| Show the worlds great eaf bricq e s I 1 7 A va az q raw X 2 Z wr 44 TX 64 Q CALIF by ELMO SCOTT WATSON anft UT in california american enterprise american daring and amerlean american engineering and construction skill are moving forward toward a new triumph which will reach its culmination in january 1937 1037 when the greatest bridge in the whole world will be thrown open to traffic to be strictly accurate one should say the two greatest bridges in the world for there are two projects under way at the same time in the san francisco bay region and each has certain characteristics which make then them pre emi nent among such man made structures it all depends upon what one means by greatest it if by greatest you mean largest and longest then its the san francisco oakland day bay bridge aull be talking about it will be eight and one fourth miles long iong almost three times as long as the present worlds largest and longest bridge that over the firth of forth in scotland if by greatest you mean the longest suspension bridge and the highest bridge then be talking about the golden gate bridge the foot length of whose main span makes it the worlds outstanding suspension bridge and whose foot towers make them the highest and largest bridge towers eier eer erected ISO feet higher than those of the george washington arld bridge e across the hudson river in either case it Is impossible to talk about these bridges without It hout dealing in superlatives for each has in one way or another exceeded all previous records as to size and taken together the two projects establish a record which probably will not be exceeded for centuries they are man made marvels on a scale so colossal us as almost to defy description the statistics alone are imposing enough but to make them understandable to anyone who Is not an engineer it Is necessary to give some such comparisons as these in building the san francisco oakland bay bridge they are using board feet of 0 lumber do you know how much that Is well its enough to build five room houses or all the houses in a town of people have you ever seen the city hall in los angeles or the russ kuss building in san francisco or the L C smith build building IlIg in seattle the concrete and steel in this bridge would make 35 such euch buildings as any of those three it would probably be difficult for you to visualize tons of cable wires but it if youre told that the cable wire used in the bridge Is long enough it if laid end to end to encircle the earth nearly three times get some idea of how much wire Is going into that bridge and the cable wire is only a small part of the metal being used the structural steel reinforcing steel and cable wire necessary for the bridge will take 07 per cent of the entire steel output of the united states in the year 1933 youve youre seen CO 00 story skyscrapers well each individual tower of the bridge standing more than feet high from the base of its pier on the floor of the bay to its tip represents a construction st Et job the equivalent of such a skyscraper so much tor for the san francisco oakland day bay bridge now for some comparative figures on the colossus which will span the famous golden gate through which rushed the gold mad argonauts of 1819 1849 its not nearly so BO long as the other one but because its the worlds largest suspension bridge they had to do a lot of digging and building to support the tremendous weight of its foot more than three quarters of a mile you know 1 span imagine a tunnel 10 feet high 10 feet wide and 20 26 miles long that was the total excavation tor for the golden gate bridge it if all the cement that will be used in it were to be delivered in barrels in the old fashioned way and these barrels were stacked one on top of 0 another they would make a pile miles high or to put it another way if all this concrete were used to lay a sidewalk you and two of your friends could walk abreast on that side walk all the way from san francisco to new york for it would be live five feet wide ulde and miles iles long youve been on top of a 22 story building remember how small the people looked on the street down below it if you drive your automobile across the golden gate bridge in 1937 and look down at the people in the boat passing under the bridge look just as small and speaking of automobiles over the six lane roadway ot of the bridge there could pass a string of automobiles reaching from the oregon line to the mexican border and moving at the rate of 0 22 miles an hour sounds like a good illace for a sunday afternoon drive it if you want to avoid traffic congestion it and no matter bow many automobiles were on the bridge at one time theres not much danger of the two cables which support it breaking and letting you drop down into the water below you see each one Is 36 inches in diameter and weighs tons there are separate wires in each one and it if all tho the wires were laid end to end they would reach miles well over ever three times around the world yes the golden gate bridge Is LARGE and so la Is the san francisco oakland bay bridge in fact the latter la Is composed of two enormous structures each longer than new york cites pride the george washington bridge across the f P X 1 aerial photograph of san francisco bay with an architects drawing of the san francisco oak land bay bridge drawn to scale upon it san francisco is in the foreground yerba buena island in the center to the left and oakland in the background 2 construction work on the golden gate bridge looking from toll plaza north san francisco side this picture shows construction of pylons nylons S 1 and S 2 south pier and fender wall completed 1125 feet from the shore at fort point san francisco tower construction now feet above the water with about tons of steel in position and 30 per cent completed across the r waters of the golden gate can be seen the completed marln marin tower standing feet above the water the hills in the background belong to marin county this Thi tower Is located at lima point 3 the golden gate bridge as it will look when completed in 1937 san francisco and the metropolitan area in the background 4 the last leg on the marln marin tower looking up to its great height of feet the steel supports at its side are for sidewalks which will be feet above the water hudson it Is a combination suspension bridge between hill bill in san francisco and yerba buena island out in the middle of the bay and a cantilever bridge between the island and oakland yerba buena island will be be crossed through the largest vehicular tunnel in the world the bore being 76 feet wide and SS 53 feet high the eay day bridge proper including the island crossing will be approximately four and one half miles long iong but its total length from the end of the western approach to the end of the eastern approach will be eight and one fourth miles long the bridge will be a double deck structure with six lanes of automobile traffic on the upper deck and three