detailing question

[longisland]

Hi,
All structural plans are drawn in 2-dimension; in most cases, the elements are drawn seperately, e.g, a beam detail, slab section & column section etc. However, during construction, I'm asked by the consultant to produce shop or construction drawings.
Any pointers on the bar arrangement at the intersection between two cross beams or column point where all the bars meet (column, beam, slab). I noticed the normal practice in structural plans is to specify the cover thickness from the main reinforcement. However, from design standpoint, the area of steel provided depends on the effective depth, therefore, at the intersection when bars of two cross beams meet, one beam may be under designed since the actual effective depth will be less than the calculated depth. Furthemore, since I'm not the designer, I won't know which beam is the main beam. Any thoughts?

 

[JedClampett]

It's not your fault for not knowing. The design should indicate, by note or detail, which reinforcing is to be deflected and which is to continue straight through. Your only recourse is to call the Engineer. The good news is that the engineer will probably remember and clear it up on his next design.
If the reinforcing drawings are to be reviewed, this is a good stage to put the question.

 

[JAE]

longisland - from an engineer's perspective you are asking a very GOOD question and one that you should definitely follow up on.

I my practice, I always design these kinds of intersecting beams with a reduced "d" to allow a fabricator to switch the steel in either way - that way I'm covered because even if you detail it on the shops one way, the steel could be switched in the field the other way.

This issue is usually dealing with top steel at intersections where negative moment is the concern. At these locations (like at columns) the bottom steel can be tapered up and over intersecting bars - reducing d slightly at the support. Not a big issue as long as the bars are properly developed into the support.

 

[idly123]

JAE said it right- The design of secondary beam should account for reduced "d" on account of main beam reinf.

As far as provision in site is concerned , general practice at at T or a L junction between main and secondary beam the secondary beam -ve reinf is taken above the main beam. This requires that a slight kink is made for the negative reinf of the main beam , thereby virtually the secondary beam top reinf is at the level of the main beam top reinf.
Hope i was clear
regds
Raj

 

[oijammu]

I believe that the reinforcement is designed for max moment at centre of span.At the support it is for shear only.So it should not be a big if 'd' is slightly smaller at the support