Design structures mod_27_8_08
- 3. STRUCTURAL CONCEPTS AND SYSTEMS FOR ARCHITECTS & ENGINEERS - T.Y.LIN & S.D.STOTES BURY - JOHN WILLEY & SONS. REINFORCED CONCRETE DESIGNER’S HANDBOOK - CHARLES REYNOLDS & JAMES STEEDMAN - RUPA & CO. HANDBOOK OF CONCRETE ENGINEERING - MARK FINTEL - CBS PUBLISHERS & DISTRIBUTORS
- 4. MULTI-STORY FRAMES – CALCULATION & MOMENT TABLES. - Dr.ENG.F.TAKABEYA - WILHELM ERNST & SONS. PLAIN & REINFORCED CONCRETE – VOL.2 - JAI KRISHNA & O.P.JAIN - NEM CHAND & BROS.
- 5. HANDBOOK ON CONCRETE REINFORCEMENT AND DETAILING – SP34 (S&T) – BIS REINFORCED CONCRETE DETAILER’S MANUAL – B.W.BOUGHTON – ELBS ACI DETAILING MANUAL – AMERICAN CONCRETE INSTITUTE
- 6. REINFORCEMENT DETAILING MANUAL – ROBIN WHITTLE – A VIEW POINT PUBLICATION. REINFORCED CONCRETE STRUCTURES – R.PARK & T.PAULAY – JOHN WILEY & SONS
- 7. REINFORCED CONCRETE STRUCTURAL ELEMENTS - P. PURUSHOTHAMAN - TORSTEEL RESEARCH FOUNDATION IN INDIA. FOUNDATION DESIGN - W.C. TENG - PRENTICE-HALL OF INDIA REINFORCED CONCRETE DESIGN - PILLAI & MENON - TATA MCGRAW-HILL
- 8. Dr.G.S.Suresh 8 Structure resists loads without appreciable deformation Assemblage of individual elements Structural analysis: Determination of forces and displacements Proportioning of members is design Analysis and design are cyclic (Fig. 1.1) 1.1 Introduction:
- 9. Chapter 1 1.1 Introduction contd. Preliminary Design Structural Analysis Compute Stresses and Deformations Is Stresses and Deformations Within Limits And Economical? Revise Section Final Design No Yes Fig.1.1 Cyclic Process of Analysis and Design
- 10. Dr.G.S.Suresh 10 Framed structures and Continuous Structure Framed structure: Buildings, Trusses, Bridges, Transmission towers, Space crafts, Aircrafts Continuous System: Shells, Domes, Plates, Retaining walls, Dams, Cooling towers 1.2 Forms of Structure:
- 11. Dr.G.S.Suresh 11 1.2 Forms of Structure Contd. Framed Structure: Building Frames
- 12. Dr.G.S.Suresh 12 1.2 Forms of Structure Contd. Framed Structure: Bridges
- 13. Dr.G.S.Suresh 13 1.2 Forms of Structure Contd. Framed Structure: Transmission Towers
- 14. Dr.G.S.Suresh 14 1.2 Forms of Structure Contd. Framed Structure: Space Craft
- 15. Dr.G.S.Suresh 15 1.2 Forms of Structure Contd. Framed Structure: Air Crafts
- 16. Dr.G.S.Suresh 16 1.2 Forms of Structure Contd. Continuous Systems: Shells and Domes
- 17. Dr.G.S.Suresh 17 1.2 Forms of Structure Contd. Continuous Systems: Flat Plates
- 18. Dr.G.S.Suresh 18 1.2 Forms of Structure Contd. Continuous Systems: Retaining Wall
- 19. Dr.G.S.Suresh 19 1.2 Forms of Structure Contd. Continuous Systems: Dams
- 20. Dr.G.S.Suresh 20 1.2 Forms of Structure Contd. Continuous Systems: Cooling towers
- 21. Dr.G.S.Suresh 21 Idealization of structure: Single line structure Identifying members as well known individual structural element Idealized as i. Real structure ii. A physical model iii. A Mathematical model 1.2 Forms of Structure Contd.
