Corrugated strandboard structural panels.

[FIGURE 6 OMITTED]

Primary direction stiffness and strength testing was done on 24-in-wide specimens because of width limitations of the testing machine. The specimens were made by ripping the 4-ft by 8-ft panels in half, longitudinally. Specimens were tested under centerpoint loadings on nominal 24- and 32-inch spans. The support and load details were the same as used for the small-specimen primary direction testing. Single- and two-span continuous specimens were tested. The two-span specimens were loaded on both spans simultaneously, through a simple beam loading fixture. Typical load-deflection curves are shown in Figure 7. A summary of the results is in Table 4. The single span specimen p/[DELTA] slopes were assumed to follow Equation [2]. The standard beam equation for the two-span case is

P / D = [(7[L.sup.3] / 768EI + 73L / 256G[A.sub.s]).sup.-1] [3]

Using the same calibration methods (Pang, 2005) as for the single-span model results in

P / D = ([L.sup.3] / 99.4EI + L / 0.79G[A.sub.s]) [4]

with E/G equal to 6.5. The flexural and shear stiffness values for the four span length/number combinations are all within 6 percent of the means. The bending strengths show more variability with the 20.5-in span value being 16 percent higher than the mean.

[FIGURE 7 OMITTED]

Comparison to APA strength and stiffness requirements

If the lowest bending strength in Table 4, 2960 in-lbs/ft, with its COV of 0.091 are used to estimate lower 5 percent exclusion value with 90 percent confidence (see Johnson 2000), the result is 2374 in-lbs/ft. If this is multiplied by a 0.80 load effect factor and by a 0.85 flexural resistance factor, the adjusted value of 1615 in-lb/ft exceeds the 1503 in-lb/ft baseline primary strength requirement for a 32-in oc APA single floor panel (AF&PA). Conservatively, using the lowest pair of mean EI and G[A.sub.s] values in Table 4 and assuming a 10 percent increase in the flexural component and a five-fold increase in the shear component of the standard deflection expression for uniform load gives an approximation of the uniform load equation analogous to Equation [4]. This results in an equivalent baseline flexural stiffness of 331,000 pound-[in.sup.2]/ft. This is higher than the 300,000 pound-[in.sup.2]/ft required for a 24-in oc APA single floor panel. So the corrugated panel appears be stiffness limited. Obviously, an underlayment is required over a corrugated panel in any all-wood based floor system. Preliminary testing indicates a 15/32 OSB is needed to provide adequate punching shear resistance in the underlayment, over the channel cavities in the corrugated panel. Even if any composite action is ignored between the corrugated panel and the underlayment, if the underlayment's primary direction matches that of the corrugated panel, the combined stiffness would be on the order of 517,000 pound-[in.sup.2]/ft. Any composite action between the two panels should get the stiffness of the two-layer system up to the 650,000 pound-[in.sup.2]/ft required of a 32-in oc single floor panel.

Conclusions

It has been demonstrated that a corrugated structural panel with moderate wave geometry can be successfully produced using conventional mat forming and pressing methods. There appears to be little advantage in using a three-layer oriented strand mat, in comparison to a random lay up. There may be an opportunity to use some degree of unidirectional alignment in the primary direction, subject to the constraints of good mat moulding behavior and adequate strength in the secondary direction for handling and construction safety.

Properties of the 3/8-in panel exceed those of a flat 23/32-in single-layer floor panel rated for 24-in oc joist spacing in stiffness and for a 7/8-in panel rated for 32-in on center in strength. Since the corrugated panel will require an underlayment for use in an all-wood floor system, the shared stiffness of a properly detailed system of corrugated panel and underlayment should be capable of achieving a 32-in span rating in both strength and stiffness.

Further work needs to be done to optimize panel geometry, adhesive type and level, and to incorporate water repellant into the formulation.

Literature cited

American Forest and Pap. Assoc. (AF and PA). 1996. Supplement-structural-use panels. Load and Resistance Factor Design (LRFD), Manual for Engineered Wood Construction. American Forest and Pap. Assoc., Washington, D.C.

APA--The Engineered Wood Assoc. (APA). 2004. Panel design specification. APA, Tacoma, Washington. 28 pp.

American Soc. for Testing and Materials (ASTM). 1999. Standard test methods for evaluating properties of wood-base fiber and particle panel materials. D1037. Annual Book of Standards, 04.10: 142-171. ASTM, West Conshohocken, Pennsylvania.

Bach, L. 1989. Manufacture of corrugated waferboard. Forest Prod. J. 39(10):58-62.

DeBruine, G.R., B.A. Haataja, and L.B. Sandberg. 1990. Method for forming articles having deep drawn portions from matted wood flakes. U.S. Patent No. 4,960,553. Washington, D.C.

Haataja, B.A., L.B. Sandberg, and R.E. Liptak, Jr. 1991. Observation and control of mat behavior in molding with wood flakes. Forest Prod. J. 41 (7/8):21-26.

Johnson, R.A. 2000. Miller and Freund's Probability and Statistics for Engineers, 6th ed. Prentice-Hall, Upper Saddle, New Jersey. 622 pp. Lau, K.K. and R.M. Knudson. 1990. Ribbed waferboard product. United States Patent 4,904,517. Washington, D.C.

Pang, W.C. 2005. Corrugated wood composite panels for structural decking. PhD dissertation. Michigan Technological Univ., Houghton, Michigan. 209 pp.

Price, E.W. and C.E. Kesler. 1974. Analysis of southern hardwoods as furnish for a wood flake-resin composite structural material. T.A. and M. Rept. No. 389, Univ. of Illinois. Urbana-Champaign, Illinois:72-85.

Sandberg, L.B., B.A. Haataja, W.W. Vandenbergh, and T.J. Baas. 1989. Deep draw molding of wood flake composites. In: Proc of the Mechanics of Cellulosic and Polymeric Materials Symp. AMD99/MDI3, ASME. pp. 231-235b

The authors are, respectively, Former Graduate Research Assistant in Civil and Environmental Engineering, Professor of Civil and Environmental Engineering, Professor of Forest Resources and Environmental Sci., and Assistant Research Scientist in Forest Resources and Environmental Sci., Michigan Technological Univ., Houghton, Michigan (wpang@civil.tamu.edu, lbsand@mtu.edu, plaks@mtu.edu, jwforsma@mtu.edu). This project was supported by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Serv. This paper was received for publication in August 2005. Article No. 10107.

L. Bogue Sandberg* Peter Laks*

* Forest Products Society Member. [c] Forest Products Society 2007. Forest Prod. J. 57(3):48-53.

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