A concept for an outdoor test facility in Vancouver for building enclosure materials and components has been under study by Forintek and others since Fall 2000. Phase One - a preliminary feasibility study - was previously completed. This report describes accomplishments to date of Phase Two, a transition phase involving identification of a project custodian, further concept development, development of a business plan, preparation for fundraising and identification of potential sites.
This study aims at assessing the changes happening within the residential construction industry with respect to walls. There are three major goals of this study. The first is to assess the attributes demanded by builders in single family wall products and systems. The second is to assess product usage and substitution in single-family walls. The third aim is to assess the move to component building in residential walls.
A mail out survey was sent to single-family homebuilders in the US, one randomly drawn list of builders plus a list of the top 100 builders in the country. The survey covered builders concerns, attributes demanded in walls, and products and systems used for walls.
Results indicated that energy codes were the top concern of builders. Interestingly, very few builders were concerned with engineered wood or prefabricated systems availability, but lumber availability was considered a constraint by some firms, especially the large ones.
With respect to walls attributes it is clear that the most important attribute of a wall is straightness and square. However, the next three most important attributes are related to on-site issues; speed of assembly, easy to handle, and low on-site waste. This was especially true for large builders. Cost factored in as moderately important with installed cost finishing ahead of material cost.
With respect to walls systems it was found that over 40% of builders have tried prefabricated wood walls. This was strongest in the North. Large builders also were high users of prefabricated wood walls. Prefabricated exterior walls were more common than prefabricated interior walls. Many builders, especially those in the West, used site-built steel for interior walls. In fact, it would appear that of the prefabricated wood interior walls and site-built steel are substitutes.
Labour availability is an equal, if not greater, factor than product availability in the competition among building products and systems for residential construction today. Further, demographic forecasts show labour availability decreasing into the future. At the same time the consolidation of residential building firms is giving rise to more automation and off-site building. For these reasons, it is safe to assume that prefabricated building will only increase into the future. Therefore, it is imperative that the wood products industry defines how the competitive advantage their products have always had in the residential construction industry can be adapted and maintained in an era of prefabricated construction.
The wood products industry wants to expand its market share in non-residential buildings. This is a challenging goal because building codes exhibit a bias against the use of wood products, particularly in the construction of non-residential buildings. The move towards adoption of performance-based building codes offers the promise of eliminating such biases. However, in order to be prepared for the introduction of performance-based codes, architects, engineers and building code officials have pointed out the need for engineering tools to assess the fire performance of buildings.
This five-year project was initiated to develop fire-safety design tools for non-residential wood-frame buildings, and to foster development and delivery of educational programs to train students and practitioners in performance-based fire-safety design. In order to achieve these goals an NSERC Industrial Research Chair in Fire Safety Engineering was established at Carleton University in March of 2001. This report summarises the progress towards these goals made by the Chair in his first year of tenure.
An effective floor serviceability design relies on a proper serviceability criterion, a reliable design method and accurate design values of the mechanical properties of the floor components. Forintek developed a tentative performance criterion to control vibrations in a broad range of wood-based floors in 2000. The criterion proposes to use the combination of 1 kN static deflection and fundamental natural frequency to control vibrations in a broad range of wood-based floors. Forintek’s members requested the development of a methodology for vibration controlled floor design that accounts for as many of the construction parameters involved in wood-based floors as possible. A comprehensive floor model was therefore needed to serve as a benchmark for the development of the desired methodology. A literature review of existing models indicates that none of them can handle all the construction parameters, especially the lateral reinforcements (cross-bridging, blocking, strong-backs, bracing, strapping, etc.) and the use of multi-span continuous joists.
