Wood-frame Buildings Research Articles

Development of a hybrid simulation controller for full‐scale experimental investigation of seismic retrofits for soft‐story woodframe buildings

SummaryHybrid simulations of a full‐scale soft‐story woodframe building specimen with various retrofits were carried out as part of the Network for Earthquake Engineering Simulation Research project – NEES‐Soft: seismic risk reduction for soft‐story woodframe buildings. The test structure in the hybrid simulation was a three‐story woodframe building that was divided into a numerical substructure of the first story with various retrofits and a full‐scale physical substructure of the upper two stories. Four long‐stroke actuators, two at the second floor and two at the roof diaphragm, were attached to the physical substructure to impose the simulated seismic responses including both translation and in‐plane rotation. Challenges associated with this first implementation of a full‐scale hybrid simulation on a woodframe building were identified. This paper presents the development and validation of a scalable and robust hybrid simulation controller for efficient test site deployment. The development consisted of three incremental validation phases ranging from small‐scale, mid‐scale, to full‐scale tests conducted at three laboratories. Experimental setup, procedure, and results of each phase of the controller development are discussed, demonstrating the effectiveness and efficiency of the incremental controller development approach for large‐scale hybrid simulation programs with complex test setup. Copyright © 2016 John Wiley & Sons, Ltd.

Closure to the Discussion of “Full-Scale Experimental Verification of Soft-Story-Only Retrofits of Wood-Frame Buildings using Hybrid Testing” by Bruce Maison

The authors of the article “Full-Scale Experimental Verification of Soft-Story-Only Retrofits of Wood-Frame Buildings using Hybrid Testing” respond to a discussion by Bruce Maison.

POSSIBLE DEFECTS IN WOOD, WOOD PARAMETERS VARIABILITY AND SOME OF ITS INFLUENCE ON QUALITY OF BUILDING STRUCTURE

Paper specifies the wood-framed with sheathing construction including phases of realization and exploitation. Methods of investigation based on practice and theory has been employed where practical identification of processes and their phases were presented with theoretical description of structure deformation within the exploitation period. Obtained results of investigations are presented in the form of technologic and mechanic of structure diagrams for buildings with adequate algorithms of analysis. Paper presents practical systematic of construction stages, technological problems and hazards in respect of loading and construction technology with method of computation of vertical deformations of building. Paper presents evaluation of contribution of wood defects in response to loading in the wood-framed residential building in exploitation process. Location of knots, allocation of pith in the elements cross section, defects of slope of grain and influence of moisture decreasing is examined in the paper. The wood-framed with sheathing in the form of large panel or modular three dimensional 3D elements are the most often used technology. This kind of buildings are actually constructed up to four story as a multifamily or varying universal buildings like school, kid-garden or offices. Low dead load from 0.30 to 1.00 kN/m2 and its favorable proportion to the live load increase energy saving factor in realization and within the exploitation time. Low own weight of structure enables complete prefabrication of wall, floor and roof panels, improving quality of construction and shortening time of construction. Process of prefabrication, wide assortment and variety of factory production does not require time consuming processes and complicated moulds or shuttering indispensable in precast RC structural elements.

Thermal Bridges At Wood Frame Construction

Abstract The paper presents the results of numerical analysis on the effects of thermal bridges at wood frame buildings with or without thermal insulation placed on the exterior surface of the wall. The heat flow crossing the wooden thermal bridges, respectively the linear heat transfer coefficients ψ and the temperature factors fRsi, can be established based on the plane temperature field in stationary thermal regime. The “PSIPLAN” computer program used to determine the temperature field, derived from the original program “CIMPLAN” with its first version developed in 1980. The program allows graphic description of the plane section of a thermal bridge and discretizes automatically the section on both axes in accordance with the stipulations of the EN ISO 10211-1:1995 standard and EN ISO 10211:2007 standard. The computer program generates automatically the system of equations that is solved using iterative methods until the heat flows on the two surfaces of the section are balanced. The calculation results are presented with numerical values and in a graphical manner by isothermal surfaces. The program has various libraries that include several types of wood thermal bridges.

