Woodframe Residential Buildings Research Articles

Review of wind loading on roof to wall connections in low-rise light wood-frame residential buildings

Several post-hurricane studies have indicated the prevalence of roof damage in low-rise wood-frame buildings. One of the major reasons for this includes failure of roof-to-wall connections (RTWCs). This has led to a lot of research on RTWCs in a bid to understand the reasons for the failures, the capacities of the RTWCs and development of better RTWCs especially in hurricane prone regions. This study reviews the research works to date on factors affecting wind loads on RTWCs. It explores the experimental tests on RTWCs in roofing structures and component tests of single RTWCs. Numerical and analytical modeling of RTWCs as part of a roof system or as single connections are all reviewed. Finally, recommendations for future research works to bridge current knowledge gaps are made.

Determination of Individual Building Performance Targets to Achieve Community-Level Social and Economic Resilience Metrics

The retrofit of wood-frame residential buildings is a relatively effective strategy to mitigate damage caused by windstorms. However, little is known about the effect of modifying building performance for intense events such as a tornado and the subsequent social and economic impacts that result at the community level following an event. This paper presents a method that enables a community to select residential building performance levels representative of either retrofitting or adopting a new design code that computes target community metrics for the effects on the economy and population. Although not a full risk analysis, a series of generic tornado scenarios for different Enhanced Fujita (EF) ratings are simulated, and five resilience metrics are assigned to represent community goals based on economic and population stability. To accomplish this, the functionality of the buildings following the simulated tornado is used as input to a computable general equilibrium (CGE) economics model that predicts household income, employment, and domestic supply at the community level. Population dislocation as a function of building damage and detailed sociodemographic US census-based data is also predicted and serves as a core community resilience metric. Finally, this proposed methodology demonstrates how the metrics can help meet community-level resilience objectives for decision support based on a level of design code improvement or retrofit level. The method is demonstrated for Joplin, Missouri. All analyses and data have been developed and made available on the open-source IN-CORE modeling environment. The proposed multidisciplinary methodology requires continued research to characterize the uncertainty in the decision support results.

Comparative Review and Assessment of Various Flood Retrofit Methods for Low-Rise Residential Buildings in Coastal Areas

Recent hurricanes indicated that retrofitted residential buildings are still susceptible to wind- and flood-induced damage in coastal areas. This poor performance indicates that flood retrofit methods need to be evaluated in terms of efficiency and effectiveness to resist hurricane wind and flood loads. This paper discusses various aspects in the hurricane-resistant design and retrofit of coastal residential buildings, including potential wind and flood-induced damage, risk mitigation, cost of retrofit methods, and the need for better standards. The cost analysis is performed for a typical one-story wood-frame residential building with a gable roof system considering several flood retrofit methods. The result indicates that selecting a flood protection level higher than the basic 100-year flood level can significantly decrease the risk of damage. This result seems appropriate and essential for specific hurricane-prone regions considering recent changes in the intensity/frequency of storms. A review of actual damage types indicates that wood-frame elevated houses are susceptible to experiencing wind-induced damage to the structural system and more extensive damage to the envelope system. The performance of breakaway walls below the base flood elevation (BFE) strongly depends on the connections between such walls and structural members. The result of cost analysis indicates that the foundation type can directly affect the total cost of retrofit solutions, such as elevation, wet, and dry methods for houses in coastal areas. Regarding the elevation method, adding a freeboard higher than the BFE does not significantly increase the total cost once the elevation method is selected as the preferred retrofit solution.

