·- ·

541 4th intemational conferenceon coasts, ports & marine structure,Nov 2000

Shahid Rajaee Pon Complex, Bandar Abbass

DESIGN OF SLIPWAY FACILITY FORREPAIRAND MAINTENANCE OF PORTCRAFfS

Dr.R.SUNDARA V ADIVELU Associa te Professor Ocean Engineering Centre, IIT Madras Chennai, India.

Dr.R.NATARAJAN Associa te Professor Qcean Engineering Centre, IIT Madras Chennai, lndia.

Abstract

Dr.::l.R.GANDHI Associa te Professor

Civil Engineering Dept., IJT Madras Chennai. lndia.

G.THILAKA VATHY Project Associare

Occan Engineering Centre, IIT Madras Chennai. Lndi:t.

The proposed slipway facility at Kandla Port where a large tida/ variation exists, is situated on a soft c/ay deposit characterised by low shear strength and high compressibility. ln arder to meet the shortfal/ ofthe dry dock capacity, a slipway track with two berth ç for repa ir and maintenance of crafts has been designed for a 'maximum vessel displacemenr of 140 tonnes. The inc/ination of the slipway track is kept as 1 in 12, since ir is found to be most economical slope. The slipway facility is provided with cradle arrangements for transferring of the \'esse! from the track to the repair yard. The slipway facility, which is of end on type, h as been analysed and designed for lhe existing soil condition usingfinite element method.

1. lntroduction

The port of Kand.la, located on the northern bank of Kandla creek is the only major port in the state of Gujarat. lt has a natural and well protected harbour. A draft of 8.14 m is available ali round the year. To augment the dy-dock capacity, 3 altematives have been suggested and finally construction of slipway with two berths capable of catering craft having displacement of 140 t01mes has been taken up for design considering the following tidal variation and craft parameters are considered:

2. Tidal Data

Mean high water spring (MHWS) Mean sea levei Mean high water neap (MHWN) Mean low water neap (ML WN) Mean low water spring (ML WS) Da tum of soundings

(+) 6.7 m (+) 3.9 (+) 5.9m (+) 0.83 m (+) 1.8 m (+) QOO

3. Vessel Data

Length Beam Draft Displacement

4. Arrangement ofSlipway

4.1. Slipway Track

-24.0 m -7.20 m -2.25 m -140T

The slipway track is planned for a slope of I in 12 from + 8.7 m levei to+ 0.2 m levei. The slipway track is of 102m length and 12.20 m wide as shown in (Fig 1). The structure consists of a deck system with a flat slab of 500 mm thick supported on 3 rows of RCC bored cast in situ pile of 900 mm dia The height of the pile increases gradually upto sh<re levei. The founding levei of ali the piles is fixed the sarne with respect to soil conditions. Fender column of900 mm x 900 mm size is provided on the end row of piles to accommodate fenders. A cantilever beam of 1350 mm x 500 mm is provided for the entire length to minimize siltation in the track.

Water jet is provided to clear the water from the slab during the repair and maintenance ofthe craft. There are two types of transportation of water (i) acreation i. e. on shore and off shore transportation (ü) erosion clearing the water along the shore using water jet As the lower end ofthe slipway track is under water, a cofferdam is constructed except when tida! range is large and vessels are proposed to be slipped of near high water.

Fender Beam 1350X900

Fender column 900X900

+8.7~

M.S.~ +3.90

-25.0 Founding Levei

Sloping crad.le

Slope I 12

Fig.J.Isometric view ofSiipway

2

5. Transfer Berth

The transfer berth which is perpendicular to slipway track as shown in (Fig 1 ).is designed for two crafts to be repaired at a time and deck levei is kept at + 8. 7 m. The size of the transfer berth is 36.0 m x 40.5 m. The structure consists of deck system with a flat slab of 500 mm thick, supported on 8 rows of RCC bored cast in situ piles of 900 mm dia. The size of main winch and transfer winch room is 6 m x 6 m each respectively. The capacity ofthe main and transfer winches are selected from the pull required for hauling conditions with design speed. The capacity of main and transfer winches for design are 35 t and 15 t respectively.

