Rocking Wall System Research Articles

Large-scale cushion type bare and partially rubber filled mechanical couplers subjected to uniaxial cyclic loading

Large-scale bare mechanical coupler (BMC), and partially rubber-filled mechanical coupler (PFMC) were developed in this study. BMC and PFMC were created to utilize especially at high-performance hybrid post-tensioned rocking wall (HPRW) systems. BMC can couple adjoining HPRWs in the vertical direction as a yielding-type supplemental damper. PFMC can couple HPRWs to the foundation beam and/or adjacent HPRWs at the story level in the horizontal direction. It can function as a supplemental energy absorber with high bearing capacity and adequate lateral strength. Since BMC and PFMC are joined externally to HPRWs, they can be replaced easily after severe seismic excitation. The quasi-static cyclic shear and axial tests were carried out on BMCs and PFMCs to evaluate their hysteretic behaviour and determine their structural properties. The experimental parameters, besides the loading type, were the plate thickness of BMCs and the density of steel sheet layers at rubber blocks of PFMC. The experimental results demonstrated the desired performance of BMCs and PFMCs under cyclic shear and axial actions. BMCs showed high-energy dissipation capability and displacement capacity. PFMCs represented high bearing capacity with sufficient lateral strength and energy dissipation capability. Although there was no Mullin effect on the PFMCs response subjected to cyclic shear loading, it was observed on the response of PFMCS under cyclic axial effect. Monotonic and unidirectional cyclic tests of tension, planar shear, and compression were conducted on the rubber pieces to simulate the rubber blocks at PFMCs, as well. Finite element models of BMCs and PFMCs were developed to grasp comprehensively the hysteretic behaviour. The validated model was established and the modeling techniques were described in detail.

Experimental Investigation of Precast Rocking Walls Incorporating Tension-Compression and Shear Steel Energy Dissipaters

To fully utilize the potential of earthquake-resistance capacity in rocking wall systems and improve repairability after earthquakes, a precast rocking wall structure is developed with the installation of multiple steel energy dissipaters, i.e., tension–compression and shear steel energy dissipaters. Quasistatic tests were carried out on three specimens to evaluate the seismic performance of the proposed system. A simulation investigation based on OpenSees was conducted to study the effects of the initial stress of strands and the main design parameters. The results indicated that the steel energy dissipaters suffer visible plastic deformation and exhibit excellent energy dissipation capacity. The proposed rocking wall structure presents excellent seismic behavior, satisfactory self-centering capacity, and repairability of the recovering function after an earthquake by replacing only the damaged energy dissipaters. Furthermore, the proposed system provides a new way to achieve the hierarchical energy dissipation mechanism of a structure.

Effect of serviceability limit state and over-strength mechanism on seismic performance of self-centring low damage structures with friction connections

Low damage design is an alternative to conventional seismic design, where earthquake-induced damage in the building is controlled and minimised. The most common approach to implement this concept is to design the structural system in a way that damage occurs in a series of specified components. This makes the designer able to predict the performance of the building under earthquakes by deliberately designing these components weaker than the other parts of the structure. These components can be replaced, repaired, or even designed to remain functional after earthquakes. Therefore, the performance of such components (e.g. weak links) is critical for evaluting the performance of the building as a whole.The New Zealand standard defines two extra limit states in addition to the design level earthquake (Ultimate Limit State (ULS)). First is the Serviceability Limit State (SLS), where the system is expected to remain linear and elastic, and the second is the collapse limit state (also known as MCE limit state), where damage is accepted, but the building should not collapse. For a low damage system, the weak links should be designed to remain linear and elastic under SLS actions. Also, they should have adequate reserve capacity to not completely fail under MCE actions. The latter is also called the over-strength mechanism (or the upper bound design level) for designing the low damage components. This study investigates the effect of the over-strength and serviceability limit state on the overall seismic performance of low damage systems. Two types of generic structural responses are considered for the study, self-centring braced frames and self-centring rocking wall systems. Numerical models for both concepts are developed and subjected to nonlinear dynamic time-history analysis with different intensities up to large, rare events (MCE). The results showed that braced frames' appropriate over-strength capacity is relatively smaller than rocking walls. The findings of this study help designers and engineers to perform more efficient and optimised designs for low damage systems. Also, this research helps them to have a better understating of the performance of such systems under large, rare earthquake events.