Fatigue performance of wood frame roof-to-wall connections with elastomeric adhesives under uplift cyclic loading

Roof-to-wall-connection (RTWC) is critical in the loading path of wood-frame residential buildings, whose fatigue performance under varying wind loading is investigated in this paper. To get an insight on the wind-induced fatigue behavior at low to moderate hourly mean wind speeds and to demonstrate the effects of adhesives on the fatigue performance of RTWC, two types of fatigue experiments, namely the constant and the varying amplitude loading tests, were conducted on three RTWC configurations with and without elastomeric construction adhesives. Based on the constant amplitude loading test results, fatigue life prediction models were developed, and the reduction in the static load capacity due to cyclic loadings were estimated. Adhesives are shown to increase the endurance limit of the RTWCs, which is desirable to enhance the life-cycle performance of wood buildings. The varying amplitude loading test results indicate that buildings in non-hurricane regions are vulnerable to fatigue damage at a low-level mean wind speed. It may induce loadings above the endurance limit of the RTWCs. On the other hand, the linear Miner’s cumulative fatigue damage model can be reasonably used to predict fatigue damage of the RTWCs when subject to multi-amplitude wind loadings. Toenailed connections generally fail in a less ductile manner at a certain number of load cycles with no warnings compared to the connections with adhesives that fail in a more ductile manner. The testing results presented herein provide essential data on the hysteresis behavior and failure modes of RTWCs to facilitate future implementation of adhesives in wood constructions.

Multi-scale cost-benefit analysis of the Los Angeles Soft-Story Ordinance

A multi-scale (building-specific and portfolio) cost-benefit analysis of the Los Angeles soft-story Ordinance for woodframe residential buildings is presented. Building-specific loss functions (shaking intensity versus loss ratio) are computed by implementing the FEMA P-58 seismic loss assessment methodology on a set of archetype buildings that reflect the variations in key structural characteristics (e.g. 1st story wall layout, number of stories) of the approximately 12,000 buildings affected by the Ordinance. The cost-benefit ratio is assessed as the retrofit cost divided by the reduction in earthquake-induced losses that result from the retrofit. At the individual building level, both intensity and time-based cost-benefit assessments are performed. The latter uses the expected annual losses to determine the break-even time, which is the duration needed to recoup the upfront cost of the retrofit. The average break-even time when considering all archetypes is four to five years. At the portfolio-scale, an average cost-benefit ratio of 0.32 is obtained for a hypothetical Mw 7.1 Puente Hills scenario earthquake. A first-of-its kind stochastic event-set cost-benefit assessment is also performed, where all events (approximately 8000) that are significant to the region are considered. From this assessment, it was determined that the probability of achieving a desirable cost-benefit ratio (value between 0.0 and 1.0) within a 50-year period is approximately 0.9.

Evaluating the Link between Low Carbon Reductions Strategies and Its Performance in the Context of Climate Change: A Carbon Footprint of a Wood-Frame Residential Building in Quebec, Canada

The design and study of low carbon buildings is a major concern in a modern economy due to high carbon emissions produced by buildings and its effects on climate change. Studies have investigated (CFP) Carbon Footprint of buildings, but there remains a need for a strong analysis that measure and quantify the overall degree of GHG emissions reductions and its relationship with the effect on climate change mitigation. This study evaluates the potential of reducing greenhouse gas (GHG) emissions from the building sector by evaluating the (CFP) of four hotpots approaches defined in line with commonly carbon reduction strategies, also known as mitigation strategies. CFP framework is applied to compare the (CC) climate change impact of mitigation strategies. A multi-story timber residential construction in Quebec City (Canada) was chosen as a baseline scenario. This building has been designed with the idea of being a reference of sustainable development application in the building sector. In this scenario, the production of materials and construction (assembly, waste management and transportation) were evaluated. A CFP that covers eight actions divided in four low carbon strategies, including: low carbon materials, material minimization, reuse and recycle materials and adoption of local sources and use of biofuels were evaluated. The results of this study shows that the used of prefabricated technique in buildings is an alternative to reduce the CFP of buildings in the context of Quebec. The CC decreases per m2 floor area in baseline scenario is up to 25% than current buildings. If the benefits of low carbon strategies are included, the timber structures can generate 38% lower CC than the original baseline scenario. The investigation recommends that CO2eq emissions reduction in the design and implementation of residential constructions as climate change mitigation is perfectly feasible by following different working strategies. It is concluded that if the four strategies were implemented in current buildings they would have environmental benefits by reducing its CFP. The reuse wood wastes into production of particleboard has the greatest environmental benefit due to temporary carbon storage.

