US2330981A

US2330981A - Bridge

Info

Publication number: US2330981A
Application number: US322064A
Authority: US
Inventors: Maddock Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-03-04
Filing date: 1940-03-04
Publication date: 1943-10-05
Anticipated expiration: 1960-10-05

Description

OCf- 5, 1943-y T. MADDQCK 2,330,981

BRIDGE Filed March 4, 1940 Patented Oct. 5, 1943 UNITED STATES raTsNT OFFICE BRIDGE Thomas Maddock, Saiord, Ariz. Application March 4, 1940, Serial No. 322,064

Claims.

The improvement relates to suspension bridges and largely to their stiffening trusses.

The object of the improvement is to reduce .the weight and cost of bridges, to reduce deflection in cables and towers, and increase rigidity.

Provision is made to combine expansion, continuity, pre-stressing and also angular deilection in trusses to largely eliminate the stresses resulting from temperature variations.

On suspension bridges the truss acts as a two hinged structure for dead loads and cable temperature deilections, as a continuous structure for live loads and in addition provision is made for truss length variation [or temperature and camber changes.

As the length of the truss varies from temperature an expanding mechanism produces angular deflections in the continuous truss to adjust it to the cable deflection. Thatis when temperature expands the truss longtitudinally the mechanism while retaining continuity in the truss, shortens its lower chord faster than its upper chord creating a Vertical deflection in the line of the truss approximately equal to the deflection of the cable at the tower caused by temperature, thus eliminating the temperature bending stress in the truss at the tower. On the contrary when the temperature drops and the truss contracts the mechanism tilts the truss upward approximately as the cable deflects upward on contracting. Complete instead of the usual half continuity is secured for the side span truss, i. e., both ends of the side span are continuous.

Figure 1 is an elevation of a portion of the main span, tower, side span and approach span of a suspension bridge.

Figure 2 is a detail of truss members at towers or abutments permitting expansion and angular deflection while retaining continuity.

Figures 3-4-5--6-7-8 are details of mechanical modiiications for obtaining same result.

Figure 9 shows a modified method of securing angular deilection at an abutment.

Figure 1 shows cable iI, towery I2, truss i3,

piers I4 and I5, stay 20, hangers 33, main span I'I, side span I8 and approach span I9.

Figure 2 shows the truss at pier I4 of Figure 1. The truss chords to the left are raised and those to the right are dropped from horizontal alignment and bent lever members 22-24--25 and 27-28-29 inserted in the chords with their long arms connected by a strut-tie -2'l. The joints 21-22-24-25-21-28-28 are pin connected. The truss is supported at 28 by a rocker resting on pier I4. Rollers are likewise used. The ver-` tical member 24-29 maintains the chord alignment. Hangers 33 are shown. The variable counterweights 44 suspended at 26 on the lower lever arm and from the pier I4 is one method of prestressing the mechanism to compensate for the diierence in distance between

pins

24 and 25 and pins 2l and 28 which dilerence causes not only angular deflection or rotation of the truss, but also a horizontal thrust in the truss.

Figure 3 diiers from Figure 2 in several separate modifications. The lever arms 32-34--35 and 31-38-39 are but slightly bent and their connecting strut-tie 35-31 is reduced in length. The truss chords to the left are increased and those to the right are reduced in vertical distance apart to provide space to insert the lever members. The distance 32--34 equals the distance 38-39 but the distance 34-1-35 is greater than the distance 31-38 so under truss expansion the inclination of 38--349 `is greater than 32-34 causing the lower chord to shorten faster than the upper chord, producing angular deflection in the truss. On the contrary when the truss contracts it is deflected upward in coordination with the cable.

The vertical member .ifi-38 is not supported on the pier I4 but as modified the truss is carried by the hangers only, to reduce bending moments of the truss at the tower by eliminating the ef fect of the difference in the temperature variations of tower and hangers, also the lengthening of hangers and shortening of towers under live loads.

