Field determination and modeling of load paths in wood light-frame structures

Low-rise buildings, constructed using wood, are vulnerable to extreme wind storms and earthquakes. While several experimental measurements of the environmental loads (mostly wind) on the building envelope have been made at full scale, none of these studies directly linked these external loads with the internal forces and displacements of the structure, as achieved in this research.The thesis presents the experimental and analytical work on two light-frame wooden structures, where one already existed (Forintek shed in Quebec City) and the other (UNB house) was built specifically for the research project on the University of New Brunswick campus in Fredericton. The research goal was to devise and demonstrate methods of identifying load paths in light-frame wood buildings subject to environmental loads. The objectives were also to improve the knowledge on the magnitude of the forces generated by environmental loads on typical low-rise buildings; to measure forces and deformations in test buildings and correlate them with the applied loads; and finally to develop accurate numerical whole-building structural models.These goals were achieved by carrying out experiments at the element level (studs, sheathings), subsystem level (shear walls) and on the whole-building level (finished and "realistic" light-frame timber buildings). The responses of these buildings to controlled static tests as well as natural environmental loads were observed and compared with a wind tunnel study and with detailed finite element models with good agreement.Shear walls were tested in isolation and as a part of the whole structure. The tests indicated that neither the strength nor the stiffness decreased by the same magnitude as the wall effective length is reduced. Therefore, the simple concept of effective length, being used presently, is invalid.For the Forintek shed, the structural monitoring was based on measurements of deformations within a representative segment of the wall and roof surfaces and a matching grid of wall and roof wind pressure taps supplemented with a wind tunnel study at Concordia University. In general, it was shown that the building surroundings had a great effect on the pressure distribution of the surface on the structure and that these effects are cannot always be determined intuitively. Both mean and peak pressure coefficient were measured and they compared well with corresponding values obtained in the wind tunnel tests. In general, the peak pressure coefficients from the full-scale tests were higher than those obtained from the wind-tunnel tests.The results from controlled static loads on the UNB house indicated that the load was distributed to all walls, and significant load sharing was observed. Mostly, this reflected not only the rigidity of the roof, but also the rigidity of transverse walls. The stiffness of the roof was sufficient to distribute load to walls farthest away from the load application point. Also, the expected vertical paths for load were not observed. It was also found that the internal forces are concentrated near the corners of the building. Under vertical loading on the roof, the load at the roof-to-wall interface was concentrated in a small region of the building plan around the application point. This was not the case at the superstructure-to-foundation interface. The test results also showed that the load was transferred to the transverse walls, even though there were only nominal connection between the wall and the roof trusses.The results from the analytical modeling showed good agreement with the full-scale test results for shear walls as well as for the whole building. The 3-D model was able to simulate the sharing of racking forces between shear walls, based on experiments reported in the literature. It was also able to reproduce static test results and predict the force measurements obtained from load cells underneath the house structure. In general, the errors in the numerical prediction were small. The model was able to predict the interaction between the roof system and the walls and the interactions amongst walls.The research relied on the collaboration of several researchers in industry and academia, and was funded by a CRD grant of the Natural Sciences and Engineering Research Council of Canada

Investigating the behaviour of typical and designed wall-to-floor connections in light-frame wood stud wall structures subjected to blast loading

The performance of light-frame wood stud walls under simulated blast loading has so far been limited to investigating the behaviour of structural elements with idealized boundary conditions. The current study investigates, experimentally and analytically, whether walls with prescriptive connection detailing for low and high seismic and wind regions are capable of resisting blast loadings such that the walls’ ultimate capacity can be reached. The study also investigates the behaviour of different connections with various design capacity levels in order to develop failure in the stud wall system rather than in the connection. A total of ten full-scale walls with different boundary conditions were tested dynamically. The results showed that typical prescriptive connection detailing did not perform adequately. Designed connections performed well, but the findings show that basing the connection design solely on capacity may be inadequate. Single degree-of-freedom modelling may only be utilized if damage in the connections is limited.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Stiffness model for gypsum wallboard-to-wood joints

Joints simulating typical connections of GWB sheathed walls were subjected to reversed cyclic loading. Three different empirical models were analyzed for the purpose of determining the most appropriate fastener slip equation. The power model was used to develop the fastener slip equations, for nails and screws, as a function of GWB density and fastener diameter. The accuracy of the developed fastener slip model is validated against full-scale shear wall tests. The predictive models seem to be able to replicate the wall behaviour with reasonable accuracy until ultimate capacity. The results show a reasonable agreement between the model prediction and those obtained from the shear wall tests. The model perdition of for shear walls constructed with low fastener spacing is less accurate. This result was expected since the small fastener spacing violate the minimum spacing requirements in the design standard (CSA 2014) and caused a brittle failure.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Experimental and numerical investigation of lateral torsional buckling of wood I-joists

This paper investigates the elastic lateral torsional buckling capacity of wood I-joists. A sensitivity analysis determined that the orthotropic material properties that affect the critical buckling load of wood I-joists are the longitudinal modulus of elasticity, the transverse shear modulus of the flanges and the elastic modulus of the web. A 3D finite element model was developed using experimentally determined material properties and initial imperfections. The study found that FE linear predictions provided reasonable agreement with the experimental buckling loads. The FE geometric nonlinear analysis was able to replicate the experimental nonlinear behavior that was observed during the test. Comparison with contemporary North American design standards showed significant conservatism in the design approach.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Dynamic Characteristics of Light-Frame Wood Buildings

