Search

In recent years, significant economic and human loses have been caused by earthquake events across the globe, particularly in developing countries, where non-seismically designed buildings constitute a significant share of the existing stock. Algeria is one of those cases and has witnessed earthquakes in the northern part of the country, which indicated the urgency to establish a robust disaster risk reduction strategy. Building exposure is one of the main model components for natural hazard risk assessment and, typically, exposure models are defined from proxies, such as national census databases or local expert opinion, for the distribution of buildings and population. However, no specific indications on the best nature or size of a regional exposure model are available to provide guidance on large-scale seismic assessment studies. In this paper, a step forward is provided by engaging different Algerian stakeholders in the collection of in-situ building data through a user-friendly smartphone/tablet application, with the aim of aiding the development of building exposure and vulnerability models, as well as increasing the risk awareness among local population and practitioners. Subsequently, earthquake damage estimates are produced and evaluated over the buildings’ lifetime in terms of exceeding slight, moderate, extensive and collapse damage states. The computed damage metrics are also used to provide input on the importance and usefulness of the in-situ collected data as a supporting data source in the development of exposure and vulnerability models. A discussion on the possible sources and size of the exposure model and preliminary guidance on conducting in-situ surveys are provided, with a view to a possible re-use in other contexts (provinces) with similar building stocks to the region addressed in this study.

In this paper, a numerical tool based on the Monkey-tail fundamental lumped parameter model is proposed for the simulation of dynamic soil-structure interaction (SSI). The proposed model has been implemented in the OpenSees finite element environment where the input parameters are merely function of the soil properties. The ease of use, accuracy and versatility of the proposed model is demonstrated in order to encourage its use within, among others, the practicing engineers’ community. Furthermore, the influence of the SSI and local soil conditions (i.e., site effect) on the seismic response of two 5-storey steel moment-resisting frame buildings has been investigated. Preliminary results shed light on the influence of these two geotechnical aspects on the structural seismic response where peak floor displacements and inter-storey drifts considering the SSI are even larger in the lower stories than those of the fixed base case. Furthermore, the results revealed the dependence of the soil amplification factor on the fundamental period of vibration, seismic intensity level and soil stiffness which are not taken into account by the current European design codes.

The research reported herein aims at the proposal of an accurate and efficient simplified numerical modelling approach for circular concrete-filled steel tubular (CFST) members under flexural loading. Experimental tests were carried out to characterize the bending behaviour of CFST members under monotonic and cyclic loading. The observed behaviour was characterized by strength and stiffness deterioration effects, as a result of the development of local buckling of the steel tube and cracking of the concrete core. Numerical simulations of these tests were conducted by resorting to existing modelling approaches, namely through Distributed Plasticity (DP) and Concentrated Plasticity (CP) models. It was found that existing modelling approaches failed to accurately capture the levels of strength deterioration and pinching effects observed in the tests. Thus, a novel CP-based simplified model, designated by matCFSTdet, was implemented in OpenSees. The hysteretic response of the CP model is based on a novel rotational spring model. An advanced calibration framework was introduced with targets to calibrate the accuracy of the model. The validation analyses indicate that the model is able to capture well the deterioration in both strength and stiffness of CFST members under cyclic flexural loading. Furthermore, the elastic stiffness, ultimate strength and the pinching effects of the hysteretic loops were also well simulated. The proposed CP model, coupled with the advanced calibration framework, thus results in a more realistic simulation of the cyclic flexural response of circular CFST members.

Current design and assessment guidelines define several seismic performance levels, aiming to ensure that structures exhibit adequate behaviour at different seismic intensity levels. Typically, the acceptance criteria at different performance levels are met by ensuring that local deformation demands are lower than pre-defined capacities. Despite the proven effectiveness of such an approach, it provides an ambiguous measure of the performance of the building, which, in most cases, is neither meaningful nor appropriate for building owners, stakeholders or decision-makers. The main objective of the research presented in this paper is to evaluate the expected direct economic seismic losses of steel moment-resisting frame structures designed according to Eurocode 8 (EC8). A set of 120 archetype buildings, representative of the current building stock in Portugal, were designed according to Part 1 of EC8 using three different behaviour factors, q: a) code-prescribed upper bound limits for medium and high ductility classes; b) behaviour factor defined according to an Improved Force-Based Design (IFBD) procedure. The PEER-PBEE methodology with the improvements proposed by Ramirez and Miranda [1] was employed for the estimation of expected seismic losses evaluated for the seismic intensity levels considered in Part 3 of EC8. The results obtained indicate that the buildings designed in accordance with EC8 comply with the non-collapse criteria. However, the level of damage could imply significant repair costs. Importantly, the results also highlight that a rational selection of the behaviour factor can result in a reduction of steel weight but still ensuring acceptable levels of expected annual losses.

Conventional seismic design of steel buildings is typically conducted, at a preliminary stage, by resorting to idealisations of member joint behaviour (e.g. fully-articulated connections). After the main structural members are defined, one proceeds with the connection design process, whose actual behaviour may or may not deviate from the assumption initially made at the design stage. This research study assesses the implications of connection-related design assumptions for steel concentrically-braced frames (CBFs) designed to Eurocode 8. This goal is achieved through the use of a Python-OpenSees-based automated seismic analysis and design framework to define an extensive set of CBF archetypes. The effect of non-explicit consideration, at the design stage, of the diagonal-to-frame gusset connections is evaluated. Full compatibility of this assumption is shown to be unassured, particularly due to the combined effects of member length reduction and boundary condition flexibility on the member's normalized slenderness. Based on the extensive suite of frame and connection designs considered, a regression-based modified normalized slenderness factor is proposed to realistically estimate, at the design stage, the normalized brace slenderness.

