Question about concreting

[HighPanda]

Hi Bridgemen

There is a steel composite bridge comprising 4 I girders and a concrete slab. The railway tracks possession time given to the erection of this bridge is short so I would like to cast the slabs over two pairs of girders and leaving the central bay/strip open. Once the two pairs of girders are in their final position, permanent formwork spans between the two interior girders and concrete will be poured on it.

My question is that if there is a construction joint running longitudinally along the bridge, is there any adverse effects on the strength of the composite section or on the serviceability (e.g. water leaking from the construction joints)? How to solve it ?

 

[civilperson]

Construction joints are equal to the slab or component that they connect. Detail a vertical joint using steel expanded mesh with all reinforcement continuous throught the joint. Many bridges are built in fractions with longitudinal closure pours to connect the parts.

 

[hokie66]

You really should make the construction joint midway between the tracks. If you make it on the beam, composite action will be compromised. If time is limited, the answer is really to design the beams without composite action.

Where the slabs are joined, you should beef up the crack control reinforcement in the slab to be poured last, as it will be restrained by the first section.

As to waterproofing, concrete is not really a watertight material, so you can expect some leaking if no membrane is used on the top.

 

[hokie66]

Why do you want the centre part to be concrete? Can it be framed in steel with floor plate or grating? That would simplify your scheduling issues.