Progress 01/01/94 to 12/31/04
Outputs
In 2004, a final report (M.S. Thesis) was prepared. A brief paper was also prepared and presented at the 8th World Conference on Timber Engineering in Lahti, Finland in August. Two technical publications from this work have been prepared and submitted to two peer-reviewed journals for publication consideration. The objective of this research was to use a three-dimensional (3D) analysis method to include system effects directly in the design of light-frame roof truss assemblies. Three types of 3D truss assemblies (i.e., T-shaped, L-shaped, and a complex assembly) were investigated. T-shaped, L-shaped, and complex assemblies were composed of 4 (total of 37 trusses), 17 (total of 56 trusses), and 27 (total of 123 trusses) different types of individual trusses, respectively. The VIEW (Visually Integrated Engineering Window) program, used by a truss plate manufacturer to design truss assemblies, was used to layout assemblies and to design individual trusses. The program
uses a conventional design procedure (CDP) by analyzing one truss at a time in two-dimensions. A commercially available structural analysis program, SAP2000, was then utilized to model 3D truss assemblies with a system design procedure (SDP). The structural responses including CSI, truss deflections, and reactions from both CDP and SDP were compared and the system effects were evaluated. From this investigation, there are three system effects observed by the SDP, but not accounted for by CDP. These effects were observed in all three assemblies. The first is the reduced applied load effect. This effect occurs because the CDP assumes a 2-ft spacing for every truss in an assembly, whereas the SDP assumes the actual tributary area, with normally a lower total applied load. In most cases, the CDP overestimated the applied loads. For example, in the complex assembly model, the total applied load assumed by the CDP was 155,000 pounds (assuming 2-ft spacing on center for every truss in the
assembly) while the total load for the SDP was only 142,000 pounds (based on the actual overall roof loading area in the assembly). The second system effect is deflection compatibility. Unlike the CDP, SDP provides deflection compatibility because it analyzes the entire 3D truss assembly as a whole. On the other hand, CDP analyzes one truss at a time and it assumes that truss supports have zero deflection. When trusses are supported by other trusses, the support at the connecting point will not have zero deflection. Thus, the CDP is not a good approach to examine this connection in the assembly. The last observation was the stiff-truss effect. As expected, stiffer trusses in the assembly attract more load. This effect can be observed by an increase in CSI values for the stiffer trusses and decrease in CSI values for the adjacent trusses that are less stiff. Based on this investigation, the maximum CSI for most trusses in all three assemblies reduces by 6 percent to 60 percent because
of system effects. SDP can help to improve the analysis of truss assemblies by directly including system effects that are not accounted for by the CDP. Graduate Students: One M.S. graduate student.
Impacts
The long-term goal of this project is to improve the analysis and design of MPC wood trusses by including load sharing, composite action, variability in material properties, and connection behavior. The benefits of using an assembly model instead of the conventional truss design method include: (a) improved truss system design by including system behavior directly; (b) increased safety through improved analysis; and (c) potential construction cost reduction. Efficient design of trusses will contribute not only to improving utilization of material, but also to increased safety and better performance of trusses in American homes.
Publications
- Gupta, R. and P. Limkatanyoo. 2004. An integrated approach to include system effects in wood assemblies. p. 217-222 In: Proceedings of the 8th World Conference on Timber Engineering. Vol. 1. (ISBN 951-758-442-3).
- Limkatanyoo, P. 2004. System behavior of three-dimensional wood truss assemblies. M.S. Thesis. Department of Wood Science and Engineering, Oregon State University, Corvallis.
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Progress 01/01/03 to 12/31/03
Outputs
During 2003, three types of 3D truss assemblies (i.e., T-shaped, L-shaped, and a complex assembly) were investigated. T-shaped, L-shaped, and complex assemblies were composed of 4 (total of 37 trusses), 17 (total of 56 trusses), and 27 (total of 123 trusses) different types of trusses, respectively. A truss plate manufacturers (TPM) truss design program was used to layout assemblies and to design individual trusses. The program uses a conventional design procedure (CDP) by analyzing one truss at a time in two-dimensions. A commercially available structural analysis program, SAP2000, was then utilized to model 3D truss assemblies with a system design procedure (SDP). The structural responses including CSI, truss deflections, and reactions from both CDP and SDP were compared and the system effects were evaluated. From this investigation, three system effects were observed by the SDP that are not accounted for by CDP. These effects were observed in all three assemblies.
