THE CANTILEVER BRIDGE

[Music] [Music] seaw seesaw margerie D what has that to do with Calver Bridges a whole lot a seesaw is a Calver beam place a weight on one end and the other end can support an equal load add another seesaw and replace the inside weights with a short beam which spans the Gap and we have a bridge a miniature Calver bridge and if we were liliputians we could ride across that is if we invited traffic by tying the weights to the underside of the beams simple isn't it now let's get technical Engineers call these falcs or pivotal points main Piers the weights or anchorages at the ends the anchor Piers to which the ends of the bridge are generally anchored the parts of the beams between the anchor piers and the main peers are the anchor arms and reaching out like extended arms trying to tag each other are the Calver arms the Gap is filled with what Engineers call the suspended span supported by the Calver arms this is a typical Canal Bridge our land is laced with thousands of canal Bridges spanning rivers and other obstacles these bridges are found in many forms beam and girder calers and Truss calers most Cal structures are built up of through trusses or variations of through trusses a through truss is so designed that the traffic passes through the structure rather than on top of it many Bridge designers prefer this type of structure where moderate main spans of 800 to 1200 ft are necessary one of the principal reasons for this preference is Simplicity of design and construction because of great rigidity and economy the canver bridge has often been chosen for Railway spans over wide navigation channels it is able to withstand minor Foundation movements without changing the stresses set up in its trust members and it can be erected without interrupting navigation Calver bridges are not a new development they've been used for hundreds of years the most famous of all Cal Bridges the fth of fourth was built by Scotsman back in 1890 which certainly speaks well for the economy of this type of bridge its tremendous 1700 ft Center span set a record that it held for 27 years in 1917 This Record was finally broken when the Quebec Bridge with a center span of 1,800 ft was thrown across the Great St Lawrence River the East Bay crossing of the San Francisco Oakland Bay Bridge built by American Bridge features the longest Calver Span in the United States it's a double decker with a center span of 1,400 ft its Upper Deck carries Passenger cars while the lower deck handles trucks and Interurban electric trains it carries one of the heaviest traffic loads in the country in 1954 plans were ready for the construction of our country's heaviest Calver Bridge spanning the Hudson River at the tapen Z to join South nyak and T town with a gracefully curving Bridge 3 m long including its approaches this bridge was to link the East and West sections of the great New York State throughway connecting New York City and Buffalo to build a bridge the size of the tapenz in less than a year required Adroid engineering and demanded a Mastery of logistics calling for perfect timing and synchronized flow of materials fabrication and Delivery at the site of construction at just the right time not too soon not too late to meet this tight schedule five American Bridge plants sprang into action simultaneously from Ambridge from Elmyra from Trenton from Gary and from Rono came a steady procession of Railroad Flat cars converging on time at the Depot selected for material sorting and storage wehawken and Hoboken next began what was perhaps the greatest Bridge floating operation ever attempted a flotilla of barges moved the fabricated members for 164 beam approach spans and 19 completely assembled deck truss spans to the bridge site the dect trust spans weigh almost 1,000 tons each are 91 ft wide 28 ft deep and vary in length from 232 to 247 ft so big that two huge railroad car floats were required to carry them mother nature dawned a Bridgeman's hat and helped out at this point high tide permitted the spans to be floated into place precisely over their final designated positions then as the tide receded the car floats lowered the spans onto their peers when necessary final adjustments were made by pumping water in or out of the car floats and by operating 500 ton Jacks provided for that purpose as soon as the steel for the approaches was permanently placed and riveted the concrete started to flow in preparation for the final surfacing of the roadway while the erection of the thousands of feet of approaches was in itself a great achievement the star role in this dramatic performance goes to the great Balancing Act the construction of the Calver portion of this giant bridge at the locations chosen for the foundations for the two main towers and the two anchor Towers Solid Rock was so far below the riverbed that conventional foundations were impractical instead the main piers and anchor Piers under the Calver Bridge were supported on cellular reinforced concrete boxes resting on the river bottom with their tops approximately 2 ft below low water these concrete boxes are called buoyant quaon from these steel pipes filled with concrete some as long as 295 ft extend down to bedrock the largest of these buoyant queson is 100 ft wide about 200 ft long and weighs about 16,000 tons 80% of the Dead load of the main bridge is supported by the buoyancy of the queson generally the first operation in the construction of a Calver bridge is the placing of the false work or temporary supports for the anchor arms falsework usually consists of a series of piles driven down to bedrock to support the anchor arms however conditions May dictate that a fabricated false workk span be placed between the anchor pier and the main Pier to support the anchor arm during