Wood Frame Shear Walls Research Articles

Experimental Cyclic Performance of Viscoelastic Gypsum Connections and Shear Walls

The shear capacity of gypsum sheathed shear walls is typically neglected in areas of high seismicity due to the susceptibility of conventional drywall screw connections to damage caused by earthquakes. This paper presents an alternative to the conventional screwed sheathing connection found in wood-framed gypsum shear walls. A viscoelastic (VE) polymer was inserted between the sheathing and the stud framing. A sheathing connection study and shear wall study were performed, and the results of the VE connection show a dramatic increase in stiffness and energy dissipation over the conventional screwed connection. Energy dissipation increases 632% for the sheathing connection and 510% for the shear wall. Stiffness of the shear wall also improves. The VE polymer improves structural performance while resisting damage when subjected to shear displacements up to 18 mm by providing a constant source of energy dissipation. This new VE sheathing connection may allow for weak or nonstructural materials, such as gypsum wallboard, to be used as structural elements for design purposes while reducing the risk of costly damages during seismic events.

Effects of Vertical Load and Hold-Down Anchors on the Cyclic Response of Wood Framed Shear Walls

Twenty one 2.4 m by 2.4 m ( 8 ft by 8 ft ) wood framed shear walls were tested to study the effect of vertical load and hold-down anchors on the cyclic behavior of the wall. Seven different configurations were investigated including walls without hold-down anchors and uniform vertical loads of 0, 6, 12, and 25 kN∕m (0, 425, 850, and 1,700 lb∕ft ) and walls with hold-down anchors and uniform vertical loads of 0, 12, and 25 kN∕m (0, 850, and 1,700 lb∕ft ). The walls were loaded cyclically according to the Consortium of Universities for Research in Earthquake Engineering test protocol. Results show that the effects of vertical load on the cyclic response of wood frame shear walls are to: (1) increase the lateral stiffness and (2) increase the energy dissipation capacity. The lateral stiffness increased by up to 80% for walls with vertical loads of 25 kN∕m (1,700 lb∕ft) , over the full range of displacement amplitudes; energy dissipation increased by up to 100% for walls with vertical loads of 25 kN∕m (1,700 ...

Performance of Wood Shear Walls Sheathed with FRP-Reinforced OSB Panels

This study addresses the development and structural testing of a hybrid sheathing panel designed to improve the lateral resistance of light wood-frame shear walls. The panel consists of thin outer sheets of oriented-strand board (OSB) bonded to strips of fiber-reinforced polymer (FRP) that are sandwiched between the OSB panels at the edges. The FRP-reinforced panel material selection and fabrication are summarized. Monotonic and cyclic tests were conducted to assess the performance of single-connector sheathing-to-framing connections using both OSB and FRP-reinforced OSB. Twenty-four full-scale shear walls were tested under monotonic and cyclic racking loads to determine the benefits of FRP-reinforced OSB to wall lateral load resistance. For a 102 mm perimeter nail spacing, FRP-reinforced OSB-sheathed walls exhibited increases in peak capacity and energy dissipation under cyclic loading of 27 and 73%, respectively, compared to walls sheathed with conventional OSB. Based on these experimental results, FRP-reinforced OSB panels appear to have significant potential for increasing the energy dissipation capacity and lateral load resistance of wood-frame structures subjected to extreme lateral loads. However, their full utilization will require higher strengths for critical shear wall components such as tension ties and framing interconnections, as well as improvements in sheathing-to-framing fastener performance.

Fragility Analysis for Performance-Based Seismic Design of Engineered Wood Shearwalls

Performance-based engineering concepts applied to both structural design and assessment have gained interest among structural engineers and researchers in recent years. Performance-based design applied to building systems includes selection of appropriate structural systems and configurations to ensure that the structure has adequate strength, stiffness, and energy dissipation capacity to respond to loadings, including those arising from natural hazards, without exceeding permissible damage states. Although performance-based design has advanced for some materials and structural types, such as steel and reinforced concrete buildings and bridges built in high seismic regions, the application to light-frame wood structures has only recently been explored. This paper investigates the application of fragility techniques to the seismic design of engineered woodframe shearwalls. The methodology developed herein provides a technical basis for the development of future performance-based design provisions for shear...