The first is the reduced applied load effect. This effect occurs because the CDP assumes a 2-ft spacing for every truss in an assembly, whereas the SDP assumes the actual tributary area, with normally a lower total applied load for a few trusses in the assembly. The second system effect is truss-to-truss support effect. When trusses are supported by other trusses, the support at the connecting point will not have zero deflection, as predicted by CDP. The last observation is the stiff-truss effect. As expected, stiffer trusses in the assembly attract more load. This effect can be observed by an increase in CSI values for the stiffer trusses and decrease in CSI values for the adjacent trusses that are less stiff. Based on this investigation, the maximum CSI for most trusses in all three assemblies reduced by 6 percent to 60 percent because of system effects.
Impacts
The long-term goal of this project is to improve the analysis and design of MPC wood trusses by including load sharing, composite action, variability in material properties, and connection behavior. The benefits of using an assembly model instead of the conventional truss design method include: (a) improved truss system design by including system behavior directly; (b) increased safety through improved analysis; and (c) potential construction cost reduction. Efficient design of trusses will contribute not only to improving utilization of material, but also to increased safety and better performance of trusses in American homes.
Publications
- Limkatanyoo, P. 2003. System Behavior of Three-Dimensional Wood Truss Assemblies. M.S. Thesis. Department of Wood Science and Engineering, Oregon State Univ., Corvallis.
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Progress 01/01/02 to 12/31/02
Outputs
The design of three-dimensional (3D), metal-plate-connected (MPC), wood truss assemblies is based on single truss design (two-dimensional analysis). In this conventional design procedure (CDP), only some of the system effects are included in the design by using a repetitive member factor in bending only. Although CDP has a good track record, it many not include all of the system effects in the design. There are system effects that are present/observed in 3D assemblies that are not accounted for by CDP, and those could be directly included by analyzing a 3D frame model of the assemblies. This phase of the study is addressing this issue by using a system design procedure (SDP) that analyzes 3D assemblies as a system to include the system effect directly. We are using a truss plate manufacturer's (TPM) truss design software (VIEW) to layout actual truss assemblies and to analyze single trusses. A commercial structural analysis software, SAP2000, is being used to analyze
single trusses and 3D assemblies. During 2002, three actual assemblies were developed and analyzed using VIEW. These are T-shape, L-shape, and complex-shape assemblies consisting of 4, 17, 32 different types of trusses, respectively. The total number of trusses in each assembly is 37, 66, 108, respectively. Single trusses analyzed in VIEW were also modeled in SAP2000 using exactly the same model as in VIEW to verify SAP2000 modeling, and using a simplified model which would be later used in 3D assemblies. The results (CSI, deflecton, reactions) for single trusses from VIEW were compared to the results obtained from SAP2000 analysis. The results match extremely well. The next step is to model and analyze 3D assemblies in SAP2000 and compare the results to the results obtained from VIEW (single truss analysis). We plan to model the above-mentioned three realistic truss assemblies to investigate and to quantify system performance.
Impacts
The long-term goal of this project is to improve the analysis and design of MPC wood trusses by including load sharing, composite action, variability in material properties, and connection behavior. The benefits of using an assembly model instead of the conventional truss design method include: (a) improved truss system design by including system behavior directly; (b) increased safety through improved analysis; and (c) potential construction cost reduction. Efficient design of trusses will contribute not only to improving utilization of material, but also to increased safety and better performance of trusses in American homes.
Publications
- Gupta, R. and B. Wagner. 2002. Effect of metal connector plate on the bending strength of solid sawn lumber and LVL - A pilot study. Forest Products Journal 52(10):71-74.
