Light-frame Timber Shear Walls Research Articles

Lateral Resistance of Reinforced Light-Frame Wood Shear Walls

In light-frame timber construction, the shear wall is one of the most important components that provide resistance to lateral loads such as earthquakes or winds. According to KDS (Korea Design Standard) 42 50 10, shear walls are to be constructed using wood-based structural sheathing, with studs connected by 8d nails spaced 150 mm along the edge and 300 mm in the field. Even though small-scale residential timber building can be designed to exhibit seismic resistance using light-frame timber shear walls in accordance with KDS 42 50 10, only the abovementioned standard type of timber shear wall is available. Therefore, more types of timber shear walls composed of various materials should be tested to measure their seismic resistance, and the results should be incorporated into the future revision of KDS 42 50 10. In this study, the seismic resistance of shear walls composed of structural timber studs and wood-based structural sheathing with reinforced nailing is tested to evaluate the effects of the reinforcement. For the nailing reinforcement, shear wall specimens are constructed by applying nail spacings of 75–150 mm and 50–100 mm. For the shear wall specimens with one sheathing and reinforced nailing, the shear strengths are 1.7–2.0 times higher than that of the standard shear wall (nail spacing of 150–300 mm). The shear strength of the shear walls with sheathing on both sides is 2.0–2.7 times higher than that of the standard shear wall.

Nonlinear FE-analysis and testing of light-frame timber shear walls subjected to cyclic loading

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.

Seismic performance of glulam timber post and beam structures with and without light frame timber shear wall infill

Timber post and beam structure is typical frame construction with a simple structural system and clear force transmission path. This work studies the seismic performance of glued-laminated timber (glulam) post and beam structures under cyclic loading, as well as the effect of light frame timber shear walls on their seismic performance. Experimental investigation on two types of full-scale glulam post and beam structures was carried out to compare the failure modes, mechanical properties, and energy dissipation. According to the test results, simplified models whose nonlinearity was assumed to be concentrated plasticity in the springs were developed. The comparison between test data and model prediction has a good agreement in terms of evaluation from backbone curves and strength degradation ratio. This calibrated model was then adopted as a benchmark model for further parametric analysis. Eight different configurations considering various aspect ratios were modeled to assess the influence of elastic stiffness and the maximum load-carrying capacity using the pushover analysis. The test investigation and numerical analysis of the glulam post and beam structures with and without light frame timber shear walls help comprehensively understand the seismic performance, providing some valuable guidance for further studies and structural design in engineering practice.

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.

Experimental investigation of OSB sheathed timber frame shear walls with strong anchorage subjected to cyclic lateral loading

Sheathed timber frame shear walls (STFSW) with strong anchorage have recently been studied to be used as the main lateral force resisting system in timber buildings. The first part of this research project highlighted the enhancement of the shear stiffness and strength of the STFSWs with strong anchorage in comparison with the established configuration of light-frame timber shear walls under monotonic horizontal loading. In this paper, the in-plane seismic behavior of STFSWs with strong anchorage was further investigated by means of quasi-static monotonic and cyclic loading tests on large-scale timber shear walls. The boundary conditions of the specimens were considered more realistically by applying a combination of vertical force and bending moment on top of the walls. In addition to the ISO 21581, the walls were tested under a new horizontal cyclic loading protocol especially developed for the low-to-medium seismicity regions. The STFSWs with strong anchorage showed a marginally higher shear resistance under cyclic loading. Nevertheless, in terms of ultimate displacement, they did not evidently perform as well as under monotonic loading when subjected to cyclic loading. Withdrawing of staples was the main failure of the stapled connections resulting in the out-of-plane displacement of the sheathing panels, which was clearly observed by the 3D digital image correlation measurement system. The low-to- moderate seismicity loading protocol was not highly influential on their shear resistance and displacement capacity.

