Concrete Pier Cap Design

Question

Concrete Pier Cap Design

dbags (Structural)

(OP)

9 Sep 03 08:01

We are designing multiple two & three bay reinforced concrete pier bents. We are utilizing LRFD and have found for the cap beam design that the ultimate moment never controls. The overwhelming control is distribution reinforcement for crack control. This typically results in the need for an entirely new mat of rebar in the cap beam. Has anyone experienced a similar thing? Also, is there any way around the crack control provisions?

Qshake (Structural) · Answer 1 · 2003-09-09 11:54:01

Crack control often does control even in LFD, ASD etc. When it does we simply address it and move on. Its never been an obstacle that I've been aware of. Usually adding more bars or changing to a smaller bar and adding more of them.

bridgebuster (Civil) · Answer 2 · 2003-09-10 18:02:39

About two years ago we finished four bridges using LRFD. It was our first experience with the new code.

We found a similar problem with temperature reinforcement [Section 5.10.8]controlling the design of abutment stems, backwalls, and footings by a significant margin. In some cases double what the Standard Specs would require for flexure. At the time I spoke to a professor from Rutgers University, who assisted in the development of the code. He stated that LRFD hadn't been perfected for substructures. Due to the vast increase in steel quantity our client agreed to a modified design methodology: We used LRFD to generate loads and LFD to determine reinforcement.

jheidt2543 (Civil/Environmental) · Answer 3 · 2003-09-14 09:51:56

Just a question, do many of you mix code requirements in a design? I should think, for the sake of consistancy, you would want to use the same code requirements throughout the design of a structure.

ishvaaag (Structural) · Answer 4 · 2003-09-15 12:39:17

During my experience as a designer and works director in buildings I have met many instances in which simply any of the mandatory codes do not address the issue at hand but in the most generic and undefined terms, or even not at all.

Hence, except you decide it out of the scope of your abilities, one is left to his wit, and so using sound engineering sources with sound engineering judgement upon it does not seem only a reasonable thing, it becomes the most viable one and the election of choice to those involved.

I must also signal that whenever these ways have been exercised (in my practice) I have never witnessed any problem related to it, so a good substitute may not bad if an original simply is not at hand.

koodi (Civil/Environmental) · Answer 5 · 2003-09-16 11:51:08

jheidt2543,
"Accepted" codes are ultra conservative.
The code, 99.999% of the time, results in an overly conservative design--little leeway is offered, regardless.

I would think most structures built are a mixture of codes?

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Concrete Pier Cap Design