Lateral Force-resisting Systems Research Articles

SEISMIC DESIGN RULES FOR LIGHTWEIGHT STEEL SHEAR WALLS WITH WOOD PANEL SHEATHING WITHIN THE EUROCODE FORMAT

Within the 2nd-generation of Eurocodes several new lateral force resisting systems (LFRS) typically used in lightweight cold-formed steel (CFS) buildings have been introduced, including shear walls with wood sheathing (SWWS). Therefore, extensive studies have been carried out to define the seismic design parameters according to the format of European code for seismic design, i.e. Eurocode 8. In current version of the 2nd-generation Eurocode 8 (prEN1998-1-2, CEN 2022), in case of SWWS the behaviour factor has been defined based on the FEMA P695 [18] methodology, whereas the other seismic design parameters have been set based on assumption validated with analyses on limited case studies. To overcome this lack, specific research devoted to defining the main seismic design parameters for SWWS belonging to Ductility class 3 (DC3) according to prEN1998-1-2 (CEN 2022) has been carried out at the University of Naples “Federico II”. The research shows that the Easley et al (1982) method gives consistent in-plane horizontal wall resistance predictions if the shear resistance of wood panel-to-steel sheet screw connections (sheathing connections) is evaluated with reliable approaches and formulas for the evaluation of the shear resistance of sheathing connections have been calibrated. Based on the results obtained from this research, a partial safety factor for resistance evaluation of SWWS according to limit state design (LSD) equal to 1.3 is proposed and an overstrength (expected resistance) factor for the design of non-ductile elements according to capacity design equal to 1.7 is recommended.

Industrial Building Structure Planning With Cranes

Industrial building structure planning complies with standards and regulations, such as Procedures for Earthquake Resistance Planning, Minimum Loads for Building Design, and Specifications for Structural Steel Buildings. Vertical and lateral loads are fundamental to the structure's load flow process. Industrial buildings handle roof, wind, earthquakes, crane, and wall loads. Structural design must consider these elements, including the choice of lateral force-resisting systems such as X-bracing. In determining building loads, including earthquake and wind loads, various parameters such as wind speed, exposure category, and other factors must be considered by standard requirements such as SNI 1727-2020 and SNI 1726:2019. Selection of site class, wind direction, topographic, and ground surface elevation factors are essential in determining wind loads. This research method focuses on supporting structures consisting of purlins and girts in the context of industrial buildings. Purlins, made from hot or cold rolled steel, generally use C and Z profiles. Girts, made from cold or hot rolled steel, have profile variations such as C, Z, or hollow square sections. The girt structure design process determines dimensions, rod sag, internal requirements, and sag rod capacity.

Machine Learning Prediction Model for Boundary Transverse Reinforcement of Shear Walls

Due to their roles as efficient lateral force-resisting systems, reinforced concrete shear walls exert a tremendous degree of influence on the overall seismic performance of buildings. The ability to predict the boundary transverse reinforcement of shear walls is critical to the seismic design process, as well as in the overall evaluation and retrofitting of existing buildings. Contemporary empirical models attain low predictive accuracy, with an inability to capture nonlinearity between boundary transverse reinforcement and different influencing variables. This study proposes a boundary transverse reinforcement prediction model for shear walls with boundary elements based on the demand of ductility. Using the extreme gradient boosting machine learning algorithm and 501 samples, some 52 input variables are considered, and a subset with six features is selected, monitored, and analyzed using both internal methods (gain and cover) and external methods. The results (R2=0.884) display superior predictive capacity compared with existing models. Interpretation and error analysis are performed. Safety analysis is conducted to obtain references for use in practical engineering. Overall, this study presents a more accurate tool for use in seismic design and provides references for the evaluation and retrofitting of existing buildings. Our contributions hold significant implications for enhancing the safety and resilience of reinforced concrete structures.

Seismic response and performance prediction of steel buckling-restrained braced frames using machine-learning methods

