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Observations on Indian High-Rise Construction | Beam (Structure) | Column
High rise construction in India
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Design Repropping beam 24F
As Hear Connection Extends Its Reach
LEDGE Beam Design
Observations on Indian High Rise Construction
Dr. Joseph Colaco & Vimal Parikh
! Assessing the appropriateness of Indian Codes for Tall Building Design.
! Detailing the use and abuse of ETABS.
! Review of Indian Construction Practices
Comparison of Indian and US Standards Codes and Standards Main Source of Information to Designers of Civil Engineering Structures. Indian Standards - IS 875, IS 1893, IS 456 US Standard - IBC - 2003
! Gravity Loads - Imposed / Live Load ! Lateral Loads Wind Load Seismic Loads
IS 875 - 1987 PART 2 IBC 2003 Table 16 A
SR. NO Item Live Loads as per IS 875 (Part 2) 1987 in KN/m^2 4.0 (With storage) 2.5 (Without storage) 4.0 2.0 3.0 5.0 No Specic Values Live Loads as per IBC 2003 in KN/m^2 2.5 5.0 2.0 5.0 2.5 26.7 KN
Ofce Typical Floor Ofce Corridors
Residential Typical Residential Corridors
Garages Car Bumper Loads
IS 875 - 1987 PART 3 IBC 2003 SECTION 1609 ! (ASCE-7-02 - Section C6.0)
Wind Sway Requirements
IS 875 (Part 3) 1987
IBC 2003 (Section 1609) ASCE 7-02 (Section 6)
Drift Requirements Structural Properties P-Delta Effects Torsion GEF Method
H/500 Not specied (Not clear whether this Generally H/400 limit is applicable for (Under Design Wind Load) Not Specied Cracked Properties Design or Service Wind Load) Not Specied Required to be Included Not Specied ASCE-7-02 (pg.48)
Old & hard to read from ASCE-7-02 based on Latest charts research
Wind Sway Drift Requirements
IS 875 (Part 3) 1987 As per IS 456 - 2000 Sec. 20.5, it shall not exceed H/ 500. (Not clear whether this limit is applicable for Design or Service Wind Load) IBC 2003 (Section 1609) ASCE 7-02 (Section 6) Not specied Generally H/400 (Under Design Wind Load)
Wind Sway Structural Properties Requirements IS 875 (Part 3) 1987
Members with Cracked Structural Properties as per Section 10.10.4.1 of ACI 318 shall be used.
Wind Sway P-Delta Requirements :IS 875 (Part 3) 1987 Not specied IBC 2003 (Section 1609) ASCE 7-02 (Section 6) Required to be included
Wind Sway Torsion Requirements IS 875 (Part 3) 1987 Not specied
ASCE-7-02 (pg.48)
Gust Effect Factor Method (GEF Method) IS 875 (Part 3) 1987
Old & hard to read from charts
ASCE-7-02 based on latest research
IS 1893 2002 IBC 2003 SECTION 1617 ! (ASCE -7-02 - Section C9.0)
IBC 2003 SECTION 1617 (ASCE -7-02 - Section C9.0)
Very old - Leads to Large design forces for Low rise Structures and Smaller Forces for High-rise Structures
Accidental Torsion (Sec. 12.8.4.2) :! Design Eccentricity, ! ! Edi = 0.05 * bi Amplication of Accidental Torsion Moment (Sec. 12.8.4.2) :-
! With max. limit of Ax = 3.0
Vertical Irregularities Weak Story
Vertical Irregularities Weak Story Examples of Weak Story Outrigger Floors MIVAN / TUNNEL FORM Systems Transferred above Ground Floor Major Transfer of Lateral Elements above Ground Floor
Misuse of Shear Wall + Slab Frame System
IS 1893 2002 Misuse of Flat slab as OMRF in Shear Wall + Frame system in high seismic Zone
Table 12.2-1 DESIGN COEFFICIENTS AND FACTORS FOR SEISMIC FORCERESISTING SYSTEMS
NL No Limit NP Not Permitted
Seismic Forces on Cantilever Projections
IS 1893 2002 As per Section 7.12.2.2 it shall be designed and checked for Five times the design vertical coefcient. (= 3.33 * Ah) For Zone III with R=5.0, Factor = 0.0533 W
As per Section 9.5.2.6.4.3 it shall be designed and checked for 0.2 * SDS*W.
For Zone III with R=5.0 Factor = 0.0373 W
IS 1893 2002 As per Section 7.11.1 it shall not exceed 0.004 * Story Height
Drift Limitations are Close
As per Section 1630.9.2 of UBC 97, The Maximum Inelastic Response Displacement, !M, !M = 0.7 * R * !S Where, !S = Storey drift based on Analysis of the structure incl. PDelta Effects
CBM Engineers ANALYSIS OF SAMPLE BUILDINGS FOR BOTH IS & US STANDARDS
Comparison for a Sample Building
A Sample building 65-Story in Mumbai is analyzed for both Indian Standards and IBC- 2006.
