What’s the difference between steel and concrete Girders
Regina Bypass will use 500 girders while building bridges on the project. Some of the bridges have steel girders and others will use concrete girders.
Bypass Project Manager of Structures and bridge expert Chris Koop explains the difference between steel and concrete girders.
1. Certainty in design – steel girders are much easier to design due the fact that the material properties of steel are very well known and understood. The material acts consistently and therefore it reacts in the way the Engineer plans it to react.
2. Steel girders can generally be used for larger spans without a large increase in girder depth – this allows for a large savings in earth fill. This is because an increase in bridge depth of 500mm does not just add to the top of the embankment, it is added to the bottom of the embankment. At 6:1 slopes, this often means a savings of 8000m3 of fill on a bridge structure reduction of 500mm.
3. More capable of being used in unique bridges including bridges with high skews (cross the under passing road at an angle), curved bridges, or long single span bridges.
Concrete NU Girders:
1. Can be fabricated very quickly and easily due to standard design proportions for girder depth, length, and stressing details.
2. Act inconsistently and therefore the engineers have to allow for an increased factor of safety in design.
3. Generally, concrete NU girders are deeper than steel girders over the same span.
Concrete Box Girders:
1. Easily fabricated and quick to design based on standard design manuals for span vs load requirements.
2. Easy to install and minimizes the use of formwork as there is no formwork required between girders.
3. Not economical for large span bridges.