The main objective of the research presented in this paper is to assess the influence of a more rational selection of the behaviour factor (q) for the seismic design of steel moment-resisting frames (MRFs) according to Eurocode 8 (EC8). To this end, a large set of steel MRFs were designed using for code-prescribed behaviour factors as well as using the Improved Force-Based Design (IFBD) methodology for a more consistent selection of q. The seismic performance of the archetypes was assessed through nonlinear static and response-history analysis. The results point to the discrepancy between the design assumptions and the real response of the structures, as significant differences between the design base shear and the lateral strength of the frames were observed for frames designed with code-prescribed behaviour factors. Moreover, it is shown that IFBD-designed steel frames exhibit more uniform inelastic demands over the building height, as well as ductility demands more compatible with the design assumptions. Finally, the fragility and seismic risk assessment conducted shows that all building archetypes, regardless of the q-scenario considered, exhibit values of mean annual frequency of collapse that comply with limits available in the literature.

The wind resource offshore is often excellent due to a higher average wind speed and lower turbulence intensity. Jacket structures are the most common offshore platforms for extraction of oil and natural gas in relative low water depths. When the offshore resources run out, these structures must be displaced to another area containing underground resources or removed in the case of reaching their design life. Therefore, one possible procedure to reduce the carbon footprint on the planet, allowing society to rely on promising sources of ’clean’ energy while salvaging these oil and gas platforms, is to consider the transformation of these oil and gas platforms into offshore wind turbine support structures. The present research focus on the possibility of converting such structures for gas extraction into offshore platforms for wind turbines. In this study, a comparison between the behavior of horizontal and vertical axis wind turbines on the same offshore platform is presented. In this comparison, two different software programs are used: MATLAB and SAP2000. The model proposed is a new simplified tool used to study the structural analysis of the jacket structures, developed and summarized in 10 steps, adopted to evaluate the behavior of the platform with the wind tower configurations.

Seismic design of concentrically X-braced steel frames to Eurocode 8 entails several difficulties to practitioners, often resulting in excessively heavy structural solutions. The main objective of the research presented in this paper is to propose modifications to the existing provisions of the code aiming to achieve more efficient designs. A number of possible amendments to the European seismic code are examined, concerning the non-dimensional slenderness parameter and the homogenous dissipative behaviour criterion. It is found that the relaxation of the design criteria leads to identical frame behaviour in comparison to frames fully designed to Eurocode 8. This is an Accepted Manuscript of an article published by Taylor & Francis in Journal of Earthquake Engineering on 16/10/2018, available online: http://www.tandfonline.com/10.1080/13632469.2018.1528912.

The fatigue crack growth (FCG) has been widely studied by the scientific community. There are several proposed FCG models, the best known being the Paris relation. The fatigue crack initiation and propagation have been studied separately, however, researchers have made an effort to study the relationship between these two fatigue phenomena. In this sense, several fatigue crack growth models based on local approaches have been proposed, the UniGrow model being well-known. The fatigue crack growth process is assumed a succession of crack re-initiations considering a certain elementary material size. Recently, Huffman developed a strain energy density based on Walker-like stress life and fatigue crack growth behavior. In this paper, the Huffman model based on local strain energy density is used to predict the fatigue crack initiation and propagation for the P355NL1 pressure vessel steel. This model is combined with the generalized probabilistic fatigue model proposed by Correia aiming the generation of probabilistic fatigue crack initiation and propagation fields. In this study, the local stress and strains at the crack tip were obtained combining linear-elastic and elastoplastic analyses. The probabilistic fatigue crack growth rates fields for several stress R-ratios are estimated considering strain, SWT, and equivalent stress amplitude damage parameters. A comparison between the experimental FCG data and the generated probabilistic FCG fields is made with very satisfactory correlations being found.

This paper focuses on the evaluation of a set of Nonlinear Static Procedures (NSPs), applied to groups of plan-regular and irregular steel structures with three stories. The NSPs selected a...

This paper focuses on the characterization of the behaviour of Concrete Filled Steel Tubular (CFST) columns made with Rubberized Concrete (RuC), and on the development of an accurate numerical model for the simulation of CFST columns under monotonic and cyclic bending. The test campaign involves 18 CFST specimens with different configurations, namely the cross-section slenderness, the concrete strength, the axial load level and the lateral loading type. All CFST members tested exhibited good ductility under monotonic loading. The Eurocode 4 design provisions was verified against the test results and the design capacities of the CFST members were validated to be conservative. A comprehensive 3D Finite Element (FE) model was developed and calibrated based on test results. The FE model proved to be reliable in predicting the bending behaviour of CFST member, in terms of local buckling deformation modes, ultimate capacity and ductility of the CFST columns.

Steel moment-resisting frames (MRFs) are well known for their ductile and stable hysteretic behaviour. For this reason, they are an attractive and effective structural system for seismic resistance. Current seismic design codes, namely Eurocode 8, provide system performance factors that should be used in the seismic design under different ductility classes. However, recent research studies have shown that the use of the code-prescribed performance factors lead to stiffer and heavier structural solutions that are not consistent with the performance-based design assumptions. A new methodology, Improved Force-Based Design (IFBD), has recently been proposed with the aim of a more rational determination of the adopted value of the behaviour factor, q, instead of using the upper bound reference values provided by the design code. This paper investigates if the obtained values of q for both EC8 and IFBD concerning steel MRFs are not only adequate, but also provide sufficient margins against collapse under maximum considered earthquake (MCE) ground motions. To this end, the methodology proposed in FEMA P695 was used. Additionally, the expected direct economic seismic losses are computed according to the PEER-PBEE methodology.

The consensual agreement that ground motion record selection plays an important role in the non-linear dynamic structural response has contributed to numerous research studies seeking the definition of accurate ground motion record selection techniques. However, most of the available tools only allow for record selection based on spectral compatibility between the mean response spectrum of a record suite and a target response spectrum. This paper presents SelEQ, a fully integrated framework that implements state-of-the art procedures for ground motion record selection and scaling. In addition to typical record selection procedures, SelEQ allows obtaining the Conditional Mean Spectrum (CMS) for the European territory, the latter making use of the open source platform OpenQuake and the recently proposed SHARE seismic hazard model. This important feature allows state-of-the-art record selection for probabilistic-based assessment and risk analysis. SelEQ incorporates a number of procedures available in the literature that facilitate preliminary record selection (e.g. disaggregation for a specific site) and that allow advanced selection criteria (e.g. control of mismatch of individual ground motion records). The framework makes use of the Adaptive Harmony Search meta-heuristic optimization algorithm in order to significantly minimize computational cost and analysis time, whilst still meeting the imposed selection constraints. Application examples of the framework indicate that it can accurately select suites of ground motion records for code-based and probabilistic-based seismic assessment.