- 22. Dr.G.S.Suresh 22 Real structures : Are subjected to actual forces Elaborate loading equipment is required Strains and deformations are measured Expensive and time consuming Performed in exceptional cases only 1.2 Forms of Structure Contd.
- 23. Dr.G.S.Suresh 23 LOAD TEST ON REAL STRUCTURES
- 24. Dr.G.S.Suresh 24 Model Study : Scaled down models are used Tested in laboratories Requires special techniques and Expensive Carried out under special circumstances only. Examples: Building frames, Shake table test of bridges and buildings, Photo elastic testing of a dam model, wind tunnel testing of small scale models of high rise buildings, towers and chimneys 1.2 Forms of Structure Contd.
- 25. Dr.G.S.Suresh 25 LOAD TEST ON MODEL
- 26. Dr.G.S.Suresh 26 Mathematical Model : Development of mathematical equations Equations are solved using suitable algorithm Requires electronic computers Process is shown in block diagram of Fig. 1.2 1.2 Forms of Structure Contd.
- 27. Dr.G.S.Suresh 27 1.2 Forms of Structure Mathematical Model Contd. : Actual Structure Idealize Structure Idealize Loads Development of Equations Response of str. Interpretation of Results Fig.1.2 Block Diagram of Mathematical modeling
- 28. Dr.G.S.Suresh 28 Idealized as One dimensional, Two dimensional or Three dimensional structures Example: i) Beams and trusses→ One Dimensional Structures ii) Plates and Shells→ Two Dimensional Structures iii) Dams, Retaining walls→ Three Dimensional Structures 1.2 Forms of Structure: 1D, 2D and 3D structures
- 29. Dr.G.S.Suresh 29 1.2 Forms of Structure: 1D, 2D and 3D structures Fig.1.3 Some Examples of Structures a. Truss b. Plane Frame c. Plate d. Shell e. Dam f. Machine Part
- 30. Dr.G.S.Suresh 30 1.2 Forms of Structure: 1D, 2D and 3D structures a. One Dimensional Model b. Two Dimensional Model c. Three Dimensional Model Fig.1.4 Cantilever Structure Modeling
- 31. Dr.G.S.Suresh 31 Plane frame: Members and forces are in one plane (Fig.1.5a) Space Frames: Members and forces in different planes (Fig.1.5b) Supports are also idealized as 1. Fixed supports (Fig.1.6a) 2. Hinged supports (Fig. 1.6b) 3. Simple or roller supports. (Fig. 1.6c) 1.2 Forms of Structure Contd.
- 32. Dr.G.S.Suresh 32 1.2 Forms of Structure Contd. Fig.1.5 a. Two Dimensional Structures
- 33. Dr.G.S.Suresh 33 1.2 Forms of Structure Contd. Fig.1.5 b. Three Dimensional Structures
- 34. Dr.G.S.Suresh 34 1.2 Forms of Structure Contd. Fig.1.6. Typical Support Conditions a) b) c) Fixed Pinned Roller
- 35. Dr.G.S.Suresh 35 Loads are also required to be idealized Minimum loading guidelines provided by codes and standards Bureau of Indian Standards, Indian Road Congress and Indian Railways have published loading standards in India Loads are idealized as Point loads, line loads or surface loads 1.2 Forms of Structure Contd.
