Lateral Force-resisting System Research Articles

Machine learning-based surrogate resilience modeling for preliminary seismic design

Early decisions made during the preliminary seismic design, particularly regarding the stiffness and strength of the selected lateral force-resisting system, have a significant impact on seismic resilience. However, the effects of these crucial decisions on resilience are not explicitly assessed until the end of the routine code-based design. The indirect design approach can bring about substantial design iterations that involve computationally expensive resilience assessment. For the support of direct resilience-informed design, this paper employs machine learning techniques to develop a surrogate model that maps site and building features to resilience indices. The surrogate model aids design practitioners in selecting satisfying design combinations of stiffness and strength in the preliminary seismic design. It provides real-time feedback on the resulting resilience, drastically reducing the time and effort required for iterative design revisions. To demonstrate the effectiveness of the proposed approach, a data set of 10,000 steel moment-resisting frames (SMRFs) with wide-ranging design combinations is created; additionally, six regression algorithms, including linear regression, support vector regression, multi-layer perceptron, k-nearest neighbors, decision tree, and extreme gradient boosting (XGBoost), are used to establish the surrogate model. Among the six algorithms, XGBoost performed the best in terms of the lowest RMSE (0.031) and the highest R2 (0.97) for the test set. Identified by the SHapley Additive exPlanations (SHAP) approach, the seismic hazard-related design basic acceleration and the stiffness-related building period coefficient have the most significant impact on the prediction of XGBoost. This enables a physical and quantitative understanding of the surrogate estimates.

Explainable AI model for predicting equivalent viscous damping in dual frame–wall resilient system

A prominent challenge in applying the direct displacement-based design (DDBD) method to the proposed dual frame–wall lateral force-resisting system lies in determining the equivalent viscous damping ratio (EVDR). However, the strong nonlinearity and complexity behind the equivalent procedure lead to limited choice, mostly trial and error based on experience, to explain and predict the EVDR in the context of traditional research. This study employs the XGBoost method to unravel intricate relationships of EVDR using over 5 million data points from nonlinear time-history (NLTH) analyses, encompassing various parameters including the fundamental period, ductility, subsystem stiffness ratios, post-yielding stiffness ratios of the subsystems and ground motion types. SHapley Additive exPlanations (SHAP) values consistently identify critical features relevant to the equivalent procedure. Comprehensive feature ablation tests further illuminate the robustness and susceptibility of each model. Additionally, the incorporation of Local Interpretable Model-agnostic Explanations (LIME) for local interpretability provides insights into the intricate decision-making mechanisms inherent in each model’s predictions. Both the predicting results from machine learning (ML) and traditional method are also compared. Findings highlight the relative importance of features for EVDR and present a refined prediction model. It underscores the pivotal role of model interpretability in reinforcing confidence in complex models and advocates for leveraging ML techniques to enhance the effectiveness and efficiency of the DDBD method in structural design.

Defining Design Parameters for Controlled Rocking Braced Frames to Control Seismic Losses

ABSTRACT Controlled rocking braced frames (CRBFs) are a self-centering lateral force-resisting system aimed at reducing structural damage potential. Previous research has shown that relatively low design forces for rocking and for structural elements in CRBFs would be acceptable based on collapse fragility analysis. However, past studies have also highlighted the potential for significant story drifts and for increased demands on acceleration-sensitive nonstructural components installed in buildings with CRBFs. Therefore, while CRBFs have demonstrated acceptable performance in terms of collapse across a wide range of design options, these design options must be evaluated considering the performance of nonstructural components if the intended low-damage potential of CRBFs is to be fully realized. To address this need, this paper investigates the influence of two key design parameters on seismic losses of buildings with CRBFs, namely the response modification factor (R) for the rocking joint design and the amplification factor (γ) used to incorporate higher-mode forces into the capacity design of frame members. Three different heights of CRBF buildings are designed using different design options, with values of R ranging from 5 to 12 and with higher-mode forces considered based on two seismic intensity levels: the design earthquake (DE) and the maximum considered earthquake (MCE). Then, following an assessment of structural responses, the paper’s primary emphasis is on earthquake-induced economic losses. While the computed total expected annual losses (EALs) using various design options are remarkably similar, the distribution of losses attributed to collapse or to nonstructural components varies. The CRBFs with lower resistance to rocking exhibit greater losses attributed to collapse and to drift-sensitive nonstructural components, but this is counterbalanced by a simultaneous reduction in losses related to acceleration-sensitive nonstructural components. Furthermore, in taller CRBF buildings, using amplified higher-mode forces based on the MCE level slightly decreases total EALs compared to those using the DE level, primarily due to a reduction in collapse losses.

Cyclic response sensitivity of coupled composite plate shear walls/concrete filled (CC-PSWs/CF)

A composite plate shear wall/concrete filled system, also known as “SpeedCore”, is a new lateral force-resisting system used as core walls in mid- and high-rise buildings. This composite wall system eliminates some of the conventional construction requirements in reinforced concrete core walls, resulting in faster construction and cost savings. This paper aims to identify factors affecting the cyclic response and limit states of coupled composite plate shear walls/concrete filled (CC-PSWs/CF). A statistical sensitivity analysis is performed using the Design of Experiments method. Finite element models of walls are developed and analyzed under cyclic loading. The accuracy of the finite element simulation is validated by using results from past experimental and numerical studies. The sensitivity analysis evaluates the effect of eight factors and their interactions on the lateral response of CC-PSWs/CF systems. Ten response parameters are considered, including the system initial stiffness, the onset of steel yielding in coupling beams and walls, the onset of compressive cracking of concrete in coupling beams and walls, coupling beam first and last steel yielding and plastic hinge in concrete, and the system lateral load capacity. The results show that the wall length is the most influential factor affecting all the response variables. The wall steel area ratio, steel yield strength, concrete compressive strength, wall thickness, and the coupling beam steel ratio and span-to-depth ratio affect at least four response variables.

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.