Isse Journal Apr-jun

7/27/2019 Isse Journal Apr-jun

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Unique project where sheet poles are used in India (t o name a few): Varoous sections available: Qo..ay Wall for Port C ol'struc toon Vaozag Port Trust Z Sheet P o l e ~

u Shee t roles Straoght Web Sec tions

Drydoc k Project Bhavnagar DrydO< k Underground Car PMk Kolkata Car Park ProJect Hydro Power Pro1ecb BASPA Hydro Project Thermal Power Project farakka Power ProJect Box Poles

Corr>bmed Walls (HZ 1 T Jbuldr Poles)DesalinatiOn Projec t Cl>ennao Desalonat o Project Under pass Constr uct on At Cochon. Kerala ProJeCt Fo C t F o Assam lrngatoon Pro1ec tDistribution Solutions India - one stop shop: steel solutoons & services Sheet piles no w readily available in India, at our stockyardArcelorMittal Distribution Solutions India Pv t. Lt d.MumbaoOffiC. T099 (160019 K< o 01 e - '9 l39417632Delho Offoce T 09 920 16u u19 1Chennao urrKe. . J9 00 7 006 800E' arTldsondoa@arce lormottal com I ww w arcelormottal com/prOJects


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STRUCTURAL ENGINEERSQUARTERLY JOURNAL

INDIAN SOCIETYOFSTRUCTURAL ENGINEERSVOLUME 14-2, APR-MAY-JUN 2012

Head Office : C/0 S. G. Dharmadhikari, 24 , Pandit Niwas, 3rd Floor, S. K. Bole Road,Dadar, (W), Mumbai 400 028 Tel. 91-22 24365240 E-mail : [email protected] Website : www.isse.org.inRegd Office : The Maharashtra Executor & Trustee Co. Ltd., Bank of Maharashtra, Gadkari ChowkGokhale Road, (N), Dadar, Mumbai 400 028Charity Commissioner Reg. No E 17940, Mumbai Donations are exempted from Income under 80-GFOUNDER PRESIDENT :Late Eng. R L NeneParent Advisors :

00 00 000000 M C Bhide0000000000 MD Mulay0000000000 S G Patil

ISSE WORKING COMMITTEE :President 00 00 00 0000 Prof. G B ChoudhariSecretary 0000000000 P B DandekarTreasurer 00 000000 00 M M NandgaonkarPast President 000000 00 00 S G DharmadhikariMember 00 00 00 0000 K L SavlaM V SantJ R RavalD S JoshiU V DhargalkarS H JainH S VadalkarN K BhattacharyyaISSE - PUNE CENTREChairmanSecretaryJt. SecretaryTreasurer

0000 00 0000 J V lnamdar 0 0 0 0 0 0 0 0 G A Bhilare. . . . 0 . . . . Kedar Phadnis00 00 00 00 .. Arun Gokhale

ISSE - SOLAPUR CENTREChairman 00 00 00 0000 Sunilkumar PatilSecretary 00 0 0 0 0 00 00 Om DarakJt. Secretary 00 . . . . 00 00 Jagdish DiddiTreasurer ......0000 Vaibhav HomkarISSE - MUMBAI CENTREChairmanSecretaryTreasurerISSE JOURNAL

00 0000 00 00 Kamal Hadker00000000 00 Shekhar Ghate0000000000 H M Raje

1

Contents! Fraternity News 2! Effect of grade of steel on load capacity ofcomposite slabs 3By Pragnya Shah,Brijesh Pandya& Harism1ta Pathak! Design and Construction of Wirewound CircularPrecast, Prestressed Concrete Tanks 10

By Sanjay Mehta

Editor Hemant VadalkarN K Bhattacharyya

Views expressed are authors' or reporters' pe rsonal and donotnecessarily reflect views of SSE. /SSE s not responsiblefor anyconsequent actionsbased on contents or nformationgiven in the ournal.

\lolume 14-2, APR-MAY-JUN 2012


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Fraternity NewsWELCOME TO NEW MEMBERS(Jan-Feb-Mar 2012)

M- 1179 Dinesh Kumar SingnalM- 1180 Rajnish Talakshi BoyadM- 1181 Elizer Saure Abrea

M- 1189 Sanjay Sureshrad And hareM- 1190 Jitendra P BhandariM- 1191 Sagar S Lodha

M- 1182 Ravishamkar v Ghodake M- 1192 Atul A ThombareM- 1193 Vijaya Baskar A- 1183 Vinayak K Chopdekar

