Earthquake resistant analysis and design of multistoried building

Earthquake Resistant Analysis and Design of Multistoried Building

1. Seismic Analysis and Design of Multistoried RCC Building Prepared by : Amrit B aral (072/BCE/009) Amrit S ubedi (O72/BCE/010) Anup Adhikari (072/BCE/016) Bed p. Neupane (072/BCE/022)

2. Objectives The Objectives of the Project are :- Identification of structural arrangement of plan Modelling of building for structural analysis Detailed structural analysis using ETABS Design of structural components To g et real life experience with engineering practices

3. Background Civilization Masonry and RCC building Earthquake resistant building

4. Literature Review Nepal National Building Code(NBC 000-1994) Indian Standard (IS) codes Bureau of Indian Standards Special Publication (SP) Resources from National Information Center of Earthquake Engineering(NICEE),Kanpur ,India Textbooks on RCC Design ,Earthquake Engineering and other books Old Reports on the same subject

5. Methodology Planning Phase Functional Planning Structural Planning Load Assessment Gravity Load Lateral Load

6. Methodology Contd … Preliminary Design Slab Beam Column Idealization of structure Idealization of support Idealization of load Idealization of structural system

7. Methodology Contd … Design and Detailing Design Philosophy Limit State Method of Design for RCC structures Detailing Principle for RCC structures Codal References Drawings

8. Earthquake Resistant Building Earthquake-resistant b uilding designed to prevent total collapse, preserve life, and minimize damage in case of an earthquake or tremor. Earthquakes exert lateral as well as vertical forces, and a structure’s response to their random, often sudden motions is a complex task that is just beginning to be understood. Earthquake-resistant structures absorb and dissipate seismically induced motion through a combination of means: damping decreases the amplitude of oscillations of a vibrating structure, while ductile materials (e.g., steel) can withstand considerable inelastic deformation.

9. Earthquake Resistant Building The objective of earthquake resistant building is to protect the structure during vibration from collapsing and the major feature to ensure in such a construction is the ductility . In the case of designing the Earthquake Resistant Building we are here using IS 1893:2002.

10. Design philosophy of earthquake resistant designs Under minor but frequent shaking, the main members of the buildings that carry vertical and horizontal forces should not be damaged; however buildings parts that do not carry load may sustain repairable damage . Under moderate but occasional shaking, the main members may sustain repairable damage, while the other parts that do not carry load may sustain repairable damage. Under strong but rare shaking, the main members  may sustain severe damage, but the building should not collapse.

11. Concepts of reducing the effect of earthquake 1)Ductility Ductility is a kind of deformation . Ductility can be defined as the “ability of material to undergo large deformations without rupture before failure ”. Ductility in concrete is defined by the percentage of steel reinforcement with in it. Mild steel is an example of a ductile material that can be bent and twisted without rupture.

12. Concepts of reducing the effect of earthquake Contd … Each design code recognizes the importance of ductility in design because if a structure is ductile it ability to absorb energy without critical failure increases. Ductility behavior allows a structure to undergo large plastic deformations with little decrease in strength.

13. Concepts of reducing the effect of earthquake Contd … SIGNIFICANCE OF DUCTILITY If ductile members are used to form a structure, the structure can undergo large deformations before failure. This is beneficial to the users of the structures, as in case of overloading, if the structure is to collapse, it will undergo large deformations before failure and thus provides warning to the occupants. This gives a notice to the occupants and provides sufficient time for taking preventive measures. This will reduce loss of life.

14. Concepts of reducing the effect of earthquake Contd … 2. Strong Column-Weak Beam In multistory reinforced concrete buildings it is desirable to dissipate earthquake induced energy by yielding of the beams rather than the columns. The columns are responsible from overall strength and stability of the structure, with severe consequences of failure.

15. Concepts of reducing the effect of earthquake Contd … Furthermore , columns are compression members and axial compression reduces the ductility of reinforced concrete columns, thus necessitating more stringent confinement reinforcement. Therefore , it is preferable to control inelasticity in columns, to the extent possible, while dissipating most of the energy through yielding of the beams. This is known as the “strong-column weak-beam concept.

16. Concepts of reducing the effect of earthquake Contd … 3. Building configuration The behavior of building during earthquakes depends critically on its overall shape, size and geometry. Hence , at planning stage itself, architects and structural engineers must work together to ensure that the unfavorable features are avoided and a good building configuration is chosen. B oth shape and structural system work together to make the structure a marvel.

