Leaderboard

Very Nice Engineer ....thank you so so so so much. You are right that depends on the fixity of the column I will try what is the new results and share..

a. yes I agree with you b. It might be SAFE, it might not. depends on the moment diagram which depends on the base fixity (pin or fixed). You must design it properly. If this is an interior column then it should be okay (only P and no M). c. If it was enlarged eccentrically, yes you have to account for the moment M = P.e

mhdhamood, IMO, by increasing column dimension in-between the slab-on-grade and the mat foundation, you are actually increasing the mat thickness, which is otherwise needed to account for larger punching. I would (in case mat foundation is yet to be poured), treat the 'enlarged column neck' and the mat portion exactly beneath it, as a single mat (of thickness equal to sum of normal mat thickness and 0.5 m i.e thickness of 'enlarged column neck') and will provide reinforcement as per requirements of larger mat thickness. This concept is similar to what has been discussed in following thread: (http://www.sepakistan.com/topic/1689-drop-in-mat-foundation/ ) BTW... (1) How are you analyzing & designing the mat foundation? Using some software (CSI SAFE etc.) or manually? (2) Has the mat foundation already been poured, or is yet to be poured?

Yes Muneeb is right about sudden geometry irregularity in column size. Please make sure you take this effect.

Just one thing I want to add that if this is highrise building then you need to check the axial forces in the adjacent beams if you increase it eccentrically and if there are some grade beams. It will not effect in all cases but better to check. ; Secondly if you increase it eccentrically then take care how you will continue the reinforcement from this column to above column as everything depends upon the reinforcement. and in this case you need to model slab on grade and check the inplane stresses if there is soil outside because your total burried area will act as one unit One last important thing, you said the column creating problem in punching and when you increase size it is solved. you can not suddenly increase the size in that small length too much. You need some curtailment for column size. For example if the column above slab on grade is 300mm in diameter then you can not provide 600 mm dia below slab on grade. So please take care of this. These are just my opinions anybody can comment of not agree...... Thanks Muneeb

AOA ! How to decide the Pattern live Load Factor value. In ETABS 2013 it is 0.75 by default....

sir , you were very much right . I got a normal pattern of my results. As it is confirmed from CSI ETAB (When nonzero Pllf is assigned to a frame object, positive design moments are calculated assuming a simply supported condition under live-load application. While this does affect design moments, analysis moments are not affected) https://wiki.csiamerica.com/display/kb/Pattern+live-load+factor

try making pattern live load factor to 0.