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

Modelling Building Frame with

STAAD.Pro & ETABS

Rahul LeslieAssistant Director,Buildings Design,

DRIQ, Kerala PWDTrivandrum, India

Presented by

STAAD.Pro & ETABS

Ground Floor

The example building:

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

First Floor

Storey ht. = 3.6m

Second Floor

Storey ht. = 3.6m

Terrace

Storey ht. = 3.6m

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

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

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.

1 2 3 4 5

1st Floor plan – Centre-to-centre distances (m):

1st Floor Key plan – Beam Size:

1 2 3 4 5

1st Floor Key plan – Column Size:

1 2 3 4 5

1st Floor Key plan – Slab thickness:

1 2 3 4 5

Modeling Framed StructureFrame:

• 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

Modeling Framed Structure

Frame:• Beam elements are oriented along the centre

line, and columns are modeled using frame elements

1616Presented by Rahul LeslieAnalysis & Design of an RC Building in STAAD.Pro & ETABS

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)

Column positions

Centre of columns as modeled

Actual centre of columns

Position of column centre lines

(Plan view from STAAD, col. Without offset)

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.

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

Modeling Framed StructureStairs:

Window on mid landing level beam

Window on floor level beam

Window on mid landing level beam

Window on floor level beam

Window on MLL beam Window on FL beam

Modeling Framed StructureFrame:

• 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.

Column positions

Bending moment released at these points

Moment releases in sub-beams

Modeling Framed StructureToilets:

• 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

STAAD.Pro & ETABSOne floor in

STAAD.Pro ETABS

One floor and columns

STAAD.Pro ETABS

Supports:For Shallow Footings and Pile Foundations

Footing Pile

Footing

• 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

Footing Pile

Whole structure

STAAD.Pro ETABS

Whole structure

STAAD.Pro ETABS

Modeling Framed StructureSlabs:

• 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.

43STAAD.Pro ETABS

Loads applied on frame

Coordinate System

Global system

GZRotational directions (MX, MY and MZ) are defined as:

When looking through the axis to the origin, anticlockwise is +ve

Coordinate System

Local system for beams

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

Coordinate System

Local system for plates

Rotational directions MX and MY are along local X and Y

Direction Z is towards that side from which the nodes i, j, k, l in order appear anti-clockwise

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.

Global & Local Coordinate Systems

Coordinate labels in STAAD.Pro & ETABS

Presented by Rahul Leslie

As shown in previous slides

STAAD.Pro ETABS

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.

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)

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)

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.

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.

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.

56STAAD.Pro ETABS

Wall loads on beams

Modeling Framed StructureWalls:

• 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

Stairs:• Stairs are usually not modeled, instead their

load applied as a UDL on its supporting beams

59STAAD.Pro ETABS

Stair load applied on model

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

Concrete• fck = 20 N/mm2

• E = 5000 √(fck) = 22360.68 N/mm2

• Poisson’s ratio = 0.2• Density = 25 kN/m3

Material Properties

LoadsDead 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, + SelfWt (for STAAD)

• Roof slabs : 2.0 kN/m2, + SelfWt (for STAAD)• 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

LoadsDead Load:

• Stairs

LoadsDead Load (IS:875 part 1):

• Stairs • Slab wt (concrete) :

• Steps (brick work):

• Finish:

• Total = 5.59 + 1.5 + 0.75 = 7.84 kN/m2

5.59kN/m253.0

3.015.02.0

2kN/m5.120215.0

2kN/m75.05.03.0

15.03.0

Dead Load (IS:875 part 1):• 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

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

Live Load (IS:875 part 2):• Stairs

• Live Load = 4 kN/m2

• Load on beams (4.57 m span) = 4x8.59/2 = 17.18

Live Load (IS:875 part 2):• Water tank on slab (5000 lts):

5000 lts = 5 m3 = 50 kNLoad = 50/(3.45x1.93) = 7.51

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

70STAAD.Pro ETABS

Run Analysis

71STAAD.Pro ETABS

Bending Moment

72STAAD.Pro ETABS

Shear Force

73STAAD.Pro ETABS

BM & SF of 2nd Floor

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

Model with initial cross sectional dimensions

Run Analysis and design

Check design results

Are design results okay?

Finish

Modify cross sectional dimensions/Layout

Design cycle for RC Structures

76STAAD.Pro ETABS

Beam Design Output

Main rein.Shear rein.

============================================================================ 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 REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) ----------------------------------------------------------------------------

============================================================================ B E A M N O. 142 D E S I G N R E S U L T S

M20 Fe415 (Main) Fe415 (Sec.) LENGTH: 1930.0 mm SIZE: 230.0 mm X 400.0 mm COVER: 25.0 mm

SUMMARY OF REINF. AREA (Sq.mm)

---------------------------------------------------------------------------- SECTION 0.0 mm 482.5 mm 965.0 mm 1447.5 mm 1930.0 mm ---------------------------------------------------------------------------- TOP 188.88 173.83 173.83 173.83 173.83 REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm)

BOTTOM 0.00 0.00 0.00 0.00 0.00 REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) ----------------------------------------------------------------------------

Beam Design Output of STAAD.Pro

7878Presented by Rahul Leslie

============================================================================ 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 REINF. (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) (Sq. mm) ---------------------------------------------------------------------------- SUMMARY OF PROVIDED REINF. AREA ---------------------------------------------------------------------------- SECTION 0.0 mm 1142.5 mm 2285.0 mm 3427.5 mm 4570.0 mm ---------------------------------------------------------------------------- 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 REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 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 Provide 2 Legged 8í @ 120 mm c/c ============================================================================

Continued...

...Continued

SUMMARY OF PROVIDED REINF. AREA ---------------------------------------------------------------------------- SECTION 0.0 mm 1142.5 mm 2285.0 mm 3427.5 mm 4570.0 mm ---------------------------------------------------------------------------- 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 REINF. 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 1 layer(s) 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 Provide 2 Legged 8í @ 120 mm c/c ============================================================================

Asv/Sv = 0.356Asv = 2Leg, #8 = 100.53.:Sv = 100.53 / 0.356 = 282 mm c/c

Provide 2L#8@180 mm c/c

Detailing as per SP 34(Sample beam)

Column reinforcement (mm2):

Column Groups:

Column Schedule:

90STAAD.Pro ETABS

Support Reactions

SBC = 160 kN/m2

Footing Design

• Further adjust size of footing considering support moments

Provide combined footing for these columns

Pile Capacity = 750 kN

Pile Design

• Further check no. of piles, considering support moments

IzdxMz

IxdzMx

nPp ii

.PileCappi

100100

Concluding remarks

101101

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.

102102

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.

103103

To be continued withSeismic Analysis/Design of Multi-storied RC Buildings using

STAAD.Pro & ETABSaccording to IS:1893-2002

Rahul Leslierahul.leslie@gmail.com

* http://www.slideshare.net/rahulleslie/seismic-analysisdesign-of-multistoried-rc-buildings-using-staadpro-etabs-according-to-is18932002-rahul-leslie

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

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