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This paper aims to evaluate the seismic response of multitiered buckling-restrained braced frames (MT-BRBFs), assess the design provisions specified by the 2022 AISC Seismic Provisions for multitiered BRBFs, and propose improvements to these provisions. A set of 17 frames is first selected by varying bracing configuration, frame height, number of tiers, and tier height ratio. The frames are then designed in accordance with the 2010 and 2022 AISC Seismic Provisions. A numerical parametric study is performed under scaled ground motion accelerations. The results of the parametric study show that when the frames are designed to the 2010 provisions, the frame inelastic deformation tends to concentrate in the tier(s) undergoing tensile yielding due to their lower postyield stiffness, compared to BRBs yielding in compression, which creates unequal story shear, contributed by braces, in adjacent tiers with BRBs in tension and compression and engages column flexure to compensate for unbalanced brace story shears between tiers. Columns experience yielding and even buckling in several cases due to combined flexural and axial load demands. MT-BRBFs designed to the 2022 AISC Seismic Provisions exhibit a more uniform deformation response between tiers and relatively lower flexural demands in their columns. However, these provisions may overestimate column in-plane flexural demands (on the order of 3), resulting in potentially uneconomical design solutions. On the basis of the numerical simulations, modifications are proposed to compression BRBs' adjusted strength to better estimate column in-plane flexure and tier deformation while achieving an economical column design. The proposed improvements are validated using dynamic analyses. [ABSTRACT FROM AUTHOR]

This paper introduces a retrofit design procedure for reinforced concrete (RC) frame buildings using alternative steel bracing systems based on the simple lateral mechanism analysis (SLaMA). Employing a displacement-based design approach, the procedure captures the actual behavior of existing buildings and the contribution of the bracing system. The retrofit design process and seismic assessment procedures are outlined, followed by the proposed SLaMA-based retrofit design procedure. The design procedure is demonstrated on pre-1970 four-story and eight-story RC case study frames, targeting maximum displacements informed by the expected failure mechanisms identified using a detailed seismic assessment (DSA). The New Zealand Society of Earthquake Engineering 2016/017 Seismic Assessment Guidelines' SLaMA method is utilized for DSA, revealing that the frames are potentially earthquake-prone with specific failure mechanisms and seismic capacities. After retrofitting with a concentric braced frame (CBF), buckling-restrained brace (BRB), and CBF with friction dampers, the failure mechanisms are modified, resulting in seismic capacities exceeding 100% New Building Standard (NBS). Evaluation of local and global behavior post-retrofit enables the determination of the advantages and disadvantages of alternative brace systems. Nonlinear time-history (NLTH) analyses using a lumped plasticity model verify the results, affirming the viability and practicality of the SLaMA-based retrofit design procedure for selecting and designing appropriate interventions in concrete frame buildings. [ABSTRACT FROM AUTHOR]

The 2020 Zagreb earthquake caused extensive damage to historically significant buildings, including the Cathedral of the Assumption of Mary, a key monument of Croatian cultural heritage. The earthquake rendered the cathedral unsafe due to significant damage to its towers and numerous cracks in its vaults and walls. Urgent measures were necessary to ensure safety and facilitate planned reconstruction and strengthening efforts. A specialised scaffolding design was developed to support inaccessible and unstable areas, involving over 1000 tonnes of steel. This paper details the structural concepts and specific scaffolding design implemented for the urgent restoration and seismic retrofitting of Zagreb Cathedral, ensuring it meets high earthquake resistance requirements. [ABSTRACT FROM AUTHOR]

This paper presents an extensive numerical study on the seismic performance of steel eccentrically braced frames (EBFs) designed according to the ASCE 7-16 standard. A series of EBF building structures ranging from 2 to 12 stories located in downtown Los Angeles are designed with different yielding links, including conventional and replaceable links. The performance of the structures is investigated through nonlinear time-history analyses (NLTHAs) under a suite of 40 ground motions, selected and scaled to match the target uniform hazard spectrum. The peak deformations are first examined to assess the performance of the buildings as well as the design procedure. Residual deformations are also evaluated and critically compared with acceptable limits, to provide insight into the downtime and recovery time of EBFs after major earthquakes. Previous studies have demonstrated that the response of stable yielding systems to major earthquakes is often accompanied by significant residual deformations, and that residual drifts exceeding 0.5% can cause hindrance to the buildings occupants. In EBFs, in addition to residual drifts, residual link rotations are also relevant and expected to be more severe due to the localization of inelastic deformations in the yielding link. For replaceable modular yielding links, significant residual link rotations after major earthquakes will hinder repairs and the link replacement process, which is one of the important design objectives. The performance of EBFs is also compared with what was observed in previous studies for buckling restrained braced frames and special moment resisting frames. In the end, the results from the extensive NLTHAs are used to establish a relationship between peak drifts and peak link rotations in EBFs. [ABSTRACT FROM AUTHOR]

Steel multitiered concentrically braced frames (MT-CBFs) not specifically detailed for seismic resistance with a response modification factor of R=3 are permitted in moderate seismic regions. Past research studies, however, have raised concerns regarding the seismic performance of MT-CBFs and CBFs designed using R=3 provisions, namely the stability of columns in MT-CBFs and connection limit states in R=3 CBFs. This paper examines the seismic response of R=3 MT-CBFs and proposes a design method to improve their seismic performance. A set of 16 prototype R=3 MT-CBFs, ranging from 8 to 20 m tall with two to five tiers and located in a moderate seismic area, was selected and designed in accordance with 2016 US design guidelines. Nonlinear response-history analyses were then performed to examine the seismic response of these frames using fiber-based numerical models. R=3 MT-CBFs designed to 2016 design guidelines are shown to experience premature fracture in brace-to-beam/column connections in a single tier, which imposes high in-plane bending demands on columns and in some cases, leads to column instability or a tier-sway mechanism. New seismic design recommendations, including requirements for intermediate struts, columns, and tier drift, are proposed. The design method aims to prevent column instability or a tier-sway mechanism and protect brace connections from excessive deformation. [ABSTRACT FROM AUTHOR]

