Dina D'Ayala

Earthquake loss estimation for Europe's historic town centres

To support decision-making on upgrading strategies of historic city centres, loss estimation techniques are needed, suitable for application to masonry buildings. This paper describes the development and application of such techniques to a case study in the Alfama District of Lisbon. The project involved a survey of 200 buildings to investigate structural features and condition, mapped using a GIS system, followed by analysis of key collapse mechanisms to define static collapse loads under horizontal forces for each building. The results, obtained in terms of earthquake ground motions likely to produce equivalent damage, led to the development of vulnerability functions for the case study, verified by comparison with functions derived from statistical analysis of world-wide damage reports and with damage reports of the 1755 Lisbon earthquake. The method is used to predict the reduction in losses achieved by the introduction of low-cost unobtrusive strengthening techniques, such as tie-rods connecting facade walls to floors and cross-walls. Cost benefit analysis, considering only structural costs, indicates that the return on the investment would be considerable.

Developing empirical collapse fragility functions for global building types

Building collapse is the dominant cause of casualties during earthquakes. In order to better predict human fatalities, the U.S. Geological Surveys Prompt Assessment of Global Earthquakes for Response (PAGER) program requires collapse fragility functions for global building types. The collapse fragility is expressed as the probability of collapse at discrete levels of the input hazard defined in terms of macroseismic intensity. This article provides a simple procedure for quantifying collapse fragility using vulnerability criteria based on the European Macroseismic Scale (1998) for selected European building types. In addition, the collapse fragility functions are developed for global building types by fitting the beta distribution to the multiple experts’ estimates for the same building type (obtained from EERIs World Housing Encyclopedia (WHE)-PAGER survey). Finally, using the collapse probability distributions at each shaking intensity level as a prior and field-based collapse-rate observations as likelihood, it is possible to update the collapse fragility functions for global building types using the Bayesian procedure.

A Challenge to Earthquake Engineering Professionals

Recent earthquakes have caused unacceptably high death tolls. We, the editors of the World Housing Encyclopedia, believe that reducing such an unacceptably high loss of life from earthquakes is the most important challenge facing the global earthquake engineering community. This paper acknowledges the continuing disparity between life loss from earthquakes in developing and developed countries, and the increasing vulnerability in developing countries. A sampling of current efforts to improve construction practices includes the publication of earthquake tips in India, construction manuals in Colombia, and the formation of various international networks to promote collaboration and information sharing. Future possibilities include more rewards for research into inadequately engineered construction, greater emphasis on small-scale, local efforts, and a stronger emphasis on advocacy. We believe that all of us, as earthquake professionals, have a responsibility to make the built environment safer worldwide.

Historic and Traditional Structures during the 2010 Chile Earthquake: Observations, Codes, and Conservation Strategies

The Maule, Chile, earthquake of February 2010 affected the Central Valley stretching from north of Santiago to the Rio Bío-Bío in the south. The architectural heritage suffered considerable losses, with some buildings seriously damaged or partially collapsed even in Santiago and Valparaíso, areas less affected by the earthquake. Exposing the vulnerability of Chilean architectural heritage, this event has renewed the debate about the national attitude towards architectural preservation and conservation engineering. From the survey conducted by the authors, it emerged that many retrofit and repair techniques implemented following prior earthquakes in Chile resulted in ineffective performance in the February 2010 earthquake. Safety and preservation requirements that are regulated in countries with similar historic heritage are presented as viable alternatives to past approaches and are compared with the Chilean pre-code for earthen buildings, currently under development, which appears to embrace modern preservation philosophies. Suitable remedial strategies conclude the paper.

The Global Earthquake Model Physical Vulnerability Database

There are almost 50 years of research on fragility and vulnerability assessment, both key elements in seismic risk or loss estimation. This paper presents the online database of physical vulnerability models that has been created as part of the Global Earthquake Model (GEM) initiative. The database comprises fragility and vulnerability curves, damage-to-loss models, and capacity curves for various types of structures. The attributes that have been selected to characterize each function, the constraints of setting up a usable database, the challenges in collecting these models, and the current trends in the development of vulnerability models are discussed in this study. The current collection of models leverages upon the outputs of several initiatives, such as GEMs Global Vulnerability Consortium and the European Syner-G project. This database is publicly available through the web-based GEM OpenQuake-platform http://doi.org/10.13117/GEM.DATASET.VULN.WEB-V1.0

Surface and passive/active air mould sampling: A testing exercise in a North London housing estate

