Propping of PT Beam

[struggle66]

Hi all,

Less say a simply supported PT beam needs to be supported by a prop during concreting the above heavy floor. But PT beam is originally designed to resist the moment at mid-span. If I prop the beam at mid-span, the moment diagram will change. There will be negative moment on top at prop support and two positive moment (two spans). How do you calculate to prop a beam? What should be the spacing of props (like depth of the beam).

Thanks

 

[Ingenuity]

Has the PT beam already been constructed, or is it still on the 'drawing board'?

I have done this a few times, but you have to be careful with your analysis to include the temporary condition during construction (for concrete placement of above floors). I have used a 'yielding support' to model the stiffness of the shoring props/frames so as to more correctly account for any negative flexural action over the temporary support/s. Then based upon the analysis results of the model you check section capacities at critical sections, and if flexural stresses are important them check them accordingly.

Alternatively, why not just places props 'under/over' - ie under the PT beam, and over to match the floor-over shoring, such that the concreting of the "heavy" floors above will not present any flexural or shear actions to the PT beam.

 

[struggle66]

Thanks Ingenuity,

I am gonna use under/over concept.