Seismic performance of damaged frame retrofitted with self-centering and energy-dissipating rocking wall

This paper proposes the novel concept of retrofitting damaged reinforced concrete frame with self-centering and energy-dissipating rocking wall. Parametric studies were carried out base on pushover and time-history analysis. In both pushover and time-history analysis, the soft-story mechanism was effectively mitigated through the rocking wall retrofit of the damaged structures. The results demonstrated that the stiffness and bearing capacity of the retrofitted system were improved compare to its intact state. Additionally, the seismic response of the damaged frame retrofitted using rocking wall in combination with post-tension and shear-type damper fell within the relevant design limits. Pushover analysis of the rocking wall indicated that there is a linear relationship between the wall thickness and the initial stiffness of the retrofitted system. The addition of post-tension tendon to the rocking wall system enables the wall to self-center and increases lateral stiffness and bearing capacity of the retrofitted system. When the shear-type damper was installed, the energy dissipation of the system was increased, and the stiffness and bearing capacity of the retrofitted system were also improved. In the time-history analysis, it was found that the thickness of the rocking wall is directly related to the maximum inter-story drift and the distribution patterns of inter-story drift of the frame. As the post-tension was added to the system, the maximum inter-story drift under rare earthquake excitation improved significantly. With the addition of shear-type dampers, the overall drift magnitude of the retrofitted system was fundamentally decreased.

Finite Element Study: Rocking Wall-Floor Connection of Precast Concrete Load-Bearing Structures Subjected to Quasi-Static Lateral Loading

ABSTRACT This paper proposes a novel semi-rigid rocking wall-floor connection. To study its seismic behavior, a preliminary study using finite element modeling (FEM) has been conducted to perceive the rocking wall response towards the precast plank before conducting a physical experimental testing in the laboratory. The finite element model was developed to investigate the lateral quasi-static-load response of the isolated rocking wall system. Subsequently, the rocking wall model was further extended by incorporating a precast concrete plank using the proposed connection. The finite element model of the rocking wall showed a good correlation with the analytical model. Furthermore, the study showed that a semi-rigid connection would result in an overstrength that should be considered when designing the rocking wall.

Effect of partition walls on the seismic response of mass-timber buildings with a post-tensioned rocking wall system

The structural-nonstructural interaction effects of nonstructural partition walls and post-tensioned CLT rocking walls in mass-timber buildings were evaluated in a parametric study. Representative 2D rocking wall units in 5-story and 12-story mass-timber archetype buildings were modeled in OpenSees. Moreover, concentrated spring models were developed to represent effective force-deformation for four different variations of partition wall detailing, and applied to the building models to represent wall densities associated with apartment and hospitality occupancies. Eigenvalue, pushover, and response-history analyses were performed on 2D models of the bare structure and those with partition wall variations. Including partition walls with fixed connection details was found to decrease story drifts and rocking wall story shears compared to the bare frame model by up to 50% in a service earthquake and up to 30% in a maximum considered earthquake. However, partition walls with deformation-compatible details were found to have negligible influence (less than 5%) on the response.

Seismic performance of controlled outrigger rocking wall system with different energy dissipation devices

Controlled outrigger rocking wall (CORW) system is a novel earthquake resilient structural system that combines a reinforced concrete wall with an outrigger and a controlled rocking base. At the ends of the outrigger and the wall base, different dampers are used to dissipate earthquake energy. In this paper, a prototype 100 m, CORW building, is designed using the novel equivalent energy design procedure (EEDP). EEDP allows engineers to design the CORW to achieve different performance objectives at different levels of earthquake shaking intensities. The design of the CORW using dampers with different hysteretic behavior is presented in this paper. In addition, detailed numerical models for the CORW system were developed, and the seismic performance of the prototype CORW system with different dampers was systematically compared using nonlinear dynamic analyses. The result shows that the CORW can be efficiently designed using EEDP, and the desired performance of the CORW can be achieved using dampers with different hysteresis behavior. Hence, this paper demonstrates that CORW can be used as an efficient alternative seismic force resisting system for high-rise applications.