Despite indoor mould being one of the most common problems in residential properties in the UK, there are not any widely accepted methodologies for its measurement. This paper focusses on this problem of measurement and reports on the findings from a rigorous testing scheme carried out to quantify air and surface mould concentrations and particle counts within 71 rooms from 64 properties in North London, some with and some without visible mould. The aim was to investigate the potential of passive and active air sampling strategies (sampling from still and actively mixed air, respectively) to explain visible mould, and understand how home/room characteristics correlate with the obtained readings. Airborne mould levels were quantified using an Andersen sampler (passively and actively), as well as by a chemical method based on the quantification of the N-acetylhexosaminidase (NAHA) activity (actively), which was also used to quantify surface mould. The mould levels were then correlated against physical characteristics of the tested homes/rooms, collected by means of survey sheets developed as part of this study. The findings did not reveal any independent variable governing all or most of the response variables, but a complex analysis suggested that whether it is a house or a flat could depict mould levels in the air and on the surfaces. It was also shown that a robust testing protocol should combine air and surface based methods, and an active air sampling strategy leads to a more accurate appraisal of airborne mould levels. Finally, the results showed that while there is some correlation between visible mould (and other moisture induced problems such as condensation) and measured air mould concentrations, lack of visible mould within a room does not necessarily mean low air mould concentrations, and thus one should not rely solely on visual inspection.

Stress tests for a road network using fragility functions and functional capacity loss functions

A quantitative approach to conduct a specific type of stress test on road networks is presented in this article. The objective is to help network managers determine whether their networks would perform adequately during and after the occurrence of hazard events. Conducting a stress test requires (i) modifying an existing risk model (i.e., a model to estimate the probable consequences of hazard events) by representing at least one uncertainty in the model with values that are considerably worse than median or mean values, and (ii) developing criteria to conclude if the network has an adequate post-hazard performance. Specifically, the stress test conducted in this work is focused on the uncertain behavior of individual objects that are part of a network when these are subjected to hazard loads. Here, the relationships between object behavior and hazard load are modeled using fragility functions and functional capacity loss functions. To illustrate the quantitative approach, a stress test is conducted for an example road network in Switzerland, which is affected by floods and rainfall-triggered mudflows. Beyond the focus of the stress test, this work highlights the importance of using a probabilistic approach when conducting stress tests for temporal and spatially distributed networks.

Inferring earthquake ground motion fields with Bayesian Networks

Bayesian Networks (BNs) have the ability to perform inference on uncertain variables given evidence on observed quantities, which makes them relevant mathematical tools for the updating of ground-motion fields based on strong-motion records or macroseismic observations. Therefore the present article investigates the use of BN models of spatially correlated Gaussian random fields as an accurate and scalable method for the generation of ground-motion maps. The proposed BN model is based on continuous Gaussian variables, as opposed to discrete variables as in previous formulations, and it is built to account for cross-correlated ground-motion parameters as well as macroseismic observations. This approach is validated with respect to the analytical solution (i.e., conditional multivariate normal distributions) and it is also compared to the USGS ShakeMap method, thus demonstrating a better ability to model jointly the inter- and intra-event error terms of ground-motion models. The scalability of the approach, i.e. its capacity to be applied to large grids, is ensured by a grid sub-division strategy, which appears to be computationally efficient and accurate within an error rate of a fraction of percent. Finally, the BN implementation is demonstrated on a real-world example (the Mw 6.2 Kumamoto, Japan, 2016 foreshock), where vector-valued shake-maps of cross-correlated intensity measures are generated, along with the integration of macroseismic observations.

Experimental Investigation on the Seismic FRP Retrofit of Realistic Full-Scale RC Beam-Column Joints

The results of four cyclic tests on full-scale beam-column joints with typical pre-1970s deficiencies are presented. The challenges incurred by the presence of a floor slab and transverse beams in retrofitting deficient specimens are often ignored, but are here fully taken into account in the experimental set-up. A realistic repair and retrofit scheme using carbon fibre-reinforced polymer (CFRP) sheets is proposed. The scheme aims to improve the ductility of the deficient joints, while providing continuity of the flexural strengthening through the joint. The results highlight that the proposed retrofit can successfully increase the ductility of the joint by activating the beams. The presence of the slab has a significant effect on the global behaviour of the sub-assembly, which ultimately does not reach failure in the beams due to the stiff slab limiting rotation. Despite significant pre-damage, the repair scheme is very efficient, with only minor differences in terms of initial stiffness and lateral strength compared to the retrofit.

System loss assessment of bridge networks accounting for multi-hazard interactions

Abstract This paper details an integrated method for the multi-hazard risk assessment of road infrastructure systems exposed to potential earthquake and flood events. A harmonisation effort is required to reconcile bridge fragility models and damage scales from different hazard types: this is achieved by the derivation of probabilistic functionality curves, which express the probability of reaching or exceeding a loss level given the seismic intensity measure. Such probabilistic tools are essential for the loss assessment of infrastructure systems, since they directly provide the functionality losses instead of the physical damage states. Multi-hazard interactions at the vulnerability level are ensured by the functionality loss curves, which result from the assembly of hazard-specific fragility curves for local damage mechanisms. At the hazard level, the potential overlap between earthquake and flood events is represented by a time window during which the effects of one hazard type on the infrastructure may still be present: the value of this temporal parameter is based on the repair duration estimates provided by the functionality loss curves. The proposed framework is implemented through Bayesian Networks, thus enabling the propagation of uncertainties and the computation of joint probabilities. The procedure is demonstrated on a bridge example and a hypothetical road network.