Design of segmental bridges by cantilever method

[steveyeung]

I'm a graduate bridge engineer and going to sit the Chartership Exam.

1. Can anybody tell me how much the design strength should be factored down to allow for creep, shrinkage and the like in preliminary design of the segmental bridges. Since I need to finish the part of design calculation within 1-2 hours without any computer program (during the exam).

2. After closure, the bridge behaves as a continuous structure. I want to know how much bending moment will be taken up by the mid-span or the mid-span moment can be worked out in the same way of a equivalent continuous beams with piers connected?

3. I have no idea how the shear strength in the joint between 2 segments. Any good reference book is available

 

[Alekk]

1 - I don't know wath is the current practice in your country, but I usually assume 0,38fc. I think you can find a better answer reading your country codes.

2 - Moments generated by long lasting actions, as self weight, vary with time in such a way depending on the construction stages. Anyway a good approximation is to consider that all changes happen at the same time. For moving loads you can consider a continuous beam or a frame.

3 - Usually this is not a matter, anyway there are different ways, as friction (about 0,4), glue resins, shear keys, etc. Probably in your country codes you can find helpful specifications.

Good luck

 

[steveyeung]

To Alekk,

Thanks for your help.

Can I go further about Q2,
After closure, if the tendons (bottom at mid span) are stressed up to produce moment of resistance, say 100kNm, can I bring down the hogging moment at piers by 100kNm accordingly?

In addioion, I really want to know the moment due to self weight is redistributed after closure. Is there any good book you can recommend?

Thanks a lot!

 

[Alekk]

It is not so symple...
You have to consider prestress as a load case, with axial load, flexure, deviation of cable axis, etc. In my opinion it is best to consider equivalent loads instead of prestressing. Further, prestress level change with time.

I'm sorry, I have no reference about books/manuals about segmental bridges in english. May be you can find something useful at

http://www.pci.org.

bye, and good luck