Coupled Wall System Research Articles

Experimental and numerical investigation of the cyclic behaviour of coupled balloon-type CLT shear walls with high-capacity base connections

Mass timber buildings have gained global popularity due to the increasing availability and affordability of mass timber products and an increasing awareness of the sustainability of timber construction. This paper presents an experimental and numerical study on coupled balloon-type cross-laminated timber (CLT) shear walls with the aim of overcoming the capacity limitations of platform CLT shear walls. Using self-tapping screws to create innovative hold-down solutions, three two-storey coupled CLT shear walls were cyclically tested and the results demonstrated that the proposed coupled wall systems could achieve significantly higher lateral strength (over 400 kN) and initial stiffness (up to 14 kN/mm) compared to platform CLT shear walls in literature. The cyclic test results were used to validate a finite element CLT shear wall model in CLTWALL2D. The calibrated model was then used to run a parametric study of a series of balloon-type CLT shear walls up to twelve storeys (42 m) in height. This study provided evidence that coupled balloon-type CLT shear walls with high-capacity screwed connections have the potential of reaching high strength and stiffness with the displacement ductility factor μ = 2–4.

New OpenSees material model for simulating reinforced concrete shear walls subjected to coupled axial tension and cyclic lateral loads

In high-rise buildings, reinforced concrete (RC) shear walls, particularly those forming part of coupled wall systems or core wall systems, may be subjected to coupled axial tension and cyclic lateral loads during strong seismic events. A new two-dimensional material model named the “Fixed Angle Model Considering Crack Sliding” (FAM-CS) was proposed for simulating the nonlinear behavior of RC walls subjected to axial tension and cyclic lateral loads. The proposed model was implemented in the OpenSees platform. Nonlinear constitutive models for shear aggregate interlock effects of concrete and dowel action of rebars were incorporated into the proposed model to represent the shear transfer mechanisms along concrete cracks. The proposed model was validated against the test data of six wall specimens subjected to coupled axial tension and cyclic lateral loads. The results indicated that the proposed model reasonably predicted the lateral strength capacity (an average error of 6.2 %) and the residual strength at the maximum drift loading (an average error of 12.3 %) of the specimens. For comparison, three other commonly used models, the Shear-Flexure Interaction Multiple-Vertical-Line-Element-Model, the multi-layer shell element model and the Cyclic Softened Membrane Model were adopted for the simulation of the specimens. Compared with the three existing OpenSees models, the newly implemented material model provided improved predictions of the wall hysteretic behavior with respect to lateral strength capacity, lateral strength degradation, pinching characteristics and cyclic stiffness degradation. In addition, the proposed model reasonably captured the localized failure pattern as well as the energy dissipation characteristics of the test specimens. Finally, a mesh sensitivity study was conducted to assess the robustness of the proposed model. The results revealed that the proposed model was robust regarding the lateral load-drift responses of RC walls, with a mesh size ranging from approximately one to three times the average crack spacing.

High-dimensional multi-objective optimization of coupled cross-laminated timber walls building using deep learning

This paper introduces a deep learning-based multi-objective optimization framework, applying for advancing the design of the Cross-Laminated Timber Coupled Wall system. While traditional optimization methods often struggle with the curse of dimensionality in high-dimensional problems, the approach proposed in this study employs an autoencoder to effectively reduce the dimensionality of the design space. Subsequently, a neural network establishes a mapping between input variables and latent spaces, with another neural network forming the crucial link between these latent variables and the output responses. The proposed framework is integrated into the design process of a 20-story Cross-Laminated Timber Coupled Wall system, where uncertainties inherent in connection elements are systematically addressed to optimize the structural parameters. The non-dominated sorting genetic algorithm-II is utilized to estimate optimal design variables by minimizing three conflicting objective functions, thereby generating a Pareto front. This optimized design is then bench-marked against three deterministic models with varying coupling beam shear strengths. A two-dimensional numerical model developed in OpenSees facilitates nonlinear time history analysis using 50 bi-directional ground motion records, representative of the seismicity of Vancouver, Canada. The results of this study not only highlight the efficacy of the deep learning-based framework in enhancing the structural integrity and resilience of high-rise timber structures in seismic regions but also significantly contribute to the evolution of computational approaches in structural engineering.

