|LEARN FLAT RAFT STEP BY STEP|
INTRO & LIMITATIONS +
EXCERPTS FROM IS : 2950 - PART 1 - 1981
|Please take Print Out of Every Step, including this page before commencing Learn. Take a Yellow Marker Pen and Mark the Learning Process while Proceeding further. This is Essential for Learning.|
performs Analysis, Design, Estimation, Costing & AutoCAD Drawing of RCC
Rigid Flat Raft Foundation.
The Software basically requires a User to enter Raft data for Joints, Columns, Beams, Slabs & Continuity. The rest of the things are taken care of by the software.
The results are displayed in the form of BM & SF, Raft Hidden Beam & Slab Schedule, Quantities, Cost & Approximate Bar bending Schedule for Beams.
Graphics option are available for display and tabular Format is available for Editing and Deleting Data.
A User should Delete / Edit Input-Data through the various Program Options only. If any editing is done outside the design environment than Data files may become corrupted. All Data should be Strictly "Entered" as explained in following steps.
Extensive Printing options are available under each display. Printing is straight forward with default set of values ( Arial Font, 8 mm Thick, Bold, Portrait ).
Only Beam Schedule will be Printed in Landscape Orientation.
The best way to go about the software is to Mark on the Foundation Plan, Joint, Beam, Column and Slab Numbers. A Joint represents a Column location or an intersection between 2 Raft Beams. The Beams are represented by its location in the form of Right Hand Side (RHS) & Left Hand Side (LHS) Joint numbers. The Slabs are represented by LEFT BOTTOM & RIGHT TOP joint numbers. All Joints will have X & Y Co-Ordinates, Top Left corner is taken as origin (0, 0). Joint / Beam / Column / Slab numbers should start with " 1 " and should not be repeated.
The Program will generate automatic Joint, Beam, Column & Slab Numbers from the information given in Project File. Some of these Numbers / Members may not be required & shall be deleted in a systematic manner as explained in the following chapters. The Final Plan Graphics should look exactly as the Raft Foundation Plan.
|Cantilever Raft beams / Slabs cannot be analyzed.|
|Beams / Columns /
Slabs shall be along two mutually perpendicular axis
(X and Y). Polygonal (Multi-sided) slabs cannot be analyzed.
|Analyze the Structure, assuming Raft Top
(Column Base) as Hinged
(Refer Graphics above). Hence there shall be no Moments on Raft Top.
Structure shall be Analyzed in Either direction. Hence User shall enter 3 Column Load Cases, i.e.
● DL + LL
● DL + LL + Wind / Seismic Load in Ton (From X-X Direction)
● DL + LL + Wind / Seismic Load in Ton (From Y-Y Direction)
End Column Reactions on Raft Beams (DL + LL + Wind or Seismic) are obtained by running 2-D or 3-D Frame Analysis programs separately.
User may use our 2-D Frame Analysis software for calculation of End Reactions.
Export to Excel :
When the " Analysis Result -> Bending Moment & Reaction " option is Run, a Text file is automatically created. This File will open in Any Text Editor. You can also Open this Text File in EXCEL.
Start Excel -> File -> Open -> Delimited ->Next : Delimiters -> Comma ->Next -> Finish.
Now you will notice that Complete Data is displayed in Excel Spread Sheet.
If more than One File is Created, Corresponding to Each of Load Cases, than Open Excel Sheet for Each File (Load Case). In Excel Sheet Editing, Deleting, Sorting, Printing & Merging of Data/Files/Excel Sheets is Extremely Easy. This way any no. of Load Cases can be Manipulated.
Similar Text files are created in " Shear Corrected BM & SF " (Design BM & SF),
" Raft Beam Schedule " and " Raft Slab Schedule option for Exporting Results to Excel Spread Sheet & its subsequent Manipulation.
|Intersecting Joints between two Beams (Main & Secondary) is assumed as Hinged. Hence no Moment transfer is envisaged.|
|Connection between End Column and Beam is considered as Hinged. Hence no Moment transfer is envisaged between Column and Beam.|
|After data input, the user has to switch over to graphic option for visual checking of joints / columns / beams / slab nos. When the data is error free the user can run the Analysis, Design and Quantity options. The various results are also available through display or print options.|
|Analysis, Design and Quantity options should be run in strict order, else program will give unexpected results.|
|Program creates automatic Joint numbers as per nos. of Horizontal & Vertical Grids. Here Grids means Beams coming along Column center lines as well as all Internal Beams not aligned with columns. A user has to input Information regarding Horizontal & Vertical Grids while creating Project File.|
|A user can delete the Joints not required by using Joint Option.|
|Joints will be automatically re-numbered when "UPDATE" button is clicked or at "EXIT".|
|Remember to Delete / Edit Corresponding Beam / Column / Slab Member, whose Joint has been deleted.|
|Always delete Beam / Column / Slab member from the "END" to facilitate further Editing. After Deleting press "UPDATE" button for re-numbering of members.|
|After Deleting corresponding Beam / Column / Slab Member & Updating, edit the required Joint Numbers of affected Beam / Column / Slab Members.|
|Go through the "READ ME" Button for better understanding of that particular Option.|
|Raft Beam & Slab Design is as per IS 456 - 2000. Refer IS 2950 : Part 1 - 1981 / 1965 For Rigid Raft Design / Relative Stiffness Factor.|
|Hidden Beam Depth < 200 mm not permitted.|
|Beam Width > 8000 mm not permitted.|
|Links (Stirrups) < 75 MM for Hidden Beams is not permitted.|
|Beam Reinforcement > 4 % not permitted.|
|Age factor is considered as 1.15.|
|For Durability aspect of Design, refer our " Super Civil CD " software.|
|All Columns are placed Centrally with respect to Beams in either direction. There is no provision to offset the column in either direction. If the offset is large than user should re-workout the Beam Span.|
