STRUCTURAL RELIABILITY TECHNIQUES FOR DETERMINATION OF DESIGN PROPERTIES FOR NEW WOOD-BASE MATERIALS

PHILLIP JOHN PRZESTRZELSKI, Purdue University

Abstract

The purpose of this thesis was to determine the design properties for new wood-base materials using structural reliability techniques. The new wood-base material selected was the oriented strand panel (OSP) which was compared to the accepted standard, plywood. The design properties that were determined were the resistance stiffness and strength bending properties of the material. In using the structural reliability techniques to derive these new properties, the probability of failure and safety index of OSP were equated to those of plywood. First, the live load only stiffness analysis was investigated with the structural reliability techniques, since it was the most critical on a conventional basis. A simulation method was used for the stiffness analysis using an assumed lognormal cumulative distribution function for the material resistance and a gamma cumulative distribution function for the live load values. Another stiffness simulation method was tried in which the resistance function was assumed "distribution-free", but the results were inconsistent. In the structural reliability strength analysis, three analyses were compared. The first analysis was based on a theoretical integration method, the second analysis was based on a numerical integration method and the third analysis was based on a "distribution-free" resistance distribution and a lognormal load distribution. There were three cases of the numerical integration analysis. The first case assumed a 50 percent lower confidence bound on the fifth percentile of the resistance distribution and a truncated load level. The second case assumed a 75 percent lower confidence bound on the resistance fifth percentile and a truncated load level. The third case assumed a 75 percent lower confidence bound on the resistance fifth percentile and no load truncation value. The results of the third case showed that OSPs allowable bending stress could be increased by 6.3 percent. Upon resolving a rational load truncation value, an additional increase in the allowable bending stresses could be realized for both plywood and OSP. The results of the "distribution-free" resistance analysis were anomalous. The final results showed that OSP can maintain a longer span compared to plywood, both on a stiffness and strength basis. The allowable design property values for OSP were lower than plywood. This effect is due to the application of the section modulus for the complete panel cross-section to OSP values and not to plywood.

Degree

Ph.D.

Subject Area

Wood|Technology

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