- 37. Dr.G.S.Suresh 37 Forces acting on structure is termed as Loads Static and Dynamic Loads Static Loads: Slowly applied force Dynamic Loads: Suddenly applied force Dynamic force produce fatigue in structures Static force is only considered here Introduction:
- 38. Dr.G.S.Suresh 38 Self Weight Weight of fixed elements in the structure Ex: Floor finish, WPC, Partitions, fixed equipments etc., Can be calculated accuratly Unit weight of material and its volume required Unit weight of materials are given in Part- 1 of IS875-1987 Static Loads: Dead Loads:
- 39. Dr.G.S.Suresh 39 Static Loads: Dead Loads (Contd..) Table 1 Average Density of Materials Material Weight in kg/m3 Material Weight in kg/m3 Metals Earth Aluminum, cast Copper, cast Steel, rolled 2643 8907 7849 Clay, dry Clay, damp Earth, dry Earth, damp 1009 1762 1201-1521 1281-1602 Concrete Plain Light weight Reinforced 2307 1201-1762 2402 Brick 1602-2083 Glass, plate 2579 Cement Plaster 2080
- 40. Dr.G.S.Suresh 40 Table 2 Average Loads of Construction Components Material Load in kN/m2 Material Load in kN/m2 Roofs Walls Mangalore tiles with battens Cement asbestos sheets Country tiles (single) with battens 0.64 0.83 0.69 Burnt clay brick of 230 mm thick Burnt clay brick of 110 mm thick Solid concrete block of 200mm thick Solid concrete block of 150mm thick Solid concrete block of 100mm thick Non load bearing hollow concrete blocks 100 mm thick 4.41 2.205 3.52 2.65 1.765 0.141-0.094 Floors Plain Concrete per 100mm thickness Reinforced Concrete per 100mm thickness Terrazzo paving 10 mm thick 2.2-2.35 2.28-2.65 0.23 Dead Loads (Contd..)
- 41. Dr.G.S.Suresh 41 Does not act at all time Gradually applied load Ex: Occupancy like personal, furniture, stored materials etc. Prediction of exact magnitude and distribution of load is difficult Empirical approach is used Equivalent loads are obtained from statistics Static Loads: Live Loads:
- 42. Dr.G.S.Suresh 42 Design loads correspond to peak load Part 2 of IS875-1987 gives live load for floors and roof Floors: Residential buildings Live load on floors is 2kN/m2 for bed rooms, kitchen, living etc and for toilets, staircase and balconies live load is 3 kN/m2 Roofs: Accessible- 1.5 kN/m2 and Inaccessible- 0.75 kN/m2 For design of columns, load bearing walls, piers, their supports and foundations, the imposed load on floors may be reduced as given in Table 3. Live Loads (Contd..):
- 43. Dr.G.S.Suresh 43 Live Loads (Contd..): Table 3 Reduction in imposed load Number of floors (including the roof) to be carried by member under consideration Reduction in total distributed imposed load on all floors to be carried by the member under considerations (%) 1 0 2 10 3 20 4 30 5 to 10 40 over 10 50
- 44. Dr.G.S.Suresh 44 Depend on elevation, latitude, wind frequency, duration of snow fall, site exposure, roof size, geometry and inclination Weight of snow is about 0.95 to 1.14 N/m2 per mm of snow depth Part 4 of IS 875 -1987 gives snow loads s = so = shape factor, so = snow load on ground Static Loads: Snow Loads:
- 45. Dr.G.S.Suresh 45 Depends on type of slab, ie., One way or two way IF Ly /Lx >2 One way slab otherwise Two way slab Loading on beams from slabs:
- 46. Dr.G.S.Suresh 46 Loading on beams from slabs Contd. : Ly Lx LOAD FROM ONE WAY SLAB
- 47. Dr.G.S.Suresh 47 Loading on beams from slabs Contd. : LOAD IN THIS SHADED AREA TO BE CARRIED BY BEAM B LOAD IN THIS SHADED AREA TO BE CARRIED BY BEAM A B A 45° 45° LOADS FROM TWO WAY SLAB
- 48. Dr.G.S.Suresh 48 Example on Load calculation 4000 4000 4000 4500 4110 3890 3040 4280 4000 4000 4000 B1 B2 B3 B4 B24 B23 B22 B10 B11 B12 B13 B16 B15 LB14 B18 B19 B20 B21 B6 B7 B8 B9 B5 B17 STRUCTURAL LAY OUT
