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EE44--E5 CIVIL E5 CIVIL (TECHNICAL)training.bsnl.co.in/DIGITAL_LIBRARY_SOURCE/UPGRADATION...WELCOME...

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For internal circulation of BSNL only E4 E4-E5 CIVIL E5 CIVIL (TECHNICAL) (TECHNICAL) Structural Design of RCC Bldg Structural Design of RCC Bldg Components Components (Session (Session – 2) 2)
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  • For internal circulation of BSNL only

    E4E4--E5 CIVIL E5 CIVIL

    (TECHNICAL)(TECHNICAL)

    Structural Design of RCC Bldg Structural Design of RCC Bldg ComponentsComponents(Session (Session –– 2) 2)

  • WELCOME

    • This is a presentation for the E4-E5 Civil Technical

    Module for the Topic: Structural Design of RCC Bldg

    Components (Session 2)

    • Eligibility: Those officers of civil wing who have got the

    Up-gradation from E4 to E5.

    • This presentation is last updated on 21-4-2011.

    • You can also visit the Digital library of BSNL to see this

    topic.

    For internal circulation of BSNL only

  • For internal circulation of BSNL only

    AGENDA

    Design of Various Structural Components

    Column Design

    Design of Slab

    Beam Design

    Isolated Footing Design – Imp. Considerations.

    Development Length

  • DESIGN OF RCC STRUCTURE

    Design of Various Structural Components –

    • After load calculation & analysis for vertical & horizontal

    loads, design & of various structural components e.g. –

    – Columns,

    – Foundations,

    – Beams,

    – Slabs & staircase etc

    are carried out as per various clauses of IS codes with

    help from charts & tables given in BIS handbooks.

    For internal circulation of BSNL only

  • Design of Columns

    Design of Columns

    • After obtaining (i) Vertical load, (ii) Moments due to

    horizontal loads on either axis & (iii) Moments due to

    vertical loads on either axis, acting on each column, at

    all floor levels of the building,

    • Columns are designed by charts of SP-16(Design

    Aids).

    • Design of each column is carried out from the top of

    foundation to the roof, varying the amount of steel

    reinforcement for suitable groups for ease in design.

    Slenderness effects in each storey are also considered

    for each column group.

    For internal circulation of BSNL only

  • Design of Columns

    Column

    A compression member, the effective length > three times

    the least lateral dimension.

    Short and Slender Compression Members

    When both slenderness ratios lex/D and ley/b are

  • Design of Columns

    Design Of Columns – Important Considerations

    (ii) Unsupported Length –

    In beam-slab construction, it is the clear distance between the floor &

    under side of shallower beam framing into columns in each direction at

    next higher floor level.

    (iii) Slenderness limits for columns –

    The unsupported length between end restraints shall not exceed 60

    times the least lateral dimension of a column.

    (iv) Minimum Eccentricity – All columns shall be designed for

    emin ≥ l/500+ D/30 ≥ 20 mm

    Where l= Unsupported length of column in mm. D= Lateral dimension

    of column in the direction under consideration in mm.

    For internal circulation of BSNL only

  • Design of Columns

    Design Of Columns – Design Approach

    • The design of column is complex as it is subjected to axial

    loads & moments which may very independently.

    Column design requires –

    – Determination of the cross sectional dimension.

    – The area of longitudinal steel & its distribution.

    – Transverse steel.

    • The maximum axial load & moments acting along the

    length of column are considered for design of the column

    section.

    • The transverse reinforcement is provided to impart effective

    lateral support against buckling to every longitudinal bar.

    For internal circulation of BSNL only

  • Design of Columns

    Design Of Columns – Reinforcement Provisions as per

    IS:456-

    A. Longitudinal reinforcement

    • Area of longitudinal reinforcement shall be not less than

    0.8% nor more than 6% of cross sectional area of the

    column.

    • However maximum area of steel should not exceed 4% to

    avoid practical difficulties in placing & compacting concrete.

