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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.

This paper presents an experimental investigation on concrete-filled steel tubular beam-columns with octagonal cross-sections (OCFST) under cyclic lateral loading with or without axial load. A total of nine specimens with different parameters, including the axial load level (n) ranging from 0 to 0.5 and concrete compressive cylinder strength (fc′) varying from 30 MPa to 90 MPa, were tested. The failure modes, ultimate strengths, displacement ductility, effective flexural stiffness and cumulative dissipated energy are presented. The results indicate that OCFST beam-columns exhibit a ductile plastic mode and excellent energy dissipation. With the increase of axial load level, the ductility and the energy dissipation capacity decreases, while the ultimate bending capacity firstly increases then drops. Concrete grades seem to have limited influence on the ultimate strength and energy dissipation capacity. The comparison results of the ultimate bending moments and effective flexural stiffness between predictions using EN 1994-1-1 and AISC 360-16 and test results reveal their applicability to the design of OCFST beam-columns.

The First International Symposium on Risk Analysis and Safety of Complex Structures and Components (IRAS 2019) was organised in-teamed with the ESIS/TC12 Technical Committee on Risk Analysis and Safety of Large Structures and Components, which took place between 1-2 July 2019 at the Faculty of Engineering of the University of Porto (FEUP), in the City of Porto, located at seaside in the northwest region of Portugal. The guest editors of the IRAS 2019 deeply acknowledges all members of the International Scientific Committee, Thematic Sessions Organizers, Keynote Speakers and authors that contributed to the success of this event, that gathered more than 126 participants presenting more than 168 papers and posters. Sponsors are also fully acknowledged for their important contributions. The ESIS/TC12 2019 winners of the Robert Moskovic Award, Award of Merit TC12, and ESIS/TC12 Young Scientist Award were announced during the conference. Additionally, the guest editors (conference chairs) sincerely thank the tireless efforts of the Organizing Committee members as well as students and other FEUP and Construction Institute staff involved in the organization. Finally, the guest editors are pleased to inform that the second edition of the IRAS event will be organised by Prof. Aleksandar Sedmak (University of Belgrade, Serbia) which will take place in Belgrade in Serbia in the year 2021.

This paper presents a new approach to estimate the fatigue life of metallic details retrofitted with bonded CFRP patch. Existing phenomenological and analytical methods to predict the fatigue life of metallic structural details retrofitted with bonded CFRP patch do not consider the cyclic degradation of the composite patch. As for all materials the composite patch (CFRP and adhesive) will experience degradation during fatigue cyclic loading. In this regard, a new approach that takes into account the fatigue cyclic degradation of the composite patch is proposed in this paper by introducing in the fatigue damage accumulation model of the metallic element, a cycle-dependent stiffness degradation parameter of the composite patch. The stiffness degradation parameter is obtained using a fatigue stiffness degradation model calibrated from experimental fatigue data of CFRP adhesively bonded double strap joints. Experimental data available in the literature of central hole aluminium plates bonded with CFRP are utilized for validation of the approach.

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.

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 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 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 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.

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.

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.

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.

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.

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.

This paper deals with the seismic performance and loss assessment of old RC wall-frame buildings in Lisbon, Portugal. These structures are characterised by non-ductile columns and RC walls made with smooth rebars and light transversal reinforcement. They were erected before the introduction of modern seismic codes in the 1980s and represent an important proportion of the city’s building stock. The research reported in this paper focuses on the seismic vulnerability assessment of this building typology. An analytical procedure is proposed to estimate the fragility functions of non-ductile reinforced concrete walls with smooth reinforcing bars and light transversal reinforcement, taking into account strength penetration effects. To illustrate the procedure, a case study building is considered. The approach used for the seismic performance assessment adopts component-based fragility and loss functions for the damage assessment of the structural and non-structural drift-sensitive elements, adapted to the Portuguese reality, and a storey-based approach for acceleration-sensitive non-structural elements. The results provide the economic loss of the building as a function of the ground motion intensity level. Finally, results are compared in terms of expected annual losses with other non-ductile RC building typologies.

