Horizontal Reaction in Hinge-roller simple span Bridge

[TLycan]

Dear All,

I am Modelling using SAP2000 a simple span bridge- R.C. deck on steel girder. My model is not 2d grillage it is a 3d shell and frame element.

the bridge consists of 4steel girder spaced 3.3mm spanning 33m and supporting a 30cm R.C. slab. the girders are hinged (the translations are restrained) from one side and the others side is roller longitudinally and hinged transversely.
the R.C slab is modeled shell element at the top flanges as the top flanges are frame element.

the PROBLEM is I get a horizontal reaction in the hinges. The summation is zero yes, but the reaction has a large value in case of eccentric live load (vehicle on the exterior girder). Vertical 70tons and horizontal 50 tons.

even when I solve the bridge as and "Eccentric-beam model" - i.e Girders are frame element , R.C. deck shell element at a distance from the frame element an connected with rigid links, I get even a higher horizontal reaction

can any one tell me what is the problem

 

[paddingtongreen]

The top of the loaded exterior girder and the adjoining slab are in high compression and strain appropriately. The middle girders not so much and the opposite outside girder might even have reversed bending. This compression mostly on one side leads to sideways bowing and your lateral reactions.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[TLycan]

Paddingtongreen,

Agree with you. But I did not hear of anyone designing bridges, that he designed his hinges base to such horizontal force.
and I don't even remember seeing any hing base with a huge number of anchors in the the abutment.

This leads that: they must've been considering something else or I am missing something .

 

[paddingtongreen]

I can't help you there, I don't know how SAP treats the shell panels. If you were to free up the two outer girders laterally from the foundation, just tie with beams to the inner girders... Worth a try for de-bugging the model, at the least you would get more information.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[BAretired]

Try rollers at each end of exterior girders and hinge/roller for interior girders only. That way, you can't generate horizontal forces in the exterior girders. It is probably a more realistic model of the actual bridge.

BA

 

[graybeach]

This is not a typical way to analyze a bridge. Are you sure a 3D shell analysis is really needed? One reason you haven't heard of anyone designing for horizontal forces due to gravity loads on a straight unskewed simple span bridge is that usually one does a line order analysis. Your horizontal reactions are probably due to the way the shell elements deform. I would expect them to be small. Are they? I am sure forces like this happen in real life, we just neglect them.

 

[TLycan]

First Thank you all for your response.

Secondly, the way suggested by BAretired is perfect, all the horizontal forces disappeared, still I have to investigate the effect of seismic.

Graybeach,

I need a 3d analysis to get the straining action on the cross-bracing and horizontal (lateral) bracing. I found that the main straining actions on cross and horizontal bracing come mainly from live load cases not wind