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Progress 01/01/01 to 12/31/01
Outputs
The current phase of the study is focusing on the truss to wall and sheathing to truss connections modeling. We are using a truss plate manufacturer's (TPM) truss design software to model and analyze actual single trusses and truss assemblies. We obtained truss design software from a major TPM. The TPM software is being used to layout full assembly and to design single trusses in the assembly. The assembly effects will be studied using a commercial structural analysis software, SAP2000. We plan to model several realistic truss assemblies (including realistic but practical model of truss to wall connection and sheathing to truss connection) to investigate and to quantify system performance. In a different study, effect of metal connector plates on the bending strength of solid sawn lumber (SSL) and LVL was studied. The statistical analysis showed that there was no effect on the bending strength of SSL and LVL. Strength of metal-plate-connected heel joints was also
determined for four different angles. The strength and stiffness of the joints were not affected by the angles.
Impacts
The long-term goal of this project is to improve the analysis and design of MPC wood trusses by including load sharing, composite action, variability in material properties, and connection behavior. The benefits of using an assembly model instead of the conventional truss design method include: (a) improved truss system design by including system behavior directly; (b) increased safety through improved analysis; and (c) potential construction cost reduction. Efficient design of trusses will contribute not only to improving utilization of material, but also to increased safety and better performance of trusses in American homes.
Publications
- Gupta, R. and B. Wagner. 2002. Effect of metal connector plate on the bending strength of solid sawn lumber and LVL. Technical Note. Forest Products Journal. (In Press).
- Gupta, R. and I. Hagenthurn. 2002. Strength of metal-plate-connected heel joints with different angles. Technical Note. Forest Products Journal. (In Press).
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Progress 01/01/00 to 12/31/00
Outputs
The previous (1999) research activity presented a practical method to model an actual Metal-Plate-Connected (MPC) roof truss assembly. We used a commercial program, SAP2000, to investigate its system performance. A truss plate manufacturer's joint model was employed for the single-truss and truss-assembly models. The load distribution in the assembly was strongly influenced by the interaction of sub-assemblies and by the boundary conditions. In the truss assembly, the predictions of location and value of maximum combined stress index (CSI) differed from those based on the single truss. Although the CSI for one truss type increased over 1.0 in the assembly, the CSI values for most other trusses decreased (by as much as 43 percent) in the assembly. In this previous research activity, the boundary conditions (supports) of the trusses in the actual roof assembly were assumed to be pin supported at both ends to simulate the same type of connection hardware used to connect
trusses to the walls at both ends. Use of pin supports at both ends not only presented realistic condition, but also helped to simplify the analysis. Thus, we avoided arbitrary selection of an end to which to apply pin or roller support. Although the behavior of a single truss does not depend on this selection, the behavior of the assembly does, because assemblies, in general, are symmetrical and irregular in shape. Therefore, to be consistent with real-life situations, both ends of the trusses were assumed to be pin-supported. Although, in reality, true boundary conditions for a truss in the assembly are in between pin-pin and pin-roller, due to the out-of-plane stiffness of the supporting walls and their proximity to end walls and partition walls. The next phase of the study will focus on the truss to wall and sheathing to truss connections modeling. We plan to use a truss plate manufacturer's (TPM) truss design software to model and analyze actual single trusses and truss
assemblies. We obtained truss design software from a major TPM. The TPM software will be used to layout full assembly and to design single trusses in the assembly. The assembly effects will be studied using SAP2000. We plan to model several realistic truss assemblies (including realistic but practical model of a truss to wall connection and sheathing to truss connection) to investigate and to quantify system performance. Graduate Students = 2
Impacts
The long-term goal of this project is to improve the analysis and design of MPC wood trusses by including load sharing, composite action, variability in material properties, and connection behavior. Efficient design of trusses will contribute not only to improving utilization of material, but also to increased safety and better performance of trusses in American homes.
Publications
- Gupta, R. and T.H. Miller. 2000. Up on the roof - Researchers study system effects in wood truss assemblies. Resource: Engineering & Technology for a Sustainable World 7(11):9-10.