The rigging arrangement consists pulley blocks and wire ropes. A retum pulley of 1 m dia is anchored in the sea bed 5 m, away from the slipway end Wire ropes are used for hauling purpose. 6 N.:>s of 1 m dia pulley blocks are used for the passage ofwire ropes to the winches.

6. Cradle Arrangement

The launching gear of an end on slipway track is equipped with a sloping cradle, vessel cradle and hauling arrangement ln order to repair two vessels simultaneously, the slipway is provided with a transfer cradle on the transfer tracks. A sloping cradle lBs no limitation as the main cradle is kept ón a sloping cradle which compensate for the slipway with a triangular structure.

6.1 Sloping Cra_dle

The sloping cradle to dry dock the vessel as shown in (Fig 2) has the following dimensions :

Length Width Height

18m 6m 0.65m (at the forward end of slipway track) 2.15 m ( at the aft end of slipway)

The sloping cradle is provided with 4 longitudinal tracks fitted with 48 wheels. The sloping cradle is designed to withstand the weight of vessel and the vessel crad1e i.e. 200 t. The cradle is a fabricated fra.me structure with I-sections (ISLB 150), channels (ISMC 350) and angles (ISA 75 x 75 x 10, 150 x 150 x 10). The cradle is fitted with CR 80 rails and wheels. The complete structural arrangerrent ofthe s1oping cradle is shown in Fig2.

c

2599 2500 I ,,:a I. ""' 1. 2599 2599 :1 Fig. 2 Sectiona/ plan of Sloping cradle

3

The strength of the structural members of the frame structure are checked as detailed below:

Load between centers of two wheels Distance between two wheels Bending moment

Section modulus oflSMC 350 Bending stress

10 t 1.4 m WU4t-m (lO X l.4Y4 3.6 t-m

571 crri' (3.6 X 1000 X 1 OOY571 1576 kg'cm2

Since, the bending stress ofthe frame structure is less than the allowable stress, the design is safe.

P x R= (W + W x n) K + J.l x Wxr W = Total Weight of the V esse! . and Cradle (200 tonnes) W = Weight ofthe Wheel N = No. ofWheels (80)

O 50 I 00 150 200 250 300 350 400 R Radius of the Axle 25 nm

WHEEL DIA lN nrn K = Coefficient of Rolling Friction (QOOS) 11 = Coefficient of Sliding Friction

(0.035)

6.2 Transfer Cradle

The Transfer cradle of the vessel as shown in (Fig 4) has the following dimensions

Length Width Height

184m 5.5 m 0.65m

Since, the cradle is moving in the horizontal plane, the length of the cradle may be less than the length ofthe vessel. The design offrame structw"es and wheels is similar to the sloping cradle rails and wheels. The cradle is moving in 9 tracks with 36 wheels.

4

2300 2300 2300 2300 2300 2300 2300 2300

ISA IOOXIOOX6

l.e------ ------ - 1840io--------------.J

FigA Sectiona/ p/an ofTransfer crud/e

7. Hauling Gear

The hauling gear consists of powerful winches operated by electro hydraulic system. Wire ropes are used for haulage. The cradles may be lowered by the back haul system similar to the up haul with the help ofthe winch by reversing the mechanism to control the speed ofthe down haul.

The pull on the hauling rope can be calculated from the following expression as per IS Code -1 0020 (Pru.t IV) 1981 :

p W (S+C)

R

Fig. 5 Acceleratiou and velocity of a sloping

c radie

Where

p w s c

Therefore

p

pull on the hauling rope in tonnes weight ofthe vessel and the cradle tan e (e = Angle of slope of lhe slipway)

Coefficient offriction which may be taken as 0.035

200 (0.083 + 0.035) 23.6 t 24 t

The sliding speed and acceleration of the sloping cradle can be determined as:

Sliding speed fi X g X s X Cose (Tan e- fs)

5

Where t is the · coefficient of sliding fiiction and asswned as 0.035 and s JS the length of the slipway.