- 49. Dr.G.S.Suresh 49 Body initially at rest continues to remain at rest as loads are applied Dynamic equilibrium is referred to the body under equilibrium during motion In two dimensional space, conditions of equilibrium are: Fx=0 ; Fy=0 ; Mo=0 ---1.1 1.3 Conditions of Equilibrium:
- 50. Dr.G.S.Suresh 50 In three dimensional space, conditions of equilibrium are: Fx=0 ; Fy=0 ; Fz=0; Mx=0 ; My=0 ; Mz=0; Used for determination of Reactions at supports and internal forces 1.3 Conditions of Equilibrium: Contd 1.2
- 51. Dr.G.S.Suresh 51 Externally Determinate Structure: All the unknown forces are computed using only equations of equilibrium (Eq. 1.1 or 1.2) Internally Determinate Structure: All the internal forces are computed using equations of equilibrium (Eq. 1.1 or 1.2) 1.4 Statically Determinate and Indeterminate Structures:
- 52. Dr.G.S.Suresh 52 Members deform due to loads Minimum number of parameters required to describe the deformed shape of structure is Degrees of freedom Displacements and rotations at joints are the parameters At supports, deformations corresponding to a reaction is zero. 1.5 Degrees of Freedom or Kinematic Indeterminacy
- 53. Dr.G.S.Suresh 53 In 2D structures, each rigid joint has 3 displacements (Fig.1.8) In 3D structures, each rigid joint has six displacements Degrees of freedom is a number equal to number of free displacements at joints. 1.5 Degrees of Freedom or Kinematic Indeterminacy Contd. Fig.1.8
- 54. Dr.G.S.Suresh 54 The response of structure is measured by both its displacements and the internal forces that developed due to loads Load-Deformation relation depends on properties of materials If material obeys Hook’s Law then it is a linear structure Principle of super position is applied for linear Structures (Fig. 1.9) 1.6 Linear and Non-Linear Structures
- 55. Dr.G.S.Suresh 55 1.6 Linear and Non-Linear Structures Contd. Fig.1.9 Super Position Principle
- 56. Dr.G.S.Suresh 56 Stress-Strain curve for most of the material is linear for smaller strain values(Fig.1.10) Young’s Modulus is constant for linear portion of the curve In a linear structure, unloading curve follows loading path (Fig.1.11) If the loading induces higher strain value, then E is not constant and structure is called nonlinear structure 1.6 Linear and Non-Linear Structures Contd.
- 57. Dr.G.S.Suresh 57 1.6 Linear and Non-Linear Structures Contd. Fig.1.10 Stress-Strain Graph
- 58. Dr.G.S.Suresh 58 1.6 Linear and Non-Linear Structures Contd. Fig.1.11 Load Path
- 59. Dr.G.S.Suresh 59 Geometrical non linearity occurs due to change in shape of overall structure Example: Cable structure Cantilever beam (Fig.1.12) which is flexible has large displacement due to small loads at free end 1.6 Linear and Non-Linear Structures Contd.
- 60. Dr.G.S.Suresh 60 1.6 Linear and Non-Linear Structures Contd. Fig.1.12 Geometric Nonlinearity
- 62. Dr.G.S.Suresh 62 COMPUTATION OF FORCES AND DISPLACEMENTS DETERMINATE AND INDERMINATE STRUCTURES ONLY EQUILIBRIUM EQUATIONS FOR DETERMINATE STRUCTURES COMPATABILITY IN ADDITION TO EQUATIONS OF EQUALIBRIUM FOR INDETERMINATE STRUCTURES ANALYSIS
- 63. Dr.G.S.Suresh 63 CONSISTENT DEFORMATION METHOD SLOPE DEFLECTION METHOD MOMENT DISTRIBUTION METHOD KANI’S METHOD MATRIX METHOD INDETERMINATE STRUCTURAL ANALYSIS
- 64. Dr.G.S.Suresh 64 STAAD.Pro STRAP NISA SCADS ANSYS LUSAS STRUDS COMPUTER AIDED STRUCTURAL ANALYSIS
- 65. Dr.G.S.Suresh 65 COMPUTER AIDED STRUCTURAL ANALYSIS
- 67. Dr.G.S.Suresh 67 Introduction RCC is a composite material comprising of concrete and steel Concrete is strong in compression and week in tension Steel reinforcing bars are used to take care of tensile stresses.