This paper proposes alternative seismic design approaches for steel moment‐resisting frames (MRFs) that improve their performance and reduce the number of undesirable one‐story and two‐story yield mechanisms that form under seismic loading, compared to MRFs designed using the conventional strong‐column‐weak‐beam (SCWB) design approach. The alternative design approaches are capacity‐design approaches that directly compare story shear force demands from nonlinear time‐history analyses (NTHA) with corresponding shear force capacities in design iterations to avoid one‐story and two‐story mechanisms. To implement the capacity‐design approach, the NTHA use special capacity‐controlled numerical models for design, in which the one‐story and two‐story shear force design demands are limited by the intended yield mechanisms of the MRF. Unlike the SCWB approach, the alternative design approaches directly address the cause of undesirable one‐story and two‐story mechanisms. The paper presents NTHA results for a set of MRFs, where some were designed using a conventional approach (including SCWB) and some were designed using the alternative approaches. The increases in nominal steel weight of the MRFs designed using the alternative approaches are relatively small compared to the weight of the MRF designed using the conventional SCWB approach. Compared to the MRF designed using the SCWB approach, the MRFs designed using the alternative design approaches have improved seismic performance with reduced tendency to form one‐story and two‐story mechanisms, more uniform story drifts, reduced maximum story drift, and improved collapse performance. [ABSTRACT FROM AUTHOR]

Copyright of Al-Andalus journal for Humanities & Social Sciences is the property of Alandalus University for Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Composite plate shear walls–concrete-filled (C-PSW/CF) are a new and innovative lateral force–resisting system intended for high-rise buildings. High-rise building applications of this system are particularly efficient in the coupled wall configuration, in which the walls are C-PSW/CF and the coupling beams are concrete filled steel box sections. This paper presents a capacity design principle for the seismic design of coupled composite plate shear wall–concrete filled (CC-PSW/CF) systems. The capacity design principle implements a strong wall–weak coupling beam approach, in which flexural yielding occurs in the coupling beams before flexural yielding at the base of walls. The coupling beams are sized to resist the calculated seismic lateral force level. The composite walls are sized to resist an amplified seismic lateral force corresponding to the overall plastic mechanism for the structure, while accounting for the capacity-limited forces from the coupling beams and the coupling action between the walls. The paper summarizes the recommendations and requirements for appropriate sizing of the composite coupling beams and walls. These recommendations were used along with the capacity design principle to design four example (8–22-story) structures and evaluate their seismic behavior. The structures were modeled using benchmarked finite-element models and fiber-based models that accounted for the various limit states, including steel yielding, local buckling, fracture, concrete crushing, confinement, and tension cracking. The numerical models were analyzed for monotonic pushover loading and scaled seismic ground motions. The structural responses from the nonlinear pushover analysis and the nonlinear time history analyses were in accordance with the capacity limited design philosophy, thus confirming its efficacy. [ABSTRACT FROM AUTHOR]

Building code implementation in developing countries is a serious concern due to poorly regulated construction practices. Deficiencies in terms of material strength and structural detailing are found the most in reinforced concrete frames in Pakistan. This paper presents the results of quasi-static cyclic tests performed on reduced-scale RC frames with and without beam-column joint detailing and considering normal and low-strength concrete respectively. Fragility functions and loss curves for the standard/sub-standard frames were derived using an experimentally validated numerical model. Furthermore, the existing RC frames building stock was rehabilitated with various configurations of steel bracing i.e. one way diagonal, one way eccentric, two way diagonal, two way eccentric and concentric. The developed fragility and loss curves for the rehabilitated frames confirmed that the two way diagonal steel bracing system outclasses the other types. Moreover, inter-story drift limits for as-built and rehabilitated frames were proposed under design base earthquakes and maximum considered earthquakes. Maximum considered earthquakes pushed the ductile as-built frame further than the moderate damage state, thus rehabilitation after such an event will be required for the structure. The presented results will help in seismic risk assessment, decision-making and public awareness. [ABSTRACT FROM AUTHOR]

The seismic design of steel systems recently experienced profound changes and progress; in Europe, the research on this topic is very prolific in terms of importance and number of results achieved, even pushed by the recent process of the updating of Eurocode 8. The paper analyzes and discusses the scientific literature on the subject produced approximately over the last twenty years, focusing on both recent research and findings on traditional steel systems and innovative structural types and solutions. The review of the state of the art suggested that most of the authors are now concerned about the numerous criticisms widely encountered in the design of traditional systems according to current Eurocode 8, as well as the difficulty of the application of the relevant detailing rules. The scientific community is also aware of the need to include specific codified design procedures for innovative and promising structural types. Further investigations are needed to deepen the design of moderate-ductile systems and to extend the seismic European prequalification of beam-to-column joints to further typologies. [ABSTRACT FROM AUTHOR]

Many existing steel multi‐storey frame buildings worldwide were designed prior to the introduction of modern seismic design provisions or based on outdated hazard maps considering low values of seismic intensity. This often resulted in buildings showing low performances with respect to earthquake loads. Assessment codes, such as the Eurocode 8 Part 3 and the ASCE 41, have been conceived to provide tools to assess the seismic performance of existing structures, to evaluate their adequacy with respect to the current safety standards and the need for seismic retrofit. However, recent research studies have revealed the necessity for a revision of these codes. In particular, for steel moment resisting frames, the current European regulation shares many similarities with older versions of the American codes, but has failed to incorporate changes based on the state‐of‐the‐art knowledge. In addition, the undergoing update of other parts of the Eurocode motivates a full revision of the current standards. This paper compares the assessment procedures of the European and American codes. Two low‐code steel Moment Resisting Frames were considered for case study purposes and the assessment was performed based on three local Engineering Demand Parameters (EDPs), i.e., column's rotation, beam's rotation and panel zone's shear distortion, and the inter‐story drift as global EDP. Incremental Dynamic Analyses were performed for the development of component and system fragility curves. The present work aims to identify some challenges and to provide some preliminary insights for the revision of the Eurocode 8 Part 3. [ABSTRACT FROM AUTHOR]

The seismic design and assessment of steel moment resisting frames (SMRFs) rely heavily on drifts. It is unsurprising, therefore, that several simplified methods have been proposed to predict lateral deformations in SMRFs, ranging from the purely mechanics‐based to the wholly data‐driven, which aim to alleviate the structural engineer's burden of conducting detailed nonlinear analyses either as part of preliminary design iterations or during regional seismic assessments. While many of these methods have been incorporated in design codes or are commonly used in research, they all suffer from a lack of consideration of the causal link between the seismic hazard level and the ground‐motion suite used for their formulation. In this paper, we propose hybrid data‐driven models that preserve this critical relationship of hazard‐consistency. To this end, we assemble a large database of non‐linear response history analyses (NRHA) on 24 SMRFs of different structural characteristics. These structural models are subjected to 816 ground‐motion records whose occurrence rates and spectral shapes are selected to ensure the hazard consistency of our outputs. Two sites with different seismic hazards are examined to enable comparisons under different seismic demands. An initial examination of the resulting drift hazard curves allows us to re‐visit the influence of salient structural modelling assumptions such as plastic resistance, geometric configurations and joint deterioration modelling. This is followed by a machine learning (ML)‐guided feature selection process that considers structural and seismic parameters as well as key static response features, hence the hybrid nature of our models. New models for inter‐storey drift and roof displacements are then developed. A comparison with currently available formulations highlights the significant levels of overestimation associated with previously proposed non‐hazard consistent models. [ABSTRACT FROM AUTHOR]

