Light-frame Shear Walls Research Articles

Structural performance of strong timber diaphragms: High-capacity light-timber frames and cross-laminated timber

The construction of tall timber buildings is not only challenging because it requires stronger vertical lateral systems but also because it demands much Stronger Timber (ST) diaphragms in comparison to the ones required by low-rise timber construction. Two main ST alternatives exist: High-capacity Light-Timber Frame (HLTF) and Cross-Laminated Timber (CLT) diaphragms. Both approaches provide more strength, stiffness, and still have the potential to provide ductile failure than traditional timber diaphragms. However, it is unclear the structural performance differences between these two ST alternatives, which is the aim of this research. In this study, an experimental program comprising the monotonic and cyclic testing of several representative sheathing-to-framing connections, plus the full-scale monotonic bending testing of six HLTF and CLT diaphragms was accomplished to characterize and compare the performance of both ST diaphragm configurations. Failure modes and mechanical properties such as stiffness, load-bearing capacity, and ductility were evaluated for all specimens. Results show that HLTF diaphragms have larger load-bearing capacity than CLT ones. Conversely, CLT diaphragms perform more ductile than HLTF ones, with a mean of μ= 1.87 and μ= 3.5, respectively, where the first was due mainly to high plastification of fasteners and the second to premature brittle failure of some components. Furthermore, the experimental findings were utilized to evaluate the precision of prevailing analytical and numerical models, thereby illustrating their capability to adequately represent the elastic and nonlinear responses of both ST alternatives. Finally, a sensitivity analysis of a two–story wall building with varying diaphragm (LTF, HLTF and CLT) and different light-frame shear walls (rigid and flexible) was studied. Both the diaphragms and shear walls were modeled under two different equivalent diagonal link models. The sensitivity analysis concluded that both flexible diaphragm assumption and envelope approach might not be an efficient solution, while semi-rigid approach with flexibility index η ranging 0–0.5 may be expected when using ST with LTF shear walls. Finally, the diaphragm model employed enabled the validation of its elastic behavior under lateral loads, with use factors under 30% for typical setups.

Experimental Investigation of Lateral Behavior of Light-Frame Shear Walls Applied with Elastomeric Adhesive

Experimental Investigation of Lateral Behavior of Light-Frame Shear Walls Applied with Elastomeric Adhesive

Lateral load carrying capacities of particleboard shear walls made by gluing with timber studs

Particleboard shear walls were developed and their lateral load carrying capacities were evaluated. The shear walls were made by connecting particleboards and timber studs with polyurethane (PUR) or nails. Seven types of particleboard shear wall specimens were manufactured by varying the wood species, size of the timber studs, and number of particleboards. The size of the shear wall specimens was 2.4 m × 2.7 m, and the bottom of the shear wall was fixed to the steel frame of the test equipment using hold-downs and angle brackets. As a result, the lateral load carrying capacities of the glued particleboard shear wall (73.4 to 75.6 kN/m) were 3.2 times higher than that of the typical light-frame shear wall and higher than the experimental data of the cross-laminated timber (CLT) wall in the CLT handbook. All glued specimens failed at the hold-down and angle bracket, and there was no damage at the glue layer between a particleboard and timber studs. The shear performance with different combinations of species, stud size, and number of particleboards was not significantly different, and the shear strength of the nailed specimen was approximately 20% lower than that of the glued specimen.

Experimental and numerical study on the deflection of multi-storey light-frame timber shear walls

This study aims at investigating the deflection behavior of multi-storey shear walls, including the effect of the diaphragm out of plane stiffness. Two-storey half-scale light-frame shear walls were investigated experimentally and numerically. Each level was loaded separately in order to isolate the effect of load transfer and deformation from one level on the other. The study shows that the deflection estimated based on the cumulative effect assumption was reasonably close to that observed in the experimental study, when no consideration for the floor diaphragm’s out of plane stiffness was included. It was observed that the majority of the cumulative effect stems from the rigid body rotation due to deformation in the hold-down devices. Results from a numerical model showed that the assumption of cumulative effects due to rigid body rotation is valid for stacked shear walls when consideration for the floor diaphragm’s out-of-plane stiffness is not included. The design expression showed a slight tendency to over-estimate the deflection especially at higher storey levels. The results of investigating the effect of the diaphragm’s out of plane stiffness showed that a significant reduction in the shear wall deflection. Diaphragm supported on multiple wall panels was found to further reduce the deflection of the shearwalls.

A SIMPLIFIED ANALYTICAL PROCEDURE FOR SEISMIC ANALYSIS OF TIMBER LIGHT-FRAME SHEAR WALLS

The seismic performance of timber light-frame shear walls is investigated in this paper with a focus on energy dissipation and ductility ensured by sheathing-to-framing connections. An original parametric finite element model has been developed in order to perform sensitivity analyses. The model considers the design variables affecting the racking load-carrying capacity of the wall. These variables include aspect ratio (height-to-width ratio), fastener spacing, number of vertical studs and framing elements cross-section size. A failure criterion has been defined based on the observation of both the global behaviour of the wall and local behaviour of fasteners in order to identify the ultimate displacement of the wall. The equivalent viscous damping has been numerically assessed by estimating the damping factor which is in use in the capacity spectrum method. Finally, an in-depth analysis of the results obtained from the sensitivity analyses led to the development of a simplified analytical procedure which is able to predict the capacity curve of a timber light-frame shear wall.