Experimental Investigation of the Effect of Vertical Load on the Capacity of Wood Shear Walls

A series of 10 tests were conducted to determine the effect of a vertical load on the lateral load capacity of wood frame shear walls. Static tests were performed on 2.4 m-by-2.4m wood walls, for varying vertical load. Tests were conducted with and without hold-down anchors. Specimens were subjected to three half cycles of lateral loading, the final being to failure. The presence of vertical load on a wood frame shear wall was found to have a significant effect on the lateral load capacity of the wall. The ultimate load capacities of walls with hold-down anchors increased by 20 and 28% for walls with a vertical load of 12 and 25kN∕m, respectively, as compared to the wall without vertical load. The vertical load was also found to have significant effect on the lateral stiffness of the wall. Results also show that hold-down anchors do not add significantly to the strength of the wall when a vertical load equal to the maximum allowable is present. Finally, the results presented suggest that current code specified allowable shear forces are conservative when a vertical load is present; the wall has additional reserve capacity than is reflected by current code specified allowable shears.

Effects of Finish Materials and Dynamic Loading on the Cyclic Response of Woodframe Shearwalls

A study on the effects of gypsum wallboard and stucco nonstructural finish materials on the seismic capacity of woodframe shearwalls was carried out. The focus was on the performance of shearwalls with these finish materials combined with a wood structural sheathing (plywood or oriented strand board). Also investigated were the effects of dynamic loading with rates on the order of a woodframe structural response to a seismic event. All testing was performed using standard construction 2.4 m square woodframe shearwalls loaded at the top plate. Findings from the study indicate that nonstructural finish materials have a substantial influence on the performance of woodframe shearwalls, causing increases in strength and stiffness, and reductions in deformation capacity. There was also a noticeable change in failure mode created by the application of finish materials. The loading rate study, comparing specimens under quasi-static loading with specimens loaded dynamically, showed only modest differences caused b...

Effects of Loading Protocol on the Cyclic Response of Woodframe Shearwalls

Standard construction 2.4m×2.4m woodframe shearwalls were tested using different loading protocols. The CUREE-Caltech protocols, recently developed by Krawinkler in 2001, were compared with other previously used protocols. The following protocols were considered in the study: monotonic, CUREE-Caltech standard (CUREE), CUREE-Caltech near-fault, sequential phased displacement (SPD), and international standards organization. Findings from the research indicate that loading sequence has a significant influence on shearwall performance. Protocols with a large number of cycles (SPD) tended to produce nail fatigue fractures, which were not nearly as prevalent in protocols with lower numbers of cycles (CUREE). The research clearly showed that the nail fatigue fractures were associated with a large energy demand related to the number of cycles, which resulted in a reduced ultimate strength and deformation capacity. The initial stiffness of the specimens was relatively unaffected by the loading protocol used; howev...

Prediction of seismic behavior of wood-framed shear walls with openings by pseudodynamic test and FE model

This article summarizes an experimental and numerical study on seismic behavior of wood-framed shear walls with an opening. The objectives of this study were to compare the results of static and pseudodynamic tests of plywood-sheathed shear walls with numerical simulation by the Finite Element (FE) model and to validate a finite element code EFICOBOIS for such an application. This software is based on a macroelement approach to limit the number of degrees of freedom for the whole system. Nonlinear laws for connections such as nails and hold-down connections, among others, are applied through macroelements that link plate elements to beam elements. Numerical results obtained for the various loading conditions showed good agreement with the experiments. Both static and dynamic computations are presented here.

