This paper proposes a macro‐model for simulating the hysteretic behavior of composite‐steel beams as part of fully restrained beam‐to‐column connections in composite‐steel moment‐resisting frames ...(MRFs). Comparisons with experimental data suggest that the proposed model captures the asymmetric hysteretic response of composite‐steel beams including the cyclic deterioration in strength and stiffness. Moreover, the proposed model captures the primary slab‐column force transfer mechanisms and predicts the slip demands in beam‐slab connections under inelastic cyclic loading. The modeling approach is employed in a system‐level study to benchmark the seismic collapse risk of composite‐steel MRF buildings across Europe. Moreover, the beam‐slab slip demands are quantified through the development of beam‐slab slip hazard curves. The simulation studies suggest that the examined composite‐steel MRFs exhibit a system overstrength of about 4. This is attributed to the drift requirements in the current European seismic provisions.1 The annualized probability of collapse of the prototype buildings is well below 1% over a 50‐year building life expectancy regardless of the design site and the degree of composite action. Beam‐slab connections with a partial degree of composite action experience minimal damage for frequently occurring seismic events (i.e., 50% probability of exceedance over 50 years); and light cracking in the slab for a design basis earthquake. The above are important from a seismic repairability standpoint. Accordingly, it is recommended that the 25% reduction in the shear resistance of stud connectors is not imperative for seismic designs that feature steel beams with depths less than 500 mm.
This paper explores the concept of dissipative exposed column base connections by means of anchor rod yielding. This concept aims at enhancing the seismic performance of low‐rise steel ...moment‐resisting frames (MRFs). A mechanics‐based model is proposed that explicitly simulates a broad range of damage mechanisms observed in exposed column bases. The model is implemented in a frame finite element analysis program, and its hysteretic performance is validated with experimental data available in literature. Incorporating this modeling feature in standard nonlinear response history analyses offers new insights in steel MRF responses. It is shown that when low‐rise steel MRFs adopt a dissipative anchor‐yield column base concept, they are less likely to experience residual story drift ratios during low probability of occurrence seismic events. It is also found that low‐rise steel MRFs designed with nondissipative exposed column base connections are more prone to demolition than dissipative ones, due to their higher column residual axial shortening, particularly when ground motion duration is an important feature of the seismic hazard. Limitations of the present work are also discussed.
•Steel frames under pulse-like near-fault earthquakes are investigated.•Basic characteristics of forward directivity and fling step effects are discussed.•Code-compliant steel braced frames are ...carefully designed.•Steel braced frames with varying bracing parameters are studied.•Residual inter-storey drift prediction model is given for performance-based design.
This paper presents the behaviour of steel moment resisting and braced frames under pulse-like near-fault earthquakes. The key properties for characterizing near-fault ground motions with forward directivity and fling step effects are discussed, and the influence of varying brace properties on the key engineering demand parameters such as maximum inter-storey drift (MID), residual inter-storey drift (RID) and peak absolute floor acceleration (PA) is revealed. Among other findings, it is shown that the structural responses are related to spectral accelerations, PGV/PGA ratios, and the pulse period of near-fault ground motions. The moment resisting and self-centring braced frames (MRFs and SC-BRBFs) generally have comparable MID levels, while the buckling-restrained braced frames (BRBFs) tend to exhibit lower MIDs. Increasing the post-yield stiffness of the braces decreases the MID response. The SC-BRBFs generally have mean residual drifts less than 0.2% under all the considered ground motions. However, much larger RIDs are induced for the MRFs/BRBFs under the near-fault ground motions, suggesting that these structures may not be economically repairable after the earthquakes. From a non-structural performance point of view, the SC-BRBFs show much higher PA levels compared with the other structures. A good balance among the MID, RID, and PA responses can be achieved when “partial” SC-BRBs are used. To facilitate performance-based design, RID prediction models are finally proposed which enable an effective evaluation of the relationship between MID and RID.
This research intends to propose an upgraded strategy for steel moment-resisting frames (SMRFs) by implementing Self-Centering Energy-absorbing Dual Rocking Core (SEDRC) systems to achieve enhanced ...seismic performance, improved seismic resilience, and avoid inter-story drift concentration. A performance-based method is developed to design the SEDRC system for upgrading the existing SMRF. The maximum inter-story drift and drift concentration factor are adopted as the design performance objectives. Two prototype SMRFs with three and nine stories are introduced to validate the proposed performance-based design procedure. Nonlinear static analyses were first performed for the original SMRFs and the updated ones (denoted as SEDRC-MRFs) to investigate the efficiency of the proposed retrofit strategy. The pushover curves of the analytical structures confirm that the SEDRC systems can increase the stiffness and strength of SMRFs, and SEDRC-MRFs upgraded through the proposed design procedure show no strength deterioration before the fracture of the brace in the SEDRC system. A set of 18 ground motions were chosen to study the seismic performance of the designed SEDRC-MRFs. The analysis results indicate that SEDRC-MRFs can obtain the desired performance objectives. The SEDRC system could reduce the maximum and residual inter-story drifts of SMRFs and promote uniform inter-story drift distribution. Moreover, the designed SEDRC-MRFs can be used immediately without the need for repairing structural members after the design basis earthquakes and can be repaired economically after the maximum considered earthquakes.