Moisture management performance of wood-frame in-fill wall in Shanghai, China

This paper discusses the results of a research project which aimed at determining the hygrothermal (i.e. thermal and moisture) performance of the Canadian wood-frame building envelope construction in the city of Shanghai in China. The performance assessments of the wood-frame walls were conducted using the two-dimensional hygrothermal simulation tool called hygIRC-2D. In this study an in-fill type wall was considered and hygrothermal simulations were carried out for the weather conditions of Shanghai. Investigations were conducted to determine the influence of the vapour barrier, exterior stucco cladding material and different types of sheathing boards on the moisture performance of in-fill walls. Additional simulations were carried out to determine the influence of air leakage on the moisture performance of in-fill walls. The outputs from the simulations were analysed with the help of a hygrothermal response indicator called RHT index. It was concluded that the design of the in-fill wall including a rain screen but omitting a vapour barrier is expected to lead to the maximum reduction in hygrothermal loading when exposed to the weather conditions of Shanghai, China.

Energy Performance of Two Multi-Story Wood-Frame Passive Houses in Sweden

Two eight-story wood-framed residential buildings with the Swedish 2012 passive house standard were built in 2009 in the Portvakten Söder quarter in the city of Växjö in Sweden. In this paper, we present the monitored specific energy use of the buildings and compare to the requirements of the Swedish building code and recommendation for passive houses. We also estimated the primary energy use and CO2 emissions and investigated the tenants’ views and experiences of the two buildings. Results show that the actual specific energy use of 40.2 kWh/m2Atemp/year in the Portvakten Söder building fulfills, by a good margin, the requirements of the Swedish building code and the recommended passive house standard, but is higher than projected. Applying a marginal perspective, the calculated primary energy use and carbon dioxide emission from operating the buildings (excluding household electricity) was 40 kWh/m2Atemp/year and zero, respectively. Responses of 20 tenants to a mail-in questionnaire survey showed that over 90% were satisfied with their apartments.

Comparison of different methods for calculating thermal bridges: Application to wood-frame buildings

Nowadays thermal bridges losses in building design (standard or dynamic simulations) are generally evaluated using heat transmission coefficients from a database of usual cases. Numerous studies exist on the thermal bridges of classic constructions (concrete, brick). The originality of this paper is to deal with the particular case of the wood-frame construction. In this case, catalogs with heat transmission coefficients have been integrated into building energy simulation software used by building engineers. First, this paper proposes a scientific hindsight and a critical overview of existing calculation methods of thermal bridges. Simulations are made in steady state conditions according to the European standard and with dynamic conditions. A series of calculations was performed in order to validate the presented method. The results for wood stud thermal bridges showed that the values that are mainly used by engineering offices often lead to important errors due to the standard method and rounding choice. Secondly different models are proposed to correctly apply the thermal behavior of thermal bridges to some examples of wood-frame structure. These are based on recent articles covering the methods for thermal bridges calculation in dynamic conditions. This section shows that the most accurate models depend on the consideration of the inertia of the wood stud that concentrates all the mass of the wall unlike more conventional configurations.

Application of Energy Dissipation Devices for Seismic Protection of Soft-Story Wood-Frame Buildings in Accordance with FEMA Guidelines

AbstractRecent earthquakes have demonstrated the vulnerability of soft-story wood buildings. A performance-based retrofit option focusing on stiffening/strengthening only the soft ground story, as regulated by FEMA guidelines, was proposed in an attempt to achieve collapse prevention of the ground story while at the same time ensuring damage control of the upper stories. This paper focuses on an alternative retrofit approach that focuses on energy dissipation, in order to achieve a performance that is essentially comparable to the inherent performance target defined in FEMA guidelines. A viscous damper retrofit is designed based on conclusions drawn from parametric studies. Then, the proposed retrofit is validated via slow pseudodynamic hybrid testing of a full-scale three-story building. The test data are presented, interpreted, and compared against both pretest numerical predictions and posttest simulation results after model calibration. It is demonstrated that a damping retrofit, as compared to a stif...

