Light-frame timber shear walls have been used as load-bearing elements in buildings for several decades. To predict the performance of such structural elements under loading, numerous analytical and numerical models have been developed. However, little focus has been on the prediction of the plastic damage behaviour and unloading of the walls. In this paper, a parametric Finite Element (FE) model is further developed by introducing elasto-plastic connectors to simulate the mechanical behaviour of the sheathing-to-framing connections. To verify the accuracy of the elasto-plastic model, full-size walls were tested and compared with results from simulations. The numerical results, from a few loading cycles, indicate that the model achieves reasonable accuracy in predicting both the nonlinear elastic and plastic deformations. Both experimental and simulation results demonstrate the importance of opening locations relating to the external racking force. The results also indicate that for a double-layer wall, its racking strength can be achieved by summation of the separate contribution from each layer. Furthermore, the internal layer was observed to contribute significantly less than the external layer since its nail pattern was based on the sheathing pattern of the external layer.
Midply shear wall, which was originally developed by researchers at Forintek Canada Corp. (predecessor of FPInnovations) and the University of British Columbia, is a high-capacity wood-frame shear wall system that is suitable for high wind and seismic loadings. Its superior seismic performance was demonstrated in a full-scale earthquake simulation test of a 6-storey wood-frame building in Japan (Peietal.,2010). Midply shear wall, however, had limited applications due to its low resistance to vertical load and difficulty to accommodate electrical and plumbing services. For broader applications of Midply shearwall, these limitations needed to be addressed.
In collaboration with APA–The Engineered Wood Association and the American Wood Council (AWC), a new framing arrangement was designed to increase the vertical load resistance of Midply shearwalls and make it easier to accommodate electrical and plumbing services. Consequently, structural, fire and acoustic tests have been conducted to evaluate various performance attributes of Midply shear wall with the new framing configuration. This InfoNote provides a summary of the structural, fire and acoustic performance of Midply shearwalls from the tests.
‘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.
Balloon type cross laminated timber (CLT) rocking shear walls are a novel seismic force resisting system. In this paper, the seismic performance of four 12-story balloon type CLT rocking shear walls, designed by a structural engineering firm located in Vancouver (Canada) using the performance-based design procedure outlined in the technical guideline published by the Canadian Construction Materials center (CCMC)/National Research Council Canada (NRC), is assessed. The seismic performance of the prototype CLT rocking shear walls was investigated using nonlinear time history analyses. Robust nonlinear finite element models were developed using OpenSees and the nonlinear behavior of the displacement-controlled components was calibrated using available experimental data. A detailed site-specific hazard analysis was conducted and sets of ground motions suitable for the prototype buildings were selected. The ground motions were used in a series of incremental dynamic analyses (IDAs) to quantify the adjustable collapse margin ratio (ACMR) of the prototype balloon type CLT rocking shear walls. The results show that the prototype balloon type CLT rocking shear walls designed using the performance-based design procedure outlined in the CCMC/NRC technical guideline have sufficient ACMR when compared to the acceptable limits recommended by FEMA P695.
The objective of this research is to address a knowledge gap related to fire performance of midply shear walls. Testing has already been done to establish the structural performance of these assemblies. To ensure their safe implementation and their broad acceptance, this project will establish fire resistance ratings for midply shear walls. Fire tests will provide information for the development of design considerations for midply shear walls and confirm that they can achieve at least 1-hour fire-resistance ratings that are required for use in mid-rise buildings.
This research will support greater adoption of mid-rise residential and non-residential wood-frame construction and improve competition with similar buildings of noncombustible construction. This work will also support the development of the APA system report for midply walls, which will be a design guideline for using midply walls in North America.
Cross-laminated timber (CLT) construction has been gaining popularity in North America. However, CLT-based seismic force resisting systems are not recognized in current U.S. design codes, which is among the many challenges preventing widespread adoption of CLT in the United States. The purpose of this study was to investigate the seismic behavior of CLT-based shear wall systems and to determine seismic performance factors, namely, the response modification factor (R factor), the system overstrength factor(O), and the deflection amplification factor (Cd), using the FEMA P695 procedure. Nine index buildings including single-family dwellings, multifamily dwellings, and commercial (including mixed use) midrise buildings were developed, from which 72 archetypes were extracted. Testing performed at the component and subassembly levels included connector tests and isolated shear wall tests. A CLT shear wall design method was developed and used to design the archetypes, which were then assessed with nonlinear pushover analysis and incremental dynamic analysis. Based on the required collapse margin, an R factor of 3 is proposed for CLT shear wall systems with 2:1 or mixed aspect ratio panels up to 4:1, and an R factor of 4 is proposed for CLT shear wall systems made up of only 4:1 aspect ratio panels. Results from this study have been proposed for recognition in U.S. building codes (such as the International Building Code) through specific change proposals to update reference standards such as ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures and Special Design Provisions for Wind and Seismic.