Building Data H = 235m Building dimensions - 24.8m x 35.0m Structural System - Ductile Shear wall + OMRF Soil Type - Hard Soil/Rock
Design Data - (As per IS 1893 2002)
! ! ! Total building Weight = 1066314 KN Zone Factor = 0.16 Importance Factor = 1.0 Soil Type = I (Hard Rock) Response reduction Factor = 4.0 Base Dimension, ! Dx = 24.8m ! ! ! ! Dy = 35.0m Code Specied Time Period, Tx = 4.247 sec! ! ! ! ! Ty = 3.575 sec Sa/g,x = 0.235 Sa/g,y = 0.280
SR. NO. 1 ITEM Seismic Base shear, Vx Vy
AS PER INDIAN STANDARDS AS PER US STANDARDS
5332 KN (0.7 times) 5972 KN (0.78 times) 17133 KN 11179 KN
7617 KN 7617 KN 13673 KN 8680 KN 2.926 sec 2.926 sec 0.32m 0.19m 0.288m 0.107m
Wind Shear, Wx Wy Code Specied Time Periods, Tx Ty Displacements @ top, !x EQ
4.253 sec 3.575 sec 0.185m 0.115m 0.368m 0.140m
!y EQ
5 Displacements @ top, !x WIND
!y WIND
Consider the same building 20-Stories tall now - in Mumbai. Analyzed for both Indian Standards and IBC- 2006.
Building Data H = 73m Building dimensions - 24.8m x 35.0m Structural System - Ductile Shear wall + OMRF Soil Type - Hard Soil/Rock
! ! ! Total building Weight = 290076 KN Zone Factor = 0.16 Importance Factor = 1.0 Soil Type = I (Hard Rock) Response reduction Factor = 4.0 Base Dimension, ! Dx = 24.8m ! ! ! ! Dy = 35.0m Code Specied Time Period, Tx = 1.32 sec! ! ! ! ! Ty = 1.11 sec Sa/g,x = 0.76 Sa/g,y = 0.90
SR. NO. 1 ITEM Seismic Base shear, Vx Vy AS PER INDIAN STANDARDS AS PER US STANDARDS
4409 KN (2.13 times) 5221 KN (2.52 times) 3186 KN 2046 KN
2071KN 2071 KN 2919 KN 1860 KN 2.926 sec 2.926 sec 0.011m 0.0077m 0.0097m 0.0039m
1.32 sec 1.11 sec 0.026m 0.017m 0.01m 0.0042m
Design Load Factors and Combinations
IS 875 Part 5, IS 456 IBC 2003 SECTION
1.5 D + 1.5 L 1.5 D +1.5 (W or E) 1.2 D +1.2 L + 1.2(W or E) 0.9D 1.5(W or E) 1.2 D + 1.6 L 1.2 D + (1.3 W or 1.0 E) 1.2 D + 0.5 L+ (1.3 W or 1.0E) 0.9D (1.3W or 1.0E)
Design Load For a Sample Residential Building
SR. NO 1 2 3 4 5 6 ITEM INDIAN STANDARD (KN/m2) 5.0 1.5 0.5 2.5 2.0 2.0 11.5 2.0 1.5 DL + 1.5 LL 20.25 (1.66 times) US STANDARD (KN/m2) 5.0 1.0 0.5 1.0 -2.0 7.5 2.0 1.2 DL + 1.6 LL 12.2
Self wt. of Slab (200mm thk.) Floor Finish Ceiling & Mechanical Partition Walls Sunk Areas Live Load Total DL Total LL Ultimate LC TOTAL (Ultimate)
IS 875 Part 5, IS 456
IS 456 Table 20
ACI - 318 05, Section 11.7.5-------0.2* fc or 5.52 N/mm^2(max.) Concrete Grade ! N/mm^2 M15! 3.0 M20! 4.0 M25! 5.0 M30! 5.52 M35! 5.52 M40 5.52
The values given above include a " factor of 0.75
Design of Post Tensioned Concrete
AISC Manual Chapter I
No Provisions available
Complete Procedure for Design of Composite Members
Other Analysis/Design Issues
Outrigger Floors
- Differential Axial Shortening
- Closeness or Combination of Torsional and Lateral Modes
Detailing the Use and Abuse of ETABS Analysis
Over Estimation of Dead & Live Loads due to Common/ Overlapping areas of Beams & Columns with Slabs.
COMPARISION OF LOADS - 3 STORY BUILDING
A 3-Story RCC building of 6.0m x 5.0m modeled in ETABS! Story Height = 3.0m Beam Size = 230mm x 300mm Column Size = 300mm x 300mm Slab Thickness = 120mm SDL = 1.5 KN/m^2 LL = 2.0 KN/m^2 Unit Weight of Concrete = 25 KN/m^3
COMPARISION OF 3 STORY BUILDING
Item Self Weight of Slab Self Weight of Columns Self Weight of Beams Total Dead Load ETABS results (KN) 1080.00 182.25 341.55 1603.8 MANUAL results (KN) 990.82 182.25 322.92 1495.99
Dead Load is over estimated by 7 % If Partition Walls are present, Uniform SDL & LL will also be Over Estimated by the Program. Dead Loads and Live Loads may be Over Estimated up to 20 % Depending Upon the Geometry of the Building.
