Lateral Force-resisting System Research Articles

Methodical Investigations on Seismic Retrofitting of Steel Plate Shear Wall Systems

An efficient retrofitting technique is expected to improve the seismic performance of a lateral force-resisting system without increasing the seismic demand on the structure, which can unfavorably lead to irreparable damages during a seismic event. On this basis, the present study aims to introduce an optimal strategy for seismic retrofitting of steel plate shear wall (SPSW) systems using low yield point (LYP) steel material and to demonstrate its effectiveness through systematic investigations. To this end, detailed nonlinear static, cyclic, and dynamic analyses, as well as fragility analyses, have been performed on single- and multi-story, code-designed as well as retrofitted SPSWs. The aim is to identify the most efficient retrofitting approach and to demonstrate its effectiveness in enhancing the seismic performance and lowering the seismic vulnerability of the system. It is shown that replacing the original, conventional steel infill plate in an SPSW system with an LYP steel plate having twice the original thickness can improve not only the buckling capacity and serviceability, but also the structural performance and seismic response of the system, without increasing the demand on the structure and creating overstrength concerns. Fragility analysis also shows that the vulnerability, as well as probability, of damage to system can be considerably lowered as a result of the implementation of such a retrofitting strategy.

Study on seismic behavior and collapse risk of super high-rise braced mega frame-core tube structural system

The braced mega frame-core tube (BMFCT) structure could provide an efficient lateral-force resisting (LFR) system for high-rise or super high-rise buildings, especially for those higher than 500 m. The BMFCT structure is a dual LFR system, including the outer braced mega frame and the inner core tube. The seismic behavior and design method of this structural system is not clear. In this study, a parametric study based on collapse risk-targeted analysis is conducted to clarify seismic mechanism and performance and to make clear means of matching reasonable stiffness and setting energy-dissipation components. Five comparable BMFCT structures with different mega brace stiffness proportions and frame-tube stiffness ratios are designed. An efficient elasto-plastic modeling method is introduced to establish the accurate FE models. The corresponding collapse risks are calculated through Incremental Dynamic Analysis and fragility theory. The results show that the structural collapse risk increases with the increased frame-tube stiffness ratio. Therefore，the stiffness and bearing capacity of peripheral frames should be strengthened to ensure the structural collapse margin. On the other hand, the collapse resistance capacity gradually decreases with the increasing of the mega brace stiffness. Thus, the stiffness proportion of mega braces should be recommended to meet the basic lateral stiffness requirements, which shall not exceed 35 % of the overall structural stiffness. Moreover, the distribution feature and ideal arrangement of the energy dissipation components are proposed. The seismic design recommendation based on the uniform collapse risk is also proposed for the BMFCT system, which serves a reference for the structural design of super high-rise buildings.

Seismic Behavior of an Inter-story Hinged Lateral Resistance Braced Frame

Based on the deflection behavior of structural components occurring at the lateral deformation of moment frames, a new lateral force-resisting system, the R-BRACE Frame (RBF) system, was proposed. This system is capable of effectively limiting the inter-story drift response of tall buildings. An evaluation was conducted using the finite element method program SAP2000 to simulate the internal force distribution and deformation of the system. The equivalent lateral force procedure (ELFP), the capacity spectrum method (CSM), a linear time-history analysis and the pushover method were applied to assess the yielding mechanism of the structure under different earthquake intensity levels. The findings revealed that the sub-unit, referred to as an R-BRACE, had a major impact on improving a structure's lateral stiffness. The placement of R-BRACE units could guarantee controllable stiffness degradation and enhanced seismic ductility, but would not alter the vertical load transfer path of the initial structure, which makes the RBF system an ideal option for seismic retrofitting. KEYWORDS: Lateral force-resisting system, R-BRACE frame, Enhanced lateral stiffness resistance, Seismic ductility

Second Generation of Eurocode 8: Seismic Design Rules for Cold‐Formed Steel Buildings

AbstractThe seismic design of Cold‐Formed Steel (CFS) building structures is not covered by the current edition of Eurocode 8. In order to update Eurocode 8 to reflect the findings of extensive research undertaken over the last ten years, the University of Naples “Federico II” is taking part in the evaluation of current seismic design criteria and the creation of new guidelines for the design of CFS systems. This paper especially examines various Lateral Force Resisting System (LFRS) types that may be found in the second version of Eurocode 8. It also provides background information on the research initiatives and reference design standards in use in various parts of the world that served as the basis for the development of design criteria included in the new version of Eurocode 8.