Due to the shortcomings of existing models, Forintek has developed a finite element model for a broad range of wood-based floors. The model accounts for almost all the construction parameters including transverse shear deformations, multi-layered sub-floor and ceiling boards, gaps perpendicular to joists in sub-floors, non-rigid connections, rigid and flexible support conditions, and most importantly, various types of lateral reinforcements including cross-bridging, blocking, strong-backs, bracing, strapping, and multi-span continuous joists. The model was developed for static and frequency analyses for the time being, but is believed to be extendable for dynamic and acoustic response analyses, and stress analysis.
The model was verified using databases consisting of 22 full-size wood-based floors tested at Forintek and other laboratories. The test floors covered a broad range of construction features included in the model. The parameters measured included the mechanical properties of the floor joists and the fastener-to-wood connections, floor static deflections under concentrated loads, and the natural frequencies and mode shapes.
Sensitivity studies were conducted to examine the effects of the mechanical properties of the fastener-to-wood connections on the predicted static deflections and natural frequencies. Based on these studies and the measured mechanical properties of the fastener-to-wood connections, reasonable values were identified for the mechanical properties for these connections used to attach lateral reinforcements or sub-floors to joists. Using these values for mechanical properties of the connections, the measured joist properties and the published properties for sub-floor and ceiling panels as the input, the finite element model predicted the static deflections under concentrated loads and natural frequencies reasonably well when compared with measured values.
To create user friendly software from the model, a pre-processing program was developed to automatically generate finite element mash blocks for wood-based floor systems, and a post-processing program was developed to graphically display the finite element floor model and results. A manual for the finite element floor software was prepared.
In conclusion, the present finite element software for wood-based floors is unique particularly in modelling floors built with multi-span continuous joists and floors having various types of lateral reinforcements. The beauty of the model comes from its exclusive use of measurable parameters including mechanical properties of the reinforcements and stiffness of the connections between joists and reinforcements to achieve good predictions for the static and dynamic behaviour of wood-based floors containing these reinforcements. This special feature, along with others discussed in this report, makes the software a benchmark for the development of a simplified design procedure for a broad range of wood-based floors and a useful tool for wood-based floor performance research and design. In addition, the user-friendly nature of the software makes it a useful tool for assisting wood industries to develop new wood-based floor construction products and systems.
The current version of the software is limited to static and frequency analyses, but it can be extended for other applications such as stress analysis and analysis of responses to dynamic loading and sound.
An increased number of occupant complaints about excessive vibrations in wood-based floors, particularly in those with long spans and large open spaces, or cementitious toppings, are being received. This is both surprising and confusing because the design of these “unsatisfactory floors” conforms to the building codes. A review of the design procedures already in the building codes and those proposed in the literature indicates that they have limited application to wood-based floors of certain classes.
To bridge the gaps in the design procedures already adopted in the building codes and those proposed in the literature, Forintek has conducted a research project to develop and implement a new vibration-controlled design procedure for a broad range of wood-based floor systems. The specific aims of this research project are:
1) To develop a design procedure to control vibrations in a broad range of wood-based floors. This design procedure should include calculation methods to determine 1 kN static deflection and fundamental natural frequency, recommendations for design values for properties of floor components, a vibration-controlled design criterion calibrated to the calculation methods and the recommended design values and test protocols to determine properties which are not currently available in codes and publications.
2) To make a proposal to the code committee for adoption of the new general design procedure to control vibrations in a broad range of wood-based floors. The proposal should also include an impact study of the new design procedure on current floor spans.
To reach these objectives, several tasks have been identified and performed. These tasks include:
1) Development of simplified calculation methods to determine 1 kN static deflection and fundamental natural frequency;
2) Development of test protocols to determine the rotational stiffness of bridging/blocking-to-joist connections required by the simplified calculation methods;
3) Recommendations for the design values of mechanical properties of floor components;
4) Proposed methods for determining bending and shear stiffness of wood trusses;
5) Validation of the calculation procedure including the calculation methods and proposed design values;
6) Formulation of a new design criterion using computed 1 kN static deflections and fundamental natural frequencies of the floors in Forintek’s field survey database;
7) Study of the sensitivity of the new design procedure to various construction parameters for a broad range of spans;
8) Study of the impact of the new design procedure on current spans for a broad range of wood floor systems;
9) Formation of a project Task Group;
10) Preparation of a code implementation proposal.