    • In pedestals, in which the longitudinal reinf. is not taken into

    account in strength calculations, nominal reinforcement

    should be not be less than 0.15% of cross sectional area.

    • Minimum dia of longitudinal bar should be 12 mm

    For internal circulation of BSNL only

  • Design of Columns

    Design Of Columns – Reinforcement Provisions as per

    IS:456

    A. Longitudinal reinforcement

    • Spacing between bars < 300mm along periphery of column

    • The minimum number of bars shall be four in rectangular

    columns & six in circular columns.

    B. Transverse reinforcement (STIRRUPS)

    • Diameter of lateral ties should not be less than 1/4th of dia of the

    largest longitudinal bar & in no case should be less than 6 mm.

    • Spacing of lateral ties should not > least of the following:-

    –Least lateral dimension of the column.

    –16 times the smallest diameter of longitudinal bars to be tied.

    –300 mm.For internal circulation of BSNL only

  • SLAB DESIGN

    TYPES OF SLABS

    Based on Ratio of long span to short span –

    • One way slab – Long span (ly)/Short span (lx ) > 2

    • Two way slab – Long span (ly)/Short span (lx ) < 2

    Based on Edge Conditions

    • Simply supported

    • Restrained – Edge Conditions of supporting edge

    • Cantilever

    For internal circulation of BSNL only

  • SLAB DESIGN

    • The design of floor slab is carried out as per –

    �Clause 24.4 &

    �Clause 37.1.2 & Annexure D of IS:456-2000 .

    � The Bending moment coefficients are taken from

    �Table- 26 or

    �Table – 27 of BIS code

    • depending on support conditions

    • Bending moment is calculated & reinforcement

    steel is obtained from charts given in SP-16.

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    Clause 22.2 Effective Span –

    • Effective Span of slab or beam to be considered in

    design is based on support condition- simply supported,

    continuous, cantilever etc. & width of support.

    • For RCC frame construction, generally centre to centre

    distance is considered.

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    EFFECTIVE DEPTH Clause 23.0

    • Effective depth of beam or slab =

    distance between centroid

    of area of tension reinf.

    & maximum comp. fiber,

    • Excluding thickness of finishing material not placed

    monolithically with member and the thickness of any

    concrete provided to allow for wear.

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    Clause 23.2 CONTROL OF DEFLECTION

    The deflection shall generally be limited to following:

    • Final deflection < span/250

    (Due to all loads & measured from as-cast level of

    supports of floors, roofs and all other horizontal

    members.)

    • Final deflection < span/350 or 20mm whichever

    is less

    (Including effects of temperature, creep & shrinkage

    occurring after erection of partitions & application of

    finishes.).

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    Clause 23.2 CONTROL OF DEFLECTION

    • For beams, vertical deflection limits may

    generally be assumed to be satisfied provided

    that span/depth ratio are not greater than the

    value obtained as below –

    (a) Basic values of span/effective depth ratios for

    spans up to 10m:

    Cantilever 7

    Simply supported 20

    Continuous 26

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    Clause 23.2 CONTROL OF DEFLECTION

    • For spans >10m, values in (a) may be multiplied by

    10/span in meters,

    Modification Factors are applied –

    • Based on area & type of steel for tension

    reinforcement (As per Fig. 4 of IS456)

    • Based on area of compression reinforcement (As per

    Fig. 5 of IS456)

    • For flanged beams (As per Fig. 6 of IS456)

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    Clause 24.1 SLABS –Control of Deflection

    • The provisions of 23.2 for beams apply to slabs also.

    • For slabs spanning in two directions shorter of the two

    spans to be used for span/effective depth ratios.

    • For two-way slabs of shorter spans (≤3.5 m) with mild

    steel reinf., span/depth ratios given below may

    generally be assumed to satisfy vertical deflection limits

    for loading class up to 3 kN/m2.