Nonlinear Numerical Model of Post-Tensioned Elastic Rocking Panels for Application in Building Structural Analysis

This paper presents a new 4-node finite element model, developed from a 2-node rocking beam element that can predict the rocking behavior of post-tensioned panels and columns. The stiffness matrix of the 2-node beam element was derived from the flexibility method. Then, the stiffness matrix of the 4-node beam element was obtained through the use of transformation matrices. The 4-node element model allows for the prediction of not only the global behavior of the rocking element (e.g., nodal displacements and nodal loads) but also the local behavior (e.g., the contact length, the vertical displacement, and the strain and stress at the rocking interface). The numerical results from the 4-node element model were compared to that from 3D finite element method (FEM) models in MATLAB 2016 and ABAQUS programs and showed a high accuracy. Moreover, the 4-node element model can be combined with the other types of elements in order to analyze building structures at a global level, especially for mid-rise and tall buildings where the nodal displacements at panel corners are vital to correctly predict the behavior of the other structural elements (e.g., light-frame shear wall elements). An example of a six-story building that included a hybrid system of post-tensioned cross-laminated timber (CLT) walls and light-frame wood shear walls was presented.

Dynamic Characterization and Vibration Analysis of a Four-Story Mass Timber Building

Mass timber construction has been gaining momentum in multi-story residential and commercial construction sectors in North America. As taller mass timber buildings are being planned and constructed, in-situ dynamic tests of this type of construction can be performed to further validate their design and use. As part of this larger effort, an in-situ dynamic characterization testing campaign based on ambient vibration measurements was conducted on a recently constructed four-story mass timber building located in Portland, Oregon. The building features cross-laminated timber (CLT) floors, a glued laminated timber (GLT) framing gravity system, and light-frame shear walls and steel HSS hold-downs that compose the lateral resisting system of the building. Ambient vibration acceleration testing data were collected using 18 accelerometers that were wired to a portable data acquisition system in two experimental setups. Approximately two hours of bi-directional horizontal acceleration data were recorded. In this paper, two operational modal analysis methods are used for estimating the modal parameters (frequency, damping, and mode shapes) based on the data collected. In addition, a multi-stage linear Finite Element (FE) model updating procedure is presented for this building type and the FE estimates of frequencies and mode shapes are compared to estimates from the collected data. The calibrated FE model provides confidence to the operational modal results, and presents a comprehensive modal characterization of the building. At ambient levels of excitation, the developed FE model suggests that stiffness of the non-structural elements, such as the exterior wall cladding and glazing affects the modal response of the building considerably. Lessons learnt on this unique and first of a kind four-story structure constructed in the United States and implications for taller mass timber buildings are summarized and provide valuable insight for the design and assessment for this building type under future dynamic excitation events.

Characterisation of the Lateral Resistance of Stapled Shear Walls

Shear walls are the major components of the lateral-force-resisting system (LFRS) in light-frame wood buildings. With the growing popularity of mid-rise prefabricated light-frame wood construction, engineers need basic design information on the shear walls to design and produce safe structures in case of high winds and earthquakes. The racking resistance of light-frame shear walls depends on many factors, including sheathing and hold-down devices and, most importantly, sheathing-to-framing fastenings. While the performance of nailed shear walls has been studied extensively, and design information is included in the design codes, there is little information on stapled shear walls, specifically in the US and Canada. The cost of staples is significantly less than that of equivalent nails; hence, the use of staples instead of nails would allow cost savings in mass production if they provide sufficient resistance and displacement capacity in the engineered shear walls. This paper presents the results of a pilot study which was focused on the comparison of the performance of nailed and stapled shear walls in laboratory tests under monotonic and cyclic loading in accordance with ASTM E564 and E2126, respectively. Several series of tests were performed on 2.4-m (8-ft) square shear walls with 11-mm (7/16-in) OSB sheathing with various hold-downs and various spacing of sheathing staples and nails on the perimeter of the sheathing panels (5-cm (2-in), 10-cm (4-in) and 15-cm (6-in)) and 19-mm and 10-mm edge distances. The staples were 16-gauge (50-mm (2-in) long with 11-mm (7/16-in) crown). The nails were 8d box steel wire nails (63-mm (2½-in) long with 2.87-mm (0.113-in) diameter). The test results revealed a similar performance of the nailed and stapled shear walls, and the need for careful detailing. Therefore, prefabrication of walls in the factory settings is preferable to the on-site construction to allow the production quality control.

Path Dependence in OSB Sheathing-to-Framing Nailed Connection Revealed by Biaxial Testing

AbstractOriented strand board (OSB) sheathing-to-wood framing connections, as typically used in light-frame shear walls, were experimentally examined in a novel biaxial test setup with respect to p...

