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Douglas Butler Bridge Book An explantation of movable bridge technical drawings

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STRAUSS

Joseph Strauss is important in the movable bridge world for inventing three types of bascule bridges. Before he became a draftsman, Joseph Strauss graduated from the University of Cincinnati, the city where Strauss grew up. He worked with Ralph Modjeski by helping him develop and improve on bascule bridges in Chicago, Illinois.

By 1903 Strauss has designed over 400 drawbridges, before that he left Modjeski's firm after 10 years of working for Modjeski. Strauss has an Innovation of bascule bridges. Strauss has his firm of the Strauss Bascule Bridge Company. In 1905 his first design was an Overhead Counterweight type trunnion bascule bridge in Cleveland,Ohio. http://www.flickr.com/photos/94273918@N06/8589860684/#photo=1The span is 150 feet long and was constructed by the Wheeling & Lake Erie railroad. Its a single track structure,the counterweight is carried by a pair of struts articulated to rearward extensions of the main trusses. The tower that supports the main trunnions on the span that revolves is extended up to the top of the counterweight. A link is pinned to the top of the tower and to the counterweight,and lies in the plane Parallel to the plane through the main trunnions ,and the pin in the end of the main truss which supports the counterweight struts. The four joints are at the corners of the parallelogram. When the span opens, the  counterweight is held parallel to its original position and a balance is maintained as this span revolves. (See Movable bridges Vol.1 Superstructure,.Hovey)

In 1908 Strauss developed a similar design of an overhead counterweight trunnion bascule bridge, a 170 double track structure constructed by the Chicago & Northwestern railroad in Chicago Illinois. http://www.flickr.com/photos/94273918@N06/8589916244/The bascule bridge structure consists of the three main parts of a fixed tower, a rotating bascule leaf and the concrete counterweight that rotates independently from the span, the spans axis of the rotation, the main trunnion is located halfway up the tower. The main trunnion is located in the truss upper chord. Extending through the tower. The truss has an inclined rear arm to support the counterweight. Parallel to this the link beam connects the top of the counterweight to the tower. Those two elements remain parallel through out the span's rotation. by the bold parallelogram. As the span raises to a full open position, the counterweight passes between the rear arms of the truss, a compact arrangement that does not require a tail pit. To prevent the span from opening further than 85 degrees. The rear arms of the truss engages a wooden bumper on the tower, motive power is provided by a pinion at the top of the tower which engages the rack on the operating strut to raise or lower the span.(See HABS HAE'S for Historic bridges of the Chicago & Northwestern Railroad Kinzie street Built in America ).