17. Size of building In tall buildings with large weight-to-base size ratio the horizontal movement of the floors during ground shaking is large. In short but very long buildings, the damaging effects during earthquake shaking are many. And , in buildings with large plan area, the horizontal seismic forces can be excessive to be carried by columns and walls.

18. Horizontal Layout of Buildings Buildings with simple geometry in plan perform well during strong earthquakes. Buildings with re-entrant corners, like U, V, H and + shaped in plan sustain significant damage. The bad effects of these interior corners in the plan of buildings are avoided by making the buildings in two parts by using a separation joint at the junction.

19. Vertical Layout of Buildings Earthquake forces developed at different floor levels in a building need to be brought down along the height to the ground by the shortest path, any deviation or discontinuity in this load transfer path results in poor performance of building. Buildings with vertical setbacks cause a sudden jump in earthquake forces at the level of discontinuity.

20. Adjacency of Buildings When two buildings are close to each other, they may pound on each other during strong shaking . When building heights do not match the roof of the shorter building may pound at the mid- height of the column of the taller one; this can be very dangerous.

21. Functional A nd Structural P lanning Functional Planning  It is a prerequisite of any type of building Functional planning of the building is governed by the client requirement, site conditions, provincial by-laws,

22. Functional And Structural Planning Contd … Planning of Space and Facilities The layout of the building plan was prepared and finalized as per client requirements For vertical mobility, dog legged staircase are provided.   Prefabricated Capsule type elevators were provided in the left part of the building Washroom for ladies and gents are provided centrally in each floor at four different location of the building

23. Functional And Structural Planning Contd … 2.Architectural planning of 3D framework of Building For reinforced concrete frames, a grid layout of beams is made considering the above functional variables. In most of grid intersection points, columns are placed. This framework for each floor is then utilized with positioning of masonry wall between the columns Arrangement of beams is done along the grid interconnecting the columns at grid intersections. With this framework of beam and column having RCC slab in the floor and roof, architectural planning of the building is complete and 3D framework is thus complete

24. Functional And Structural Planning Contd …

25. Functional And Structural Planning Contd … Structural Planning Structural System structural orientation of the building in horizontal and vertical plane avoiding irregularities mentioned in IS 1893 (part 1):2002. The following types of irregularities mentioned in Table 4 & 5 of IS 1893 (part 1):2002 should be avoided

26. Functional And Structural Planning Contd … Plan Irregularities Torsion Irregularity Re-entrant corners Diaphragm Discontinuity Out of plane Offsets Non-parallel Systems Vertical Irregularities Stiffness Irregularity –Soft Storey Mass irregularity Vertical Geometric Irregularity In-plane discontinuity in vertical elements resisting lateral force

27. Torsion Irregularity To be considered when floor diaphragms are rigid in their own plan in relation to the vertical structural elements that resist the lateral forces. Torsional irregularity to be considered to exist when the maximum storey drift, computed with design eccentricity, at one end of the structures transverse to an axis is more than 1.2 times the average of the storey drifts at the two ends of the structure

28. Re-entrant corners Plan configurations of a structure and its lateral force resisting system contain re-entrant corners, where both projections of the structure beyond the re-entrant corner are greater than 15 percent of its plan dimension in the given direction

29. Diaphragm Discontinuity Diaphragms with abrupt discontinuities or variations in stiffness, including those having cut-out or open areas greater than 50 percent of the gross enclosed diaphragm area, or changes in effective diaphragm stiffness of more than 50 percent from one storey to the next

30. Out of plane Offsets Discontinuities in a lateral force resistance path, such as out-of-plane offsets of vertical elements.

31. Non-parallel Systems The vertical elements resisting the lateral force are not parallel to or symmetric about the major orthogonal axes or the lateral force resisting elements.

32. Stiffness Irregularity (soft storey ) A soft storey is one in which the lateral stiffness is less than 70% of that in the storey above or less than 80% of the average of the stiffness of the three storeys above.

33. Mass irregularity Mass irregularity shall be considered to exist where the seismic weight of any storey is more than 200 percent of that of its adjacent storeys . The irregularity need not be considered in case of roofs .