Nowadays, Buckling-Restrained Brace Frames (BRBFs) have been used as lateral force-resisting systems for low-, to mid-rise buildings. Residual Interstory Drift (RID) of BRBFs plays a key role in deciding to retrofit buildings after seismic excitation; however, existing formulas have limitations and cannot effectively help civil engineers, e.g., FEMA P-58, which is a conservative estimation method. Therefore, there is a need to provide a comprehensive tool for estimating seismic responses of Interstory Drift (ID) and RID with novel approaches to fulfill the shortcomings of existing formulas. The Machine Learning (ML) method is an interdisciplinary approach that makes it possible to solve these types of engineering problems. Therefore, the current study proposes ML algorithms to provide a prediction model for determining the seismic response, seismic performance curve, and seismic failure probability curve of BRBFs. To train ML-based prediction models, Nonlinear Time-History Analysis (NTHA) and Incremental Dynamic Analysis (IDA) were performed on the 2-, to 12-Story BRBFs subjected to 78 far-field ground motions, and 606944 data points were prepared for different prediction purposes. The results indicate that the considered approaches are justified. For instance, the proposed ML methods have the ability to predict the maximum ID, maximum RID and maximum roof ID with the accuracy of even 98.7%, 95.2%, and 93.8%, respectively, for the 4-Story BRBF. Moreover, a general preliminary estimation tool is introduced to provide predictions based on the input parameters considered in the study.

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.

Comparative Performance Evaluation of Retrofit Alternatives for Upgrading Simply Supported Bridges Using 3D Fiber-Based Analysis

This study aims to select an effective mitigation approach from different alternatives to upgrade substandard RC bridges to meet the seismic performance objectives of current design standards. The performance assessment results for an existing benchmark bridge confirmed that the bent curvature ductility and bearing displacement control the seismic response. Thus, five contemporary retrofit solutions were investigated, including adding different supplementary lateral force-resisting systems (SLFRSs), replacing old bearings with those equipped with shape memory alloy (SMA), and combinations of these retrofit options. Fourteen earthquake records representing long- and short-period seismic events and the seismo-tectonic characteristics of a moderate seismic region were progressively scaled and applied separately in the two orthogonal directions of detailed simulation models representing the retrofitted benchmark bridge. This study provided insights into the impact of combining contemporary seismic risk mitigation techniques on improving the seismic performance of substandard bridges and presented a range of fragility functions for delaying structural damage and minimizing disruption of existing bridges to avoid traffic interruption. The dynamic response simulation results in the longitudinal direction (LD) confirmed that utilizing SMA bearings reduces curvature ductility and bearing displacement demands. Although the probabilistic assessment study in the transverse direction (TD) indicated that SMA bearings adequately reduce displacement demands, the bridge should be equipped with SLFRSs to overcome the bents’ high curvature ductility demands. Therefore, the most effective retrofit technique in TD is achieved using both SMA bearings and steel bracings.

Macro-Seismic Assessment for Residential Buildings Constructed in the Soviet Union Era in Almaty, Kazakhstan

Southern and southeastern Kazakhstan is a region of intraplate seismicity characterized by several destructive earthquakes. Almaty, the largest metropolis in this region, has many structures with different construction materials and seismic-resistant systems. Among them, residential buildings constructed in the Soviet Union era (before the 1990s) may possess low seismic resisting capacities due to limited seismic design and detailing provisions. Therefore, it is essential to assess seismic risks for these buildings. This paper collected information from a government agency (i.e., KazNIISA), including construction materials, lateral force-resisting systems, and structural ductility capacities for residential buildings constructed in this era. These buildings were then categorized in terms of their seismic vulnerabilities following the European Macro-seismic Scale (EMS-98). Vulnerability curves and probability of damages were developed under different earthquake intensities and peak ground accelerations. The likelihood of varying levels of damage was established for the design basis and maximum considered earthquakes in the Almaty region. It was found that unreinforced masonry and wood buildings tend to be very heavily damaged and even collapse under the maximum considered earthquake. The reinforced and precast concrete buildings have a high probability of heavy to very heavy damage, which may require further analytical assessment since the structure at this damage level will undergo a significant nonlinear response and has a high uncertainty in the seismic performance.

Seismic performance evaluation of steel buckling-restrained braced frames including SMA materials

The permanent deformation of the building after seismic excitations can be determined by the Maximum Residual Interstory Drift Ratio (MR-IDR), which may be used for measuring the damage states. Low-post yield stiffness of the steel buckling-restrained braced frame (BRBF) makes this system vulnerable to large MR-IDR after a severe earthquake event. To overcome this issue, this paper investigates the seismic limit state performances of low- to mid-rise BRBFs with two- to eight-story levels (i.e. 2-Story, 4-Story, 6-Story, and 8-Story) adopting different lateral force-resisting systems using Viscous Dampers (VDs) and Shape Memory Alloys (SMAs). For this purpose, BRBFs improved with different implementation of SMAs and VDs, and Incremental Dynamic Analyses (IDAs) were performed based on Maximum Interstory Drift Ratio (M-IDR) and MR-IDR demands. Results showed that VDs and SMAs can decrease the values of maximum moment and rotation of hinges of structural members. Implementing both SMAs and VDs can significantly improve the seismic performance level and collapse failure probability of BRBFs more effectively than using one of the VDs or SMAs; then, it can be recommended to control the MR-IDR of BRBFs. To use the results, graphical user interface has been developed to estimate the improvements in the M-IDR and MR-IDR demands.