The other innovation of the bascule design is a vertical overhead counterweight trunnion bascule bridge designed by Strauss. http://www.flickr.com/photos/94273918@N06/8644821503/The span has a counterweight that are connected by the links that supported on posts that rested on the trunnions, and by the bearings that mounts on the tail end of the bascule girders to the rear of the main trunnions on the opposite side of the main trunnions. From the navigation channel the counterweight is stabilized by the links to the rigid post that are mounted on the pivot pier. The counterweight is connected at its top to pivot struts extending forward from the top of each side of the counterweight connecting to the top of the post on each side of the roadway. When the span raises the counterweight, it bears down while the bridge raises to an open position. The Underneath counterweight trunnion bascule bridge the counterweight is connected to the end of the girder span by pivot pins that is balanced and extends to the rear of the bascule girders by the main trunnions with hangers to balance the span similar to the trunnion type. But the counterweight dips below when the span is open. When in the closed position the counterweight that is suspended from hangers is tuck under snugly.http://www.flickr.com/photos/94273918@N06/8601437548/The heel trunnion bascule bridge is constructed and is commonly use for railroad service as well as vehicle traffic. The first heel trunnion type was constructed in 1910 in Massachusetts by the New York New Haven & Hartford railroad, the bascule span is 159 feet and 4 inches and crosses the Cape Cod canal.http://http://www.flickr.com/photos/94273918@N06/8590035570//Today is a lift bridge, the heel trunnion bascule bridge early designs the operating machinery was mounted on the bascule span and the operating struts are pinned fixed to the rear panel or bridge tower, like the Hx New Jersey Transit line bascule bridge in Secaucus New Jersey. http://bridgehunter.com/nj/bergen/bh50217/ This and the other early designs the amount of power is used to deaccelerated the span. The operating towers are on each side of the bridge like the Hx bascule bridge I mention earlier, one tower operates the span and the other operates the counterweight.When the span is open the weight of the struts are carried by the span and the strut is halfway out into the span as a result making the span heavy.When in the closed position the counterweight is heavy in the lower position.The later designs the operating mechinery is mounted on the bridge tower and the struts pinned fixed to the bascule truss. As the bridge raises the strut goes to the counterweight supports that make the counterweight heavy.When lowered the span is heavyhttp://www.flickr.com/photos/94273918@N06/8588711933/.  the span is supported by the trunnions which are fixed to the end of the span and the rear panel bridge tower.The rocker link is connected or fixed between the trussed framework to the span on the bridge tower were the operating mechinery and struts are connected the struts with racks are pinned fixed to the span and the pinions engages the racks on the operating struts to raise the bascule span. The counterweight is made with a single block or two wing which attaches to the trussed framework on the bascule span and on the bridge tower. When the span raises the counterweight that is fixed to the trussed framework swings down under the bridge tower to offset the bascule span and the link arm folds against the framework. The operating machinery that mostly mounts on the bridge tower are better suited for operation.

An example of the strauss heel trunnion bascule bridges one in Ashtabula Ohio the operating machinery is mounted on the bascule span http://www.flickr.com/photos/94273918@N06/9680891974/the other in Detroit Michigan the operating machinery mounts on the bridge towerhttp://www.flickr.com/photos/94273918@N06/9680892114// The heel trunnion bascule bridges are often the single leaf, but they're double leaf heel trunnion bascule bridges. An example of a double leaf Strauss bascule bridge is a 336 foot single track railroad bridge (formerly Canadian Pacific) now Wisconsin Central railroad that crosses the U.S Ship canal (St Mary's river) in Sault Ste Marie between Ontario and Michigan. http://www.flickr.com/photos/94273918@N06/8588712065/This double leaf heel trunnion type is still in service, and a few double leaf heel trunnion bascule bridges in California, and one (formerly) in Hamilton Ontario Canada. Edit Text

SCHERZER

William Scherzer patented his first 4 track rolling lift bridge in 1893 at Metropolitan Westside railroad in Chicago Illinoishttp://www.flickr.com/photos/94273918@N06/8665923540/ After his death, his brother Albert Scherzer took over the firm of the Scherzer rolling lift bridge Company. Albert Scherzer designed many rolling lift bridges in many parts of the world.

They are popular around when the span rolls back and forth in open and lowered positions without the the connection like other bascule bridges have. Its easy to navigate in the raised position for marine traffic. This span has curved tracks called Quadrants with the holes in them to mesh with the horizontal track lug or teeth to keep the bridge from slipping while rolling back and forth opening and lowering. The counterweight is attached to the quadrants, and has rack beams on each side of the span with the operation drive mechinery and the pinions to open and closed the span. The tread plates are achilles heel to the segmental girders that connects to the bascule span to the curved tread plates .The horizontal girders supports the flat tread plates which uses for the teeth with the quadrants on all rolling lift bridges. Also while rolling back and forth during operation.

The varition type is a Rall type rolling lift bridge patented by Theodore Rall and design by Ralph Modjeski. Rall's patents are held at the Strobel Steel Construction Company. An example a large 278 double leaf Rall type rolling lift bridge in Portland Oregon, http://www.flickr.com/photos/94273918@N06/8666318870/The span operates by rollers that rolls on the horizontal track girder that rolls of the track in the closed position.The counterweight is fixed to the pier with swinging struts that turn the pins on. Also when the span is closed the pedestal on the main girder sits on the pinion on the pier and the rollers lifts from its track. And the strut is hinged to the main girder, the bottom rack engages the pinion similar to the Strauss heel trunnion bascule bridge on the fixed span and abutments. Then the pinion draws the operating strut with racks causing the contact with the track and with the trunnions.