34. Vertical Geometric Irregularity Vertical geometric irregularity shall be considered to exist where the horizontal dimension of the lateral force resisting system in any storey is more than 150 percent of that in its adjacent storey

35. In-plane discontinuity in vertical elements resisting lateral force A in-plane offset of the lateral force resisting elements greater than the length of those elements

36. Load Assessment And Preliminary Design Load Assessment Assessment of loads on the structural system thus planned is based on IS 875(part I-V):1987 Gravity Load Assessment The gravity loads on the building are derived from IS 875 (part I) dead loads and IS 875 (part II) imposed loads. Total seismic weight of building is found out

37. Load Assessment And Preliminary Design Load Assessment Gravity load assessment I Lateral Load Assessment S 875(part II ) for imposed loads

38. Load Assessment And Preliminary Design Contd … Lateral Load Assessment Earthquake Load on Super Structures According to IS 1893(part-I) : 2002 Theory of Base Shear Calculation

39. Theory of Base Shear Calculation Theory of Base Shear Calculation According to IS 1893 (Part I): 2002 Cl. No. 6.4.2 the design horizontal seismic coefficient A h for a structure is, Where , Z = Zone factor given by IS 1893 (Part I): 2002 Table 2, Here for Zone V Z=0.36 I = Importance Factor, I = 1.5 for assembly building R = Response reduction factor given by IS 1893 (Part I): 2002 Table 7, R = 5.0 Average response acceleration coefficient which depends on approximate fundamental natural period of vibration (Ta).  

40. Theory of Base Shear Calculation C ontd … Vs Time period  

41. Theory of Base Shear Calculation Contd … Base Shear, Where ,W= Seismic Weight of building According to IS 1893 (Part I): 2002 Cl. No. 7.7.1 the design base shear (V B ) computed above shall be distributed along the height of the building as Where , Q i = Design lateral force at floor i W i = Seismic Weight of floor i h i = Height of floor i measured from base n=No. of stories in the building  

42. Theory of Base Shear Calculation Contd …

43. Load Assessment And Preliminary Design Contd … Preliminary design of RCC elements SLAB 127 mm thick spanning in two directions. BEAM = 254mm x 355mm – Primary beam 220mm x 290mm-Secondary beam COLUMN 650mm square sections.

44. Drift Calculation Lateral (story) drift is the amount of sidesway between two adjacent stories of a building caused by lateral (wind and seismic) loads . Should not exceed 0.004 times the floor height.

45. Load path from the structure  slab to the ground

46. Design and detailing Design of slab Design of beam Design of column Design of staircase Design of footing Design of basement wall

47. Design of Slab Types of Slab One way Two way If L y /L x < 2, two way slab L y /L x < 2, One way slab Where L y & L x are the larger and smaller dimension of slab

48. Design of Slab Contd … One way Slab Two way slab

49. Two way slab Slabs are considered as divided in each direction into middle strips and edge Moments for each strips are calculated by using this expression M x = α x wl x 2 M y = α y wl x 2

50. Design of Slab Contd … Design Steps Calculation of thickness Calculated from deflection control criteria αβγδλ Acc. to IS 456: 2000 Cl. 23.2 Thickness=127mm Calculation of effective calculation Effective span of the slab is taken as minimum of C/C distance of the slab or clear span + effective depth of the slab for x- and y- direction separately  

51. Design of Slab Contd … Calculation of design Moment Maximum Negative Moment ( M x – ) = α x - ×w f ×l x 2 Maximum Positive Moment ( M x + ) = α x + ×w f ×l x 2 Design of Negative and Positive Reinforcement Both direction 8 mm Ø bars c/c 250mm  

52. Design of Slab Contd … Check for Shear Maximum shear force intensity in either direction can be taken as where l x is clear short span. Nominal shear stress ( τ v ) = Percentage of steel P t = ( A st , provided / bD ) ×100 From Table 19 IS 456:2000 Permissible shear stress ( τ c ’ ) = k× τ c from Clause 40.2.1.1 of IS 456 k I s founded for slab thickness Table 20 of IS 456; τ c , max = 3.1 N/mm 2 (for M25)  

53. Design of Slab Contd … Check for Development Length The development length ( L d ) is given by (IS 456: 2000, Cl. 26.2) ; L d = Also from IS 456:2000 Cl. 26.2.3.3 L d ≤ + l Here M l = moment of resistant of the section assuming all the reinforcement at the section to be stressed to f d . Corner Reinforcement: Area of each layer of reinforcement = 75% of area of the total reinforcement provided.  

54. Design of Beam Beams are a structural members assigned to transmit the loads from slab to the column through it. There are three types of reinforced concrete beams: Singly reinforced beams Doubly reinforced beams Singly or doubly reinforced flanged beams

55. Design of Beam Contd … In singly reinforced simply supported beams, reinforcements are placed at the bottom of the beam A doubly reinforced concrete beams are reinforced in both compression and tension regions. A complete design of beam involves consideration of safety under ultimate limit state in flexure, shear , torsion serviceability limit states of deflection, crack width, durability.