Hence,

Sliding speed .fi X 9.81 X 90 X Cos 4.96 (Tan 4.96 - 0.075)

.fi X 9.81 X 90 X Cos 4.96 X 0.012

9.19 rnlsec

Acceleration is determined from the following equation:

J i +2 as

9.1~ 0+2ax90

180a

a 0.469 m!sed-

The acceleration otthe sloping cradle in the hauling conrution can be found out as detailed below:

P = mg Sine+ f.Ullg Cose +ma

Therefore

24 X 9.81 = 200 X 9.81 X 0.083 + 0.035 X 200 X 9.81 X 0.996

235.44

a

= 162.85 + 200 x a+ 68.40 + 200 a

= 0.02 mlsec2

The hauling speed caJculated fium the following equation :

J ul + 2as 0+2x0.02x 18 0.72

v 0.85 m/sec.

8. Analysis and Design

The influencing factors in determinmg the Jength of the sEpway are (i) length a..nd draft of the vessel to be catered. (ü) Slope ofthe slipway (iii) Height ofthe blocks above raillevel. Slipway are designed to be not less than 2 I /2 times the Jength of the largest vessel to be accommodated. The following expression takes these factors in to consideration.

L= 21 +s (d+h) + b

Where

L = Length of slipway in meter I = length of vessel between perpenrucular in meter. S = Horizontal rustance for unit rise of slipway incEnation d = draft of vessel at forecastle bulk head in meter h = height from raiJ levei to top of block in meter

6

The inclination of slipway is kept as I in I 2 as it is found to be the most commercial and econom.ical slope. A steeper slope ora tlat slope has got its own disadvantage ofheavy hauling and a shore-end too high for convenient work.

ln arder to facilitate the construction of slipway a cofferdam has been designed using braced sheet pile wall (Fig 6) instead of an earthern bund since the soil is weak. A braced cofferdam is formed by driving two rows of vertical sheeting and bracing with wales and struts at 3000mm ele. It is similar to sheeting and bracing system for braced cut. It is constructed to prevent cave in. After the pit is dewatered, the structure will be concreted and cofferdam removed.

The slipway is analysed used Structural Analysis & Design Package ST AAD lll. The analysis and design of slipway track depend upon the type of crafts handled, the environmental factors which is subjected to and soil strata. The fuúte element method is adopted to model the structures

The founding levei cf pile is taken as - 25.0 m based on the bore profile (Fig.7) and axialload on the pile (2160.85 kN.) The fix.ity levei of pile is taken as 10 D below the dredge leve! according to the sai! conditions as per IS 2911. Thus, the height of pile for analysis varies form 9.6 m to 14.98 m for a slope of 1 in 12 (i.e. from fixity levei to m.id depth of slab ). The criticai forces goveming the design ofslipway are wheelload, seismic force, earth pressure and sue load.

I. Wheel Load : A wheelload of 40 kN is calculated by taking the weight of the cradle as 40% the weight of the vessel (i.e. 1400 kN) and taking 50 wheels per cradle (Fig.8).

2. Seism.ic Force: The seism.ic force acting on each pile is taken as point loads in STAAD analysis i.e. 61.50 kN by taking deadload and 50% ofthe live load in the seismic load calculations.

3. Earth pressure : The earth pressure is calculated by assuming the earth deposition of3 m above the bottom slab"!evel outside the slipway. The necessary soil characteristics such as <1> ,y were assumed and active earth pressure coefficient Ka is calculated. The total pressure acting at different depths on the side walls were calculated as points load and applied in the ST AAD analysis.

4. Sue load: Sue load is a concentrated load induced on the cradle and the tracks at inboard and out board ends ofthe cradle while hauling. Sue load is calculated as 7260 kN which nonnally varies from 1/3 to 118 ofthe light displacement ofthe vessel depending upon the shape and size The necessary load combinations as per IS 4651 part UI is considered in the analysis.

Based on the rnaxirnurn moments, axial forces, shears and torsion from the ST AAD analysis, design of ali the structural members has been canied out The maximurn bending moment is obtai.ned for a load canbination of 1.2 Dead Load + 1.2 Live Load + 1.0 Earth Pressure + 1.5 Seismic Force. For the deflection and crack width check, "A Knowledge Based Expert System for Design of Berthing Structures" has been made use of A flat slab is provided instead ofbeam since cleaning the settled sediments due to tida! action will be easier with the flat slab. ln addi.tion the flat slab will provide an i11tegral connection of ali the piles.

ACKNOWLEDGEMENT

1l1e authors would lik.e to thank the authorities of Kandla Port Trust for extending their kind cooperation in providing the technical data required for the design of slipway and permission to publish this paper.