M- 1184 Aniruddha V Nakhawa M- 1194 Sandhya S LulekarM- 1185 Rajesh Ashok KadamM- 1186 Rajkumar K Bhonde M- 1195 Nitish P BeriM- 1196 Nishant YadavM- 1187 Kaushik Vijayanand DeshpandeM- 1188 Sudhir Shriram Sutrave M- 1197 Harshwardhan H Shinde

OM- 1121 Ketan Kapasi

Patrons: 29Members : 1178

Organisation Member : 20Junior Members : 11

Sponsors: 8

TOTAL STRENGTH 1246

FIELDS CONSIDERED AS ASPECTS OF STRUCTURAL ENGINEERING

*Structural Designing &Detailing

* Construction Technology&Management* Computer Software * Geo-Tech & Foundation Engineering* Materials Technology, Ferrocement * Environmental Engineering* Teaching, Research & Development * Non Destructive Testing* Rehabilitation of Structures * Bridge Engineering&Other related branches

AIMS & OBJECTIVES1. To restore the desired status to the Structural Engineer in construction industry and to create awareness about the profession.2. To define Boundaries of Responsibilities of Structural Engineer, commensurate with remuneration.3. To get easy registration with Governments, Corporations and similar organizations all over India, for our members.4. To reformulate Certification policies adopted by various authorities, to remove anomalies.5. To convince all Govt. & Semi Govt. bodies for directly engaging Structural Engineer for his services.6. To disseminate information in various fields of Structural Engineering, to all members.ISSE JOURNAL 2 Volume 14-2, APR-MAY-JUN 2012


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Grade of concrete M25 Shear Stud Details:25 mm diameter ;100

mmhigh Reinforcement Detail: 8 mm diameter@ 100 mm c/c-atsupports8 mm diameter @ 315 mm c/c - at bottomtransverse Span: Double- Un propped

DESIGN EXAMPLEDesign of Composite slab with profiled steelsheeting (As per BS 5950: part 4, Euro code 4and IS 456:2000 wherever applicable)Span of slab = 1.75 mSpan of beam = 5 mThe characteristic strengths and the partial safetyfactors for materials (YM) are as follows:

5m

Jl J-.....~ J ~a"'-....

~ APLAN

I . 5m . ISECTIONB-B

ISSE JOURNAL 4

Sm.

JJ

PLAN

Profiled steel sheet: fyp = 250 N/mm 2, ya = 1.1Concrete; cube strength: fck =25 N/mm2 , yc= 1.5Reinforcement;yield strength:fy=415 N/mm2 ,v.=1 .15Structural steel; yield strength:fy=250 N/mm2,Ya=1.1Shear connector; 25-mm headed stud , 100 mmhigh; ultimate strength=540 N/mm2 , yv= 1.25Resistance of the shear connector Qk= 93.5 kN(IS: 11384-1985 Clause 9.3 Table 1)(25 mm diameter shear connector 100 mm highand M25grade concrete)Dead loadsFloorfinish =1 kN/m2Live load = 2.0 kN/m2Design a continuous composite slab with profiledsteel sheeting.1. Profiled steel sheeting as shutteringThe profiled steel sheeting must resist the weig htofwet concrete and the construction loads.Assuming the following trapezoidal type ofprofiled sheet;

9!11.4r___ 48. 1c4H -r - _35 1~ L ~ ~ ~

31_5 - __!22_ IIFigure ) Srction of Profiled Steel Sh!'1'1

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(Effective Span of profiled sheeUoverall depth ofslab= 35)Assuming total thickness of slab as 120 mmLoadingsDead loads Self weight of sheet = 0.2 kN/m(assumed)Weight of concrete = 25 x (0.948 x0.12-0.5x(124+191 )/1 000x52/1 000x3)=2.23 kN/mLive load(BS 5950:4-1994-Ciause 2.2.3.1 )/ (EC4-Ciause9.3.2.1)A construction load of 1 5 kN/m2 is consideredon the sheet. No allowance is made for

C


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= 3.81 kN/m2 The maximum deflection in spanAB,if BC is unloaded, isw L.4/185 E I= 1.597 mm(Textbook-Composite structures of steel andconcrete-R. P.Johnson)Permissible deflection (effects of ponding nottaken into account)(885950:4-1994-Ciause 5.3)L./130 = 12.71 mm > 1.597 mm, thus safe.Permissible deflection (EGG-Clause 0 .6[2])=Le/180=9.7 mm 1.597 mm, thus safe.2 Composite slab- flexure and vertical shear

top f ~

91-1 :b

hgurc / - Cru.- S8.41 kN/m, thus safe

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4. Composite slab-serviceabilityCracking of concrete above supporting beamsContinuity across the steel beams should beprovided by reinforcement of area 0.4 % of thegross sectional area of concrete fo r proppedconstruction. Hence,~ = 0.004 x 948 x (120-52) = 258 mm2/m((EC4-Ciause 9.8.1 (2))The detailing is best left until longitudinal shear inthe beam and fire resistance have beenconsidered.DeflectionMaximum deflection is given by;(885950:4-1994-Ciause 6.6.2) & ((EC4-Ciause9.8.2(4))Moment of inertia of unreinforced compositeslab is given by;I = (lucr + lcr )/2 in steel units