56. Design of Beam Contd … Design Steps Check for member size According to, IS13920:1993 cl.6.1.3 and cl.6.1.2 Breadth/Depth>0.3 Clear span/Depth>4 Check for limiting longitudinal Reinforcement Acc. To IS13920:1993, cl.6.2.1b A st,min = Acc. To IS13920:1993, cl.6.2.2 Max. Reinforcement, A st,max = 0.025BD  

57. Design of Beam Contd … Design for flexure According to IS 456:2000 Cl. 41.4.2 . M ulim =0.1336f ck bd 2 for Fe500. Calculation of Positive and Negative Reinforcement By calculating by using and Using these values in SP 16 table 55 for Fe500 and M25 Using these values in SP 16 table 16 for Fe500 and M20 Calculation of tensile and compression reinforcement  

58. Design of Beam Contd … Check for shear Maximum shear force intensity in either direction are taken from ETABS Analysis. Nominal shear stress ( τ v ) = Percentage of steel P t = ( A st , provided / bD ) ×100 From Table 19 IS 456:2000 Permissible shear stress ( τ c ’ ) = k× τ c from Clause 40.2.1.1 of IS 456 k i s founded for slab thickness Table 20 of IS 456 ; τ c , max = 3.1 N/mm 2 (for M25)  

59. Design of Beam Contd … Design shear strength of concrete= τ c bd For each end Equivalent shear force is calculated Using 4-legged 8mm dia stirrups. Calculation of spacing of stirrups is done acc to IS 456:2000 Cl. 40.4 by using this expression S v = Providing two 2L- 8dia stirrups @100c/c Providing two 2L- 8dia stirrups @ 150c/c  

60. Design of Column Design Steps Calculation of the Influence Area of the Columns The Influence Area of a column is the area of which load is being transferred to the column to be designed for . Calculation of the Loads Coming on Columns from the Influence Area The Loads acting are broadly classified as Dead Load (DL) and Live Load (LL). Dead Loads are the load of objects which cannot be moved from on place to another like the loads of Brick Work, Beams, Slabs etc. and the Live Loads The Factor of Safety for Dead Load + Live Load Combination is 1.5

61. Design of C olumn Contd … According to I.S.: 456-2000, The Ultimate Load of biaxially loadedColumn is given by, P u  = 0.4.f ck .A c  + 0.67.f y .A sc     Where, P u  = Ultimate Load of the Column in N/mm 2               f ck = Yield Strength of Concrete in N/mm 2               A c  = Area of Concrete (Cross-Sectional Area) of Column in mm 2               f y   = Yield Strength Of Steel in N/mm 2              A sc  = Area of Steel (Cross-Sectional Area) in Column in mm 2

62. Design of Column Contd … 3. Check For Long/Short Columns Effective Length /Least Lateral Dimension>12,Long Column Effective Length /Least Lateral Dimension<12 Short Column A short column mainly fails by direct compression and has a lesser chance of failure by buckling All are short column

63. Design of Column Contd … Check For Eccentricity Check For Eccentricity The eccentric load cause the column to bend towards the eccentricity of the loading and hence generates a bending moment in the column .

64. Design of Column Contd … IS 456-2000 says, the eccentricity which we have to consider for design must be taken as the greater of the followings :- i ) 20mm. ii) ( l ef /500) +b/30) Where, ( l ef = Effective Length of the Column b = Lateral Dimension of the Column Permissible Eccentricity:- 0.05b where b is the dimension of a side of a column

65. Design of Column Contd … Calculating The Area Of Steel Required Area of Steel Required A sc   is to be calculated from the A g  as the predetermined percentage of A g . Determining The Diameter and Spacing Of The Lateral Ties Determine the Diameter and the Spacing of the Lateral Ties The Diameter of the Ties shall not be lesser than the Greatest of the following two values   5mm   1/4 th  of the Diameter of the Largest Diameter Bar

66. Design of Column Contd … The Spacing of Ties shall not exceed the least of the followings three values  Least Lateral Dimension  16 Times of the Diameter of the Smallest Diameter Longitudinal Bar  48 Times of the Diameter of Ties Check <1  

67. DESIGN OF STAIRCASE M eans of access between the various floors staircases may be classified largely into two categories, depending on the predominant direction in which the slab component of the stair undergoes flexure: Stair slab spanning transversely (stair widthwise) Stair slab spanning longitudinally (along the incline)

68. Design of Staircase Contd … General consideration Between consecutive floors there should be an equal rise and going for every parallel step. Should have at least 2m headroom. The sum of going of single step plus twice the rise should be between 550-700mm. The rise of step should not be about more than 200mm and going not less than 240 mm. The pitch should not be more than about 38 .