Displacement-Based Seismic Design of Symmetric Single-Storey Wood-Frame Buildings with the Aid of N2 Method

This paper presents a new methodology for the displacement-based seismic design of symmetric single-storey wood-frame buildings. Previous displacement-based design efforts were based on the direct displacement-based design approach, which uses a substitute linear system with an appropriate stiffness and viscous damping combination. Despite the fact that this method has shown to produce promising results for wood structures, it does not fit into the framework of the Eurocode 8 (EC8) provisions. The methodology presented herein is based on the N2 method, which is incorporated in EC8 and combines the non-linear pushover analysis with the response spectrum method. The N2 method has been mostly applied to reinforced concrete and steel structures. In order to properly implement the N2 method for the case of wood-frame buildings, new behavior factor–displacement ductility relationships are proposed. These relationships were derived from inelastic time history analyses of 35 SDOF systems subjected to 80 different ground motion records. Furthermore, the validity of the N2 method is examined for the case of a timber shear wall tested on a shake table and satisfactory predictions are obtained. Last, the proposed design methodology is applied to the displacement-based seismic design of a realistic symmetric single-storey wood-frame building in order to meet the performance objectives of EC8. It is concluded that the simplicity and computational efficiency of the adopted methodology make it a valuable tool for the seismic design of this category of wood-frame buildings, while the need for extending the method to more complex wood-frame buildings is also highlighted.

Tornado Risk Analysis for Residential Wood-Frame Roof Damage across the United States

AbstractApproximately 1,200 tornadoes impact the United States every year with a percentage of these resulting in significant damage, injuries, and fatalities. Initially, a probabilistic tornado hazard analysis was performed in order to develop tornado hazard curves at select locations across the United States. This analysis resulted in the annual probability of experiencing a tornado of any strength at the specific locations, which varied as a function of location-specific occurrence rates. Five different residential wood-frame building archetypes were designed at each of the locations based on current residential building code and/or practice. Fragilities for the roof sheathing and truss to wall top-plate connections were developed for each archetype. Because fragilities are independent of location, they were then convolved with the tornado hazard curves to compute annual failure probabilities for select roof components. This represents the first time absolute risk of roof failure due to tornadoes has b...

Impact of Moisture and Load on Vertical Movement of a Simulated Platform Frame Wood Structure

Abstract The objective of this study was to assess the relative contributions of wood shrinkage and building dead loads to vertical displacement in the form of height loss for wood-frame structures. Identifying the relative contributions of these factors while monitoring full-sized buildings presents significant challenges; therefore, a laboratory test was conducted under controlled hygrothermal conditions and loading. Two small-scale wood-frame structures were constructed with dimension lumber wall assemblies and floor joists. Both model structures were equipped with vertical movement and moisture content (MC) monitoring systems. The structures were conditioned in a chamber to a MC of approximately 20 %, and then moved into the laboratory environment for drying and loading. Model Structure No. 1 was loaded immediately; model Structure No. 2 was not loaded until after the wood had dried to the equilibrium MC. By using a unique lever system, the applied load simulated a dead load that could be experienced by the bottom floor of a six-story wood-frame building. Shrinkage coefficients were measured using samples cut from the horizontal framing members. The results suggested that the loads “forced” the structures to displace downward. At the driest time in the laboratory, the total movement of model Structure No. 1 reached a maximum of about 19 mm after 10 months, which is comparable to in situ recorded measurements from the bottom floor of a four-story wood-frame building in coastal British Columbia. Shrinkage appeared to account for 70 % of the total vertical movement, with the remaining 30 % contributable to load-induced displacement under the conditions of this test. Model Structure No. 2 showed less vertical movement but more initial displacement than model Structure 1 due to a larger settlement. This study suggested that there may be a need to consider the effect of loads in addition to wood shrinkage when estimating building height loss.

