Impact loading on bridge superstructure

[Edu09]

Hi chaps,

I've been tasked with looking at the effect of an accidental impact on a replacement bridge we're designing(the new design does not meet the clearance over footways). I've been searching the eurocode and it seems to me that accidental actions are always taken as with a partial factor of 1.0 so, effectively I'm just taking the design value for this type of road - 410kN.

I've modelled this as point load going into the edge girder as the N.A so I've classified and checked the section for shear.

It's probably worth mentioning that this is not at the detailed design stage yet.

So my question really, any comments and thoughts on what I've done. Any other useful knowledge about this topic(accidental loading to EC or otherwise) anyone may wish to share.

Thanks

Ed

 

[SlideRuleEra]

As a bridge contractor, we replaced an overpass girder that had been damaged by multiple accidental impacts. For the model, I suggest moving the expected point of impact from the neutral axis to the edge of the bottom flange. Many accidental impacts just barely strike the beam, few are high enough to hit the beam squarely on on it's side (at the neutral axis).

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[Lomarandil]

Agreed, definitely account for the impact being at the bottom flange -- doubly so if it's an I-shaped edge girder.

 

[Edu09]

Thanks for the replies. This is what I was getting to thinking too, apply the load at the bottom flange and check the section for torsion and then the connections into the existing abutment. It's good to hear it and it makes sense when I think about the practical situation.

Cheers

 

[Edu09]

Just a few more questions relating to this, I've attached another sketch. As a first check of this impact force acting in the flange I've checked it's within the shear capacity of the flange(it is well in) and then the shear flow where the flange joins the web to establish if the weld is sufficient.

Does this look like a reasonable approach? Any and all comments welcome, I really learn a lot on this forum.

Thanks

 

[SlideRuleEra]

Edward09 - Based on the beam's dimensions, and depending on the point of impact along the beam's length plus how the beam is braced (diaphragms), resistance to bending at the top of the web may be more critical than shear.

Try making simplifying conservative assumptions and see what impact force it takes for the web to yield in bending. I believe the force will be so low that errors in the accuracy of the assumptions will be unimportant. Also check to make sure the beam's anchorage to the superstructure does not fail on impact.

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[Edu09]

Thanks a lot for you replies SlideRuleEra and Lomarandil!

Apologies for not saying this earliet!