Load Testing a Prestressed HCS 1

[structuralengr89]

I've got a project where I need to load test an existing Prestressed Hollow Core Slab floor system. I'm following ACI-318 Chapter 20 for "strength evaluation of existing structures". Does anyone have any experience with this? Looking for loading ideas...I've heard of using sandbags and also using water for applied load.

Thanks.

 

[JAE]

I've used steel barrels, lined with plastic, and spaced at a spacing that would equate a particularly desired uniform load.

According to ACI, I believe we followed their procedure and filled each up 1/4 at a time, measured the deflections, and continued until they were full. Then we emptied them by tipping over (make sure you have drainage) and re-measuring the rebound deflections and then again 24 hours later. Seemed to work just fine.

I've also seen where another engineer actually had a contractor build a wood framed tub about 2 feet high and lined it with plastic and used water.

With water, however, you need to make sure that the tubs, or whatever, are compartmentalized so a deflection will not initiate a ponding effect in the center of the span.

 

[structuralengr89]

Thanks for the info. A colleague had mentioned the wood frame with liner idea. My concerns were the increased water depth at midspan due to deflection or ponding effect. I like the steel drum idea, thanks.

 

[dik]

A couple of comments... if special hangers are fabricated and the barrels are hung close to the ground, then with deflection/failure, the barrels contact the ground and no more load... I've used that approach and works really well.

Another issue... about 30 years ago when I was a know it all rookie... I had the brilliant idea that we could load the HC slabs from below and with the moment from the strand, it would be easy to push the slabs upwards to grout relatively flush... we applied a load of 14000 lbs upwards and it didn't move a smidge... a lesson learned and remembered...

Dik

 

[structuralengr89]

The architect is insisting on using sandbags for this particular project. Has anyone used sandbags? I'm concerned about arching effect.

 

[JAE]

If you don't let the sandbags touch each other at occasional gaps, I'd think you'd negate the arching action.

 

[Dinosaur]

Why not ask if you can use the highway drums used to protect gore areas at ramps. There are a series of these drums that are designed to be filled with water to create a dynamic impact barrier. The drums are lightweight and should be transportable to your location. I also assume they may be rented at highway contractor equipment outlets. Put some of those up there, spaced accordingly, and you are in business. Also, I would use a hose and siphon the water out to a drain when you are done. It may take some time, but it sounds better to me than dumping the water out in a building. No ponding effects to worry about because the volume of water in each barrel is easily regulated. Good Luck