US2402124A - Bridge construction - Google Patents

Description

5m@ iig, 94@ F. @Mmmm BRIDGE CONSTRUCTION Filed Fem 26., 1.941?

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F1611. @MM lN-VENTOR Patented June 18, 1946 UNITED VSTAT-ES PATENT OFFICE Paul Chapman, Bayside, N. Y. Application February 26, 1941, Serial No. 380,659

My invention lin bridge construction provides means whereby bridges and especially longespan suspension bridges, may be `-louilt safer, more economically, more rigid with shallower` girders, and

moregraceful in appearance. My improvements J are useful in reconstructing existing bridges, :since they provide greater strength with lessmaterial .so that A1re-used parts,v having less dead Aweight-to support, have greater live 'load capacity. My invention uses discontinuous construct-ion for economical dead load support, and continuity under live `and wind loadings for rigidity, 4economy and substantial elimination of vibrations and thermal-stresses.

In suspension kbridge construction, ymy invention may rprocure the foregoing' results 'by the combination, longitudinal stifiening .girders continuous throughout for live loadings, .a torque-resisting roadway fsystem comprising "a rigid traffic- -carrying-roadwayetop .attached` at each side to the gir-ders, a bottom-lateral .system between the 'girders and the girders with longitudinallyspaced iioorbeams, and .lateral sway-bracing systems connecting the girders and suspensioncablestogether. v

In the drawing, Fig. 1 'is van elevational `view oi `a-suspension bridge,A Fig. 2 is va 'plan view with roadway-top lcut away to `show bottom .lateral bracing, Fig. 3 is an enlarged elevational vview near midspan where diagonal suspendersand sway-bracing systems connect to cables, Fig. 4. yis ya partial plan View showing connections of swaybracingfsystems to cables, Fg.'5'is a sectional view 4of half of bridge showing torque-resisting road- Way system and sway-bracing system, Fig. 6 is Va plan view `of 'half of bridge near` tower with roadway-top cut away to show bottom lateral-bracing and `tie-strut, Fig. 'l is a sectional view `of ,portion shown -in Fig. 6, Fig. 8 is va sectional view near tower showing lever attower, Fig. Vv9 is :an enlarged view of moment-transferring lexpansion joint .in 'girder, Fig. 10 is an enlarged sectional view of shear-transmitting expansion `joint in top-chord of Fig. 9, and Fig. 11 is ya sectional "view of the `she:ir-transmitting expansion ljoint vadapted to Vallowslightrotation-al movement.

In Figs. 1 Yand 2, cable i3 extends `between anchorages l and over towers V2. Stiffening girder mid-section 5a connects to intermediate tower sections Ebthrough load and moment-transferring lexpansion joints Sab, sections bvoonnectvto end-sections c through loadand moment-transferring expansion joints 5bc, and sections 5c are `fixed 'against longitudinal rotational movement at anchorages l by 'two fixed connections 5h, 5i,

9 Claims. (01.14-20) so ythat thegirder :is continuous throughout 'for live and Vvertical wind loadings. Load and moment transferring joints 5de, 5fg similarly make the bottom lateral-bracing .system continuous throughout for lateral loadings. of a uniformly-loaded bea-m makes vit live times as rigid, so the ,incr-eased rigidity of my vconstruction is apparent since it is fixed `at anchorages l and continuous over and supported at towers 2. Suspenders 4a .near towers Vand an- Vchorages, are adjusted Lto take tension substantially only .from live loadings, dead load thereat being supported by lcantilever action of girder from towers and anchorages, with .economy resulting from `reduction of tension throughout the entire cable, .and lessened cable curvature near towers :and anchorages increases rigidity .under live and wind loadings.v For the .rest of the bridge, vertical suspenders '4, 4b, diagonal suspenders do andsway-,cables 6d, Be, Bf may be adthereby,

justed `to take the entire roadway dead loadings, with no bending on the .stiffening girder therefrom. vExpansion joints Sab, 5de, Bbc, 5f@ permit only longitudinal l.movement of the parts joined and transfer loads and bendingmoments, thus `avoiding longitudinal `thermal stresses due to .xing the` girdens to the 4anchorages, and provide continuity throughout. In Figs. 2, 6, 7, load and 'moment-'transferring .expansion joint 5de .is .composed .of oorbeams la, Tb, midsection diagonals 5e each jointly connected at .one end to ;a bottom-chord 5cl and o'orb'eam 1.a and :merging at other end into a glongitudinal extension .through a Vhole in floorbeam 'lb allowing longitudinal movement only therein, and intermediate-section diagonals .5d .each jointly ,connected at .one end to a bottom-.chord 5bl 'and iioorbeam lzb -and merging at .other end into a `longitudinal extension through a hole in oorbeam la sallowing longitudinal movement .only-therein. Diagonale 5d, 5e pass but .do .not connect to each other. .Floorbeams la, lb actas tie-struts .to (deliver half the, lateral transverse load received Afrom respective extension to .diagfonals 5e, 5d respectively. The bending-moment transferred from :nld-.section to vintermediate section equals stress .in a chord iial times distance to .other chord 150.1., or transverse load on extension lof fdiagonals 5e `timesdistance between floorbeams V1a, :1b. Expansion joint 'Efg is y.constructed in similar manner.