Experimental and numerical evaluation of seismic behavior of coupled walls connected by post-tensioned, unbonded, precast concrete coupling beams

To investigate the seismic performance of coupled shear walls, which are connected by post-tensioned, unbonded, precast concrete coupling beams (PCCB), two 1/7-scale experiments with 8-story coupled shear walls under cyclic lateral loadings were conducted. Coupling of concrete shear walls is achieved by post-tensioning concrete beams to the wall piers using unbonded post-tensioning tendons (UPT) at the floor and roof levels. Experimental results show that little damage occurs in the coupling beams and the wall regions when the specimen undergoes large nonlinear displacements. The residual displacements of the specimen are small because of the restoring effect of the post-tensioning force. The seismic performance of three systems including CW-RC (coupled wall systems that use traditional RC coupling beams), CW-UP (coupled wall systems which use only post-tensioning tendons without steel reinforcement through the beam-wall joints), and CW-HUP (shear walls and PCCB that use combinations of steel reinforcement and post-tensioning tendons) are evaluated by means of nonlinear dynamic analysis. The calculation results indicate that the inter-story drift and peak lateral displacements of CW-HUP and CW-UP are greater than that of CW-RC, whereas the residual deformations are reduced because of the self-centering effect of the post-tensioning tendons.

Multi-variate seismic fragility assessment of CLT coupled wall systems

The cross-laminated timber coupled wall (CLT-CW) system, a recently proposed timber-based structural system, has limited understanding of its seismic performance. The existing research in probabilistic seismic fragility assessment (PSFA) of CLT buildings reveals gap, particularly regarding comprehensive evaluation of CLT-CW systems and the impact of its various design parameters. To fully describe the state of the post-earthquake performance of structures, state-of-the-art studies recommend using multi-variate fragility analysis. Accordingly, this article presents a bi-variate PSFA of CLT-CW systems using two engineering demand parameters: the maximum and residual inter-story drift ratios. For the seismicity of Vancouver, British Columbia, Canada, 11 prototype buildings are evaluated considering different design parameters: coupling ratio, coupling beam shear force profile, CLT wall configuration, building story height, and ductility-related seismic force modification factor. Bi-dimensional numerical models of the systems are developed in OpenSees, and incremental dynamic analyses are performed using 30 ground motion records. Three limit state capacities and three limit state function combinations are utilized to develop probabilistic seismic fragility curves. The fragility curves under the different limit state function combinations are compared, and the effect of the different design parameters is investigated. This study contributes to a deeper understanding of the seismic performance of CLT-CW systems, assisting engineers and researchers in assessing seismic risk and developing seismic-resilient structures.

Innovative hybrid coupled wall systems to resist seismic action – HYCAD

AbstractThis article summarizes the research carried out in the ongoing HYCAD project, which aims to improve the performances of a hybrid coupled wall (HCW) system for buildings in seismic areas, by further developing the HCW originally studied in the RFCS project INNO‐HYCO. This HCW system consisted of a reinforced concrete (RC) wall coupled with two steel side‐columns via steel coupling links. Encouraging outcomes were obtained such as: controlled post‐elastic ductile behaviour under medium‐ and high‐intensity earthquakes, suitable lateral stiffness, seismic energy dissipation concentrating in the easily‐replaceable steel links and very limited damage in the RC wall. However, advanced studies were required to bring this system into practice, addressing issues and develop advancements in the analysis, design, and detailing. This article summarizes the primary steps taken towards that purpose. Five new components were chosen in order to improve the performance of the HCW system: (1) Link‐to‐wall connections using post‐tensioned tendons; (2) Composite walls with encased steel profiles instead of a conventional RC wall; (3) Rocking coupled wall system; (4) Dissipating devices as links and (5) Precast double slab wall systems. Combining these components, four new HCW systems were developed, pre‐designed and analysed through numerical and experimental studies. Advanced yet simple techniques were proposed for the numerical analyses while test specimens are used to characterize local and global behaviour.

