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Detailed explanation for Gravity column design in RCDC
Why only 50% of longitudinal reinforcement considered For Column Shear Calculation?
Why RCDC shows message of “Elevation of Column has been Omitted” while generating elevation of combined wall?
There is option under shear wall for detailing as Boundary Element or Equi Spaced rebar. I wish to have detailing as equi-spaced rebar, but it never gives detailing as equi spaced and redesign consume lot of time
Does RCDC calculate the effective length factor based on ACI 318M -14 Fig. R6.2.5 (b) for sway frames?
On what basis does RCDC perform the Joint shear check based on the Aspect ratio of vertical member as per Clause 7.1.2 IS13920 - 2016 & Amendment no.1 - 2017?
Can RCDC handle columns of shape L, T and other odd shapes?
When equal number of bars are provided in all columns from plinth to top floors, after design it’s showing lesser bars at the bottom and more at top
Some of the columns are missing at lower level even if they have exist in Staad model
Forces for column do not match with analysis
In edit link arrangement all the internal links can be removed. It doesn’t affect the design of links in column design. Please clarify
Does RCDC calculate the Effective length factor automatically or it is user defined? Is it same for all columns in model or different?
Spacing of confining reinforcement for column as per IS13920 2016
In RCDC, we can group columns and design them. But, when we go on creating elevation there is no way to create a single elevation for all the columns in a group. This feature is available only for detailed drawing. Can we incorporate the same for elevation
How can we change the Un-supported length in RCDC when column is tied in one direction and is free in another direction?
In Failure Diagnostic We Can Get Only Reason Of Failure But Not Get The Calculation. How We Know The Failure Calculation Of Column?
RCDC consider 0.4% reinforcement for column minimum reinforcement by default. Is there any clause in IS code to reduce column minimum reinforcement from 0.8% to 0.4%?
A parametric wall is having different thickness at different levels. RCDC is unable to show the correct thickness. What may be the cause?
In my model I have grouped the columns. Instead of column name I want to see group names. How to do that?
Does RCDC designs shear wall for out of plane moments in addition to in plane moments?
Can we design shear wall/wall with single layer (mesh) of reinforcement?
Please clarify the braced and un-braced design conditions
Pl refer to Annexure A off IS 13920 which states walls are to be designed for uniaxial bending. Columns are considered as biaxial. Hence, their design cannot be clubbed under one set
Can we have calculations for boundary zone length in wall design?
RCDC follows ductile detailing as per 13920 for outer ring of boundary element but reduces link dia. & spacing for inner links
What is the basis for only 20% of vertical reinforcement is considered for the calculation of Shear capacity (Tc)?
How and when Modulus of rupture check performed in RCDC?
In which cases we should not consider perform slenderness check - When to and when not to consider slenderness?
Provide detailed explanation for identification of section as a wall with respect to Depth and Width of member in RCDC
[[RCDC uses the formula of column for the “Minimum Eccentricity Calculation” (in IS code), though it is different for shear walls as per Clause: 32.2.2 of IS 456-2000]]
Customization of column reinforcement after auto design
As per clause 39.7.1 (Notes), IS code allows user to design column based on Braced and Un-braced conditions. The end moments are calculated based on end conditions given in this clause.
In Euro code, the braced and Unbraced option is available for calculation of effective length factor.
Slenderness check is an option given in RCDC. If the structure is analyzed with the Non-linear load cases (P-Delta) it is not recommended to consider this check. If the structure is analyzed with linear load cases, it is recommended to consider this check. If this check is selected, slenderness check will be performed, and additional slenderness moments will be calculated if column is slender.If this check is not selected, slenderness check will not be performed.
Please note the points below followed in RCDC for design of Columns based on provisions of IS 13920 (2016). This is as per our understanding of the code and based on discussions with some experts on the code –
Gravity columns is a choice that you as structural engineer have to make in your system. To reflect this correctly in analysis, ideally these columns should not participate in lateral load resistance in carrying shear and bending moments. These should be defined as ‘pinned’ ends in lateral load analysis. As per current limitations in E-tabs and STAAD, this is not easily manageable. Hence, we have allowed the users to select the required columns in RCDC and treat them as ‘Gravity’ columns. RAM software has the option to analyse the structure with combination of Lateral and Gravity columns.
As per code, the Gravity columns should be designed for the forces from analysis as well as effects of lateral displacement (known as ‘displacement compatibility’). This is done by considering moment due to Pu (Axial load from Gravity load combinations with DL +LL) acting at R*Delta distance away (Delta is displacement due to lateral loads). We would request you to go through Clause 11 of IS 13920 (2016) for more details on this.
In RCDC, we follow the above procedure in detail. Please check detailed design calculation report for Gravity columns for more information.
Please note that, in RCDC the member can be defined as ‘Gravity column’ only if that qualifies as column based on D/B ratio. Walls can’t be design as Gravity members. It can be either Non-ductile or Ductile. Further, the Gravity columns are designed for Vertical gravity loads with effect of later displacement due to lateral loads as explained earlier. Click on below link to understand the implementation of Gravity column in RCDC.
Combined walls are consisting of more than one walls. If the wall shape and size is same at all floors, RCDC generally generates the elevation of combined wall showing one face only.