 

BROWN

Thomas Ellis Brown was better known as a mechanical engineer of bridges than the designer. In 1896 Brown turned his specialist in movable bridges,his innovation of the design was was a drawbridge in Brooklyn New York crossing the Harlem river when Brown worked with another bridge engineer Alfred Boller for a short time. (See Connecticut's Historic Highway Bridges Notable Bridge and Builders of Connecticut or Connecticut's Historic Movable bridges Mystic River main page.)

Brown patented a balanced beam heel trunnion type bascule bridge in 1922,and was constructed by the American Bridge Company Fabricator. http://www.flickr.com/photos/94273918@N06/8628986318/The bascule span is 84 feet 8 inches between centers of the end bearings and provides a clear channel of 75 feet between fenders. Vertically the moving counterweight is connected to the span by wire ropes were not used. The arrangment or method of varying the leverage by an articulated links. The movable span is counterbalanced by two concrete counterweights placed on the center lines of the main girders and carried by balanced beams in the form of trusses which rest on the trunnions at the top of the tower bents. These trusses are are 60 feet long over all, and the forward ends are connected with the plate girders of the moving span by hanger links or suspenders consisting of eyebars and short links having double settings of pivots at the span end. Butt blocks or stops are suitably placed on the upper flange of the movable span girders to make contact with the short links at the proper time during motion, and change the point of rotation of the eyebar hangers from one set of pivots to the other."

A new Brown type built in 1924 was improved by locating the articulated butt links on the channel end of the balanced beams. The betted details is a result from moving the butt links to the end of the balanced beams, and control of the balancing is simple equally. The bull wheel toggle action affords an effective and a simple method of operating a small bridge like the Mystic bridge( mention earlier, ) but for a large and heavy structures an operating strut and rack would be chosen ( A Brown type in Ashtabula County Ohio). http://www.flickr.com/photos/94273918@N06/8629322162/The unbalancing of the leaf by cantilever action of these struts near the open position, can be corrected by the proper selection of the points of articulation of the butt links.

The first Brown type was constructed in Buffalo New York at Ohio street crossing the Buffalo river.http://www.flickr.com/photos/94273918@N06/8686876170/ A cam girder is attached to the trusses that is substituted for the articulated eyebar linkages, the counterweight ropes are wrapped around the face of the girder and anchord to the main trusses at the first lower chord panel point from the trunnion. The face of the girder carries grooves for the ropes is curved so that as the leaf is open and the ropes are unwrapped from the cam girders, their effective lever arms are reduced and a balance of the moving leaf is obtained in all positions, the counterweight moving vertically.(See Movable Bridges Superstructure Vol 1 by O .E. Hovey).

ABT

Hugo A F Abt patented an unusual trunnion type bascule bridge that the counterweights moves in the opposite direction. Abt worked with the American Bridge Company and constructed a few of the types, the first type was constructed in Detroit Michigan used by the Norfolk Southern ( Wabash railroad Company) across the Rouge river,http://www.flickr.com/photos/94273918@N06/8595689390/ its a 162 feet long double track structure between the centers of bearings,and counterweight is 73. 5 ft long."From the upper chord panel point 2 the main truss a tension member extends diagonally upward and rearwarded. A rocker link connects to its heel of the truss at 1. The counterweight is a steel box with arms which are hinged to the top of the tower. A compression link pin connected to the counterweight box, is articulated to a tension operating link which is hinged to the rocker link joint. A track in the tower, is inclined with a horizontal plane ,this joint is pinned connected to a truck adapted to roll down the inclined track with rack. The trucks at the two sides of the bridge are connected by boxed girders which carries the mechinery and the operater's house. Power is applied by the pinions engaging the racks on the inclined track girders. As the counterweight and the operating link joint rotate in the arcs of circles and power is applied long the bisector of the scissors joint angle, an almost exact balance that attained in all positions of the moving leaf. The scissors joint link, trucks, and the ends of the counterweight are in the plane of the moving leaf trusses and move within the the tower, which must be wide enough to allow clearance. The operating mechinery is driven by two 100-h.p electric motors, through an equalizer and reduction gearing located on the mechinery girder. When the bridge is open the trunnions carry their maximum loads made up of the counterweight and its connectings and the counterweight box swings inside the the triangler tower and hangs like a pendulum,when in the closed position the trunnions are only lightly loaded by the counterweight and its connections swings up with the truck on the inclined track. ( See Abt on page 134 on Movable bridges Superstructer Vol 1 by O.E.Hovey). They'e two other Abt trunnnion bascule bridges in the State of Michigan, three in California, one in Texas and one in Wisconsin a total of eight Abt bascule bridges in the United States.They only carries railroad traffic,Abt had some success developing these bridges and still in operation. Edit Text