This paper focuses on the assessment of the behaviour of Concrete Filled Steel Tube (CFST) columns with square/rectangular cross-section, made with Rubberized Concrete (RuC), under flexural loading. The study aims to evaluate the differences between this type of composite members and typical CFST members made with standard concrete (StdC), namely in terms of the influence of the rubber aggregate replacement ratio on member strength, ductility, and energy dissipation capacity. The experimental campaign comprised the testing of 16 square members, 12 RuCFST and 4 StdCFST, and 4 rectangular RuCFSTs. A number of parameters were investigated, namely the cross-section slenderness (i.e., the width-to-thickness ratio of the steel tube), the aggregate replacement ratio (i.e., the percentage of sand aggregate of the concrete mixture that is substituted by rubber particles), axial load level and lateral loading type. The test results are compared with the member capacities obtained with the application of Eurocode 4. The results show a minimal influence of the type of concrete infill on the monotonic and cyclic behaviour of the members and also allow concluding that the European code is conservative in predicting the capacity of the specimens. Furthermore, the results obtained demonstrate that the cross-section slenderness has an important role on the behaviour of these members. Nonetheless, the requirements pertaining this parameter that are currently defined in Eurocodes 4 and 8 can be relaxed.

This paper focuses on the characterization of the rotation capacity of steel deep and shallow members made with European profiles subjected to cyclic flexural loading by considering several influencing parameters such as geometrical imperfections, material ductility, lateral unbraced length, and member length. For this purpose, an advanced finite element model, validated with past experimental data, was developed and an extensive parametric study was conducted. The numerical simulations revealed that shallow and deep members have different buckling behaviours and rotation capacity trends. Based on the numerical results and the experimental data collected from the literature, empirical equations are derived to quantify plastic rotation capacity limits. Compared with existing estimations, the proposed empirical equations show a more reasonable estimate. These rotation limits can be useful as modelling parameters for nonlinear static and response-history analysis and for the identification of the damage states in the context of Part 3 of Eurocode 8.

This paper reports on a study performed on steel moment-resisting frame buildings with the aim of evaluating the safety margins against collapse of buildings designed according to Eurocode 8 (EC8) when subjected to maximum considered earthquake ground motions. To this end, the methodology proposed in FEMA P695 is employed. A set of 360 archetype buildings are designed according to EC8 using code-prescribed behaviour factors for medium and high ductility class structures. Additionally, behaviour factors determined according to an Improved Force-Based Design (IFBD) methodology are also adopted. IFBD allows for a more rational selection of the behaviour factor and is fully compliant with the EC8 prescriptions. The results from the seismic performance assessment of the structures allow for an improved understanding of the seismic behaviour of steel MRFs designed according to EC8 and highlight the efficiency that is achieved with the adoption of the IFBD methodology, both in terms of reductions of steel weight as well as in terms of the consistency between the design assumptions and the ductility demand that is explored from the buildings. Moreover, the results also indicate that moment-resisting frame buildings designed according to EC8 are characterized by acceptable safety margins against collapse.

This paper presents the probabilistic seismic performance and risk assessment of cold-formed steel (CFS) sheathed shear wall panel (SWP) structures adopting conventional steel moment-resisting frame (MRF) systems as a benchmark with the aim of exploring the viability of using CFS-SWP as a new structural solution in seismic prone regions. A set of 12 building structures of both systems, with 2-, 4- and 5-storey, have been designed for two seismic intensity levels. To simulate their nonlinear behaviour, the structures were modelled adopting recently developed deteriorating hysteresis models. Based on probabilistic seismic hazard analyses (PSHA), a site-specific selection of ground motion records for Incremental Dynamic Analyses (IDA) has been carried out adopting the Conditional Mean Spectrum (CMS) as a more realistic target response spectrum. Subsequently, the seismic risk was evaluated over the structure lifetime ( i.e. , 50 years) in terms of the annual probability of exceeding the Damage Limitation, No-Local Collapse and Near Collapse limit states. The importance and usefulness of the risk metrics are highlighted and adopted as an indicator to explore the behavioural features of both structural systems. Overall, the assessment procedure showed that both systems present an acceptable seismic performance and therefore the CFS-SWP can be seen as a reliable structural solution to achieve performance-based objectives in seismic regions.

This paper seeks to contribute to the development and improvement of displacement-based design procedures, proposing improved ductility-equivalent viscous damping relationships for steel moment-resisting framed structures with dissipative beam-to-column partial-strength joints. These relationships can be used directly in procedures like the Direct Displacement-Based Seismic Design (DDBD) that uses effective stiffness, ductility-equivalent viscous damping relationships and period-displacement relationships in a performance-based design approach. To this end, a finite element model of a steel beam-to-column sub-assemblage, characterized by an extended end-plate, is developed in ABAQUS. The model, which is validated against monotonic and cyclic experimental data obtained in previous research, is employed to carry out non-linear time-history (NLTH) analyses, using real records scaled to target several levels of ductility demand. A procedure is then proposed and applied to determine the ductility-equiv...

One issue of major importance regarding the application of seismic assessment guidelines is that of the deformation capacity limits prescribed for the various limit states. In the case of existing steel structures, Part 3 of Eurocode 8 (EC8-3) defines the limits in terms of plastic rotations, which are only applicable to cases where normalized axial load levels are lower than 0.3 and to cross-section classes of type 1 and 2. These limits resemble the ones defined in ASCE 41, suggesting a direct reproduction from the latter document despite their derivation on the basis of typical American profiles. Hence, this paper aims at evaluating the deformation capacity of European steel members and to answer the question of how adequate are the current EC8-3 limits. Based on detailed FE models, the influence of member imperfections, axial load and real ground motion records is assessed. Fracture due to ultra-low cycle fatigue is taken into account and general expressions for predicting the rotation capacity of a wide number of European cross-section profiles are proposed.

