Light-frame Wood Research Articles

Assessment of ASCE 7-10 for wind effects on low-rise wood frame buildings with database-assisted design methodology

The design wind pressure for low-rise buildings in the ASCE 7-10 is defined by procedures that are categorized into the Main Wind Force-Resisting System (MWFRS) and the Components and Cladding (C&C). Some of these procedures were originally developed based on steel portal frames of industrial buildings, while the residential structures are a completely different structural system, most of which are designed as low-rise light-frame wood constructions. The purpose of this study is to discuss the rationality (or irrationality) of the extension of the wind loads calculated by the ASCE 7-10 to the light-frame wood residential buildings that represent the most vulnerable structures under extreme wind conditions. To serve this purpose, the same approach as used in the development of Chapter 28 of the ASCE 7-10 that envelops peak responses is adopted in the present study. Database-assisted design (DAD) methodology is used by applying the dynamic wind loads from Louisiana State University (LSU) database on a typical residential building model to assess the applicability of the standard by comparing the induced responses. Rather than the postulated critical member demands on the industrial building such as the bending moments at the knee, the maximum values at the critical points for wood frame buildings under wind loads are used as indicators for the comparison. Then, the critical members are identified through these indicators in terms of the displacement or the uplift force at connections and roof envelope. As a result, some situations for each of the ASCE 7 procedures yielding unconservative wind loads on the typical low-rise residential building are identified.

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 building’s fundamental period for seismic analysis, through intensive field testing and numerical modeling. The project also aims to propose an alternative simplified rational approach to seismic analysis of these structures. The paper presents ambient vibration 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 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 finite element model results and ambient vibration testing measured periods. A formula was developed based on the regression analysis of the 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 results.

Effects of Ground Motion Duration on the Seismic Performance and Collapse Rate of Light-Frame Wood Houses

AbstractThis paper studies the effects of long duration ground motion on three conventional low-rise light-frame wood houses with different sheathing configurations. These are two-story residential...

Nonlinear Modeling of Wood-Frame Shear Wall Systems for Performance-Based Earthquake Engineering: Recommendations for the ASCE 41 Standard

AbstractWood shear wall systems are the primary elements of seismic force-resisting system (SFRS) in virtually all light-frame wood buildings. Wood-frame buildings are unique because their nonstruc...

Seismic behavior of Chuan-Dou type timber frames

Chuan-Dou type timber constructions are popular structural systems in ancient China, which consist of planar frames jointed with mortise-tenon connection in two directions. Three types of four full scale single story and two-bay Chuan-Dou type timber frames were tested under low-cycle reversed cyclic loading. The ultimate load carrying capacity, stiffness, energy dissipation, deformation and damage characteristics were investigated. Results indicate that the Chuan-Dou type timber frame has exceptional deformation capacity, good energy dissipation capacity and poor ultimate load carrying capacity and stiffness. The load carrying capacity and stiffness of the Chuan-Dou type bare frame can be improved by infilling wattle and daub panel or light frame wood shear wall panel. Light frame wood shear wall panel can be used as a measure for seismic retrofit of Chuan-Dou type timber structures.

Development of Vermiculite Board to Secure the Fire Resistance Performance of Light-Frame Wood Structural Wall

Development of Vermiculite Board to Secure the Fire Resistance Performance of Light-Frame Wood Structural Wall

Seismic assessment of a three-story wood building with an integrated CLT-lightframe system using RTHS

This paper presents the results of an experimental study whose objective was to investigate the behavior of a hybrid wood shear-wall system defined herein as a combination of traditional light-frame wood shear walls with post-tensioned rocking Cross-Laminated Timber (CLT) panels. The post-tensioned CLT panels in the hybrid system offer both vertical and lateral load resistance and self-centering capacities. The traditional Light-Frame Wood Systems (LiFS) provide additional lateral load resistance along with a large amount of energy dissipation through the friction of nail connections. Thus, a combination of these two types of structures, in which traditional light-frame wood shearwalls are utilized as structural partition walls, may provide an excellent structural solution for mid-rise to tall wood buildings for apartments/condos, where there is a need for resisting large lateral and vertical loads as well as structural stability. In this study, a real-time hybrid testing algorithm using a combination of time-delay updating and Newmark-Beta feed forward to reduce the undesirable effects of time delay was introduced. The top two-stories of a three-story building were modeled as a numerical substructure with the first story as the experimental CLT-LiFS substructure. The experimental results of the hybrid wall are presented and discussed in this paper.