PAGE

This page trunnion type bascule bridge was patented by John W Page and designed by William M Hughes. Page had worked with Strauss on bascule bridges, they're only a few Page type bridges a double trunnion type formerly in San Francisco California, one in Hammond Indiana that no longer operates and one in Chicago Illinois. It's the only one still in service for the Chicago and Alton railroad." http://www.flickr.com/photos/94273918@N06/8604001556/This bascule span contains the counterweight in the approach span which pivots with the bascule span when raised for river traffic. The approach span is a riveted steel plate girder while the bascule span rests on the concrete abutments. The bridge tender's cabin is located along the north approach, the cabin is one story brick building with a hipped roof and chimney. (See HABS HAE'S on Chicago & Alton railroad bridge) or (See Bridge Engineering = J.A.L.Waddell on page bascule bridges on the pages 708, through 716.) Edit Text

BELIDOR BASCULE BRIDGES

Benard F Belidor (1729) is a drawspan with a sliding curved track that rolls down with the counterweight when the bascule span is raised." The bascule span is hinged at the balanced beam with the cables attaching between the upper beam to the end of the drawspan the pinions rests on top of the balanced beam on the approach pier. At each side of the span is a chain which leads from the end floorbeam on the pinions upward over the sheaves near the rolling counterweight and track to the rolling counterweight. As the bridge rotates about the hinge counterweight rolls down the track with rails, the track is curved in order to obtain the balance of the rotation leaf with a counterweight of fixed value at all angles of the bridge opening.

The example of a few Belidor bascule draw bridge is the Glimmer Glass bridge in Brielle New Jersey crossing the Glimmer Glass Channel, http://www.flickr.com/photos/94273918@N06/8685741733/a railroad drawbridge also in New Jersey crossing the Berry's creek a double leafed Ohio street bridge (formally) in Buffalo New York, and one in Coney Island New York. Which are a few Belidor bascule bridges in the United States ,but are commonly in Australia. (See Historic Bridge Confrence on Belidor Bascule bridges). Edit Text

DUTCH STYLE BASCULE BRIDGES

The Dutch style type is a balanced beam heel trunnion type pantented and designed by an unknown inventor, but they're more common in Europe, Holland, the Netherlands etc.They're a few Dutch type drawbridges in the United States. A couple of them in the upstate New York and one in Minnesota that has a double section for pedestrian walkway.http://www.flickr.com/photos/94273918@N06/8646141172/The Dutch type heel trunnion bascule bridges" a single leaf trunnion bascule provide balancing of the span through a connection of a tensile link and the balanced beam frame to the leaf at the forward of the main trunnions. Some links are are far placed enough forward the bascule span is like a simple span for the dead load. Some bascule links are connected to the bascule leaf at midpoint on the span of the thereabouts the bascule span acts like an two span continuos bridge for live load with both spans cantilvered for the dead load. The center link heel trunnion bascule bridges are cantilevered that causes of the counterweight bottom structure and the operating mechinery. The end of the link to the bascule span allows the leaf to act like a simple span that eliminates a live load stresses in the operating mechinery.(See Movable Bridge Engineering Koglin on pages138,139 and 217). Edit Text