Wood Diaphragm Deflections. I: Generalizing Standard Equations Using Mechanics-Based Derivations for Panel Construction

Horizontal wood diaphragm systems, whether decked with conventional or mass timber panels, transfer wind and seismic loads to vertical elements of a lateral force-resisting system (LFRS), in flexible, rigid, or semirigid fashion. Characterizing and calculating the resulting diaphragm deflections determines the distribution of forces to critically loaded components and a significant portion of lateral building translations and rotations. Deflection equations for sheathed wood structural panel (WSP) diaphragms are well established in US design standards in a four-term expression that models flexural, shear, and fastener-slip deformations, and its full derivation using principles of mechanics is provided herein. Derivations of similar equations for cross-laminated timber (CLT) diaphragms have yet to unfold, despite growing industry consensus that CLT panels make efficient slabs and decks. In this first of two companion papers, the corrected full derivation of the current four-term WSP diaphragm deflection expression is provided and assessed, and two ways to quantify the cumulative contribution of fastener slip are presented to expand its usage to a wider variety of WSP and CLT configurations in current use. Building on this generalized mechanics-based derivation, the authors are able to propose and assess in the companion paper a unified diaphragm deflection model to compute both WSP and CLT diaphragm deflections as implemented under current practice and guide further development.

Behaviour of small-scale glulam timber connections with slotted-in steel plates and dowel-type fasteners reinforced with self-tapping screws

Braced frames are a common lateral force-resisting system in mass timber structures. In timber braced frames, timber-steel dowel connections are relied upon to provide ductility and energy dissipation capacity under earthquake loads. However, the ductility and energy dissipation capacity of these connections can be limited by the onset of a brittle failure mechanism (e.g., row-shear or group tear-out) prior to significant dowel yielding. This paper presents an experimental campaign investigating the structural performance of timber-steel dowelled connections reinforced with self-tapping screws. Twelve connections were tested; with 8 tested under monotonic loading and 4 tested under a cyclic loading regime. The tested connections included two different fastener diameters of 11 mm and 16 mm, with one or two internal steel plates, both with and without reinforcing screws designed to prevent brittle shear failure. The results demonstrate that the reinforcing screws are most effective for improving the ductility and energy dissipation for connections with similar design values of dowel yield and row shear capacities. In addition, the increases in ductility and energy dissipation with reinforcement were greatest for connections with high slenderness (defined as the ratio of dowel diameter to timber thickness) dowels. There was little improvement in the ductility of connections whose design capacity was dominated by row shear, although there was improvement in the energy dissipation of the connections. Overall, results of this study demonstrate the potential for using self-tapping screws to reinforce steel dowel connections and improve the seismic performance of mass timber braced frames.

Seismic reliability analysis of plan-asymmetric reinforced concrete buildings with dual special frame-wall lateral force-resisting system

The seismic reliability analysis of plan-asymmetric reinforced concrete (RC) buildings with dual frame-wall system has been targeted in this paper by combining record-to-record uncertainty with model uncertainty in the estimation of analytical collapse fragility functions. To the purpose, three building case studies, equipped with dual special RC system, were designed by modal response spectrum analysis. The mathematical models were next developed for these buildings by including lumped plastic hinge model in beams and fiber-section model in columns and walls. Both of pushover and incremental dynamic analysis (IDA) were conducted to estimate the capacity of the structural system under static and dynamic loading conditions. Collapse fragility functions were derived in terms of several earthquake intensity measures (IMs) and engineering demand parameters (EDPs) as random variables with log-normal distribution. The median and standard deviation values were then employed to estimate the probable value of percentage risk of collapse (PROC), as an index to which the structural reliability of the system could be verified. The statistics mostly indicated lower values of probable PROC when the random variable was defined in terms of the EDPs.