!=..._- ~ . . : : . . ; . : . . . - r - - ~ -

" . . -

l ----\==l .h " ' 1;----f = -, b - ~ f_ J r " -----!--t 1\ r . 1L _';:::7 L(;.!(. .

hglat 8 Sfcltooof C 0.322 mm, thus safe(885950:4-1994-Ciause 6.6.1) & ((EC4-Ciause9.8.2(3))5. Transverse reinforcement(885950:4-1994-Ciause 6.9)Minimum area of reinforcement= 0.1% of crosssectional area of concrete above ribs= 0.1/100 x 948 x (120-68) = 64.46 mm 2/mProvide 8 mm bars@ 300 c/c (167.5 mm 2/m).6.Composite slab-fire designThe slab is designed fo r a fire duration of 60minutes.Criterion "I "(EC4-part 1.2-Ciause 4.3.1.2)The effective thickness ofslab is given by,he=h 1+0.5h2(11+1/1 1+13 }for h/h 1 1.5 and h 1> 40 mm

'I'he T'Figure 9 - Section ofComposite Slabfor Pire d ~ s i g n

The dimensions are:h1=thickness of concrete above ribs =68mm,h2=depth of sheet=52 mm,h3=depth of screed layer above slab assumed =20 mm,1=158 mm,l2=124 mm,l3=124 mmh.=68 + 0.5x52 ((158+124/ 158+24))=94mmThe minimum thickness required is(EC4-part 1.2-Table 8)h. ;:: (90-h3 ) = 90-20) = 0mmSo criterion 160 is easily satisfied.Criterion

(EC4-part 1.2-Ciause 4.3.1.3)The moment to be resisted during fire isRrd, ll*Rd11 *=resistance ratio given byll*=llrEJRd111=0.6

II R J/

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Ed= maximum mid span bending moment= 2.842 kNm/mRd= moment of resistance = 17.32 kNm/m11*=11 1EiRd=0.098Rd > 0.098 X 17.32 =1.705 kNm/m < 17.32 kNm/m,thus safeGraph (Span Vs Capacity) with grades250/350/550 MPAfv=250 N/mm2 ,h=120 mm

load (kg/m)unpropped1600140012001000800600400200

00 0.5 15 2.5 3

fv=250 N/mm2 ,h=145 mmload {kg/m)unpropped

160014001200 t1000800 +600 ;400 ---- -200 "

0 t0 0.5 1.5 2

fv=250 N/mm2 ,h=240 mm25 3

load (kg/m)unpropped160014001200 t1000 : I800 60 0400200

00 0.5

ISSE JOURNAL

1.5 2.5 3

.....-o.Smm

- - -1 .2mm-16mm

3.5

o . s m m--lmm

-L6mm

3.5

- - - - o.8mm- - lmm---1.2mm

35

8

fv=350 N/mm2 ,h=120 mmload (kg/m)unpropped

2500 T2000 I1500 1000 -500

00 0.5 1 5 .2.5


2500 r2000 t

1500 T -

0 0.5 1 5 2.5 3


2500 r2000 I1500

I 1000 t-500

00 OS 1.5 2

f..=550 N/mm7 .h=120 mm2 5

I Load (kg/m)unpropped350030002500200015001000500

00 0.5 2 2.5

.....-os mm--l mm---l2mm- 1.6 rnm

3.5

.....-osmm-+-lmrn

-16tnm

.....-osrnm- - lmm--- 1.2 rnm-1 .6mm

3 s

- - s c n e ~ 3

3.5



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fv=SSO N/mm2 ,h=145 mmload (kg/m)unpropped

35003000 t-

2 ~ 0 0200015001000soo

00 05 1.5 2.$ 3.5

fv=SSO N/mm2 ,h=240 mmload (kg/m)unpropped

350030002500100015001000500

00 05 1 1 5 2: ; 3 3 5

-r-Sencs3- - s e n ~ l..,._Senes2-ser1


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DESIGN AND CONSTRUCTION OF WIREWOUNDCIRCULAR PRECAST,PRESTRESSED CONCRETE TANKSSanjay Mehta