HOPKINS FRAME

"The Hopkins Frame Drive trunnion type bascule bridges designed by L.O Hopkins are mostly in the State of Florida. They have an unusual drive systems of the trunnions on the Hopkins Frame. The Hopkins Frame has a connection between the bascule leaf and the pier on which are mounted, the drive motor brakes and the reduction gearing. The frame is connected to the bascule leaf in such a way that the rack pinions are mounted on the Hopkins Frame and constantly in mesh with the rack segments that are fixed to special rack girders on the bascule leaf inboard of the two main girders. The frames flexes when in open position and closes causes of the changing in the shape of the bascule leaf in the open position as opposed to the closed positions. Some Hopkins Frames has a single rack and pinion on the bascule leaf and most bridges have two pinions that drives two racks. The single rack is on the longitudinal centerline a few feet from it. The Hopkins Frame Drive trunnion bascule bridge works against the two raks and pinions are usually parallel shaft differntial reducer mounts on it and usually additional exposed or open reduction gearing between the differntial reducer output shafts and the rack pinions.http://www.flickr.com/photos/94273918@N06/8685703491/ (See Movable Bridge Engineering Koglin on page 212). Edit Text

WADDELL & HARRINGTON TRUNNION BASCULE BRIDGES

" The Waddell & Harrington trunnion bascule bridge has a number of distinctive features. The trunnions which are in line with the top chords of the trusses are made of special steel castings with are rigidly attached to a boxed girder spanning the distance between the trusses, the free end of each trunnion has a cylindrical bearing with it's axis parallel to the plane of the truss. This bearing fits into the cup mounted on the standard or tower anchored to the pier. The object of the this cylindrical bearing is to permit a slight rotation due to the deflection of the box girder connecting the trunnion, between the cylindrical bearing and the end of the box girder is an enlargement of the trunnion or segmental ring having a spherical surface. A hub casting bored to fit this spherical surface, turns on the segmental ring and supports the truss. This gives a bearing of a large area and permits of using a lower unit pressure. This spherical surface also provides for for the slight bending of the trunnion in a plane perpendicular to the truss as the deflection of thebox girder varies with the change in loads thereby preventing binding or any unequal distrution of loading on the two sides of the truss, that would involve high sencondary stresses. The span is operated by a system of cables cinnected by equalizer bars to each truss at the ends of the segment of the short arm of the bascule. These cables follow the curve of the segment and pass around a nearby idler sheave under the floor and then to the other attachment at the segment. Provision is made for reversing the rotation of the winding drum. As the span is balanced about the centre of rotation by a concrete counterweight, at the upper end of the segment extending from truss to truss only sufficient power to overcome the friction and intertia of the moving parts is needed to operate the span. An example shown of the Waddell & Harrington trunnion type bascule bridge crossing the False creek in Vancouver British Columbia Canada.http://www.flickr.com/photos/94273918@N06/8686382312/(See Bridge Engineering Waddell on page 711). Edit Text

Roller bearing trunnion bascule bridges

The Roller bearing trunnion type bascules are pantented by diferent inventors, some such as Montgomery Waddell, and John P Cowing Roller Bearing trunnion bascules." The First roller bearing bascule bridge was developed by Montgomery Waddell. There are two distinct designs for this type of bascule. In one the circular end of each truss of the moving span rests on a nest of solid rollers that are effectively connected to each other by spacers and which are supported in a cylindrical cup shaped bearing. These rollers have trunnions which rest on the curve track and which have a diameter one half of that of the rollers. Consequently the traslation of the rollers is only on fourth as rapid as that of the cylindrical surface which bears on them. In the other design the surface rest on two stationary compound rollers per truss of the type rolling bearing bascule.