The paper explains the impact of metallic dampers on the seismic performance of a nine-story steel moment frame. The design technique for an X-shaped Added Damping and Added Stiffness (ADAS) type steel damper is examined. With a minimal activation load, the damper is designed to give well before the building yields. A series of Finite Element (FE) simulations were used to verify the performance of the proposed device under constant and increasing cycle loads. The suggested steel dampers exhibited comparable hysteretic curves and steady hysteretic behavior, according to the simulation findings. ABAQUS software was used for FE analysis. Then, utilizing El centro (1940) ground motion recordings in SAP2000 software, nonlinear time history studies were done to evaluate the seismic behavior of steel frames using this sort of passive control system. Through the dampers, the seismic reactions of the frames were investigated and compared in terms of maximum displacement, maximum story drift, roof displacement time history, input energy and dissipated energy. The results showed that the constructions with dampers outperformed the original structure in terms of seismic performance. [ABSTRACT FROM AUTHOR]

This paper explores the use of sliding friction dampers (SFDs) as dissipative floor connectors to mitigate higher mode effects and earthquake‐induced absolute acceleration demands on steel concentrically braced frame (CBF) buildings. The dampers connect each floor of the steel CBF system to the diaphragms of the gravity framing system (GFS) and they allow for a relative in‐plane movement between the two systems. For this purpose, a design methodology is first proposed to define the activation forces in the SFDs so as to ensure damage‐free seismic performance in the steel CBF and the diaphragms of the GFS. The efficiency of the design methodology is demonstrated through nonlinear response history analyses on a low‐ and high‐ductility six‐story steel CBF building. The simulation results suggest that (a) the determined activation forces of the SFDs are effective in mitigating higher mode effects and in preventing story drift concentrations regardless if capacity design is employed for the CBF system; (b) the absolute acceleration demands are reduced by approximately 50% relative to those in the rigid diaphragm counterpart. Similar reductions are achieved in the lateral drift demands of the GFS at seismic intensities with return periods of 475 and 2475 years. The reduction in the variability of seismic response, both in terms of absolute floor acceleration demands and story drift ratios (SDRs) in the CBF system, is noteworthy. Limitations as well as suggestions for future work are discussed. [ABSTRACT FROM AUTHOR]

In this paper, the seismic response of a steel truss arch bridge subjected to near-fault ground motions is studied. Then, the idea of applying buckling restrained braces (BRBs) to a steel truss arch bridge in near-fault areas is proposed and validated. Firstly, the basic characteristics of near-fault ground motions are identified and distinguished. Furthermore, the seismic response of a long span steel truss arch bridge in the near fault area is analyzed by elastic-plastic time analysis. Finally, the braces prone to buckling failure are replaced by BRBs to reduce the seismic response of the arch rib through their energy dissipation properties. Four BRB schemes were proposed with different yield strengths, but the same initial stiffness. The basic period of the structure remains the same. The results show that near-fault ground motion will not only obviously increase the displacement and internal force response of the bridge, but also cause more braces to buckle. By replacing a portion of the normal bars with BRBs, the internal forces and displacements of the arch ribs can be reduced to some extent, which is more prominent under the action of pulsed ground motion. There is a clear correlation between the damping effect and the parameters of BRB, so an optimized solution should be obtained by comparison and calculation. [ABSTRACT FROM AUTHOR]

The research object of this paper is to investigate the mechanical behavior and develop an analytical model of the prestressed circular-section rocking steel piers with external energy-dissipating devices under the horizontal cyclic load. Based on the method of monolithic beam analogy under monotonic loading, the concept of generalized rotation angle and intercept strain in the pre-decompression state was introduced. The geometrical equations for the pre- and post-decompression stages are deduced. The calculation formulas for internal forces of each component and the analytical calculation method for the entire process of the rocking steel pier under horizontal cyclic loading are established in detail. To reproduce the hysteresis curve of the test, some special test conditions, such as the retraction effect of prestressed tendons and increase of the compressed area due to the vertical plates, were considered in the analytical model. The results show that the analytical method based on generalized rotation angle and intercept strain can ensure an ideal transition of the hysteresis curve of the pier in pre- and post-decompression stages. Except for the pier with particularly severe local buckling and ovalization deformation, the calculated results obtained from the proposed analytical model agrees well with the test results for the rocking steel bridge piers. The effect of prestressed tendons and the P –Δ effect on the lateral load–displacement curve of rocking steel bridge biers was further analyzed through parametric study using the proposed model. The analytical calculation method presented in this paper provides a theoretical tool for seismic design of the rocking steel pier in engineering practice. This paper provides important guidance for the establishment of seismic design method of rocking steel piers. • to deduce the geometrical equations for the pre- and post-decompression stages of the rocking steel pier. • to establish the analytical calculation method for the entire process under horizontal cyclic loading. • to analyze the effect of prestressed tendons and the P –Δ effect on the lateral load–displacement curve. [ABSTRACT FROM AUTHOR]

The seismic design of conventional structures is mainly addressed considering the direct construction cost; the life cycle costs (LCCs) are often neglected. This paper proposes a performance-based framework for optimal seismic design of irregular steel structures; the LCC is involved as an optimization criterion. Two regular 7- and 10-story structures are first designed based on the design earthquake; their geometries are then changed to make them setback irregular having in overall four cases to investigate. Nonlinear analyses are performed to estimate the target displacement for annual exceedance probabilities, different specified acceleration levels, and, accordingly, the extent of the structural damage. The LCCs of the cases studied are calculated to achieve two objectives: an LCC-based optimal design of steel structures, and evaluating the extent of irregularity on the structures' LCCs. Results indicate that in the regular and irregular 7-story structures, a 40% and a 50% increase in the seismic loads can respectively reduce the LCCs by 31.3% and 34.9%. In the same vein, in the 10-story regular and irregular structures, increasing the seismic loads by 50% can reduce the LCCs by 33.4% and 31.7%, respectively. The results highlight the point that irregular structures, overall, require a higher initial cost than regular structures when the LCC is taken into account as an optimization criterion. [ABSTRACT FROM AUTHOR]