    Simply supported slabs 35

    Continuous slabs 40

    For HYSD bars grade Fe 415 & Fe500, values given

    above to be multiplied by 0.8.

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    26.5.2 Requirement of Reinforcement – SLABS

    26.5.2.1 Minimum reinforcement

    • Mild steel reinf. in either direction in slabs ≥ 0.15 %

    of total cross sectional area.

    • For high strength deformed bars ≥ 0.12 % of total

    (Fe415/Fe500 bars) cross sectional area.

    26.5.2.2 Maximum diameter

    • The dia of reinforcing bars < 1/8th of total thickness

    of slab

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    Requirement of Reinforcement – SLABS

    26.3.3 Maximum distance between bars

    �The horizontal distance between parallel main

    reinforcement bars ≤ 3d or 300 mm

    �The horizontal distance between parallel

    reinforcement bars provided against shrinkage

    and temperature ≤ 5d or 300 mm whichever is

    smaller.

    For internal circulation of BSNL only

  • SLAB DESIGN

    Steps for Design of Slabs –

    • Step 1: Selection of preliminary depth of slab

    • Step 2: Calculate design loads, bending moments

    • Step 3: Determination/checking of the effective and

    total depths of slabs

    • Step 4: Determination of areas of steel

    • Step 5: Selection of diameter & spacing of

    reinforcing bars

    For internal circulation of BSNL only

  • BIS 456 EXTRACT

    • Torsion reinforcement is provided at any corner

    where the slab is simply supported on both edges

    meeting at that corner.

    • It consist of top and bottom reinforcement, each with

    layers of bars placed parallel to sides of slab &

    extending from edges a minimum distance of one-

    fifth of the shorter span.

    • Area of reinf. in each of these four layers is three-

    quarters of the area required for maximum mid-span

    moment in slab

    For internal circulation of BSNL only

  • BEAM DESIGN

    26.5.1.1 Tension reinforcement

    a) Minimum reinforcement -

    As = 0.85

    bd fy

    where

    AS =minimum area of tension reinforcement

    b =breadth of beam or the breadth of the web

    d =effective depth of T-beam

    fy =characteristic strength of reinforcement in N/mm2 &

    b) Maximum reinforcement - The maximum area of

    tension reinforcement not to exceed 0.04 bD.

    For internal circulation of BSNL only

  • BEAM DESIGN

    • Compression reinforcement

    • The maximum area of compression reinforcement not to

    exceed 0.04 bD

    • Side face reinforcement

    •Where depth of web in a beam >750 mm, side face reinf is

    to be provided along the two faces.

    •The total area of such reinf. should not < 0.1 percent of

    web area and

    •It shall be distributed equally on two faces at a spacing not

    > 300 mm or web thickness whichever is less.

    •Also to be provided in beams having torsion & with width or

    depth >450mmFor internal circulation of BSNL only

  • BEAM DESIGN

    Minimum shear reinforcement (Clause 26.5.1.6)

    • Minimum shear reinforcement in the form of stirrups shall

    be provided such that:

    Asv = 0.4

    bsv 0.87fy

    Maximum spacing of shear reinforcement (Clause 26.5.1.5)

    • The maximum spacing of shear reinforcement measured

    along axis of member shall be < 0.75 d for vertical

    stirrups and d for inclined stirrups at 45 degrees.

    • In no case shall the spacing to be >300 mm.

    For internal circulation of BSNL only

  • BEAM DESIGN

    Steps for Design of beams–

    • Step 1: Selection of preliminary cross sectional

    dimension of beam

    • Step 2: Calculate design loads, bending moments &

    shear force

    • Step 3: Determination/checking of the effective and

    total depths of beam/ Revise if necessary.

