Bridge construction/Design 1

[azh]

I am working on a bridge project which is undergoing construction. It is a three span bridge . The longest being 25 metres simply supported. This longest span is to be supported on piers (bolted on the sides of the piers) founded on a pad footing at one end and the other on bored piles.The bridge is inclined at 25 degrees. The pad footing being at the top end.The bridge is to support traffic loading for maintenance of a reservoir.
The bridge consists of 5 units of 914 x 350x38 UB.
10 M25 bolts with 12mm ms plates are used for the side connections.

Can Carl , dik and others comment on the design ? Is it workable? Please suggest any recommendations? Thanks

 

[Qshake]

I don't understand the bolting to the side of the pier. Usually girders simply rest on simple pads on top of the pier.

I have seen other pier caps where the beam is an inverted tee. This allows the longitudinal girders to sit in the notch for support. If its not possible to place the girder on top of the beam I favor placing the girders in the notch of the inverted tee-beam for the simple reason of redundancy.

As described now, you're girder connection is subject to shear and must provide the necessary rotation to allow for a nearly moment free end restraint. This rotation concerns me with fatigue on the bolts. If the bolts give way what is there to prevent collapse of the span? If you have the beam sitting on a pad (designed to allow the needed rotation) the beam cannot fall unless the pier fails.

 

[dik]

I don't have much experience on bridge design, and none on public bridges. Will add my 2 cents and sit back and see what I can pick up...

From the description given, I don't know why the different foundation types unless there is a change in soils/bearing in the 25m span or the spread footing restrains an embankment or something.

I don't follow your description, but would understand that the ends of the girders are connected by bolts to the piers and the support is in shear on the connecting bolts with no provision for thermal movement. For stress, fatigue, corrosion, and possibly a couple of other reasons, I wouldn't use this type of connection. I would support the girder ends by bearing only. I would fix one end against horizontal movement and allow the other to move, carrying the expansion throught the pavement with a conventional 'toothed' expansion joint.

Any simple span bridges I've encountered usually have a pinned end (actual pin construction using a fixed elastomeric plate reinforced or otherwise) and a sliding end usually a series of teflon and stainless with/out an elastomeric pad. The bearings are commercial products and come as a complete package (bearing plate, polished sheet, teflon and bearing plate sandwich).

The main girders have an end girder that bears on a rebate/notch in the pier and I would assume that the roller support would be constructed at the most rigid pier type (either spread footing or pile depending on geometry and soils).

Might be that Ron or Carl can jump in and help/clarify.

 

[azh]

Is it of any help if the span is halved(the connection still remains)

 

[Qshake]

The way I view it, halving the span doesn't address the redundancy issue.

By the way, are these concrete or steel piers? I have seen many steel piers supporting a superstructure. Usually, the longitudinal girders are framed into a floorbeam which is then supported by steel columns. The connection is designed for shear and any rotation or additional flexibility is readily available in the steel columns.