Outrigger Platform

[dylansdad]

To help facilitate the movement of materials from a buck hoist to elevated decks of a multi-story hotel I came up with the idea of an outrigger platform (for lack of a better term). I believe something similar is widely used in the construction industry. What would be a conservative method to estimate the loads imparted to the floor slab and the forces transmitted to the upper floor? Beam on elastic foundation concept? One of the floors is a composite deck/concrete and the rest are 8" Hollow Core planks. Thanks for any comments, concerns, or suggestions.

 

[phamENG]

Where is the nearest support for the lower slab?

I think I'd start by assuming a force couple at the end of the concrete slab and the shoring and iterate to get a reaction on the slab based on the center of an area experiencing stress equal to the allowable bearing stress of the concrete. Then look at the lower slab's deflection. Does the point below the shoring move down? If so, your system will self-loosen, for lack of a better term. If it moves up, then hopefully it's enough to counter any upward deflection of the slab above the shoring and you'll keep a tight fit.

 

[ldeem]

I think you will be imparting a fairly significant load on the edge of the slab. My gut feeling for looking at the floor slab is assume rigid outrigger beam and shortest possible couple between edge of slab and first back support shore. Spreading out the slab edge load will be a challenge because the slab is rigid and whatever you use to try and spread the load will need to be even more rigid. You could try beam on elastic foundation method but making a determination on the relative stiffness will be hard.

The longer the distance from the slab edge to first shore the lower the loads. The issue here is in the field you will need sufficient controls to be sure someone doesn't place shores closer than your design assumptions. From a laypersons perspective it would seem more shores the better but that is not the case as I think the first one will pick up most of the load.

If people are putting material on the outrigger you should include a healthy factor for dynamic loads of dropped material.

 

[r13]

This the way how I look it. Suggest to add positive anchorages to make up for the uncertainty of the shoring posts.

 

[r13]

Another notes:

1. Uplift due to wind could be critical.
2. What is the safety factor required for industry/construction lifting setups.
3. Shoring post tends to buckle, and influenced by upper floor movement.
4. Bolting through/into hollow core slab should be avoid.

 

[DTGT2002]

For our internally generated details, we resolve the loads through the force couple with uplift at the "hold down reaction" (resisted through a minimum of two shores sized for one redundant to the other, with the innermost reaction location being used to size the shores) and the loading at edge of slab, which we treat like a typical shoring load and reshore the edge of slab as needed.

That said, we work in cast-in-place construction and generally our structures do not need any supplemental design to handle these loads on a local level, meaning the concentrated loads are within an acceptable range for stresses.


From time to time, we will anchor to the slabs to avoid the hold down shores, but generally have not had an issue with dislodging the shores when the assembly is treated with due regard and only in use by trained personnel.

It would be considered a scaffold by OSHA in our interpretation.


We use wide flange beams and tube steel. Our backspan is at least 1.5 the cantilever, but still must pinch off prior to crane release.


We analyze for a uniform load across the platform as well as individual concentrated loads of a typical material bundles.

When you step back from it all, we have ours sized to be shored with the same materials we use to build the follow on levels of the structure, and overall are imparting loading of a like magnitude locally and lower magnitude globally than we are when we are actively shoring and reshoring. Your situation is not identical, but your approach to resolving loads to concentrated loadings and applying a rational approach to resolve those loads into a structure designed for uniform loading is similar.

The rating of the platform is certainly the key to most of this. I am a little apprehensive of cart or wheel loads on that plate. Certainly no fork truck loads there, no?


There are a number of commercial solutions to this on the market, but many have reactions so high I can't imagine the EOR wants to deal with such and many contractors don't have the understanding of the challenges imposed.