Codal Practices Rcc Design Part b Design by vkmehta

CODAL PRACTICES FOR CIVIL ENGINEERS

PART B :DESIGN ASPECTS

DESIGN CRITERIA 

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PROJECT SPECIFIC DESIGN BASIS. 

LOCAL CONDITION AND SITE SPECIFIC DATA

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SPECIAL CONSIDERATIONS.

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DESIGN REQUIREMENTS

STANDARD GUIDES AND SPECIFICATIONS.

DESIGN CONSIDERATION SAFETY AND SERVICEABILITY REQUIREMENT LIMIT STATE DESIGN AS PER IS 456-2000 

STRUCTURES ARE DESIGNED TO WITHSTAND SAFELY ALL LOADS LIABLE TO ACT ON THE STRUCTURE AND IN ADDITION SATISFY THE SERVICEABILITY REQUIREMENTS OF DEFLECTION AND CRACKING.

DESIGN CONSIDERATIO CONSIDERATION N 

LIMIT STATE OF COLLAPSE

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THE STRUCTURE SHALL BE DESIGNED AND CHECKED AT EVERY SECTION FOR ITS RESISTANCE TO BENDING, SHEAR, TORSION AND AXIAL CAPACITY AGAINST ALL THE LOAD COMBINATIONS USING APPROPRIATE PARTIAL SAFETY FACTOR.

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SEISMIC AND WIND ARE NOT COMBINED.

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LOADS ARE FACTORED USING PARTIAL SAFETY FACTORS

DESIGN CONSIDERATION 

LIMIT STATE OF SERVICEABILITY

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THE STRUCTURE ARE CHECKED TO ENSURE THAT ITS DEFORMATION UNDER WORST LOAD COMBINATION ARE COMPATIBLE WITH THE DEGREE OF MOVEMENT ACCEPTABLE FOR VARIOUS SUPPORTING COMPONENTS LIKE PIPING JOINTS ,SAFE OPERATION OF PLANT AND EQUIPMENT AND FINISHES, GLAZING OF BUILDING ETC.

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SPECIFIC CHECK FOR CRACK WIDTH FOR  LIQUID RETAINING STRUCTURE.

LOADS & LOAD COMBINATIONS 

DEAD LOADS

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EQUIPMENT WEIGHT 

ERECTION/EMPTY

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OPERATING

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HYDROTESTING

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PUSH/PULL EFFECTS

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DYNAMIC LOADS

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LIVE /IMPOSED LOADS

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PIPING LOADS/ANCHO LOADS/ANCHOR/FRICTION R/FRICTION LOADS/ANCHOR/FRICTION

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ELECTRICAL/INSTRUMEN ELECTRICAL/INSTRUMENT T CABLE TRAYS ELECTRICAL/INSTRUMENT

LOADS & LOAD COMBINATIONS 

CRANE GANRTY/MONORAILS LOADS.

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WIND LOADS(AS PER IS 875 PART 3)

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ON STRUCTURE (using factor k1,k2,k3)

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SHIELDING EFFECTS

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ON EQUIPMENT

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DYNAMIC ANALYSIS -refer Cl. 7 (Height/width ratio >5)

SEISMIC LOADS (IS 1893-Part 1 &4) 

SEISMIC COEFFIENT

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RESPONSE SPECTRUM ANALYSIS

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IS 1893 SPECTRA

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SITE SPECIFIC SPECTRUM

PARTIAL SAFETY FACTOR FOR LOADS Limit state of collapse ˘ Load combination

DL+IL DL ± WL / EL

DL

1.5 1.5 or

IL

1.5

WL

-

1.5

0 .9 DL + IL ± WL/EL

1.2

IL-IMPOSED LOADS

1.2

1.2

VALUES OF PARTIAL SAFETY FACTOR ΓF FOR LOADS Limit states of serviceability

DL

IL

WL

DL + IL

1.0

1.0

-

DL ± WL/EL

1.0

-

1.0

Load combination

DL+ IL ± WL/EL

1.0

0.8

0.8

LOAD COMBINATIONS 

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WIND 

EACH DIRECTION WIND (Unidirectional)

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DIAGONAL WIND FOR SQUARE SHAPES.

SEISMIC 

CALCULATE RESPONSE FROM EACH DIRECTION .

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COMBINED WITH MULTICOMPONENTS AS COMBINES AS SRSS (SQUARE ROOT OF THE SUM OF THE

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SQUARES)

LIMIT STATE OF COLLAPSE BEAMS COLUMN SLABS

FLEXURAL BEAMS DESIGN

*FOR DUCTILE FAILURE STRAIN IN STEEL

BEAM DESIGN TABLE 

CALCULATE Mu/bd2 & Select steel grade to get ’ p’.

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Table 1 to 4 for singly reinforced beams . 

TABLE 4 FOR f ck=30

and f y =415/500 etc.→ Table 45 to 59 for doubly reinforced beams.