In both types and more especially in the second the frictional resistance to motion is reduced to a very small Quantity. The compound roller consist of a single large solid cylinder surrounded by a nest of small solid rollers that are encased by a large hollow cylinder. Such a combination approximates closely in efficiency to a bull bearing. To operate the bascule span a pinion engages a rack on the outside of the segment in the planes of the trusses. An overhead counterweight is provided at the upper end of the segment. No pit is required in the pier to recieve either the tail end of the span or the countweweight, the centre of gravity corresponds to the centre of rotation so that only friction and inertia have to be over come. The rollers were to be stationary and the counterweights were to be attached to long arms extending beyond the rolling segment and outside thereof. For this bridge the moving rollers were selected a small amount of concrete is needed for the substructure. The Cowing roller bearing bascule designed by John.P Cowing is similar to the Montgomery Waddell type. The semicicular segment forming the tail end of the lifting span moves on a nest of solid rollers which in turn move on a track girder curved to correspond with the rolling segment. The countweight is partly above the floor and the leaf is balanced in all positions as the centre of gravity of the mass. When the bridge is closed, the live load reaction comes on a bearing placed upon the pier in front of the curved track or cradle. The Cowing type double leaf roller bearing bascule bridge was formerly constructed in Cleveland Ohio in 1904.http://www.flickr.com/photos/94273918@N06/8656306694/(See pages 711 and 712 Bridge Engineering Waddell, and See Roller Bearing Bascule of John Cowing Historic Bridge Confrence page 142) Edit Text

Trunnion Bascule Chicago type and Simple trunnion types

"The Chicago type trunnion bascule bridge was developed by the City of Chicago Engineering Department. The trusses are supported on trunnions in line with the lower chord placed a short distance back from the centre of gravity of the span. The counterweights are rigidly attached to the end of the shore arm and a pit is provided in the pier for their reception when the bridge is open. The leaf is operated by a pinion and segmental rack attached at the end of the short arm. Elastic bumpers are provided to absorb the shock in the opening and closing of the span. A worm gear brake is also supplied to check any downward motion of the leaf, should occasion require. For a double leaf bridge centre locks are employed, but no rear locks are needed as the centre of gravity is ahead of the pivot.http://www.flickr.com/photos/94273918@N06/8666258432/ (See Bridge Engineering Waddell on page 709.

Simple trunnion bascule bridge are mostly of the double leaf trunnion for highway traffic. They open with racks that are curved with pinions and shafts with the mechinery that pivots around the rack and pinion that balances both leaves with the counterweight balance system. Double trunnion bridges are the most common of the true simple trunnion type built in 1894 when the tower bridge which has a double section crossing the Thames river in London England and is widely Known is drawbridges worldwide.

Most double bascule bridges are of the plate and deck girder types, and quite popular of the truss type. They are still constructed as new bridge applications by different bridge companies by the designers who works with the engineering firms.Theyre some single leaf trunnion bascules that uses a narrow channel, and the double leaf uses two channels for each leaf that meets at the centre when the leaves lower in the closed position." Some single and double leaf bascule bridges are twinned by having two parallel spans across the navigation channel. Soome bridges are connected so that the pair of leaves on one side of the navigation channel acts as one, and some are left independently so that each leaf acts separately. Simple trunnion bascule bridges consists of a unitary rigid displaceable structure supported on the horizontal pivot. Sometimes thepivot shaft is stationary and the bridge pivots around it mentioned earlier. The pivot shaft is more often fixed to the bascule span which is a true trunnion arrangement and the ends of the trunnion are supported in sliding or antifriction bearings. http://www.flickr.com/photos/94273918@N06/8686297136/(See pages 35 and 36 Movable Bridge Engineering Koglin).

WADDELL

John Alexander Lower Waddell is a chief engineer in designing vertical lift bridges. His first design was a lift bridge at halsted street in Chicago Illinois crossing the South branch Chicago river in 1893. http://www.flickr.com/photos/94273918@N06/8750575409/Waddell built a reputation as one of the 20th century's best known and highly respected bridge builders. Then prior forming his own firm of engineering and designs of bridges, then he taught engineering in Japan.

Waddell was a prolific bridge designer, with more than a thousand lift bridges to his credit in the United States of America, Canada and as well as Mexico, Russia, China, Japan, and New Zealand. His Lift bridges spans the Mississippi, Missouri, Niagara, and the Colorado rivers.