In Figs. 1, 9, l0, 11, a shear-transmitting exparisien joint allowing longitudinal movement, is formed :by telesc'oping` top-chord Sblc inside-topchord alc, with plates Baflxed to chord Bak-hav- Fixing the ends i ing longitudinal grooves Sap meshed with ribs formed by longitudinal grooves Sbp in plates 9b attached to chord bk. In Fig. 10, plates 9b are xed to chord Ebk so that longitudinal movement only, is provided for between chords Sak, 511k. In Fig. 11, plates 9b are connected to chord Sblc by pin 9c to provide for some longitudinal rotation in addition to longitudinal movement between chords 5a7c, 5bk. With grooves 5ap, 51m rectangular, there would be a slight tendency to spread apart due to elastic deformation under stress, so some of the grooves on each side of chords Sak, 512k are dove-tailed so that the contacting sides of the ribs formed by the grooves, through which loads are transmitted, slope toward the load-receiving part, thus causing plates Sa, 9b to cling together. A sheartransmitting expansion joint also connects bottom-chords Sal, Sbl to allow longitudinal movement, spaced longitudinally so that girder- sections 5a, 5b overlap a required distance. The two shear transmitting expansion joints thus prevent relative transverse movement of sections 5a, 5b at ends of overlap, and together with the overlapping ends oi the sections, constitute load and moment-transferring expansion joint Sab. Diagonal Eibm of overlap of section 5b is shown dotted and moves freely inside diagonal 5am of overlap of section 5a. Load and moment transferring joint 5ba is of similar construction.

In Figs. 1, 2, 6, '7, 8, tie-strut 8 connects at one end to girder mid-sections 5a through merged ends of diagonals holes in oorbeams 5e, extends loosely through 1c, and connects at other end to ends of levers 8a. Levers 8a fulcrum about pins 2b attached to tower strut 2a and connect to respective tower girder-sections 5b. Tie struts 8b extend loosely through the floorbeams and connect tower sections 5b to anchorages l through bottom diagonals 5g, movement in expansion joints 5bc, 5fg thus being the diierence in thermal expansion of tie-strut 8b and end-section 5c. Levers 8a are thus connected at one end to a line of steel extending to respective anchorage l, and at other end to a line extending over the mainspan, s that with respective lever-arms proportional to thermal expansion of line to anchorage and half that of mainspan, no temperature stresses result, and longitudinal loads are carried to towers and anchorages at roadway level. Section b with strut 8b, and section 5c may be considered to form together an end section freely supported at an intermediate support, comprising the tower, and xed to an end support, comprising the anchorage.

Diagonal wind may cause a longitudinal load almost half the lateral load of a. direct wind, due to the obstruction of web-members of girders or vertical stiieners of plate-girders. In customary construction this load is carried by the cables from midspan over the towers to the anchorages, Iwith consequent movement of mainspan girder and flexures at quarter-points. The foregoing movement and flexures are avoided in my invention, by carrying the longitudinal wind load tothe towers at roadway level through the levers 8a.

Diagonal Suspenders 4c adjusted to support some dead load near midspan, serve to prevent relative longitudinal movement of cable 3 and girder section 5a, and since they are approximately on lines projected from girder at midspan to respective tower-tops, assist in transferring shear across midspan, thereby reducing vertical ilexures of cable resulting from such transfer under unsymmetrical loadings.

For lateral Wind, in customary construction the reaction points are the tower tops and the girder connections at the towers. Except near midspan, the Suspenders transfer little roadway wind load from girders to cables, and because this load is applied far above the girder connections 2c, Fig. 1,to towers, a serious torque arises which raises the Windward girder and lowers the leegirder, especially at quarter-points. In my invention, this condition is substantially eliminated by the cable sway-bracing systems and the torque-resisting roadway system.