EVALUATION OF RETROFIT EFFECTIVENESS AND COST IMPLICATIONS OF MRF STRUCTURES USING DISTINCT FRCM COMPOSITE SYSTEMS

This paper summarizes the results of a numerical investigation to assess the effectiveness of retrofitting pre-seismic code concrete framing structural systems using two distinct fiber-reinforced cementitious matrix (FRCM) composites. While FRCM composites were focused in the literature at the member level, this study focuses on implementing this retrofit technique effectively at the structure level. Several static pushover analyses (SPAs) and inelastic dynamic simulations (IDSs) are carried out for FRCM-retrofitted RC frames representing the lateral force-resisting system of a moment-resisting frame (MRF) structure. Correlating the numerical simulation results and experimental results obtained from another study verified the selected fiber discretized section modeling technique for FRCM retrofitted MRFs and reflected the effectiveness of the adopted approach in prolonging local and global damage states. The verified modeling technique of the risk-mitigation measure is then employed to evaluate the performance of an upgraded RC building using three-dimensional fiber-based numerical models. Finally, a parametric study using SPAs and IDSs using multiple seismic scenarios is conducted to select the most effective FRCM retrofit material for the seismic performance enhancement of the benchmark structure. The study concludes that using the selected FRCM retrofit technique effectively mitigated the structural collapse damage state of the substandard building at the design and maximum considered seismic intensity levels by 28% and 32%, respectively.

Investigation of effective parameters on seismic performance of steel frames with CFST columns

The seismic performance of steel frames with composite columns is evaluated by the seismic performance factors. Despite the essentiality of appropriate coefficient values, there are limitations in the building code regarding seismic performance factors of composite structures. These values have been presented in the regulations based on engineering judgment and comparison with similar steel and concrete structures. However, limited research exists on the determination of seismic performance factors for composite structures, where these coefficients are affected by numerous parameters. This article aims to cover the existing gaps and examine the parameters that have received inadequate attention in regulations and articles, despite their significance in the seismic design of composite structures. The present study conducts a nonlinear static pushover analysis of steel structures with concrete-filled tubular steel columns (CFST) to investigate the influential parameters in seismic performance factors. The variables studied in this research encompass the height of the structure, soil type, lateral force-resisting system, and structural irregularity. The findings demonstrate that changes in structural height influence the value of the response modification factor in all examined soil types for IMFs and SMFs. Also, the response modification factors provided in ASCE 7 prove to be conservative for the studied lateral force-resisting systems excluding SMFs in composite structures. In addition, the seismic performance of the studied models has dropped due to the geometric irregularity of the plan and the irregularity of non-parallel systems. Besides, the response modification factor values for composite structures surpass those specified for similar steel structures, while Eurocode 8 and ASCE 7 consider these values to be equal and similar to steel structures, respectively.

Research on the Overstrength Performance of Lateral Force-Resisting System of Guangzhou West Tower Based on Story Overturning Moment

ABSTRACT The factors of the building’s structure’s overstrength performance need to be researched to decrease the large amount of the structural materials and the investments caused unreasonably by the overstrength performance. Taking the Guangzhou West Tower as an example, the main reasons why the Guangzhou West Tower model structure was not damaged after encountering an earthquake (PGA = 620 gal) in the shaking table test was revealed. The overstrength performance of lateral force-resisting system of the Guangzhou West Tower building’s structure was researched, which is caused by the artificially adjusted earthquake influence coefficient of the long-period segment of response spectrum. The response spectrum analysis and the elastic/plastic incremental dynamic time history analysis were conducted to obtain the overstrength coefficient of the lateral force-resisting system that was calculated with the overturning moment at structural base. The analysis results showed that the yield overturning moment at structural base exceeds the seismic demand at the point where PGA = 400 gal, which could verify the reliability of the results of shaking table test. The artificial magnification of the long-period segment of response spectrum and the irrational correlation between the seismic grade and the building’s height are important reasons that increase the overstrength capacity of long-period building’s structure.