Wind Performance Enhancement Strategies for Residential Wood-Frame Buildings

Extreme winds such as tornadoes and hurricanes are relatively common natural hazards in the United States and can result in fatalities as well as damaging physical and socioeconomic infrastructure. Buildings are a critical sector within the built environment of a community and studying their performance under natural hazards is a major step for the risk and resilience assessment of a community. More than 80% of the total building stock in the United States and more than 90% of the residential buildings in North America are wood-frame construction; a construction type that is vulnerable to wind damage because they are light and typically are not engineered, only prescriptive in their design. Performance enhancement strategies for wood-frame residential buildings were investigated in this study by exploring combinations of roof coverings, roof sheathing nailing patterns, and roof-to-wall connection types. In this regard, a total of nine construction product combinations were considered. Further, recent changes to the wind standards were also explored. Specifically, the damage fragilities of five wood-frame building archetypes are considered for four damage states defined based on the performance of the building envelope, including roof coverings, doors and windows, roof sheathing, and roof-to-wall connections. The fragility curves are explained at the component level and then the building level for one archetype as an example, and the building fragility parameters are provided for all archetypes and for all construction product combinations. Comparison between fragilities developed using the last two versions of the wind standards are also presented. Then, an existing approach that amplifies the wind pressures in the wind standards to represent a tornado load is also compared. The fragility curves provided in this study can be used to represent residential buildings within a community for risk or resilience assessment/mitigation under hurricane or tornado loading.

Monitoring of Vertical Movement in a Four-Story Wood-Frame Building in Coastal British Columbia

Abstract Vertical movement and lumber moisture content (MC) were monitored during the construction of a four-story wood frame residential building in the winter of 2010–2011 in coastal British Columbia, Canada. The work was part of a long-term study to assemble field performance information and validate movement prediction methods to assist in the design of five- and six-story wood frame buildings. The MC readings of dimensional lumber generally remained around 20 % on average before the building was completely protected from rain with its roof and wall sheathing membrane under rainy construction conditions. With the data collection started when the roof sheathing was installed and continued into occupancy of the building, the vertical movement was found to occur during the process of wood drying and the installation of non-structural elements such as drywall and cladding etc., which increased the local loads. The total movement amount, contributed by wood shrinkage, gap closure (settlement), and other factors, reached about 34 mm at an exterior wall, 43 mm at an interior hallway shear wall, and 45 mm at an interior partition wall, after a total monitoring period of 17 months. These values were fairly comparable to the values predicted from wood shrinkage alone for this building.

Nonlinear Time-History Analysis of a Six-Story Wood Platform Frame Buildings in Vancouver, British Columbia

In 2009, the British Columbia Building Code was amended to increase the allowable height of wood-frame residential buildings to six stories from four stories. This paper presents the details of a numerical study undertaken to understand the seismic performance of six-story wood-frame buildings designed in accordance with the 2006 British Columbia Building Code. To investigate the seismic behavior, a four-story building was used to represent the benchmark seismic performance prior to the amendment. Two independent analyses using computer programs DRAIN-3DX and SAPWood were carried out on representative buildings located in the city of Vancouver, BC, using a suite of 20 earthquake records scaled to the design seismic hazard level for the site. The analyses showed that six-story wood-frame buildings had similar performance to four-story wood-frame buildings.

Prescriptive Approach to the Performance-Based Seismic Design of Low-Rise Wood-Frame Residential Buildings

Performance-based seismic design (PBSD) is considered by many to be the next generation of design philosophy that focuses on the system performance of a structure during earthquake loading. For steel and concrete structures, this design philosophy is being used by a select group of practitioners. However, application to wood-frame buildings is still in the research stages; several approaches for PBSD are proposed with rehabilitation concepts available in ASCE 41. Currently, most of the PBSD methods for wood-frame buildings require designers to utilize a level of approach that is far more detailed than current design approaches. This increases the cost of any engineering for the design of wood-frame buildings. Therefore, in this study, a simplified design approach is developed that allows a designer to employ the PBSD methodology without complex analysis. Different from most existing PBSD procedures, this prescriptive approach was developed based on a significant number of numerical simulations using a sim...

