R.A.Ganorkar* et al. / (IJITR) INTERNATIONAL JOURNAL OF INNOVATIVE TECHNOLOGY AND RESEARCH Volume No. 1, Issue No. 6, October - November 2013, 588 - 590. ISSN 2320 –5547 @ 2013 http://www.ijitr.com All rights Reserved. Page | 588 R.A.GANORKAR Assistant Professor Department of Civil Engineering, PIGCE, Nagpur. ASHTASHIL V. BHAMBULKAR Assistant Professor Department of Civil Engineering, REC, Raipur, P.I.RODE Assistant Professor Department of Civil Engineering, PIGCE, Nagpur. Abstract:- Offshore flare bridge is a connecting bridge, it connects the process platform and flare platforms. The bridge is used for transport men, material and unused crude oil. Offshore design is slightly complicated due to harsher environment, also construction and installation of structures to suit offshore environment makes design challenging due to heavier weights. These structures are analyzed by, In place analysis, Lift analysis, and Load-out analysis. At offshore, tubular construction recommended due to the shape, circular cross section which attracts fare less wind loads, hence majority of the offshore structures are of steel tubular construction. In this paper analysis and design of an offshore flare bridge of length 132.76m, width 5.5m and height 8.5m, done for gravity load like self-weight of the bridge and live load from men, materials and unused crude oil weights and wind load. The behavior of the bridge is analyzed for 4 different wind speeds; similar procedure is followed by, China, Abu Dhabi, Canada and India. Keywords- offshore Bridge, lift analysis, load out analysis, gravity load, wind load I. INTRODUCTION The design of structures can be broadly divided into onshore structural design and offshore structural design. Offshore structural design is slightly complicated due the harsher environment. Also construction and installation of structures to suit offshore environment makes design challenging due to heavier weights. Offshore structures can be broadly divided into fixed type template platforms and floating units. Fixed type platforms mainly comprises of well head platforms (oil extraction platforms), process platforms, living quarter platforms, flare platforms and bridges. The present study regarding fixed type platforms like bridges, the bridge is connected process platforms to flare platforms. In this study the flare bridge is analyzed by following methods, In-place analysis, Lift analysis, Load-out analysis and study the behavior of bridge for different wind speeds for different places like, China, Abu Dhabi, Canada and India. 1.1 Historical Development The first oil and gas operations over water took place in Summerland, California, in 1896, where wells were drilled from piers extending from shore. In 1909, wells were drilled in Ferry Lake Louisiana, using a wood deck erected on a platform supported by cypress trunks driven as pilling. The technology of offshore platform design and construction has grown steadily over the past four decades as the industry has spread throughout the world and into deeper water. However new types of platforms offer promise of extending platform capability significantly. These are loosely identified as complaint structures, which were design to move with the forces of wind, wave & current rather than rigidly resist them. 1.2 Offshore Developments in India Bombay High is an offshore oilfield 160 km off the coast of Mumbai. The oil operations are run by India’s Oil and Natural Gas Corporation (ONGC). The first offshore well sunk in 1974. As of 2004, it supplied 14% of India’s oil requirement and accounted for about 38% of all domestic production. Crude oil produced from Bombay High is of very good quality as compared to crudes produced in Middle East. Bombay High crude as more than 60% paraffinic content while light Arabian crude has only 25% paraffin. II. ANALYSIS AND DESIGN The flare bridge is analyzed and designed using Staad Pro software, the flare bridge consists two horizontal levels, one is walk way and other is crude oil carrying flare pipe support. The walk way supports grating and hand rail. The crude oil carrying flare pipe support is 3.104 m above from the bottom chord of the bridge, the flare lines are of 4 pipes with diameters 10”, 14”, 28”, and 16” respectively. The present flare bridge is designed using tubular steel section except walk way, walk way is designed using I-sections. 2.2 Support condition The flare bridge designed with one end as pinned end and other end as sliding support. At the pinned end, all the 3 (three) translations are held and at the sliding end, only vertical and across translations are held. Along the bridge translation is released for any expansion that may occur due to temperature variations.
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R.A.Ganorkar* et al. / (IJITR) INTERNATIONAL JOURNAL OF INNOVATIVE TECHNOLOGY AND RESEARCH Volume No. 1, Issue No. 6, October - November 2013, 588 - 590.