Performance of Beam-Column Connections with Mass Ply Lam and Steel Dowels under Cyclic Loads

A mass timber lateral force resisting system (LFRS) is proposed using a mass timber buckling restrained brace (TBRB) to improve the seismic resilience of mass timber buildings. To develop a resilient braced frame, it is essential to understand and quantify the behavior of the connections, including the possible failure modes and moment-rotation capacities. Cyclic and monotonic tests were conducted on six mass timber beam-column connections to study the response of a mass timber joint connected with slotted-in steel plates and mild steel dowels. The primary goal of the subassembly tests was to measure the maximum rotation, stiffness, ductility, and failure modes of such connections for both monotonic and cyclic loads. The tests showed that the connections with three steel dowel details reached a maximum rotation of 0.11 radians (6.3 degrees) with no loss of strength. In addition, a numerical model was developed to represent the moment-rotation relationship of the mass timber beam-column connections.

Experimental and Numerical Investigation of Integrated Steel Shear Walls with Varying Web Width-to-Thickness Ratios

The cold-formed steel-framed shear wall sheathed with steel sheet is widely used as a lateral force-resisting system for light-framed construction. However, the boundary conditions of the screw joint are not clear when steel is screwed to the frame. To address this issue, experimental methods have been used to calculate shear strength, but these methods have many limiting factors. In this study, we investigate the structural performance of integrated steel shear walls with varying web width-to-thickness ratios as an alternative to steel-sheathed shear walls used in light-gauge steel frames. The proposed design equation for cold-formed steel integrated shear walls is validated by three specimens and 72 finite element models. This equation allows designers to determine the strength of integrated steel shear walls without conducting full-scale shear-wall tests.

Experimental Investigation and Numerical Simulation of Corrugated Steel Plate Shear Wall Considering the Gravity Load

The corrugated steel plate shear wall (CSPSW) has high strength, ductility, and energy dissipation capacity and can be used as the lateral force-resisting system of multi-story and high-rise buildings. The vertical load transmitted by the upper floor and frame columns may inevitably act on the corrugated steel plate shear wall. However, the influence of the gravity load on the performance of the corrugated steel shear wall is not considered in most studies. To investigate the behavior of corrugated steel plate shear walls considering the actual gravity load, four scaled SPSWs under lateral and vertical loading were tested. The specimens’ failure mode, envelope curves, and hysteretic curves were analyzed. A numerical simulation model was established based on the validation of the experimental test on the SPSWs. The results showed that the hysteresis curves of the test were consistent with those of the simulation results. Finally, parametric analysis was conducted on the SPSWs with different types of infill plates, height-to-thickness ratio, and gravity loads.

Performance of Reinforced Concrete Shear Wall In Dual Structural System: A Review

A dual structural system consists of a momentresisting frame, and vertical reinforced concrete walls called shear walls. Shear walls used in tall buildings are generally located around elevator cores and stairwells. Many possibilities exist in a tall building regarding the location, shape, number, and arrangement of shear walls. Shear walls generally start at the foundation level and are continuous throughout the building height. Their thickness can be as low as 150mm in lowrise to medium-rise buildings or as high as 400mm in high-rise buildings. To establish an effective lateral force-resisting system, the shear walls are located in preferable positions in a structure that minimizes lateral displacements. The shear walls are situated in ideal locations to be symmetrical and torsional effects get reduced. Based on the comparison of various literature regarding the shear wall positions, the shear wall placement at the core or the corners of the structure symmetrically gives the best performance to reduce displacement and story drift. Also, lateral displacement diminishes when the shear wall’s thickness increases.