construction where practical actual Bridge Approach spans are used as temporary falsework this was done by American Bridge in erecting the Calver portion of the Sunshine Skyway which spans Tampa Bay in Florida this dual use of material incidentally is but one of many cost-saving devices available to alert Bridge Engineers here we see the false workk in its temporary position under the anchor arm after the two anchor arms were erected the false workk spans had done their job and were floated to their preminent positions in the bridge as approach spans there the spans were eased into place by jacks and water pumped in or out of the barges either lowered or raised the spans onto their [Music] peers and here they are in their Final locations but the tapen Z approach spans were not suitable to serve as false work so the engineers designed two Expendable temporary falsework spans which were assembled at Grassy Point each span is 93 ft wide and over 500 ft long each of these enormous false workk structures weighs 1,500 tons the false workor was floated into place and supported on the edges of the concrete kons of the main Foundation structures directly underneath the anchor arm locations the steel Towers which will support the bridge were erected by crawler cranes mounted on barges and Derek Travelers operating from the false work with the main Towers completed and ready to serve as falum points the balanced erection or seesaw method of construction begins as soon as the first section of the super structure is placed a precise record is maintained a sort of Daily Ledger of the material erected its weight the location of the center of gravity and a check is kept of the changing stresses in the false workor at all times by measuring the def ctions at the center of the false workor [Music] spans the building of the superstructure moves out simultaneously from each of the main towers with the Derek working in opposite directions weight balance is precisely controlled to avoid overloading the false work the anchor arm just enough heavier than the Calver arm to prevent the bridge from teetering during construction a miscalculation here would cause quite a splash it's tough enough to build a bridge by the delicate balanced erection method but throw in a couple of devastating nearby hurricanes namely Connie and Diane ladies in name only at a time when the structure was at its most critical erection stage and you can see that there must have been some KingSize headaches for a while in this type of construction the further apart the Derek Travelers the greater the progress they move in opposite directions and until the entire anchor arm and a portion of the main span are erected those Derek Travelers weigh 350 tons a piece including the big stiffle Derek and the guy Derek which rides piggyback to do the lighter work behind the big fellow as the bridge progresses the role played by the temporary false workor becomes more apparent notice how the Jacks mounted on the false workor hold up the load above they were designed to support in addition to their own weight about 1 ,000 tons of unbalanced load during construction this bridge is so massive that it dwarfs the men putting it together look close and you can see them way way up there those aren't just men they're bridg men a Fearless breed sure footed as cats with a Brawn and skill necessary to build the bridges which contribute so much to our progress here comes a boatload to take over The Late Shift replacing the early morning crew the erection of the tapenz bridge required 300 of these bridge building Specialists working two 8 hour shifts during the long summer days just climbing to their stations requires more physical effort than most of us put out in a day then they really start to [Music] [Applause] [Music] work it's a safe bet that not many bridgemen are overweight here's the bridg men's elevator going up he's not worried nor should he be he's safer up there than most of us are going upstairs in our own homes one of the advantages of spanning a river with a Calver bridge is that River traffic is not interrupted the nature of the construction is such that the channel is always open to shipping and fishing there goes a secondary bracing member moving into position that hand signal says keep it coming you're doing okay because of construction noises whims and distances too far to be heard even when shouting these bridg men depend on hand signals with huge steel members swinging through the air these signals must be right and right on time another example of the teamwork required in this rugged business of Building [Music] Bridges every steel member designed for the bridge has an identifying Mark and is waiting on a barge below when the call for red Iron comes from above then 150 T Capac capacity Derek Hoist the member at the same angle at which it is to be fitted into its truss Engineers have computed the point at which a hitch is to be fixed for lifting this positions the member in such a way that a minimum of time and effort is required to guide it into place every step has been carefully planned by American Bridge engineers and every member is erected in the exact sequence specified during construction the members are often subjected to Greater loads than they will have to bear even after the bridge is in use as each member is lifted into place bridg men known as connectors lose no time in ramming home bolts or drift pins to temporarily hold the member in place until the bolts or drift pins are replaced with white hot rivets and here's the answer to a call for more rivets rivets the exact length and diameter specified and made from the right steel for the job this bridg man known as a heater is really a rivet Chef who does the rivets to a turn he can tell by the color when