No detail is shown in this ligure to compensate for the difference in distance 34-35 and 3l-38.

Figure 4 shows a modication consisting of two toggle joints 4I-42-43 and 4'l-48-49 in the upper and lower chord of the truss connected by the strut-tie l2- 48. The toggle arms iI-42-43-44 are unequal in length' to the toggle arms 41-48 and 48-49 thus under temn perature Variations deilectingthe truss in coordination with the cable as related of Figures 2 and 3. The toggle arm 41-48 is extended and a differential counterweight hung at 46. Pins 4l and 49 are supported by roller bearings on pier 44.

Figure 5 shows a modification of two toggle joints in the chords. tended as a lever arm to 4 where it is connected by the strut-tie 54-59 to the elbow of the toggle 5S--59-50. Angular deection is produced by truss length variation as the distance 52-53 is less than the length of 5.3-54 and 58-59 in the same manner that truss deflection is coordi- Toggle arm 2-3-is eir-` nated with cable deflection asrelated of Figures 2 and 3, etc. Toggle arm 53-59 is extended and a differential weight 44 suspended at 5t. Pin 58 is supported by a roller bearing on pier I4.

Figure 6 shows a modication in which the chords of the truss are connected by two equally long hangers or supporters (il-62 and 63-64 separated horizontally. Angular deflection is secured by inclining the hangers ,in opposite directions. For instance as the left and right portions of the truss separate due to tempera- Figure '7 shows'a, modi'cat'ion consistingor two' toggle's 85-82--83' and 88;-892-8il inserted* in the chords with' theA elbows ofy the t'ogglcs con nested-by they strut-tie'y l2- 39; The toggle.y arm.

552-83 is longer than the: arm 83-39' so asi the truss and' cable expand from temperature the' distanceV 258-80 shortens faster than the distance Eli-'83 and the truss deflection'i's- Goor-di'- nat'edi to that of the cable'. The member BBL-S8 transmit shear and apply to suspended as Well as supported positions. All movable joints in the various figures of trusses are shown by a small circle representing a pin. Other joints may be rigid.

In commonpractce suspension bridge trusses are designed as two hinged at towers, three hinged at towers and span center, or continuous on main span with side span xed at tower and supported at abutment.- Temperature changes result in large stresses and transfers of dead loads from cables to trusses, etc. This application provides for continuity throughout by providing inis shown.' inclinedv to compensate or-A pre-stress.-

tlie truss against horizontal thrust.

Figure 8 shows a modication in lthat'lthei' truss is i connectedbyan expanding' mechanism: co'n-- Y sisting'of a, turn-buckle 2 in eachV chord-y con-V nected to operate simultaneously bythe'lihk belt' chain S'running on the sprocket' wheels) 3 v andl 6i Angular deflection` issecured by.l differing" the dia-meters ofv the" sprocket Wheels; The'sprocket wheel 3 is larger' than the wheel irso.I that the: turnbucllei in the lower chord revolves faster thanrthe turnbuckle in the upper chord deflect'- ing the truss downward with expansion'anizlE upward` with contraction in coordination with: the deiiecticn in the cable." 'Ihe'fpitch` of the left andright hand screws on bolts l` and dis regu'- latedl to provide frictional resistance tovv absorbthe diierence in rotating force produced by the difference in diameter of the sprocket wheel when' theyare working'in.V opposition but not. tore'sist movement when chords are subject to stresso'fV like direction, i.-e'.,temp'erature adjustment oc- Y curs between the 'reversal' stresses: of! live loads.

Figure 9 shows a` method of securing angular deflection and continuity where there is'n'o approach span or where the' stress` in` the. trussv chord is relatively smallas compared to that in theA cable and thepier i5 is relatively short or can sustainhorizontal thrust.v The cable' i-'iy is attached tothe truss lit-and the stay-Zfat lfl'l'. The -truss rotates on pin H2; thedefl'ecting-angle depending upon the length and stress in 'the stay 20.