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REFERENCES

l. Code ofPractice for Design and Construction ofPile Founclation, IS 2911, 1979.

2. Code of Practice for Plaruúng and Design of Ports and Harbour, IS 4651

3. Recommenclations for Design and Construction of Port and Harbour Components, IS

10020 (Part IV)- 1981.

4. Jolm P.Comstock, "Principies of Naval A.rchitecture", Society of Naval Architects and

Marine Engineers, New York, 1967.

5. Nina Morgan, Butterworths "Marine Teclmology Reference Book", United Kingdom,

19W.

6. Ranga ~o, A.V. and Sunclaravadivelu, R "A Knowledge Based Expert System for

Design of Berthing Structures", Ocean Engineering, 1999, Vol.26, pp 653 - 673.Robert

Taggart, "Ship Design and Construction, Principies of Naval A.rchitecture", Society of

Naval Architects and Marine Engineers, New York, 1981.

8

DESIGN OF SLIPWAY FACILITY FOR REP AIR AND MAINTENANCE

OF PORT CRAFfS

r.,,..,.

-'·N-::L -s.-:x_

SECI!ON - I X

12J(ID

I----III---4----'""LI1B • 3000 o/o X X

T 111---+-- WAU:S T ----------~, ,., _.,..,.,. . ....

-+-- 811140

11200

ri51.G. BRACEO SHEET PILE WAU.

9

OEPTH SOll CLASSIFlCATION R.L

+4.2 +32 GREY SDfT CLAY

+1.2 GREY SOFT SILTY CU.Y 0.0 GRE.Y f1 NE S*JOY SIL lY CLAY

-0.7

GRE'r' CLAYEY flNE SANDY -2.6 SILT ~D SOFT SILTY CLAY

GREY SOfT SILT'f CLAY'

-5.0 GREY FlNE S~~~J SILTY

-6..3

OREY FlNE SANDY SILTY

CLAY -9.3

-10.0 CREY FlNt SANDY SlllY CLAY

GREY GRAVELLY SILlY 1.4EO

-1:2.4 TO rnARSE SANOY Q.AY

WllH PIECES Of SltEU.S

MXED WnH0~ROWN CLAYEY -14.3 SANO\' SELT

-15.0 8RO'M-J CLAYEY !>ANDY SILT

OREY FINE :1-'NDY ::IIUY CLAY -1.5.9

BRO't.N SILTY CLAY lrilXED WITH Kmi<AIIS

-H!.6

-2.0.0 -Do-

-21.6 3TIFf IIROIYN Cl.II'YEY SILT lfll1-l U.YERS OF G'YPSVM

STIFf

-25.0 BROWN SILTY

CLAY WTH LAYER

OF' GYPSVM

29.1

-30.0 STIFF' BROIVN SIL TY

CLAY lltXED lfllH NtOIUM TO COARSt

-35.0 CLAY Wmt LAYER SMID /NO PIECES Cf

bYPSUIA •

-37.3 BRnWN ISH CLAYEY 5\NDY SILT WllH LAMINATIDN OF'

VEDIUIA TO COARSE SANO

-40.0 BROII'N GRAVELLY -o40.B Q.A'IEY FlNE

So\NOY SILT

SHEAR STRENGll- N.VALUE KG/CM'

l'l' .'I.' ~ 1.1 'I I ll l o.z 1\0.t 0.6 0.8 o 40 60 1!1

\

r

/

40 l

~

1727 17.27,41

41

49

56

52

x/ \

\ \

NfJC %

( 41.&34

45.008

42.606

40.211 ~~~

~.619

35.900

2.).660

( 26.753

2&.815

.3<1.257

26.713

21.713

J0:296

J5.B19 '!U.7UZ

27.194 ' ~ ..,,,

21.776 ?.~ ?ffi

29.628 .'IAM?

39.300

[353õ5' 37.462

1C.250

17.650

12.63ó

1 J.Bil:Z

12.2~0

15.B08

17.2

19.515

22.48 R: 110 BLOVS FO l6cr~ R: 10~ BLD ~S F'O 1.3a~~. 1 64

lO Fig.7 SOll PROFlLE

7.

I I