Stair treads

Thanks to their multiphase constitution, block copolymers have the originality to add advantageously the properties of their constitutive sequences. These very attractive materials can display novel properties for new technological applications. In this respect, thermoplastic elastomers are demonstrated examples (l, 2, 3) they are currently used without any modification as elastic bands, stair treads, solings in the footwear industry, impact resistance or flexibility improvers for polystyrene, polypropylene and polyethylene whereas significant developments as adhesives and adherends are to be noted (5.). 

Quantum mechanics is a highly mathematical view of the atom and expands the classical physics viewpoint to explain atomic structure. A staircase is a useful analogy in discussing quanta, in that you climb the stairs in certain quanta or in certain discrete units, namely, the steps themselves. You cannot step anywhere other than on a stair tread, and standing in between steps is not possible. In the same way, electrons have certain permitted locations and cannot exist between these locations. 

Spatulas, rubber Sponge rubber and sponge rubber products Stair treads, rubber Stationers sundries, rubber Stoppers, rubber... 

There are two main situations concerning deflection of boards that may not pass the building code requirements deck boards at a certain span (distance between neighboring joists) and stair tread at a certain span. Let us consider these situations using the same examples Trex composite deck boards and GeoDeck composite deck boards. These examples would illustrate general shortcomings of plastic-based composite deck boards in terms of their flexibility and deflection. 

These records show that flexural modulus of commercial WPC deck boards (and the respective span on decks) certainly has room for improvements. This in turn will improve quality of WPC boards and save money and material on deck joists. This conclusion is supported by consideration of support spans for stair treads (see below). 

The building code requires that the maximum deflection of deck boards used as stair treads under concentrated load of 300 lb placed at midspan shall be 1/8 in. (3.2 nun) or l/180th of the span (AC 174, Section 4.1.1 2000 International Building Code, Section 1607.1). For 16-in. span, the allowed deflection is either 0.125 in. or 16"/180 =... 

At a span of 16 in. on center, deflection of stair tread under 300 lb of load will be approximately defined by the following equation ... 

Even for a span of 12 in., with the allowed deflection of 12 7180 = 0.067", the deflection for this solid board under concentrated load of 300 lb would be 0.069", which is slightly higher than the allowed one (L/180). Indeed, in ICC-ES Report ESR-1190 maximum stair tread span for Trex boards is listed as 10.5 in. 

Overall, for 12 WPG deck board brands for which allowable stair tread span is on ICC-ES record (published in the respective ICC-ES reports), only two (CorrectDeck and GeoDeck) have allowable span of 16 in., six have allowable span of 12 in., and four have allowable span of 10.5", 9", or even 8 in. 

A deck board used as a stair tread has to withstand a much more severe flexural test compared to a regular deck board. This test is described in AC 174, and ASTM D 7032. Principally, the acceptance criteria aim at determining a span rating indicating the ability of stair tread to comply with the building code. For example, a deck span rating is typically 12/100 or 16/100, that is, the deck board is recognized by the code when installed on deck joists spaced maximum 12 or 16 in. on center, respectively, and supports the load of 100 Ib/ft multiplied by a safety factor of 2.5. 

According to AC 174, the performance of deck boards used as stair treads shall meet the following structural requirements, besides specified requirements to deck boards (referred to in ASTM D 7032) ... 

These requirements to deck boards used as stair treads are much more severe compared to requirements to regular deck board, among them an ability to hold a uniformly distributed load of 100 Ib/fC multiplied by a safety factor of 2.5, hence, 250 Ib/fC. 

Let us consider GeoDeck deck boards used for stair tread at 16 in. at center. The code requires that a stair tread should hold a concentrated load of 750 lb, or about 10 times higher than the load in Table 7.27, that is, 10 times than the deck code requirement including 2.5 times safety factor (100 Ib/ft X 2.5). 

An actual test with GeoDeck at 16 in. at center showed that of 906 lb, 21% above the stair tread code requirement. 

The code also requires that a stair tread should deflect no more than span/180 under the concentrated load of 300 lb (on average of 15 specimens). A test showed that at a stair tread span of 16 in., the deflection at 16/180 = 0.0889 in., is reached at 301 + 20 lb, just one pound above the requirement, on average. 

This is a rather high figure for flexural modulus for composite deck boards (see the next section). Hence, for many composite deck boards stair tread, in order to satisfy AC 174, support span for stair tread should be a step down from 16 in., that is, 12 in. 

Table 7.28 shows maximum spacing of constructions supporting commercial deck boards accepted as stair treads by ICC-ES and published in manufacturers ICC-ES reports. 

A DECK BOARD USED AS A STAIR TREAD A CRITICAL ROLE OF FLEXURAL MODULUS... 

That is why Trex recommends its composite boards only for a 12-in. span, and only for thick 2X6- and 2 X 8-in. boards, when used as a stair tread. For a standard 5/4 X 6-in. board, Trex recommends only a maximum center-to-center spacing of... 

For the hollow GeoDeck board (see above) at a span of 16 in. with the allowed deflection of 0.089", the calculated deflection would be equal to 0.093". Close, but not enough. To pass with these numbers for flex modulus (374,000 psi) and moment of inertia (0.733 in. ), a span should be of 15-3/4". In reality, the hollow GeoDeck Traditional board passed the requirement for 16-in. span for stair tread (L/180) at 301 lb concentrated load (average of 15 tests), a pound above the required 300 lb. 

Calculations show that for a stair tread with a 24-in. span (allowed deflection 0.133"), a composite board should have aEX I value of 548,016 lb X in.. This would be applicable to a hollow GeoDeck Heavy Duty composite deck board (8.1" X 1.55,1 = 1.858 in., E = 374,000 psi, and EX I = 694,892 lb X in. ). For a solid board of a standard dimension (5.5" X 1.25", I = 0.895 in. ), flexural modulus should be at least 776,416 psi, and composite deck boards of such stiffness are not available as yet on the current market (see Table 7.34), except those made of wood. For thin solid board, such as 5.5" X 15/16" (/ = 0.378 in. ), flexural modulus applicable for stair tread with 24" span should be at least 2,054,000 psi, which is much higher than that for typical wood (Table 7.34). 

Table 7.28 above shows the recommended support span values (on center) for commercial composite and plastic lumber deck boards used as stair treads. 

We have considered the above deflection of deck boards that serve as stair treads. Obviously, the same principle can be applied in the calculations of deflection of composite profiles in other cases deflection of soundwalls under force of wind (in this case an equation for uniformly distributed load should be applied), deflection of an animal farm fence under weight of an animal leaning toward a board, deflection of a deck board under a hot tub installed on the deck, deflection of a handrail under a cantilever force, and so on. 

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