Force-based seismic design of mixed CLT/Light-Frame buildings

This paper presents the results of a numerical study aimed to investigate the seismic behaviour of mixed multi-storey wood buildings made of CLT and Light-Frame shear walls acting at the same level. Eurocode 8 provides little information on the seismic design of buildings with different lateral load resisting systems working at the same level. A suggestion is given to perform non-linear static or non-linear dynamic analysis to design the structure. The application of linear analysis methods using the force-based procedure is not possible since the value of the behaviour factor q of the mixed system is unknown. The aim of this investigation is to propose a simple analytical formulation to estimate the value of the q-factor of the mixed system, so as to enable the use of the force-based philosophy of Eurocode 8 for the seismic design of mixed CLT/Light-Frame buildings. This was achieved by analysing the results of non-linear dynamic (time-history) analyses performed on a four-storey case-study building with different combinations of CLT and Light-Frame shear walls. Finally, the validity of the proposed formulation is checked by means of non-linear dynamic (time-history) analyses performed on the same four storey case-study building in one of the hybrid combinations of CLT and Light-Frame shear walls.

Strength Reduction Factors for High-Aspect-Ratio OSB Cold-Formed Steel Frame Shear Walls

Design provisions for cold-formed steel (CFS) light frame shear walls with wall height-to-width/length ratios (aspect ratios) greater than 2∶1, and less than 4∶1, requires a reduction in nominal strength based on the wall aspect ratio. This reduction is attributed to increased wall flexibility. The current strength reduction is not supported by existing data and it is not justified given building code lateral displacement limits and the availability of expressions to estimate wall displacement. Additionally, a significant underestimation of nominal or peak strength is not helpful where capacity-based design is adopted. In this paper, the results of an experimental program that included 11-mm oriented strand board (OSB) sheathed CFS shear walls with aspect ratios between 2∶3 and 8∶1 are presented, and a conservative, more consistent and less severe strength reduction expression is offered—an expression that facilitates more sustainable design and meets the intention of the current standards of engineering practice.

Seismic Design Strength of Cold-Formed Steel-Framed Shear Walls

A method for estimating the available strength level (load and resistance factor design) seismic resistance of light-frame cold-formed steel shear walls is discussed. The proposed method attempts to account for the early onset of inelastic behavior in light-frame shear walls by evaluating the strength level resistance in terms of an equivalent shear wall yield strength. Application of the proposed method is illustrated using shear wall data from an independent test program and wall performance is compared to current light-frame bearing wall design requirements and expected system performance. It is shown that the proposed method results in design values that are generally conservative compared to current design recommendations and the overall performance of the tested walls is characterized using five parameters that relate common design strength and displacement quantities.

Performance of Log Shear Walls Subjected to Monotonic and Reverse-Cyclic Loading

Low-rise buildings are typically designed with shear walls and horizontal diaphragms to resist lateral load during windstorms and earthquakes. Although seismic performance and lateral load resistance behavior are generally well-understood for light-frame wood construction, this is not true for log construction. Research is needed to characterize log shear wall behavior subject to racking loads, and to develop recommendations for designing log walls to resist lateral loads from seismic or wind events. Monotonic and reverse-cyclic tests were conducted on log shear walls with 1:1, 2:1, and 4:1 aspect ratios. These walls showed higher resistance than conventional light-frame shear walls and similar hysteretic behavior to concrete and masonry shear walls. Log walls withstood large in-plane displacements without significant load reduction using lateral bracing typical of that used for light-frame wall testing; however, the test procedure would be improved by providing full-wall support to resist out-of-plane displacements of log shear walls. Design recommendations were developed based on the experiments reported herein.

Development of a Wood-Frame Shear Wall Model in ABAQUS

After modifications, the Bouc-Wen-Barber-Wen (BWBN) model was used in simulating the hysteretic behavior of wood light-frame shear walls. A complete shear wall model is composed of boundary framing members and two-diagonal modified BWBN hysteretic springs. The parameters of the springs can be estimated based on the shear wall test data or detailed shear wall simulation results. To verify the accuracy and efficiency of this shear wall model, a two-story residential building was simulated and a three-dimensional dynamic analysis was conducted on it. The resultant structural responses agreed with the test results well.

Study on half-scale model test for light-frame shear wall

A half-scale model of a light-frame shear wall was developed to evaluate the racking performance of a fullscale shear wall (prototype). The effect of nail size on the performance of the shear wall was also investigated using models constructed with three types of nail. Materials for the model were determined through experimental methods, which included nail-head push-through, stud-to-sheathing nail connection, and static bending tests. Materials with which the model was made to be “in similarity” to the prototype were three-layer 4.8-mm plywood, 39.72-mm long nails, and 1 × 2 lumber cut from 2 × 4 studs. In accordance with ASTM E 72 and ASTM E 564, racking resistance tests were conducted on 20 shear walls. The results showed that the maximum load capacities of the prototype walls could be evaluated by the model without significantly different failure modes. Tests on the effect of nail size revealed that increasing the nail head diameter may improve the performance of shear walls.