STRUCTURAL ANALYSIS IS A SCIENCE , HAVING DEFINITE VALUE.

BUT

STRUCTURAL DESIGN IS AN ART, VARIES FROM DESIGNER TO DESIGNER

STRUCTURAL DESIGN IS AN ITERATIVE PROCESS

OF APPLYING ENGINEERING MECHANICS AND

PAST EXPERIENCE TO CREATE A FUNCTIONAL,

ECONOMIC, AND, MOST IMPORTANTLY, SAFE

STRUCTURE FOR THE PUBLIC TO ENJOY.

STRUCTURAL DESIGN IS AN EXPRESSION OF AN UNDERSTANDING OF THE FLOW OF FORCES. ITS MODERN REFINEMENT THROUGH HARD LESSONS LEARNED FROM VARIOUS STRUCTURAL FAILURES.

USING STRUCTURAL ANALYSIS TECHNIQUES AND CONFORMING TO DESIGN SPECIFICATIONS, THE DESIGN ENGINEER WORKS TO CREATE A SOLUTION THAT IS TO EVERYONE'S BENEFIT.

THE FLOW OF FORCES IS INITIALLY UNDERSTOOD DIAGRAMATICALLY AND MATHEMATICALLY.

BASED ON THIS SCIENTIFIC UNDERSTANDING, SKETCHES OF MEMBERS AND CONNECTIONS ARE DEVELOPED.

STRUCTURAL DESIGN WHICH IS HIGHLY EXPRESSIVE OF THE FLOW OF FORCES IS ALSO ASSOCIATED WITH MODERN ARCHITECTURAL DESIGN.

STRUCTURAL DESIGN INCLUDES ACCOMMODATION FOR THE PRACTICALITIES OF CONSTRUCTION, INCLUDING ON SITE ASSEMBLY, SHOP ASSEMBLED COMPONENTS, ACCESSIBILITY, AND MAINTENANCE.

COMPLETE KNOWLEDGE OF IS CODES.

KNOWLEDGE ON CIVIL ENGG ASPECTS ARTICLES AND PRESENTATION, BOOKS & INTERNET.

DUCTILING DETAILMENT OF RCC STRUCTURES. TD DRS , RCC NOTES, COMPLETED DRGS AND SP.

FAMILIAR WITH ANALYSIS AND DESIGN SOFTWARE.

SIMPLE DESIGN USING EXCELL SHEET.

INTERNATIONAL CODES AND DESIGN PROCEDURE.

KNOWLEDGE IN ACAD AND 3D MAX SOFTWARE.

Material Properties.Cement - Grade 33, 43, 53- Comp strength of 5cm cube CM 1:2 after 28 days.Concrete Grade and Minimum cement content based onExposure condition (Ref IS 456 Table 5)Steel Grade- Fe250, Fe415, Fe500, Fe550, Yield strength of steelCover Based on Exposure condition and Fire Rating (Ref IS 456 Table 16&16A)Slab-25mm, Beam 30mm, Column- 40mm, Footing 50/ 75 mmStress- Strain relation of concrete and steelConfinement of steel in columnMember PropertyBeam: Size, Steel rft size, Stirrups, 135 degree hook, Cover, Lapping, Ld, rft for connecting two different beam size.Column: Size, Min rft size and Nos, Hook, tie spacing & arrangement, Lapping zone, Cover, Starter bar dist (300mm) , Rft for reducing column, core area, spacing of rft (

Loads and Load CombinationDead Load: Concrete 25 KN/Sqm, Brick 20 KN/Sqm Live Load : As per IS 875 Part II Wind Load : As per IS 875 Part III ( 0.75 to 1.5 KN/Sqm) Seismic Load: as per IS 1893 ( Zone II to V)

Load Combination of above loads

Force and MomentsActing in RCC menberSteel

Axial LoadColumnMain RftShear ForceBeamStirrupsBending MomentBeam and ColumnMain RftTorsion Converted as Shear Force BeamMain &Stirrupand Bending Moment

Cracked and Uncracked section DesignElastic, Ultimate and Limit State DesignLoad transfer (Concrete to steel, Cracking of concrete, Yielding of Steel)Plastic Hinge Formation and Moment redistributionCover requirement and function

Nominal Mix and Design Mix Difference between Wind and Earthquake loadT Beam action of Beam and SlabPrimary and Secondary beam concept (More rigidity absorb more moment)Staircase detailsLift well detailsOHT performance during earthquake loading

Familiar with IS 456, IS 13920 and SP 34 for rft detailmentDevelopment length concept (Ld in Compression and Tension)Lapping of rft in Beam, Column, Slab and FootingCurtailment rules for Beam and SlabRft at Beam Column junctionReinforcement details in two different section of Beam and ColumnReinforcement profile during bend Water quality (Chloride and Sulphate)Soil Content (Chloride and Sulphate)W/C ratio controlCuringStripping periodTime for RMC useUse of Vibrator, Concrete segregation Lift Well sizeStaircase starter bar Anti-termite treatmentWater Proofing Treatment Retaining WallSump and Fire tank construction