Analytical and numerical investigation of a low-damage uplift friction damper for self-centering cross-laminated timber rocking walls

Cross-Laminated Timber (CLT) rocking wall systems have gained considerable attention in recent years as a potential Seismic-Force Resisting System for mass timber construction in regions of moderate to high seismic risk. It is well understood that CLT rocking walls do not provide any measurable amount of ductile energy dissipation on their own but instead rely on energy dissipation through their connections. A common approach has been to provide replaceable metallic yielding elements or structural fuses located at the base of the wall or the vertical interface between coupled walls. However, hysteretic yielding dampers are susceptible to both strength and stiffness degradation. To overcome these limitations, this paper presents a newly proposed Uplift Friction Damper (UFD) as an alternative to hysteretic dampers installed at the base of CLT rocking walls. The proposed UFDs provide stable energy dissipation and enhanced self-centering capability. This paper presents details of the UFD device along with analytical and continuum finite element numerical models that inform the kinematic response of the UFD. Furthermore, the tunability of the UFD device is investigated by changing select governing parameters of the UFD in a limited parametric study. First, the fundamental response of a single UFD device is presented to inform the basic local response. Next, the system response of the UFD installed on a SC-CLT wall is investigated through cyclic pushover analyses using continuum finite element models. Results show that the amount of energy dissipation depends primarily on the inclination angle of the friction interface, stiffness of the bolt-disc springs providing the normal clamping force, and coefficient of friction between the sliding interfaces.

Numerical investigation of the lateral load behavior of core and coupled rocking walls

During last few decades, the researchers have developed new structural systems which have no or minor damage after being hit by severe events like earthquake. Development of self-centering wall having alternative energy dissipation mechanisms was one of these achievements. A wide variety of rocking wall systems, such as jointed walls, hybrid walls, precast walls with end columns (PreWEC), and PreWEC core wall systems, are proposed and studied. This paper describes an analytical investigation of the lateral load behavior of two new types of hybrid rocking wall systems. Core rocking wall is achieved by merging four single hybrid rocking walls and coupled rocking wall is accomplished by coupling two rocking walls using embedded reinforced concrete beams. The concept of coupling hybrid rocking walls using embedded reinforced coupling beam is emerged from previous coupled conventional shear walls studies. As single rocking wall system, in coupled and core rocking wall, post-tensioning tendons are used as a mean to provide self-centering force, and mild steel bars are used to dissipate energy. The nonlinear behavior of the wall is due to the gap opening at the base joint. Three-dimensional finite element model of each system was developed. The stress distribution, crack propagation, and critical sections of these systems are investigated. The effect of spalling concrete cover in the toe region due to rocking action is explained. In addition, the reduction in stiffness and lateral load resisting capacity of the systems due to cracks is monitored. Finally, the lateral load behavior of single rocking walls is compared to that of core and coupled rocking wall systems.

Structural Vibration Control with the Implementation of a Tuned Mass Rocking Wall System

A tuned mass rocking wall (TMRW)-frame structure system is proposed to improve the energy dissipation ability of the traditional rocking wall-frame system. Based on the energy dissipation principle of the traditional tuned mass damper (TMD), a TMRW is designed with proper mass and stiffness according to the dynamic characteristic of the host structure. Firstly, considering the presence of inherent structural damping, the dynamic amplification factor of the main mass was derived from the dynamic equations of the TMRW mechanism. A practical design table was then obtained after parameter study. Secondly, by taking a six-story frame structure as an example, the dynamic time-history analysis was conducted to study TMRW’s seismic performance. The inter-story drift ratios of the TMRW-frame, the traditional rocking wall-frame, and the frame structures were compared, and the seismic responses of the controlled and uncontrolled structures were also compared. The results demonstrate that the TMRW can effectively reduce the inter-story displacement of the host structure, and the lateral deformation mode of the host structure tends to be more uniform. However, compared with the traditional rocking wall-frame system, the proposed TMRW has less ability on coordinating deformation.

