Paul Armitage Jan 28, 2018:

box girder Thanks for the comment and link, Michael. In my engineering days, I used to work underground as opposed to overground, so bridges are not my strength. Box girder makes sense to me. I have seen the terms 'hollow box girder' and 'hollow box' but I think hollow is superfluous in the first example and the second is not quite descriptive enough because it lacks 'girder'.

The first paragraph of the Wikipedia entry reads:

"A box girder bridge is a bridge in which the main beams comprise girders in the shape of a hollow box. The box girder normally comprises either prestressed concrete, structural steel, or a composite of steel and reinforced concrete. The box is typically rectangular or trapezoidal in cross-section. Box girder bridges are commonly used for highway flyovers and for modern elevated structures of light rail transport. Although normally the box girder bridge is a form of beam bridge, box girders may also be used on cable-stayed bridges and other forms."

I'll give it a little more time in case a bridge expert can comment further!

Michael Ellis Jan 28, 2018:

Box Girder Paul I think you should enter this as your answer and reference:
http://www.st.nu/medelpad/sundsvall/en-skakande-kansla-inne-...
, third para from the end describes a footpath inside the superstructure girder and there is a picture.

Michael Ellis Jan 28, 2018:

Flower box I agree box girder, but there is just a possibility that it could be flower boxes decorating a bridge - look at "Bilder på brolåda" on Google

Paul Armitage Jan 27, 2018:

box girder? For example:
"Box girders, distinguished by their trapezoidal or rectangular box shapes, function as both deck and superstructure. Box girders are used for long span or curved bridges and can be precast and erected in segments or cast in place. Spans lengths can range from 130 to 1000 feet."
Source: https://www.dot.state.mn.us/bridge/pdf/insp/birm/birmchapt3-...

Also:
https://en.wikipedia.org/wiki/Box_girder_bridge