- 68. Dr.G.S.Suresh 68 Introduction (contd..) Design Procedure Idealization of Structure Estimation of Loads Analysis for Determination of axial thrust, shear, BM and deflections Design of Structural Elements Detailed structural drawings and scheduling of Reinforcing bars
- 69. Dr.G.S.Suresh 69 Philosophies for Design Working Stress Method (1900-1960) Ultimate Load Design (1960-1970) Limit State Design(1970- till date) Most of the codes follow Limit State Design. IS456-2000: LSM as primary method and WSM included in appendix
- 70. Working Stress Method A section is plane before and after bending Materials are assumed to behave as linear elastic Perfect bond between steel and concrete Tensile strength of concrete is ignored Modular ratio = 280/(3*cbc) Stress due to worst combination of load < permissible stress
- 71. Working Stress Method (Contd) d b h Ast NA c st st cbc T C Lever Arm Cross Section Strain Distribution Stress Distribution
- 72. Working Stress Method (Contd) Factor of Safety is used on ultimate strength to obtain permissible stress FS is used to account for uncertainties in materials Stresses due to working loads is less than permissible stress R/Fs> L
- 73. Working Stress Method (Contd) Disadvantages 1. Actual Stress-strain diagram for concrete is non linear 2. Does not account for uncertainties 3. Creep and shrinkage are not accounted
- 74. Ultimate Load Method Uses non linear stress-strain diagram Designed for Ultimate loads. Load factor is used to get ultimate Load Whitney’s theory is popular Rectangular stress block replaces parabolic stress diagram Ultimate strain in concrete is 0.3%
- 75. Ultimate Load Method (Contd) d b h Ast NA cu su cu T C Lever Arm Cross Section Strain Distribution Actual Stress Distribution T Lever Arm C Whitney’s Stress Distribution xu a
- 76. Ultimate Load Method (Contd) Ultimate Load method can be expressed as R>LF * L IS456-1964 specifies that ultimate load as U= 1.5 DL + 2.2 LL (without lateral loads) U= 1.5 DL + 2.2 LL + 0.5 WL or U= 1.5 DL +0.5 LL + 2.2 WL; WL =WL or EL
- 77. Ultimate Load Method (Contd) Advantage 1. Total safety factor is nearer to actual value 2. Reinforcement required is < WSM Disadvantage 1.Load factor is used only on loads 2.No control over deflections
- 78. LIMIT STATE METHOD Probability that a structure will not become unserviceable in its life time Structure should withstand ultimate load and should also satisfy serviceability requirements such as deflection and vibration All relevant limit states must be considered in design
- 79. LIMIT STATE METHOD (Contd) Limit State Collapse Serviceability Flexure, Compression, Shear, Torsion Deflection, Cracking, Vibration
- 80. LIMIT STATE METHOD (Contd) Different theories for different limit states WSM for serviceability limit state Ultimate Load theory for limit state of collapse Stability analysis for overturning Provides unified rational basis
- 81. LIMIT STATE METHOD (Contd) Limit state collapse can be expressed as R > i Li and are partial safety factors < 1 and > 1 Limit State of serviceability is expressed as /l 1/; l= span or length
- 82. LIMIT STATE METHOD (Contd) d b h Ast NA cu sy cu T C Lever Arm Cross Section Strain Distribution Stress Distribution xu 0.46 fck 0.2%
- 83. Dr.G.S.Suresh 83 DETAILING OF RC MEMBERS
- 84. DETAILING DETAILING IS AN ART REQUIRING CREATIVE POWER AS MUCH AS THAT FOR STRUCTURALANALYSIS.