Wood Frame Building Response to Rapid-Onset Flooding

Floods are considered to be among the deadliest, costliest, and most common natural disasters. Rapid-onset, catastrophic floods inundate the shore quickly and manifest as deep water with high velocities, inflict great pressures and forces on the built and natural environments, and pose a threat to human safety. Current building codes, design practices, and disaster planning methods account for potential earthquake and wind loads on simple wood-frame buildings typical of North American residential construction. However, flood impacts have not been considered to the same degree of detail. A theoretical model is developed that describes flood impacts on wood-frame residential buildings and relates building response to flood depth and velocity. The failure mechanisms considered and the model logic are described and applied to assess the response of a typical Canadian wood-frame home to flood conditions that might be experienced in a rapid-onset flood event.

Risk-Based Decision-Making for Multi-Hazard Mitigation for Wood-Frame Residential Construction

Damage to wood-frame residential construction in the United States caused by hurricanes, earthquakes and other natural hazards can be significant. To mitigate risk from natural hazards cost effectively, decision-making tools must be based on a better understanding of residential building performance with different levels of hazard-resistant design practices. The focus of this paper is to demonstrate a framework for optimal engineering decision-making utilising multi-hazard performance and risk assessment tools for residential building construction. The framework contains the following key ingredients: probabilistic modelling of the occurrence and intensity of the natural hazard; structural system fragility modelling to represent the conditional probability of damage; and a model of total expected cost during different service intervals. The risk framework is illustrated using a typical one-storey wood-frame residential building in Charleston, South Carolina, that is exposed to significant hurricane and earthquake hazards. This framework can support improvements in construction practices, appropriate underwriting by the insurance industry, and planning community response to natural hazards.

Methodology for earthquake-induced loss estimation: An application to woodframe buildings

A probabilistic framework to estimate long-term earthquake-induced economical loss for woodframe structures was proposed and demonstrated in this paper. The concept of a damage fragility system which can be used to quantitatively model the uncertainty in the response-damage-loss relationship was developed and applied to woodframe residential building components. Bayesian models were used in the framework in order to incorporate subjective engineering experiences and test data. A simulation procedure was used to implement the loss estimation framework and was investigated with several numerical examples. Specifically, the analyses of two typical woodframe residential structures were examined in order to illustrate the concepts and methods. Such a procedure has not yet been developed for woodframe structures within performance-based seismic design (PBSD) procedures that are under development, thus incorporating economic losses within the PBSD of wood structures is novel. The methods and concepts explained in this paper could provide a viable path towards the design, optimization, and assessment related to long-term earthquake-induced loss for existing woodframe structures and new designs.

Seismic Evaluation and Retrofit of Asymmetric Multi-Story Wood-Frame Building

The presented research focuses on large-scale seismic testing under multi-directional ground motion of a three-story high, wood-frame residential building representing late 1960's California construction. Earthquake lateral resistance is provided by plywood shear walls around the perimeter of the building with an open front in the first story for tuck-under parking. Accordingly, the as-built structural configuration is asymmetric in plan and discontinuous in elevation with tendency to twist about a vertical axis and to form a weak story mechanism. The test results confirm this tendency. They also reveal the sensitivity of the response to multi-direction ground motion. Asymmetric damage patterns are induced by the multi-component motions in the walls oriented perpendicular to the open front for the as-built test structure, with or without finish materials. However, the observed damage remained noncritical as far as structural integrity is concerned even for ground accelerations exceeding 120% of that recorded during Northridge earthquake. This is viewed as a consequence of the better construction of the test building compared to actual construction. Investigated retrofit includes adding a welded moment resisting steel frame around of the garage opening and strengthening the diaphragm to header beam connections. The study indicates that the retrofit significantly reduced the maximum story drift in the open front. Moreover, the finish material and the retrofit greatly reduce the maximum rotation of the building about the vertical axis.