Construction-Centric Building Information Modelling to Facilitate Building Panel Prefabrication

Building information modelling (BIM) is an information technology that has the ability to change the Architecture, Engineering, and Construction (AEC) industry in terms of enhanced communication and productivity. With the rise of BIM, panelized/off-site construction is gaining momentum within the home building industry. However, BIM has not yet been leveraged to its full capability with regard to construction prefabrication, due in part to the fact that BIM models are only roughly designed by architects and engineers. Furthermore, some construction-centric information, such as drywall and sheathing layouts, which require substantial manual modelling efforts, is not presented explicitly in the BIM model. In this regard, this research exploits a BIMbased automatic approach for designing and modelling drywall and sheathing layouts in order to facilitate building panel production in the prefabrication plant. The prototype system is built on the basis of Autodesk Revit through the use of Application Programming Interface (API). This system, taking architectural BIM information as the input, generates a detailed constructioncentric BIM model in accordance with construction specifications, and further enables users to obtain shop drawings and a thorough quantity take-off and cut list in order to manage the plant production. In addition, the prototype system is capable of optimizing drywall and sheathing layout design with the objective of minimizing material waste and joint length. A case study of a wood-framed residential building is adopted to demonstrate the developed prototype system.

ISO 10211 전열해석을 통한 경량목구조의 주요 구조부 단열성능 데이터베이스 구축

This study aimed to establish a thermal performance database for various lightweight wood-frame house envelopes in order to increase the accuracy of insulation assessment and energy performance analysis for lightweight wood-frame buildings. The differences in energy and insulation performances were analyzed based on the thermal transmittance calculation method for composite walls. The linear thermal transmittance (<TEX>${\Psi}$</TEX>), equivalent thermal transmittance (Ueq), and thermal conductivity of various composite walls for lightweight wood-frame houses were calculated. PHYSIBEL Trisco V.12 was used for the heat transfer analysis, and DesignBuilder V.3.4 was used for the energy performance analysis. The thermal transmittance in the case studies was compared with the heat transfer analysis, and the results confirmed a difference of 3.8%-22.7% for the thermal transmittance and a difference of 3.2%-12.1% for the heating energy. When heat transfer analysis was conducted for various configurations of the lightweight wood-frame house such as the stud spacing, stud thickness, stud placement, and presence of an airtight layer, the results showed a linear thermal transmittance (<TEX>${\Psi}$</TEX>) difference that was approximately 4.8 times depending on the wall configuration. The thermal conductivity (<TEX>${\lambda}$</TEX>) of the inversion stud and insulation layer was <TEX>$0.0433-0.0492W/m{\cdot}K$</TEX>, indicating a maximum of 11.9% on the stud interval of 406 mm (16 in) and <TEX>$0.0404-0.0452W/m{\cdot}K$</TEX> indicating a maximum of 10.6% on the interval of 610 mm(24 in). With the database established in this study, the thermal performance of the composite walls in lightweight wood-frame houses can be calculated without a complex heat transfer analysis and can be used as basic data for the construction of eco-friendly low-energy wooden structures.

Kinematic Finite-Source Model for the 24 August 2014 South Napa, California, Earthquake from Joint Inversion of Seismic, GPS, and InSAR Data