This paper presents a numerical and analytical study on single-storey cross-laminated timber (CLT) shear-walls with openings subjected to lateral loads. The main objective was to investigate the location and distribution of maximum values of axial and shear forces in relevant wall sections. The influence of parameters such as wall geometry (different sizes of wall openings, door openings, lintel/parapet lengths and heights, wall thickness) and different stiffness levels of mechanical anchors for CLT wall connection with floor/foundation were studied. Finite element (FE) parametric analyses were performed on a set of single-storey CLT shear-walls with door and window openings and were compared with analytical models for determination of internal forces. The importance of wall connections’ flexibility was identified, as the distribution of internal forces in walls with rigid and flexible anchors were considerably different. The obtained outcomes of this study provide a solid base for the next step, an experimental investigation of in-plane internal force distribution in CLT walls with openings, which will serve for further development of numerical, analytical and design approaches.
In this study, the lateral resistances of mass timber shear walls were investigated for seismic design. The lateral resistances were predicted by kinematic models with mechanical properties of connectors, and compared with experimental data. Four out of 7 shear wall specimens consisted of a single Ply-lam panel and withdrawal-type connectors. Three out of 7 shear wall specimens consisted of two panels made by dividing a single panel in half. The divided panels were connected by 2 or 4 connectors like a single panel before being divided. The applied vertical load was 0, 24, or 120 kN, and the number of connectors for connecting the Ply-lam wall-to-floor was 2 or 4. As a result, the tested data were 6.3 to 52.7% higher than the predicted value by kinematic models, and it means that the lateral resistance can be designed by the behavior of the connector, and the prediction will be safe. The effects of wall-to-wall connectors, wall-to-floor connectors and vertical loads on the shear wall were analyzed with the experimental data.
Midply shear wall, which was originally developed by researchers at Forintek Canada Corp. (predecessor of FPInnovations) and the University of British Columbia, is a high-capacity shear wall system that is suitable for high wind and seismic loadings. Its superior seismic performance was demonstrated in a full-scale earthquake simulation test of a 6-storey wood-frame building in Japan. In collaboration with APA–The Engineered Wood Association and the American Wood Council (AWC), a new framing arrangement was designed in this study to increase the vertical load resistance of midply shear walls and make it easier to accommodate electrical and plumbing services. In this study, a total of 12 midply shear wall specimens in four wall configurations with different sheathing thicknesses and nail spacing were tested under reversed cyclic loading. Test results showed that the modified midply shear walls have approximately twice the lateral load capacity of a comparable standard shear wall. The drift capacity and energy dissipation capability are also greater than comparable standard shear wall. Seismic equivalency to standard shear walls in accordance with ASTM D7989 was also conducted. Results show that an overstrength factor of 2.5 and can be used to assign allowable design strengths of midply shear walls with 7/16” and nail spacing at 4” or 3” on center. For midply shear walls with 19/32” OSB, a higher overstrength factor must be used to meet the ductility criteria. The information from this study will support code implementation of the midply shear walls in Canadian and US timber design standards, thereby providing more design options for light wood frame structures in North America.
Cross-laminated timber (CLT) is a mass timber product that has recently garnered considerable attention for lateral-force resisting system (LFRS) applications. The main objectives of this study were to investigate the rocking behavior of a high-aspect-ratio (height/width) CLT shear wall without post-tensioning, and to validate a finite-element (FE) model based on the cyclic and dynamic response of the wall. To this point, high-aspect-ratio walls in the literature have primarily been post-tensioned. The testing component of this study included connector tests, quasistatic cyclic shear wall tests, and shake-table tests under four different ground motions scaled to design earthquake (DE)- and maximum considered earthquake (MCE)-level intensities. A generic shear connector was used for this study to allow for proprietary and other systems to demonstrate equivalence. The connectors were tested under shear and uplift, and shear-wall tests were performed using the Consortium of Universities for Research in Earthquake Engineering (CUREE) displacement protocol, which has been widely used for light-frame wood structures. Interstory drift (ISD) ratios in the shake-table tests ranged from 0.97% to 2.02%, and the tests demonstrated the system’s ability to resist seismic loading. An FE model of the CLT wall was developed that showed good agreement with the cyclic and shake-table tests. The difference between the ISD ratios in the numerical model and the shake-table tests ranged from 5.4% to 31.3%, with an average of 17.9%, which was in good accordance with the accuracy of the existing CLT models. This system can be utilized as a retrofit option, in conjunction with light-frame wood shear walls, where lack of space may be a challenge.
Cross Laminated Timber (CLT) and Light Timber Frame (LTF) shear walls are widespread constructive technologies in timber engineering. Despite the intrinsic differences, the lateral response of the two structural systems may be quite similar under specific connection layouts, boundary constraints, and size of the shear walls. This paper compares the experimental cyclic responses of CLT and LTF shear walls characterized by the same size 250×250cm, and loaded according to the EN 12512 protocol. The rigid-body rotation of the shear walls prevails over the deformation and rigid-body translation in the post-elastic displacement range. As a consequence, a capacity model of the two systems based on the sole hold-down response accurately seizes the observed cyclic response, despite ignoring the other resisting contributions. The authors examine the differences exhibited by the CLT and LTF shear walls and the related error corresponding to a capacity model based on the sole hold down restraints. Additionally, it is assessed the overstrength of the CLT panel and LTF sheathing to the shear walls collapse due to the hold-down failure. The estimated overstrength factor is the most meaningful difference between the two structural systems in the considered experimental layouts.