|Minimum Computer RAM memory of 1 GB is recommended.|
|Use Laser OR Ink Jet Printer.|
1. IS - 2950 - Part 1 - 1981.
2. BS - 8110 - 1997.
3. IS - 456- 2000 / 1978 / 1964.
4. SP 24 - 1983.
5. Advance Reinforced Concrete Design by P. C. Varghese.
6. Reinforced Concrete Designers Handbook by C. E. Reynolds.
|IMPORTANT FEATURES OF FLAT RAFT|
Beam marking in flat Raft Slab is different than the normal Raft plan GA.
1: Mark the Hidden
Strips) in the same way as you Mark the
2: Hidden Beam (Column Strips) depth shall = Flat Raft (Middle Strips) Thickness.
3: All Flat Raft Slab (Middle Strips) thickness shall be uniform.
4: Initial (Trial) Flat
Raft Slab Thickness =
5: Keep Column Size as
Large as Possible, Larger the Column size lesser
6: Minimum Column size allowed is 300 x 300 MM.
7: Try to Avoid secondary beams, i.e. hidden beams resting on one another.
8: Concentrated loads Loads are not Permitted.
9: Convert wall line load
in to UDL as w ÷ (0.6 * slab_span). and avoid beam
10: Hence convert all internal partitions in to equivalent UDL & avoid beams.
11: Try to Keep Minimum spacing of beams at 2.0 M C/C.
12: In order to get most
optimum design keep the slab and beam spans
13: Spacing of columns
shall be as uniform as possible within say 20 % of each
14: Avoid Eccentricity of Walls vis a vis Hidden Beams and Columns.
15: One Way Shears are
calculated at effective depth from Column face and
are calculated at Column face.
17: Raft Slab depth to be revised, if steel area exceeds 245 cm2.
18: In Case of Un-safe
Hidden Beam design Reframe the Plan or Revise Slab
19: Flat Raft Slab Design is
meant for Vertical Loads only.
21: Convert Non
Rectangular Column into Equivalent Square Column
22: Min Reinforcement % in Either Direction in Hidden beam = 0.20 %.
23: Reinforcement Spacing
Shall not Exceed 2 x Depth.
25: At Ends and Corners
the Flat Raft Slab shall Extend up to or beyond Outer
26: Large openings cannot be provided in Flat Raft Slab.
27: Small openings say <= 300 MM can be located near the center of Slab.
28: Staircase / Lift Well panel shall
be treated as normal slab & not as opening,
|Export to PDF:
A free PDF Creator Program is available with this Software. Designer can directly export to PDF instead of printing various reports.
|EXCERPTS FROM IS : 2950 - PART 1 - 1981|
|IS : 2950 - Part 1 is CP for Design & Construction of Raft Foundation.|
|In granular Soil,
the SBC of Raft is generally very high, however for rafts placed at
considerable depth (Like Basements) the punching mode of failure shall be
investigated. The Influence of soil compressibility & related scale
effects should be assessed.
For Rafts on cohesive soils, the stability against deep seated failures & effect of long term settlement shall be taken in to consideration.
The Depth of Raft Foundation shall not be Less than 1.0 M.
|Rigidity of Foundation tends to iron out uneven deformations & thereby modifies the contact pressure distribution. High order of rigidity is characterized by large moments & relative small uniform settlements. A rigid Foundation may also generate high secondary stresses in structural members. The effects of Rigidity shall be taken in to account in the analysis.|
design is based on the assumption of linear distribution of contact pressure.
The basic assumption of this method are :
(a) The Foundation is rigid relative to the supporting soil & the compressible soil layer is relatively shallow.
(b) The contact pressure is assumed as planner, such that the centroid of the contact pressure coincides with the line of action of the resultant force of all loads acting on the foundation.
This method may be used when either of the following conditions is satisfied.
(a) The structures behaves as rigid (due to combine action of the superstructure & the foundation) with a relative stiffness factor K > 0.50. (Refer Appendix C)
(b) The Column spacing is less than 1.75 / Ã. (Refer Appendix C)
The Raft is analyzed as a whole in of the two perpendicular direction & analysis is based on statics.