the right temperature is reached the rivets in this Forge are heated to a temperature of 1,900 to 2,000 de if it's too hot the rivet will burn if it's too cold it will not drive properly tossing hot rivets is no job for an amateur this is Big League stuff every pitch better be a strike right over the plate and no umpire to call it if you think the last pitcher was hot just watch this fella toss a few over up and over right into the steel mint there's another way of delivering hot rivets when it's too long a pitch for the heater when the catcher may be out of sight maybe up on the top Court of the tapenz bridge and about 155 ft above the pitcher down on the bridge floor it's really simple just drop a hot one into a pneumatic tube it works just like in a department store and with the aid of the tube he curves him right to the waiting Riveter most shop rivets are driven by huge pneumatic or hydraulic riveters but they're far too large and cumbersome for use in the cramped areas that bridgemen move around in so they use smaller easier to handle riveting guns the river's teammate the bucker up crawls through one of the manholes into the member and pushes hard against the head end of the rivet while the Riveter shapes another head on the other side since the rivets are just the right size there's just enough metal to form the other rivet head too little or too much would be unacceptable here are just a few on this bottom cord it takes a lot of field rivets to assemble a bridge almost 300 th000 on this Cali alone and that doesn't include the hundreds of thousands driven in the shops as the anchor Arms Reach closer and closer to the Anchor Pier the importance of the false work becomes more obvious these temporary support points with their built-in Jacks make it possible to extend the arms right out to meet the anchor Towers tie downs capable of resisting an uplift of 750 tons each are attached to the ends of the anchor arms and the Jacks Are freed of their loads before erection proceeds Beyond this point the false workor truss has now served its purpose and may be removed at any convenient time and there it goes this high level conference session to determine the next member to be installed these bridg men aren't worried they know from past experience that every piece will fit into the jigsaw puzzle if the right member is put in the right place at the right [Music] time and behind the lines Engineers on the drawing boards and the designing and erecting offices have left nothing to chance they even know the exact batch of molten steel from which every member was made and they know that each member was made and rolled to their exacting specifications it's all on the record the template makers too the men in the shops each is proud of his part in building the great tap Z Bridge it won't be long now here's the next to the last bottom cord about to be raised there goes more than 100 tons of steel in perfect balance these giant steel links or connecting plates fastened at one end play an important part in the final closing of the bridge an exciting moment for all bridg men is the preparation of the bottom cord which will tie the two cevers together for the first time the American flag proudly announces to the world that this is the member which Bears the honor of closing the span there's still plenty to be done but the Hudson has been bridged every man will remember for the rest of his life that he helped Bridge the tapenz we don't know the name of the first man across but you can be sure his grandchildren will know about it when the center span is closed the bridge is not yet complete for the engineers have intentionally left a small space at the center of the bridge to comp compensate for rolling and Fabrication tolerances temperature changes and other factors to close the gap and complete the job there remains one very intricate maneuver Engineers call this swinging the suspended spam and that's just where those connecting links prove their importance by adjusting some built-in Jacks the two halves of the suspended span are rotated slightly the elongated holes in the bottom cords allow enough room so that the center of the bridge can be lowered into its final position to become a simple trust span hanging from the ends of the Calver arms in many Calver Bridges the center suspended span is well defined and can be easily recognized but in the tapen Z Bridge the suspended span Blends so smoothly into the canal liever arms that it is difficult to distinguish over 30,000 tons of steel went into the erection of this great Canever Bridge that's more than twice the amount of Steel required for the 39-story United Nations Secretariat building in New York City today spanning the broad tapenz is this beautiful structure one of the 75 bridges built by American Bridge on the New York State throughway between Rochester and and the Hudson this elevated road with its gently flowing curves provide safe travel for millions of motorists over a great modern Highway link Ing New York City and buffalo it was created not only for today's heavy traffic but with an eye to the Future its six Lanes will care for tomorrow's traffic as well its graceful S curve can be interpreted as a symbol of the safety uppermost in the minds of the bridge Builders witness the two broad 37t roadways each accommodating three wide traffic Lanes the 10t center mall which separates opposing traffic and also provides room for disabled cars and the 3-ft safety walks on each side just in case of emergency this handsome Calver bridge is as safe for motorists as modern engineering science can build and it is made of steel the only construction material that could translate such ambitious plans into this magnificent [Music] reality seaw marjerie da the Hudson has a new master l