www.sefindia.org

[someshwar ganti]

Dear All

I have a Truss Less Roof, for which I need to do a supporting RCC Framed structure,
I have Modeled the shed in 3D,  the RCC columns are failing perhaps due to Horizontal load on the Roof beam due to the CURVED roof.

If someone can help me to correct the STAAD input file ( I have commented all the other Loads in order to correct this issue first) I would really be thankful.

If anybody can help me solve this issue for me,
I will give 6 months Free usage of my software "ARC BDS", that can be used to extract
1. RCC Column, Beams Ast, from a STAAD output file with click of a button, besides generating Great quality Beam L.S drawing directly from STAAD output file

Sorry for putting the above reward, but I need to put that issue to rest as it has been tormenting me for long.

[PREETI_SARKAR]

Have you tried posting your question on the STAAD forum at the Bentley website?

https://bentleysystems.service-now.com/community?id=community_forum&sys_id=f420bf06475e31109091861f536d43f6

[someshwar ganti]

There is no issue with STAAD or its analysis,
it is the Modeling assumption i want clarification.

as in Reality both the columns at each Side walls are connected to each other by the Truss-less ROOF,

They may not behave as a pure cantilever column frame like in the current model,

it is because of the Horizontal Load due to the TRUSS Less roof as UDL on the top beam , the column is failing due to heavy moment generated at the BASE of the column


I wanted to know if I can use hinge supports at the column top or points in the roof beams, because practically that is how the structure will be behaving.

However, I am not aware as how much of % SWAY can ignored or considered,

because the moment you give a hinge I am sure all the columns will pass, but can we really consider that hinge is my question

[vikram.jeet]

Structure will, first behave as per it's Natural behaviour,, If it finds yielding at some place - It will redistribute the forces to survive,, and therefore - if section fails, Needed strength at other section must be available for survival of structure.

For example - If a portal beam is Monolithic with columns there is bound to be  support moments in beam  as slso same transferred to columns at ends of beam. That is Natural behaviour ,, But if some body wants to design besm as simply supported, with some  70 percent steel for Natural monolithic support moment - Redistribution is addressed as far as Vertical loading is concerned,, But for Horizontal Forces of EQ / Wind - Entire forces need to taken in column design .

Therefore in yr case of arch steel shed roof - Horizontal forces bound to act on column tip which will give maximum moment at base.

If you want to adopt Redistribution :- Prepare two Models

MODEL 1  MONOLITHIC AT JUNCTION OF COLUMN - ARCH,,
COLUMN FIXED AT BASE (Natural)
MODEL 2 HINGE JOINT AT JUNCTION OF COLUMN AND ARCH  ,  BUT COLUMN BASE FIXED

DESIGN AS UNDER :-
A) VERTICAL LOADS

ARCH DESIGN - MID SPAN AREA AS PER MODEL 2 PLUS SUPPORT PORTION AREA AS PER 70  PERCENT OF MODEL 1

COLUMN BASE DESIGN - AS PER 70 PERCENT OF MODEL 1

COLUMN TOP DESIGN - 70 PERCENT OF MODEL 1

B) HORIZONTAL FORCES  - N O  REDISTRIBUTION  - FORCES AND THEIR MOMENTS TO BE CONSIDERED FULLY

IS 456 ALLOWS 30 PERCENT REDISTRIBUTION,  HENCE FIGURE OF 70 PERCENT STRENGTH AT LEAST FOR REDISTRIBUTED SECTIONS,

[vikram.jeet]

Further :- If it is possible and Aesthetic s permit
PLEASE TIE THE ARCH AT CERTAIN LEVEL ( HIGHER THAN SPRINGING LEVEL) ,  THIS  WILL REDUCE HORIZONTAL FORCE AT SPRINGING AS PART FORCE IS BALANCED THROUGH TIE.

[someshwar ganti]

Thank you Virkram Sir,

can i use ENFORCED BUT FY FZ MX MY MZ

(basically telling STAAD to ignore the X force or Horizontal force on the column ONY) as the column and entire ROOF beam is connected to the curved roof through 2 bolts that will prevent any sway in the column

BTW :- cannot have a horizontal member as you have suggested because the width of the bldg is too long 22.5 m

somesh

[vikram.jeet]

As said in earlier post,,  Model 1  without any release will be Actual Model  - Adopt about 70 %

Model 2 will be one with  Release at joint of Fx,, Mz, My  to achieve Maximum moment at midspan of Arch as result of column inability to bear forces and joint moments. ADOPT THIS MOMENT, BETTER FULLY, FOR MID SECTION OF ARCH,,

AS SPAN OF ARCH IS
22.5 M,, YOU CAN PUT A TIE MEMBER  OF LENGTH 10 M AT HIGHER ELEVATION THAN SPRINGING LEVEL, IN CASE IT DO NOT INFRINGE AESTHETICS,,

[someshwar ganti]

Thank you vikram sir,
I am supposed to design only the RCC supporting structure of the TRUSS -LESS ROOF, so the changes in roof is not under my control

Because of the Horizontal UDL on the Top RCC Beam by the Roof Member, there is a big moment being caused at the bottom,

So i put the question in the forum to check if I make hinge at top of column

as in my opinion the RCC column column cannot move at top due to roof horizontal load because it is restrained at the other end also.

will try as per you suggestion,

Vikram sir, thank you for supporting and taking time to answer the question i have put,

if you are interested in checking and using my software please download it from www.zaxises.com , install the "ARC BDS" , please send me the license request file from the software I shall activate your system . (by default it is activated for 15 days from 1st usage, )

ARC BDS software will Extract the
a. Column Reinforcement Summary
b. Beam Reinforcement summary (in PDF & EXCEL) also as Layout Drawing
c. Generate Beam L.S drawings (you can edit the reinforcement in excel)

many more features

regards
somesh

[vikram.jeet]

Just to say :-
Taking Hinge joint , at top of column,, will not relieve column of Horizontal force.

Also my view point is that go for two models and use Model 1 ( Natural)  taking Redistribution to extent of 30%  I. e  70% values to be taken from Model 1 , in respect of,, Column design and Arch support moment design.

For Arch beam design ,, Values of Model 2 in respect of Mid span moments to be adopted. Model 2 is Having column top as Fixed But release of Fx, Mz, Mx  so that Maximum value of mid span is achieved.

But for Horizontsl forces 100 percent to be taken,,

But if Your role is only to design columns and No control on Arch design,, Then you have to intimate momrents for Arch design :-
Support - 70% of Model 1
Span  mo - 100 percent of model 2

[vikram.jeet]

IF YOUR ROLE IS ONLY LIMITED TO COLUMN DESIGN,, ( AND NOT ARCH DESIGN) ,,
THEN IS OBLIGATORY ON PART TO DESIGN COLUMNS FOR FULL MOMENTS BASED ON ACTUAL MODEL WITH COLUMN TAKING FULL HORIZONTAL FORCE AT TIP.

IF BOTH COLUMNS AND ARCH ARE IN YR SCOPE - THEN ONLY YOU CAN ADOPT REDISTRIBUTION FACILITY - SINCE TWO  ITEMS OF STRUCTURE  CAN NOT BE SEEN IN ISOLATION. AS BOTH ARE INTERDEPENDENT IN CASE ADVANTAGE OF REDISTRIBUTION IS TAKEN.