Jack-up sys­tem per­forms huge bridge lift safely

DEMM Engineering & Manufacturing - - PRODUCT WATCH - DE­TAILS, NEVILLE STU­ART, PH 021 667 716, E- MAIL: NEVILLE@EN­ER­PAC.CO.NZ

An En­er­pac heavy jack­ing sys­tem of a type be­ing de­ployed through­out Aus­trala­sia has demon­strated its power, pre­ci­sion and safety in in­ter­na­tional use by re­mov­ing more than a kilo­me­tre of high bridge spans in the United States in record time.

Burkhal­ter Rig­ging Inc used the world’s tallest JS-70 multi- point in­cre­men­tal jack-up sys­tem to re­move a to­tal of 14 bridge sec­tions, each of 87.78 m, stretch­ing more than 1200m on the east­ern sec­tion of the old San Fran­cisco- Oak­land Bay bridge, which was dam­aged in an earth­quake. Use of the jack-up sys­tem cut each span re­moval from six weeks to about one week per span.

The en­gi­neer­ing task – which in­volved to­tal weights of hun­dreds of thou­sands of tons of steel at up to 20m above a surg­ing tide in fluc­tu­at­ing winds – is highly rel­e­vant to Asia- Pa­cific na­tions lo­cated on the re­gion’s earth­quake- prone “Rim of Fire”, which cir­cles the Pa­cific, says En­er­pac Aus­trala­sia Min­ing and Heavy Lift­ing Tech­nol­ogy Man­ager War­ren Balti­neshter.

In ad­di­tion to re­pair­ing dam­aged road and rail struc­tures, the jack- up tech­nol­ogy is used for the lif ting and low­er­ing of heavy equip­ment such as min­ing shov­els, ex­ca­va­tors and elec­tri­cal plant; lif ting and low­er­ing of struc­tures and build­ings; and de- prop­ping and load trans­fer from tem­po­rary steel work.

The San Fran­cisco– Oak­land Bay Bridge – which car­ries about 270,000 ve­hi­cles a day on its two decks, and has one of the long­est spans in the United States – was built in two sec­tions, the east­ern one of which was dam­aged ex­ten­sively dur­ing the 1989 Loma Pri­eta earth­quake.

The east­ern span would have been too ex­pen­sive to retro­fit so it was re­con­structed as a sin­gle deck with the east­bound and west­bound lanes on each side, mak­ing it the world’s widest bridge. De­mo­li­tion of the old east span, mean­while, is ex­pected to last un­til 2018.

RE­MOV­ING THE EAST SPAN

Dis­man­tling and re­moval of the old Bay Bridge East Span is pro­ceed­ing in three phases: Phase 1 was com­pleted at the end of 2015, with the de­mo­li­tion of the can­tilever sec­tion and S- curve to Yerba Buena Is­land. Phase 2 of the de­mo­li­tion process in­volved the re­moval the bridge’s 771,000kg truss sec­tions, which stretch east to the Oak­land shore, and in­cluded five 153.61m seg­ments, fol­lowed by the 87.78m sec­tions stretch­ing from Pier E9 to Pier E22.

Burkhal­ter Rig­ging, Inc., a spe­cialised lift­ing, rig­ging and trans­port ser­vice provider, was awarded the con­tract to re­move the 87.78 seg­ments. The project posed sig­nif­i­cant chal­lenges. At its high­est point, the bridge is 36m above wa­ter level, with a progressive down­ward slope to the shore to 12.192 me­tres above the wa­ter.

This meant that each span was at a de­creas­ing an­gle as the seg­ments reached the shore­line. More­over, lif ting would need to take ac­count of tidal changes and wind/weather on the bay. Im­por­tantly, all the bridge seg­ments had to be re­moved be­tween Novem­ber 2016 and April 2017 ahead of mi­gra­tory birds re­turn­ing to the area and nest­ing on the bridge, af­ter which fur­ther re­moval work would have to be sus­pended un­til the birds mi­grated again.

Burkhal­ter pro­posed the use of their En­er­pac hy­draulic jack- up sys­tem to lif t each 87.78m bridge sec­tion. Ear­lier re­moval of the longer truss sec­tions has been ac­com­plished us­ing strand jacks mounted within a supporting frame. The same lif ting method was considered for the 87.78m sec­tions; how­ever, it would have re­quired

more time to set up and lif t each truss than us­ing the jack-up tech­nique.

“We al­ready had some ex­pe­ri­ence of the speed and ease of de­ploy­ing the En­er­pac jack-up sys­tem on a barge from in­stalling the Fore River bridge in Bos­ton. The ma­jor dif­fer­ence here was that al­though the Fore River bridge lif t was twice as heavy as the Oak­land bridge sec­tions, the height was much lower at 20m. For the Oak­land project, we’d have to al­most dou­ble the lif t height to 36m,” said Mike Cas­si­bry, Di­rec­tor of Special Ap­pli­ca­tions at Burkhal­ter.