Dissipation in sheathing-to-framing connections of light-frame timber shear walls under seismic loads

The present study is concerned with the seismic analysis and design of light-frame timber shear walls, with focus on the energy dissipation ensured by sheathing-to-framing connections under in-plane lateral loads. In this perspective, a suitable parametric finite element model for light-frame timber shear walls is first developed using the software OpenSees. By means of such model, the equivalent viscous damping of the wall is assessed numerically, together with the damping factor adopted within the capacity spectrum method. Furthermore, the optimal layouts of slender (1.2 m × 2.4 m/3.94 ft × 7.88 ft) and squat (2.4 m × 2.4 m/7.88 ft × 7.88 ft) light-frame timber shear walls are found by solving a multi-objective optimization problem in which racking capacity and total material cost are optimized simultaneously (this task is accomplished via simple enumeration because of the low cardinality of the design variables set). So doing, it is shown that the total material cost of the optimal (non-dominated) wall configurations has a strong influence on the racking capacity whereas it does not affect the equivalent viscous damping ratio, which remains almost constant. A novel simplified analytical procedure for predicting the capacity curve of light-frame timber shear walls is finally proposed.

Performance of Light-Frame Timber Shear Walls Produced with Weathered Sheathing

AbstractLight-frame wood construction is the most common construction method used for single- and multifamily residential structures in the United States. Shear walls made with engineered wood stru...

Lateral Resistance of CLT Wall Panels Composed of Square Timber Larch Core and Plywood Cross Bands

Thinned, small larch logs have small diameters and no value-added final use, except as wood chips, pallets, or fuel wood, which are products with very low economic value; however, their mechanical strength is suitable for structural applications. In this study, small larch logs were sawed, dried, and cut into square timbers (with a 90 mm × 90 mm cross section) that were laterally glued to form core panels used to manufacture cross-laminated timber (CLT) wall panels. The surface and back of these core panels were covered with 12-mm-thick structural plywood panels, used as cross bands to obtain three-ply CLT wall panels. This attachment procedure was conducted in two different ways: gluing and pressing (CGCLT) or gluing and nailing (NGCLT). The size of the as-manufactured CLT panels was 1,220 mm × 2,440 mm, the same as that of the plywood panels. The final wall panels were tested under lateral shear force in accordance with KS F 2154. As the lateral load resistance test required 2,440 mm × 2,440 mm specimens, two CLT wall panels had to be attached in parallel. In addition, the final CLT panels had tongued and grooved edges to allow parallel joints between adjacent pieces. For comparison, conventional light-frame timber shear walls and midply wall systems were also tested under the same conditions. Shear walls with edge nail spacing of 150 mm and 100 mm, the midply wall system, and the fabricated CGCLT and NGCLT wall panels exhibited maximum lateral resistances of 6.1 kN/m (100%), 9.7 kN/m (158%), 16.9 kN/m (274%), 29.6 kN/m (482%), and 35.8 kN/m (582%), respectively.

OSB sheathed light-frame timber shear walls with strong anchorage subjected to vertical load, bending moment, and monotonic lateral load

One of the common lateral load resisting systems in multi-story timber buildings in Central Europe are reinforced concrete shear walls. The RC shear walls are not optimal for timber buildings for several reasons such as: (i) the difference in tolerance between concrete and timber construction procedures, (ii) elevated construction time caused by necessary curing of concrete, (iii) moisture of concrete affecting the integrity and mechanical properties of timber, (iv) relatively high shear stiffness resulting in increased forces in seismic design, and (v) eccentricity with regard to applied seismic forces depending on the location of the shear walls. A light-frame timber shear wall (LFTSW) with OSB sheathing stapled to glued-laminated timber framing and strong anchorages has been investigated in this research program to be used as the single lateral load resisting system being located in the perimeter of the building. Results of experiments and numerical calculations showed 20% and 37% increases in shear stiffness and shear resistance, respectively, of the investigated LFTSWs in comparison with established LFTSW configurations. In addition to the conventional racking tests, vertical loads and bending moment were applied to the edge studs in order to study their effect on the in-plane behavior of the investigated LFTSWs. A marginal decrease in shear stiffness and shear resistance was observed due to the vertical load and bending moment applied. The decrease was more significant when applying the vertical loads due to the deformation, to which the staples were exposed, before applying the lateral load. Independent from level and combination of internal forces a ductile behavior was observed experimentally on the investigated LFTSWs, where the failure was governed by ductile displacements in the stapled connection between sheathing and framing.

