Progress 10/01/04 to 09/30/07
Outputs
OUTPUTS: Diaphragm action provides a systems approach to design of post frame buildings. Current design procedure underestimates the capacity of buildings. This project generated data and information about diaphragm design of metal-clad timber framed rectangular buildings and developed a comprehensive design procedure for diaphragm design of post frame buildings. The study also established the limitations associated with diaphragm action of post frame buildings. Results from the project were presented through invited seminars at the annual meetings of the National Frame Builders Association (NFBA), paper presentations at the annual meetings of the American Society of Agricultural and Biological Engineers (ASABE), paper presentations at the World Conferences on Timber Engineering (WCTE), through peer reviewed publications in the Practice Periodical on Structural Design and Construction Journal, as well as publication of articles in the Frame Building Professional, which is the
official publication of the NFBA, and Wood Focus- Journal of Contemporary Wood Engineering, etc. Our study in this area (diaphragm design) has become the bases for an ASABE standard, and is being used by post-frame building design engineers, architects, builders, contractors and code officials. Materials from this study have been incorporated into lectures of courses on timber engineering to educate students about the state-of-the art on diaphragm design.
TARGET AUDIENCES: Post-frame builders, architects, engineers, code-enforcing officials, and post-frame contractors
Impacts
Through extensive and advanced full-scale testing, modeling and analysis, we were able to understand the true behavior of post-frame buildings and have developed methods for incorporating their behavior into design. We learned that post-frame buildings are much stiffer than designers previously believed. Erecting a full-scale (40 ft wide by 80 ft long and 16 ft to the eave height) metal-clad, post-frame building near campus, and subjecting it to engineering tests which simulate wind loads, we were able to understand the global three-dimensional behavior of the building, which otherwise would not have been able to know whether the building is over-built or under-built. A post-frame building effectively acts as a system. The entire building acts like a rigid box to resist wind forces or any lateral load such as sway developed due to unbalanced snow loads. Thus, incorporating diaphragm action by utilizing existing materials and systems already in the building, that is,
roof and wall cladding, roof purlins and wall girts, posts and truss top chords, and fasteners translates into material and labor savings. A systems approach to designing post-frame buildings (including diaphragm action) reflects in substantial reduction in post sizes and post-embedment depth requirements. In economic terms, the saving is in terms of material and labor requirements. These savings occur when designs are consistent with actual building performance that is considering the strength and stiffness contributions and load sharing of the different structural components that exist in the building. One specific example is, in our full-scale test building, the deflection of the critical post (mid-span post) reduced from 6 inches to 0.44 inch for the same simulated wind loads when the metal skin on the walls and roof (normally not included in design) were included. This reduction in deflection can be translated into smaller size posts and reduced post-embedment depth requirements,
mentioned previously. Therefore, post-frame designers and code officials should be mindful of the load sharing characteristics and positive stiffness contributions of the different sub-assemblies and elements of the building. The ultimate beneficiaries are the commercial, industrial, or agricultural building owners, which post-frame building is most commonly used.
Publications
- Gebremedhin, K.G. 2007. Design and construction practices that affect diaphragm strength and stiffness of post-frame buildings. Practice Periodical on Structural Design and Construction, 12(3):153-160.
- Gebremedhin, K.G. 2006. Evaluation of design practices of post-frames building diaphragms. 9th World Conference on Timber Engineering (WCTE), August 6-10, Portland, Oregon, Editors: Bender, D.A., Gromala, D.S. and Rosowsky, D.V.
- Gebremedhin, K.G. 2002. Testing a full-scale building after nine years in service. Wood Focus- Journal of Contemporary Wood Engineering 12(3): 20-24.
- Gooch, C.A. and Gebremedhin, K.G. 2001. Practices that enhance post-frame construction. Frame Building Professional 3(4): 30-36.