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Progress 01/01/99 to 12/31/99
Outputs
The research activity in the past year focused on a practical method to model an actual Metal-Plate-Connected (MPC) roof truss assembly using a commercial program, SAP 2000, to investigate its system performance. Truss assembly modeling was examined because the conventional single truss design method ignores system effects, such as variability of modulus of elasticity (MOE), interaction of sub-assemblies, realistic boundary conditions, etc. It was found that the load distribution in an actual roof truss assembly is strongly influenced by the interaction of sub-assemblies and by the boundary conditions. In the truss assembly, the prediction of location and value of maximum CSI are different from those for the single truss. The truss with the maximum CSI value of 0.91 among fourteen individual truss types decreased to 0.52 and 0.51 when this truss is in the assembly with design and random material properties, respectively. Moreover, the truss with a maximum CSI of 1.03
in the assembly (with design properties) had a CSI value of only 0.95 as an individual truss. Although the CSI of one truss type increased over 1.0 in the assembly, the CSI of most other trusses decreased (by as much as 43%). So, the behavior of a single truss is different when the truss is in the assembly. The benefits of using an assembly model compared to the conventional truss design method are in providing increased safety through improved analysis and in a potential reduction in construction cost.
Impacts
The long-term goal of this project is to improve the analysis and design of MPC wood trusses by including load sharing, composite action, variability in material properties, and connection behavior. Efficient design of trusses will contribute not only to improving utilization of material, but also to increased safety and better performance of trusses in American homes.
Publications
- Dung, D-R. 1999. A practical method to analyze the system effects of a metal-plate-connected wood truss assembly. M.S. Thesis. Oregon State Univ., Corvallis.
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Progress 01/01/98 to 12/31/98
Outputs
The research activity in the last year focused on small-scale modeling of a metal-plate-connected (MPC) wood truss joints using similitude theory. A one third scale model of full size (Prototype) MPC wood truss joint was developed. The prototype metal connector plates in MPC joints were modeled using thin galvanized sheet metal and short staples. Truss grade wood material was ripped to one third scale dimensions to be used as the modeling material. To provide verification of the model material properties, a modulus of elasticity study was performed that compared prototype and one third scale model boards. The results indicated that although the variation in MOE of the model was eleven percent greater than that of the prototype, the average design stiffness was within 1 percent of the prototype joint stiffness, while the ultimate load was 7 percent lower than the prototype. Stiffness and strength of model heel joints were within 22 percent and 17 percent of the
stiffness and strength of prototype heel joints, respectively. The results indicate that it may be possible to model full size truss connection behavior up to the design load and possibly to failure.
Impacts
(N/A)
Publications
- Kittel, M., Gupta, R. and Miller, T.H. 1998. Small scale modeling of metal-plate-connected wood truss joints. In: Proceedings, Fifth World Conference on Timber Engineering, August 17-20, Montreux, Switzerland). Natterer, J. and Sandoz, J.L., eds. Presses polytechniques et universitaires romandes, CH-1015 Lausanne.
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Progress 01/01/97 to 12/31/97
Outputs
Research activity in the last year moved from testing full-scale MPC joints to small-scale modeling of these connections using similitude theory. The specific objective of the research is to investigate small-scale physical modeling of wood truss assemblies in order to better predict the behavior of full-scale trusses and truss assemblies. The prototype metal connector plates in MPC joints will be modeled using thin galvanized sheet metal and short staples. Truss grade wood material will be ripped to one-third scale dimensions to be used as the modeling material. Tension splice and heel joints will be modeled using this technique. The remaining truss connections will be developed from projections based on tension splice joint and heel designs. One-third scale tension-splice joints were tested and the resulting average design stiffness was within 1 percent of the prototype joint stiffness, while the ultimate load was 7 percent lower than the prototype. Finally, model
trusses will be fabricated and tested.
Impacts
(N/A)
Publications
- VATOVEC, M., MILLER, T.H., GUPTA, R. and LEWIS, S. 1997. Modeling of metal-plate-connected wood truss joints: Part II-Application to overall truss model. Trans. of ASAE 40(6):1667-1675.