In Figs. l, 2, 3, 4, 5, sway-bracing systems comprise, iloorbeams 'l and portions of girder sections 5a to which are connected balancers 6g by pins 6h, Suspenders 4b and sway-cables 6e with clamps Si at intersections in a vertical transverse plane, diagonal sway-cables 6rd, 6j, and tie- struts 6a, 6b, 6c attached at ends to cable- bands 3d, 3c, 3b respectively. Tie- struts 6a, 6b, 6c may be made flexible members where cradling of cables 3 from towers to sway-bracing is enough to keep them in tension. Axes of sway-cables 6d, Ee, 6j are a common distance from pin 6h and on the opposite side thereto of the axis of suspender 4h, so that balancer 6g, rotatable about pin 6h, fixes dead load tension in diagonals and suspender in inverse proportion to axial distances to pin 6h. An adaption may be made wherein balancer Gy is ixed against rotation, and tension in sway-cables 6e is adjusted by moving clamps 6i along the cables. Roadway lateral wind tends to move iloorbeam 1 leeward, thereby reducing tension in sway- cables 6d, 6e, Gf attached to Windward balancer By thus tending to raise lee cable 3, and increasing tension in sway-cables attached to lee balancer thus tending to lower Windward cable 3. The torque from lateral Iwind tended as described to raise Windward and lower lee cable 3, so the sway-bracing systems tend to counteract that torque. In Figs. 3, 5, 6, '7, the torque-resisting roadway system comprises, the rigid trafficcarrying roadway-top 7f attached continuously to floorbeams 1, 1a, 1b, 1c supported also by intermediate floorbeams 'le and attached continuously at sides by curb 'lg to girder- sections 5a, 5b, 5c, floorbeams, girder sections, and my improved lateral-bracing system consisting of girder bottomchords, iloorbeam bottom-flanges and diagonals 'ld each attached at ends to midpoint of a iloorbeam and midpoint of a bottom-chord between iloorbeams. The roadway system is continuous with expansion joints in roadway-top 1f and curb ently of lee cable and girder, with reaction points at towers, so that with shallow-girder construction even small changes in wind velocity give rise to serious undulations. Anchorage-spans contribute to mainspan undulations even with maximum mainspan moment unchanged, because of hammock-like action of the cable, which varies horizontal cable-pull. In my torque resisting roadway system, lateral-wind torque tends to raise Windward and lower lee lgir-der a at quarter-points, and because floorbeam 1 maintains a rectangular cross-section, tends to flex roadwaytop 1f leeward and the bottom-lateral system Windward. Compression in windward bottomchord Sal 'from raising of girder 5a is `Silbstantially eliminated by tension therein from Windward flexure of the bottom-lateral system, and tension in Windward top-chord :Sak is vastly reduced by compression therein arising .from the leeward fiexure of roadway-'top 1f. Similarly .reverse yaction occurs in lee chords Sal, Sak, so lateral-wind torque is resisted with .substantially little chord stress, and lflex-tires, of girders 5a are consequently small and arise 'from shearing stresses lin rigid roadway-top 1f, diagonals 1d and girder web-members 5m, En. Thus, in some bridges, my torque-resisting roadway system ,may suffice to eliminate undesirable tilting of the roadway.

Tilting due to unequal live loadings carried by the two cables and gifrders is also substantially eliminated by the cable sway-bracing systems and the torque resisting roadway system. The continuous girder construction also `serves to reduce live load iie'xures.

My. torque-resisting roadway system would function with customary X or customary K bottom lateral-bracing systems, however, my improved lateral-bracing` system procures more rigidity and economy. In the X system wherein intersecting diagonals are jointly connected at ends to chord and floorbeam, equal length-change of the two chords due to independent stresses, causes elastic length-change of both diagonals and floorbeams, with resultant stresses in diagonals and lloorbeams not arising from their functions in the lateral bracing system. In the K system wherein each diagonal is connected jointly at one end to chord and floorbeam and at other end jointly to a counterpart diagonal and the mid-point of a consecutive fioorbeam, each floorbeam must be reinforced to carry the Ishear transmitted to it by the diagonals at mid-point to its ends. In my improved lateral-bracing system wherein diagonals ld each connect at one end jointly to mid-point of a chord and a counterpart diagonal id and at other end to midpoint of a fioorbeam and three counterpart diagonals and wherein floorbeams 1, 1c are connected to chords to transmit vertical shear only, and transmit panel lateral shear to the bracing system at mid-point, equal length-change of the two chords merely moves the chords laterally with no length-change of diagonals 1d, and floorbeams 1, 'ic are unaifected by the shear in the bracing system. My improvement thus effects economy and rigidity.

The girder sections 5a, 5b, 5c are shown with articulated webs, however the improvements are adaptable for use with girders having plate webs or with I-beams.

I claim:

1. In a bridge having supporting cables extending between anchorages and over towers; road-way supporting girders each supported at its ends by aforesaid anchorages thereat, and each supported at aforesaid towers; a torque resisting roadway system comprising, aforesaid girders, a rigid roadway top and a rigid bottom lateral bracing system both attached at each side to said girders throughout, and floorbeams at longitudinal intervals each attached to said roadway top said bracing system and said girders; cable sway bracing systems `at longitudinal intervalsV each comprising, a tie-strut attached at each end to an aforesaid supportingcable, sway cables each extending from an end of said tie-strut diagonally downward to an aforesaid girder, and vertical 'Suspenders each extending from an end of said tie-strut to a said girder; and diagonal suspenders each extending from a point on aforesaid supporting cable to the aforesaid girder beneath said cable at a point nearer mid span; the combination of said roadway system, said sway bracing systems, and said diagonal Suspenders serving to render bridges safe, rigid, and economical, substantially as described.

