Minimum Number of Stirrup Legs in Wide Beams
Minimum Number of Stirrup Legs in Wide Beams
(OP)
REQUIRED: I am looking for a written publication or a consensus on this issue.
As an example take a 48" wide concrete beam. The shear in the beam requires the use of only 2 shear legs. Given a large number of top bars the top horizontal leg of the stirrup will want to sag due to the weight of the bars. How many bars vertical stirrup legs should be placed in this beam to prevent the sag?
Say for a beam width of 30" to 48" 3 legs would be required. Or for a beam width of 48" to 60" 4 legs would be required.
There is a graphic in CRSI 2002 (page 12-4)close to what I am looking for. However, this is not directed at my question.
Any and all help would be greatly appreciated.
As an example take a 48" wide concrete beam. The shear in the beam requires the use of only 2 shear legs. Given a large number of top bars the top horizontal leg of the stirrup will want to sag due to the weight of the bars. How many bars vertical stirrup legs should be placed in this beam to prevent the sag?
Say for a beam width of 30" to 48" 3 legs would be required. Or for a beam width of 48" to 60" 4 legs would be required.
There is a graphic in CRSI 2002 (page 12-4)close to what I am looking for. However, this is not directed at my question.
Any and all help would be greatly appreciated.





RE: Minimum Number of Stirrup Legs in Wide Beams
RE: Minimum Number of Stirrup Legs in Wide Beams
RE: Minimum Number of Stirrup Legs in Wide Beams
I don’t have the CRSI pub you mention, and I’m not exactly sure I understand what you’re describing. But, I would think that if the top longitudinal bars were causing the top horizontal leg of the stirrups to sag, the top longitudinal bars could be supported off the formwork to prevent the stirrups from sagging.
RE: Minimum Number of Stirrup Legs in Wide Beams
Any other opinions?
RE: Minimum Number of Stirrup Legs in Wide Beams
Whiie I agree that our design should be buildable, I don't think we have to go to the extent you describe necessarily. It's good that you want to though. The easier you make it for them, the easier it will be for you during construction.
How are you modeling the stirrup to figure up it's strength?
RE: Minimum Number of Stirrup Legs in Wide Beams
The Australian concrete code specifies and maximum transverse spacing of legs of the lesser of D or 600mm (24"). So minimum 3 legs for your 48" beam.
RE: Minimum Number of Stirrup Legs in Wide Beams
This is not necessarily a totally means and method thing. For very wide beams, it think the research is somewhat lacking so the idea here is to follow the standard of practice in all concrete engineering...i.e. - always try to distribute reinforcing evenly in sections and slabs, unless the stress (following stiffness) demands an uneven distribution.
RE: Minimum Number of Stirrup Legs in Wide Beams
As you mentioned, only 2 are required, but it is good practice to use 4 legs for wide beams in my opinion.
In the site, maybe all it takes to hold up with middle bars in a wide beam is tying the middle top steel every so often to the slab steel running accross it above. I wouldn't worry about how the guys in the site deal with it, but there are several options for them, and all of them should fall in means and methods.
RE: Minimum Number of Stirrup Legs in Wide Beams
In my career, often when I try and go the extra mile for the contractor by detailing my structure to accommodate construction outside the normal standard of care, he will offer an alternative. His alternative will require less work, diminishes the quality somewhat or increases his compensation.
The most comical of these is in the bridge industry. Deck slabs are detailed in this market with main bars perpendicular to the traffic. Every other row of bars is a bar pair, same size top and bottom, to provide capacity against positive and negative bending. The remaining alternating rows have something called a truss-bar. The truss bar is bent into the top over beams and the bottom between where the moment peaks occur. Contractors are always complaining about the truss bar. They say we could do it cheaper if we did the whole bridge using the straight bars because bending the truss bar is so expensive. On the surface this all sounds reasonable except ... If we replace the truss bar with a bar pair the quantity of deck reinforcing steel (the basis of payment) goes up about 15-20%. Contractor says, "But I'll save more than that in labor." Instead we place a plan note saying the contractor can replace the truss bar with a bar pair at no additional cost to the owner. I have yet to see this happen. Bottom line, contractor is not telling the truth. He wants to be paid more (remember the total bar weight is the basis of payment) for doing less work, since he won't have to have the truss bars fabricated.
I'll get off my soap box now.