This paper addresses the characterization of the behaviour of the column web panel components in bolted end-plate steel joints subject to cyclic loading. Based on experimental test results, a calibrated parametric FE model of a double extended beam-to-column end-plate steel joint is implemented, that allows characterizing the behaviour of the joints both globally and in terms of the dissipative components. The numerical models have been developed using the ABAQUS FE package considering a detailed representation of the various joints components and taking into account the different sources of geometrical and material nonlinearities. Finally, based on the integration of the stress and displacement fields in predefined paths along the column web, a detailed extraction procedure for the cyclic force-deformation behaviour of the column web panel components is proposed, however extensible to other components. These relationships are needed for implementation in a components based approach that accounts for cyclic loading conditions.

The publication of Part 3 of Eurocode 8 (EC8-3), dedicated to the seismic assessment of existing buildings, took place a decade ago. However, its application in engineering practice has been limited. Moreover, no studies have been conducted regarding the application of EC8-3 to steel structures. In this paper, a critical review and practical application of EC8-3 and ASCE41-13 are carried out. Issues related to the definition of the performance requirements, compliance criteria, and the consistency of the analysis procedures proposed by both standards are identified. Conceptual differences between both documents are highlighted, and several inconsistencies in EC8-3 are discussed.

A seismic design procedure for CFS structures employing sheathed shear wall panels (SWP), compatible with the framework of the Eurocodes, is proposed in this paper. In order to assess the structural behaviour and generate the required data for the appraisal of the seismic design procedure, the OpenSees finite element environment was used to simulate the nonlinear behaviour of CFS-SWP adopting a novel deteriorating hysteresis model. Nonlinear static (pushover) and incremental dynamic analyses (IDA) have been carried out on 54 CFS-SWP frames having 2-, 4- and 5-storeys designed with varying seismic intensity levels. Fragility curves based on buildings collapse probability have been developed following the FEMA P695 methodology. Based on the defined design requirements, the CFS structural system evaluated in this study is shown to meet the acceptance criteria for a behaviour factor (q) equal to 2 for low- and moderate-seismicity. Furthermore, the results reveal that the lateral overstrength has a relevant influence on the probability of collapse and that an improved performance could be achieved if continuity of the CFS-SWP chord studs along the height is enforced.

This paper proposes an extension of the Improved Forced Based Design procedure to 3D steel structures. The Improved Forced Based Design (IFBD) procedure consists of a more rational sequence of the design checks proposed in Eurocode 8 and involves a more realistic selection of the behaviour factor instead of selecting an empirical value based on the ductility class and lateral resisting system adopted. The design procedure was tested on a group of four 3D steel structures, composed by moment-resisting frames with three storeys height and the same plan configuration in all storeys. The plan configuration was defined in order to target lateral restrained or unrestrained systems as well as plan regular or irregular structures. The same group of structures was also designed according to the force-based process prescribed in Eurocode 8. The member sizes obtained through the two approaches were compared and the seismic performance was assessed through nonlinear static and time-history analyses. The limit states referred to structural and non-structural damage, considering the two levels design approach, which are the serviceability and the ultimate limit states, were examined. The results obtained reveal that the IFBD leads to more economical structures that still comply with the performance requirements prescribed in Eurocode 8.

Performance-based earthquake engineering has created the need for practical ways to assess the response of non-structural components (NSCs), which may be affected by deformation and/or acceleration demands of the superstructure. In the research study detailed in this paper, peak floor accelerations (PFAs) and floor response spectra (FRS) are computed using non-linear time history analysis (NTHA) for a comprehensive suite of 30 steel moment-resisting frame (MRF) archetypes, designed in accordance to Eurocode 8, considering different levels of non-linear seismic demand. The mean trends observed were compared with the most recent approaches proposed in the literature for prediction of acceleration demands. It was found that for PFAs, the available methods provide accurate predictions of the actual structural response under elastic and inelastic demands. However, the estimation procedures for the FRS yielded relevant differences in comparison to the observed elastic and inelastic responses, which entails the need for further development of such methods. It was also concluded that the existing PFA and FRS estimation methodologies present in several guidelines for seismic design and/or assessment do not provide reliable estimates of the acceleration demands incurred by the building. This highlights the very important need for an improvement of these codified procedures for a more reliable prediction of the seismic structural response.

Maritime Engineering covers the investigation on safe and sustainable engineering in the salt-water environment and includes scientific and technical works regarding management, planning, design, analysis, construction, operation, maintenance and applied research related to renewable energy and oceanic engineering. In this journal are published articles from industry and academia that convey advanced research that those developing, designing or constructing schemes can begin to apply, as well as papers on good practices that others can learn from and use. The themed issue on Renewable Energy and Oceanic Structures, Part I, was intended to be a forum of discussion of the recent advances in the domain of the structural integrity, inspection, monitoring, repair, maintenance, fatigue, fracture mechanics, structural design, stability, safety, reliability, offshore materials technologies, computational fluid dynamics, ocean renewable energy and environment. Contributions were proposed from engineers, scientists, consultants among others, in the field of ocean, offshore, polar, artic, naval, marine renewable energy, subsea, marine environmental engineering, coastal and aquaculture engineering, as well as by other specialists interested in these fields. This issue of ICE's Maritime Engineering journal reflects on the following topics: structural integrity of offshore structures; dynamic response of pipelines under flexural loads; and finally, assessment of wave energy resources. The first paper (Rege and Pavlou, 2019) presents a procedure for modelling the stop hole induced fatigue crack growth delay for a crack propagating under mixed-mode I + II conditions. This procedure combines the S–N curve for fatigue crack initiation and the Paris law for fatigue crack propagation. The procedure is implemented to evaluate the structural integrity of a plate with circular hole used in offshore structures applications. In the second paper (Pavlou and Correia, 2019) proposed an exact solution for pipeline response under transient and harmonic loads. In this way, the authors modelled the fluid-pipe interaction under transient loading conditions through the equilibrium and motion partial differential equations. A system of 8 first-order coupled partial differential equations and the integral transforms are used for achieving an analytical solution. Additionally, the methodology is based on double integral transforms. The methodology proposed is applied for pipelines subjected to impact and harmonic loads, and their results are provided. The paper by Jiang et al. (2019) presents an assessment of wave energy resources in the South China Sea and prepares the basis of plans for developing and using wave energy at the referred region. Additionally, a guidance to site wave power stations as well as the design criteria for wave energy convertors are provided. According to this study, the results showed that areas with abundant and stable exploitable wave energy in the South China Sea, mainly between the Luzon Strait and the southeast of the Indo-China Peninsula, the annual average wave energy fluxes ranged from 10 to 18 kW/m. In this way, the authors have concluded that the wave energy resources and the frequency of high sea states need to be considered when choosing sites for wave energy farms.

