Flexural Strength of Composite Deck Boards

The following values, listed in Tables 7.12 and 7.13, were determined in December 

It should be noted that a shorter support span (such as 14 in., as in Table 7.13) and center-point load give somewhat higher flgnres for flexural strength compared to a longer span (20 in.) and four-point load (see, e.g.. Table 7.12). 

TABLE 7.11 Flexural strength for GeoDeck composite material (cut from a deck board) at two different span-to-depth ratios for third-point load  

Width (in.) Depth (in.) Span (in.) Span-to-depth ratio Ultimate load (lb) Flex strength (psi) 

A comparison of Tables 7.3, 7.5-7.8, and 7.11-7.13 allows us to outline some pattern regarding flexural strength of composite deck boards, as materials and the whole profiles. Here are the main features of this pattern  

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These examples illustrate that the flexural strength of composite deck boards is quite satisfactory. It is several times higher than the respective building code... 

FLEXURAL STRENGTH OF COMPOSITE DECK BOARDS English Units and SI Units... 

TABLE 7.8 Effect of support span on apparent flexural strength of composite deck boards... 

Effect of Commercial HDPE Materials on Flexural Strength of Composite Deck Boards... 

Hence, direct comparisons of flexural strength data published on different composite deck boards should be viewed with the respective reservations. Data on flexural modulus, as it is shown below, are subjected to these factors even much greater. 

Table 7.22 shows a series of flexural strength values obtained for the same composite deck boards (the same composition and profile), but made from different HDPE (and LLDPE in one case). 

TABLE 7.24 Effect of density (specific gravity) of GeoDeck composite deck boards on their flexural strength... 

Other words, composite deck boards show 500-1200% of the flexural strength compared with that required by the building code. 

It seems that an ordinary composite deck board (flexural strength of 2000-3000 psi, see Table 7.13) of a standard size (5.5 in. by 1-1.5 in.) with moment of inertia of... 

The main (potential) problem with a hot tub on a composite deck is not a deck deflection or a flexural strength of deck boards but a (potential) creep of a plastic-based composite material, particularly in the South. This can lead to a partial sinking of a hot tub into the deck. Of course, joists would eventually stop the sinking even in a worst case scenario however, this might leave a permanent dent on the deck of a size of the hot tub base. Warranty would not cover the damage. 

As with the effect of water absorption on flexural strength, effects of a few repeated freeze-thaw on composite deck boards are also not very significant. For example, three-cycle freeze-thaw (hygrothermal) test on GeoGeck composite deck boards, conducted by PFS Corporation (Madison, WI), showed an increase in flexural strength from 1909 + 59 to 2033 + 35 psi, or by 6.5%. 

TABLE 3.13 Flexural strength and modulus of composite 2X6 deck boards, filled with rice hulls (57% by weight) and those filled with rice hulls (32% w/w) and Biodac (29% w/w)... 

TABLE 3.15 Flexural strength and modnlns of composite 2X6 tongue and groove deck boards... 

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