This paper deals with the experimental behaviour of blind-bolted angle connections between open beams and tubular columns. A number of connection configurations with different geometric arrangements and bolt properties are examined. The experimental set-up, connection details and material properties are first described. A detailed account of the results and observations from seventeen monotonic and cyclic connection tests is then presented, and the main behavioural aspects are discussed. The specimens include connections with top and seat angles as well as others in which web angles are also incorporated. The experimental results offer direct information on the influence of important geometric and material properties, such as angle dimensions, column face thickness, gauge length and bolt class, on the key response characteristics including stiffness, strength, energy dissipation and failure mechanism. Based on the findings, simplified approaches through which the initial stiffness and yield parameters can be estimated, are assessed. The test results also provide essential data for the future validation of detailed numerical and analytical studies which can be employed for further assessment of the response, with a view to the development of design-oriented procedures.

This paper examines the seismic performance of composite steel–concrete moment-resisting frames. A number of studies are carried out in order to assess the influence of key parameters, related to the structural configuration as well as design and loading considerations, on the inelastic seismic behaviour. Several sensitivity and parametric investigations are undertaken using an advanced analysis program that accounts for material and geometric nonlinearities. Particular emphasis is given to composite frames designed according to the provisions of the European seismic code, Eurocode 8. The validity of employing simplified nonlinear-static loading approaches is evaluated by comparison against the results of incremental dynamic time-history analysis. Natural earthquake acceleration records, which are specifically selected and adjusted for compatibility with the adopted design spectrum, are utilised for this purpose. In terms of frame configuration, it is shown that the span of the composite beam, the extent of gravity loading and the number of stories can all have significant implications on the actual inelastic response characteristics of the structure. Moreover, several design assumptions and decisions, such as those related to the behaviour factors, drift considerations, moment redistribution and panel zone contribution, can also have a direct impact on the resulting performance. The studies presented in this paper highlight important behavioural observations and trends, some of which point towards the need for further consideration and refinement of current design procedures.

This paper deals with the behaviour of composite beams with particular focus on the effective slab width, which is required for simplified structural analysis and design. Current design codes propose values for the effective width which are mostly a function of the beam span ignoring in this way the influence of other important parameters. Several 3D numerical simulations are conducted in this paper in order to illustrate these parameters and accordingly a new methodology is suggested for evaluating the effective width. The proposed approach is easier to apply in comparison with other existing methods based on stress integration, and provides effective width values which result in a more reliable representation of the actual beam state when simplified analysis is carried out. The application of the new method indicates that the effective width is mostly related to the actual slab width and, in many cases, the values obtained can significantly differ from those proposed in design codes. Validation of the new approach is carried out through comparison of simplified 2D models with the results obtained from a recent experimental investigation as well as from more complex 3D numerical simulations.

This paper deals with the modelling of the panel zone region within beam-to-column connections in steel and composite moment-resisting frames. Existing analytical models for representing the panel zone response are first reviewed and their scope and limitations are discussed. A new approach, which is particularly suited for modelling steel and composite joints within frame analysis procedures, is then proposed and described. The method rationally accounts for the effect of different boundary conditions, as well as shear and flexural deformation modes, in evaluating the elastic and inelastic response. Validation of the proposed approach is carried out through comparisons against available experimental results in addition to more detailed continuum finite element analyses. The results demonstrate that the approach developed provides a more realistic representation of the behaviour in comparison with available models, especially in the case of composite connections. It is shown that, for composite joints, commonly used simple moment–distortion relationships may not be adequate. This is primarily due to the dependency of the behaviour on the internal force distribution at the joint. The study describes the implementation of the suggested approach within frame analysis procedures, and substantiates the important role played by the panel zone in the response of moment frames under lateral loading conditions.