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•An upgraded strategy for SMRFs by implementing SEDRC systems was proposed.•A performance-based design method is developed to design the SEDRC system for upgrading the existing SMRF.•The SEDRC-MRFs designed with the proposed design method can achieve the desired performance objective.•The SEDRC-MRFs can be used immediately without repairing structural members after the design basis earthquakes.
The performance of beam-to-column connections is a key factor in the behaviour of moment-resisting frames (MRFs) under fire conditions. In this work, the behaviour and failure mechanisms of a ...half-scale 3D frame, composed of single-bay, single-storey MRFs and Braced Frames, in two perpendicular planes, equipped with 6 mm thick flush end-plate connections, under fire conditions was studied. A ‘scaled’ ISO 834 standard fire curve was followed during fire loading of the frame. The maximum reached temperature was 1100 °C. The temperatures of the elements of frames were measured at 2-minute time intervals. The rotations of the connections and the deflections of the MRFs’ beams at these time points were worked out using an image processing technique. Furthermore, the effect of the ductility of connections was investigated by comparing the results of this study with those of a previous one in which less ductile connections were used. The results showed that the connections used in this study could sustain large rotations of up to 0.7 radian and endure 65 min under fire. Moreover, it was found that using flexible connections (connections with thinner end-plates) enhances the ‘robustness’ of moment frames in fire.
•Scaled experimental models can be used to predict behaviour of structures in fire.•Image processing can be used for measuring deformations and rotations in fire tests.•Thickness-induced flexibility of thinner end-plates increases structural robustness.•Thinner end-plates reduce risk of over-stretching of bolts & structural collapse.•Simulated ‘real fire’ in this work triggered all forms of failure but overall collapse.
Nowadays, there is a lack of adequate code provisions for the seismic performance and risk assessment of steel structures to be used within European countries. At the same time, in several occasions, ...existing steel moment resisting frames (MRFs) have demonstrated to be very fragile with respect to seismic actions due to their inadequate ductility capacity. This combination highlights the urgent need for an update of the current Eurocode 8 – Part 3 (EC8‐3), thus promoting a reliable assessment of existing steel structures. To this aim, the present study provides a comprehensive and quantitative comparison of the EC8‐3 with the three versions of the American ASCE 41 (i.e., ASCE 41‐06, ‐13 and ‐17), which are here assumed as a reference, as they reflect the evolution of ‘similar’ assessment procedures during the last two decades. The comparison of the capacity values provided by the codes for different engineering demand parameters (EDPs) highlights significant differences pointing out drawbacks of the EC8‐3. In addition, the comparison is made by assessing the seismic performance of two existing steel MRFs, by performing Incremental Dynamic Analyses and deriving fragility curves in a probabilistic approach which considers local EDPs which are compliant with the codes, and that are conventionally used in deterministic studies, e.g., chord rotations in beams and columns, shear strain in panel zones. The comparison of the codes, and the probabilistic assessment of the case studies by using code-based (i.e., local) EDPs, provide significant insights and directions for revision of the EC8‐3.
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•Critical comparison of assessment procedures and capacity limits for steel MRFs in EC8–3 and different versions of ASCE 41.•Comprehensive comparison of code-established capacity limits, through the probabilistic assessment of two case-study MRF structures.•Focus on the urgent deficiencies to be addressed in the updated version of EC8–3 for the assessment of existing steel MRFs.
Nowadays' earthquake engineering is coping with the challenging task of providing low-cost seismic resilient structures. Among others, a viable solution for seismic resilient Steel Moment Resisting ...Frames (MRFs) is based on the use of Self-Centering Damage-Free (SCDF) joints at Column Bases (CBs) and Beam-to-Column Joints (BCJs), ensuring both the energy dissipation capacity and self-centering behavior of the structure. Past studies demonstrated the beneficial effects gained in damage and residual drifts reduction by including SCDF joints at all BCJs and CBs. However, this solution leads to the highest structural complexity, limiting the practical application. Significant improvements can be obtained including a limited number of SCDF BCJs, but there is a lack of generalized recommendations on the number required and their effective placement. In this work, a Genetic Algorithm (GA) is proposed to define the optimal placement of SCDF BCJs in steel MRFs. The GA is implemented in Matlab, and non-linear time-history analyses are performed in OpenSees to calculate the Fitness-Function. The results of the GA are validated against a Brute-Force Approach. An 8-story 3-bays steel MRF and a type of SCDF joint are selected for case study purposes, non-linear Finite Element Models are developed in OpenSees, and the GA is applied. The results show that the proposed GA is an efficient methodology to solve the considered optimization problem.