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Progress 01/01/06 to 12/31/06
Outputs
The objectives of this study were: 1. To compile design and construction practices that affect diaphragm strength and stiffness in post-frame buildings. 2. To conduct sensitivity analyses to determine the effect of changes in stiffness of roof diaphragm, post frame, or end wall on eave deflection and diaphragm shears. 3. Analyze and discuss construction practices that affect strength and stiffness of diaphragms and post-frame buildings. Including diaphragm action in sizing building posts (columns) and post-embedment depths (foundation) is more consistent with actual building performance. Large portion of in-plane loading, such as wind, is transferred to the end walls through in-plane shear via metal roofing-- a phenomenon called 'diaphragm action'. Because of load sharing and redundancies that are not accounted for, post-frame buildings are stronger and stiffer than what is normally assumed. Various construction and design practices that increase diaphragm strength
and stiffness of post-frame buildings are analyzed. The report is based on data and information obtained from the full-scale metal-clad, timber-framed, post-frame building tested over a period of nine years and the literature. Understanding the functions, contributions, interactions and load sharing characteristics of the different framing, cladding and redundant elements are analyzed. The study compiles design and construction practices that affect diaphragm strength and stiffness in post-frame buildings. We have previously published some of the information in different articles but the main elements are now compiled in this study. The paper is organized by discussing the main structural sub-assemblies that play major roles in diaphragm design of post-frame buildings, and they are: 1. roof diaphragm, 2. shear-wall diaphragm, 3. side-wall frames, and 4. post foundation. Diaphragm action results from the interaction of these sub-systems. Sensitivity analyses were performed to determine
the effect of changes in stiffness of roof diaphragm, post frame, or end wall on eave deflection and diaphragm shears. Stiffness values obtained from the full-scale test were used as reference values. Finally, construction practices that affect strength and stiffness of diaphragms and post-frame buildings are discussed. These include: end fasteners, screws on flats or through the ribs, screw length, nails versus screws, Ring-shank nails, panel length, trusses and purlins, post-to-truss connection, truss bracing, knee bracing, insulation between steel sheet and wood framing, and building length.
Impacts
A post-frame building effectively acts as a system. Interaction between the primary and secondary framing systems results in the overall building stiffness much higher than the sum of its parts. To optimize designs of post-frame buildings, it becomes necessary to understand the interactions, functions, contributions and load sharing characteristics among the different framing, cladding and redundant elements. A metal-clad, wood-framed roof diaphragm is often the most cost effective method of resisting the overturning forces due to wind. For effective diaphragm action, each panel of roof and wall cladding must be connected along all four edges to adjacent framing and cladding. This causes the entire building to act like a rigid box to resist wind forces or any lateral load such as sway developed due to unbalanced snow loads. Thus, incorporating diaphragm action by utilizing existing materials and systems already in the building, i.e., roof and wall cladding, roof
purlins and wall girts, posts and truss top chords, and fasteners translates into material and labor savings. Savings are reflected in reduced post sizes and post-embedment depth requirements. For example, load sharing that may exist between frames, lateral bracing added to stabilize the truss bottom chords or other all contribute to improved structural system performance, but are not included in conventional design. The study benefits engineers, architects, builders and code officials of post-frame buildings.
Publications
- Gebremedhin, K.G. 2006. Evaluation of design practices of post-frames building diaphragms. 9th World Conference on Timber Engineering (WCTE), August 6-10, Portland, Oregon, Editors: D.A. Bender, D.S. Gromala and D.V. Rosowsky.
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Progress 01/01/05 to 12/31/05
Outputs
The test results of a full-scale metal-clad, wood-framed post-frame building collected over the years will be coalesced and analyzed and reported in one publication. The post-frame building was tested in stages (as it was being built) in order to determine the stiffness contributions of the wood frames and metal skin fastened to the different components of the building. The next year, the building was tested with different sizes of openings in the end wall to determine the lost stiffness of the end wall due to the opening. Subsequently, the building was tested with application of different reinforcements in the end wall that had the opening to restore the lost stiffness. After three years without testing, tests were again conducted to determine the strain profile of the roof purlins across the building width, load sharing between frames, and to examine the effect of an interior make-shift shear wall on diaphragm behavior of the building. Finally, after nine years, the
building was tested again to determine if in-service conditions, such as cyclic natural wind loading and weather, had an effect on the stiffness of the elements during the nine years the building has been in service. The information collected over these years has been published in different papers and journals. The idea now is to bring all the important findings into a single paper. The paper is accepted for presentation at the Annual International Wood Council (IWC) meeting this summer.
Impacts
A systems approach to designing post-frame buildings (including diaphragm action) reflects in substantial reduction in post sizes and post-embedment depth requirements. In economic terms, the saving is in terms of material and labor requirements. These savings occur when designs are consistent with actual building performance that is considering the strength and stiffness contributions and load sharing of the different structural components of the building. One specific example is, in our full-scale test building, the deflection of the critical post (mid-span post) reduced from 6 inches to 0.44 inch for the same simulated wind loads when the metal skin on the walls and roof (normally not included in design) were included. This reduction in deflection can be translated into smaller size posts and reduced post-embedment depth requirements, mentioned previously. Therefore, post-frame designers and code officials should be mindful of the load sharing characteristics and
positive stiffness contributions of the different sub-assemblies and elements of the system. Our initial study in this area (diaphragm design) has become the bases for an ASAE (American Society of Agricultural Engineers) standard, and is being used by post-frame building design engineers, architects, builders, contractors and code officials. The ultimate beneficiaries are the commercial, industrial, or agricultural building owners, which post-frame building is commonly used. We are continuing with this work to further refine and validate some of the assumptions involved in the design procedure.
Publications
- No publications reported this period
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