LOAD COMBINATIONS

LOAD COMB COLLAPSEIS 456, T-18IS 1893DLLLWLEL1.51.51.21.21.2(X&Z)1.51.5(X&Z)0.91.5(X&Z)1.21.21.2(X&Z)1.5 1.5(X&Z)0.91.5(X&Z)

LOAD COMB SERVICEIS 456, T-18DLLLWL1.01.01.0 1.0(X&Z)0.80.80.8(X&Z)

BEAM MEMBERDepth of a beam varies from L/10 to L/15. In general ,1 length will have 1 depth ie L/12). But outer beam, without wall beam may be L/15 depth.. The typical rules are as follows:In 230 mm width, max 4 rods can be accommodated. With 2 legged stirrupsExtra rods are in the 2nd layer. Then increase the beam depth to accommodate in 2nd layer. Max 5 rods with 4 legged stirrups.Max 25 mm dia and min 12 mm dia bars are used. 32mm dia rods are difficult to bend.

SL.NOMEMBERSPAN/OVERALL DEPTH RATIO1.PLINTH BEAM15 TO 182.TIE BEAM18 TO 203.FLOOR BEAMS12 TO 154.GRID BEAMS20 TO 30

The section sizes are 9x9 9x12 9x15 9x18 9x21 9x24 12x18 12x21 12x24 12x30 12x36etc

The minimum size of reinforcement is 12mm diameter.

Maximum 4 bars in 230mm , 5 bars in 300mm width may be accommodated and balance to be accommodated in the second layer.

Continuous top compressive reinforcement shall be minimum size, extra bars shall be larger size.( For example 2-12# + 2-16# or 2-12# + 2-20#)

More than 750 depth , 0.2%of skin bars @the sides shall be provided.

The stirrups will be useful for resisting shear force .it does not contribute for flexural strength.

Torsion will be corner to shear &moment . Additional reinforcement is considered for extra shear and moment.

Minimum cover for beam is 30mm. Exposure condition and fire rating will be the deciding factors for cover.

Curtailment rules are follow.

Beam sections should be designed for:

Moment values at the column face & (not the value at centre line as per analysis)

Shear values at distance of dfrom the column face. (not the value at centre lineas per analysis)

Moment redistribution is allowed for static loads only.

For beams spanning between the columns about the weak axis, the momentsat the end support shall be reduced more and distributed and the span moments shall be increased accordingly to account for the above reduction.

Moment distribution shall be done in such a way that 15% of the support moments shall be added to the span moment without the support moments getting reduced.

The section within the span shall be designed for the increased span moment which will account for the concentrated & isolated loading that may act within one span.

Moment redistribution isnot allowedifmoment co-efficient taken from code tabledesigned for earthquake forces and for lateral loads.

At least 1/3 of the +ve moment reinforcement in SIMPLE SUPPORTS & the +ve moment reinforcement in CONTINUOUS MEMBERS shall extend along the same face of the member into the support, to a length equal to Ld/3. (Ld-development length)

Use higher grade of concrete if most of the beams are doubly reinforced. Also when Mu/bd^2 goes above 6.0.

Try to design a minimum width for beams so that the all beam reinforcement passes through the columns. This is for the reason that any reinforcement outside the column will be ineffective in resisting compression.

Restrict the spacing of stirrups to 8(200mm) or of effective depth whichever is less.(for static loads)

Whenever possible try to use T-beam or L-beam concept so as to avoid compression reinforcement.

Use a min. of 0.2% for compression reinforcement to aid in controlling the deflection, creep and other long term deflections.

Bars of Secondary beam shall rest on the bars of the Primary beam if the beams are of the same depth. The kinking of bars shall be shownclearly on the drawing.

Length of curtailment shall be checked with the required development length.Keep the higher diameter bars away from the N.A(i.e. layer nearest to the tensionface) so that max. lever arm will be available.

Hanger bars shall be provided on the main beam whenever heavy secondary beam rests on the main beam.(Try to avoid the hanger bar if secondary beam has less depth than the main beam, as there are enough cushions available).

The detailing for the secondary beam shall be done so that it does not induce any TORSION on the main beam.

For cantilever beams reinforcement at the support shall be given a little more and the development length shall be given 25% more.

As a short cut, bending moment for a beam (partially continuous or fullycontinuous) can be assumed as wl^2/10 and the same reinforcement can be detailed at span and support. This thumb rule should not be applied for simply supported beams.

