(a) Unless
otherwise specified in subsection (c) or other provisions of this chapter, wood
side rails for all ladders shall have a minimum dressed cross section of the
following dimensions:
|
Full working length of ladder
(feet)
|
Dimension of side rails at
center
|
| Thickness
(inches) |
Depth (inches) |
| Up to and including
19 |
1-3/8 |
2-3/4 |
| Over 19, up to and including
30 |
1-3/8 |
2-3/4 |
| Over 30, up to and including
38 |
1-3/8 |
3 |
| Over 38, up to and including
42 |
1-3/8 |
3-1/2 |
| Over 42, up to and including
45 |
1-1/2 |
2-1/2 |
| Over 45, up to and including
52 |
1-5/8 |
3-3/4 |
| Over 52, up to and including
55 |
1-3/4 |
3-3/4 |
(b)
The dimensions of subsection (a) are based upon a 7/8 inch mortise, 1/8 inch
gain, or equivalent for step attachments. Where the strength of side rails is
reduced more than this by the step attachments or where it is desired to use a
rail section, either dimension of which is less than that specified in
subsection (a), the rail section shall develop an actual working stress for the
wood listed in §
21.63 (relating to group three
woods), not exceeding 1,600 pounds per square inch when computed by the
following formula applying to rectangular sections:
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where
P = pounds, which is the normal component on each rail of a
load of 200 pounds at the center of the ladder, equally distributed between the
rails, when the foot of the ladder is moved out of the perpendicular by 1/4 of
its length.
W = weight of ladder, in pounds.
L = length of ladder, in inches.
B = net thickness of each side rail, in inches (deducting
depth of gain, if any, for flat treads).
D = depth of side rail, in inches.
d = diameter of hole drilled for rung (d3
shall be taken as not less than 0.67, regardless of the method
of step fastening used).
(c)
Wood side rails of ladders having cleat steps shall be not less than 3/8 inch
greater in thickness and 1/2 inch greater in depth than is specified under
subsection (a) of this section, but no such ladder shall be less than 1 5/8
inches thick and 3 5/8 inches in depth (2 by 4 inches nominal).
(d) Metal side rails when made of mild steel
or wrought iron shall be not less than 9/16 of a square inch in cross section
for lengths 12 feet and under, and not less than 3/4 of a square inch in cross
section for lengths over 12 feet with a minimum thickness not less than 3/8
inch. These dimensions are based upon the removal of not more than 1/2 inch of
material for the attachment of the steps. When more material is removed from
the side rails for step attachments or when side rails are made of other metal
or shapes, they shall have the same strength.
(e) Except as otherwise provided in this
chapter, wood side rails shall not be spliced.
