Climbing the Ladder

MecaStack allows the user to enter ladders and platforms on their stack. These are considered an appurtenance, and not adding any structural stiffness to the stack. MecaStack does consider the wind area and weight added by these ladders and platforms, which can be significant on a stack.

Ladder Weight and Wind Area:

MecaStack considers the stack as a series of beam elements. The loads are applied to each element, therefore it is most convenient to simulate the wind loads on the ladders and platforms by applying them as uniformly distributed wind loads. To do this we need to calculate the wind load per unit length of stack. The wind areas calculated have the units [Length^2 / Length] which effectively reduce to [Length]. This can be physically interpreted as the wind area that exists in 1 linear foot (or meter) of stack.

The following is the basis for the loads used within MecaStack:

Ladders:

Ladder Only:
Area = 0.5 ft^2/ft [0.15 m^2/m] Wt = 15 lb/ft [22.3 Kg/m]

Caged Ladder Only:
Area = 0.75 ft^2/ft [0.23 m^2/m] Wt = 23 lb/ft [34.2 Kg/m]

Caged ladder w/ Platform every 30 ft [9.1 m]:
Area = 1.0 ft^2/ft [0.30 m^2/m] Wt = 35 lb/ft [52.1 Kg/m]

Cf = Shape Factor for L&P {Default 2.0}

Wind_Area = Area * Cf {ft or m}

Total_Wind_Area = Wind_Area * (Length of Ladder)

Platforms Weight and Wind Area:

If the Platform is 90 degrees or less, then the following is the wind area:
W = Platform Width

If the Platform is > 90 degrees, then:
W = Platform Width * 2 {Since platform exists on both sides of stack}
H = Platform Height (3 ft [0.9144 m])
Cf = Shape Factor for L&P’s {2.0 by default}
Fac = Solidity Ratio (0.5), since wind hits front side and then back side of platform.

Wind_Area = (W + Stack_OD) * Fac * Cf {Length^2 / Length}

Total_Wind_Area = Wind_Area * H

Weight of Platform Calculated using this formula:
(Uses a curve fit from some old company standards)
Platform Weight = (165 * Stack_OD + 1150) * (Plat_Ang / 360) * (Plat_Width / 3.5)^2

Note: Stack_OD and Plat_Width are in feet, 3.5 is assumed height of platform handrail in feet.

OSHA Changes on Caged Ladders:

There have been some changes to the OSHA regulations for ladders that is causing some confusion in the industry. Unfortunately, we can’t resolve this confusion, but we wanted to make you aware of it. With the way the new requirements are written, it no longer requires caged ladders but rather ladders with a fall protection device (i.e. Safe-T-Climb, or similar product). Meca has involvement with the ASME STS-1 committee, and the committee is currently trying to determine the complete impact of these new requirements. There is a lot of confusion about how to interpret these requirements. As of this writing it will be several years before the regulations go into effect.

Note: If you have any insight on this topic, we would appreciate any feedback that you can provide.