This study investigates the structural vulnerability of an old reinforced concrete dual wall-frame building structure, in Lisbon, Portugal. The building presents non-ductile behaviour and detailing typical of buildings designed before the introduction of modern seismic codes (pre– 1980). An analytical methodology is adopted in which multiple stripe analysis are performed on a three- dimensional model of the building. Fragility and vulnerability functions are developed for this structure, representative of a typology of old RC buildings. The fragility is derived taking into account the brittle shear failures of RC vertical members, i.e. columns and shear walls. The nonlinear dynamic analyses clearly indicate that these failure modes have a critical influence on the seismic performance of the structure. The results of this study can be used for seismic loss assessment and for the identification of appropriate mitigation strategies for this typology of existing RC buildings.

This paper presents an analytical model to predict the mode I fatigue crack growth of steel Central Cracked Tensile (CCT) specimens repaired with Carbon Fiber Reinforced Polymer (CFRP) bonded on the two sides of the plate. A review of the behaviors observed in past experimental tests is provided. The CFRP-steel stiffness ratio, as well as the level of the initial crack length and the location of the CFRP patch, influence the performance of the CFRP crack repair. A total of 69 experimental and 7 numerical results of CFRP repaired specimens were collected from the literature and a database is created. Seventy percent of the data (Experimental only) were used for the development of the model and thirty percent for verification. The fatigue crack propagation of each pair of unrepaired and repaired experimental specimens was calibrated for the development of the model. The effect of the CFRP on the fatigue crack propagation is represented by a SIF reduction factor, β . An analytical law based on nonlinear regression analysis is proposed to evaluate β which depends on the CFRP-steel ratio, level of damage of the steel plate, and patch location. The model is fairly validated with experimental and numerical results. A parametric study is conducted for further verification, the model shows reasonable trends.

A reliable evaluation of dynamic amplification effects is crucial in bridge design in order to achieve safer and economical solutions. In engineering practice, these effects are commonly taken into account through dynamic load allowance factors (IM) specified by the codes. However, some codes allow the calculation of these IM factors through more advanced dynamic analysis in order to achieve more realistic results. Therefore, a methodology to numerically evaluate the IM in bridges is described. The methodology is based on a vehicle-bridge interaction model that can take into account any configuration of pavement irregularities. A case study consisting of two modular steel bridges is presented. In order to reach a comprehensive characterization of the IM factors, a probabilistic analysis is conducted, taking into consideration the stochastic generation of random irregularity profiles based on pavement roughness and experimentally measured manufacturing imperfections, as well as a wide range of vehicle speeds. The results obtained in this study demonstrate the advantages of performing a probabilistic numerical evaluation of the IM factor in comparison to the use of pre-defined factors proposed by design codes. The consideration of IM factors based on probabilistic assessments can lead to relevant material savings in the design of steel modular bridges.

Summary The implementation of performance-based design and assessment procedures in seismic codes leads to the need for an accurate estimation of local component demands. According to Part 3 of Eurocode 8 safety checks should be always conducted in terms of plastic rotations, even when linear elastic methods of analysis are used. This paper demonstrates that linear analysis fails to predict inelastic deformation demands at the member level. Therefore, a simplified procedure that allows for the estimation of beam inelastic deformation demands using linear elastic methods of analysis in a simple and conservative way is presented herein. A number of moment-resisting steel frames designed according to different criteria and exhibiting different column-to-beam strength ratios were analysed and used for the derivation of the proposed procedure. A comparative study between alternative methods of quantifying inelastic deformation demands using linear analysis is also carried out. The results obtained allow concluding about the efficiency and conservativeness of the proposed procedure which makes it attractive to be employed in engineering practice. Copyright © 2016 John Wiley & Sons, Ltd.

The main objective of the research presented in this paper is to study the bending behaviour of Concrete Filled Steel Tube (CFST) columns made with Rubberized Concrete (RuC), and to assess the seismic performance of moment-resisting frames with these structural members. The paper describes an experimental campaign where a total of 36 specimens were tested, resorting to a novel testing setup, aimed at reducing both the preparation time and cost of the test specimens. Different geometrical and material parameters were considered, namely cross-section type, cross-section slenderness, aggregate replacement ratio, axial load level and lateral loading type. The members were tested under both monotonic and cyclic lateral loading, with different levels of applied axial loading. The test results show that the bending behaviour of CFST elements is highly dependent on the steel tube properties and that the type of infill does not have a significant influence on the flexural behaviour of the member. It is also found that Eurocode 4 is conservative in predicting the flexural capacity of the tested specimens. Additionally, it was found that the seismic design of composite momentresisting frames with CFST columns, according to Eurocode 8, not only leads to lighter design solutions but also to enhanced seismic performance in comparison to steel frames.

This paper presents a numerical investigation on the ductility and strength of short steel tubes filled with Rubberized Concrete (RuC), which is a composite material that mixes concrete with rubber particles. This research concerns the enhancement of both ductility and energy absorption of CFST by considering a core of RuC instead of normal concrete (NC). First, a brief literature review on the topic is presented. Then, based on an experimental programme conducted by the authors, numerical models of CFST and RuCFST columns are developed. The results of non-linear analyses (ultimate strengths, load-shortening curves and failure modes) are validated using experimental data, and good agreement is shown. Finally, a numerical study on the properties of confined NC and RuC is conducted. It is concluded that the concrete damaged plasticity model can be used to simulate RuC. The dilation angle plays a key role in RuC and its lower value (compared to that of NC) influences the concrete confinement. Taking into account the RuC dilation angle, steel yield stress and tube local slenderness, a new formula is proposed to predict the concrete core confinement of the studied CFST and RuCFST columns with circular sections.