Seismic behaviour of connections between replaceable coupling beam and double skin composite shear wall

In order to optimize the performance of hybrid coupled wall system, a novel of connections between replaceable coupling beam (RCB) and double skin composite shear walls (DSCSWs) are proposed. The seismic design of RCB-to-DSCSW connection is very important for structural safety. This study investigates the seismic behaviour of RCB-to-DSCSW connections. Two specimens with different layout schemes of embedded rebars and one with embedded steel I-beam were subjected to reversed cyclic loading. The failure process of all the specimens was basically the same, mainly by steel faceplate local buckling, weld tensile fracturing and the concrete crushing at both ends of the joint. The strength and ductility of connections were highly affected by the weld tensile fracturing and concrete crushing. At the current loading level or the next loading level of weld tensile fractured, the connection specimens reached its peak loading capacity, and then the concrete rapidly crushed. The ductility coefficients of all the specimens were smaller than those of RC structures. In addition, the mechanical properties of these two kinds of embedded rebar connections were similar. The steel I-beam connection exhibited higher initial stiffness. Under the same rotation of loading, the cumulative energy consumption of the steel beam was higher. Finally, according to the stress pattern of each component, the simplified mechanical model and calculation formulae of the connection bearing capacity were developed.

Experimental evaluation of post-tensioned hybrid coupled shear wall system with TADAS steel dampers at the beam-wall interface

Considering the optimal seismic resistance of coupled shear walls and the perks of self-centering systems, throughout this research, the hysteretic performance of post-tensioned concrete “Coupled Wall” (CW) subassemblies with “Steel Coupling Beam” (SCB) equipped with “Triangular Added Damping and Stiffness” (TADAS) steel dampers was experimentally evaluated. To dissipate the energy input from the earthquake, metallic yield dampers of the TADAS type were used at the connection zone between the beam and the wall in this structural system. Using a SCB rather than a concrete beam was suggested to reduce beam damage and maintain the system’s self-centering capabilities during lateral loading. High-strength steel strands were employed to generate post-tensioning along the beam’s longitudinal axis in the “Coupled Wall System” (CWS) to reduce structure residual deformation under seismic loading. In the first portion of this research, an experimental assessment of the load–displacement behavior of TADAS dampers exposed to cyclic loads was performed. Then, at floor level, three ⅔-scaled CW subassemblies were constructed using a post-tensioned SCB and subjected to lateral quasi-static cyclic loading of increasing amplitude. Various post-tensioning stresses were applied to one subassembly lacking energy dissipation devices and two subassemblies with TADAS dampers. The findings demonstrate that TADAS-equipped subassemblies can endure major non-linear deformations up to 8% drift without struggling either residual deformation or severe injury. Installing TADAS dampers at the beam-wall interface heightened the specimens’ capacity to withstand lateral loads by 71% to 90% and considerably increased their potential to dissipate energy.

Seismic performance of self-centering hybrid coupled wall systems: Preliminary assessments

Hybrid Coupled Wall (HCW) systems consist of reinforced concrete walls connected with steel coupling beams. HCWs benefit from the superior lateral stiffness of the reinforced concrete walls, while the coupling mechanism reduces the moment demand at the base of the walls. The present study investigates the seismic performance of a new HCW system equipped with friction-damped self-centering coupling beams and examines the efficiency of the new system in reducing residual deformations. The coupling beams of the intended HCW system consist of self-centering links, which can be easily repaired after severe earthquake events. The self-centering system utilized in this study features the following advantages distinguish it from conventional self-centering solutions: (i) it eliminates the coupling beams elongation problem (ii) it facilitates the application of pre-fabricated self-centering components to mitigate uncertainties raised by post-tensioning the connections on site. In this paper, the seismic behavior of the proposed lateral load-bearing system is investigated under several ground motion records and intensities. It is demonstrated that the applied self-centering mechanism has the capacity to minimize earthquake-induced residual deformations and repair time without increasing the damage level expected for the concrete walls in conventional HCWs.

Design and cyclic testing of bolted end plate connections between steel link beams and cross-laminated timber for coupled shear walls

Coupled cross-laminated timber (CLT) wall systems with ductile steel link beams offer an efficient, high-capacity lateral load resisting system for buildings in earthquake-prone regions. This study proposes a type of beam to CLT wall connection using a bolted end plate in a notched CLT panel edge to create a semi-rigid joint. A simplified analytical method is proposed to predict the connection strength and is compared against the results of full-scale experiments. The experimental strength values were all greater than the predictions from the proposed method. Therefore, the strength method seems conservative and is suitable for the capacity design of similar connections in coupled wall systems. The final specimen in the test programme was capacity designed and its cyclic test results demonstrated adequate connection strength and relatively high stiffness were achieved for a 200 mm-deep wide flange link beam. The specimen’s link beam yielded at an applied shear load of 180kN and reached a maximum strength of 278kN while dissipating a large amount of energy through steel yielding. The bolted end plate connection appears to be a practical solution for application in coupled CLT shear walls.