    • Step 4: Determination of areas of steel for flexure

    • Step 5: Determination of shear reinforcement

    • Step 6: Detailing as per IS 456 & IS13920

    provisions

    For internal circulation of BSNL only

  • FOUNDATION DESIGN

    Design of Foundations – Important Considerations

    • Foundations transfer loads from the building or individual

    columns to earth. Foundations must be designed to

    prevent –

    • Structural Failure

    • Shear failure of soil

    • Excessive settlement &

    • To minimize differential settlement

    • Depth of footing is determined from the consideration of –

    (a) Bending Moment

    (b) One way shear

    (c)Two way shear

    For internal circulation of BSNL only

  • FOUNDATION DESIGN

    Design of Foundations – Important Considerations

    • To determine area required for proper transfer of total

    load on the soil, the total load (the combination of dead,

    live and any other load without multiplying it with any load

    factor) need to be considered.

    Total Load including Self Weight of footing

    Plan Area of footing = -----------------------------------------------

    Allowable bearing capacity of soil

    Thickness of the edge of footing –

    The thickness at the edge shall not be less than 15 cm for

    footing on soils.

    For internal circulation of BSNL only

  • FOUNDATION DESIGN

    Design of Foundations – Important Considerations

    Bending Moment (Reference Clauses- 34.2.3.1 & 34.2.3.2)

    • The critical section for bending Moment is considered

    at the face of column, Pedestal or wall.

    Shear (Reference Clause 33.2.4.1)

    • The critical section for one way shear is at the vertical

    section located at a distance equal to the effective

    depth (d) from the face of the column, pedestal or wall

    of the footing in case of footings on soils.

    For internal circulation of BSNL only

  • FOUNDATION DESIGN

    Design of Foundations – Important Considerations

    For one way action

    For one way shear action, the nominal shear stress is

    calculated as follows:-

    Vuτv = -------

    b.d

    Where

    τv = Shear stress, Vu = Factored vertical shear force

    b = Breadth of critical section, d = Effective depth

    τv < τc ( τc = Design Shear Strength of concrete based on % of

    longitudinal tensile reinforcement refer Table 61 of SP-16)

    For internal circulation of BSNL only

  • FOUNDATION DESIGN

    Design of Foundations – Important Considerations

    For Two Way Action (Punching shear )

    Critical section for punching shear is at d/2 from the face of

    column or pedastal

    For two way shear action, the nominal shear stress is calculatedin accordance with clause 31.6.2 of the code as follows:-

    Vuτv = ----------

    b0.d

    Where b0 = Periphery of the critical section

    For internal circulation of BSNL only

  • FOUNDATION DESIGN

    Design of Foundations – Important Considerations

    Development Length (Reference Clause 34.2.4.3)

    • The critical section for checking the development length in a

    footing shall be assumed at the same planes as those

    described for bending moment in clause 34.2.3 of code and

    also at all other vertical planes where abrupt changes of

    section occur.

    Reinforcement –

    � Minimum % of steel in footing slab should be 0.12% &

    � Maximum spacing should not be more than 3 times

    effective depth or 300mm which ever is less.

    For internal circulation of BSNL only

  • DETAILING

    • Reinforcing steel of same type and grade shall be

    used as main reinforcement in a structural member.

    • Simultaneous use of two different types or grades of

    steel for main and secondary reinforcement is

    permissible.

    • The calculated tension or compression in any bar at

    any section shall be developed on each side of the

    section by an appropriate development length or end

    anchorage or by a combination thereof.

    For internal circulation of BSNL only

  • Development Length

    Development Length of Bars

    Ld = φσst /4τbd,

    φ = nominal diameter of bar, τbd = design bond stress

    σst = stress in bar at the section considered at design load

    • Design bond stress in limit state method for plain bars in

    tension is given in clause 26.2.1.1

    • For deformed bars conforming to IS 1786 these values

    are to be increased by 60 %.

    • For bars in compression, the values of bond stress for

    bars in tension is to be increased by 25 percent

    For internal circulation of BSNL only

  • Development Length

    For internal circulation of BSNL only

  • For internal circulation of BSNL only


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