SHEAR STIRRUP

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 Nominal Shear Stress for beams of uniform uuniform niform depth

τv = VU/ b. d where,

VU = shear force due to design loads;  bb = breadth of the member, which for flanged section shall be taken as the the breadth of the web ; and d = effective depth.

Design of Shear Reinforcement 

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When τv exceeds τc ,shear reinforcement shall be  provided in following forms: a) Vertical stirrups,  b) b) Bent-up bars along with the stirrups, and c) Inclined stirrups. For vertical stirrups: strength of shear reinforcement Vus = 0.87 f y Asv d sv fy = characteristic strength of stirrups, Asv= total cross-sectional area of stirrup legs, d = effective depth, sv = spacing of the stirrups along the length of the member.

Design for stirrups 

Table 62 of SP16 Provides The value of’ Vus /d ‘in KN/cm for  FE 415 for different diameter & spacing .

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The Table for Fe500 can  be developed.

TORSION 

SHEAR AND TORSION(cl.41.3) Equivalent Shear , V e V e =Vu + 1.6 T u /b Where, V e = Equivalent Shear, Vu = Shear, T u = Torsional Moment,  b b = Breadth of beam.

Equivalent Nominal Shear Stress ,

τve

τve = Ve /b.d Values of τve shall not exceed the values of  τcmax . If τve does not exceed τc (Table 19) , minimum shear  reinforcement shall be provided as per 26.5.1.6. If τve exceeds τc (Table 19) , both longitudinal l ongitudinal and transverse reinforcement shall be provided in accordance with 41.4

Reinforcement in Members Subjected to Torsion(Cl. 41.4) 

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Torsional reinforcement consists of longitudinal and transverse reinforcement. Longitudinal Reinforcement Designed to resist an equivalent bending moment , Me1 = Mu +Mt Where Mu = bending moment at the cross-section, & Mt = Tu ((1+D/b)/1.7). Tu = Torsional moment, D = Overall depth& b = Beam breadth.

• Transverse Reinforcement Two legged closed hoops enclosing the corner longitudinal bars shall have an cross-section Asv,

Asv

=

Tu Sv  b1 d1 (0.87 fy)

+

Vu Sv 2.5 d1 (0.87 fy)

But total transverse transverse reinforcement reinforcement shall not be less less than

(τv e - τC) b. Sv 0.87 fy

Where, Tu = Torsional moment, Vu = shear force, Sv = spacing of the stirrup reinforcement, b1 = centre-to-centre distance between corner   bars in the direction of the width, d1 = centre-to-centre distance between corner   bars, b = breadth of the member, f y = characteristic strength of the stirrup rebars

τve = equivalent shear stress, τc = shear strength of the concrete (see (s ee Table 19).

CONTROL OF DEFLECTION BEAMS 

Basic values of Span to depth up to 10m span:-

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Continuous Beams...26

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Simply supported....20

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Cantilever.................7

Chart23 of SP16

COLUMN DESIGN 

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1) All COLUMN MUST BE DESIGNED FOR A MINM. ECCENTRICITY OF 

e min = l/500+D/30

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Where l is the unsupported column length &

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D column size

Design charts in SP 16 for different concrete & Steel grade 

Comp +uni axial bending ( chart 27 to to 38)

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Comp +bia axial Bending ( chart 39 to 50) 50)

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Tension +Bending ( chart 68 to 85)

COLUMN DESIGN -COMPRESSION 1) Short Axially Loaded Members in Compression Pu = 0.4 f ck ck .AC + 0.67 f y .A sc Where,

Pu = axial load on the member, f ck ck = characteristic compressive strength of the concrete,

AC = Area of concrete, f y = characteristic strength of the compression reinforcement, and A sc = area of longitudinal reinforcement for 

INTERACTION DIAGRAM FO 

Interaction diagrams in SP 16 in the forms of charts chart chartss with Pu /b D f ck 

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& Mu/ b D2 D2 are are Plotted Plotted for  different values of p/fck.

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Dotted lines for fyd 

Above fyd=0 NA at end of  Tension face §ion in comp.

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Below fyd=1.outer most bar  reaches design yield strength.

Members Subjected to Combined Axial Load and Biaxial Bending 

[Mux /Mux1]^α + [Muy /Muy1]^α ≤ 1.0 where,

Mux, Muy

= moments

about x and y axes due to design loads,

Mux1, Muy1 = maximum uniaxial moment capacity for 

an axial load of  Pu, bending about x and y axes respectively, and α is related to Pu / Puz. where, Puz = 0.45 f ck  ck .AC + 0.75 f y .Asc

RELATION BETWEEN Pu / Puz AND (Refer Chart 64 IN SP16)

Pu / Puz`

α

< 0.2

1.0

0.2 to 0.8

1.0 to 2.0 (linear variation)

>0.8

2.0

α

Design chart for biaxial bending

ADDITIONAL MOMENTS due to Slenderness  

Additional moment shall be taken into account . M = Pu D{l ex/D}^2 ax

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2000 M = Pu b{l ey/b}^2 2000 ay

Where,

l ex = effective length in respect of major axis, l ey = effective length in respect of minor axis, D = depth of the cross-section at right angles to the major  axis, and  b = width of the member.  NOTE :- Column are slender when L/d>12.