Evaluation of Seismic Acceleration Demands on Mechanical Support Systems

Earthquakes are among the most influential force of nature that affect human life. Reconnaissance after the severe earthquakes pointed out that seismic performance of non-structural members and elements could be as significant as the structural members in lateral force-resisting systems. As such, it is important for design engineers to recognize the seismic demand on the mechanical systems that support the critical non-structural components (e.g., sprinklers, electrical and mechanical equipment, etc.) in terms of the safety during and after an earthquake as well as functionality and retrofitting cost after an earthquake. The primary goal of this study is to systematically investigate the seismic demands on the mechanical support systems of a typical mid-rise steel structure. For this purpose, non-linear time history analyses are carried out using a suite of ground motion acceleration records to evaluate the seismic demands on both seismic force-resisting system and the support system by means of inter-story drift angle and horizontal accelerations, respectively. Results obtained from the analyses are discussed considering the requirements stipulated in the current national and international buildings and recommendations are made.

A critical review of cold-formed steel seismic resistant systems: Recent developments, challenges and future directions

Cold-formed steel (CFS) systems have seen an increased application in the past few decades, especially in the construction of low- to mid-rise buildings. CFS members offer considerable structural and environmental advantages, such as low weight, ease and speed of construction, greater manufacturing flexibility, recyclability and low embodied carbon. Despite the significant potential offered by CFS structural systems, the seismic design of lateral force-resisting systems (LFRS) for CFS multi-story buildings is challenging. There are many different types of systems capable of providing the lateral load resistance capacity of the CFS framing, and this paper provides a comprehensive review of the research developments made in CFS braced-wall systems and moment-resisting frames, as the most conventional systems, to study their structural performance and identify the research gaps, challenges, and future directions. The major research developments are summarised in terms of load capacity, stiffness, energy dissipation capacity and failure mode. As an outcome of the crucial review, it was found that CFS LFRSs can generally offer more efficient design solutions regarding seismic characteristics such as high ductility and energy dissipation capacity. Despite a rather large body of research on CFS braced walls, it is necessary to assess the response of these systems in various aspects, such as developing an optimisation framework to withstand the combination of vertical and horizontal loading plus resist the impact of severe fire. With respect to moment-resisting frames, one of the main research needs is to develop systems suitable for multi-story buildings, especially in seismic regions.

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.

Failure Mode Detection of Reinforced Concrete Shear Walls Using Ensemble Deep Neural Networks

Reinforced concrete structural walls (RCSWs) are one of the most efficient lateral force-resisting systems used in buildings, providing sufficient strength, stiffness, and deformation capacities to withstand the forces generated during earthquake ground motions. Identifying the failure mode of the RCSWs is a critical task that can assist engineers and designers in choosing appropriate retrofitting solutions. This study evaluates the efficiency of three ensemble deep neural network models, including the model averaging ensemble, weighted average ensemble, and integrated stacking ensemble for predicting the failure mode of the RCSWs. The ensemble deep neural network models are compared against previous studies that used traditional well-known ensemble models (AdaBoost, XGBoost, LightGBM, CatBoost) and traditional machine learning methods (Naïve Bayes, K-Nearest Neighbors, Decision Tree, and Random Forest). The weighted average ensemble model is proposed as the best-suited prediction model for identifying the failure mode since it has the highest accuracy, precision, and recall among the alternative models. In addition, since complex and advanced machine learning-based models are commonly referred to as black-box, the SHapley Additive exPlanation method is also used to interpret the model workflow and illustrate the importance and contribution of the components that impact determining the failure mode of the RCSWs.

Contemporary and Novel Hold-Down Solutions for Mass Timber Shear Walls

‘Mass timber’ engineered wood products in general, and cross-laminated timber in particular, are gaining popularity in residential, non-residential, as well as mid- and high-rise structural applications. These applications include lateral force-resisting systems, such as shear walls. The prospect of building larger and taller timber buildings creates structural design challenges; one of them being that lateral forces from wind and earthquakes are larger and create higher demands on the ‘hold-downs’ in shear wall buildings. These demands are multiple: strength to resist loads, lateral stiffness to minimize deflections and damage, as well as deformation compatibility to accommodate the desired system rocking behaviour during an earthquake. In this paper, contemporary and novel hold-down solutions for mass timber shear walls are presented and discussed, including recent research on internal-perforated steel plates fastened with self-drilling dowels, hyperelastic rubber pads with steel rods, and high-strength hold-downs with self-tapping screws.