Unbonded Post-tensioned Precast Concrete Walls With Rocking Connections: Modeling Approaches and Impact Damping

Over the past two decades, precast concrete members have been utilized in seismically resilient structures. In developing these structures, different techniques have been used for connecting the precast members to the foundation. In building construction, unbonded post-tensioning (PT) tendons can anchor a precast wall to the foundation, resulting in the so-called rocking wall system. The rocking wall system develops a dry connection with the foundation and provides moment resistance by means of the PT tendons. The PT tendons remain elastic when the wall is subjected to design-level ground motions to preserve the re-centering capability of the wall. Moreover, the structural damage is concentrated near the wall toes and can be minimized with proper detailing of the toes. Rocking wall systems can consist of a Single precast Rocking Wall (SRW), which uses no supplemental damping, or walls with supplemental damping in the form of viscous or hysteretic energy dissipating devices. In addition to the supplemental damping, rocking walls dissipate the seismic energy through their impacts on the foundation base, their inherent viscous damping, and the hysteresis of concrete near the wall base. While the investigation of rocking walls continues to gain interest, there is no widely accepted means of modeling their dynamic behavior. This paper investigates two popular approaches for modeling rocking walls with and without supplemental damping: the finite element method and analytical modeling. The ability of the two approaches to capture the local and global responses of the walls is evaluated against shake table tests of walls with multiple-level intensity base motions. Next, the behavior characteristics of the two modeling approaches and their ability to simulate impact damping are discussed.

A posttensioned rocking infill wall–frame system for multistory precast concrete buildings

SummaryBy proposing a multiple rocking infill wall–frame (MRWF) system, this paper investigates the effects of wall–frame interaction on the seismic response of self‐centering walls. In the MRWF system, infill walls are connected to the adjacent beams through posttensioned tendons, which provide the self‐centering ability, and the energy dissipation capacity of the system is enhanced using O‐shaped steel dampers. The seismic behavior of the MRWF system, with various wall configurations, is evaluated alongside conventional shear wall and typical rocking wall systems at three height levels of two, four, and six stories. After developing the numerical models, the cyclic and time history analyses are carried out. The results of cyclic analysis show that the energy dissipation capacity of MRWF models is much higher than that of typical rocking wall models. Furthermore, for the MRWF models, by increasing the number of walls with a smaller width, the effect of wall–frame interaction is mitigated, resulting in minimal damage to the structural members and self‐centering ability of more than 90%. The time history analysis results illustrate that for the MRWF models, the residual drifts and plastic rotation at the beams are significantly reduced by applying the proper structural layout of the multiple rocking walls, especially for six‐story models.

Optimizing displacement-based seismic design of mass timber rocking walls using genetic algorithm

This paper presents a rational procedure to optimize design for mass timber rocking wall systems utilizing a genetic algorithm (GA) beyond typical displacement-based design metrics for wood buildings. Traditional displacement-based design is limited to simple displacement targets, with optimization techniques (GA), it is feasibly to consider more performance chrematistics (e.g. costs, serviceability, etc.). By formulating drift targets and other structural design limit states within an elimination step of the GA optimization process, the method proposed here optimizes rocking wall design with multiple criteria that factor much more than lateral displacement targets in the seismic analysis. This type of optimization is difficult to perform using traditional manual trial-and-error approaches. An existing simplified nonlinear time-history simulation model (validated through full-scale shake table test data) of a wood rocking wall is employed in this process. The design for an example building in Seattle with a six-story rocking wall is presented using the proposed procedure. The results revealed that the optimization of the mass timber rocking wall lateral system can be achieved in a reasonable time frame using the proposed method. Even though the same drift limits were applied, final designs produced by GA varied, depending on the other optimization objectives. This demonstrates how the seismic design of wood rocking wall systems could be readily improved with computerized optimization tools that factor in other aspects of the design including cost.