Seismic performance assessment of steel frame infilled with prefabricated wood shear walls

Steel-timber hybrid structural systems offer a modern solution for building multi-story structures with more environmentally-friendly features. This paper presents a comprehensive seismic performance assessment for a kind of multi-story steel-timber hybrid structure. In such a hybrid structure, steel moment resisting frames are infilled with prefabricated light wood frame shear walls to serve as the lateral load resisting system (LLRS). In this paper, drift-based performance objectives under various seismic hazard levels were proposed based on experimental observations. Then, a numerical model of the hybrid structure considering damage accumulation and stiffness degradation was developed and verified by experimental results, and nonlinear time-history analyses were conducted to establish a database of seismic responses. The numerical results further serve as a technical basis for estimating the structure's fundamental period and evaluating post-yielding behavior and failure probabilities of the hybrid structure under various seismic hazard levels. A load sharing parameter was defined to describe the wall-frame lateral force distribution, and a formula was proposed and calibrated by the time-history analytical results to estimate the load sharing parameter. Moreover, earthquake-induced non-structural damage and residual deformation were also evaluated, showing that if designed properly, desirable seismic performance with acceptable repair effort can be obtained for the proposed steel-timber hybrid structural system.

Performance and risk to light-framed wood residential buildings subjected to tornadoes

Light-framed residential wood buildings constitute the majority of residential construction in the U.S. These buildings seldom are engineered for specific hazards. As a result, they may be inadequate to ensure life safety, let alone continued functionality during and after a severe natural hazard. The aims of this study are twofold: to assess the performance of light-frame wood residential buildings under tornado hazards, and to link performance of individual building components to building system performance so that the effect of implementing improved construction techniques can be quantified. These goals were realized through the development of detailed finite element models to capture individual building component behavior and building system performance under tornado wind pressure loading. Based on the data acquired from the finite element models, tornado wind fragilities (damage state probabilities) were developed for several building archetypes. First, typical construction quality was considered to establish a frame of reference; subsequently various improved construction techniques were considered in an effort to meet community resilience performance targets provided from concurrent research. The study shows that, while current construction practices fail to meet risk-informed building performance criteria needed to achieve community resilience goals, these goals can be achieved by modest improvements to existing construction techniques.

Experimental and numerical investigations into seismic performance of timber-steel hybrid structure with supplemental dampers

Although building structures can be designed to meet the life safety criterion and to deform inelastically without inducing collapse under major earthquakes, the structural and nonstructural damage associated with inelastic responses is normally very costly to repair. In this paper, friction dampers are utilized to upgrade the seismic performance of timber-steel hybrid structure, which has been proposed asan alternative structural solution for multi-story buildings. The hybrid structural system consists of steel moment resisting frame and infill light wood frame shear wall, both of which serve as the main lateral load resisting components, and friction dampers are introduced as frame-to-wall connectors to mitigate earthquake-induced damage. Pseudo-static loading tests were carried out on three timber-steel hybrid lateral load resisting subassemblies, and test results showed that the friction dampers were very effective in dissipating earthquake input energy, and correspondingly, much less damage was observed within the main structural members. The software package OpenSees was used to simulate the hysteretic behavior of the hybrid structure, and the developed finite element model was further validated by test results. Moreover, an optimal damper design solution was provided for a four-story timber-steel hybrid prototype building according to the numerical results from massive time-history analyses. Finally, the floor acceleration and inter-story drift responses of the prototype building with optimal damper configurations were assessed. This research aims to contribute to the development of novel timber hybrid structural systems with enhanced seismic performance.

Synergistic structures from magnetic freeze casting with surface magnetized alumina particles and platelets.

