Modelling Building Frame with STAAD.Pro & ETABS - Rahul Leslie

1
Modelling Building
Frame with
STAAD.Pro &
ETABS
Rahul Leslie
Assistant Director,
Buildings Design,
DRIQ, Kerala PWD
Trivandrum, India
Presented by

3 3
Ground Floor
The example building:
Presented by Rahul LeslieAnalysis & Design of an RC Building in STAAD.Pro & ETABS

4 4
First Floor
Storey ht. = 3.6m

5 5
Second Floor
Storey ht. = 3.6m

6 6
Terrace
Storey ht. = 3.6m

7
Initial member size fixing
Beams:
• Width:
– According to architectural requirements: 20, 23 or 25 cm.
– Preferably keep width not less than one-third depth.
• Depth:
– Fix an initial size between (span/12) and (span/15).
– Choose sizes such as 35, 40, 45, 50, 60, 70, 75, 80 cm or more
– This may have to be increased depending on Ast required (from
analysis) at a later stage.
Analysis & Design of an RC Building in STAAD.Pro Presented by Rahul LeslieAnalysis & Design of an RC Building in STAAD.Pro & ETABS

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Initial member size fixing (cont…)
Column:
• Width:
– What architectural requirements permit: 20, 23, 25 or 30 cm.
– Preferably keep width of column grater than that of beams to facilitate
passing of beam reinforcements.
– Increase width, wherever possible, to be preferably not less than half
depth.
• Depth:
– This is usually done from experience. For beginners, the following may be
taken as a starting point:
• Fix an arbitrary (and reasonably small) size for columns.
• From the axial force, find area required for each column based on short column
design formula, for 2% reinforcement.
• Increase this area requirement by 25% for all internal columns and by 50% for
all periphery columns. For the decided width, find depth for the area required.
• Based on above, choose depth such as 35, 40, 45, 50, 60, 70, 75, 80 cm or
more.
– The dimension may be suitably re-sized later based on the Asc required
from analysis.
Analysis & Design of an RC Building in STAAD.Pro Presented by Rahul LeslieAnalysis & Design of an RC Building in STAAD.Pro & ETABS

9
Initial member size fixing (cont…)
Slabs:
• Depth:
– Calculated as minimum of [shorter span]/32
– but same depths in adjacent slabs can be convenient
– Depths of 10, 11 and 12 cms are most common.
– In case the depth required is more than 12 or 13 cm, one may spit the slab
using sub-beams, to bring the slab thickness to 12cm or within.

10 10
B
C
D
A
1 2 3 4 5
1st
Floor plan – Centre-to-centre distances (m):

11 11
1st
Floor Key plan – Beam Size:
B
A
C
D
1 2 3 4 5

12 12
1st
Floor Key plan – Column Size:
1 2 3 4 5
B
A
C
D

13 13
1st
Floor Key plan – Slab thickness:
B
A
C
D
1 2 3 4 5

14 14
Modeling Framed Structure
Frame:
• Beams & columns are modeled using frame elements
• Each beam and each column is represented by single
frame element (no subdividing by meshing is done)
• Beams and columns are of homogeneous isotropic
elastic material with properties (E, μ) that of concrete –
properties of reinforcement are not considered

15 15
Frame:
• Beam elements are oriented along the centre
line, and columns are modeled using frame
elements

16 16

17 17
Frame:
• Beam elements are oriented along the centre line, and
columns are modeled using frame elements
• Columns are located at the intersection of beams (not
the centre line of the columns)

18 18
Column positions

19 19
Centre of columns
as modeled
Actual centre of
columns
Position of column centre lines

20 20
(Plan view from STAAD, col. Without
offset)

21 21
Frame:
• Beam elements are oriented along the centre line, and
columns are modeled using frame elements
• Columns are located at the intersection of beams (not
the centre line of the columns)
• Columns can later be moved to its actual centre line by
‘offsetting’ it.

22 22
(Plan view from STAAD, col. Without &
With offset)

23 23
Stairs:
Window on mid landing level beam
Window on floor level beam

24 24
Window on mid landing level beam

25 25
Window on floor level beam

26 26
Window on MLL beam Window on FL beam

28
Frame:
• At the points where sub-beams (or secondary beams) connect to
the main-beams (or primary beams), nodes have to be introduced
in the latter by splitting them (though not in ETABS*).
• The bending degree of freedom of the sub-beams are released at
either ends to prevent torsion in the main-beams. (Where sub
beams run continuous over the main beams, only the extreme ends
are released)
* This is because ETABS uses a duel model approach: the one we model is the
‘physical model’. On clicking the Analysis button, ETABS, in background, builds a
an ‘analysis model’ (ie., it’s corresponding Finite Element model) which it uses for
analysis. This model will have the primary beams split and nodes introduced to
connect the secondary beams.