BRACED FRAME STRUCTURE WITH RIGID DIAPHRAGM UNDER LATERAL LOAD
ZERO AXIAL LOADS in Beams since there is no relative displacement of end nodes of beams.
BRACED FRAME STRUCTURE WITH RIGID DIAPHRAGM UNDER LATERAL LOAD SOLUTION Release one node of the beam from the Rigid Diaphragm. Provide Semi-rigid Diaphragm - Parametric study with diaphragm exibility required to obtain correct amount of axial force.
CRACKED PROPERTIES OF COUPLED SHEARWALL
CAN NOT BE MODELED ACCURATELY due to inherent
CRACKED PROPERTIES OF COUPLED SHEARWALL ACI 318-05 Provisions
CRACKED PROPERTIES OF COUPLED SHEARWALL CORRECT WAY TO MODEL Reduce both Axial Area and Moment of Inertia. Add a Frame Element with only with missing axial area and Zero Moment of Inertia ( Like a Column).
INCORRECT DESIGN OF COLUMNS WITH SMALL AXIAL LOAD ETABS Column Design module for ACI-318 does not check it correctly when Ultimate axial load (phi * Pn) < (0.10 * fc * Ag) where: phi = Strength Reduction Factor Pn = Nominal Axial Load Strength fc' = Compressive Strength of Concrete Ag = Gross Area of Section The design shall be done like a flexural member (like a beam)
MODELING AND ANALYSIS IN ETABS
TYPES OF ELEMENTS MEMBRANE Use only when In-plane stiffness properties of member are desired. PLATE Use only when Out-of-plane bending stiffness properties of member are desired. SHELL Use when both In-plane and Out-of-plane stiffness properties of member are desired.
LOAD TRANSFER FOR FLOOR AND RAMP SLAB Simple RC Solid Slab. By default modeled as 2-way slab. Can also be modeled as 1-way slab. DECK Used as 1-way load Transfer. Metallic Composite Slab. Filled Deck, Unlled Deck & Solid Slab Deck. PLANK By default use 1-way load transfer mechanism. Generally used to model pre-cast slabs. Can also be a simple RC solid slab.
ELEMENT USED FOR WALLS
Walls can be modeled with membrane or shell elements depending on the desired type of behavior.
Shell type of elements are generally recommended.
AT BASE For Typical RCC building, it is FIXED - All translational and rotational degrees of freedom are restrained. AT GROUND FLOOR Restrained in both Horizontal directions to account for the lateral restraint provided by Basement walls.
Not Providing the restraint at the ground level will result in A Fictitious Structure that is more Flexible. Over design of Foundation Structure. May Result in Under Design of Basement Walls.
Appropriate Modeling Technique shall be used for Outrigger Floors. A Separate Sequential Analysis Required for Axial Shortening and Transfer of Forces. Appropriate Cracking Coefcient shall be used.
MODELING OF MAJOR TRANSFER ELEMENTS
Appropriate Modeling Technique shall be used to Account for Arching Action and Flow of Forces. A Separate Sequential Analysis required for Gravity Loads. Appropriate Cracking Coefcient shall be used.
P-Delta Analysis For Lateral and Torsional Deections. Temperature and Creep/Shrinkage Analysis. Construction Sequence Analysis for Correct Force transfer and Design of Structural Elements.
Column/Wall Axial Shortening Analysis and Column/ Wall Height Adjustments for Floor Levelness Especially For Tall structures. Performance Based Design and Non-Linear Analysis.
REVIEW OF INDIAN CONSTRUCTION PRACTICES
Overall Dead Load of Structure
Structures in India ~ 25 KN/m^2 Structures in the US ~ 11 KN/m^2
Heavy Partition Load Brick Partitions. Screed of 50-100 mm is commonly used. Heavy Water Proong Load.
Impact on Seismic Loads, Structure and Foundations.
Review of Indian Construction Practices Sunk Slabs at Toilets, Decks
Structurally Challenging. Does not Allow the use of Certain Types of Framing Systems such as Post-Tensioning, Flat Slabs. Difcult for Construction Complicated Formwork. More Cost and Time for Construction.
Review of Indian Construction Practices Suggestions/Recommendations
Try to Reduce Overall Weight of Structure. Use of Light Weight Partitions Reduction in Wall Weight up to 50% with Siporex, AAC blocks, Gypsum Walls. Elimination of Screed Especially in garages. Elimination of Sunk Slabs.
Lower Weight results in - Lower Design Seismic Loads. - Lighter Structure. - Reduction in Foundation Sizes and Cost. Elimination of Sunk Areas - Easier Construction. - Easy Formwork System. - Flat Slabs and Use of PT Systems Possible. - Saves Cost and Time.
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