Evaluation of seismic performance factors for dual steel SMF-SCBF systems using FEMA P695 methodology

The present study evaluates the seismic performance factors of typical buildings with dual lateral force resisting system (LFRS) consisting of special moment frames (SMFs) combined with special concentrically braced frames (SCBFs) using FEMA P695 methodology. For this purpose, six building archetypes with 2-, 4-, 8-, 12-, 16- and 20-stories, in two short- and long-period performance groups were analyzed by the response spectrum method and designed based on the requirements of ASCE 7–16 and AISC 341–16. Validated nonlinear models were developed for each building in the OpenSees software platform. Then, the static and dynamic behavior of each building was investigated up to the collapse stage by nonlinear static analyses and nonlinear time history analyses under 44 far-field ground motions of FEMA P695. In this investigation, the peak and residual drift ratios, hysteresis behavior of the stories during the earthquake, collapse fragility curves, and seismic performance parameters (R, Ω, and Cd) were obtained and discussed. The results of nonlinear analyses demonstrated that code-compliant long period dual SMF-SCBFs (16 stories or higher) performed poorly and can be severely damaged in strong earthquakes.

Sustainability evaluation for selecting the best optimized structural designs of a tall building

To resolve social and environmental issues and prepare the required residences in megacities, a sustainable development analysis of the structural designs should be carried because a building is designed for a long life span. Based on CEN TC350, life cycle assessment (LCA) indicators, and EN standards, the life cycle assessment of a building should be conducted in the initial steps of the design process. The main target of this study is related to the sustainability evaluation of the optimized structural designs by the various lateral force-resisting system to select the best structural system for a tall building. According to interviews with 28 experts, condition and location of the study area, and intensive observation, 12 lateral force resisting systems were proposed to design a 17-storey five-bay structure. Each structural design was optimized by the optimization modules of SAP2000. Eleven indicators were selected based on data availability, experts' opinions, and authors' opinions. The weight and effect value (EV) of changes intensity were calculated based on interviewing experts. The values of the indicators were calculated using an indirect and direct manner based on SAP2000 results. A technique for order of preference by similarity to ideal solution (TOPSIS) approach was employed for integrating the values of the proposed indicators. Moreover, an applied effect of changes intensity in each indicator (AECIEI) method, which is one of the simplified MCDA approaches, was utilized to evaluate the sustainability of all scenarios. After sorting all scenarios based on TOPSIS and AECIEI, the results of these methods were compared. The results show that AECIEI can apply the effect of changes intensity and critical indicator on sustainability evaluation; thus, its results are more accurate than the results of TOPSIS. The combination of the steel moment frame and the special reinforced concrete shear wall in both directions was chosen as the best optimized structure based on AECIEI's results. This scenario with sustainable value (SV) of 0.014 was selected as the best option with respect to ductility with a value of 4.17 and the emitted air pollution with a value of 20.40 Ton.

Seismic performance of concrete coupling beams subjected to prior nonlinear wind demands

The ability to assess the role of pre-existing damage on the residual (reserve) capacity and reparability of buildings following a damaging event or events is essential to achieving the goal of functional recovery. If performance-based wind design is applied, where limited nonlinear deformations in some elements are allowed under extreme wind events, or if a design earthquake occurs, there are likely to be a significant number of buildings with modest damage (in addition to some with more severe damage, that obviously need to be evaluated and repaired). For tall concrete buildings that utilize structural coupled (core) walls as the primary lateral force-resisting system, coupling beams are the main fuses that limit force demands on other elements and actions and provide a reliable mechanism for energy dissipation during extreme events, and thus, are most likely to impact building performance in future events and to require repair. Therefore, tests were conducted on eight coupling beams, seven reinforced concrete (RC) beams and one W-shaped steel-reinforced concrete (SRC) beam, subjected to simulated windstorm loading protocols that introduced modest nonlinear deformations followed by a standard seismic loading protocol to large inelastic deformations. The test variables included aspect ratio, presence of an RC floor slab, type of wind loading protocol, level of detailing, and type of concrete coupling beam (RC vs SRC). The findings indicated that the limited damage due to the prior wind demands did not impact strength, axial growth, rotation capacity, and failure mode of the beams under the seismic loading protocol; however, a significant reduction in the initial stiffness of all beams and a minor reduction in energy dissipation capacity of the conventionally reinforced beams were observed.