This paper addresses the application of conventional (force-based) seismic design methodologies to hybrid RC-steel systems. The q-factor-based EC8-3 seismic assessment procedure is first reviewed. A case-study application follows, analyzing and discussing the difficulties a practitioner will face when assessing the efficiency of a steel-brace retrofitting system designed within the framework of EC8-1. Afterward, the performance of the obtained retrofitted structure is evaluated using nonlinear analysis. The obtained results are discussed in light of the EC8-3 performance requirements, and conclusions are drawn about the adequacy of the force-based design (FBD) methodology (and associated q-factors) for such situations. The study shows that the process does not ensure the adequate seismic behavior of the retrofitted structures. It thus calls for the development of an effective performance-based design methodology that explicitly considers the interaction between the two structural systems (RC structure and steel braces), namely the influence of the steel braces' resistance on the deformation capacity of RC members. [ABSTRACT FROM AUTHOR]

According to the AISC Seismic Provisions for Structural Steel Buildings (AISC341‐16) and EC8, the inelastic rotation demand at the design story drift is limited to 0.08 rad for I‐shape shear links in eccentrically braced frames (EBFs). Numerical studies on EBF archetypes show that the single‐sided inelastic rotation demands can be much higher than the limiting value. In addition, these links can fail due to low‐cycle fatigue (LCF) which depends on the loading history. A mid‐spliced end‐plated detachable replaceable link has recently been developed to promote easy replacement of end‐plated links. In this paper, a frictional mid‐spliced shear link is developed to increase the inelastic link rotation capacity and LCF life of shear links. The proposed link utilizes a splice connection at the mid‐length, where frictional faying surfaces are introduced to dissipate energy. Slip at the mid‐splice connection causes a relative vertical displacement between the link ends which eventually reduces the rotation demands on the I‐shape members. Experimental and numerical studies were conducted to study the proposed link concept. Three conventional and eight frictional mid‐spliced links were tested using a nearly full‐scale test setup. The results showed that the proposed links have a pinched link shear versus link rotation response. The links were able to sustain a link rotation demand of 0.23 rad together with a significant increase in their LCF life. Numerical studies were conducted to investigate the link rotation, interstory drift, and residual interstory drift of EBF archetypes equipped with the proposed frictional link. [ABSTRACT FROM AUTHOR]

Current bridge codes in the US, Europe, and China specify vehicular collision loads for the design of piers. However, the performance of piers designed according to current codes in the three countries or regions is unknown yet. This paper presents a performance evaluation of concrete-filled steel tubular (CFST) piers subjected to vehicle collision. Before the evaluation, bridge specimens with a single CFST pier were designed in accordance with current bridge and structural codes in the three countries or regions, respectively. Then, a detailed finite-element (FE) model for simulating a truck collision with a CFST pier was developed and validated. By comparison with seven simplified FE models, the detailed FE model was further confirmed to be employed for the evaluation. In the evaluation, the effects of current codes in the three countries or regions, whether or not the vehicular collision load is considered, two pier heights (i.e., 6 and 12 m), two truck weights (i.e., 20 and 40 tons), and three impact speeds (i.e., 60, 100, and 140 km/h) on the performance of CFST piers were investigated. The evaluation results indicated that when a CFST pier in seismic zones is designed to resist vehicle collision according to current codes in the US and China, it only needs to meet the requirements of seismic design without additional consideration of the vehicular collision load. Moreover, a preliminary application condition should be added for the vehicular collision load specified by the current bridge code in Europe, that is, when the truck weight is more than 20 tons and/or the pier height is lower than 12 m. [ABSTRACT FROM AUTHOR]

This paper intends to provide quantitative seismic response characteristics of steel moment resisting frames (MRFs) with inelastic beam‐to‐column panel zone joints. Two modeling approaches are proposed for this purpose along with a methodology to consider the fracture potential at the bottom beam flange in steel MRFs due to panel zone kinking. Both approaches, which are validated with available experiments, preserve the behavioral insights of inelastic panel zones. Nonlinear static and dynamic analyses are then conducted to quantify the seismic demands of 32 prototype steel MRFs while their panel zones exhibit various levels of inelastic deformations. Engineering demand parameter hazard curves are developed to interpret the results for a risk‐targeted seismic performance. The results demonstrate that steel MRFs with panel zone shear distortions of 10 to 15 times the shear distortion at yield, γy${\gamma _y}$, have a mean annual frequency of collapse ranging from 1.5×10−4$1.5 \times {10^{ - 4}}$ to 2.5×10−4$2.5 \times {10^{ - 4}}$, which is up to two times lower than corresponding results with code‐compliant steel MRFs (i.e., γ≤4γy).$\gamma \le 4{\gamma _y}).$ It is shown that steel MRFs with inelastic deformations of 10γy${\gamma _y}$ in their panel zones, (a) enjoy up to 50% reduction in residual story drift ratios at a design basis earthquake; (b) their beam‐to‐column connections do not experience fractures due to panel zone kinking; and (c) local buckling in steel beams is very limited even at low probability of occurrence earthquakes. The above hold true when the current detailing and fabrication practice is employed. The findings have implications on seismic design and the post‐seismic repairability of steel MRFs. [ABSTRACT FROM AUTHOR]

This paper proposes a new variant of the genetic algorithm (GA), called the oriented genetic algorithm (OGA), for optimum seismic design of steel special moment resisting frames. Since GA is mainly based on random operators, its computational burden is usually high. To overcome this issue, OGA takes advantage of the violation values of design constraints of the problem, such as elements' demand-to-capacity ratios, strong column-weak beam requirements, and story drift ratios, to direct the search procedure. OGA is applied to a set of steel frames with different geometrical properties to demonstrate, and the results are compared to those of GA. The numerical results indicate that OGA significantly reduces the total number of function evaluations (NFE) required to obtain the optimum solutions. Also, the convergence history of OGA is compared with Particle Swarm Optimization and Ant Colony Optimization algorithms. It is shown that for a specified NFE limit, OGA gives better-optimized results. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic behavior of a steel beam-to-concrete-filled steel tubular column connection with external diaphragms. In addition to the multiple advantages observed for manufacturing and assembly, this type of connection is expected to provide an adequate plasticizing mechanism based on its ductility, energy dissipation and moment resistance capacity. However, guidelines have not been provided for this type of connection within the AISC 358 standard, which makes experimental studies under cyclic loads necessary. This work presents such a study, which was carried out in accordance with the FEMA 350 standard for earthquake-resistant structures. The results for the failure modes, hysteretic performance, strength and stiffness degradation, rigidity classification and energy dissipation are provided and analyzed. The results indicate that this connection exhibits large hysteretic loops and develops ductility and dissipation capacity, as expected. More importantly, the maximum rotation of the beam was 0.07 rad with a resistant moment above 80% of the beam capacity measured from the face of the column. Thus, the ductility design requirements for earthquake resistance are met according to the current regulations. Consequently, the proposed connection is suitable for use in special moment frame structures located in areas of high seismic threat. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Civil Engineering is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hybrid masonry is a new structural concept for buildings that incorporates the in-plane strength and stiffness of reinforced concrete masonry with the ease of erecting conventional steel framing. Because the masonry structural panels can also serve as architectural elements, hybrid masonry has the promise to be highly competitive with conventional lateral force resisting systems including reinforced masonry or concrete shear walls, steel braced frames, or concrete or steel moment-resisting frames. As part of an integrated program of multi-institutional research, seismic response and behavior of this construction type have been studied at the University of Illinois at Urbana-Champaign with a series of full-scale tests that are described in this paper. This paper provides an introduction to this innovative seismic structural system, summarizes the experimental research, and outlines how this research can be used to transform current seismic design practice, and by so doing make structural masonry more competitive in regions of moderate and high seismicity. [ABSTRACT FROM AUTHOR]

