to check if beam crack is live or not 1

[zeeshanahmed]

There are minor cracks in the midspan of the beam, i want to check if the cracks are "LIVE" and still increasing or not. I usually paste 2mm thick 5" long glass stips exactly below the crack, so if glass breaks it means crack is still expnading ? is this correct or not ? any better suggestions ?

 

[cooperDBM]

How old is this beam? If it's newer construction then the crack will grow due to creep even if caused by external loading. If older construction then the crack is due to external loading and will only change with changes to the external loading (particularly live loading). If most of the load is non-transitory (dead) then I wouldn't expect the crack to grow much if at all.

Is the beam prestressed? If the beam is not prestressed or only partially-prestressed then cracks are to be expected.

Is the "failure ratio" based on the serviceability concrete tensile stress check? If so then this isn't usually a hard-limit - particularly with newer design codes. It's just an indication whether crack control detailing needs to be considered. Do you have a single crack or a few cracks spread out near mid-span?

If the "failure ratio" is based on ultimate strength then the beam is unsafe.

 

[corus]

I'm not sure if it makes any difference if the crcks are in steel, concrete, or ivory tusks, nor if the cracks are hairline or ones you can out your fist into. As long as the cracks go through the whole width and are not some surface crack then I'd do as VoyagerofDiscovery suggests and... run away!

corus

 

[hokie66]

cooperDBM has given you more good advice. Whether the hairline cracks change in width at all is not really as important as whether the beam has the required ultimate strength for the design loading and existing loading.

Corus, you are incorrect. There is a lot of difference in the significance of cracks in a steel beam as opposed to a reinforced concrete beam. Suggest you do some study on the subject of cracking in concrete structures before you offer advice in this regard.