Stability Check for Penstock Pedestal Support
Stability Check for Penstock Pedestal Support
(OP)
Hi.
I am new to this forum and this is my first post/questions.
We are basically in the process of designing reinforced concrete pedestal or saddle support for a penstock.
I have almost completed the design including the checks for sliding, stability and bearing pressure (with more than adequate factors of safety). But our Senior Engineer suggested that i should also include the check for resultant force lying between middle third of the base.
Now in order to satisfy this check I will have to increase the size of the pedestal by quite a bit. The question is that is this check really necessary? I mean i am already getting adequate FOS for overturning (2.6) and also sliding (22). So what if i do not include this check and how can i justify it.
Also please clarify if this check is only for vertical forces or we have to include horizontal forces as well because when we include horizontal forces, the resultant force acts at an angle which takes it completely out of the middle third of the base.
Sorry for such a long and such a basic question.
Any answers/views would be really appreciated.
Regards,
I am new to this forum and this is my first post/questions.
We are basically in the process of designing reinforced concrete pedestal or saddle support for a penstock.
I have almost completed the design including the checks for sliding, stability and bearing pressure (with more than adequate factors of safety). But our Senior Engineer suggested that i should also include the check for resultant force lying between middle third of the base.
Now in order to satisfy this check I will have to increase the size of the pedestal by quite a bit. The question is that is this check really necessary? I mean i am already getting adequate FOS for overturning (2.6) and also sliding (22). So what if i do not include this check and how can i justify it.
Also please clarify if this check is only for vertical forces or we have to include horizontal forces as well because when we include horizontal forces, the resultant force acts at an angle which takes it completely out of the middle third of the base.
Sorry for such a long and such a basic question.
Any answers/views would be really appreciated.
Regards,






RE: Stability Check for Penstock Pedestal Support
RE: Stability Check for Penstock Pedestal Support
Its bearing on rock.
RE: Stability Check for Penstock Pedestal Support
I've seen a number of projects have this as a design requirement. But, I personally feel it would be overkill when combined with the 0.6 DL factors.
RE: Stability Check for Penstock Pedestal Support
But I have checked that taking 0.6D gives a factor of safety less than 2 (1.83 to be precise). So i guess i will have to satisfy the check for resultant force.
RE: Stability Check for Penstock Pedestal Support
The 0.6DL is from ASCE 7, and may or may not be applicable to your project. You wouldn't normally apply a factor of safety over and above the 0.6DL overturn check, though.
RE: Stability Check for Penstock Pedestal Support
RE: Stability Check for Penstock Pedestal Support
aakalim152
"So what if I do not include this check and how can I justify it."
I agree with the others that you need to check the location of the resultant, especially if your boss told you to do just that. Your question above concerns me with the "so what" statement. If that persists, eventually it will get you in trouble, if not fired. DO not try to second guess your boss's authorithy in the office. It is OK to ask questions though, always. Just watch how you phrase it. You might be misread. I am probably one of those.
Just trying to help. Cheers.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Stability Check for Penstock Pedestal Support
If you are concerned about the size of your base then maybe you should express your concerns to your boss. I am sure he/she is well aware of how the numbers work and what this requested change will mean to the size of your base.
RE: Stability Check for Penstock Pedestal Support
RE: Stability Check for Penstock Pedestal Support
RE: Stability Check for Penstock Pedestal Support
I finally increased the size of the pedestal which satisfied the middle third requirement.
Regards,
RE: Stability Check for Penstock Pedestal Support