29
Column positions
Bending moment
released at these
points
Moment releases in sub-beams

30 30
Toilets:

31 31
Toilets:
• Toilet slabs are sunk from the floor level (to
accommodate outlet pipes. The portion is then filled
with lean or brick concrete. The depth of sinking is:
• 30 cm for European styled water closets and
• 45 cm for Indian styled water closets
• 20 cm for bath rooms
• The beams separating the sunken slab from floor slabs
should bee deep enough to accommodate the floor slab
as well as the sunken slab
Analysis & Design of an RC Building in STAAD.Pro & ETABS Presented by Rahul Leslie

32
STAAD.Pro & ETABS
One floor in
STAAD.Pro ETABS

34
One floor and columns
STAAD.Pro ETABS

35 35
Supports:
For Shallow Footings and Pile Foundations
Footing Pile

36 36
Supports:
Footing

37 37
Supports:
Pile

38 38
Supports:
• For shallow foundation, plinth beams will be at plinth
level above ground (GL), while support point is located
at founding level below GL.
• For pile foundation, the support point is located at top
of pile cap, which is at a level 30 cm below GL.
• The grade beams will also be at the pile cap level (connecting
support points in the model).
• Thus the GF columns will have a ht. = storey ht. + plinth ht. +
depth of pile cap below GL

39 39
Supports:
Footing Pile

40
Whole structure
STAAD.Pro ETABS

41
Whole structure
STAAD.Pro ETABS

42
Slabs:
• Floor slabs are not structurally modeled – the
load on the slab (its self wt., finishes, live load,
etc.) are applied as 2-way distribution on to its
supporting beams
• In STAAD.Pro this is done by the 2-way
distribution ‘Floor Load’ facility
• In ETABS, this is done by defining a floor object
‘membrane element’ in place of the slab, with loads
on it. The membrane converts it to 2-way
distribution.

43
STAAD.Pro ETABS
Loads applied on frame

44
Coordinate System
Global system
GX
GY
GZ
Rotational directions (MX, MY
and MZ) are defined as:
When looking through the axis to
the origin, anticlockwise is +ve

45
Coordinate System
Local system for beams
GX
GY
GZ
X
Y
Z
X
Y
Z
Rotational directions (MX, MY
and MZ) are defined as:
When looking through the axis
towards origin, anticlockwise is
+ve.
Presented by Rahul Leslie
Rotational directions MY and
MZ are about local Y and Z
Analysis & Design of an RC Building in STAAD.Pro & ETABS

46
Coordinate System
Local system for plates
Rotational directions MX and
MY are along local X and Y
XY
Z
Direction Z is towards
that side from which the
nodes i, j, k, l in order
appear anti-clockwise
k
j
i
l
Direction X is parallel to
i-j, and directed from i
end to j end.
Direction Y is
perpendicular to X
direction, and directed
from j end to k end.

47
Global & Local Coordinate Systems

48
Global & Local Coordinate Systems

49
Coordinate labels in STAAD.Pro & ETABS
As shown in
previous slides
STAAD.Pro ETABS

50
Loading
STAAD.Pro and ETABS have facilities for:-
• Self-weight (Gravity load of elements)
• Nodal loads (eg. Loads of Trusses)
• Beam loading for Uni. Distr. loads, Uni. Vary. loads,
Concentrated loads, etc.

51
Beam Loading
Along local X, Y, Z
(-ve Y shown)
Along global GX, GY,G Z
(-ve GY shown)
Along projected PX, PY, PZ
(-ve GY shown)

52
Slab load on Beams
In addition, almost all packages have facility to distribute
floor loads on to the supporting beams directly (without
modeling the slabs as elements)

53
Slabs:
• RCC Shell roofs (like domes, hyperbolic
parabolas, cylindrical roofs, etc) and pitched
roofs without skeletal beams are modeled using
shell elements
• Flat slabs and flat plates are modeled using
plate elements.

54
Slabs:
For RCC pitched roofs with skeletal beams:
• In STAAD.Pro this is done by a special Floor Load
distribution facility
• In ETABS, this is done by modeled using shell
elements.

55 55
Walls:
• Masonry walls are not modeled, but its weight
applied as a UDL on its supporting beams.
• No deductions are made for window or door
openings, nor additions made for lintels.