ISSN 2320 –5547 @ 2013 http://www.ijitr.com All rights Reserved. Page | 588
R.A.GANORKARAssistant Professor
Department of Civil Engineering, PIGCE, Nagpur.
ASHTASHIL V. BHAMBULKARAssistant Professor
Department of Civil Engineering,REC, Raipur,
P.I.RODEAssistant Professor
Department of Civil Engineering, PIGCE, Nagpur.
Abstract:- Offshore flare bridge is a connecting bridge, it connects the process platform and flareplatforms. The bridge is used for transport men, material and unused crude oil. Offshore design isslightly complicated due to harsher environment, also construction and installation of structures tosuit offshore environment makes design challenging due to heavier weights. These structures areanalyzed by, In place analysis, Lift analysis, and Load-out analysis. At offshore, tubular constructionrecommended due to the shape, circular cross section which attracts fare less wind loads, hencemajority of the offshore structures are of steel tubular construction. In this paper analysis and designof an offshore flare bridge of length 132.76m, width 5.5m and height 8.5m, done for gravity load likeself-weight of the bridge and live load from men, materials and unused crude oil weights and windload. The behavior of the bridge is analyzed for 4 different wind speeds; similar procedure is followedby, China, Abu Dhabi, Canada and India.
Keywords- offshore Bridge, lift analysis, load out analysis, gravity load, wind load
I. INTRODUCTION
The design of structures can be broadly dividedinto onshore structural design and offshorestructural design. Offshore structural design isslightly complicated due the harsher environment.Also construction and installation of structures tosuit offshore environment makes designchallenging due to heavier weights. Offshorestructures can be broadly divided into fixed typetemplate platforms and floating units. Fixed typeplatforms mainly comprises of well headplatforms (oil extraction platforms), processplatforms, living quarter platforms, flareplatforms and bridges. The present studyregarding fixed type platforms like bridges, thebridge is connected process platforms to flareplatforms. In this study the flare bridge isanalyzed by following methods, In-placeanalysis, Lift analysis, Load-out analysis andstudy the behavior of bridge for different windspeeds for different places like, China, AbuDhabi, Canada and India.
1.1 Historical Development
The first oil and gas operations over water tookplace in Summerland, California, in 1896, wherewells were drilled from piers extending fromshore. In 1909, wells were drilled in Ferry LakeLouisiana, using a wood deck erected on aplatform supported by cypress trunks driven aspilling. The technology of offshore platformdesign and construction has grown steadily overthe past four decades as the industry has spreadthroughout the world and into deeper water.
However new types of platforms offer promise ofextending platform capability significantly. Theseare loosely identified as complaint structures,which were design to move with the forces of
wind, wave & current rather than rigidly resistthem.
1.2 Offshore Developments in India
Bombay High is an offshore oilfield 160 km offthe coast of Mumbai. The oil operations are runby India’s Oil and Natural Gas Corporation(ONGC). The first offshore well sunk in 1974. Asof 2004, it supplied 14% of India’s oilrequirement and accounted for about 38% of alldomestic production. Crude oil produced fromBombay High is of very good quality ascompared to crudes produced in Middle East.Bombay High crude as more than 60% paraffiniccontent while light Arabian crude has only 25%paraffin.
II. ANALYSIS AND DESIGN
The flare bridge is analyzed and designed usingStaad Pro software, the flare bridge consists twohorizontal levels, one is walk way and other iscrude oil carrying flare pipe support. The walkway supports grating and hand rail. The crude oilcarrying flare pipe support is 3.104 m above fromthe bottom chord of the bridge, the flare lines areof 4 pipes with diameters 10”, 14”, 28”, and 16”respectively. The present flare bridge is designedusing tubular steel section except walk way, walkway is designed using I-sections.
2.2 Support condition
The flare bridge designed with one end as pinnedend and other end as sliding support. At thepinned end, all the 3 (three) translations are heldand at the sliding end, only vertical and acrosstranslations are held. Along the bridge translationis released for any expansion that may occur dueto temperature variations.
R.A.Ganorkar* et al. / (IJITR) INTERNATIONAL JOURNAL OF INNOVATIVE TECHNOLOGY AND RESEARCH Volume No. 1, Issue No. 6, October - November 2013, 588 - 590.