This paper deals with dynamic field testing of light-frame wood buildings with wood based shear walls. The primary objective of the investigation is to provide an estimate of the fundamental period of such buildings, through field testing and numerical modelling. An experimental program is established to perform ambient vibration testing on forty-one light-frame wood buildings of both regular and irregular layouts, located in moderate to high seismic zones in different regions in Canada. The research objective is to develop a reliable method of estimating the building period of light-frame wood buildings and develop an accurate expression for building period estimate based on field testing and numerical modeling. The study found that significant scatter is observed in the measured data when plotted as a function of building height. Finite element models were developed and compared with the natural periods of the buildings with reasonable accuracy. Using the validated FE models to examine different commonly used stiffness models showed that in general current analysis approaches overestimate the building periodThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Effect of nonstructural components on the dynamic characteristics of light-frame wood buildings

This research deals with ambient vibration measurements (AVM) in 16 multi-storey light-frame wood buildings with wood-based shear walls as the main lateral load resisting system. Its primary objective is to evaluate the effect of nonstructural sheathing panels and the connectivity between firewall-separated buildings, on the modal properties of the tested buildings. Lower natural frequencies, corresponding mode shapes and equivalent structural damping were extracted from the AVM records. The study confirmed that the increase in stiffness of the finished buildings was dominant over their increase in mass when sway mode periods of finished buildings and bare structural frameworks are compared. The stiffening effect of gypsum wallboard was deemed significant and should be accounted for in seismic design. The study also indicates that even when the building section were only nominally connected to the firewall, composite action in the lateral response was taking place.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Establishing the Fundamental Period of Light-Frame Wood Buildings on the Basis of Ambient Vibration Tests

This research project deals with dynamic field testing of light-frame wood buildings with wood- based shear walls. The primary objective of the investigation is to evaluate the building code formula for estimating light- frame wood buildingâ s fundamental period for seismic analysis, through intensive field testing and numerical modelling. The project also aims to propose an alternative simplified rational approach to seismic analysis of these structures. The paper presents ambient vibration (AV) testing results of light-frame wood buildings in Canada. The dynamic characteristics of the measured buildings, such as natural frequency, mode shapes and equivalent structural damping were obtained from Frequency Domain (FD) analysis of ambient motion records. Using a simplified method of period estimation based on the Rayleigh approximation while using the building mass and replacing the stiffness of shear walls by their length showed reasonable fit when compared with the FE model results and AVT measured periods. A formula was developed based regression analysis of tested buildings. The expression is a function of building height, floor area and shear wall length and it was shown to provide a reasonably good fit with the measured resultsThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Nailed connection behavior in light-frame wood shear walls with an intermediate layer of insulation

The shear strength and stiffness of light-frame wood shear walls is highly dependent on the behavior of their individual nailed connections. Eighty-four nailed connection specimens were tested under shear loading to determine the effect of including rigid insulation as an intermediate material between the sheathing and framing elements in a light-frame wood shear wall. Each specimen contained common 10d or 16d nails, 15.9 mm oriented strandboard sheathing, spruce-pine-fir lumber, and rigid insulation in varied thicknesses between 0 and 38.1 mm. From the load-deformation results, maximum load, yield load, and stiffness were assessed using curve-fitting and yield-point determination methods. The results indicate that, as the insulation thickness increases, the connection strength and stiffness both exhibit a steep reduction. In addition, nonlinear two-dimensional (2D) finite-element models of the same nailed connections were developed. These models showed good correlation with experimental data and served to confirm that the decline in strength and stiffness observed in the tests is due to the introduction of the insulation

DAMAGE LEVEL ASSESSMENT OF RESPONSE LIMITS IN LIGHT-FRAME WOOD STUD WALLS SUBJECTED TO BLAST LOADING

Currently, no systematic approach exists for damage evaluation of light-frame wood structures subjected to blast loading. This paper presents a detailed assessment of the behaviour of thirty-three full-scale light-frame wood stud walls subjected to a total of forty-eight shots of simulated blast loading. Detailed documentation of the observed damage allowed for the development of an accurate evaluation strategy of the response limits. The observed response limits are compared to limits derived from single-degree-of-freedom modelling using scaled pressure-impulse diagrams and to current code performance levels. It was concluded that the assumption made in contemporary blast design codes overestimates the ductility ratios for light-frame wood stud walls, and that using a maximum ductility of 2 is more appropriate and safer for blast design. Based on the observed damage levels obtained from the experimental study, the authors propose new ductility ratios corresponding to four damage regions.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Testing and analytical modelling of intermediate gypsum wallboard in wood shear wall sheathing to framing connections

Light frame wood shear walls resist lateral loads primarily through the individual nailed connections between the sheathing and framing. The most common arrangement for such shear walls is to have sheathing on one side and gypsum board on the other. In various situations it can be desirable to increase the capacity of this type of walls by fastening a layer of sheathing overtop of the drywall. This study considered the effect that an intermediate layer of gypsum has on the strength of nailed connections in shear walls, while maintaining code-defined minimum nail penetrations. Results show that intermediate gypsum placed between the sheathing and framing resulted in significantly reduced capacity and stiffness. Analytical modelling showed good correlation with experimental results. The implications of the experimental testing and modelling are that code provisions allowing the use of intermediate gypsum wallboard should not be relied upon