Ship Ladder Loading

[FootNMouth]

thread507-337483

I received a submittal for a ship ladder which services a mechanical room in a stadium. Per ASCE 7-10 §4.5.4:
"The minimum design live load on fixed ladders
with rungs shall be a single concentrated load of 300
lb (1.33 kN), and shall be applied at any point to
produce the maximum load effect on the element
being considered. The number and position of
additional concentrated live load units shall be a
minimum of 1 unit of 300 lb (1.33 kN) for every 10 ft
(3.05 m) of ladder height.

In the submittal the speciality engineer has designed for a 300 lb point load but he has also placed this load at an 18" eccentricity from the rung. He is using the moment from this eccentricity to design the stringers. Is this required?I understand that the center of gravity of whoever is on the rung will be at some distance away from the center line however his feet will always be on the rungs, thus no eccentricity.

 

[jayrod12]

The users feet will be applying a load at an angle typically on the edge of the step which would cause some twisting in the ladder. I would almost be concerned more about the moment couple created by the users hands and feet when holding themselves away from the ladder.

 

[RHTPE]

Think about it for a moment - if the center of mass of the person is 18" away from the rung, there is both the gravity load (vertical) on the rung (300#) AND a lateral force due to the fact that his/her body is 18" away from the ladder. Thus there is an eccentricity.

If you've ever climbed a ladder with a weak rung you would see that the rung deflects both downward as well as away from one's body.

I feel the approach is correct.


Ralph
Structures Consulting
Northeast USA

 

[FootNMouth]

Thanks for the responses. I tend to agree with jayrod12 that there would be a horizontal couple created by the users hands and feet. If I take the moment from the vertical couple (300# @ 18" eccentricity) and translate it into a horizontal couple (assuming hands and feet are 4ft apart) this would results in horizontal concentrated loads of 112.5lbs. This seems reasonable to me. Thanks again for the input.

 

[charliealphabravo]

With all due respect for going above and beyond, the 300 lb load is applied to the member in question as a single concentrated load not as a 300 lb worker. The load must be applied only once per 10 ft of ladder.

There is no way for a single point load passing through a member to apply a moment to the member. I think the whole point of the standard being written this way is so that we don't have to imagine the infinite number of ways that the worker might be moving or postured.

 

[JStephen]

charliealphabravo- do you interpret that requirement to mean 300 lbs in any direction also? (IE, horizontal out, horizontal sideways, up, etc.)

 

[charliealphabravo]

Yes I think it is clear that the load must be applied for maximum effect. I guess my main point is that the load is applied directly to the member in question as a point load and not as a couple or at multiple points on the ladder.