia proposta utiliza a informação referente aos custos de reparação de acordocom uma abordagem de mitigação do risco sísmico visando, deste modo, integrarcritérios de análise de estratégias de mitigação e de avaliação específica de edifícios.Adicionalmente, discute-se o efeito de algumas simplificações possíveis à metodologiaproposta e os principais obstáculos atualmente existentes à inclusão de variáveis dedecisão como base dos regulamentos atuais para a avaliação da segurança sísmica deedifícios

Simplified modelling of in-plane behaviour of masonry infilled RC frames under seismic loading: advantages and barriers

Due to the significant contribution of the infill walls on the global seismic response of reinforced concrete (RC) buildings, several studies were carried out over time in order to identify this contribution. These studies led to the development of several models to simulate realistically the interaction between the infill and the adjacent RC frame. Due to the larger variety of masonry properties, several models can be found in the literature and these proposals are seen to be different in terms of their modelling refinement. The various techniques available to model the in-plane behaviour of infills are addressed, highlighting their application feasibility. Due to their low computational effort, the use of strut elements to model the behaviour of infill panels is a popular approach and several proposals are discussed in more detail. The reliability of using a strut model to simulate the infill panel behaviour is discussed based on experimental data from ten different test campaigns. In light of this comparison, several recommendations in terms of the characteristics of the strut models that need to be considered to achieve more realistic results when analysing the behaviour of masonry-infilled RC frame structures were established

Assessment of the in-plane nonlinear behaviour of masonry-infilled RC frames using micro-modelling approaches

Experimental tests are considered the most realistic approach to assessing thenonlinear behaviour of masonry-infilled reinforced concrete (RC) frames. Therefore,their results can be used to validate the properties of macro-models such as strut-typemodels, which are widely used in performance studies of masonry infilled RC framesdue to their computational efficiency. However, the significant cost of experimentaltests is the main barrier to their use. This paper introduces the use of detailed finiteelement models as an alternative to experimental tests to model the behaviour ofinfilled RC frames. The proposed modelling approach was developed using commercialsoftware (ANSYS®) in order to be more easily replicated by other researchers. Thecomparison between numerical and experimental results shows the developednumerical models can capture the nonlinear behaviour of the physical specimens andpredict their overall strength and failure mechanisms. Therefore, they can be used asan alternative to experimental tests

Determination of the critical angle of seismic incidence in standardised procedures for the seismic safety assessment of 3D RC buildings

This study proposes an analytical expression for the straightforward determination ofthe angle of seismic incidence that leads to the maximum structural demand ofreinforced concrete buildings when subjected to Lateral Force Analysis. The demandparameter under consideration is the maximum total displacement of single storey andisotropic multi-storey buildings, while the maximum interstorey drift may also beemployed. The proposed expression is defined based on the geometrical andmechanical characteristics of the structure. The characteristics of the seismic loadingrepresented by the elastic response spectrum are also integrated into the formulationof the expression

Statistically-based survey plans to estimate the concrete strength in existing RC buildings

In the proposed study, a framework for the definition of a safety factor leading to a reliableestimate of the mean concrete strength in existing reinforced concrete (RC) buildings is presented. Themain objective is to provide a methodology capable of establishing a reliable correlation between a givenlevel of knowledge that is required (which implies that a number of destructive tests have to be carriedout) and the confidence in the corresponding mean estimate of the strength that is obtained. Thedevelopment of this approach requires dividing the building into areas with a potentially homogeneousconcrete strength (e.g. each building storey). Furthermore, the methodology also uses the notion ofdiscrete structure where the concrete strength of each structural element of a given homogeneousbuilding section is assumed to be defined by a single strength value, which can be different than thoseof the remaining structural elements. The reliable value of the mean concrete strength is established bya boundary value defined according to an admissible variation with respect to the true mean value andincludes the effect of uncertainty due to sampling. This admissible variation is defined by a procedurethat uses both destructive and non-destructive test results. The referred boundary value allows thedefinition of a safety factor which represents the maximum admissible ratio between the true mean valueand the corresponding reliable estimate. The presented study also proposes an alternative approachregarding the definition of the Eurocode 8-Part 3 knowledge levels based on the relation between thenumber of structural members that were tested and the total number of structural members. An adaptiveconfidence factor for the mean value of the material strength is then provided for each knowledge levelas well as an approximation for the admissible global variability of the concrete strength in eachhomogeneous area of the discrete building. The proposed framework can be seen to be a more consistentstatistically-based alternative to the confidence factor values proposed by Eurocode 8-Part 3