56
STAAD.Pro ETABS
Wall loads on beams

57 57
Walls:
• Masonry walls are not modeled, but its weight
applied as a UDL on its supporting beams
• No deductions are made for window or door
openings, nor additions made for lintels
• Shear walls are modeled using plate elements
• Surface elements in STAAD
• Wall elements in ETABS
• Retaining walls cast monolith with the structure
may be modeled using plate elements

58
Stairs:
• Stairs are usually not modeled, instead their
load applied as a UDL on its supporting beams

59
STAAD.Pro ETABS
Stair load applied on model

60 60
Foundation:
• Pile and Raft foundations are modeled as fixed
support.
• Isolated footings are modeled as fixed or
pinned, depending on the SBC & Nature of soil
at founding depth

61
Concrete
• fck = 20 N/mm2
• E = 5000 √(fck) = 22360.68 N/mm2
• Poisson’s ratio = 0.2
• Density = 25 kN/m3
Material Properties

62
Loads
Dead Load (IS:875 part 1):
• Slabs (10 cm) :
• STAAD: 0.1x25+1.25 = 3.75 kN/m2
(SelfWt: 0.1x25=2.5 kN/m2
)
• ETABS : 1.25 kN/m2
• Toilet slabs :
• Indian closet: 0.45x20 = 9 kN/m2
, + SelfWt (for STAAD)
• Euro. closet: 0.3x20 = 6 kN/m2
• Roof slabs : 2.0 kN/m2
• Walls (23 cm brick, with 40 cm beam overhead) :
(3.6 - 0.4)x0.23x20 = 14.72 kN/m
• Sun shade projection (60 cm wide, 7.5 cm average
thickness): 0.6x0.075x25 = 1.13 kN/m

63
Loads
Dead Load:
• Stairs

64
Loads
• Stairs
• Slab wt (concrete) :
• Steps (brick work):
• Finish:
• Total = 5.59 + 1.5 + 0.75 = 7.84 kN/m2
2
22
5.59kN/m25
3.0
3.015.0
2.0 =








×
+
×
2
kN/m5.120
2
15.0
=×
2
kN/m75.05.0
3.0
15.03.0
=×
+

65
Loads
• Stairs
• Total = 5.59 + 1.5 + 0.75 = 7.84 kN/m2
• Load on beams (4.57 m span) = 4.57x7.84/2 = 17.92
kN/m

66
Loads
Live Load (IS:875 part 2):
BUSINESS AND OFFICE BUILDINGS:-
• Office/Conference: 2.5 kN/m2
• Stores: 5 kN/m2
• Dinning: 3 kN/m2
• Toilet: 2 kN/m2
• Corridors/Stairs: 4 kN/m2
• Roof: 1.5 kN/m2

67 67
Loads
• Stairs
• Live Load = 4 kN/m2
• Load on beams (4.57 m span)
= 4x8.59/2 = 17.18 kN/m

68
Loads
• Water tank on slab (5000 lts):
5000 lts = 5 m3
=50 kN
Load = 50/(3.45x1.93) = 7.51 kN/m2

69
Loads
Load Combination for Design
• 1.5 x Dead Load + 1.5 x Live Load
Load Combination for Foundation
• 1.0 x Dead Load + 1.0 x Live Load

70
STAAD.Pro ETABS
Run Analysis

71
STAAD.Pro ETABS
Bending Moment

72
STAAD.Pro ETABS
Shear Force

73
STAAD.Pro ETABS
BM & SF of 2nd
Floor

74
RCC Design
Parameters specified
• Load case used =
1.5 Dead Load + 1.5 Live Load
• Code = IS 456 : 2000
• fck = 20 N/mm2
• fy(main) = 415 N/mm2
• fy(shear) = 415 N/mm2

75
Model with initial cross
sectional dimensions
Run Analysis
and design
Check design
results
Are design
results okay?
Finish
Modify cross sectional
dimensions/Layout
Yes
No
Design cycle for RC Structures

76
STAAD.Pro ETABS
Beam Design Output
Main rein.Shear rein.

77
============================================================================
B E A M N O. 141 D E S I G N R E S U L T S
M20 Fe415 (Main) Fe415 (Sec.)
LENGTH: 4570.0 mm SIZE: 230.0 mm X 400.0 mm COVER: 25.0 mm
SUMMARY OF REINF. AREA (Sq.mm)
----------------------------------------------------------------------------
SECTION 0.0 mm 1142.5 mm 2285.0 mm 3427.5 mm 4570.0 mm
----------------------------------------------------------------------------
TOP 584.24 0.00 0.00 0.00 645.83
REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)
BOTTOM 0.00 173.83 429.94 173.83 0.00
----------------------------------------------------------------------------
============================================================================
----------------------------------------------------------------------------
----------------------------------------------------------------------------
TOP 188.88 173.83 173.83 173.83 173.83
BOTTOM 0.00 0.00 0.00 0.00 0.00
----------------------------------------------------------------------------
Beam Design Output of STAAD.Pro

78 78
============================================================================
----------------------------------------------------------------------------
----------------------------------------------------------------------------
TOP 584.24 0.00 0.00 0.00 645.83
BOTTOM 0.00 173.83 429.94 173.83 0.00
----------------------------------------------------------------------------

