Displacing Longitudinal Reinforcing in Kerbs
Displacing Longitudinal Reinforcing in Kerbs
(OP)
Hi guys,
Referring to my rough freehand sketch schematic. I have a prestressed deck unit bridge with a composite in-situ concrete deck bridge structure which has a slight cantilever overhang (2' / 600mm). I need to provide drains through the kerb units and as a result, some of the longitudinal reinforcement in the kerb needs to be displaced to avoid any clashing with the drains. This bar serves as a longitudinal bar for the torsional reinforcement for any traffic barrier loads which are imposed on the kerb.
What is the best solution / what are my options for this problem?
Referring to my rough freehand sketch schematic. I have a prestressed deck unit bridge with a composite in-situ concrete deck bridge structure which has a slight cantilever overhang (2' / 600mm). I need to provide drains through the kerb units and as a result, some of the longitudinal reinforcement in the kerb needs to be displaced to avoid any clashing with the drains. This bar serves as a longitudinal bar for the torsional reinforcement for any traffic barrier loads which are imposed on the kerb.
What is the best solution / what are my options for this problem?





RE: Displacing Longitudinal Reinforcing in Kerbs
RE: Displacing Longitudinal Reinforcing in Kerbs
I can't see that the kerb is in torsion. I would just move the bar inside the drain. You need one at the top of the slab also. If you are concerned about impact loads cracking the kerb, you may want to add some diagonal bars across that corner, with 45 degree bends each end.
I'm sure this is not the first time this has been done. How does Main Roads normally detail it?
RE: Displacing Longitudinal Reinforcing in Kerbs
Hope you do not mind but I have provided a sketch with a bit more info for those that do not get to play with crash barriers very often.
I believe placement of the drain needs to be between the crash barrier posts, if possible. I would not like to see the displacement of the reo for the length of the kerb, because you do have large forces at the post location. I would prefer to splice at at drain locations only. However, the slab will help with the tensional strength, however I never found out how to calculate the slab effect.
Note: the crash rail from the main roads standard is not designed for all of the 250kn (for a medium) to be transferred in bending to the kerb at one post location, the design is to take this loading over a few posts. If you do an analysis of the crash rail, you can reduce the amount of loading, thus the torsion in the beam.
When in doubt, just take the next small step.
RE: Displacing Longitudinal Reinforcing in Kerbs
FEM solid model always helps.
Anyway, as in any RC in bending action we have two situations: cracked and un cracked. One has to examine whether the tensile stresses standing on the analyzed plate will be causing cracking, upon which situation one needs to reinforce not only by mandatory clause, but technical requirement. The usual approach of using some tributary tensile force may or may not be safely applied depending on how such force is derived; for it is obvious it is between other things a flexural situation and sometimes is not thought this way.
RE: Displacing Longitudinal Reinforcing in Kerbs
the kerb goes into torsion when it is transferring the collosion load from the top of the kerb to the slab which goes into negative moment bending before the load can be taken out in the deck units back to the abutments.
rowingengineer,
I like the ideas that you present in your post and I will dig through AS5100 tomorrow to see what provisions I can make to reduce the distribution of barrier loading. I also like the idea of redirecting the drainage and I will put this idea forward to the appropriate people.
Thanks
RE: Displacing Longitudinal Reinforcing in Kerbs
When in doubt, just take the next small step.
RE: Displacing Longitudinal Reinforcing in Kerbs
Yes, the kerb is in torsion. I just don't think of it that way. The wheel load is like any point load in a bending element, where the problem is deciding over what length the bending occurs. The moment and shear is greatest at the point of load, and dies out over some length each side. The top kerb bars would be the most important thing in distributing the load.
RE: Displacing Longitudinal Reinforcing in Kerbs
I am talking about the 250KN load at 800mm above deck.
When in doubt, just take the next small step.
RE: Displacing Longitudinal Reinforcing in Kerbs
RE: Displacing Longitudinal Reinforcing in Kerbs