Influence of composite floor slab on seismic performance of steel plate shear walls

Steel plate shear walls (SPSWs) consisting of unstiffened thin steel plates attached to the horizontal and vertical boundary steel elements are often used as the lateral force-resisting systems in buildings. The presence of composite floor slabs may not only alter the force demands on the boundary elements but also influence the failure mode of SPSW systems under seismic loading. This study addresses this research gap through experimental investigation of a single-story single-bay SPSW with floor slab subjected to constant gravity load and gradually increasing reversed cyclic lateral displacement. A ductile detailing of beam-column joint has been proposed as an alternative to the conventional reduced beam sections. The test specimen demonstrated a stable hysteretic response up to 5.5% story drift without significant reduction in the lateral strength. The proposed connection ensured the desired hinge mechanism and high ductility of the SPSW specimen. Additionally, numerical analysis of SPSW systems with and without composite slabs has been conducted to predict their load-resisting capacities and modes of failure under lateral loading. The presence of the floor slab increased the axial load demand on the vertical boundary element and the shear deformation demand on the horizontal boundary elements of the SPSW system.

Cyclic Performance of Corrugated Steel Plate Shear Walls with Beam-Only-Connected Infill Plates

Lately, Corrugated Steel Plate Shear Walls (CSPSWs) have gained significance and reputation for being effective lateral force-resisting systems. Corrugated plates are characterized by greater out-of-plane stiffness and buckling stability than flat plates, ensuring their enhanced hysteretic behavior. In ordinary Steel Plate Shear Walls (SPSWs), infill plates are fixed to beams and columns. But, detaching the infill plate from columns and connecting it to the beams only is assumed here as a method for reducing column demands. The current study explores the cyclic performance of CSPSWs with beam-only-connected infill plates. The design of a one-story single-bay specimen was done and its finite element model was developed. Parametric studies have targeted CSPSWs with different geometric variables, including orientation, thickness, and aspect ratio of the infill plate. Noteworthy responses were ultimate strength, initial stiffness, energy dissipation capacity, and force-deformation relationship. The obtained results indicated that selecting the right geometrical parameters could yield a desirable cyclic performance. Finally, an analytical method was proposed for calculating the ultimate shear strength of beam-only-connected CSPSWs.

Investigation of bearing capacity of the proposed circular lateral bracing system with friction seat connection with column

To reduce the damage and casualties caused by earthquakes, researchers made efforts to introduce seismic resistant structural systems. One of the new lateral force-resisting systems is the steel circular braced system called “Ogrid”. Previous studies shown the high energy dissipation and ductility of this system. This system has a high capacity to withstand nonlinear deformations after the formation of the first plastic hinge until collapse. In the present study, an attempt has been made to introduce a new type of this brace with different types of brace connection to beam and column and to evaluate its performance. For this purpose, the OGrid is used and different connections of the frame to the circular brace that embrace the connection of the brace to the beam and to the columns, as well as comparing the presence of friction and the absence of friction between the brace and the frame are modeled and the results are reviewed. It is found that by releasing the connection of the circular brace with I-shaped cross section to the column and creating friction between them with a coefficient of 0.5, the bearing capacity increases up to 22% compared to the restrained connection. In this case, before yielding, softening is observed in the proposed model, but after yielding compared to the model with restrained connection, better energy dissipation occurs due to deformations in the circular brace. Meanwhile, bearing capacity increases up to 8% by considering friction between the brace and increases up to 17% by considering friction between the brace and the column comparing with the released connections. On the other hand, the use of H-shaped circular brace with friction connection to the column and/or beam is not recommended due to the reduction of bearing capacity by at least 9% compared to the restrained connection.