- 85. IN RCC DETAILING ISSUES ADDRESSED ARE: PROTECTION AGAINST CORROSSION - COVER TRANSFER OF FORCE BETWEEN STEEL AND CONCRETE - DEVELOPMENT LENGTH - ANCHORAGE - BEARING - SHEAR SPACING - COMPACTON, AGGREATE SIZE, EMBEDMENTS, CRACK WIDTHS. SPLICING - CHANGE OF BAR SIZE, CHANGE OF DIRECTION OF BAR & LENGTH OF BAR.
- 86. MANY FAILURES OF STRUCTURES ARE ATTRIBUTED TO POOR OR BAD DETAILING.
- 87. DETAILING IS NOTHING BUT PLACEMENT OF REINFORCEMENT IN STRUCTURES. IT INCORPORATES THE WHOLE THOUGHT PROCESS BY WHICH THE DESIGNER ENABLES EACH PART OF THE STRUCTURE TO PERFORM SAFELY AND EFFICIENTLY WHEN SUBJECT TO DESIGN LOADS
- 88. IN ESSENCE, DESIGN IS JUST NOT PROPORTIONING A STRUCTURAL SECTION OR DETERMINING STRESSES. ECONOMY, DURABILITY, EASE OF CONSTRUCTION ARE EQUALLY IMPORTANT ASPECTS, TO BE LOOKED INTO. THIS CAN BE THROUGH APPROPRIATE DETAILING. DETAILING IS BOTH AN ART AND SCIENCE
- 101. CONTINUOUS BEAM INTERMEDIATE SPAN END SPAN
- 112. WELDED SPLICES:
- 117. MECHANICAL SPLICES:
- 122. I. Nominal cover for Durability Exposure Min. cover (mm) Mild Moderate Severe Very severe Extreme 20 30 45 50 75 Notes: 1. Main bars upto 12 mm in mild exposure, cover may by reduced by 5 mm 2. Deviation in cover ±10 mm 3. For ‘severe’ and ‘very severe’ cover may be reduced by 5 mm for concrete M-35 and above Contd/…..
- 123. II. For columns cover not less than 40 mm or bar dia, whichever is more for footings 50 mm. In columns of minimum dimension 200 mm and below bars of dia 12 mm, cover of 25 mm may be used.
- 124. FORCE TRANSFER, INTERNALLY, BETWEEN REINFORCEMENT AND CONCRETE IS DUE TO ANCHORAGE BEARING BOND SHEAR
- 125. DEVELOPMENT LENGTH
- 128.
- 133. STAGGERING OF LAPS:
- 134. L= 1.3 ld L= 1.7 ld L= ld L= 1.3 ld 25 50 75 100 25 50 75 100
- 135. CUMULATIVE TRANSVESE EXPANSION T T T T OVERLAPPING TRANSVERSE EXPANSION TRANSVERSE EXPANSION DOES NOT OVERLAP OVERLAPPING OF TRANSVERSE EXPANSION IS NOT CRITICAL EFFECT OF ADJACENT WHEN DISTANCE BETWEEN SPLICES IS 12 db
- 136.
- 141.
- 142.
- 144. DO’S AND DONTS
- 145. IN CONSTRUCTIONS
- 154. IN DETAILING OF BEAMS
- 170. IN SLABS
- 175. A FEW TIPS FOR DETAILING OF REBARS IN SPECIAL COMPONENTS…
- 181. A FEW CARTOONS….
- 191. STIRUPS
- 192. DE-SHUTTERING
- 194. PROTECTION AGAINST CORROSSION – COVER:
- 198. Dr.G.S.Suresh 198