Experimental investigation of friction stresses between adjacent panels made of Oriented Strand Board (OSB) and between OSB panels and glued laminated timber (GLT) frame members

The paper presents experimental investigations of friction properties (a) between adjacent sheathing panels made of Oriented Strand Board (OSB) and (b) between OSB panels and glued laminated timber (GLT) frame members as they occur, for example, between parts of light-frame timber shear walls. The friction stresses are evaluated for different levels of compressive stress and different loading rates in monotonic and cyclic tests. The test results confirm that the static friction coefficients are larger and have a larger variability than the kinetic friction coefficients. The friction coefficients between the GLT frame members and the OSB panels are in general smaller than the friction coefficients between the sheathing panels themselves. The tests show that the friction coefficients decrease with increasing cumulative sliding displacement. Analysis of the contact surface before and after the shear test indicates that the sliding reduces the height of the asperities of the contact surfaces. However, after a cumulative displacement of about 100 mm the friction coefficients remain approximately constant.

The effect of simulated flooding on the structural performance of light frame timber shear walls – An experimental approach

This paper presents the results of a series of tests on timber shear walls exposed to simulated flooding and drying. Load tests were conducted on three wall types; control, wet and restored. The mechanical properties of each of these wall types were compared. It was found that there were significant losses in mechanical strength for the wet and restored walls tested. For wet walls, ultimate strength was reduced by 20% and for the restored walls ultimate strength was reduced by 25%. The restored walls were observed to fail due to sheathing buckling caused by swelling of the OSB during simulated flooding. This failure mode following flooding and restoration is one that is not currently accounted for by design codes or designers.

Open scientific problems about the Platform Frame constructive system

The aim of this paper is to provide a numerical simulation for giving a technical answer to some problems that a structural engineer has to solve when designing a timber building based of Platform Frame technology, i.e., composed of light-frame timber shear walls. For a fully anchored wall, a finite element model, aimed at determining wall stiffness, strength and ductility, is presented. The shear wall is considered as lacking of any constructive imperfection.

Plastic models for analysis of fully anchored light-frame timber shear walls

In order to stabilise timber-framed buildings against lateral loads, the diaphragm action of roofs, floors and walls is often used. This paper deals with plastic analysis models for fully anchored sheathed shear walls. The models are based on the assumption of plastic load–slip relations for the sheathing-to-framing joints. Only static loads are considered. The basic structural behaviour and assumptions for the plastic models are elucidated. Both upper and lower bound methods are applied. The load-bearing capacity and the deformation of the shear walls in the ultimate and serviceability limit states, respectively, are derived. Both a discrete point description and a continuous flow per unit length modelling of the fasteners are discussed. Also, the forces and displacements of the fasteners and sheathing are derived. The influence of flexible framing members and shear deformations in the sheets, and also the effect of vertical loads on the shear wall, both with respect to tilting and second order effects, on the horizontal load-bearing capacity and displacement are evaluated. The stress distribution and the reaction forces at the ends of the different framing members are derived. The elastic model is experimentally verified and an illustrative example is given. The main objective of this work is to contribute to a better understanding of the structural behaviour of these fully anchored walls and form the basis for establishing a new plastic design method for partially anchored shear walls, i.e. a design method capable of analysing the more practical conditions of no or partial anchorage of the studs and/or bottom rail in real structures.