Evaluation of seismic response of coupled wall structure with self-centering and viscous damping composite coupling beams

In order to reduce the residual displacement and floor acceleration of coupled wall structures, a novel self-centering and viscous damping composite coupling beam is proposed. The proposed coupling beam consists of the elastic beam segments and the fuse part, which incorporates self-centering friction dampers and viscous dampers. The self-centering friction damper can provide strength and stiffness for the proposed coupling beam and reduce the residual displacement of the coupled wall structure. The viscous damper can add supplemental damping to the system, and this can control the peak lateral displacement demands and floor accelerations of the structure. Moreover, the proposed coupling beam can eliminate the beam elongation effect of the self-centering coupling beam with a rocking behavior. Design methodology and nonlinear numerical model of the proposed coupling beam are developed. The seismic behaviors of the coupled wall structure with the self-centering and viscous damping composite coupling beams (CW-SCVCCB) are assessed and compared with the structure with reinforced concrete coupling beams (CW-RCCB), the structure with steel coupling beams (CW-SCB) and the structure with self-centering coupling beams (CW-SCCB). Analysis results showed that the supplemental viscous damping can effectively reduce the peak interstory drift ratio and floor accelerations of the structure. The residual displacement of the novel coupled wall system is larger than that of the CW-SCCB, however, it is significantly reduced compared with the CW-SCB and the CW-RCCB.

Performance of coupled CLT shear walls with internal perforated steel plates as vertical joints and hold-downs

Cross-laminated timber (CLT) constitutes a promising solution for numerous structural applications, including as shear walls in lateral load resisting systems. The research presented herein investigated the viability of internal-perforated-steel-plates with self-drilling dowels as high-performance connections for CLT shear walls. To achieve this objective, quasi-static monotonic and reversed cyclic tests at the material level (dowels and steel plates), the component level (shear connections and hold-downs), and the system level (full-scale shear walls) were conducted. The component level tests demonstrated that it is possible to control the strength, stiffness, and ductility only through the yielding of the internal-perforated-steel-plates and avoid bending of the self-drilling dowels or crushing of the CLT. The full-scale shear walls achieved coupled-wall kinematic behaviour at yield and ultimate loads, enhancing the energy dissipation. The strength of the coupled wall system was governed by the capacity of the vertical joints.

Seismic Performance of a Hybrid Coupled Wall System Using different Coupling Beam Arrangements

This study implemented multirecord nonlinear dynamic and fragility analysis in order to gain more insight into the hybrid coupled wall (HCW) system. Two potentials are used to construct coupling beams, which are the typical steel coupling beam and the replaceable steel coupling beam. Furthermore, an innovative idea for replaceable beams is discussed utilizing reinforced concrete infill instead of steel stiffeners. A new simplified FE model for such beam is carried out in order to explore how this new beam influences the seismic performance of HCW system. An additional equivalent bare RC wall case study is also taken into account for a comprehensive comparison. A precise 2D modelling method using Opensees platform is adopted after validation against experimental and complex 3D numerical simulations. The results indicate a good effect of the replaceable coupling beams concept upon reducing the vulnerability of wall piers under low and moderate events. In terms of coupling beams fragility, the replaceable steel coupling beams also demonstrate better damage resistance when compared with typical steel beams under low and moderate seismic events. Using reinforced concrete infill instead of steel stiffeners can significantly protect beams maintenance without affecting wall piers’ vulnerability.

Test, Analysis, and Seismic Design Approach of RC Infill Walls Isolated by PVC Tubes in Coupled Shear Wall Systems

Test, Analysis, and Seismic Design Approach of RC Infill Walls Isolated by PVC Tubes in Coupled Shear Wall Systems

Simplified Design of Coupled Shear Wall Systems for Typical Building Configuration

Simplified Design of Coupled Shear Wall Systems for Typical Building Configuration

Moment-resisting self-drilling dowel connections between steel link beams and CLT for coupled walls

Coupled cross-laminated timber (CLT) walls can be created by connecting steel link beams between adjacent CLT wall panels and are an efficient alternative to conventional cantilevered CLT shear walls. Effective coupling in the coupled wall system requires the beam to wall connections to have adequate strength to ensure a ductile link beam response and adequate stiffness to yield the link beams at relatively low inter-storey drifts. This study evaluates beam to wall connections with a group of self-drilling dowels (SDDs) installed through an 8mm steel knife plate to connect 200UB18 steel link beams to 5-ply CLT walls. A simplified method for determining the connection strength is presented and used to capacity design the test specimens. The capacity design method was validated for the tested specimens because the damage was concentrated in the steel link beams and the connection’s peak strength was not exceeded. This study indicates that the SDD connections may be a feasible beam to wall connection solution in coupled CLT wall systems because the capacity protected connections had adequate strength and relatively high stiffness.