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Progress 01/01/96 to 12/30/96
Outputs
Five different types of actual metal-plate-connected (MPC) wood truss joints from a scissors truss were tested to failure to evaluate their behavior. Strength, stiffnesses (axial and rotational), and failure modes for bottom chord splice joints at web, heel joints, crown joints, bottom chord ridge joints, and top chord splice joints at web were determined. The majority of bottom chord joints failed in plate tearing, whereas top chord joints generally failed in a web member withdrawal mode. A commercially available finite element analysis program was used to model MPC joints. The load-displacement results from the model and experimental result from tensile and bending tests of splice joints with different teeth-to-grain orientations showed a good agreement. The joint stiffness data were used in a finite element analysis of the same truss, and the analytical results compared well to actual full-scale truss test results.
Impacts
(N/A)
Publications
- GUPTA, R., VATOVEC, M. and MILLER, T.H. 1996. Metal-plate-connected wood joints:A literature review. Forest Research Laboratory, Oregon State Univ., Corvallis. Research Contribution 13. 37 pp.
- VATOVEC, M., GUPTA, R. and MILLER, T.H. 1996. Testing and evaluation of actual metal-plate-connected wood truss joints. Journal of Testing and Evaluation 24(2):63-72.
- VATOVEC, M. 1996. Analytical and experimental investigations of the behavior of metal-plate-connected wood truss joints. Ph.D. Thesis. Oregon State Univ., Corvallis.
- VATOVEC, M., MILLER, T.H. and GUPTA, R. 1996. Modelling of metal-plate-connectedwood truss joints. Transactions of the American Society of Agricultural Engineers 39(3):1101-1111.
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Progress 01/01/95 to 12/30/95
Outputs
Five different types of actual metal-plate-connected (MPC) wood truss joints from a scissors truss were tested to failure to evaluate their behavior. Strength, stiffnesses (axial and rotational), and failure modes for bottom chord splice joints at web, heel joints, crown joints, bottom chord ridge joints, and top chord splice joints at web were determined. The majority of bottom chord joints failed in plate tearing, whereas top chord joints generally failed in a web member withdrawal mode. A commercially available finite element analysis program was used to model MPC joints. The load-displacement results from the model and experimental results from tensile and bending tests of splice joints with different teeth-to-grain orientations showed a good agreement. The joint stiffness data were used in a finite element analysis of the same truss, and the analytical results compared well to actual full-scale truss test results.
Impacts
(N/A)
Publications
- VATOVEC, M., MILLER, T.H. and GUPTA, R. 1995. Finite element modelling of metal-plate-connected joints in wood trusses. ASAE Paper No. 954586. American Society of Agricultural Engineers, St. Joseph, MI 49085.
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Progress 01/01/94 to 12/30/94
Outputs
Five different types of actual metal-plate-connected (MPC) wood truss joints from a scissors truss were tested to failure to evaluate their behavior. All joints (about fifty) were tested in the unique testing apparatus where in-plane loads along with moments were applied to simulate loads carried by the truss members. Strength, stiffnesses (axial and rotatinal), and failure modes for bottom chord splice joints at web, heel joints, crown joints, bottom chord ridge joints, and top chord splice joints at web were determined. The majority of bottom chord joints failed in plate tearing, whereas top chord joints generally failed in a web member withdrawal mode. The joint stiffness data were used in a preliminary finite element analysis of the same truss, and the analytical results compared well to actual full-scale truss test results. Stiffness and strength data will be used in a future finite element study.
Impacts
(N/A)
Publications
- VATOVEC, M., GUPTA, R. AND MILLER, T.H. 1994. Strength and stiffness of metal-plate-connected scissors truss joints. ASAE Paper No. 944550, St. Joseph, MI-49085.
- GUPTA, R. 1993. Testing of metal-plate-connected wood-truss joints. Presented at the 26th Meeting of CIB-W18, August 22-26, Athens, GA.
- VATOVEC, M., GUPTA, R. AND MILLER, T.H. 1993. Influence of joint stiffness on the behavior of wood trusses. ASAE Paper No. 93-4004.
- GUPTA, R. 1992. Testing apparatus for metal-plate-connected wood-truss joints. Wood Design Focus 3(2):3-5.
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