Recent interests in adopting sustainable materials and developments in construction technology have created a trend of aiming for greater heights with timber buildings. With the increased height these buildings are subjected to higher level of lateral load demand. A common and efficient way to increase capacity is to use shearwalls, which can resist significant part of the load on the structures. Prefabricated mass timber panels such as those made of Cross-Laminated Timber (CLT) can be used to form the shearwalls. But due to relatively low stiffness value of timber it is often difficult to keep the maximum drifts within acceptable limit prescribed by building codes. It becomes necessary to either increase wall sizes to beyond available panel dimensions or use multiple or groups of walls spread over different locations over the floor plan. Both of the options are problematic from the economic and functional point of view. One possible alternative is to adopt a Hybrid system, using Steel Plate Shear Walls (SPSW) with timber moment frames. The SPSW has much higher stiffness and combined with timber frames it can reduce overall building drifts significantly. Frames with prefabricated timber members have considerable lateral load capacity. For structures located in seismic regions the system possesses excellent energy dissipation ability with combination of ductile SPSW and yielding elements within the frames. This paper investigates combination of SPSW with timber frames for seismic applications. Numerical model of the system has been developed to examine the interaction between the frames and shear walls under extreme lateral load conditions. Arrangements of different geometries of frames and shear walls are evaluated to determine their compatibility and efficiency in sharing lateral loads. Recommendations are presented for optimum solutions as well as practical limits of applications.
Seismic force resisting systems based on cross-laminated timber (CLT) shear walls have garnered considerable attention for in mid-rise construction around the world. The purpose of this study was to determine seismic performance factors for CLT shear wall systems in platform type construction. These factors, namely, the response modification factors, R, overstrength factor, Oo and deflection amplification factor, Cd, have been developed in this study for CLT walls and proposed for inclusion in ASCE 7. The study follows the FEMA P695 methodology that incorporates testing, evaluating a design methodology, defining the design space representative of typical construction, and comprehensive performance evaluation. The testing phase of the project consisted of connector testing and CLT shear wall testing, all with nonproprietary generic connectors to facilitate building code recognition. The design methodology and archetype development process are also discussed in this paper. A total of nine index buildings were developed from which 72 archetypes were extracted for this study. The archetypes were designed based on the design methodology and assessed with nonlinear pushover analysis and incremental dynamic analysis. Based on the required collapse margin, an R factor of 3 is proposed for CLT shear wall systems with 2:1 or mixed aspect ratio panels up to 4:1, and an R factor of 4 is proposed for CLT shear wall systems made up of only 4:1 aspect ratio panels.
Technical Guide for Evaluation of Seismic Force Resisting Systems and Their Force Modification Factors for Use in the National Building Code of Canada with Concepts Illustrated Using a Cantilevered Wood CLT Shear Wall Example
The objective of this guideline is to provide a simple, systematic, and sufficient procedure for evaluating the performance of Seismic Force Resisting Systems (SFRSs) and to determine the appropriate ductilityrelated (Rd) and over-strength related (Ro) force modification factors for implementation in the National Building Code of Canada (NBC). The procedure relies on the application of non-linear dynamic analysis for quantification of the seismic performance of the SFRS. Note that the procedure is also suitable for assessing force modification factors (RdRo values) of systems already implemented in the NBC.
The audience for this guideline are those (called the “project study team” in this document) who submit proposals for new SFRSs with defined RdRo values to the NBC for inclusion in Subsection 4.1.8., Earthquake Loads and Effects, of Division B of the NBC. This guideline can also be used by a team performing an alternative design solution for a specific project and seeking acceptance from authority having jurisdiction. In such cases, not all aspects of this guideline (e.g., having different archetypes) will be needed.
This paper presents the direct displacement-based design (DDD) procedure, structural modelling method, and structural performance calibration for post-tensioned CLT shear wall structures (PT-CLTstrs). Numerical models of the post-tensioned (PT) CLT shear walls were developed and calibrated with the experimental results. Based on the developed shear wall models, parametric analysis were conducted to investigate the lateral performance influencing factors. Then, a DDD procedure was developed and demonstrated by the design examples of a set of 8-, 12-, and 16-storey PT-CLTStrs. The corresponding simplified structural models were developed, and then a series of pushover and time-history dynamic analysis were conducted to calibrate the calculated structural performance objectives with the design targets of the DDD procedure. Finally, the empirical cumulative distribution functions (CDFs) of the maximum inter-storey drift (MaxISDR) were constructed. It is found that when the width of the PT CLT shear walls increases from 1.8 m to 3.0 m, the base shear at the drift of 2.0 % increases by twice accordingly. When the diameter of the PT strand increases from 15.2 mm to 34.6 mm, the base shear at the drift of 2.0% increases by up to five times. Additionally, the MaxISDR limitation of the PT-CLTStrs is recommended as 2.2% under the collapse prevention (CP) hazard level. The study results can serve as guidelines for the development of engineering design methods for the PT-CLTStrs.