Test Results

These tests were conducted during summer and fall 2001 at Georgia Tech’s Structural Engineering and Materials Laboratory in Atlanta, Georgia, under the direction of Dr. Abdul Zureick, laboratory director (see Figure 1). Full-scale sections of SEAPILE and SEATIMBER materials, including several different lengths, cross-section sizes and shapes, and reinforcing bar configurations, were tested to failure.

Sample test results are shown for one size of product, a 10" x 10" (250mm x 250mm) SEATIMBER product with four 1" (25mm) fiberglass reinforcing bars. The different curves show the results of testing the same product with different distances between support points (spans) (see Figure 2).

By using the results of testing specimens of several lengths, both the modulus of elasticity, E, (flexural modulus) and the shear modulus, G, can be obtained using the equation,

In this equation, E_f is the “apparent” modulus of elasticity, I is the moment of inertia, A´ is the modified shear area equal to AK, L is the span, A is the cross-sectional area of the beam, and K is a shear coefficient.

A linear regression plot of 1/ E_f vs 12I /(A´L²) for a series of span lengths will have a slope of 1/G and an intercept of 1/E. Using the resulting values of G and E in the above equation will predict the deflection for any span length of a particular product (see Figure 3).

For this test, the results at 1% strain indicate a value of E of approximately 420,000 psi (2,900 MPa) and a value of G of approximately 21,600 psi (150 MPa). K was determined by numerical analysis to be approximately 0.80. These values are the results of only this one series of tests, and should not be used for design.

During one series of tests, Georgia Tech tested Seaward 10" x 10" (250mm x 250mm) SEATIMBER material as well as 10" x 10" (250mm x 250mm) material manufactured by a plastic lumber manufacturer that is reportedly made with recycled plastic reinforced with chopped fiberglass. The test results are shown below, all at a constant span of 6.5' (1.98m) (see Figure 4).

The competitor’s material was found to be not only markedly less stiff than even the unreinforced SEATIMBER material, it failed at a very low loading (less than half the load of unreinforced SEATIMBER material). Compared to reinforced SEATIMBER material, the contrast is even greater. The reinforced SEATIMBER material had a strength at failure more than five times greater than the competitor’s material, as well as much greater stiffness.

For additional information about the test results, and for design information, please contact Seaward.