I have a ground floor building, which I want to design in RCDC.
Some of the column sizes required(while designing in RCDC) are reduced, If I extend the column above roof slab (around 1m and categorize this 1m height as gravity column).
What is reason behind this, whether is the right way to design column?
(pic: extra projection of column above roof slab is marked in red)
Dear Sir,Thank you for your query. The column above roof can be designed as ductile. Option is available to change the column type from Gravity to Lateral.Please share STAAD and RCDC file if possible.
In my case there is no need for column projection over roof slab. However, if I extend column over roof slab - column dimensions got reduced.
My question is whether we can project columns over roof slab to optimize the column sizes?
Also what can we do if first three modes contribute less than 65% mass participation factor in each principal plan direction?
Please find the attached staad file.O22064-C-FB-07-DC-0001_A.std
Dear Sir,
Thank you for sharing STAAD file.
As per my understanding, you are using IS 456 + IS 13920-2016 to design structure. As you perform the ductile design, column joint check is performed. IS 13920 + 2016 recommend performing joint check at top level of column joint in case column is having less than four stories. refer IS 13920-2016 snap,
the stiffness of the members connected to joint are considered to perform joint check. Column below and above the joint check are considered in the joint check. The column flexural capacity should be more than the 1.4 times the beam flexural capacity.
Case-1
in your case, the structure is one story, the flexural joint check is performed at top level.If column above roof is not modelled, flexural capacity of column below joint check would be considered in the joint check. there are chances that this joint might fail. As only one column flexural capacity is considered compared to beams present at this level.
Case-2
In case of if you model column above roof level, flexural capacity of column below and above joint would be considered. there are chances that joint check could satisfied. this is because the one more column which is actually cantilevered above roof level is considered in the joint check. There is possibility that the lesser column size might pass in joint check compared to case-1.
it is not recommended to model the cantilever column above the roof level. Code suggestions are to consider framed members connected to joint for joint check. Cantilever column cannot participate in the lateral moment resisting frame.
Answer Verified By: Ashok Yarrabothula
Regarding the Mass participation issue, i would suggest you see the warning messages provided by STAAD. please try to resolve these warning.
Thank you
Regarding this base shear warning: There is no need to increase base shear for industrial structures for seismic loads that defined as per IS 1893 (Part 4):2015 (clause: 9.3 - Notes) right?
If it's - IS 1893 (Part1): 2016, multiplying factor is used.
I have limited knowledge of IS 1893 (Part 4):2015. If you have any questions related to RCDC software, please feel free to ask.i would request others to answer this question.