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(a) General Requirements. The stresses and deflections in car frame and platform members shall be based on the data and formulas listed in this section. For cars with corner-post or subpost car frames, the formulas and data do not generally apply and shall be modified to suit the specific conditions in each case.
(1) The maximum stresses in car frame uprights which are normally subject to compression shall be such that the quantity [(fa/Fa) + (fb/Fb)] does not exceed unity.
Fa = Allowable axial compressive unit stress (not exceeding 17,000-0.485(L/R)2).
Fb = Allowable bending unit stress (15,000 psi if area basis is gross section or 18,000 psi if area basis is net section).
fa = Actual axial compressive unit stress based on gross section.
fb = Actual bending unit stress.
L = Free length of uprights in inches (distance from lowest fastening in crosshead to top fastening in plank).
R = Least radius of gyration of section in inches.
(2) The stresses in the car frame crosshead shall be based on the total load, if any, supported by the crosshead.
The moment of inertia in the crosshead shall be not less than twice that of the stile section about an axis parallel to that of the crosshead section. The connection between the crosshead and the stile shall have sufficient rigidity to transmit the bending moment in the stile into the crosshead.
(3) The normal stresses in the car frame plank for elevators having a single plunger shall be based on a load equal to 1/2 the maximum static load on the plunger concentrated at each end of the plank with the plunger force applied at the middle. Where multiple plungers are used, the stresses shall be analyzed for the specific case. Stresses resulting from oil buffer engagement shall be calculated in accordance with Design Section 3101(d).
(4) The stresses in each car frame upright due to compression and bending and the slenderness ratio of each upright and its moment of inertia shall be determined in accordance with the following formulas:
(A) Stresses due to bending.
KL fb= ---- 4HZu
fb = The bending stress in each upright in the plane of the frame due to the live load W on the platform for the class of loading A, B, or C for which the elevator is to be used.
K = Turning moment in inch-pounds as determined by the class of loading by the following formulas:
1. For Class A freight loading or passenger loading:
WE K= ---- 8
2. For class B freight loading:/ E \ WE K= W | -- - 48 | or K= ---- \ 2 / 8 whichever is greater
3. For Class C freight loading:WE K= ------ 4
For explanation of symbols L, H, and Zu see Design Section 3101(g).
(B) Stresses due to compression:
fa = Compressive stress in each upright.
(C) Slenderness Ratio:
The slenderness ratio L/R for uprights subject to compressions other than those resulting from buffer action shall not exceed 120.
EXCEPTION: Where the upper side-brace connections on passenger elevator car frame uprights are located at a point less than 2/3 of L from the bottom (top fastening in car frame plank), a slenderness ratio of L/R not exceeding 160 shall be permissible.
(D) Moment of Inertia.
The moment of inertia of each upright shall be not less than determined by the following formula:
KL3 I= ------ 18EH
For explanation of symbols see Design Section 3101(g).
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