3D modelling of Bridge- dynamic analysis

[sfat]

Is it necessary to do dynamic analysis of bridge structure?
bridge is in two parts; first is a curved portion to be made in RCC- (cast in place). 200 feet of first part elevates up from ground level and turns left, then comes second part which is a straight stretch of 160 feet consist of post-tensioned box girder. i have modelled the first part (RCC) in 3D separately as it is RCC with column piers at 20 feet center to center and is separated by an expansion joint from the second part. i have done static linear analysis (considering EQ forces) and have also considered several vehicular loading combos to get maximum shear and moment in girders and for deck design. The second part of box girder is designed manually by considering the maximum shear and moment resulted from several vehicle loading patterns too.

vetting Engineer is asking for dynamic analysis model for the bridge. shouldn't the model i have made suffice?

 

[klaus.]

well on the latest bridge collapses ( Miami and Italy) you can see what can go wrong with bridge design

 

[WARose]

IIRC, AASHTO (like a lot of codes) requires a dynamic analysis for irregularities in layout and so on. Your criteria should come from it.

 

[sfat]

OK. Thanks a lot!

 

[Whoopdedo_LSU]

I would find your natural frequency and see if you need to apply dynamic loads. If you're rigid (>30Hz for me) don't worry about it. FYI Iv'e never designed a bridge, just grandstands ect.

 

[BridgeSmith]

Dynamic analysis (multi-mode spectral) is generally required whenever the center of gravity does not coincide with the center of the resistance to horizontal movement (an irregular bridge). From your description, it sounds like this bridge would fall into that category. Predicting the direction and magnitude of inertial forces for such a bridge is not at all straightforward. The boundary conditions a very difficult to define.

 

[Whoopdedo_LSU]

AKA, buy software and do it. You'll learn a lot from it. Be prepared to read a ton of crap.