Experimental investigation into the seismic behavior of squat reinforced concrete walls subjected to acid rain erosion

Acid rain erosion will continuously deteriorate the physical and mechanical properties of materials and finally degrade the seismic performance of reinforced concrete (RC) structures. Nevertheless, the effect of acid deposition on squat RC walls, an important part of lateral force-resisting systems, has not been reported in existing research. Thus, in this paper, an artificial climate simulation method was used to accelerate the acidic attack process on four squat RC wall specimens with an aspect ratio of 1.0. Then quasi-static loading tests were conducted to observe their cyclic behavior under different acid rain spraying cycles (ARSCs). The results show that as ARSCs increase, the degree of degradation of concrete strength and the corrosion weight loss of steel bars have a rising trend, and the bearing capacity and deformation capacity of the squat RC walls deteriorate gradually. Simultaneously, the ratio of shear displacement to total lateral displacement increases, indicating a more noticeable shear failure characteristic with the addition of ARSCs. Moreover, the failure mode shifts from the mixed flexure and diagonal compression mode to the diagonal tension mode with a significant decrease in ductility and energy-dissipation capacity. It is also found that the degradation rate of the shear strength of squat walls under acid rain erosion is larger than that of the flexural strength, which may lead to the transition of failure mode.

Lateral Force Resisting Systems Made of Cold-Formed Steel Material: Proposal of Seismic Design Criteria for 2nd Generation of Eurocode 8

The current edition of Eurocode 8 does not cover the design of the Cold-Formed steel (CFS) building structures under the seismic design condition. As part of the revision process of Euro-code 8 to reflect the outcomes of extensive research carried out in the past decade, University of Naples “Federico II” is involved in the validation of existing seismic design criteria and development of new rules for the design of CFS systems. In particular, different types of Lateral Force Resisting System (LFRS) are analyzed that can be listed in the second generation of Eurocode 8. The investigated LFRS’s include CFS strap braced walls and CFS shear walls with steel sheets, wood, or gypsum sheathing. This paper provides the background information on the research works and the reference design standards, already being used in some parts of the world, which formed the basis of design criteria for these LFRS systems. The design criteria for the LFRS-s common to CFS buildings would include rules necessary for ensuring the dissipative behavior, appropriate values of the behavior factor, guidelines to predict the design strength, geometrical and mechanical limitations.

Cyclic behavior of wood-frame shear walls with vertical load and bending moment for mid-rise timber buildings

In light wood-frame buildings, the gravitational and lateral force-resisting systems are composed of floor diaphragms and shear walls. During an earthquake, these walls are subjected to the simultaneous action of in-plane vertical force, shear force, and in-plane bending moment. In a mid-rise building, these internal forces can reach large magnitudes, especially on the lower stories, and could have an important influence on the lateral behavior of the walls. The historical use of light wood-frame construction has been in low-rise buildings. Consequently, few investigations have analyzed the effects of high gravitational forces or in-plane bending moment on the lateral behavior of wood shear walls designed for multi-story buildings. This paper presents an investigation of the cyclic lateral behavior of light wood-frame shear walls, designed for mid-rise buildings, subjected to large axial compressive load and in-plane bending moment. Eight wall specimens were experimentally tested with a cyclic lateral displacement protocol, a constant compressive load, and a cyclic in-plane bending moment. The effects of axial compressive load and in-plane bending moment were analyzed. Also, the wall length and the spacing of sheathing nails were varied to study the effects of these variables on the response. A numerical study was performed to show how these effects could influence the response of mid-rise timber buildings. An improvement in the lateral performance of the walls was observed compared to walls tested without compressive force nor bending moment, showing an increase in stiffness, load-carrying capacity, and dissipated energy.

Seismic fragility of steel special truss moment frames with multiple ductile vierendeel panels

Special truss moment frames (STMFs) are used as the lateral force-resisting systems in buildings. Under seismic loading, the hysteretic energy dissipation in STMFs mostly occurs through the flexural plastic hinges developed in the special segments only. This study presents the seismic fragility assessment of low to high-rise STMFs with ductile Vierendeel panels as the special segments. Four building frames (i.e., 3-, 6-, 9-, and 15-story) with three different configurations of special segments in STMFs have been considered as the study frames. Nonlinear incremental dynamic analyses of the study frames have been carried out using computer software PERFORM-3D using forty-four ground motion records. The probability of exceeding the drift levels corresponding to three performance levels, viz., immediate occupancy (IO), life safety (LS), and collapse prevention (CP) of the study frames have been investigated under the design-basis earthquake and maximum considered earthquake hazard levels. The presence of intermediate vertical members in the Vierendeel panels resulted in the gradual loss in the post-peak lateral strengths of STMFs. The use of multiple Vierendeel panels significantly reduced the probability of failure of low-rise (namely, 3- and 6-story) STMFs. However, STMFs with single Vierendeel panels are found to be beneficial in 9- and 15-story building frames. The inter-story drift limits have been proposed for the performance levels of IO, LS, and CP of STMFs.