The main objective of the research presented in this paper is to investigate the flexural behaviour of concrete filled steel tube (CFST) columns of circular cross-section, made with rubberized concrete (RuC). A second objective is to identify behavioural differences between this type of composite members and typical CFST members made with standard concrete (StdC), namely in terms of the influence of the rubber aggregate replacement ratio on member strength, ductility, and energy dissipation capacity. The paper describes the preparation and development of an experimental campaign, involving the testing of 16 circular specimens, 12 RuCFST and 4 StdCFST. The definition of the test campaign considered a number of parameters, namely cross-section slenderness, aggregate replacement ratio, axial load level and loading type. A special device was developed as part of an innovative testing setup, aimed at reducing both the cost and preparation time of the specimens. This paper also describes the comparison of the test results with design provisions from Eurocode 4. The test results show a marginal influence of the type of concrete infill on the monotonic and cyclic behaviour of the members and also allow concluding that Eurocode 4 is conservative in predicting the capacity of the tested specimens. Moreover, it is found that the cross-section slenderness does not have a significant influence on the monotonic and cyclic behaviour of the specimens, pointing out for the possible relaxation of the cross-section slenderness limits currently specified in Eurocodes 4 and 8.

An experimental investigation on the strength and ductility of short steel tubes filled with rubberised concrete (RuC), sourced from recycled scrap tyres, is presented in this paper. Firstly, a brief literature review on (i) concrete-filled steel tubes (CFST) and (ii) mechanical characterisation of rubberised concrete is presented. Then, the experimental investigation is described and test results are shown and discussed, namely, the assessment of (i) RuC and steel mechanical properties and (ii) RuCFST column structural properties. The influence of various parameters, such as the cross-section shape (square, rectangular, circular), steel grade, and concrete mix (standard concrete versus RuC), on the short column strength and ductility is analysed and discussed. Eurocode 4 is considered (i) to determine the strength of the tested columns and, in particular, (ii) to assess its applicability to RuCFST columns based on a comparison with the experimental results. The main conclusion of this research is that RuCFST short columns present higher ductility than those made of standard concrete, even though they also show lower strength. This improved ductility is noticeable in columns with circular sections, rather than in square and rectangular sections. From a practical viewpoint, this could be a major benefit for structures in seismic areas where energy dissipation is needed.

The application of performance-based design and assessment procedures requires an accurate estimation of local component deformation demands. In the case of steel moment-resisting frames, these are usually defined in terms of plastic rotations. A rigorous estimation of this response parameter is not straightforward, requiring not only the adoption of complex nonlinear structural models, but also of time-consuming numerical integration calculations. Moreover, the majority of existing codes and guidelines do not provide any guidance in terms of how these response parameters should be estimated. Part 3 of Eurocode 8 (EC8-3) requires the quantification of plastic rotations even when linear methods of analysis are used. Therefore, the aim of the research presented in this paper is to evaluate different methods of quantifying local component demands and also to answer the question of how reliable are the estimates obtained using the EC8-3 linear analysis procedures in comparison to more accurate nonlinear methods of analysis, particularly when the linear analysis applicability criterion proposed by EC8-3 is verified. An alternative methodology to assess the applicability of linear analysis is proposed which overcomes the important limitations identified in the EC8-3 criterion.

This paper presents an experimental investigation on the cyclic behaviour of short steel tubes filled with rubberized concrete (RuC), a composite material that mixes concrete with rubber particles. A brief literature review on the cyclic behaviour of CFST columns, the mechanical properties of RuC and recent research on RuC-filled steel tubes (RuCFSTs) is presented. Then, the tested specimens are characterized, comprising three cross-section shapes (square, rectangular, circular), three steel grades (S235, S275, S355), three concrete mixes (0%, 5%, 15% of rubber particles content) and two axial load levels (10%, 20% of axial plastic load). After that, the loading protocol, test rig and experimental procedure are described in detail. The experimental results are extensively discussed, focusing on the columns’ cyclic strength, failure modes, hysteretic and envelope curves, as well as on the energy-based ductility factors. Finally, conclusions are drawn regarding all these parameters. The most relevant achievement is that a concrete mix with a low content (5%) of rubber particles leads simultaneously to the lowest decrease (5%) in the cyclic strength and the highest increase (52%) in the ductility of RuCFST columns, thus being the most suitable mix to use in seismic areas, where ductility and energy dissipation requirements are mandatory.

The prediction of the behaviour of joints relies on experimental and numerical tests that provide accurate information for the characterization of the various joint components. This paper presents the calibration and validation of a parametric FE model of a beam-to-column double extended end-plate steel joint, using test results, and characterizes the web panel components using the validated FE models. The model implemented in the ABAQUS FE package which takes into account the non-linear geometrical and material behaviour, non-linear contact and slip. The calibration/validation of the model is based on results from an experimental research programme on three double-extended end-plate partial-strength beam-to-column joints. The behaviour of the joints is characterized both globally and in terms of the critical components. The experimental and numerical results are compared, revealing good agreement, allowing their further use in the more detailed components assessment. Thus, based on the validated stress and deformation fields of FE results, a procedure is proposed to extract the force-deformation behaviour of the column web components. The results are compared with those obtained from Eurocode 3 and from the literature.

The main objective of this study is to investigate the implications of the explicit brace-to-frame gusset connection modelling on the seismic performance assessment of steel concentrically-braced frames (CBFs). Two key modelling alternatives are considered, namely through the simulation of CBFs with: i) a benchmark experimentally-validated model, in which the gusset plates are explicitly designed and simulated; and ii) a more simplified option, whereby diagonals are simulated through a centreline-to-centreline approach with fully-pinned boundary conditions. Anticipating the consequences of a less refined modelling approach, a simplified regression-based design process to Eurocode 8 for these gusset connections is proposed, therefore avoiding the need for an explicit connection design for seismic assessment purposes. A third modelling option, an identical approach to the benchmark but with the gusset dimensions being determined through the aforementioned regression-based design process, is also considered. The importance of the explicit modelling of the gusset plate connections to obtain reliable estimates of seismic performance is shown through the comparison of the seismic performance of various building archetypes, considering different metrics (e.g. lateral deformations, earthquake-induced collapse risk and economic losses). Furthermore, the validity of the proposed gusset-design methodology is discussed, by comparing the resulting gusset dimensions against those associated with a rigorous seismic design process, as well as by comparing the seismic performance assessed with numerical models incorporating explicitly-designed or simplified-designed gusset geometries.