Axial slip-friction connections for cross-laminated timber

Cross-laminated timber (CLT) rocking walls limit internal building forces and dissipate seismic energy mostly through severe connection damage and related wood crushing. While collapse-prevention and life-safety performance can be achieved, the connections and CLT walls are permanently damaged and may be unreliable for resisting aftershocks. Slip-friction connections (SFCs), also known as slotted-bolted connections, are highly resilient passive dampers originally developed for steel structures. As part of a thorough research program to apply SFCs to CLT rocking walls, connection tests were conducted to better understand a novel application of multiple modern timber technologies. The research objectives were to design and test a slip-friction connection connected to cross-laminated timber with inclined self-tapping screws (STS) to determine the stiffness and passive damping properties of the assembly. The SFC system was designed for use as a slip-friction hold-down in a self-centering CLT rocking wall system. A series of quasi-static, cyclic axial tests with slip-friction connections was shown to impart ductile and elastic–plastic characteristics to an otherwise non-ductile CLT connection. Because the timber connection forces were limited below the STS yield strength by the slip-friction connectors, no wood damage was observed during SFC sliding. Compared to other sources, passive damping was found to be excellent and close to typical idealized friction hysteresis models. The slip-friction connections are a unique design using an efficient CLT to SFC connection, with no slack, that performs consistently after consecutive tests. Additionally, cursory equivalent-viscous-damping ratios were extracted for the elastic range of the STS to steel connection for small amplitude excitations below the slip force threshold.

Simplified Dynamic Model for Post‐tensioned Cross‐laminated Timber Rocking Walls

AbstractThis paper presents a computationally efficient numerical model for predicting seismic responses of post‐tensioned cross‐laminated timber (CLT) rocking wall systems. The rocking wall is modeled as a simple linear beam element with a nonlinear rotational spring at the base. The model is primarily intended for preliminary design and assessment of multistory buildings using this particular lateral system. A method was developed to determine the nonlinear rotational spring parameters by considering the dimension of the CLT wall panel and post‐tensioned steel rods and energy dissipating devices’ contributions. The proposed model was validated by comparing the simulated results with the responses from a series of shake table tests of a full‐scale two‐story building with CLT rocking walls. The numerical results show reasonable agreement with the shake table test results considering the simplicity of the model.

Influence of different damping components on dynamic response of concrete rocking walls

Precast concrete rocking walls with unbonded post-tensioning, as a seismic resilient system, dissipate energy imparted to them during an earthquake through inherent viscous damping, impact damping due to the wall rocking on top of the foundation, and any available hysteretic damping. A shake table study on eight rocking walls designed with different quantities of hysteretic damping ratio varying between 4% for a Single Rocking Wall (SRW) to 15% for a rocking wall system, known as PreWEC, with supplemental hysteretic dampers, i.e., O-connectors, generally demonstrated their satisfactory seismic performance during design-level and higher intensity earthquake motions. The test results confirmed lower participation of energy dissipation due to impacts as the hysteretic component increased. Larger hysteretic damping also led to a reduction in the maximum drift of rocking walls as well as the number of large drift excursions after the first peak of response. Using the area enclosed by the force-displacement hysteresis response of O-connectors, recommended design values for hysteretic damping of PreWEC systems are presented in this paper. While larger displacement amplitudes were achieved for the walls with lower hysteretic damping (i.e., SRWs), it is shown that the duration of their dynamic responses was reduced due to a negative rate of input energy in these rocking walls, which favorably removed a part of the seismic energy imparted to the system. Contrary to a common belief that rocking walls without additional damping devices are not dependable lateral load resisting systems, this paper concludes that these walls attract less seismic input energy and perform satisfactorily with a small amount of inherent damping, suggesting their potential application in seismic resistant structures.