In using Van expanding mechanismf on= pie-ir:A i5' the side span I8 is xed to the pier and thea'n' gular rotation of f the' side` span truss* isi controlledbythe length of-4 thel approach' spang or" The expanding continuous meclfia'nisriiv1 shown in Figures 2-3'-5-5-7 .transmit shearl aswell,v

as moment and are either'suspended'orA sup'-v pc'rte'd by rollers' or' rockers; The'- tur-nLbuckle mechanism showndn Figure? Ba'lsdis modiiied t0v ternal expansion at towers on multiple spans or ing ofmain and side spans.

B'y rotating the Ytrusses to correspond with cable" sag',v deflections on continuous trusses are increasednear towers and thus decreased at center of t'he'span when subject to higher temperatures', also'y the' full' Weight off the' dead' load and the strength oi" the' trusses' resist the upliftY on the cable ofi an; empty' span; or' portion' thereof induced: by? l-ve load'sf elsewhere.

Likewise at*V low temperaturesthe' strength of the truss doesnot inc'rea'sefthe4 cable load.

Essentially' thelmechanism" takes up slack in the' cables: thus reducing d'eilect'ion in towers 'and Itrusses.

Pre-'stressing the truss before connecting hangers or toggles islaE substitutionifor the counterweigh'ts' showniin" some or the drawings, also inclined? hangers;. springs; reducing gears, etc., are used'. No'detailslare' shown' of slowl motion controllers to dampen longitudinal movement whentrusses are suspended, also when'supported it dec'eleration,y wind', etc.,: stresses' are greater than resistance of' roller bearings.

l2 A suspensionbridge comprising-a suspension cabie; a continuous'stiieningl truss suspended'by hangersy from the cable; movable means in thev truss connectingA adjacent portions`- of its upper chord'l and bottom' chord;V respectively, for perf mit'tingy opposite longitudinal movement' of' the portions'f oi veach chord' as temperature varies; and' intermediate-v means?` connecting thef respective'fmean'sof theA chords' and Vfio-ordinating the' the movement` ofI-themeans in'the'other chord' for'producing angular vertical deilection'in the 'truss'lsubstantially' equal to thel deflection produced in the? cablebyl temperature'variation;

3.' A? suspension bridge comprising." a4 suspension' cable; a' continuous stiflfening:` truss' suspen'dedl byI hangers'- from the cable; movable' toggley joints in the truss connecting adjacent portions-'of itsiupper andlbo'ttom chord, respectively; for permitting opposite longitudinal' movementl of l'the portion of each'chordas temperature varies;- said i toggleswhile `being-connected to; op-

erate simultaneously; having@ arnis of different4 length co-ordinating the said longitudinal movement with angular vertical deection in -the truss substantially equal to the deiiection producedin the cable by temperature deections.

4. A suspension bridge comprising a suspension cable; a continuous stiffening truss suspended by hangers from the cables; movable oppositely inclined hangers in the trusses connecting portions of its upper and bottom chords respectively for permitting opposite longitudinal movement of the portions of each chord as temperature varies; and co-ordinating the movement in one chord in relation to the movement in the other chord for producing angular vertical deection in the truss substantially equal to the deflection produced in the cable by temperature variation.

5. A suspension bridge comprising a suspension cable; a continuous stiffening truss -suspended by hangers from the cable; movable turn-- buckles in the truss connecting adjacent portions of its' upper and bottom chord respectively, for

permitting opposite longitudinal movement .of the portions ,of each chord as temperature varies;4 said turnbuckle being connected with a sprocket chain running over sprockets of diierent diameter co-ordinating the movement in one chord in relation to the movement in the other chord for producing angular vertical deflection in the truss substantiallyvequal to the .deflectionpron duced in the cable by temperature variations.

THoMAsMADDoCK.