Elasto-plastic model for analysis of influence of imperfections on stiffness of fully anchored light-frame timber shear walls

In order to stabilize timber-framed buildings against lateral loads, the diaphragm action of roofs, floors and walls is often used. This paper deals with the influence of imperfections such as gaps and uplift on the stiffness and the horizontal displacement of fully anchored shear walls. The significance of analyzing the effects of imperfections is evident when evaluating the stiffness of shear walls; tests of walls show that the horizontal displacement is underestimated in calculations using the stiffness of sheathing-to-framing joints as obtained from experiments. Also, in real structures where hold-downs are used, the influence of gaps and uplift should be included in order to obtain realistic displacements in the serviceability limit state. The analytical model is based on ideal plastic behavior of the mechanical sheathing-to-timber joints with stresses parallel to the perimeter of the frame and on linear elastic behavior for stresses perpendicular to the bottom rail. Using this elasto-plastic model, the equations for the stiffness and the deflection versus the number of segments in the wall are derived. The fully anchored condition for the shear walls is simulated by applying a diagonal load to the shear wall. Three types of imperfections are evaluated: Walls with gaps at all studs, a gap only at the trailing stud, and gaps at all studs, except at the trailing stud. It is shown that the effect of imperfections on the stiffness of the wall in the initial stage is considerable. Depending on the distribution of the gaps and the number of segments included in the shear wall, the displacement of the shear wall is increased several times compared to that of a fully anchored wall diaphragm with no gaps; e.g. for a single segment wall more than four times. However, for walls with more than six segments the effect of imperfections can be neglected. Finally, the theoretical model is experimentally verified.

Analysis of fully anchored light-frame timber shear walls—elastic model

In order to stabilize light-framed timber buildings against lateral loads, the diaphragm action of roofs, floors and walls is often used. This paper deals with an elastic analysis model for fully anchored sheathed wood frame shear walls. The model is based on the assumption of a linear elastic load-slip relation for the sheathing-to-framing joints. Only static loads are considered. The basic structural behaviour and assumptions for the elastic model are elucidated. Formulas for the load-bearing capacity and the deformation of the shear walls in the ultimate and serviceability limit states, respectively, are derived. Both a discrete point description and a continuous flow per unit length modelling of the fasteners are discussed. Also, the forces and displacements of the fasteners and sheathing are derived. The effect of different patterns and spacing of the fasteners on the capacity and displacement of the wall is illustrated. The influence of flexible framing members and shear deformations in the sheets, and also the effect of vertical loads on the shear wall, both with respect to tilting and second order effects, on the horizontal load-bearing capacity and displacement are evaluated. The stress distribution and the reaction forces at the ends of the different framing members are derived. The elastic model is experimentally verified and an illustrative example is given.

Analysis of influence of imperfections on stiffness of fully anchored light-frame timber shear walls—elastic model

In order to stabilize light-frame timber buildings against horizontal loads, the diaphragm or in-plane action of roofs, floors and walls is often used. This paper deals with the influence of imperfections such as gaps and uplift on the horizontal displacement of fully anchored shear walls. The significance of analyzing the effects of imperfections is evident when evaluating the stiffness of shear walls; tests of walls show that the horizontal displacement is underestimated in calculations using the stiffness of sheathing-to-framing joints as obtained from experiments. Also, in real structures where hold-downs are used according to the elastic design method, the influence of gaps and uplift should be included in order to obtain realistic displacements in the serviceability limit state. A new elastic model for the analysis, based on linear elastic behaviour of the mechanical sheathing-to-framing joints, is presented and the equations for the stiffness and the deflection versus the number of segments in the wall are derived. The fully anchored condition for the shear walls are modelled by applying a diagonal load to the wall. Three types of imperfections are evaluated: gaps at all studs, a gap only at the trailing stud, and gaps at all studs, except at the trailing stud. It is shown that the effect of imperfections on the stiffness of the wall in the initial stage is considerable. Depending on the distribution of the gaps and the number of segments included in the shear wall, the displacement of the shear wall is increased several times compared to that of a fully anchored shear wall with no gaps; e.g. for a single segment wall more than three times. However, for walls with more than six to ten segments, the effect of imperfections can be neglected. Finally, the theoretical model is experimentally verified.