Review on the rocking wall systems as a self-centering mechanism and its interaction with floor diaphragm in precast concrete structures

Abstract The severe damage of precast concrete wall structures that have been recorded in the past earthquake has led to the innovation of the rocking wall concept which can demonstrate free or minimum damage aftershock of an earthquake. Furthermore, extensive research works have been well conducted in the past three decades on the establishment of precast rocking wall systems, designs, details, and techniques. Despite this extensive development, little attention has been devoted to investigate the interaction between the rocking wall systems and the flooring diaphragm. The historical perspective on the development of rocking wall systems over the past few decades in the precast concrete structures is presented. Subsequently, the limited research works on the interaction of precast rocking wall to the floor diaphragm are described. Apart from that, this paper attempts to highlight the application of rocking wall systems in the context of precast connection for the precast load-bearing structures. In this contribution, the precast rocking wall-floor connection for precast load-bearing structures is proposed and presented in this paper.

Shake table testing of unbonded post-tensioned concrete walls with and without additional energy dissipation

Recently an innovative unbonded Post-Tensioned (PT) concrete wall system was developed that consists of a Precast Wall with End Columns (PreWEC). Dynamic testing was conducted to better understand the seismic response of PreWEC systems and to provide further dynamic test results of PT rocking wall systems. Three unbonded PT concrete walls, including one SRW and two PreWEC systems that incorporated O-connector dissipaters were subjected to a suite of seven spectrum compatible ground motions at different intensity levels in addition to three recent ground motions at natural scale. Negligible damage to the concrete wall panels was observed for all three systems throughout the entire sequence of testing. As expected both PreWEC systems demonstrated higher energy dissipation and lateral-load capacity in comparison to the SRW due to the addition of the O-connectors. This resulted in SRW-A experiencing higher average drifts and lower accelerations than the two PreWEC systems. An intensity measure referred to as an ‘Achieved return period factor’ was defined based on comparing the measured table acceleration response spectrum to a target code response spectrum. The increased spread of both peak acceleration and peak drift versus the achieved return period factor for SRW-A in comparison to both PreWEC systems highlights the more sensitive and unpredictable nature of the SRW as a result of limited damping. The measured inherent damping from the white noise tests was found to range between 3.5% and 4.0% for the three walls. Negligible residual drifts were measured for all walls despite higher static residual drifts being estimated from previously performed cyclic testing on identical walls.

Performance evaluation of infilled rocking wall frame structure

SummaryConventional reinforced concrete (RC) frame structures are prone to soft‐story mechanism. This deficiency can be eliminated by introducing rocking wall system. Previously studied rocking wall systems usually have the rocking wall situated outside the frame, which results in some challenges and inconvenience. In the study, a novel infilled rocking wall frame (IRWF) system is proposed, which uses infilled RC wall to create a rocking wall within the RC frame. To evaluate seismic performance of the proposed system, both an IRWF model and an RC frame (RCF) model were designed according to Chinese seismic design code. Time history analysis and incremental dynamic analysis were conducted to compare both systems. The results show that IRWF system has more uniform drift and higher collapse margin ratio compared to the RCF system. Economic evaluation of IRWF system was investigated using the state‐of‐the‐art ATC‐58 performance‐based assessment methodology. The result shows superior performance of the IRWF system. The annualized loss of the IRWF model is about 28% less than the RCF model. This shows IRWF system is a viable and efficient alternative resilient seismic force resisting system.

Computer modeling of dynamic behavior of rocking wall structures including the impact-related effects

Precast post-tensioned concrete rocking wall system is an innovative damage avoidance structural system for seismic regions. Past experimental works on the dynamic performance of rocking walls have identified the presence of high-frequency acceleration spikes in both lateral and vertical directions during the impact of wall base with the foundation. These acceleration spikes, acting together, can cause shear slip at the wall–foundation connection. This study is focused on the development of a computer model that can predict these acceleration spikes along with the identification of their effects on the dynamic performance of rocking walls. For this purpose, impact phenomenon at the wall–foundation joint has been discussed in detail and some general guidelines are set for the two important parameters of impact or contact modeling named as contact stiffness and contact damping. The finite element numerical models, based on the proposed guidelines, are found to predict the overall dynamic behavior of rocking walls along with the acceleration spikes quite efficiently. The acceleration spikes are found to be dependent on the lateral velocity at impact and the initial contact stiffness. So a velocity-dependent energy dissipation device along with a soft contact is found to be suitable for reducing these effects.