•A Genetic Algorithm is developed to define the optimal placement of a limited number of Self-Centeing Damage-Free Beam-to-Column Joints.•A sensitivity analysis is performed to evaluate the effect of the input parameters on the final solution.•Validation of the Genetic Algorithm is developed comparing the proposed methodology with a Brute-Force approach.•The Genetic Algorithm is applied to a case study steel MRF with a different number of Self-Centering Damage-Free Joints.
This paper proposes a performance-based seismic design (PBSD) method for self-centering moment-resisting frames with shape memory alloy (SMA)-bolted endplate connections. PBSD can be used to achieve ...different performance objectives, resulting in several benefits, such as cost-effectiveness and customization of the design. This study develops a PBSD framework by establishing a relationship between the fundamental period, ductility demand, and seismic force reduction factor and using an energy-balanced concept. The design method is facilitated using an artificial neural network (ANN)-based predictive tool and an efficient experimentally-validated phenomenological model for SMA-bolted endplate connections. Maximum drift and ductility ratios are adopted as performance objectives. Two 3- and 6-story prototype frames are designed and evaluated to illustrate the proposed PBSD method. The seismic response and collapse safety of the prototype frames at different shaking intensities are evaluated. The results show that the prototype frames designed using the proposed PBSD framework meet the prescribed design objectives and the collapse safety requirements in FEMA P695. The illustrative examples confirm that the designed moment frames possess the intended self-centering capability with negligible residual deformations as low as 0.05% at the maximum considered earthquake (MCE) hazard level. The results also confirm that the designed frames exhibit uniform drift distribution along their height.
•Developing a performance-based seismic design framework for SMA-based self-centering moment resisting frames.•Investigating seismic performance of SMA-based moment resisting frames through nonlinear response history analyses.•Illustrating the application of a predictive tool for SMA-bolted endplate connections in seismic design and analysis.•Showing the effectiveness of the developed design method to achieve the prescribed design objectives.
In recent years there have been significant advancements in the definitions of innovative seismic-resilient structural systems, chasing the urgent need to reduce repair costs and downtime in the ...aftermath of severe earthquake events. In this regard, self-centring Column Bases (CBs) represent a promising solution to improve the seismic performance of steel Moment Resisting Frames (MRFs) for both damage and residual drifts reductions. However, although several technologies have been conceived, studied, and experimentally tested in this direction, only a few research studies investigated the significant properties of the connections influencing the behaviour of these systems. In this context, the present study focuses on the steel damage-free Self-Centring Column Base (SC-CB) previously investigated by the authors and performs a parametric Finite Element (FE) analysis to evaluate the influence of some design parameters over the global and local response of the joints. An advanced FE model is developed in ABAQUS and validated against experimental results. Successively, FE models of three SC-CBs belonging to different case-study MRFs are developed considering sixteen Configurations for each case characterised by different design parameters and structural properties. The parametric analysis provides a more comprehensive view of the assumptions and limitations of the design methodology and suggests additional recommendations to improve the design requirements of the SC-CB connections.
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•A type of self-centring steel column base connection is studied.•The analytical design procedure is investigated highlighting assumptions and limitations.•Finite element models are built in ABAQUS and validated against experimental results.•The influence of three design parameters is investigated over the global and local response of the connection.•Design recommendations are given in view of performance objectives toward enhanced structural resilience.
A modal pushdown analysis procedure is developed for progressive collapse assessment of multi-storey steel frame buildings under sudden removal of a column due to catastrophic events. Since the first ...vertical bending mode generally dominates the behaviour of the structure after column removal, the global response is assumed entirely in this mode shape while no contribution is considered from other modes. Thus, the target displacement of the column-removed point is estimated from the nonlinear response–history analysis of a modal inelastic single degree-of-freedom (SDOF) system under a rectangular pulse force that simulates the abrupt column removal. The properties of this SDOF system are calculated from the nonlinear static (pushdown) analysis of the damaged structure using the modal properties of the first bending mode shape. A two-step pushdown analysis procedure is developed to estimate the inelastic response of the structure and the dynamic amplification factor (DIF) to use when conducting the nonlinear static analysis. The accuracy of the proposed procedure is estimated and compared to other formulations in the literature. For this reason, a series of three-dimensional steel frame buildings with varying number of spans and storeys have been considered in the analysis. Different loading levels and column removal scenarios are investigated. The study results show that the modal pushdown procedure gives accurate solution, accounting for both real plastic deformation demand and catenary stiffening action in steel beams.
•A modal pushdown analysis procedure is proposed for progressive collapse analysis of buildings.•The dynamic analysis of an equivalent inelastic single degree-of-freedom model is performed.•A two-step pushdown analysis is developed to predict the dynamic increase factor.•Both actual plastic deformation demand and hardening of the catenary action are accounted for.•The procedure is accurate enough in the whole range of displacement (elastic, plastic, hardening).
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