lanes of trucks plus two interurban tracks on the lower deck the building of this bridge involved some of the most difficult engineering problems ever attempted by man never before has a bridge been reared above piers which were sunk by the caisson method from the surface of the water down through both mud and water to rock bottom sight unseen never before have suspension towers reared themselves lifted by their own bootstraps boot straps one might say until their hollow steel frames rose feet above the water and their concrete bases sank in some cases feet below water level no other bridge yet built has called for so many piers 51 in number in fact it was the belief tor for more than halt half a century that lack of adequate foundations in the bay tor for piers as well as the impossibility of stretching a span from yerba buena to san francisco would prevent the bay from being bridged but in 1929 9 a survey of the bottom of the bay directed by state engineers revealed a high ridge of bedrock extending between san francisco and the island which would provide a foundation at higher levels than surrounding bedrock and make a practicable route the water along this route Is from 50 to feet deep and bedrock lies from to feet below the mud on the bottom of the bay so the most serious problem was the work below the water level and the building of the five major piers between the island and san francisco because of the depth of the water and the mud sand hogs as underwater laborers are called who work in pressure chambers to clear away the mud to the rock bottom could not be used the solution of the problem was in a compressed air flotation caisson method which enabled the bridge builders tor for the first time to construct their piers from the surface of the water down using the jaws of huge clamshell buckets instead of men to do the excavating each caisson consists of a cluster of huge steel tubes 15 feet in diameter held together by an outer casing compressed air made the caisson buoyant as it was towed into place and anchored in the space between the tubes concrete was poured forming an enormous box something like an egg carton except that the openings were round each tube was sealed with an airtight cap the concrete poured around the tubes caused the caisson to sink slowly and as it sank additional lengths were added to the tubes and more concrete poured around them when the bottom of the caisson sank to the mud in the bottom of the bay a steel cutting edge pushed down through the mud the caps were viere cut oft off the tubes and dredge buckets were dropped down through them to scoop out the mud below the caisson gradually each caisson was worked down through the mud to rock bottom in one case feet below the surface of the water thus the piers were built s 0 L 4 tr another problem was the two mlle mile suspension between san francisco and yerba terba buena which had been deemed impossible so the engineers decided upon two suspension spans in tandem anchored in the middle of the bay to a gigantic pier it Is feet long nearly GG yards by 92 feet wide and rises feet from the rock bottom of the bay nearly twice as large as the biggest skyscraper in san francisco since the two spans are anchored to this they actually pull against each other the san francisco anchorage Is a huge mass of 0 concrete containing GS CS cubic yards of cement in spinning the cables the entire miles of 0 cable are pulled in place by shuttle wheels which run over the towers all the way from san francisco to the concrete center anch anchorage orage on the west suspension bridge and from tbt th center anchorage to yerba terba buena on the eat east suspension bridge spinning the cables Is by far the most protracted job on the bridge and will require a year each piece of wire in the cable Is approximately two miles long iong A total of strands must be drawn over the suspension towers each cable will exert a pull of pounds against its anchorage in san francisco and yerba buena island just as the building of the bay bridge presents knotty problems to be solved so does the building of the golden gate bridge bring up difficulties never before encountered in such work outstanding among these were the great length of the suspension span more than twice that of any previously attempted and the difficulty of erecting a foundation tor for the tower to td support the south span because of the depth of the water and the swirling of the tide in the open ocean waters at the golden gate but 1200 feet offshore at a depth of feet an adequate foundation formation was discovered although the water here Is constantly turbulent because of the seven mile an hour it tide de which constantly sweeps in and out through the golden gate at times breakers 20 feet high crash over this point first it was necessary to level ot oft the site for this pier by blasting rock over an area of approximately an acre under water after which the rock was dredged up carried out and dumped in the sea construction of the pier the first ever attempted in the open ocean swept by the tides was made possible only by the erection of a giant concrete tender fender feet in cIrcum circumference ferenc e around the pier site an original idea never before tried this fender Is being built in see sections eions first a huge steel box Is lowered into place on n the bottom after which it Is bolted to adjoining boxes boses by deep sea divers working in complete darkness then concrete Is poured into the boxes gradually the structure is built up until its top rim Is fifteen feet above high water the east wall of the fender Is omitted above elevation until the enormous caisson to be sunk bunk and filled with concrete for the pier itself Is floated into place inside the fender then the fender will be completed and the builders will have quiet water unaffected by tides inside the fender in which to complete the pier the fender will serve as a permanent protection to the pier when the bridge Is completed meantime the marln marin tower built on solid rock above the water line was completed ahead of program program its slender steel columns rise above a foundation of concrete embedded in the rock the tower Is of cellular steel construction the inside being a veritable labyrinth of chambers in which even the designer could be lost without his charts steel ladders connect the hundreds of 0 chambers from the foundation to the top of the tower 7 10 feet high the twin anchorage blocks which support tho the weight of the worlds longest suspension span are arc enormous solid concrete con crote masses weighing tons each so constructed that they push against solid rock when supporting tho the cables the cable pull at each anchorage Is pounds but the anchorage block has a resistance sufficient to support two golden gate bridges between the piers and the anchorage blocks are supporting pylons nylons for the cables and the bridge bridga 0 by 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