69. Design of Staircase Contd … Known data Floor height= 4m No of flight=2 No of riser in each flight = 13 No of tread in each flight = 12 Length of riser =150mm Length of Tread = 300mm Nosing = 20mm Going =280mm

70. Design of Staircase Contd … Design Steps THICKNESS OF WAIST SLAB,W = 30 Load calculation Dead Load = (WB+ ) 25 + Floor Finish Design Load 1.5(DL+LL ) Calculation of bending moment M u =  

71. Design of Staircase Contd … Checking depth d= Area of steel A st =  

72. Design of Staircase Contd … Distribution steel 12% of gross area Check for Shear V= =V/ bd Check for deflection  

73. Design of Foundation Introduction Substructure which interfaces the superstructure and the supporting ground. Transfers loads from the superstructure to the soil safely. Foundation must not settle sufficiently. 

74. Types of foundation

75. Design of Footing Contd … Selection of appropriate footing is governed by following major factors: Soil strata Bearing capacity of soil Type of structure Type of load Permissible differential settlement Economy

76. Design of Footing Contd … Raft foundation Raft foundation is done due to load transmitted by the columns in a structure are so heavy allowable soil pressure so small that individuals footing would either overlap or cover more than about one half of the area

77. Design of Footing Contd … Design Steps Known data: Size of column = 650 mm X 650 mm Strength of concrete = M25 Grade of steel = Fe500 Allowable Bearing capacity of soil = 120 KN/m 2 Vertical load, P = 41660.5 KN  

78. Design of Footing Contd … Foundation Type Selection Area occupied by isolated footing is greater than 50% of plan area. Determination of C.G. of column load on footing : For Load Combination1.5 (DL+LL ), Data taken from EATBS

79. Design of Footing Contd … Determination of C.G. of column load on footing: For Load Combination1.5 (DL+LL), Data taken from EATBS

80. Design of Footing Contd … Eccentricity Calculation Difference between geometric C.G. of Mat and C.G. of Column load e x =0.3169m e y =-0.1226m Load to Area ratio check P/A<SBC

81. Design of Footing Contd … Calculation of soil pressure Soil pressure at different points is given by σ s = (P/A)±(M y / I y )×X ±( M x /I x ) × Y Calculation of Bending Moment M oment = wl 2 /10 Taken maximum moment from both direction

82. Design of Footing Contd … Calculation of depth of foundation: Calculation of depth at the position of all column Taken maximum depth Two way shear consideration Reinforcement is given by As per IS 456 : 2000 ANNEX G-1.1 b Moment= ) Minimum reinforcement in slab =0.12% of total cross-section as per IS 456 : 2000 CL 26.5.2.1  

83. Design of Footing Contd … Calculation of spacing of bars Calculation of Development length As per (IS456 : 2000 Cl. 26.2.1 ) L d = (0.87×f y ×φ)/ (4×Ԏ bd ) From IS456:2000Cl. 26.2.3.3.c Ld≤1.3M/ V+Lo Lo=12Ф or d whichever is greater

84. Design of Footing Contd … Summary of Design of the Mat Foundation S t r i p s Bot t o m R e i nf o rc e me n t Top R e i nf o rceme n t   Di a met e r S p ac ing Di a met e r S p ac ing X- direction 16 mm 100 mm 16 mm 100 mm Y- direction 16 mm 120 mm 16 mm 120 mm

85. Design of Basement W all Basement wall is constructed to retain the earth and to prevent moisture from seeping into the building. Since the basement wall is supported by the mat foundation, the stability is ensured Design of the basement wall is limited to the safe design of vertical stem.

86. Design of Basement Wall Contd … Design Constants Earth height(h) =8 m unit weight of soil, γ = 17 KN/m3 Angle of internal friction of the soil, ө = 30 ֯ Safe bearing capacity of soil , q s = 120 KN/m2 Moment calculation Lateral load due to soil pressure, Pa = Ka 3 γ sat h Characteristic Bending moment at the base of wall can be calculated as Mx =Pa  

87. Design of Basement Wall Contd … Design of section Bending moment, M=0.133fckbd2 Design of main reinforcement Check for minimum reinforcement and max. diameter Ast,min =0.0015*b*D Maximum diameter of bar = D/8  

88. Design of Basement Wall Contd … Calculation of horizontal reinforcement Minimum reinforcement required=0.0025*D*h Check for shear V=WL/3 Nominal shear stress=V/ bd Permissible shear stress from IS 456:2000,Table-19 Check.

89. THANK YOU!!!