Abstract:Circular precast, prestressed circular concretetanks, although common in the North AmericanContinent, are only now making their way in theIndian subcontinent. Circular concrete tanks,prestressed with continuous, spirally wrappedhigh strength steel wires offer superiorperformance, liquid tightness and service life ascompared with the reinforced concrete tanks.Once hydro tested after initial construction, suchtanks can be virtually maintenance free. Liquidtightness of such tanks is particularly appealing interms of Indian context because of significantwater loss in storage and distribution systems.Furthermore. replacing a system of UndergroundSump Reservoir (USR) and Elevated StorageReservior (ESR) with a single. tall prestressedconcrete tank can result in significant savings inpumping electricity cos.t in addition to savings inland and excavation cost. Precasting operationhas an added advantage of speeding up theconstruction. Tanks as large as 100m in diameterand 25m in height have been successfullydesigned and constructed across the UnitedStates. This article is written to explain salientfeatures ofdesign and construction of such tanks.INTRODUCTION:

Circular reinforced concrete tank walls aredesigned and constructed to keep concrete hoopstress within modulus of rupture when subjectedto liquid load. Amount and spacing ofreinforcement is designed to control crackingwithin the tank wall as per the applicableprovisions of IS 3370 and IS 456. Typically, baseof the tank wall is either fixed or hinged to the

ISSE JOURNAL 10

footing. This traditional approach to reinforcedconcrete tank design has three major problems:1. Concrete is in tension in circumferential

direction when subjected to liquid load. Noamount of mild steel reinforcement canprevent concrete from cracking or microcracking. The problem is exacerbatedwhen shrinkage and thermal stresses areadded to tensile hoop stresses.At best, it ispossible to design for crack control asexemplified in IS 33701

2. The fixed or hinged base prevents lateralmovement of wall base when subjected tothe liquid load. This results in verticalbending of the tank wall. Flexural tensilestress well in excess of modulus of ruptureof concrete can develop due to this baserestraint.

3. In case of a seismic event, the load pathfrom tank wall, subjected to liquidconvection and impulse, goes through thewall-footing joint. Although this joint can bedesigned and reinforced to provide therequired ductility, it is not possible to controlcracking in case of an extreme seismicevent. The liquid tightness of the tank willbe compromised during such a seismicevent, precisely the time when waterrequirement is very critical to control postearthquake fires.



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3.

always less than total inward radialmovement, ensuring residual compressionin the tank wall under full hydrostatic loads.The liquid tightness of the wall-footing jointis achieved by use of a specially designedPVC waterstop. This waterstop, about275mm long, has ability to move radially byabout 75mm without compromising liquidtightness of he tank.Typically, seismic restraint cables areplaced on the outside of the precast corewalls. The cables are activatetf only whentank wall begins to slide either duringearthquake or wind or any such lateralloads. Under normal operating conditionsthe restraint cables remain inactive andalmost unstressed. Thus, lateral loadresistance is separated from the verticaland hydrostat ic loadresistance , providingsu pe r i o r se i sm i cperformance.

BENEFITS OF PRECASTTECHNOLOGY:

service, due this tilt-up operation. In contrast tocast-in-place walls, the precast wall castingoperation can start simultaneously with the floorpour. This significantly reduces the constructiontime of the entire project since wall concreting isno longer along the critical path.DISCUSSION OF CRITICAL DESIGN ANDCONSTRUCTION CONCEPTS:Figure 3 shows a typical section of wirewoundprecast, prestressed concrete tank. Accordingly,there are five critical elements in the design andconstruction (1) Floor and Footing (2) Wall BaseJoint (3) Precast\Wall Panels and Joints (4) WallPrestressing and Shotcreting and (5) DomeConstruction and Prestressing. Each element isdiscussed as follows:

DOME PRESTRESSING - - - - 'PRECASTCONCRETE WALlt is well known that better concretequality control can be exercisedwhen concrete is poured under INCt.AVED STEEl DIAPHRAGMSHOTCRET COATCOntrolled COndition ThiS iS CIRCUMFERENTIAL WIRE PRESTRESSINGparticularly true in case of tankwalls because poor quality ofconcrete is the primary reason forleakage from liquid containingconcrete structures. Furthermore, ifit were possible to cast circular

walls in sections, shrinkagestresses due to restraint could bedrastically reduced . Small sectionsof walls are easier to pour andfinish, especially when concrete

SHOTCRETE COVERCOATCONCR11: WAltRSTOPENCASEMENT ----,

ElASTOMERIC BEARING PAD ~SEISMICCABLES ----,

rpour is in horizontal direction. Sincewall panels are cast in horizontal Figure 3: Typical Cross Section of Wirewound-Prestressed Concrete Tankposition, they have to be tilted up and placed inposition on the circular ring footing. The tilt-upoperation generates high flexural stresses in thewall panel. Thus, the strength and quality ofconcrete is tested even betore the tank is placed in

ISSE JOURNAL 13

1) Floor and FootingTypically, 0.3m deep footing is cast monolithicallywith 0.1 m membrane slab. Figure 4 shows crosssectional details of footing-floor connection. As



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I

SEE ENCASEUENT DETAL MS SHEET.V.C. WATEJMtJI (COO.)