Lateral loads are resisted by braces in concentrically braced frames. Therefore, braces meet the demand for the load combination based on the seismic provisions. The rest of the system including the connections are determined according to the capacity‐based design, where the brace members yield under tension and buckle under compression. Chevron or inverted V‐braced frames are generally preferred because they allow large openings for doors and windows. However, the seismic‐design requirements in current building codes lead to deep, heavy chevron beams to resist the unbalanced load at beam members due to pre‐ and post‐buckling compressive strength deterioration and full tensile yielding of the braces. This results in uneconomical design. Recent large‐scale experiments of chevron‐braced frames have demonstrated that limited beam yielding is not detrimental to chevron‐braced frame behavior and on the contrary, it utilizes a second yielding mechanism and thereby increases the story drift capacity at which the braces fracture. Also, they propose a new design method for chevron braced frame with yielded beam. This paper expands the previous findings by investigating the seismic performance of 9‐story structures which are designed according to provisions and proposed method. Structural analysis program SAP2000 is utilized for linear design by modelling the full‐scale 9‐story building. Nonlinear finite element analysis software Perform 3D is utilized for the nonlinear time history analysis in which only a single chevron braced frame is modelled. Results show that the proposed building design has larger interstory drift ratios. However, the adjusted collapse margin ratio and the collapse probability for maximum considered earthquake satisfy the required limitations. In other words, the proposed chevron frame design offers a more economical alternative with no significant tradeoff in seismic performance. [ABSTRACT FROM AUTHOR]

In the last few decades, increasing research efforts have been devoted to the definition of innovative seismic resilient design strategies with the aim of reducing direct and indirect losses. Among others, the use of Friction Devices (FDs) for Beam‐to‐Column joints (BCJs) has emerged as an effective solution to ensure the damage‐free behaviour of steel Moment Resisting Frames (MRFs). Additionally, more recent research studies have revealed the benefits of replacing traditional full‐strength Column Bases (CBs) with innovative CBs promoting the residual drift reduction of steel MRFs. Additionally, several research studies developed and investigated structures that could be easily repaired after an extreme event, promoting a functional recovery of the structures and able to reinstate the original seismic performance in a short time. However, experimental research on suitable structural repair techniques is still marginal and the lack of confidence in the performance of repaired structures are relevant issues contributing to the high demolition rates. In this direction, an experimental campaign has been performed on a large‐scale steel structure equipped with BCJs with FDs and innovative CBs. Several pseudo‐dynamic tests have been performed and at the end of each test, the structure have been repaired by simply loosening the bolts of the FDs. Results demonstrated the effectiveness of repairing methodology. [ABSTRACT FROM AUTHOR]

The present paper deals with the seismic behaviour of bolted steel and steel‐concrete composite partial‐strength beam‐to‐column joints with endplate connections. In a series of experiments in total 12 two‐sided internal joint specimens were tested, of which 3 were all‐steel and 9 steel‐concrete composite. For those, 5 parameters were varied, (i) thickness of endplate tep, (ii) vertical distance of T‐stub bolt rows e4, (iii) distance of first shear stud to face of the endplate l, (iv) reinforcement ratio of concrete slab ρ and (v) number of bolt rows. The design of the specimens was performed with the help of both the component model as given in EN 1993‐1‐8 and a FEM model. The chosen parameter values were optimised to provide, for given beam and column sections, an upper and lower limit regarding moment capacity and rotational stiffness, for sufficient energy dissipation and ductility. The experimental results show that the stiffness of the concrete slab leads to a significantly different response of composite compared to all‐steel joints, especially regarding rotational stiffness and capacity of the joint as well as flexural stiffness of the (composite) beams. The composite joints present an overall better seismic behaviour compared to all‐steel ones. [ABSTRACT FROM AUTHOR]

Precast reinforced concrete panels are commonly used as wall claddings in precast buildings. The cladding panels are generally evaluated as non-structural members and are joined to structural systems via mechanical, welding, and bolted dry connections. Several failures were observed in the last seismic events in Southern Europe, which demonstrate the deficiencies of the cladding connections in terms of strength and ductility. A comprehensive research activity named SAFECLADDING was conducted in Europe to provide knowledge for proper seismic design of precast structures with cladding panels. In this context, energy dissipative steel cushions were developed and evaluated through the extensive experimental and numerical studies. Steel cushions can provide robust interaction of the structural system with the cladding panels. This paper numerically evaluates the effects of cladding panels with steel cushions on the global seismic behaviour of the buildings. An existing representative industrial building is selected to perform intensive nonlinear dynamic analyses. Analyses performed on the bare and hybrid systems showed that the hybrid system has high performance in terms of story drifts, internal forces, and deformations with respect to the bare system. The overall drifts in longitudinal and transversal directions of the building are reduced by about 78 and 54%, respectively. Average residual drifts of cladding panels and steel cushions indicated that the applied steel cushion placement scheme has a promising re-centring capability during seismic action. [ABSTRACT FROM AUTHOR]

Hysteretic steel dampers have been effectively used to improve the seismic performance of framed buildings by confining the dissipation of seismic energy into sacrifical, replaceable devices which are not part of the gravity framing system. The number of cycles sustained by the dampers during the earthquake is a primary design parameter, since it can be associated to low-cycle fatigue, with ensuing degradation of the mechanical properties and potential failure of the system. Current standards, like e.g. the European code EN 15129, indeed prescribe, for the initial qualification and the production control of hysteretic steel dampers, cyclic tests in which the devices are assessed over ten cycles with amplitude equal to the seismic design displacement dbd. This paper presents a parametric study focused on the number of effective cycles of the damper during a design earthquake in order to assess the reliability of the testing procedure proposed by the standards. The study considers typical applications of hysteretic steel dampers in low and medium-rise steel and reinforced concrete framed buildings and different ductility requirements. The results point out that the cyclic engagement of the damper is primarily affected by the fundamental period of the braced building and the design spectrum, and that, depending on these parameters, the actual number of cycles can be substantially smaller or larger that recommended by the standards. A more refined criterion for establishing the number of cycles to be implemented in testing protocols is eventually formulated. [ABSTRACT FROM AUTHOR]

