Hello,
I have a question regarding shear and torsion design in RC Pier.
In RC Pier, under Analysis---AD Parameters---Shear and Torsion Calculation, there is option which says "Shear force is equally distributed among stirrups".
I read the Help Document, and find it hard to understand. It says "Option of Shear force is equally distributed among stirrups, and the default is unchecked. However, when this option is checked, it assumes the equal distribution of shear force among all legs at failure, where the demand of transverse reinforcement is based on the controlling case of exterior legs." Can someone help me explain what it means?
I did an example to see what this option does, see the screen shots. Basically one is check shear force is equally distributed among stirrups and the other is not.
I compared the shear design result at a specific location between the two method, see below.
According to the comparison I noticed that when you check the shear force is equally distributed among stirrups , Av/s is calculated as the sum of Avs/s and quantity of Ats/s times the number of legs. When unchecked, Av/s is calculated as the sum of Avs/s and quantity of Ats/s times two.
But I also noticed phi*Vn is different, because Vs is different. I can't understand why. Can someone explain this for me?
Thanks.
Lin,
I did create a quick example out of Tutorial one of Substructure in LEAP Bridge Concrete v20.0.0.46 which is the latest release (see screen shot below).
Vs increases proportionally with provided area of shear reinforcement. Please make sur you are using this latest version of the program. Also do not check locations where red flags are present since the internal iterative algorithm of the program stops at some point. You should pass the design (lift the red flags) and then verify the figure you are questioning. Concurrent shear and torsion is a more conservative option which some designers prefer to use. For further assistance you can contact me at Alexandru.Oancea@bentley.com
Alex,
Thanks for your response.
The LEAP Bridge Concrete I used is the most updated version.
I got confused by the option of shear force is equally distributed among stirrups under Analysis---AD Parameters---Shear and Torsion Calculation and the help document doesn't do a good job explaining it makes me more confused what it really does. It says "Option of Shear force is equally distributed among stirrups, and the default is unchecked. However, when this option is checked, it assumes the equal distribution of shear force among all legs at failure, where the demand of transverse reinforcement is based on the controlling case of exterior legs." Could you explain that to me?
To find out what that option does I did an example. The flexure and shear reinforcement layout are the same. For the first one I checked the shear forces is equally distributed among stirrups and the second one I didn't check and compared the result. Please see the attached figures above. After saw the result, that raised me another question, which is why Vs is different.
Exterior stirrup legs resist both shear and torsion which implies that the shear is not equally distributed in between exterior and interior legs. If you add the torsion demand to all legs then the shear is equalized (from which the name of the options is derived). Some designers prefer it this way.