Hi i am looking for help on Post Tensioned Box Beam girder bridge assessment.I have modelled the bridge as 2D Grillage.I have split the box beam into I section and C section at ends.I would like to know that how can you calculate stressess in the web & diaphragm opening in 2D Model.
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Post Tensioned Bridge 1
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I would say that hyothesis by hypothesis. I mean, otherwise you wouldn't be able to separate the maximum torsional effects etc.
For the diaphragm, draw it in elevation, place the supports. Then start to apply hypothesis bty hypothesis the reactions at the diaphragm, and subject a model of the same to such forces. This will still be a 2D model (of the diaphragm made bt plates etc) and logically will fail in better capture the whole effect as a 3D model would.
Along the beam, you must be enough satisfied by the forces extant in your model or otherwise you wouldn't have modeled it such way; hence dimension or check everything for the standing forces. I mean, torsion should be extant already for the component C and I beams, and other than assuring the satisfactory behaviour of the links atop and bottom for any hypothetical force of those mandatory you should have a valid design for the limitations of your model.
For the diaphragm, draw it in elevation, place the supports. Then start to apply hypothesis bty hypothesis the reactions at the diaphragm, and subject a model of the same to such forces. This will still be a 2D model (of the diaphragm made bt plates etc) and logically will fail in better capture the whole effect as a 3D model would.
Along the beam, you must be enough satisfied by the forces extant in your model or otherwise you wouldn't have modeled it such way; hence dimension or check everything for the standing forces. I mean, torsion should be extant already for the component C and I beams, and other than assuring the satisfactory behaviour of the links atop and bottom for any hypothetical force of those mandatory you should have a valid design for the limitations of your model.
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Well, these tendons what are making is to make the whole beam bring its loads to bearing point, which is the one we are considering. As long you have enough shear connection for this between web of beam and diaphragm, the downwards reaction of the tendons I don't believe that (at least generally) need have any explicit acknowledgement (presence) in your 2D model of the diaphragm. Normally one tends to assume that the same web of the beam is able to provide the required struts to counteract the downwards action.
Yet it could be convenient to place the structural reaction as 4 point loads at the tendons apices over webs just to such way acknowledge the overall compression (and maybe more than that) that they are exerting on the intersection of the webs and diaphragms. Buckling normally won't be a problem since 4 sides constrained but I think it is important not disregard the whole transfer in shear of the respective load to the diaphragm, each side. If this proves too prohibitive, since the load will be being passed by the named struts and only a portion in true shear (i.e., the tendons are just reducing the shear seen by the concrete webs out of inclination) you may apportion the shear transfer just to the shear standing in the beam, what I would try to do in shear friction theory, stirrups apart.
For as near the diaphragm with the important downwards reactions we have some corbel-like behaviour; irrespective of if there is a main tensile party, in this case the tendons, it is good practice to apportion horizontal and vertical passive reinforcement.
Yet it could be convenient to place the structural reaction as 4 point loads at the tendons apices over webs just to such way acknowledge the overall compression (and maybe more than that) that they are exerting on the intersection of the webs and diaphragms. Buckling normally won't be a problem since 4 sides constrained but I think it is important not disregard the whole transfer in shear of the respective load to the diaphragm, each side. If this proves too prohibitive, since the load will be being passed by the named struts and only a portion in true shear (i.e., the tendons are just reducing the shear seen by the concrete webs out of inclination) you may apportion the shear transfer just to the shear standing in the beam, what I would try to do in shear friction theory, stirrups apart.
For as near the diaphragm with the important downwards reactions we have some corbel-like behaviour; irrespective of if there is a main tensile party, in this case the tendons, it is good practice to apportion horizontal and vertical passive reinforcement.
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