Experiments on Partially Coupled Concrete Wall System with Perforated Steel Beam

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A novel damped braced tube system for tall buildings in high seismic zones

SummaryThe damped outrigger system is known to efficiently provide additional damping in buildings with heights of over 250 m. However, particularly for supertall buildings in the center of Tokyo, Japan, the outrigger truss from the center core to the exterior columns need to span distances of more than 20 m. This increases the flexural stiffness demand on the outrigger that leads to larger truss depths making the damped outrigger system inefficient. For such tall buildings with large plans, a new damping modification system, the “damped braced tube system” is proposed, where the exterior surface of the elastic mega braces are partially removed vertically to create a split and are replaced with dissipaters (energy‐dissipation devices). The damped braced tube system enhances the seismic performance as the exterior surfaces of the elastic mega braces work together with the damped slits like in a coupled wall system and increases the overall damping ratio. In this paper, numerical models were constructed based on a real project in Japan consisting of a 397‐m supertall building employing the damped tubular braced system using oil dampers (referred to as viscous dissipaters). A series of generalized response spectrum based numerical analyses and optimizations were performed to minimize the seismic response. The proposed system exhibited improved damping performance with the first to third mode damping ratios reaching to more than 7% while providing a wide range of options for dissipater distribution for design. Finally, the elevation of the slit's base is recommended to be equal to 0.22 of the total building height considering the trade‐off relationship between the first modal damping ratio and the fundamental period.

The Effect of a Rigid Connection between the Slab and the Coupled Beam on the Seismic Performance of the Coupling Wall System

The evolution of the construction building is one of the urgent matters in the current era, especially for high and medium-rise buildings. The widely used frame shear wall system has the main sign for the resistance of the lateral load (seismic and wind loads), so adding the coupled shear wall system to the construction building can give sufficient lateral stability, which can be achieved by increasing stiffness, strength, and ductility of the system. However, much research had been studied the coupling beams in the shear wall system theoretically and experimental; the effectiveness of the slab performance on the system has a short thesis executed experimental with limiting factors. In other words, only a few studies have shown the effects of slabs on the behavior of the coupled beam, and these studies did not mention the representation of the model. This study aims to investigate the effect of the rigidity connection between the slab and coupled beam and to create a finite element model in 3D to get a full understanding of the behavior of the system with different cases and hence to get recommendations for constructing stability system, the interaction between the slab elements and the shear wall system can effect on the behavior of the building. Deformation, shear, and moment in the coupled beam consider as the main measurements of structure response; the measured responses with different models of building 4, 8, 12 stories have been investigated in 3D models to obtain the behavior of the interaction of the slab with the coupled wall system. Two cases have been created; one is made without slab between coupled beam, and the other with existence the slab. The results prove that the rigidity between the coupled beam and the slab diaphragm is more effective for stability versus the seismic load. It shows the response reduction in the coupled beam and hence the overall response of the structure modeling, which can be returned to the effects of interaction rigidity between elements of the coupled beam and slab.

Inelastic seismic shear amplification due to higher mode effects in reinforced concrete coupled walls

Recent numerical and experimental studies on reinforced concrete shear walls and coupled walls have shown shear forces greater than expected when the walls are subjected to earthquakes at an intensity level that does not exceed the design values. This amplification of shear forces is attributable to the effects of higher modes after the walls develop a plastic hinge at the base. These effects have been recently recognized in North American design codes for cantilever walls and is currently neglected in the design of ductile coupled walls. As part of the research program described in this article, a parametric study was carried out on coupled wall systems to identify the geometric and physical parameters having the greatest influence on the seismic shear amplification. Using the results of this parametric study, an extensive numerical study was conducted on classes of ductile coupled walls subjected to seismic excitation representative of Western and Eastern Canada. This extensive study led to the establishment of shear amplification prediction equations for use in building codes.