SLAB

EFFECTIVE DEPTH:

Sl.noSLABSPAN/EFFE.DEPTH1.One- way simply supported slab302.One-way continuous slabs353.Two-way simply supported slabs38 for L/B=1.535 for L/B>1.54.Two-way continuous slabs40 for L/B=1.538 for L/B>1.5

Whenever the slab thickness is 150mm, the bar diameter shall be 10mm for normal spacing.(It can be 8mm at very closely spaced).

Slab thickness can be 100mm,110mm,120mm,125mm,150mm, etc.

The maximum spacing of Main bar shall not exceed 225mm(9) and the distribution bars @ 250mm(10).

If the roof slab is supported by load bearing wall (without any frames) a bed block of 150/200mm shall be provided along the length of supports which will aid in resisting the lateral forces.

If the roof is of sheet(AC/GI) supported by load bearing wall (without any frames) a bed block of 150/200mm shall be provided along the length of supports except at the eaves. The bed block is provided to keep the sheets in position from WIND.

For the roof slab provide a min. of 0.24%of slab cross sectional area reinforcement to take care of the temperature and other weathering agent and for the ponding of rain water etc since it is exposed to outside the building enclosure.

Minimum size of column is 230mm x 230mm , Some time 200mm x 200mm Typical size are 9x9, 9x18, 9x12 9x18, 9x21 and 9x24. when d > 4b, column will behave as wall.

Minimum 0.8% of steel, 4No-12# bar in rectangular, 6No-12# in circular column shall be adopted.

When the column size is large, 0.8%of minimum size required to carry the axial load shall be provided.(Refer IS 456-2000).

Generally 40 mm cover is provided for the column. When column orientation is changed , then size and reinforcement to be changed.

Column width / breadth to be larger than beam width. No overhanging in beam width is recommended.

Strong column weak beam concept shall be adopted.

Starter reinforcement L distance at the bottom in min 300mm.

40d in compression & 50d in tension overlapping at mid third size should be provided.

COLUMN

Section should be designed for the column moment values at the beam face.

Use higher grade of concrete when the axial load is predominant.

Go for a higher section properties when the moment is predominant.

Restrict the maximum % of reinforcement to 3.

Detail the reinforcement in column in such a way that it gets maximum leverarm for the axis about which the column moment acts.

Position of lap shall be clearly mentioned in the drawing according to thechange in reinforcement. Whenever there is a change in reinforcement at a junction, lap shall be provided to that side of the junction where the reinforcement is less.

Provide laps at mid height of column to minimize the damage due to Moments (Seismic forces).

Avoid KICKER concrete to fix column form work since it is the weakest link due to weak and non compacted part.

FOOTING:Never assume the soil bearing capacity and at least have one trial pit to get the real site Bearing capacity value.

Check the Factor of Safety used by the Geotechnical engineer for finding SBC.SBC can be increased depending on the N-value and type of footing that is going to be designed. Vide IS-1893-2000(part-I).

Provide always PLINTH BEAMS resting on naturalgroundin orthogonal directions connecting all columns which will help in many respect like reducing the differential settlement of foundations, reducing the moments on footings etc.

Always assume a hinged end support for column footing for analysis unless it is supported by raftand on pile cap.

The Common assumption of full fixity at the column base may only be valid for columns supported on RIGID RAFTfoundations or on individual foundation pads supported by short stiff piles or by foundation walls in Basement.

Foundation pads supported on deformable soil may have considerable rotational flexibility, resulting in column forces in thebottom story quite different from those resulting from the assumption of a rigid base. The consequences can be unexpected column HINGES at the top of lower story

columns under seismic lateral forces. In such cases the column base should bemodeled by a rotational springs. (Ref:page 164-Seismic design of Reinforcedconcrete and Masonry buildings by T.Paulay & M.J.N.Priestley.)

Also refer the Reinforced concrete Designers Handbook by Reynold where it is clearly mention about the column base support.

The pressure distribution of footing under sandy and clay soil are different. However , the uniform pressure is considered under the footing.

Minimum depth of foundation is d=q ( 1-sin /1+sin)2 /

Un factored load is considered for calculation of footing size. But for footing thickness and reinforcement, factored load to be considered.

Minimum thickness at the edge of footing is 200mm . Minimum cover is considered as 50mm. Minimum diameter of reinforcement is 10mmD/2 or 150 mm (which ever is maximum) pedestal offset shall be given for resisting punching shear.

The value of punching shear for different grade of concrete is as below:Minimum SBC is 7.5 t/sqm, less then that, raft foundation or pile foundation to be considered.

Column orientation will have on spacing of square or rectangular footing because the lever arm will change for the face of the column.The reinforcement is provided to counter the deflection of footingISOLATED FOOTING

The angle of pressure distribution to be depth of soil is 45. Hence the intensity of the pressure reduce over the depth because the size of area of influence is increasing. But overlap of the footing area of influence to be verified.