Waddell specialized in modern vertical lift bridges and his partner is John Lyell Harrington who works with Waddell in developing lift bridges. These lift span are mostly of the span drive because the mechinery is mounted on the span, with operating rope drums. Each drums are mechanically with four synchronizes, that pulls in and plays out pairs of ropes as the bridge opens and closes. The ropes of each drum connects to the corresponding corner of the moving span. One pair extending to fixed connections at the top of the tower are the uphaul ropes and one pair extending and fix to the tower base are down haul ropes. Most lift bridges of the span drive or Waddell type have counterweight sheaves that are cast or welded subjected to real high loadings that proper design and high quality fabrication are essential for a long while. Some lift bridge variations has auxiliary counterweight,the diagonal ropes extending from the center of the lift span to the towers reaching down and connects to the weights hanging alongside the tower legs, these ropes pull up on the span when its down and down when its up compensating for the weight of the ropes. and other variation auxiliary counterweight the diagonal ropes extending form the mast reaching up from the center of the lift span to the tower tops reaching down and connects to weight hanging alongside the tower legs. The ropes pull up on the span when when its down and down when its up.( See Movable Bridge Engineering Terry L Koglin).

Some lift bridges of the Waddell type have balanced chains made with cast iron heavy links which were once commonly used to compensate for the counterweight or operating ropes that passes over the sheaves. The one end of each chain hangs from the bottom of the counterweight and the other is attached to the fixed point on the tower, as the span lifts the counterweight lowers and the weight of the chain passes from the counterweight to the tower. As the span lowers the weight of the chain is transferred back to the counterweight.Another variation type vertical lift bridge is a tower span (Note" not of the Waddell type) this lift span has no mechinery on the lift span but is mounted on each tower with counterweight ropes with sheave shaft bears similar to the other lift bridges. The counterweight ropes are the main structural supports to the countweight attachments,some lift bridges also has balanced chains mention earlier but also has tower tied together by means of a strut the reaches across between two tower tops. They aren't related to the drive system, an example the Willow street lift bridge in Cleveland Ohio. http://www.flickr.com/photos/94273918@N06/8645273255/A span tower drive lift bridge has the drive mechinery on the platform suported on fixed girder extending across the channel between top towers on each side above the lift span. An example a span tower drive lift bridge in Point Pleasant New Jersey,http://www.flickr.com/photos/94273918@N06/8707185429/ Theyre less popular than other lift bridges.

STRAUSS AND RALL LIFT BRIDGES

Joseph Strauss, who specialized in bascule bridges, also developed vertical and direct lift spans. An example is the Strauss lift bridge in Hardin Illinois crossing the Illinois River. http://www.flickr.com/photos/94273918@N06/8751372394/ The lift span is operated by racks and pinions instead of ropes. A gear rack is mounted vertically with the axes of the teeth parallel to the bridge axis. Motor and gear reduction, located in a house atop the center of the span, drives a long shaft reaching to the ends of the lift span. At each end of the lift span a additional gear reduction drives the rack pinion which is held in mesh with the vertical rack that mounts in each tower. An expansion end of the bridge with extra wide teeth are provided so that meshing is maintained and contraction of the lift span. A direct lift bridge Strauss type, these are odd separated variation. Innovation direct lift designs that uses the counterweight arrangement of heel trunnion bascules to balance the lift span. Each tower supported a counterweight on a trussed frame linked to its end of the lift span, they’re no counterweight ropes or sheaves by providing a pivot counterweight plan. The rack and pinion machinery is used to operate the lift spans. A few of these types of bridges were built. The countweight and truss rides on rollers on a track and moves toward and away from the lift span as it raises and lowers. One Strauss direct lift bridge is still in use for the Burlington Northern & Santa Fe railroad is located between Tacoma and Steilacoom Washington crossing the Chambers creek. http://www.flickr.com/photos/94273918@N06/8627987435/A Rall type has one formerly in La Salle Illinois for the Chicago Burlington & Quincy railroad over the Illinois river constructed by the Strobel Steel Construction Company.http://www.flickr.com/photos/94273918@N06/8604001666/ Edit Text

