Hi,

I am a structural engineer with lots of experience in buildings, but have very little to no experience in bridge design. The bridge expert in our company is about to retire and it has been decided that he transfer as much knowledge as he can to myself and inlove me in bridge projects so that in 5 years time I will be a fairly competent bridge engineer. I will have to do lots of self study and of course EngTips will help me considerably in this regard. I will in the next few months be asking what to some are very simple questions as I try to get a basic understanding of bridge design. Please bear with me:

1) Does one have to provide joints if temperature movement is little, say 20mm? Why can one not just provide enough reinforcement to control the crack widths as done in buildings? Is it a durability issue because cracks in bridges would allow water to penetrate? Joints are expensive and create their own problems thus I would think where ever possible one should try to avoid them.

Welcome to bridge engineering. I think you'll enjoy it. With the introduction of computers in design in the 60's and 70's most multi-span bridges became continuous, or semi-continuous, eliminating joints over the piers. In the last 20 years or so bridge engineers have tried to eliminate end joints at the abutments whenever possible through the use of integral, or semi-integral abutments. An integral abutment is designed with sufficient longitudinal flexibility (e.g. a single row of piles) to allow some shrinkage and seasonal movement. A semi-integral abutment uses a horizontal joint at the end to eliminate a gap open to the road surface. As you noted joints don't stay sealed for long and lead to a lot of deterioration, particularly where road salt is used.

If you're referring to a joint over a pier I would go for continuity. Joints at abutments are a different story, usually DOT's - here in the US. I assume you're not because you mention mm's - have there preferences. On a conventional design - non-integral abutments - 20 mm joint can be formed with elastomeric concrete and filled with backer rod and pourable sealant. Here in the northeast US they seem to be working out very well.

I would say listen and pay attention!! Seems like you might have 5 years to learn this??? Shouldn't be a problem.

My thoughts have always been that I can learn 90% in a year or less - the rest will take a lifetime.