Magnetic freeze casting utilizes the freezing of water, a low magnetic field and surface magnetized materials to make multi-axis strengthened porous scaffolds. A much greater magnetic moment was measured for larger magnetized alumina platelets compared with smaller particles, which indicated that more platelet aggregation occurred within slurries. This led to more lamellar wall alignment along the magnetic field direction during magnetic freeze casting at 75 mT. Slurries with varying ratios of magnetized particles to platelets (0:1, 1:3, 1:1, 3:1, 7:1, 1:0) produced porous scaffolds with different structural features and degrees of lamellar wall alignment. The greatest mechanical enhancement in the magnetic field direction was identified in the synergistic condition with the highest particle to platelet ratio (7:1). Magnetic freeze casting with varying ratios of magnetized anisotropic and isotropic alumina provided insights about how heterogeneous morphologies aggregate within lamellar walls that impact mechanical properties. Fabrication of strengthened scaffolds with multi-axis aligned porosity was achieved without introducing different solid materials, freezing agents or additives. Resemblance of 7:1 particle to platelet scaffold microstructure to wood light-frame house construction is framed in the context of assembly inspiration being derived from both natural and synthetic sources.

Development of wood and steel diaphragm hysteretic connector database for performance-based earthquake engineering

Performance-based earthquake engineering (PBEE) considers certain metrics to assess the seismic response of buildings, which integrate economic losses into the design process. PBEE requires the development and use of reliable nonlinear response analysis models to simulate the seismic performance of structures through collapse. The structural damage is assessed by evaluating physical damage caused by engineering demand parameters (EDPs), while the nonlinear numerical models are used to conduct dynamic analyses for varying levels of seismic intensity to compute the values of the representative EDPs. Accurate representation of structural members’ stiffness and strength deterioration (hysteretic) parameters plays an important role into simulating dynamic response through collapse. These parameters’ values are usually calibrated to a large number of experimental data. The development of a hysteretic parameter database for wood and steel diaphragm connectors is presented in this paper. The wood diaphragm connectors are commonly used in light-frame wood building construction for shear walls or roof diaphragms. The steel diaphragm connectors are used for building structures that incorporate steel frame roof diaphragms. The experimental data were used for quantifying the hysteretic parameters of two well-known nonlinear models considered into structural modeling as well as evaluating their energy dissipation properties. Case studies on the collapse performance assessment of a light-frame wood wall system and a low-rise building incorporating a steel roof system were conducted to demonstrate the usefulness of the diaphragm connector database.

Seismic Design of Cross-Laminated Timber Platform Buildings Using a Coupled Shearwall Concept

Cross-laminated timber (CLT) is an engineered wood material that was introduced in the last decade as a promising candidate for building wood structures higher than 10 stories. Thus far, a handful of tall residential CLT buildings have been built in low seismic regions around the world. Previous full-scale seismic shaking table tests of multistory CLT buildings revealed that this system is susceptible to overturning damage as a result of lateral seismic loads. To effectively resist overturning, a new floor connection detail was proposed to engage CLT floor panels as coupling elements for CLT shearwall stacks in the building floor plan. This approach is fundamentally different from traditional isolated shearwall stack design methods used in multistory light-framed wood buildings. The proposed method was illustrated through the seismic design of a 12-story CLT building located in Los Angeles, California, which was then subjected to the design equivalent lateral force to evaluate the conservativeness in the proposed simplified calculation.

Airtightness of Light-Frame Wood Houses built in Daejeon and Chungnam Area

Among the energy consumption in building, the heating energy takes the largest part. Therefore, it is important to minimize the heat energy loss in building for the reduction of overall energy use in construction. The most important points for the minimization of energy loss in building are insulation and airtightness. Especially, in wood houses, airtightness is very important for energy saving as well as increase of durability. However, the researches on airtightness of wood buildings have been started recently and are very deficient especially in Korea. In this study, air leakage properties and airtightness performance were evaluated for light-frame wood houses built in Daejeon and Chungnam area. Total 7 houses were evaluated, among which four houses (Case 1 to Case 4) were in the construction stage before interior finish and the other three houses (Case 5 to Case 7) were after completion of construction work. The tests for airtightness were conducted by pressurization- depressurization method, and the factors included in the measurements includes air leakage rate at 50 Pa (CMH50), air change rate at 50 Pa (ACH50), equivalent leakage area (EqLA) and EqLA per floor area. As a result of this study, key air leakage points in wood houses were found to be the gaps between floor and wall, the holes for wiring and plumbing, the double glasses windows and the entrance doors. The average value of ACH50 for the houses after completion of construction work was 3.5 h-1 that was similar to Europe standard (3.0 h-1). ACH50 was proportional to EqLA per floor area but inversely proportional to the internal volume, the net floor area and the area of window.