WHIPPLE

Squire Whipple designed a few of the 15 operating precursor lift spans in the Western upstate New York area in the 1870's crossing the Erie Canal." This lift span has an overhead rigid truss structure, supported on towers with the roadway deck suspended from tension rods. The deck was lifted to clear the canal, and the bridges were manually operated by tread wheels mounted on the overhead truss. These lift spans are small of 60 foot long and 18 feet wide,the lift portions of the lift span were counterweighed like modern vertical lift bridges but actual operation of the lift span was accomplished by falling weights which were lift back into position by the tread wheel. Each bridge is lifted and counterbalanced by mechanisms that are under the roadways which push the bridge up less than 10 feet to provide clearance over the canal.http://www.flickr.com/photos/94273918@N06/8701371609/ A tower-less lift-bridge (not a Whipple type) similar to the Erie Canal bridges, crosses the Milwaukee River at Milwaukee Wisconsin. These lift bridges are nonhydraulic examples of the similar drive system.http://www.flickr.com/photos/94273918@N06/8617214792/ (See Movable bridge Engineering Terry Koglin).

SWING BRIDGES, CENTER AND RIM BEARINGS

Swing bridges operate by pivoting or swinging aside for ship and vessel traffic. A few swing span bridges were designed by George Morrison and other swing type constructed by bridge construction companies and railroad firms. Swing bridges were popular since in the 1800s, but some where replaced with bascule and lift bridges. There are two types of swing bridges center bearing and rim bearing. The center bearing swing span is a loading girder, transferring a dead load weight of the swing span to the center pivot (center bearing three points each end truss and center). Some swing bridges have balanced wheels and end wedges that require stabilization and not in live support, the balance wheels is spaced around a circular track. Rim bearing swing bridges have rollers around the rim with rack teeth to open and close the span. The rack has a pinion and track with taper rollers built in the low elevated around the edge of the perimeter pier. Rim bearing with 4 points each end side of the drum at the center.

Some swing bridges have combined rim and center bearings with the part of the load carried a center bearing connected to a rim bearing by radical struts. These struts are present on a pure rim bearing but serve only to maintain the position of a rim girder about the bridge center. On the combined bearing bridge the struts are primary load carrying members. The trusses or main girders rest directly on them while the outer end of each strut is supported by the rim girder and the inner end is supported on the center pivot. The distribution of load between the rim and center bearing varies but on most bridges of this type the major part of the load is carried on the rim bearing. With Bobtail swing bridges there some examples of asymmetrical swing bridges with truss and girder type on all swing span bridges. Some short lightweight bobtail swing bridges are not cantilevered at their long arms when in closes position, but act as simple spans with a very short cantilevered span extending from the other side of the pivot point not reaching beyond the extremity of the pivot pier. (See Movable Bridge Engineering Koglin pages 92 and 93)

Some bobtail swing bridges have counterbalanced weights at the end of the span. An example of a counterweighted swing span a railroad swing span in Chicago Illinois over the Chicago river canalhttp://www.flickr.com/photos/94273918@N06/8664823551/ and one in St Paul Minnesota crossing the Mississippi river. http://www.flickr.com/photos/94273918@N06/8666436232/Another variation type of swing span is a shear pole type that is pivot at one end of the bobtail type. The free end of the shear pole swing span is supported by tension rods or cables reaching down from and overhead structure. This span usually consist of derrick type posts forming an A frame around and above the pivot end of the bridge A frame is guyed by cables stretching to rear and side of the frame, the operation of the bridge may be of cable drum arrangement that pulls the bridge open and closed, and some bridges have racks and pinion machinery drives similar to a swing span. This is a simple span with a long end simply sliding into the closed position onto supporting masonry plates or strike plates. One shear pole swing bridge for rail traffic is still in operation in Paulsboro New Jersey.http://www.flickr.com/photos/94273918@N06/8708367272/

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