If the wall shape and size is not same throughout the height of all floors, it is difficult to generate elevation of these walls. The combined junctions of walls are detailed separately to satisfy the percentage reinforcement in both the walls. Also showing elevation of each face of combined wall would be difficult in case of thickness changes, thus RCDC generally ignore or omit the elevation of combined walls for elevation. Cases like major variation of reinforcement along height of wall and if combined wall consist of column are omitted.
When you select the option of “Detail with Equi-spaced rebar arrangement" RCDC design and detail the wall with Zones, however rebar spacing in all zones are maintain same. refer below snap showing rebar arrangement with same setting,
if you unselect "Detail wall with Boundary element" it will design as a ductile wall without Boundary element but it will try to provide zones to optimized the reinforcement.
when you select both the options i.e. Boundary element and Equi-spaced, it will design as Boundary wall with equi-spaced rebar arrangement. This setting is applicable for Non-ductile wall if you want t provide equal spacing.
if you want to design wall as column and with same rebar having equal spacing, then you have to perform the redesign step, however in redesign column tool allows user to change the type from "Zonal" to "Equi" in one step for wall along height. refer below snap,
for wall, RCDC tries to optimize the reinforcement by providing higher diameter at edges.
23.Does RCDC calculate the effective length factor based on ACI 318M -14 Fig. R6.2.5 (b) for sway frames?
Reply:
Reply: RCDC calculates the column effective length factors as per above charts based on type of frame.
Type of frame is identified as per story height, axial load, relative displacement and story shear. Refer below snap,
Based on the column at top and bottom along with beam stiffness of story considered, value of Ѱ is calculated. Refer below snap,
As per Ѱ, effective length factor (k) is calculated based on fig. 6.2.5
24.On what basis does RCDC perform the Joint shear check based on the Aspect ratio of vertical member as per Clause 7.1.2 IS:13920 - 2016 & Amendment no.1 - 2017 ?
As per clause 7.1.2 IS;13920 - 2016, the vertical members of structure whose B/D >= 0.4 (or D/B <= 2.5), shall be designed as per requirements of Clause 9.
The first print of IS;13920 - 2016, 'Clause 8' talks about 'special confining reinforcement'. Later in Amendment no.1 - 2017 to IS;13920 - 2016 , this clause was renamed as 7.6. Hence, the old clause 9 now automatically becomes 8 and clause 10 (which is for shear walls) becomes 9.
Further, in the same amendment, they have mentioned that 0.45 in 7.1.2 should be replaced by 0.4. With this background, one can interpret 7.1.2 as below - It is preferred to provide D/B as 2.5 or less (B/D 0.4 or more) for columns. In clause for walls it is very clearly mentioned that D/B should be more than 4. Also,
So, for D/B between 2.5 and 4, the behavior is in between and should be avoided. However, if one has to use these ratios then those members can be designed as walls as per clause 9, and can be done in RCDC by changing the D/B ratio in Design Settings form.
25.In RCDC, we can group columns and design them. But, when we go on creating elevation there is no way to create a single elevation for all the columns in a group. This feature is available only for detailed drawing. Can we incorporate the same for elevation drawings also? If not, can you please let me know the reason?
26.How can we change the Un-supported length in RCDC when column is tied in one direction and is free in another direction?
Considering below example when there is a case where a column is not tied along one direction and is tied along another direction, the unsupported length of the column along the direction where it is not tied is to be manually entered in RCDC using the 'Redesign Section' tool available in RCDC.
With this option, the actual unsupported length = (Floor height - the Beam depth) needs to be manually entered in RCDC.
Once this height is entered; the column section is redesigned and the redesigned data is accepted, the revised height of the column at selected floor will be displayed in the design calculation report as well.
Below are the snips for reference;
27. IN FAILURE DIAGNOSTIC WE CAN GET ONLY REASON OF FAILURE BUT NOT GET THE CALCULATION. HOW WE KNOW THE FAILURE CALCULATION OF COLUMN?
RCDC provides the reason for failure in the Failure Diagnostics report. There are multiple type of Failure suggested by RCDC as follows:
28. RCDC consider 0.4% reinforcement for column minimum reinforcement by default. Is there any clause in IS code to reduce column minimum reinforcement from 0.8% to 0.4%?
As per code, Min As = 0.8% of the required C/s area of the column. RCDC follows the same.
RCDC internally calculates the c/s area required for the Maximum Pu and then takes 0.8% of the Required c/s area.
The 0.4% mentioned on the reinforcement setting form is used to calculate the Asmin with the Provided c/s area of the column.
Finally the Asmin is considered as Max (0.8*Required c/s area of column, 0.4*Provided c/s area of column) where the required c/s area of column is calculated in RCDC internally with Max Pu.
29. A parametric wall is having different thickness at different levels. RCDC is unable to show the correct thickness. What may be the cause?
Note that whenever a single parametric surface is modeled and 2 different plate thicknesses are found to be assigned to a single surface, RCDC considers the minimum of the thicknesses obtained. If it is desired to have different thicknesses at different levels, then you should model separate parametric surfaces and then assign the desired thickness to different surfaces. Then only RCDC will read and show the correct thickness at different levels.
30. In my model I have grouped the columns. Instead of column name I want to see group names. How to do that?
This can be achieved by changing the Drawing Style. To do that go to Modify > Drawing Style > Modify Drawing Style as shown below.
Now a new window will open. There you need to check the box against "Use Group Names in Output" under Display Style. This will show the group names instead of column names.