The main objective of this paper is to understand and characterize the level of expected earthquake-induced economic losses of steel buildings designed to Eurocode 8. This is attained through the use of a comprehensive population of case-study buildings that considers different lateral load resisting systems, plan configurations and building heights. Different locations of low and high seismicity, reflecting the majority of the European seismic reality, are considered. The results indicate that EC8-compliant steel moment-resisting frame (MRF) buildings and concentrically-braced frame (CBF) buildings generally exhibit good seismic performance in terms of mean annual frequency of reaching collapse. Although all buildings showed good performance against collapse, when compared to the requirements present in literature, clear indications on a lower performance of chevron-braced CBFs are observed. Furthermore, low expected annual losses (EALs) are recorded across the population of steel buildings considered, with a predominant contribution of losses coming from structural and non-structural damage. Based on the findings reported in this paper, different insights towards the incorporation of loss performance objectives in the European seismic design code are provided.

The objective of this paper is to validate finite element (FE) modeling protocol for screw connected, back-to-back built-up cold-formed steel (CFS) columns. The protocol is developed and validated using results from previously conducted experiments. The effort is motivated by two applications: (1) to augment experimental findings on built-up CFS columns, particularly for fastener demands and (2) to provide a simulation path for modeling the built-up CFS columns that are used as shear wall chord studs. Shell FE-based models were created in ABAQUS and include monotonic loading, nonlinear geometric and material behavior, geometric imperfections based on laser scanned measurements of tested specimens and a contact model that includes friction. Additionally, the screw fasteners were integrated into the modeling protocol using user-defined element subroutines capable of reproducing strength and stiffness deterioration under monotonic load as well as the pinching that occurs when screw fasteners are subjected to cyclic loads. Monotonic, concentric compression tests on 17 back-to-back CFS columns using two cross-section sizes and varying fastener layouts with sheathing conditions were simulated. Deformations, strength, and collapse mechanisms obtained by the models were in close agreement with the experimental results. An assessment of the loading demand on screw fasteners reveals the conservatism in built-up column fastener layout and design as required by the North American Specification for the Design of Cold-Formed Steel Structural Members (AISI S100-16 Section I1.2). Also, under the tested semi-rigid column end conditions, there is a little boost in axial capacity with the addition of member end fastener groups (EFGs) at the top and bottom of the columns. Numerical models are also used to assess the cyclic performance of axially-loaded columns so that chord stud buckling limit states could be captured in seismic simulations of CFS-framed shear walls in future work.

One of the major concerns in offshore structures are the welded connections where fatigue failures are highly relevant. In many cases of offshore welded connections, the fatigue cracks initiated may grow from the weld to the base material, but also from the root of the weld. In this study, the evaluation of design S-N curves for a double-side welded connection made of S355J2 steel used in offshore applications is proposed. The characteristic fatigue curve of the double-side welded connection is obtained using statistical analyses based either in the ASTM E739 standard as well as the probabilistic fatigue model proposed by Castillo & Fernández-Canteli. This study concludes with a comparison between the experimental fatigue curves obtained and the design S-N curves proposed in design codes for offshore structures. Existing code recommendations are very conservative when comparing the design S-N curves with the proposed new characteristic S-N curves. For the joint under investigation the hot spot and nominal stress approaches yield very similar S-N results.

The research reported herein aims to propose an accurate and efficient simplified numerical modelling approach for circular Concrete-Filled Steel Tubes (CFST) under flexural loading. Experimental tests were carried out to characterize the monotonic and cyclic behaviour of CFST members under bending. To assess the seismic performance of a composite structure with CFST members, both Distributed Plasticity (DP) and Concentrated Plasticity (CP) models were considered as potential simplified models for CFST members. The DP model was developed on the basis of a fibre discretization of the composite cross-section and displacement-based beam-column finite element. It was concluded that one could not accurately capture the development of local buckling of the steel tube and the development of multi-axial stress state effects (e.g. concrete confinement). Thus the DP model was found to be unsuitable for modelling of CFST members under cyclic flexural loading. Regarding the CP modelling, the modified Ibarra-Medina-Krawinkler deterioration model (with peak-oriented hysteretic response) was selected to define the behaviour of the plasticity spring associated with the plastic hinging region of the member. In order to accurately simulate the cyclic behaviour of the CFST section within the response of the spring, the deterioration model was calibrated, within a parameter-optimization framework, on the basis of 3D comprehensive numerical models in ABAQUS. The CP model was found to capture well the deterioration in both strength and stiffness of the hysteretic loops of the CFST members, which may be mostly associated with the development of local buckling phenomena. Furthermore, the elastic stiffness, the ultimate strength and the pinching effects of the hysteretic loops were also well simulated. Thus, the proposed CP model, coupled with the advanced calibration framework, was concluded to have a high level of accuracy in terms of simulating the cyclic flexural response of CFST members.

Torsional effects may significantly modify the seismic response of a building and the distribution of damage throughout the structure. In this paper, the torsional response of a case study Reinforced Concrete (RC) wall-frame building built between 1960 and 1980 is presented. The building was constructed without considering appropriate seismic design criteria and without taking into account the forces induced by torsional vibrations. A numerical investigation on the seismic behaviour of the case-study building is carried out by means of nonlinear static pushover analyses performed on a 3-D numerical model of the building; the Extended N2 method is adopted to take into account the influence of higher mode effects in plan and in elevation. The results are then compared with the ones obtained from nonlinear Time-History (TH) analysis. It is concluded that the shear demand evaluated according to the Extended N2 method provides a conservative estimate in comparison to TH analysis. Thus, an improved procedure is proposed for the application of the Extended N2 method in the evaluation of shear demand.

