Our name is missleading!
We are on of the major suppliers of bridges with steel beams and timber deck and parapets.
As the bridges get longer the use of timber beams becomes an issue.
The stiffness of the beam is achived, as the span increased, by incresing the depth of the beams and/or the thickness of the beams.
The beams get huge and become hard for our kit bridge useres to manage on site.
Our prefered installers mutter darkly when given bridges with huge beams.
In softwood we run into 3 issues.
Firstly:
The avaliablity of beaming in large sections.Trees are ususaly felled in small diameters, then we need to convert them into sutible beams in the right species.
Secondly:
The suitablilty of the timber for stress grading.
Thirdly:
The cost.
it is possible to get longer lenghts in hardwood. However the cost is off the clock.
It is possible to use laminated beams, These are thin layers of wood held together by glue and dowels to "make" a glue lam beam.
These do not last well in the UK for reassons we dont undertand, and seem to last better in countrys with harsher climates.
Some years ago we were taking glu lam beams out with rotten ends once every other month.
Water had migrated down the deck fixing screw holes and rotted the beam from the inside out.
In our view using a bridge with steel beams viable at or around 9 meter spans.
our steel fabricators offer high quality supply of steel beams galvanised and ready to receive our wooden components, these can be supplied either as kits or assembled.
Our clients Sensible Access have adopted the same policy.