L 1--- WATER'S'Itft BASt CNl.EOUtsi)E FAa. CJ' F'001lNG

VAlE SUaaw AS REQI.RDTO RACH FilM BEARIIG SlRAlUU.PlACE AN> CXIIPACT SElCT FU TOI'ROWlE tJIFlR,I !IEARINC SURFACt

Figure 4: Wall-Floor-Footing Detai ls

perACI 350-062 , Appendix G, floors upto 0.15m inthickness are classified as "membrane" floors.Membrane floors are designed with a single layerof reinforcement in each direction for creep andshrinkage of concrete. They have very littleflexural capacity and liquid load is transferred"directly" to the supporting soil. That is, the slab isflexible enough to conform to the deformed shapeof supporting soil. The key to the successfulperformance of a membrane floor lies in theuniformity and strength of subgrade. So long assupporting soil is compacted properly to avoidlocalized settlement, the membrane slab willdeform in "dish-type" settlement shape. ACI 372RISSE JOURNAL 14

-033 , Appendix A, Section A.3.2 describesdeflection limits on various deformation modes ofmembrane slab-on-grade, along with designconsiderations.The ring footing is connected to the membranefloor using haunch and reinforcement as shown inFigure 4. The membrane floor acts as a "tie"which prevents footing rotation due to eccentricityof the vertical load. The design approach requireschecking tie stress at floor-footing haunch toensure that the tensile tie stress is well within themodulus of rupture of concrete to ensure liquidtightness. The width of he footing is selected suchthat stresses from vertical loads are within theallowable soil bearing capacity.

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Figure 5: Floor-Footing Reinforcement

As far as possible, it is preferable to cast floor andfooting in one pour to avoid construction joint.Construction joints in liquid containmentstructure are a maintenance problem.Special care is required to vibrateconcrete around horizontal water-stop atthe construction joint to prevent"honeycombing". Membrane floors aslarge as 60m have been cast in one pour.Figures 5 through 8 show various stagesof membrane floor and ring footingconstruction.2) Wall Base JointAs mentioned earlier, unlike reinforcedconcrete tanks, circular prestressedconcrete tanks are designed to move inand out in the radial direction. This isachieved by setting elastomeric bearingpads between top of the footing and wallbase. Bearing pads allow radial tankmovement with minimum resistance. Thedesign approach requires calculation ofbearing pad resistance and vertical

computed assuming noreduction in stresses due topad resistance. As can beseen in Figures 3 and 4, liquidtightness at the wall base jointis achieved by casting aspecial waterstop into thefooting on the inside face ofthe wall. After wall panels areerected, the waterstop isencased in a concrete curb,as shown in Figures 9 and 10.The design approachrequires computation of wallbase joint displacement whensubjected to combined effecto f c i r cumfe ren t i a lprestressing and liquid load.The wall base movement isrestricted to about 40mm toensure sufficient factor of safety on thedisplacement capacity of waterstop. In somesituations, partial prestressing may be required.That is, curb may have to be cast after

moment in the wall due to this resistance. ~ ~ ~ ~ E = = : : = ~ J S i JThe hoop forces in the tank wall are Figure 6: Floor Concrete Pour

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Figure 7: Screeding and Finishing Operation

Figure 8: Flooding and Curing of Concrete Floor(Waterstop and Seismic Cables Embeded in Footing)

ISSE JOURNAL 16

Figure 10: Concrete Encasement for Waterstopprestressing the tank to some extent. Theremaining prestressing will be applied aftercasting curb.3) Precast Wall Panels and JointsTypically, the wall panels are cast in 3m sections.The panel curvature is developed by computingordinates for 3m section based on the tank radius.A sand bed is prepared on the ground with propercurvature. A thin steel sheet metal diaphragm(similar to corrugated steel sheet) is placed on thesand bed. It is this steel diaphragm that separatesthe concrete wall panels from shotcrete and



