Load testing of concrete structures

[w12x26]

Are there any guidelines on what loads to use when load testing a concrete beams (post-tensioned beam). I am inclined to use the factored design loads. Something tells me I should use the service loads (unfactored loads) and somehow I also feel I should even increase the factored loads further. I do not want to reach failure. This is proof testing. Any thoughts?

 

[Ron]

Refer to ACI 318, Chapter 20. The load must be at least 85% of the factored loads, applied in 4 equal increments.

 

[w12x26]

I will do that. Thanks for the help.

 

[BAretired]

In Canada, where an entire structural system in doubt is load tested, use 90% of factored loads Mf, Vf and Pf.

Where only a portion of a structural system in doubt is tested and the results of tests are taken as representative of other portions of the system, the test load shall be equal to the factored load Mf, Vf and Pf.

The test load shall be maintained for 24 hours.

The code goes on to stipulate deflection recovery after the test load has been removed.

BA

 

[w12x26]

It a good point you're introducing the time factor. One of the ASTM standards (static load testing of structures) specify that the load is to be applied for 5 minutes. What is the basis for the 24 hours requirement?

I will check the ACI document to see if this is also addressed.

Thanks.

 

[BAretired]

w12x26,

I don't know the basis for the 24 hours. I am simply reiterating what the code says. I might be able to find out more about it in time if you are interested.

BA

 

[w12x26]

If you can give the name of the reference and relevant section it would then be very helpful.

 

[BAretired]

I was referring to Section 20 of CSA A23.3-94 and particularly Article 20.3 "General Requirements for Load Tests".

I do not have the latest edition of CSA A23.3-2004 and cannot confirm that the requirements are the same, but that could easily be checked by members of this forum.

BA

 

[WpgKarl]

You should pre-calculate the expected failure mode for your beam if possible....if it is a ductile failure mode (flexural), go ahead and take it up to 90% ultimate, or whatever the proof load is, but if it is expected to be a brittle failure mode (in shear for example) I wouldn't take it right up to ultimate loads.

 

[w12x26]

Ron,

I checked ACI 318 and the procedure was very detailed. It's been years since I deal with a concrete structure.

Your tip was very helpful.

Thanks.

 

[w12x26]

BAretired,

ACI 318, Chapter 20 also recommends the test load to remain in place for 24 hours which I am using for this exercise.

 

[BAretired]

Gotcha.

BA