The uplift pressure due to water table is to be verified. This is a serious failure at later stage.

When the water table is high, reduce the SBC or calculate for the water table.

Strip raft foundation increase the depth of influence of pressure. Hence check for soil strata down below. If the bottom strata is bed, do not go for strip foundationFOUNDATION ISOLATED FOOTING

R.C.C.WALLS:The minimum reinforcement for the RCC wall subject to BM shall be as follows:Vertical reinforcement:a)0.0012of cross sectional area for deformed bars not larger than 16mm in diameter and with characteristic strength 415 N/mm^2 or greater.b)0.0015of cross sectional area for other types of bars.c)0.0012 of cross sectional area for welded fabric not larger than 16mm in diameter.Maximum horizontal spacing for the vertical reinforcement shall neither exceedthree times the wall thickness nor 450mm.Horizontal reinforcement.a)0.0020 of cross sectional area for deformed bars not larger than 16mm in diameter and with characteristic strength 415 N/mm^2 or greater.b)0.0025of cross sectional area for other types of bars.c)0.0020 of cross sectional area for welded fabric not larger than 16mm in diameter.Maximum vertical l spacing for the vertical reinforcement shall neither exceed three times the wall thickness nor 450mm.NOTE: The minimum reinforcement may not always be sufficient to provide adequate resistance to effects of shrinkage and temperature.The Ht for a RCC wall shall not exceed 30 as per IS:456=2000, where Ht is the effective height of the wall and t is the thickness of the RC wall.Ht for a braced wall will be :a)0.75H, if the rotations are restrained at the ends by floors where h is the height of the wall. b)1.0h .

Increasing the stiffeners of member will absorb more load/ moment (stiffness factor is to be considered).

Excess of load resulted to crack in concrete, Steel will take extra load & start yielding.

The moment redistribution take place. Up to 20% of gravity load redistribution is permitted.

T beam action is not consider in design. Which can take additional10% of load and moment.

No physical measuring for secondary beam or release of moment. Lesser than stiffness less than load absorption. ( force flow to higher stiffness members). Bond and development length ,Ld = 0.87fy / 4 (bxd)

Bending moment co efficient foe cantilever beam and slab

STRUCTURAL BEHAVIOUR

PERMISSIBLE STRESS IN CONCRETE

PERMISSIBLE STRESSES IN CONCRETE IN N/MM^21 N/MM^2= 10 KG/CM^2GRADECOMPRESSIONSHEARBONDBEARINGTENSILEFLEXURALMOD RATIOBENDINGDIRECTAVERAGELOCALM103.02.50.30.40.72.01.23.1631.11M155.04.00.50.61.03.02.23.8718.67M207.05.00.70.81.34.02.84.4713.33M258.56.00.80.91.55.03.25.0010.98M3010.08.00.91.01.76.03.65.489.33M3511.59.01.01.11.87.04.05.928.12M4013.010.01.11.21.98.04.46.327.18

FORCES IN A LINE ELEMENT(BEAM AND COLUMN)

DirnForceDispForceMemberRCC Resisted byXUxxAxialColumnLong RftYUyyV ShearBeamStirrupsZUzzH ShearBeamStirrups

@XMxxTorsion=Shear&MColumn,BeamLong + Stirrups@YMyyMyColumn,BeamLong Rft@ZMzzMzColumn,BeamLong Rft

Development Length for Single Deformed Barsfy N/SqmmTension BarsCompression BarsM20M25M30M35 >=M40M20M25M30M35>=M40415484138343038333127245005749464036463937322955063545044365043403632

Para 26.2.1.1, IS 456 Design Bond Stress in Limit State Design Ld= s/(4bd)= 0.87 fy/(4Tbd)Grade of ConcreteM15M20M25M30M35>=M40Design Bond Stress in Plain Bar N/Sqmm1.11.21.41.51.71.9Design Bond Stress in Deformed Bar N/Sqmm(1.6Times)1.761.922.242.42.723.04Design Bond Stress in Deformed Bar in comp N/Sqmm2.22.42.833.43.8

BENDING MOMENT COEFFICIENTS FOR CONTINUOUS BEAMType of LoadSpan MomentsSupport MomentsNear Middle of End SpanAt Middle of Interior SpanAt the End SupportAt Support next to End SupportAt other Interior SupportDL+IL(Fixed)+1/12 WL+1/16 WL-1/24 WL-1/10 WL-1/12 WLIL(Not Fixed)+1/10 WL+1/12 WL-1/24 WL-1/9 WL-1/9 WL SHEAR FORCE COEFFICIENTS FOR CONTINUOUS BEAMType of LoadAt the End SupportAt Support next to End Support Inside OutsideAt other Interior SupportDL+IL(Fixed)0.4W0.6W0.55W0.5WIL(Not Fixed)0.45W0.6W0.6W0.6W

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