compressive strength

[Goodstreng]

Dear Members,

What will you do as an engineer when the compressive strength has failed for 4th floor and the contractor has reached 8th floor?

 

[rowingengineer]

first - is the the compressive strength correct?, is this a concrete batch test? and is it Representative of the slab?, ie is it a 28 day strength and could the concrete have gained more strength since the test.

if the compressive strength is found to be correct do an assessment of the structure with the reduced compressive strength. once all the issues have been identified, figure out solutions.

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[rb1957]

if it's a near miss (and a correct test as mentioned above) then rework the calcs to see if reparing is needed.

if it's a big miss then does it become a harzardous work site ?

another day in paradise, or is paradise one day closer ?

 

[JAE]

Here's an FAQ on ACI's 318 chapter 5 process of evaluating concrete. I'm not sure if this is all applicable to your situation but
the first thing you need to do is determine a fair estimate of what f'c strength you have and recheck your analysis and designs of those areas with the lower f'c.

faq507-1575



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[concretemasonry]

You probably took other samples for testing at different ages, so the results while you built the 5th, 6th, 7th and 8th floors could shed some light on the situation. Breaks at 7 and 14 day ages would be a help.

If it was a single cylinder from an undetermined location, you have a lot of analysis and work to do. If it was an average from a set of 3 cylinders, that would be more representative and reliable of the indicated strength.

If the difference between the specified and actual is dramatic, look at the sampling, handling and curing of the samples.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Canuck67]

I am aware of one past project where something similar occurred and the end result was that the entire floor and columns had to be shored, while the floor was removed and replaced. This was only after very indepth testing and a reanalysis that explored many potential options. The first priority is to get a number of cores tested from various locations throughout the slab, plus possibly some representative ones from other locations on other floors for comparison.

 

[concretemasonry]

A reality check ---

I may have erroneously assumed the"compressive strength" for concrete cylinders for a total concrete structure (columns and slabs) where strength specifications may have been different for the columns and slabs.

Is the structure totally concrete or is it a steel frame with concrete floor slabs?

The specifications, mix designs and sampling/testing information could avoid speculation.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.