This paper presents a rapid method for calculating the expected earthquake repair costs incurred by steel concentrically braced frame structures designed to Eurocode 8. The method adopts the FEMA P‐58 performance assessment methodology which is based on the predicting Engineering Demand Parameters (EDPs), such as peak inter‐story drift and peak floor acceleration, at various seismic hazard intensity levels of interest and then using these EDPs to calculate expected damage and associated economic losses. Typically, multiple nonlinear time history analyses (NLTHA) are employed to calculate the required EDPs, however this can be computationally expensive and technically challenging. This paper proposes the use of regression equations, developed from a large number of nonlinear analyses, as an alternative to NLTHA for EDP prediction. This allows loss assessment to be carried out without the need for multiple NLTHA, a process termed rapid loss assessment. The proposed equations are applied in loss assessment for three case study CBFs. It is shown that the economic losses predicted by the rapid method compare well with results obtained from conventional NLTHA‐based assessment. [ABSTRACT FROM AUTHOR]

Summary: This paper presents influence analysis of bracket set on seismic performance of steel eave columns in Chinese traditional style buildings. Eight 1/1.5‐scale steel eave columns were constructed and tested under low cyclic reversed loading, including 4 specimens with bracket set and 4 specimens without bracket set. Based on the analysis of the strain of the specimens, the failure modes of the specimens were obtained. In addition, the hysteresis loops, skeleton curves, degradations of stiffness and strength, ductility, and dissipation capacities of the specimens were analyzed. Bracket set changed the force transfer mechanisms and failure modes of the specimens and had a significant influence on the seismic performance of the specimens. Compared with the specimens without bracket set, the yielded and ultimate bearing capacities of the specimens with bracket set improved by 30.7% and 24.0%, respectively. And also, the stiffness of the specimens with bracket set at the yielded and ultimate points increased by 52.8% and 135.6%. The dissipation capacities of the specimens with bracket set were 2.12 times those of the specimens without bracket set at yielded load. However, the ductility of the specimens with bracket set slightly decreased by 8.5%. It was shown that the seismic performance of the specimens with bracket set was better than that of the specimens without bracket set. The work in this paper provides a basis for further theoretical study on the seismic performance of steel eave columns in Chinese traditional style buildings. [ABSTRACT FROM AUTHOR]

The component method provided by Eurocode 3 for the evaluation of strength and stiffness of beam-to-column joints is considered a very laborious procedure that is often difficult to apply. This is owing to the large number of geometrical and mechanical parameters involved in the analytical formulations. Hence, the component method is only seldom used for practical applications, with the consequence that the real behaviour of joints in terms of strength and stiffness is not accounted for. The aim of this paper is to provide an automatic tool that allows an easy-to-use application of the component method for the evaluation of beam-to-column joints stiffness and strength, and also enables plotting of the moment-rotation curve describing the joints' behaviour. Moreover, the proposed tool is used to carry out parametric analyses for two bolt-rows in end-plate beam-to-column steel joints. This is addressed to the definition of design charts for the optimal selection of joints. [ABSTRACT FROM AUTHOR]

This paper analyzes the ductility and overstrength of steel deck diaphragms and composite concrete on steel deck diaphragms and computes associated diaphragm design force-reduction factors, Rs. First, a database of past tests on steel deck and composite diaphragms was created, and more than 750 specimens were compiled into the database. A subset of 95 cantilever diaphragm specimens with postpeak inelastic behavior was identified for which specimen ductility and overstrength were calculated. The effects of variables such as fastener type, fastener spacing, and deck thickness on diaphragm ductility are explored. A method is then developed for converting cantilever diaphragm specimen ductility to diaphragm system-level ductility. Finally, diaphragm design force-reduction factors, Rs , are calculated consistent with an accepted methodology to be Rs=2.09 , Rs=1.13 , and Rs=2.36 for bare deck diaphragms with mechanical fasteners, bare deck diaphragms with welds to the supports, and concrete on steel deck diaphragms, respectively, for cyclically loaded specimens and assuming a long period structure. [ABSTRACT FROM AUTHOR]

This paper studies the dynamic seismic behavior of a typical highway bridge in New York State. The topological layout and structural details of this multispan simply supported steel-girder bridge are identified as the most typical of the New York State Department of Transportation bridge inventory database. Three-dimensional finite-element models of the bridge are established considering the nonlinear behavior of critical bridge components. An in-depth parametric study is carried out to evaluate the sensitivity of the bridge’s seismic response to variations in its structural parameters. The parametric analysis determined that uncertainties associated with the steel reinforcement’s yield strength, the superstructure’s weight, the expansion joints’ gap size, the friction coefficient of expansion bearings, and the concrete compressive strength should be considered during the fragility analysis of the bridge system. The Latin hypercube sampling (LHS) approach is used to obtain representative samples for the fragility analysis based on the mean values and probability distributions of each critical random variable. The LHS is thus used to create a set of nominally identical but statistically different bridge samples for performing the fragility analysis. The individual bridges from this statistically representative set are matched with earthquake samples of various intensities for the nonlinear seismic demand analysis. The seismic capacity of critical bridge components are estimated for each bridge sample from published experimental data. Through extensive numerical simulations, the sensitivity analysis identified the most vulnerable bridge components. Two seismic retrofit strategies for reducing the seismic risk of multispan simply supported steel bridges are studied: (i) steel bearing replacement by elastomeric bearings and (ii) deck/girder-splicing (continuity) with steel bearing replacement by elastomeric bearings. The analysis verified that retrofit option ii is the most effective. The finite-element model of the bridge samples, along with the assembled data on parameter uncertainties and member capacities, as well as a simulated set of ground motion records are suitable for use during the development of fragility curves for bridges with and without retrofit. Detailed description of the fragility analysis is presented in the companion paper. [ABSTRACT FROM AUTHOR]