The research reported in this paper focuses on the assessment of the seismic performance of conventional steel moment-resisting frames (MRFs) and steel-concrete composite moment-resisting frames employing circular Concrete-Filled Steel Tube (CFST) columns. Two comparable archetypes (i.e. one steel MRF, with steel columns and steel beams; and one composite MRF, with circular CFST columns and steel beams) are designed, and used as the basis for comparison between the seismic performance associated with each typology. Both structures are designed against earthquake loads following the recommendations of Eurocode 8. The comparison of the obtained design solutions allows concluding that the amount of steel associated with the main structural members is higher for the steel-only archetype, even though the composite MRF has the higher level of lateral stiffness. This aspect is particularly relevant when one considers that a minimum level of lateral stiffness (associated with the P-Δ inter-storey drift sensitivity coefficient, θ), is imposed by the European code, which may ultimately govern the design process. The two case-studies are then numerically modelled in OpenSees, and their seismic performance is assessed through fragility assessment for a number of relevant limit states, and, finally, earthquake-induced loss estimation. In general, the results obtained clearly indicate that the composite MRF with circular CFST columns exhibits better seismic performance than the equivalent steel-only archetype. This is noticeably shown in the comparison of the fragility curves associated with the collapse limit state, which tend to show substantially higher probabilities of exceedance, at similar levels of 1st-mode spectral acceleration, for the steel-only case. Furthermore, seismic losses at several seismic intensity levels of interest tend to be higher for the steel MRF.

Summary The recent concerns regarding the seismic safety of the existing building stock have highlighted the need for an improvement of current seismic assessment procedures. Alongside with the development of more advanced commercial software tools and computational capacities, nonlinear dynamic analysis is progressively becoming a common and preferable procedure in the seismic assessment of buildings. Besides the complexity associated with the formulation of the mathematical model, major issues arise related with the definition of the seismic action, which can lead to different levels of uncertainty in terms of local and global building response. Aiming to address this issue, a comparative study of different code-based record selection methods proposed by Eurocode 8, ASCE41-13 and NZS1170.5:2004 is presented herein. The various methods are employed in the seismic assessment of four steel buildings, designed according to different criteria, and the obtained results are compared and discussed. Special attention is devoted to the influence of the number of real ground motion records selected on the estimation of the mean seismic response and, importantly, to the efficiency that is achieved when an additional selection criteria, based on the control of the spectral mismatch of each individual record with respect to the reference response spectrum, is adopted. The sufficiency of the methods with respect to the pairs of M–R of the selected group of records and the robustness of the scaling procedure are also examined. The paper closes with a study which demonstrates the suitability of a simplified probability-based approach recently proposed for estimating mean seismic demands. Copyright © 2015 John Wiley & Sons, Ltd.

Portugal has its past marked by the occurrence of very destructive earthquakes. In the well-known 1755 Lisbon earthquake, more than 50 % of the building stock was heavily damaged or destroyed and about 10 % of the population in Lisbon perished. In the beginning of the last century, a moderate event of magnitude 6.0 Mw struck the village of Benavente, causing 46 fatalities and damaging more than 3000 dwellings. The Portuguese building stock in highly populated centres is characterized by a large fraction of masonry buildings, which typically have a higher seismic vulnerability. For these reasons, it is clear that a reliable and accurate platform for damage estimation based on deterministic earthquake scenarios is fundamental, in order to create adequate post-disaster response plans, or to understand which structure types are contributing to the human and economic losses. This study provides an overview of the initial development of this framework for Portugal, as well as a description of the components and input models required for the generation of the seismic input and estimation of damage. In order to demonstrate the capabilities of the platform, two seismic events were considered to assess structural damage throughout mainland Portugal. This framework has been established at the Faculty of Engineering of the University of Porto. It allows earthquake engineers and seismic risk modelers to access damage information and to launch calculations of losses for scenario events. The products can also be of interest to experts and decision makers, who may wish to consider specific types of outputs such as the distribution of building damage, fatalities and the number of homeless.

POSSUM system is widely used and validated for 30-day mortality and morbidity prediction. The aim of this study was to evaluate the performance of five POSSUM's equations (POSSUM, P-POSSUM, V-POSSUM, V-POSSUM physiology and V-POSSUM Cambridge) on predicting 30-day mortality and morbidity in elderly patients undergoing major elective vascular surgery.A retrospective longitudinal cohort study.A study conducted at an University Hospital.208 elderly patients (≥ 60 years) undergoing major elective vascular surgery.Data collected from the clinical files included patient's characteristics, diagnosis, surgery, comorbidities, parameters from POSSUM score, 30, 60 and 90-day mortality and 30-day morbidity. POSSUM system's goodness-of-fit for predicting mortality and morbidity was assessed by Hosmer-Lemeshow test (H-L T) and Standardized Mortality/Morbidity Ratio (SMR) and discriminative ability by the area under the ROC curves (ROC-AUC). Patients' average age was 70.8 years, 81% males.None.The overall 30-day mortality rate was 2.97% (n=6) and 30-day morbidity was 29.2% (n=59). POSSUM, P-POSSUM, V-POSSUM, V-POSSUM physiology and V-POSSUM Cambridge equation predicted an overall of 29.1, 4.43, 15.3, 21.9 and 13.5 deaths, respectively. POSSUM morbidity equation predicted 105.0 complications. H-LT p-values were 0.001, 0.164, 0.208, 0.011, 0.331 and0.001, respectively. SMRs and 95% confidence interval (CI) were 0.21[0.04-0.37], 1.35[0.27-2.44], 0.39[0.08-0.71], 0.27[0.06-0.49], 0.44[0.09-0.80] and 0.56[0.42-0.71], respectively. ROC-AUC and 95% CI were 0.72[0.49-0.95], 0.72[0.49-0.95], 0.73[0.51-0.94], 0.69[0.50-0.89], 0.72[0.52-0.92] and 0.71[0.63-0.79], respectively.P-POSSUM had the best performance predicting 30-day mortality. All the other overestimated 30-day mortality. Prediction of morbidity was inadequate. POSSUM scoring models may not be robust tools for risk prediction in elderly patients undergoing major elective vascular surgery and need further calibration and discrimination.