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Figure 11 : Diaphragm for Wall Panelsprestressing wires. The barrier provided by thesteel diaphragm prevents the water from reachingthe prestressing wires. Liquid tightness providedby the steel diaphragm, when combined withalkaline rich shotcrete encapsulating theprestressing wires, prevents corrosion of wires.Hence, it is possible to use plain prestressingwires without any need for galvanizing .Thousands of prestress concrete tanks using thisapproach have been designed and constructed inthe United States using non-galvanizedprestressing wires.Figure 11 shows field preparation of steeldiaphragm for casting 3m wide panels. Figure 12shows concrete operation for panel casting. Awood screed cut to the curvature of he tank radiusis used to "strike off' concrete.AWWA Standard 0110-044 restricts allowablestress in the steel diaphragm to 125MPa (18ksi)when counted as reinforcement in the verticaldirection. The bond stress between plain steelmetal diaphragm and concrete in the verticaldirection is one of the reasons for restricting theallowable stress to 125MPa. This bond is fullytested during the panel pick up operation becauseof high flexural stresses developed in the precastwall panel. Frequently, the panel tilt up operationgoverns the reinforcing steel requirements in thepanel. Figure 13 shows panel tilt up operation.Figure 14 shows adjacent wall panels set on thetop of the bearing pads over footing . As can beseen, there is vertical joint between wall panels,abut 178mm to 203mm wide. Horizontalreinforcement placed at 1200mm on centerprojects out from the panel ends. Thisreinforcement is welded to 18mm X 18mm X 6mmISSE JOURNAL

Figure 12: Panel Casting and Finishing

Figure 13: Tilt Up Operation for Precast wall Panel

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Figure 14a: Wall Panel Set on Bearing Pads

Figure 14b: Vertical Joints between Wall Panels

ISSE JOURNAL 18

Figure 15: Shotcreting of Wall Panel Jointsthick steel angles, 150mm long. Welding ofreinforcement to steel angles provides stability towall panels during construction and prestressingoperation. This joint is then filled with shotcreteapplied against the projecting ends of thediaphragm sheets. Figure 15 shows jointshotcreteing operation.The design approach requires that the wall paneljoints remain in compression under full hydrostaticand hydrodynamic fluid pressure. Minimumprestressing is provided even above the waterlineto ensure residual compression in the wall paneljoints.4) Wall Presrtessing andShotcretingAfter shooting all vertical wall panel joints, 12mmthick coat of shotcrete is applied over the steeldiaphragm. Figure 16 shows steel diaphragm onthe outside of the tank wall. Figure 17 showssimilar view after shooting shotcrete overdiaphragm. The prestressing operation startsafter shotcrete coat has gained the requiredstrength. Typically, 5mm diameter high strengthsteel wire (1517Mpa) is pulled through the dieusing a prestressing machine. Pulling highstrength steel wire through die reduces the wirediameter before it is placed on the wall. Thereduction in the wire diameter corresponds toprestressing force applied on the wall. Thismethod of "wirewinding" or prestressing ensurescontinuous and uniform prestress along the tankcircumference at a particular elevation from thetank floor. This is the most distinguishing feature of

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Figure 16: View Showing Steel Diaphragm onOutside of Wall Panels

Figure 17: Tank Exterior After ShotcreteCoat Over Diaphragm

ISSE JOURNAL 19

Figure 18: Wirewinding Machine for Circular Prestressingwirewound tanks as compared to the tendonprestressed tanks, in which case (1) Thecircumferential prestressing is discontinuous and(2) Prestres, at a given height from the tank floor,is not uniform along the circumference due tocurvature and friction losses. Figures 19 and 20shOVI{Wirewinidng operation.Design and detailing requirements dictate thatwires be spaced at least 1 wire diameter apartalong the height of the wall so as to completely