Timber shear walls with large openings: experimental and numerical prediction of the structural behaviour

A numerical model based on the finite element method is presented for prediction of the cyclic response of wood frame structures. The model predicts the cyclic response of shear walls. Nonlinear phenomena are assumed to be concentrated in the connections that are modelled through elements linking the structural elements including the posts, beams, and sheathing panels. Identification of model parameters relies on tests on individual connections. Connection tests on different nail lengths were conducted under monotonic and cyclic lateral loads. Based on the results from past studies that indicate the pull-through failure is an important failure mode in common nail connections with lumber and oriented strand board (OSB), washers were considered as a means to reinforce the connection. The influence of reinforced nailing on the static and dynamic performance of full-size wood frame shear walls with large openings, sheathed with OSB panels, was evaluated experimentally. Combinations of parameters were studied, such as the number of hold-downs, the panel shapes, the nail distribution, and the bracing systems. Comparisons of the dissipated energy per cycle revealed a higher capacity for walls using nails with washer reinforcement than without. Results from numerical simulations of the monotonic and cyclic tests performed on the walls are presented.Key words: timber shear wall, connections, finite element, dissipated energy.

Sensitivity study of the finite element model for wood-framed shear walls

A sensitivity study was performed with a nonlinear elastic finite element model for monotonie analyses of wood-framed shear walls. The objective was to provide information about simplifying a model of wood-framed shear walls with no significant loss in accuracy. The simplifications concern features such as slips in joints between frame members, slips in hold-down connections, and bearing between adjacent sheathing panels. The results from analyses of a shear wall with an opening of window shape show that the effect of constraint by the bearing between sheathing panels and slips in frame joints on the overall stiffness of the wall is limited. Thus, there are great possibilities for reducing the calculation time by not taking these phenomena into account, avoiding an excessive number of degrees of freedom and iterations. The influence of the simplifications on the distribution of vertical reaction forces along the wall is more significant. Furthermore, if each simplification is introduced separately, the effect on the overall stiffness is greater. The difference, however, is less than 10%. The failing pattern of the nail connections is also clearly influenced by the simplifications when they are introduced separately. The results from the analyses show that slips in frame joints can be sufficiently represented by those in connection with the opening.

Validation of seismic design parameters for wood-frame shearwall systems

A methodology for assessment of seismic design parameters for a wood-frame shearwall system is developed, consisting of a test program of shearwalls and the application of nonlinear time history analyses to a four-storey wood-frame building that was designed to resist the seismic requirements for Vancouver, British Columbia. Analyses employed 22 selected earthquake accelerograms that were scaled upwards until an ultimate peak ground acceleration (Au) was reached where the shearwall reached a "near-collapse" state. The 22 values of Au were found to be greater than the "design" peak ground acceleration, indicating the adequacy of the current design procedures for the particular shearwalls investigated. The influence of gypsum wallboard on the behaviour of the shearwalls was also evaluated, and a new force modification factor "R" for walls composed of a mixture of wood-based and gypsum panels was proposed. The effect of flexibility of floor diaphragms was considered separately for a symmetric building and was found to have 5-30% reduction on the Au values obtained for the rigid diaphragm case.Key words: seismic design, earthquake loads, timber structures, wood shearwalls.

Model for Dynamic Analysis of Wood Frame Shear Walls

A discrete three-degree-of-freedom model of a wood frame shear wall has been developed that is suitable for design-type analyses. The model captures the salient features of the wall response, is amenable to exact closed-form solution, and has the flexibility to account for variations in wall geometry, framing and sheathing materials, fastener type, and spacing. Sheathing-to-stud connections are modeled using a linear viscoelastic element; a method is presented for determining the connection properties using the results of full-scale shear wall tests and a closed-form solution for the test excitation. Results show that the model accurately predicts the hysteretic behavior of the wall for low to moderate displacements; at larger displacements the linear model captures the overall behavior (effective stiffness and energy dissipation), but, as would be expected, fails to predict the pinched hysteresis observed in the tests. Finally, a response spectrum analysis is conducted of a single-story wood frame structure to demonstrate how the model can be used for design-type analyses.

