topic Re: Reinforcement sets and shear (2018) in Structural Bridge Design Forum

Reinforcement sets and shear (2018)

Anonymous — Fri, 10 Jul 2020 14:27:38 GMT

Good afternoon,

I’m looking for some advice on designing the steel for a RC Pier which is integral to an RC Pile Cap (4No piles). This is my first-time using FE for this sort of thing and I find myself asking questions that cannot be explained by the provided SBD examples.

My main concern is that the design moments which are provided by the reinforcement set does not specify if shear is accounted for. I understand that the Wood Armer equations are used however it’s still unclear if shear is considered.

The implications of this is that:
a) shear is not accounted for and the section needs additional longitudinal rebar + links
-or-
b) shear is accounted for and thus minimum steel is only required

I would appreciate any guidance on the above.

Re: Reinforcement sets and shear (2018)

dave_geeves — Fri, 10 Jul 2020 19:03:23 GMT

Hi Daniel,

A very valid question. The reinforcement moments derived from the Wood Armer equations will only provide the design moments in the direction of the reinforcement (based upon the integration of plate bending moments and plate torsion). It does not provide the corresponding shear forces which may be necessary for the design of links and possible additional longitudinal reinforcement for shear. For flat slab decks then this additional shear reinforcement is usually unnecessary, as the shear stresses are relatively low, but for a pile cap this will probably not be the case.

The basic finite element results will provide out of plane shear forces (which are shear forces per unit width in both directions and these could be incorporated into your design checks. You don't say if you are using design sections or design beams to carry out the design or if you are doing this by hand.

As a suggestion you may like to create "Virtual members" of the strips of the finite elements across the piles (a number if elements wide) which will provide beam moments and forces which will include shear forces along the length of the virtual member. These can be incorporated with the reinforcement moment in either a design section or design reinforced concrete beam to carry out the design checks.

If you would like to attach your zipped up data file (after removing any personal or customer information like titles etc) I will take a look and see if I can provide a short example to illustrate what I mean. Remember to include any associated section or beam files if they are linked into the structural project rather than being imbedded

I hope this has provided some help.

Kind regards

Dave Geeves

Re: Reinforcement sets and shear (2018)

Anonymous — Sun, 12 Jul 2020 15:20:41 GMT

Thank you Dave for the information and offering help on the subject. A virtual member sounds like a good idea although something i haven't done in FE so id have to read up on it. I was, as you say planning on using the shear from the out of plane bending although wanted to make sure i wasn't over designing. I was initially using the section design function to confirm hand calculations.

I have attached my zipped file which should provide you with more information. Continued help on the matter would be appreciated, especially the application of a virtual member. As far as the query is concerned i believe you have answered it and so I've accepted the solution.

Thank you!