Summary: The relatively large number of structural elements and the variety of design code requirements complicate the design process of tall buildings. This process is exacerbated when the target is to obtain the seismic code‐compliant optimal design with minimum weight. The present paper aims at providing a practical methodology for the optimal design of steel tall building structures considering the constraints imposed by typical building codes. The applicability of the proposed approach is demonstrated through the determination of the optimal seismic design for 20‐, 40‐, and 60‐story buildings with a framed tube as well as a tube‐in‐tube system. Such a design gives rise to a basis for the fair comparison of the behavior of the framed tube with that of the tube‐in‐tube system under applied loads. The optimal weight of the buildings with the tube‐in‐tube system turns out to be slightly less than that of the buildings with the conventional framed‐tube system. [ABSTRACT FROM AUTHOR]

Summary: This paper investigates the response of tall setback irregular steel moment resisting structures under traveling fires. A seven‐story steel regular structure (RS) is first designed for gravity and seismic loads and then it is fireproofed for a fire resistance rating (FRR) of 120 min based on the ISO834 fire. Some architectural changes are then imposed on the RS to make it a setback irregular structure (SBS). Based on the traveling fire methodology, both structures are then subjected to fire curves ranging from 1% to 100% for the fire load density (qf) of 570 MJ/m2. As in the SBS, the distribution of gravity loads is not uniform; the structural fire analyses are performed twice: when the fires start from left to right and then vice versa. The results show the FRR of the RS is minimized under the fire size of 22% with the collapse time of 87.0 min. In the SBS, when the fires start from left to right and then from right to left, the FRR is minimized under the fire size of 20% with the collapse times of 75.0 and 79.0 min, respectively. This shows that the SBS is more vulnerable toward traveling fires than the RS. In order to monitor the role of qf in the FRRs of the structures, qf is then reduced, and the required analyses are repeated. This process continues to where no collapse is observed under all the fire sizes. The results indicate that the RS would remain stable if the qf is decreased to 480 MJ/m2, implying that a 16% increase should be considered to the required FRR. As for the SBS, the qf should be decreased to 440 MJ/m2 to make it stable, meaning that a 25% increase should be considered to the required FRR. [ABSTRACT FROM AUTHOR]

Summary: In order to effectively utilize results from quasi‐static cyclic testing on structural components for the earthquake‐induced collapse risk quantification of structures, the need exists to establish collapse‐consistent loading protocols representing the asymmetric lateral drift demands of structures under low‐probability of occurrence earthquakes. This paper summarizes the development of such protocols for experimental testing of steel columns prone to inelastic local buckling. The protocols are fully defined with a deformation‐ and a force‐controlled parameter. They are generally applicable to quantify the capacity and demands of steel columns experiencing constant and variable axial load coupled with lateral drift demands. Through rigorous nonlinear earthquake collapse simulations, it is found that the building height, the column's local slenderness ratio, and ground motion type have the largest influence on the dual‐parameter loading protocol indexes. Comprehensive comparisons with measured data from full‐scale shake table collapse tests suggest that unlike routinely used symmetric cyclic loading histories, the proposed loading protocol provides sufficient information for modeling strength and stiffness deterioration in steel columns at large inelastic deformations. [ABSTRACT FROM AUTHOR]

A posttensioned (PT) steel moment resisting frame is a self-centering earthquake resistant steel frame that uses posttensioning steel to compress the beam flanges against the column flanges at the connections. The posttensioning contributes to the moment capacity of the connections and provides an elastic restoring force that returns the frame to its pre-earthquake position. This paper describes the behavior and design of PT frames and PT frame systems, where a PT frame system is a PT frame with the collector elements that connect it to the floor system. The interaction of the floor system with the PT frame produces axial forces in the beams that add to those from the posttensioning. This paper outlines a performance-based seismic design approach for PT steel frame systems. Seismic performance levels, seismic input levels, structural limit states and capacities, and structural demands for PT frame systems are defined. The design objectives are outlined, design criteria are given, and a step-by-step design procedure is given. The design approach is evaluated via comparisons with time-history analysis results. [ABSTRACT FROM AUTHOR]

This paper uses the experimental results presented in a companion paper to develop a seismic design approach for unbonded posttensioned hybrid coupled wall subassemblages. The test results are also used to verify and refine analytical models for the subassemblages. The proposed design approach includes guidelines for the selection of the coupling beam cross-section and the posttensioning steel area, as well as the design of the top and seat angles, their connections, and the design of the concrete wall contact regions. [ABSTRACT FROM AUTHOR]

This paper focuses on an innovative system for mitigating seismic actions on industrial steel racking, called Load-Level Isolation System (LLIS). It consists of placing isolators directly between the pallet masses and the load level, thus exploiting the pallet masses (much greater than the structural mass) as tuned mass dampers. Specifically, the paper aims to derive a general design procedure for the LLIS, based on the amount of mass isolated, the position of the LLIS within the rack, and the main dynamic characteristics of the structural system. To this end, an analytical optimization method is proposed, based on the minimization of the displacement variance of a reduced structural model, representative of the rack dynamics with the LLIS. This method is applied parametrically to derive the optimal damping and frequency values of the LLIS in various design situations, and a sensitivity analysis is subsequently conducted to propose cost-effective LLIS design solutions. Prediction models of the LLIS parameters are therefore provided, as well as a simple step-by-step procedure for designing the control system. Finally, a case study is presented, with the dual objectives of showing the application of the design procedure and the effectiveness of the LLIS in mitigating seismic effects in a standard pallet rack. The results of the Time-History analysis demonstrate the validity of the proposed design method and the possibility of achieving large reductions in the seismic response of the rack using this control system, and up to 60% for both maximum displacements and axial forces of the uprights. • Investigation on the Load-Level Isolation System (LLIS) for mitigating seismic actions on industrial steel racking. • Definition of the equivalent reduced-order model of the LLIS-equipped racking. • Optimal and cost-effective LLIS solutions as a function of isolated mass, its position, and rack dynamic. • Provision of a step-by-step design procedure for the LLIS. • Evaluation of LLIS effectiveness through a case study pallet rack and bidirectional Time-History analyses. [ABSTRACT FROM AUTHOR]