Figure 19a: Prestressed Wires on Wall

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encapsulate them in shotcrete wire coat. Thisrequirement restricts number of wires toapproximately 22 per 300mm height of wall. Thus,many "layers" of wires would be required at thebase of the wall to counteract higher liquidpressure as compared to only one "layer'' ofwiresat the top of the wall. In terms of construction , thefirst layerofw1res is applied along the full length ofthe wall over diaphragm shotcrete coat. This layerof wire is covered with shotcrete to provideminimum 6mm cover coat over wires. The nextlayer of wire is placed on the wall after shootingshotcrete over the first layer of wires. As many as15 layers of wires may be required for bottom 2mof wall in case of all , large diameter tanks.At least 25mm of shotcrete cover coat is appliedover the final layer of prestressing wire to provideadequate cover protection. The normal practice isto coat the wall shotcrete with "breathable" paintafter applying final shotcrete cover coat.5) Dome Construction and PrestressingThe most popular method of roof over potablewater tanks is spherical dome. Clear spanningdomes are aesthetically pleasing and provide tankinterior that is free of any obstruction for cleaningand maintenance purposes. This is particularlyimportant in case of digesters because rotatingequipment inside the tank will function only whenthere are no obstructions. Furthermore, ascompared with flat slabs, domes require lessconcrete and steel and hence, are economicallyattractive.Typically, concrete domes are cast in-situ due todouble curvature. However, many precast domeshave also been built mainly for small diametertanks. Seismic performance of cast-in-placedomes is far superior to precast domes and manyhigh seismic regions in United States precastdomes are not preferred.Construction of cast-in-place domes requiresfalse work erection and formwork as shown inFigures 20 and 21 . The dome concrete is pouredin "pie" sections. Typically, 6 to 8 "pie" sections arerequired to complete the dome pour.The thickness ofdomes is in the range of 75mm toISSE JOURNAL 20

Figure 20: Falsework for Dome Construction

Figure 21 : Formwork before Dome Pour125mm and hence domes are classified as "th1nshell structures". As is well known, the behavior ofthin shell structures is governed by buckling.AWWA 0110-04 provides an equation to computedome thickness based on the buckling resistancewhen subjected to vertical dead and live loads.This equation accounts for the fact that there

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could be flat spots on the dome surface because offalsework fabrication and erection tolerance.The design approach requires computing flexuralstresses in the end regions of the spherical domedue to the "edge effect". The dome tension ring isprestressed to counteract the dead load and liveload thrust. Typical dome design requires "hinged"connection between dome edge and top of thewall. Detailed discussion of all design aspects isbeyond the scope of this introductory paper.However Billington5, Timoshenko6 and T.Y. Lin7have covered this topic in great detail.Dome prestressing operation begins after domeconcrete has gained the required strength.Typically, dome is prestressed for both dead andlive loads. Most of the times, dome "lifts" off theformwork support after application offull prestressbecause full live load is never applied on the domesurface. This "lifting" up of dome facilitatesfalsework and form work removal operation.HYDROTSTING OF TANK:Mostof he design and construction Specificationsrequire that prestressed concrete tank be hydrotested to demonstrate the liquid tightness.Depending on the intended use of the tank, theextent of "liquid tightness" varies from bottle tightto measurable loss within the specified limit. Asper AWWA D11 0-04, an ANSI standard for potablewater tank, the tank is filled with potable water tothe maximum level for 24 hours before starting thehydro test. The liquid drop is measured over thenext 72 hours to determine the liquid volume lossfor comparison with the allowable leakage. Thetank is accepted if the net liquid loss for a period of24 hours does not exceed % of 1% of the tankcapacity. Furthermore, wet spots on the exterior oftank walls and flowing water at the base of the wallfooting joint are not permitted. Necessary repairsare carried out if tank does not pass the hydro testat no expense to the owner.PAINTING AND ARCHITECTURALTREATMENT:

23: Architectural Treatment- Brick PilastersSUMMARY:Circular wirewound, prestressed concretetanks offer superior performance anddurability as compared to reinforced concretetanks because it eliminates all the problemareas associated with reinforced concretetanks. In addition, it is possible to constructground supported tanks as tall as 25m whichcan replace a system of USER and ESR.Replacing two tanks (USE and ESR) with oneprestressed concrete tank providessignificant savings in pumping electricitycost, increased storage capacity and savingsin land as well as construction costs. Thesuperior water tightness of prestressedconcrete tanks, demonstrated by hydrotesting after completion of construction, isparticularly important in the Indian contextbecause of significant water loss in storageand distribution system.REFERENCES:

The exposed surface of dome and wall is paintedto improve aesthetics and durability of the tank. In 1) IS 3370, Vol. 1 through Vol. 4- "Code ofPractice- Concrete Structures fo rStorage of Liquids," Bureau of IndianStandards, 2000addition, various architectural treatment, asshown in Figures 22 through 23 can be applied onthe tank exterior to improve aesthetics.

l f O J g U I @ ~ ~ . . f i l o r m w o r k before Dome Pour 21 Volume 14-2, APR-MAY-JUN 2012


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2) ACI 350-06 , "Code requirements forEnvironmental Engineering ConcreteStructures and Commentary", AmericanConcrete Institute, 2006

3) ACI 372R-03, Design and Construction ofCircular Wire- and Strand-WrappedPrestressed Concrete Structures, AmericanConcrete Institute,20034) AWWA D110-04, "Wire-and Strand-WoundCircular, Prestressed Concrete WaterTanks," American Water Works Association,20045) David P. Billington, "Thin Shell ConcreteStructures," 2nd Edition, McGraw-Hill BookCompany

