Rui Pinho

Development of the OpenQuake engine, the Global Earthquake Model’s open-source software for seismic risk assessment

The Global Earthquake Model aims to combine the main features of state-of-the-art science, global collaboration and buy-in, transparency and openness in an initiative to calculate and communicate earthquake risk worldwide. One of the first steps towards this objective has been the open-source development and release of software for seismic hazard and risk assessment called the OpenQuake engine. This software comprises a set of calculators capable of computing human or economic losses for a collection of assets, caused by a given scenario event, or by considering the probability of all possible events that might happen within a region within a certain time span. This paper provides an insight into the current status of the development of this tool and presents a comprehensive description of each calculator, with example results.

Numerical Issues in Distributed Inelasticity Modeling of RC Frame Elements for Seismic Analysis

The sustained development of computational power continues to promote the use of distributed inelasticity fiber frame models. The current article presents a comprehensive application and discussion of state-of-the-art formulations for the nonlinear material response of reinforced concrete structures. The broad character of the study is imparted by the joint analysis of the effects of the type of formulation (displacement based versus force based), sectional constitutive behavior (hardening versus softening response), and numerical integration parameters (such as quadrature method, mesh definition, or number of integration points). Global and local responses are assessed, along with a critical review of existing regularization techniques. An experimentally tested cantilever is used to conduct the study and illustrate the previous features. The example shows that the convergence of displacement-based meshes under objective response can be much slower than what preceding studies indicate, unlike their force-based counterpart. Additionally, the physical interpretation of the local response under softening behavior supports the proposal of a novel regularization scheme for displacement-based elements, validated through comparison against experimental results.

Flexure-Shear Fiber Beam-Column Elements for Modeling Frame Structures Under Seismic Loading — State of the Art

Whilst currently existing modeling approaches of reinforced concrete (RC) behavior allow a reasonably accurate prediction of flexural response, the determination of its shear counterpart needs further developments. In the last 20 years, models that predict shear response with acceptable accuracy for conditions of monotonic loading have been introduced, whilst, on the other hand, models capable of predicting the shear response under cyclic loading are less common. Among the approaches used for performing nonlinear analyses of frame structures, fiber beam-column elements have shown high capability in reproducing axial and flexural response, whereas the coupling between normal and shear stresses has been accounted for in very few models only. In this research work, the existing fiber beam-column elements with shear have been reviewed, underlying their most prominent characteristics and shortcomings, where relevant, with the objective of providing those interested in the topic with a relatively comprehensive overview of the subject. From this review, it can be concluded that thanks to the models proposed in the literature (and in particular, the ones herein presented) important and significant steps have been done towards the development of an analytical tool capable of modeling RC frame structures under cyclic and seismic loadings. However, further developments and improvements are still required in this research area.

Simplified Pushover-Based Earthquake Loss Assessment (SP-BELA) Method for Masonry Buildings

A simplified pushover-based earthquake loss assessment (SP-BELA) method, which was originally developed to study the vulnerability of reinforced concrete buildings has been adapted in the current work to produce vulnerability curves for unreinforced masonry buildings. The main target of the current article is to adopt various components of existing methodologies, which define the capacity of masonry buildings, within the probabilistic framework of SP-BELA to generate vulnerability curves. In the current application, the curves have been calibrated using data related to the structural characteristics of Italian buildings. Although more data on the characteristics of masonry buildings is necessary to increase the confidence in the results presented herein, a validation exercise has nevertheless been carried out to compare the vulnerability curves with independent studies related to the vulnerability of masonry buildings. These preliminary results show that there is a good agreement between the vulnerability predictions, especially for those which apply to the Italian building stock.

DEVELOPMENT OF A SIMPLIFIED DEFORMATION-BASED METHOD FOR SEISMIC VULNERABILITY ASSESSMENT

The state-of-the-art earthquake loss estimation techniques make use of pushover analysis to define the performance of structures under earthquake loading, represented by a demand spectrum whose ordinates reflect the inelastic response. The performance point defined in this way is then used as input to the fragility or loss curves. This rigorous approach represents the earthquake actions by a parameter that is known to have a good correlation with damage and also takes into account the dynamic characteristics of different buildings. However, for many applications, the available data on key input parameters, such as soil conditions and the type and distribution of the exposed building stock, are limited to the extent that the rigorous capacity spectrum approach can become either impractical or unjustified. It is for such case scenarios that a much simpler deformation-based assessment methodology, presented herein, has been developed. The proposed method possesses all the inherent advantages of a displacement-based approach, whilst reducing the required calculations by one or more orders of magnitude when compared to conventional vulnerability assessment procedures.