2. A shear transmitting expansion joint providing longitudinal movement and rotation between two members, comprising, a hollow part of one member and part of other Said member telescoped therein, plural longitudinal grooves in opposing inside faces of said hollow part and plural longitudinal grooves throughout outside raised vfaces of said telescoped part, a pin connecting said outside faces to the body of said telescoped member to permit relative longitudinal rotation of said outside faces and said body, said `grooves in said inside faces being meshed with ribs formed by Said grooves in said outside faces to transmit transverse pressures.

3. A moment transferring expansion joint between two sections of a bracing system, comprising, a tie-strut extending perpendicularly between longitudinal chords for each of said sections, diagonal-S extending from the ends of said tie-strut lto their junction and forming thereat a longitudinal extension, for each of said sections, and a hole in each of said tie-'struts through which said extension of other said section extends for longitudinal movement only, loads parallel to aforesaid tie-struts being transmitted through said holes.

4. In bridges having supporting cables extending between anchorages and over towers and having Suspenders at panel points extending between said cables and girders beneath, means to support panel dead loads on said girders adjacent to anchorages and towers without increasing stresses in said cables and upper portions of said towers, comprising, moment transferring connections between said girders and anchorages, girders continuous across and supported on said towers, and said Suspenders at a plurality of panel points adjacent to each of said towers and anchorages adjusted to support no dead load.

5. In a bridge having a pair of supporting cables extending betweenanchorages and over towers with roadway construction supported by Suspenders from said cables, said cables being spaced apart a distance not less than substantially the width of said roadway construction, cable sway bracing systems, longitudinally placed in said bridge, to restrain relative lateral and vertical movement of said cables and said roadway construction and transfer lateral loads between roadway and cables, each sway bracing system comprising, a tie-strut attached at each end to a said cable, a floorbeam and a vertical part of said roadway construction attached thereto at each end, vertical Suspenders extending between said cables and said roadway construction, and sway cables each extending between one of aforesaid cables diagonally downward to one of aforesaid Vertical parts at opposite side of roadway construction, the dead load of roadway construction at panels where said 7` i bracing systems occur' being carried jointly by said vertical suspenders and said sway cables.

6. Girder construction with two end and two tower-supports, continuous throughout and free from temperature stresses, comprising, a girder mid-section, girder tower-sections, girder endsections, moment-transferring expansionv joints between said tower-sections and said other sections, tie-struts connected by lateral bracing to said mid-section and extending to respective tower-supports, balancing levers fulcruined about pins on said tower-supports and connected at ends to Said tie-struts Iand said tower-sections, said levers serving to balance longitudinal loadings on said mid-section and said tower-sections.

7. Girder construction, continuous throughout, with intermediate supports, fixed against 1ongitdinal rotation and movement at end supports, and free from stresses due to thermal length change, comprising, a girder mid-section and two end sections, moment transferring expansion joints connecting said sections together, said end sections being freely supported at said intermediate supports, two xed connections attaching each of said end sections to respective said end supports, and fixing said girder against longitudinal movement and rotation thereat, tiestruts attached to said mid-section through a latera1 bracing system and extending to respective said intermediate supports, and levers fulcrumed about pins on said intermediate Supports with leverl arms connected to said tie-struts and said end-sections, and proportional to the thermal length of tie-strut with half girder inidsection and girder end-section between intermediate and end supports.

8. In bridge construction, a lateral bracing System between two longitudinal chords wherein stresses in diagonals thereof are substantially unaffected by the stress deformation of said chords, comprising, said chords with fioorbeams at longitudinal intervals extending between said chords and connected thereto to transmit vertical shears, and said diagonals extending from each said chord mid-point vbetween said floorbeams to each adjacent floorbeam mid-point, each said diagonal being attached at one end to a said chord and an adjoining said diagonal, and at its other end to said lioorbeam and three counterpart diagonals, said loorbeams serving to transmit lateral loads to lsaid latera1 bracing system.

9. In bridge construction, a. balancer apportioning dead load between a vertical ilexible tension member and diagonal ilexible tension members, comprising, a pin attached to and receiving said load from a girder, the body of said balancer rotatable about said pin, and connections between said body and said between said body and said diagonal members. the axes of said diagonal members being equidistant from lsaid pin and on the opposite side thereof to the axis of said vertical member, and said body serving as a lever to apportion said load between said vertical and bers inversely proportional to the two respective axial distances from said pin.

PAUL CHAPMAN.

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