En­er­pac’s JS-Se­ries jack- up sys­tem is a multi- point lif ting sys­tem com­pris­ing four jack- up tow­ers, one po­si­tioned un­der each corner of a load. The lif ting frame of each jack- up tower con­tains four hy­draulic cylin­ders, which lif t and stack steel bar­rels. The load is lif ted in in­cre­ments as bar­rels are in­serted via an au­to­mated sys­tem, lif ted, and stacked, form­ing the lif ting tow­ers. The lif t ca­pac­ity per tower ranges from 113.398 – 680.389 tonne. Burkhal­ter used a JS-750 jack-up sys­tem for the Oak­land bridge lif t with bar­rels mea­sur­ing 2.3m x 2.3 x 1m.

In reach­ing the high­est truss sec­tion at 36m above the wa­ter, side load on the jack-up tow­ers was a ma­jor fac­tor in planning the lif t. Fol­low­ing ex­ten­sive anal­y­sis and mod­el­ling by En­er­pac, the con­cept of a box type brac­ing sys­tem was de­vel­oped for lif ts above 20m. This is based on us­ing a special fab­ri­cated in­ter­me­di­ate bar­rel with con­nec­tion points for crane booms and steel wires at­tached to strand jacks to pro­vide hor­i­zon­tal brac­ing – cre­at­ing a hy­draulic ten­sion­ing de­vice used to sta­bilise and mon­i­tor the side load.

As the tow­ers are raised, the crane booms, rest­ing on steel sup­ports above ground are au­to­mat­i­cally latched on. The brac­ing wires and strand jacks rest­ing on the boom sec­tions were pinned to the special bar­rels. Each of the tow­ers was then raised to the height re­quired to lif t the bridge sec­tion. For lif ts be­low 20m, the brac­ing sys­tem was dis­pensed with.

In ad­di­tion, Burkhal­ter also min­imised the side load dur­ing move­ment of the jack-up on the barge by per­form­ing ad­di­tional lif t and trim cal­cu­la­tions and main­tain­ing the spans’ cen­tre of grav­ity at a pre­cise point to keep the barge level, as well as con­stant mon­i­tor­ing of tide lev­els, dur­ing truss re­moval.

“The stiffer and heav­ier in­ter­me­di­ate bar­rels pro­vide sup­port and rigid­ity for the brac­ing sys­tem, which keeps the lif t sta­ble,” notes Mike Beres, Sales Leader – Amer­i­cas, En­er­pac Heavy Lift­ing Tech­nol­ogy.

TRUSS SEC­TION RE­MOVAL

Given the length of each truss sec­tion, the four jack-up tow­ers were de­ployed on a twin barge as­sem­bly to form a sin­gle float­ing plat­form, with two jack-up tow­ers on each barge. Ahead of the ar­rival of the barge, the bridge sec­tions were cut from the ad­join­ing seg­ments ready to be lif ted from their foun­da­tions. The barge was floated in po­si­tion un­der the seg­ment and the jack-up tow­ers raised. The west and east fac­ing tow­ers were each con­nected by a beam on which the truss would rest when lif ted. Be­cause of the an­gle of the seg­ment, the west side tow­ers were ap­prox­i­mately 1m higher than the east side tow­ers.

The East Span re­moval be­gan in the mid­dle sec­tion, at the in­ter­me­di­ate fixed pier, and re­moved pro­gres­sively to­wards the shore­line in the di­rec­tion of the low­est sec­tion. Then, the spans were re­moved from the mid­dle work­ing to­wards the high­est truss sec­tion.

Height flex­i­bil­ity of the jack- up sys­tem meant that the same process could be used for the high­est span and low­est near the shore, where only a sin­gle bar­rel was needed. Once the bridge sec­tion was re­moved, the barge was then moved away from the bridge, the tow­ers low­ered, and the span trans­ported to the Port of Oak­land for dis­posal and re­cy­cling.

“Us­ing the En­er­pac jack-up sys­tem was a mas­sive ad­van­tage. It has great lat­eral sta­bil­ity and the el­e­va­tion is quick and sim­ple to change. More­over, the speed with which each span was re­moved us­ing the jack-up was a pleas­ant sur­prise. Once in po­si­tion, the time to stroke up and take the load took just a cou­ple of min­utes to lif t the span clear. Us­ing the En­er­pac jack- up sys­tem, we were able to cut each span re­moval from six weeks to about one week per span,” said Cas­si­bry.

PROD­UCTS: JACK- UP SYS­TEM

The JS-se­ries is part of the En­er­pac range of heavy lif t, shift, bal­ance and place so­lu­tions, which in­cludes the world’s largest port­fo­lio of heavy lif t and load con­trol ap­pli­ca­tions. En­er­pac sys­tems – such as hy­draulic gantries, strand jacks, skid­ding sys­tems, self- erect­ing tow­ers, self- pro­pelled mod­u­lar trans­porters (SPMTs) and syn­chro­nous lif t sys­tems – can han­dle some of the world’s most chal­leng­ing lif ts, in­clud­ing awk­wardly shaped and some­times mas­sive struc­tures weigh­ing tens of thou­sands of tons in mar­itime, min­ing, en­ergy and heavy in­dus­trial ap­pli­ca­tions.

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