Hybrid self-centering companion spines for structural and nonstructural damage control

This paper intends to develop a new lateral force-resisting system – the hybrid self-centering companion spines system (denoted as the HSCS system) – for obtaining better seismic resilience by controlling both structural and nonstructural damage. The HSCS system consists of two rigid spines pinned to the ground and several hybrid dampers. The two rigid spines can facilitate the structure to avoid soft-story mechanisms and control higher mode responses by promoting uniform inter-story drift distribution under strong earthquakes. The hybrid damper is made of a friction spring damper and a viscous damper in parallel and provides the self-centering feature, energy-absorbing capacity, and acceleration- and velocity-control capacity for reducing structural and nonstructural damage. A performance-based design (PBD) procedure was developed for the HSCS system based on the concept of the direct displacement-based design method. The three-story and six-story demonstration buildings were considered in this study to investigate the seismic performance of steel buildings equipped with the proposed HSCS systems. Four designs with different design parameters were performed for the demonstration buildings based on the proposed PBD procedure. The three- and six-story self-centering companion spines systems (denoted as SCS systems) were considered for highlighting the benefits of adopting HSCS systems. Nonlinear dynamic analyses were conducted to evaluate the structural and nonstructural damage of the designed buildings under earthquakes. The analysis results indicate that the designed HSCS systems can achieve the desired performance objective and nonlinear behavior under dynamic excitations. The HSCS systems can show excellent structural damage control performance and post-earthquake recoverability by controlling the residual inter-story drift much smaller than 0.2% even under MCE excitations. The excellent nonstructural damage control capacity can be also observed in the designed HSCS systems, while most of the nonstructural components are only slightly damaged even under MCE excitations. Moreover, the HSCS systems can achieve smaller absolute floor acceleration and floor velocity responses than SCS systems under both DBE and MCE although they are designed to achieve similar maximum inter-story drift responses under DBE.

Performance-based design of steel frames with self-centering modular panel

The self-centering modular panel (SCMP) is an emerging seismic resilient lateral force-resisting system. This paper intends to develop a performance-based design (PBD) method for steel buildings equipped with the SCMPs based on the concept of direct displacement-based design methodology. The theoretical hysteretic model of the SCMP consisting of the post-tensioned frame (PTF) and four replaceable hysteretic dampers (RHD) is proposed and validated in this paper. Based on the proposed theoretical hysteretic model, the equation for the equivalent damping ratio of the steel buildings with SCMP is developed and the PBD method is proposed. The 3-story and 6-story steel frames equipped with the emerging SCMP are established through the developed PBD procedure. Static analyses were performed to investigate the nonlinear responses of the established buildings. Twenty ground sequences were chosen and scaled to evaluate the seismic responses of the designed steel frames subjected to different seismic intensity levels through nonlinear dynamic analyses. The results of the research show that steel structures equipped with SCMPs established through the developed PBD procedure can display the expected hysteretic behavior and performance under earthquakes. The designed buildings can achieve excellent post-earthquake recoverability by keeping the residual displacement in each story less than 0.5% even under earthquakes with MCE intensity.

Seismic Performance and Cost Analysis of UHPC Tall Buildings in UAE with Ductile Coupled Shear Walls.

The superior mechanical characteristics of ultra-high-performance concrete (UHPC) have attracted the interest of many researchers worldwide. Researchers have attempted to perform comparative analyses on the behavior of UHPC versus conventional and high-strength concrete, with their aim being to gain more insights into the difference between different types of concrete. However, the current state-of-the-art revealed no direct comprehensive comparisons between their behaviors in ductile coupled shear walls under seismic loading. This paper explores a comprehensive side-by-side comparison in terms of seismic behavior and cost analysis for four 60-story archetype buildings. The reference building was designed using high-strength concrete with a strength of 60 MPa. The other three archetype variations incorporated three different UHPC grades: 150 MPa, 185 MPa, and 220 MPa. The plan configuration and the lateral force-resisting system (LFRS) were chosen according to the most common practice in the UAE. The main objective is to report the effect of UHPC on the LFRS (ductile coupled shear walls). Moreover, a simplified initial cost analysis (materials and labor) design was performed. The findings of this paper indicate that the use of UHPC is capable of improving the seismic performance behavior of the lateral system as well as reducing the total initial costs.