Vertical Load Path Failure Risk Analysis of Residential Wood-Frame Construction in Tornadoes

Since the devastating 2011 tornado season, there has been renewed interest in understanding tornado wind loads and developing methodologies to reduce the risk of tornado damage. This study focuses on the assessment of the system-level performance of five different residential light-frame wood building archetypes subjected to tornado winds. The system-level performance considered three critical components along the vertical load path within each building, namely, the roof sheathing, roof-to-wall connection, and wall-to-foundation anchorage. Although there has been significant work on each of these components independently, combined uplift and lateral forces have received less attention. Therefore, a laboratory testing program for wood shear walls, reported herein, was performed to determine the wall-failure mechanisms and capacities when subjected to combined shear and uplift forces. Each building archetype was designed at varying locations across the United States based on the current residential building code and/or observed practice. Fragilities were developed, based on the assumption that failure of any component along the vertical load path results in failure of the system. Because the forces in each connection along the vertical load path arise from the same tornado wind load, the connection failures are not statistically independent, and Monte Carlo simulation was applied to perform the system reliability analysis.

Reinforced Wood I-Joists with Web Openings

AbstractPrefabricated wood I-joists with web openings are commonly used in light-frame wood construction. The capacity and the failure pattern of such I-joists in the presence of a circular web ope...

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 33 full-scale light-frame wood stud walls subjected to a total of 48 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.

短竹片钉接腹板楼面搁栅

楼面搁栅是轻型木结构主要的楼面承重构件。本文介绍了一种新型楼面格栅技术，用小截面锯材作为楼面搁栅骨架，把短竹片按45度倾角用气钉固定在骨架两侧，形成楼面搁栅腹板，进而形成竹木复合楼面搁栅。本技术简单易行，用短竹片和小截面锯材组合成具有较大跨越能力和较高承载力的楼面搁栅，可以降低轻型木结构的造价，推动装配式竹木结构的发展。 Joist is used for supporting floor. A new type of joist which uses slender square timber as skeleton was put forward. The web of the joist composed of short bamboo strips which nailed on the timber skeleton with a dip of 45 degree. By using short bamboo strips and slender square timbers, the joist can perform a large span and have good bearing capacity. This technology can promote the development of light wood frame construction by reducing the project cost.

Semi-rigid Behavior of Joints in Wood Light-frame Structures

The problem of behavior of the joint in wood light-frame structures were discussed in the paper. Two types of joint flexibility and their impact on the behavior of the structure were discussed. The results of the experimental investigation of rotational and axial stiffness of joint in wood light-frame structures were presented. The micro-scale tests of specimen representing joist-to top plate and top plate-to-stud joints in wall diaphragms were conducted. The representing load-displacement relationships for rotation and bearing at the joints were calculated. These relationship are described by the non-linear function. The comparison of rotational angle and relative translation obtained from experiment with displacement calculated using theoretical formulas were provided.

Life risks due to fire in mid- and high-rise, combustible and non-combustible residential buildings

CUrisk, a comprehensive model available for assessing fire risks in buildings, is used to assess and compare the life risks due to fires in mid-rise and high-rise residential buildings of non-combustible, light wood frame, and cross laminated timber constructions. The non-combustible buildings and some of the light wood frame buildings are explicitly code compliant designs, while some of the light wood frame buildings and the cross laminated timber buildings are alternative solutions. The computation results show that, the life risks of the simulated buildings are very low due to the installation of sprinkler systems and the risks are limited to the occupants in the rooms of fire origin. The effects of building area and storeys on life risk are minor. However, the area of the room of fire origin affects life risk significantly. Properly designed and protected combustible buildings do not impose higher life risk to occupants than non-combustible buildings. Life safety performance of buildings depends more on the design solutions as a whole rather than the selection of the construction type.