• The theoretical equations governing the post-rocking stiffness of a multiple-rocking-column system (MRCS) were derived and validated experimentally. • Scaled shaking-table tests were performed to investigate dynamic responses of MRCSs with positive, quasi-zero and negative post-rocking stiffness. • Low frequency and broadband effective vibration isolation can be achieved through quasi-zero or negative post-rocking stiffness. • Seismic design of the MRCS should consider the balance between displacement and acceleration demands. Ancient wooden pagodas have shown remarkable seismic resistance, surviving strong earthquakes over millennia. This impressive performance is credited to the unique seismic mitigation and isolation mechanism. The discontinuity between the timber columns allows each story to rock freely like a "balancing toy", effectively reducing inertia forces. Inspired by this fascinating phenomenon, an innovative steel multiple-rocking-column system (MRCS) has been designed. This system includes continuous beams, discontinuous columns, and springs. The post-rocking stiffness of the MRCS can be adjusted to be positive, quasi-zero, or negative by varying the stiffness of the springs. This paper mainly focuses on the effects of post-rocking stiffness on the dynamic behavior of the MRCS, both theoretically and experimentally. Initially, analytical models were developed to assess the stiffness properties of the MRCS. After that, a scaled MRCS model consisting of three stories and featuring seven different post-rocking stiffness levels was designed. Shaking-table tests were conducted to investigate the dynamic response of the model under seismic excitations. The equations governing the post-rocking stiffness of the MRCS demonstrated good accuracy with test results. As the post-rocking stiffness decreased, displacement response increased gradually but significantly mitigated horizontal acceleration responses along the structural height. Wavelet transform-based time-frequency analysis provides a comprehensive understanding of the dynamic features of the MRCS. Furthermore, a finite element model was established to verify the proposed theoretical model, and the numerical results agree well with the experimental findings. This study provided valuable insights into the design of innovative multiple-rocking systems for post-rocking stiffness. [ABSTRACT FROM AUTHOR]

A set of seismic analysis and design requirements are presented to improve seismic stability of steel two-tiered eccentrically braced frames (EBFs) with I-shaped link beams. The proposed requirements include strength, stability, and stiffness provisions for braces, intermediate beams, and columns. In particular, these requirements aim to make use of intermediate beams to limit out-of-plane deformation of diagonal braces, torsionally brace the link beam in the intermediate level using diagonal braces, utilize column stiffness and strength to brace the intermediate beam out-of-plane, estimate and account for in-plane bending demands of the columns due to uneven yielding of the links, and control inelastic link rotation. The proposed special analysis and design requirements for two-tiered steel EBFs prevent excessive out-of-plane deformation of the intermediate beam and columns, promote sequential yielding of link beams, and limit inelastic rotation of the link in the tier experiencing the largest lateral deformation. The proposed requirements are demonstrated for a case study two-tiered EBF. Nonlinear static and dynamic analyses are performed to evaluate the seismic response of the case study frame against the frame designed without special design provisions and to validate the proposed requirements. [ABSTRACT FROM AUTHOR]

Highlights • This paper conducted a statistical analysis of the material properties of low yield point steels. • The reliability analysis was performed using probabilistic theories and structural reliability theories. • The suggested partial factors for resistance of low yield point steels were provided. Abstract As promising structural materials in seismic isolation and energy dissipation systems, low yield point (LYP) steels have been developed and have begun to be adopted in seismic design. This article reports statistical analyses of the material properties of LYP steels and calibration of their partial factors for resistance. An extensive range of mill test data collected from major steel manufacturers in China was analyzed using a mathematical statistical method. On the basis of the statistical analyses and existing research results, reliability analysis was performed for LYP steels using probabilistic theories and structural reliability theories. Finally, suggested partial factors for the resistance of LYP steels were provided. As an important part for codifying the Technical specification for application of low yield point steel in China, this paper may provide valuable reference for further research and promote the engineering applications of LYP steels in China. [ABSTRACT FROM AUTHOR]

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-equivalent viscous damping relationships of the sub-assemblages. The equivalent linearization technique is applied to the non-linear responses obtained in the NLTH analyses, using an elastic single degree of freedom structure and the elastic displacement spectra. The influence of joints mechanisms and of the dynamic characteristics of the structure in the equivalent viscous damping is investigated, and an expression for ductility-equivalent viscous damping is proposed. The proposed expression represents a clear improvement in relation to the existing expressions available in literature. [ABSTRACT FROM AUTHOR]

During an earthquake, steel frame buildings with bracings are prone to high absolute floor acceleration demands, thereby causing damage to acceleration‐sensitive non‐structural elements and building content. Inelastic deformations in steel bracings and/or their end connections often necessitate the use of capacity design rules to meet the life safety requirements established by seismic design standards. This paper presents an alternative steel frame building configuration where energy dissipation is mostly achieved through friction dampers acting as dissipative connectors between the floor diaphragms and the steel frame(s) with bracings. The dampers consist of friction pads made from composite materials which are not susceptible to galvanic corrosion. Physical experiments suggest that the friction pads are effective in dissipating the seismic energy through friction. Nonlinear response history analyses of a prototype 6‐storey steel frame building featuring friction dampers as dissipative floor connectors demonstrate that a) higher mode effects are mitigated; b) capacity‐design in the steel frame(s) with bracings is not imperative to ensure a uniform lateral drift distribution; and c) the seismic response variability in storey‐based engineering demand parameters is reduced remarkably compared with that of the conventional counterpart with rigid diaphragms. All‐in‐all, the alternative building configuration has high potential to minimize earthquake‐induced repairs over a building's service life. [ABSTRACT FROM AUTHOR]

The paper addresses philosophical concepts on the seismic design criteria of moment resisting steel frames. The ductility approach that is based on the capacity design rules adopted by the modern seismic codes is illustrated. The effectiveness of seismic provisions for the design of moment resisting steel frames as given in the codes is assessed. Emphasis is made on the response modification factor, overstrength factor, strong column weak beam philosophy, cross section limitation, second order effects and interstorey drift limitations. The applicability and the effects of such rules on the overall performance of rigid steel frames are presented. Furthermore, the pros and cons of the use of steel moment resisting frames are also given. The paper also presents information about the design criteria of steel frames. [ABSTRACT FROM AUTHOR]

This paper details a direct displacement-based design procedure for steel eccentrically braced frame (EBF) structures and gauges its performance by examining the non-linear dynamic response of a series of case study EBF structures designed using the procedure. Analytical expressions are developed for the storey drift at yield and for the storey drift capacity of EBFs, recognising that in addition to link beam deformations, the brace and column axial deformations can provide important contributions to storey drift components. Case study design results indicate that the ductility capacity of EBF systems will tend to be relatively low, despite the large local ductility capacity offered by well detailed links. In addition, it is found that while the ductility capacity of EBF systems will tend to reduce with height, this is not necessarily negative for seismic performance since the displacement capacity for taller EBF systems will tend to be large. To gauge the performance of the proposed DBD methodology, analytical models of the case study design solutions are subject to non-linear time-history analyses with a set of spectrum-compatible accelerograms. The average displacements and drifts obtained from the NLTH analyses are shown to align well with design values, confirming that the new methodology could provide an effective tool for the seismic design of EBF systems. [ABSTRACT FROM AUTHOR]