ISSN 2320 –5547 @ 2013 http://www.ijitr.com All rights Reserved. Page | 589
2.3 Loads
The flare bridge is analyzed for following loads,dead load, live load, and wind load. The selfweight of the modeled structure shall becomputed by the STAAD Pro V8i. A contingencyof 15% has been considered for calculation ofweights to account for stiffeners and internal ringstiffeners and paint weights. The live load isapplied directly on the walk way bridge i.e 2.415kn/m2, and flare pipe content weight is taken as25% of its volume. Eight direction windincidences are considered in compliance with thedirectional environmental data. The wind loadshave been calculated based on recommendationsof API-RP-2A (4.4).
The bridge is analyzed by following conditions
a) In place condition – when the bridge isinstalled, it will remain there for itsservice life. During this period, thebridge will be subjected to operationalwind loads, extreme storm wind alongwith operational loads like live loads,flare pipe dead and content loads.
b) Offshore Lift condition – This analysisis mandatory to check the structuraladequacy when bridge is lifted in onepiece during installation.
c) Yard Load out condition – This analysischecks the adequacy of bridge structureduring loading out the bridge fromconstruction yard on to the transportbarge. The present study considers theloading out the bridge using trailers.
The maximum unity ratio for all the load case is1.0 except extreme wind load case. For extremestorm wind load case unity ratio is restricted to1.33, due to the fact that 1/3 increase in allowablestress can be considered based on codalprovisions.
III. RESULTS
The allowable global deflection for in-placeanalysis is (l/360) i.e. 368.77mm, the maximumvertical deflection is 285.83, and hence, design isok.
The allowable deflection for lift analysis and yardload out analysis is (l/180) i.e.231.27mm, themaximum deflection is 91.67mm, and 33.41mm,respectively, and hence, design is ok.
The bridge deflections are also checked toinvestigate abnormal behavior. From theanalyses, it is found that bridge deflections arewithin allowable limits. Also sensitivity study hasbeen performed on the bridge configuration byconsidering the different wind speed extracted atvarious locations across the globe Canada, United
Arab Emirates, China and Bharatha). Thefollowing figs show the variation of deflectionand base shear for different wind speed across theglobe.
Fig. 1 Wind Load against Deflection
Fig. 2 Wind Load against Base Shear
IV. CONCLUSIONS
From the above studies it can be concluded thatbridge is safe for intended operation, i.e. in-service condition of the bridge as well as load-outand lift condition and it is observed that centraltop chord and bottom chord members are moresensitive to wind loads. The base shear variationof the bridge is approximately linear.
SOFTWARE USED AND REFERENCES
[1] STAAD Pro V8i`-Release 20.07.04.12.
[2] IS: 800 - 1998 Code of Practice ForGeneral Construction in Steel, reaffirmed2007.
[3] API-RP-2A – Recommended Practice forPlanning, Designing and ConstructingFixed Offshore Platforms – WorkingStress Design - December 2000.
0
50
100
150
200
250
300
0 50 100
Def
lect
ion
in m
m
Wind speed in m/s
Deflection in X directionDefletion in Y directionDeflection in Z direction
0200400600800
10001200140016001800
0 50 100
Base
she
ar in
kn
Wind speed in m/s
Base Shear in kn
R.A.Ganorkar* et al. / (IJITR) INTERNATIONAL JOURNAL OF INNOVATIVE TECHNOLOGY AND RESEARCH Volume No. 1, Issue No. 6, October - November 2013, 588 - 590.
ISSN 2320 –5547 @ 2013 http://www.ijitr.com All rights Reserved. Page | 590
[4] DNV – RP – C205 EnvironmentalCondition & Environmental Loads.
[5] Various literatures for extraction of windspeeds at different locations across theglobe.
[6] Bitner-Gregersen E.M. (1996),“Distribution of MultidirectionalEnvironmental Effects”, Proceedings of15th International Conference of OffshoreMechanics and Arctic Engineering;OMAE 1996; Florence, Italy.
[7] Bitner-Gregersen, E. M. and S. Haver(1991) “Joint Environmental Model forReliability Calculations”, Proceedings ofthe 1st International Offshore and PolarEngineering Conference, Edinburgh,United Kingdom, August 11-15, 1991.
[8] Chakrabarti, S.K. (1987) “Hydrodynamicsof Offshore Structures”. WIT Press.
[9] Sarpkaya, T. and Isaacson, M. (1981).“Mechanics of wave forces on offshorestructures”. Van Nostrand ReinholdCompany.
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