To date, tasks 1-9 have been completed. The simple calculation methods along with the approaches for lateral bracing (bridging, blocking, strapping, strong-back and ceiling), cementitious topping, and wood panel overlay were validated using a database consisting of 91 laboratory tested floors. The simplified calculation methods were implemented into an Excel file ready for distributing to the wood industry.
Two forms for a tentative design criterion were formulated using the combinations of computed 1 kN static deflection and fundamental natural frequency, or computed 1 kN static deflection, fundamental natural frequency and area mass. The tentative design criterion was validated using a database consisting of 106 field floors. The database includes the floors with the most common construction parameters encountered in practice and a board range of span coverage from 10 feet to 44 feet. Floor acceptance rated by the new design criterion was well matched with the occupants’ ratings.
The preliminary impact study on 10” and 18” wood I-joist floors, and 2x6”, 2x10”, and 2x12” solid sawn lumber joists floors revealed that for floors having spans shorter than 16 feet, the vibration-controlled spans allowed by the new design procedure were comparable with the spans allowed by the Part-9 criterion or CCMC provision. For long-span floors, the new design procedure provided more rational spans than those provided by the CCMC provision. The new design procedure showed great potential to properly address such unresolved issues as long span, bridging/blocking/strapping/strong-backs, topping, etc in current design procedures in the codes and in the literature.
A CWC/Forintek Task Group (TG) was formed to review the progress and to facilitate implementation of the final recommendations and obtain code recognition of the new design procedure to control vibrations in a broad range of wood-based floors. The TG is composed of representatives from proprietary product manufacturers, CCMC and CWC and floor research scientists. Dr. Chui of the University of New Brunswick chairs the TG. It is expected that TG members will assist in conducting full-scale studies of the impact of the new tentative design procedure on their current floor spans, and in finalising the procedure, making a collective proposal to the code committee to consider for adoption.
At present, it can be concluded that the new design procedure shows the potential to provide rational solutions for vibration-controlled spans for a broad range of wood-based floor systems. The new design procedure shows the potential to resolve issues in current floor design such as long spans, overestimated spans of floors with various types of lateral bracing or with cementitious topping. The approach proposed to account for the contribution from installation of bridging/blocking type of discontinuous lateral bracing provides freedom for the innovation of new types of bridging/blocking systems.
Lumber trusses are an essential part of residential and other light frame building construction. The use of metal plate connectors has been an accepted form of connecting wood members to build up the trusses for these constructions. Wood trusses are a potentially viable application for fingerjoined structural lumber. However, little information is available on the strength of the fingerjoined member when truss plates are applied on or in the vicinity of a fingerjoint. This project deals with issues that may arise from the use of fingerjoined lumber in metal plate-connected truss applications aimed at optimizing the use of wood to meet end-user expectations in terms of structural performance. To meet the objective, a phased approach was taken involving representatives from both the lumber producing and wood truss industries. Phases included: (i) creation of an Industry Working Group (IWG) to discuss the issues that may arise from the widespread use of fingerjoined lumber in truss applications and identify relevant studies, (ii) carrying out the identified priority studies, (iii) and identification of issues that would need additional research. The IWG was composed of 12 members representing truss fabricators, truss plate manufacturers, and lumber producers. The industrial partners in the project are Canadian Forest Products Ltd., Jager Building Systems, Inc., and Weyerhaeuser Canada Ltd. The members of the IWG convened last year, and discussed potential research items for the project. As a result of the meeting, two basic studies were identified as priorities, namely: (i) effect of fingerjoint offset on truss plate capacity, and (ii) effect of truss plate over-pressing on plate capacity. These two studies have been completed and results are reported.