Strain distribution in interaction curve

SLAB DESIGN 

SLAB IS DESIGN AS ONE WAY OR TWO WAY SPAN DEPENDING UPON THE RATIO OF THE TWO SIDES.

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TABLE 26 OF ANNEX .D PROVIDES B.M. COEFFICIENT FOR SLAB DESIGN.

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SPAN TO DEPTH RATIO FOR  DEFLECTION CHECK: 

S.S SLAB

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CONTINOUS SLAB=0.8*40=32 

=0.8*35=28

(Factor of 0.8 for FE 415/500 )

SLAB DESIGN 

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Table 5 to 44 provided the moment of resistance of  slab/m in KN/m for given concrete & steel grade& depth it provides the bar dia. and spacing.  Note:-

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1)All values are with 15mm cover.

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2) concrete Grade limited to M20

SLAB Moment in KN/M

Enhanced Shear Strength of Sections Close to Supports Shear Failure At A Beam/Canti Beam/Cantilever Beam/Cantillever ever Occurs At An Angle Of 30°. 

Strength may be enhanced near support where the loads are closure and make an angle of 30°.

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Design of sections near a support is done by increasing design shear strength of concrete to

τc* = 2 d τc / av  provided that τc* at the face of the support less than τc max.

remains

SHEAR FAILURE NEAR SUPPORTS

SECTION FOR ENHENCED SHEAR 

DESIGN AIDS 

ESTIMATE PRELIMANARY SIZES MANUALLY/ PAST JOB EXPERIENCES

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ALL ANALYSIS ARE PERFORMED USING STAAD

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INHOUSE CALCULATION SHEETS AND DESIGN AIDS IN LOTUS/EXCEL AVAILABLE FOR  DESIGN OF COLUMN/BEAMS SLABS & FOOTING.

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INVARIABLY TRY TO MAINTAIN SYSTEMATICALLY ,DESIGN FILES & BACK UP OF ALL DESIGN CALCULATIONS. CALCULATIONS.

ATTACHMENTS

IS 875:-DESIGN LOADS FOR BLDGS.& STR. (OTHER THAN SEISMIC) 

PART 1 DEAD LOADS

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PART 2 IMPOSED LOADS

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PART 3 WIND LOADS

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PART 4 SNOW LOADS

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PART 5 SPECIAL LOADS & LOAD COMBINATIONS. 

TEMPERATURE EFFECTS

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HYDROSTATIC & SOIL PRESSURE.

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STRUCTURE SAFETY DURING CONSTRCUTION

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ACCIDENTAL LOADS.

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LOAD COMBINATIONS

1893 :CRITERIA FOR EARTHQUAKE RESISTANT DESIGN OF STRUCTURES 

PART 1(2002) fifth Revision

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GENERAL PROVISION IN BUILDINGS.

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PART 2*

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LIQUID RETAINING TANKS(GROUND & ELEVATED).

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PART 3*

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BRIDGES & RETAINING WALLS

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PART 4(2005)

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INDUSTRIAL STRUCTURE INCLUDING CHIMNEY

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PART 5* DAMS & EMBANKMENTS * to be issued?

STRESS STRAIN DIAGRAM FOR  DIFERRENT STEEL GRADES

TABLE 26 :BENDING MOMENT COEFF. FOR RECTANGULAR SLAB

SHEAR STRESS τ

c IN N/mm2

MAXM. SHEAR STRESS τ

c MAX IN N/mm2

AXIAL + BENDING CASE SH 1 STRAIN DIAGRAM

Stress Block With NA Outside The Section

FORMULA FOR DESIGN CHARTS SH 2/2

IMPOSED LOADS AS PER  IS875-PART 2

IMPOSED LOADS AS PER EIL DESIGN BASIS 

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Process Building/Technological Building/Technological Structure (Open/Enclosed type) 

Operating area

-

5.0 kN/m2

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Maintenance area

-

7.5 kN/m2

Com  pressor House/TG house Compressor 

Operating area

-

7.5 kN/m2

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Maintenance area

-

7.5 kN/m2

Substation/Control Room 

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Panel floor 

-

10.0 kN/m2

* FOR OTHER AREA REFER DESIGN BASIS

FIGURE 1 OF IS875 PART 3

SPEED VARIES FROM 33 TO 55M/S

SEISMIC ZONE OF INDIA

Sa/g vs TIME PERIOD

HORIZONTAL SEISMIC COEFF. DESIGN HORIZONTAL SEISMIC COEFF.

ZONE FACTOR 

EARTHQUAKE RESPONSE

!!!!

THANK YOU!