6) S. P. Timoshenko and S.W. Krieger, "Theoryof Plates and Shells," 2nd Edition, McGrawHill Book Company7) T.Y. Lin and Ned H. Burns, "Design ofPrestressed Concrete Structures," ThirdEdition, John Wiley & Sons

About the Author :

Dr. San ay Mehta is the Chief TechnicalOfficer and Vice President ofEngineering at Preload Inc. USAE-mail : [email protected]

Publications available at !SSE head officeTitle

Publications :Donation amount Rs.

Design of Reinforced Concrete Structures for Earthquake Resistance 800 Professional Services by Structural Design Consultant - Manual for Practice 200Proceedings:

National Conference on Corrosion Controlled Structure in New Millenium 400 Workshop on IS0-9001 for Construction Industry 200 Brain Storming Session on Use of Speciality Products in Structures 250 Workshop on Software Tools for Structural Design of Buildings with CD 550 Workshop on Structural Audit 200 Workshop on-Seismic Design of Building 200 Workshop on Effective Use of Structural Software. 200 Workshop on Effective Use of Structural Software - CD 150 Workshop on Shear Walls in Highrise Buildings 200 Seminar on Innovative Repair Materials I Chemicals 250 Seminar on Foundations for Highrise Buildings 200 Seminar on Structural Detailing in RCC Buildings 250 Workshop on Pile Foundations 200 Seminar on Pre-engineered Structures 200



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REPORT ON INAUGURATION OF ISSE AURANGABAD CENTRE22 JUNE 2012

Hemant VadalkarAuranagabad centre of Indian Society of Structural Engineers was inaugurated on 22nd June 2012, atAurangabad Gymkhana Club. The first body ofelected office bearers was sworn in . Kamal Rao has beenelected the Chairperson of the local chapter, Ravindra Bansode the Secretary, Shushan Joshi theJointSecretary and A mol Joshi the Treasurer.The ceremony started with welcoming the guests and traditional lighting of lamps. The dignitaries wereinvited to the dais and the programme began with technical presentations of the main sponsor, RajuriSteel. The presentation depicted the care and efforts taken by Raj uri Steel in manufacturing quality steel.Ravindra Bansode, Secretary,Aurangabad centre, spoke about the inception of the chapter and a briefaccount of he activities carried out so far.Hemant S. Vadalkar, Advisory Trustee of ISSE mentioned about the various publications that areregularly published. He also spoke on various aspects of the ISSE Web site.P.B. Dandekar,Secretary, ISSE high lighted the activities carried out by the Society at the National level.K.L.Savla, former Secretary, ISSE emphasiged the need and method of setting up new chapters atvarious centres of activities in the country.Prof. G. B. Chaudhari, President ISSE enlightened all about the vision and need of having an institutionlike that of ISS E. He pointed at the technical marvels ofAjanta and Ellora, the grace and beauty of thecaves and the highly specialised technical craftsmanship required in carving out the Kailash temple atEllora,on the rock mass.Kamal Rao as Chairperson accepted the challenges and responsibilities entrusted on the office bearers.She spoke about the challenges that have to be faced by her eam boldly, bravely and squarely.Senior Structural Consultants, N.R. Varma and Ravindra Babulay and Senior professors, Prof. Achwal ,Prof.J.D. Koparkar and Prof. J.D. Koparkarwere felicitated on this occasion.Structural consultant N.R. Varma and N.G. Karkhane addressed the junior engineers and encouragedthem towork to the bestof heir capacities for the profession.The key note speaker at the ceremony was Dr. Sidharth Ghosh from liT Powai. He spoke on theadvantages of steel as a construction material. He gave special emphasis to the use of light gauge steelframes and tubes in residential structures. He also mentioned about the need to revise academiccurriculum to meet the demands of ndustry

ISSE JOURNAL 23 Volume 14-2, APR -MAY-JUN 2012


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VISUALS FROM INAUGURAL FUNCTION OF AURANGABAD CENTRE OF ISSE

Edited and published by N K Bhattacharyya for ISSE, C/o S G Dharmadhikari, 24 , Pandit Niwas, 3rd floorS K Bole Marg, Dadar, Mumbai400028. Tel91-22-24365240, Fax-9122-24224096, email [email protected] Web( www.isse.org.in) for private circulation andprinted by S L Bengali, Bensan Printers, 15, Pandit Niwas, S K Bole Road,Dadar, Mumbai 400 028



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