Online Material: Movie of wave propagation, GPS coseismic displacements, rupture velocity, waveform comparisons, geologic and 3D seismic structure, and moment rate functions. On 24 August 2014 at 10:20:44.06 UTC, a large earthquake struck the north San Francisco Bay region, approximately 10 km south‐southwest of Napa, California, causing local damage in older wood frame and masonry buildings, road surfaces, sidewalks, and masonry wall structures (Bray et al. , 2014). Using long‐period (50–20 s) three‐component, complete displacement records, the Berkeley Seismological Laboratory (BSL) estimated the scalar seismic moment at 1.32×1018 N·m for a depth of 11 km, corresponding to a moment magnitude of M w 6.0. The strike/dip/rake from the seismic moment tensor solution was 155°/82°/−172°, which is in overall agreement with the trends of structures comprising the West Napa fault system (Fig. 1). Geologic mapping revealed an approximately 14 km long surface rupture with 40–45 cm maximum observed slip on a complex multibranched fault system (Bray et al. , 2014; Earthquake Engineering Research Institute [EERI], 2014; Mike Oskin and Alex Morelan, written comm., 2014). The largest surface offsets were found on a northwest‐striking trend located approximately 1.8 km west of the mapped West Napa fault. Aftershocks are generally located west of the western branch of the surface fault, which had the largest offsets, and indicate a westward dip of the primary fault plane (Fig. 2). Figure 1. Locations of Berkeley Digital Seismic Network (BDSN) stations are shown as labeled squares. Plate Boundary Observatory (PBO) Global Positioning System (GPS) sites are shown as circles, and the positions of Interferometric Synthetic Aperture Radar (InSAR) returns are small gray squares. San Francisco and Napa Valley are indicated by SF and NV. The Berkeley Seismological Laboratory focal mechanism is shown, and the thick line shows the mapped surface trace (EERI, 2014). Figure 2. (a) Coseismic fault‐slip model based on the joint inversion of …

Assessment and comparison of experimental and numerical model studies of cross-laminated timber mechanical connections under cyclic loading

Earthquake engineering is a major consideration for structures along the west coast of North America. The current building code of Canada is based on design criteria, which are defined by stresses and member forces calculated from prescribed levels of applied lateral shear force. Traditional wood-frame buildings are known to perform well in earthquakes. However, with the development of new engineered wood products, such as CLT (cross-laminated timber) and more consideration to build higher than the existing six stories limit in wood-frame structures, highlights the need to use innovative hybrid techniques for buildings. Hybrid buildings with steel frame structures incorporated with CLT infill walls offer one possible solution to residential and commercial multi-level buildings to overcome the height limitation. In order to make such a structure applicable for an earthquake prone area, it is important to understand the structural performance of the connection between steel and CLT elements. In this research, six connection combinations have been tested and modeled in a finite element program. The load–displacement test results are assessed with two evaluation methods. The first method follows the American Society of Testing Method, where ductility ratio, elastic shear stiffness, and the EEEP-curve (equivalent energy elastic–plastic curve) are generated and assessed. The second method follows an energy-based accumulation principle, where the test results are used to calculate a damage index at each time step. Both methods are used to compare test and model results and assess the accuracy of the model as well as addressing the capability of each assessment method. Depending on the purpose of the model one or the other assessment method might be suitable. For an analysis of the overall ductility or elastic shear stiffness, applying the method provided by ASTM will give relatively accurate results to assess a hysteretic load–displacement model such as the SAWS model in this research. The assessment with a damage accumulation method is a great tool to capture more details of the hysteretic load–displacement curve. Energy dissipation is valuable indicator besides ductility and elastic shear stiffness to evaluate the model.

An estimate of tornado loads on a wood-frame building using database-assisted design methodology

Thunderstorms and related tornadoes caused over $25 billion in damages in 2011, the majority of which occurred to residential structures. Over 13,000 homes were damaged or destroyed by two tornadoes in Tuscaloosa and Joplin alone. Such substantial losses should not be surprising because as yet, no design guidelines exist for tornadoes, and with the current wind provisions in accepted building codes there is limited capacity in any wood-framed structure to withstand tornado loads. The objective of this current study is to develop appropriate design structural reactions for light-framed wood structures that is subjected to tornado loads. The study uses tornado simulator-generated surface pressure data from a fully sealed 1:100 scale gable roof model, experimentally-determined structural influence functions, and a modified database-assisted design (DAD) methodology to predict the reactions. Forces are established at structural connections for a tornado with peak wind speeds of 60.3m/s (135mph). Results are compared against structural reactions due to straightline winds with an identical peak wind speed, as determined using ASCE 7–10 wind pressure distributions. It is shown that for a sealed building (i.e., no pressure equalization between the building interior and exterior), the peak shear forces under tornado loads are 1.8 times as strong for roof-to-wall connections and twice as strong for wall-to-foundation connections, as compared to those from ASCE 7–10 wind loads. The peak vertical loads on connections are even higher, nearly four times as high for the roof-to-wall and wall-to-foundation connections. Nearly 60% of the peak loads can be attributed to the assumption of a fully sealed building mode, which results in the full effect of the pressure drop within the vortex being experienced on all surfaces of the building.

