Creep of Composite Deck Boards

When composite deck boards are loaded for an extended time period, they develop creep. This property of plastic-based materials is quite understandable, because plastic flows. The real issue is not to prevent creep bnt to minimize it. Three obvious ways to minimize creep are (a) to change the span, (b) to lower the weight/load, and (c) to reinforce the composition. 

Deflection of the loaded board can be predicted provided that the load and its location on the board is known, as well as the span, the moment of inertia, and the flexural modulus of the board, and assnming that the load and the deflection are within the linear relationship between each other. If the load is outside of this relationship (higher), a deflection wonld be higher than calculated using formulas 

Let us consider all the three ways (see the first paragraph of this section), using practical examples. 

Example 1. A Trex board, width 5.5 in., depth 1.25 in., moment of inertia 0.895 in. , flexural modulus 175,000 psi (the manufacturer s data), support span 22 in., and a third-point load of 100 lb. 

In reality, the immediate deflection was of 0.095 in., that is, 26% lower than predicted, not higher. This can be explained by an inaccurate value of the flexural modulus reported by the manufacturer. Indeed, flex modulus for this particular Trex product, calculated from the above experiment, was 221,000 psi, not 175,000 psi. Other figures for Trex board flexural modulus were of 193,000 + 19,000 psi (Table 7.30), 214,000 + 8,000 psi and 224,800 psi (Table 7.34, footnote). 

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Deca-bromodiphenyl ether, 471 Decay fungi, 412 Dechlorane Plus , 473 Deck boards, 207, 208, 215, 225 Catastrophic damage, 207 Commercial, 215 Flame spread, 208 Half-life time, 207 Higher density, 207 Ignition time, 208 Lower density, 207 Span rating, 225 Deckjoists, 288, 289 Deck Lok, 60 Deck surface, 21, 206 Temperature, 21, 206 Deflection and creep of composite deck boards, 291... 

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