79
============================================================================
----------------------------------------------------------------------------
----------------------------------------------------------------------------
TOP 584.24 0.00 0.00 0.00 645.83
BOTTOM 0.00 173.83 429.94 173.83 0.00
----------------------------------------------------------------------------
SUMMARY OF PROVIDED REINF. AREA
----------------------------------------------------------------------------
----------------------------------------------------------------------------
TOP 6-12í 2-12í 2-12í 2-12í 6-12í
REINF. 2 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 2 layer(s)
BOTTOM 2-12í 2-12í 4-12í 2-12í 2-12í
SHEAR 2 legged 8í 2 legged 8í 2 legged 8í 2 legged 8í 2 legged 8í
REINF. @ 120 mm c/c @ 120 mm c/c @ 120 mm c/c @ 120 mm c/c @ 120 mm c/c
----------------------------------------------------------------------------
SHEAR DESIGN RESULTS AT DISTANCE d (EFFECTIVE DEPTH) FROM FACE OF THE SUPPORT
SHEAR DESIGN RESULTS AT 540.0 mm AWAY FROM START SUPPORT
VY = 74.90 MX = -0.90 LD= 3
Provide 2 Legged 8í @ 120 mm c/c
SHEAR DESIGN RESULTS AT 540.0 mm AWAY FROM END SUPPORT
VY = -79.08 MX = -0.90 LD= 3
============================================================================

80
============================================================================
----------------------------------------------------------------------------
----------------------------------------------------------------------------
TOP 584.24 0.00 0.00 0.00 645.83
BOTTOM 0.00 173.83 429.94 173.83 0.00
----------------------------------------------------------------------------
Continued...

81
...Continued
SUMMARY OF PROVIDED REINF. AREA
----------------------------------------------------------------------------
----------------------------------------------------------------------------
TOP 6-12í 2-12í 2-12í 2-12í 6-12í
BOTTOM 2-12í 2-12í 4-12í 2-12í 2-12í
SHEAR 2 legged 8í 2 legged 8í 2 legged 8í 2 legged 8í 2 legged 8í
REINF. @ 120 mm c/c @ 120 mm c/c @ 120 mm c/c @ 120 mm c/c @ 120 mm c/c
----------------------------------------------------------------------------
SHEAR DESIGN RESULTS AT DISTANCE d (EFFECTIVE DEPTH) FROM FACE OF THE SUPPORT
SHEAR DESIGN RESULTS AT 540.0 mm AWAY FROM START SUPPORT
VY = 74.90 MX = -0.90 LD= 3
SHEAR DESIGN RESULTS AT 540.0 mm AWAY FROM END SUPPORT
VY = -79.08 MX = -0.90 LD= 3
============================================================================

82 Presented by Rahul LeslieAnalysis & Design of an RC Building in STAAD.Pro & ETABS

83
Asv/Sv = 0.356
Asv = 2Leg, #8 = 100.53
.:Sv = 100.53 / 0.356 = 282 mm c/c
Provide 2L#8@180 mm c/c

85
Detailing as per SP 34
(Sample beam)

87
Column reinforcement (mm2
):

88
Column Groups:

89
Column Schedule:

90
STAAD.Pro ETABS
Support Reactions

92
SBC = 160 kN/m2

93 93
Footing Design
• Further adjust size of footing considering
support moments
Zz
Mz
Zx
Mx
A
P
p ++
×
=
1.1
SBCp <

94
Provide combined
footing for these
columns

96 96

97 97
Pile Capacity = 750 kN

98 98
Pile Design
• Further check no. of piles, considering support
moments
Iz
dx
Mz
Ix
dz
Mx
n
P
p ii
i ++
×
=
2.1
∑= 2
dzIx
∑= 2
dxIz
.PileCappi <

99 99

101 101
Concluding remarks
• To use a software package, one has to know it
• More importantly, one has to know its limitations,
• Still more important, one has to know its pitfalls.
• Software Demonstrators/Instructors may tell you the
limitations, but not the pitfalls. Mostly it can be learned
only through experience.
• They are also fond of promoting the idea that “The
software does everything; You don’t have to know
anything!”. Please don’t take the software for granted.

102 102
Concluding remarks
• A basic understanding of FEM is desirable (but not
necessary), especially when flat-slabs, shear walls or shell
roofs are included.
• Also one has to know the code provisions, and have them
ready reference (IS:456, SP-34, IS:875 Part-I & II,
IS:1904, IS:2911)
• For seismic design, refer to IS:1893 & IS:13920 and to
include wind forces, refer to IS:875 Part-III.

103 103
To be continued with
Seismic Analysis/Design of Multi-storied RC Buildings using
STAAD.Pro
& ETABSaccording to IS:1893-2002
*
Rahul Leslie
rahul.leslie@gmail.com
* http://www.slideshare.net/rahulleslie/seismic-analysisdesign-of-multistoried-rc-buildings-using-
staadpro-etabs-according-to-is18932002-rahul-leslie

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