A risk-mitigation approach to the management of induced seismicity

Earthquakes may be induced by a wide range of anthropogenic activities such as mining, fluid injection and extraction, and hydraulic fracturing. In recent years, the increased occurrence of induced seismicity and the impact of some of these earthquakes on the built environment have heightened both public concern and regulatory scrutiny, motivating the need for a framework for the management of induced seismicity. Efforts to develop systems to enable control of seismicity have not yet resulted in solutions that can be applied with confidence in most cases. The more rational approach proposed herein is based on applying the same risk quantification and mitigation measures that are applied to the hazard from natural seismicity. This framework allows informed decision-making regarding the conduct of anthropogenic activities that may cause earthquakes. The consequent risk, if related to non-structural damage (when re-location is not an option), can be addressed by appropriate financial compensation. If the risk poses a threat to life and limb, then it may be reduced through the application of strengthening measures in the built environment—the cost of which can be balanced against the economic benefits of the activity in question—rather than attempting to ensure that some threshold on earthquake magnitude or ground-shaking amplitude is not exceeded. However, because of the specific characteristics of induced earthquakes—which may occur in regions with little or no natural seismicity—the procedures used in standard earthquake engineering need adaptation and modification for application to induced seismicity.

Evaluation of Nonlinear Static Procedures in the Assessment of Building Frames

In recent years a number of nonlinear static procedures (NSPs) have been developed and proposed. Such pushover-based seismic assessment procedures are relatively straightforward to employ and are generally chosen over nonlinear dynamic analysis, especially within the realm of design office application. Parametric comparisons between the different NSPs available, however, are still somewhat sparse. In this work, five commonly employed NSPs (the N2 method, capacity spectrum method, modal pushover analysis, adaptive modal combination procedure, and the adaptive capacity spectrum method) are applied in the assessment of 16 frames subjected to a large number of input motions with a view to assess the accuracy level of such approaches through comparison with nonlinear dynamic analysis results. The evaluation shows that all the NSPs are able to accurately predict displacements and to produce reasonable estimates for other response parameters, with limited dispersion. Even though no single NSP tested led to consistently superior results, modal pushover analysis and the adaptive capacity spectrum method seemed to perform slightly better.

Assessment of Continuous Span Bridges through Nonlinear Static Procedures

Nonlinear static procedures constitute an important tool in design office application of performance-based earthquake engineering concepts, and for this reason, they have been extensively developed and promoted in the last decade or so. However, these efforts focused predominantly on the assessment of buildings, rather than bridges, and hence there is currently a need to verify the validity in the application of such pushover-based methods for the assessment of bridges or viaducts. In this work, therefore, by considering a wide set of bridge configurations subjected to equally varying seismic input intensity levels, four commonly employed nonlinear static procedures (CSM, N2, MPA, ACSM) are scrutinized and compared, with a view to establish their adequacy for the seismic assessment of existing continuous span bridges. Results seem to indicate that all methods are able to predict displacement response with good accuracy, while force estimation, on the other hand, is reasonably attained only by those approaches where higher modes effects are explicitly accounted for.

A Prioritization Scheme for Seismic Intervention in School Buildings in Italy

A seismic rehabilitation program is being implemented to address the vulnerability of a large proportion of Italian building stock. A risk-management framework, initially only for Italian school buildings, has been developed to assign priorities for the rehabilitation, and to give timescales within which retrofit or demolition must take place. Since it is not practical to carry out detailed assessment for around 60,000 Italian schools, the framework is a multiple-level procedure that aims to identify the highest-risk buildings based on filters of increasing detail, and reduces the size of the building inventory at each step. Finally, priorities and timescales are assigned based on vulnerability, seismic hazard, and building occupancy, within a general framework with parameters that must be assigned by the relevant authorities. The methodology is transparent, technically based, and flexible enough to be adapted for other building types or regions.

Repair and retrofitting of RC walls using selective techniques

In the context of capacity design philosophy, where a desired failure mode exhibiting adequate levels of energy absorption capacity is envisaged, control must be exercised on the member behaviour t...