Full-Scale Experimental Investigation of Second-Story Collapse Behavior in a Woodframe Building with an Over-Retrofitted First Story

AbstractSoft-story woodframe buildings have been identified as a disaster preparedness problem throughout California and are present in many other states of the United States. These buildings can be readily identified by their large openings at the ground floor, often for parking, which results in a soft and weak first story that is prone to collapse in moderate to severe earthquakes. This paper presents the hybrid test results of a full-scale collapse test program that was carried out on a 3-story soft-story woodframe building with an overretrofitted first story. The overretrofitted design was constrained to the soft story only, essentially representing a retrofit that would likely drive the soft-story failure mechanism into the upper stories. The objectives of the collapse testing were to (1) quantify the collapse shift into the upper stories when the first story is overstrengthened, (2) investigate the collapse mechanisms of a woodframe building constructed with archaic building materials and style in ...

Using Parallel Computer Systems to Examine Seismic Reliability of Structures

Structural response under seismic loadings is typically nonlinear and related to many factors, such as structural configurations, material properties, occupancy loads, earthquake hazards and incomplete knowledge of the system. As all these factors have their sources of uncertainties, structural response under seismic loading has its probabilistic nature. Therefore, the random variable for any structural demand follows a multivariate probability distribution over the integration domain defined by the limit states. Examining the probabilistic behaviour of structures under earthquake loadings has to consider the sources of uncertainties from all factors. It is also known that numerical methods, such as the finite element method, are commonly used to predict nonlinear structural response. The probabilistic structural demand is a discrete probability function of its related variables. In order to examine seismic risks and mitigate potential damages to structures, it is important to accurately quantify seismic reliability of structures. The traditional seismic reliability analysis uses approximate algebra equations with parameters obtained from aggregation of data points of dynamic analysis, which may not be able to produce accurate results. In this paper, probabilistic seismic demands are solved with numerical procedures of the traditional SAC method and the Monte Carlo simulation. These methods rely on the results from repeatable nonlinear dynamic analyses, which were traditionally considered to be a bottle-neck due to limited computing resources. The recent progress in parallel computing technology and open-source software has made such scientific computation affordable for the engineering community. Two parallel computer systems were used to analyze seismic reliability of the structures. One system is based on multiple personal computers in typical computer labs. The other system is to use high performance computer clusters. Both systems were applied to analyze a two–storey wood frame building and a three-storey steel moment building, respectively

Experimental Seismic Behavior of a Full-Scale Four-Story Soft-Story Wood-Frame Building with Retrofits. II: Shake Table Test Results

AbstractSoft-story wood-frame buildings have been recognized as a disaster preparedness problem for decades. The majority of these buildings were constructed from the 1920s to the 1960s and are pro...

Experimental Seismic Behavior of a Full-Scale Four-Story Soft-Story Wood-Frame Building with Retrofits. I: Building Design, Retrofit Methodology, and Numerical Validation

AbstractSoft-story wood-frame buildings have been recognized as a disaster preparedness problem for decades. There are tens of thousands of these multifamily three- and four-story structures throughout California and other parts of the United States. The majority were constructed between 1920 and 1970 and are prevalent in regions such as the San Francisco Bay Area in California. The NEES-Soft project was a five-university multiindustry effort that culminated in a series of full-scale soft-story wood-frame building tests to validate retrofit philosophies proposed by (1) Federal Emergency Management Agency’s recent soft-story seismic retrofit guideline for wood buildings and (2) a performance-based seismic retrofit (PBSR) approach developed as part of the NEES-Soft project. This paper is the first in a set of companion papers that presents the building design, retrofit objectives and designs, and full-scale shake table test results of a four-story 370-m2 (4,000-ft2) soft-story test building. Four different ...