RESPONSE TO: C. Higgins's and K. Kasai's Discussion of “The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers”

<i>RESPONSE TO:</i> C. Higgins's and K. Kasai's Discussion of “The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers”

DISCUSSION OF: “The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers”

<i>DISCUSSION OF:</i> “The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers”

The Dynamic Response of Wood-Frame Shear Walls with Viscoelastic Dampers

Results are presented of an experimental investigation, the objectives of which were to evaluate and compare the performance of conventional plywood shear walls with walls that include viscoelastic (VE) dampers. Cyclic tests were conducted on conventional walls and walls with VE dampers; five different damper configurations were tested. The walls with the VE dampers showed an increase in the total energy dissipation and an increase in the effective stiffness, relative to the conventional wall, with increases in energy dissipation as high as 59 percent. Tests demonstrated that the sheathing-to-stud and corner dampers can easily be installed within the confines of the wall and can be utilized without impacting the design, construction, or finishing of the shear wall. The results demonstrate that addition of the viscoelastic dampers significantly enhanced the dynamic performance of the walls by increasing the energy dissipation capacity and providing a constant source of energy dissipation.

Stiffness and energy degradation of wood frame shear walls

Tests have been conducted on wood frame shear walls to characterize the degradation of stiffness and energy dissipation that occurs under cyclic loading. A total of eight walls were tested, four sheathed in plywood and four sheathed in oriented-strand board. The tests were conducted in accordance with a draft test procedure recently proposed by the Structural Engineers Association of Southern California, which is based on a sequential phased displacement command input. The results indicate that effective stiffness decreases linearly with continued cycling at the same displacement and decreases with increasing amplitudes of displacement. Furthermore, the energy dissipation capacity of the wall decreases by 15-20% with the first cycle at a given amplitude, then decreases slightly with continued cycling at the same amplitude. The changes in effective stiffness and energy dissipation are generally independent of the type of sheathing for loads less than the wall ultimate, suggesting that the wall performance under cyclic loading is influenced more by the fastener and frame behavior. The results presented should be useful for design and for verifying hysteretic models of the shear wall behavior.Key words: cyclic, dynamic, energy dissipation, experimental, seismic, shear wall, stiffness, testing, timber, wood frame.

Comparison of Static and Dynamic Response of Timber Shear Walls

Static and dynamic tests were conducted on wood frame shear walls to (1) determine the wall resistance to lateral loading; (2) examine the wall performance under fully reversed cycles of dynamic loading; and (3) compare the static and dynamic performance as measured using the same test facility. Tests were conducted on standard 2.44 by 2.44 m (8 by 8 ft) walls, constructed of plywood or oriented strand board sheathing. Four specimens were tested statically using the traditional ASTM E-564 test procedure: three half-cycles, loading monotonically to failure. Eight specimens were tested dynamically, using a proposed test standard that was recently developed by the Structural Engineers Association of Southern California. A comparison of the static and dynamic test results demonstrates several key differences. The ultimate loads measured in the dynamic tests are slightly less than those measured in the static tests; however, the ductility of the wall, when measured dynamically, is between 34 and 42% less than ...

Stiffness and energy degradation of wood frame shear walls

Stiffness and energy degradation of wood frame shear walls

Formulas for Wood Shear Walls

Formulas are presented for the analysis of typical wood-frame shear walls with sheathing attached by nails or other types of discrete fasteners. Formulas are derived for the sheathing fastener forces, for the linear shear stiffness of a wall, and for the nonlinear shear load-strain behavior of a wall. These formulas are shown to be in agreement with the results of load tests and of finite element, linear, and nonlinear analyses. Details of the load tests and finite element analyses are given. The formulas are relatively simple and should be applicable to the design of wood frame shear walls with plywood or other types of sheathing.