US2953797A

US2953797A - Space frame support for skew bridge

Info

Publication number: US2953797A
Application number: US745996A
Authority: US
Inventors: Robert M Dodds
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-07-01
Filing date: 1958-07-01
Publication date: 1960-09-27
Anticipated expiration: 1977-09-27

Description

Sept. 27, 1960 M. nouns 2,953,797

SPACE FRAME SUPPORT FOR SKEW BRIDGE Filed July 1, 1952 s Sheets-Sheet 1 DIRECT/ON UPSTREAM/ L 0W7 fl/VGULAR POSITION OF BRIDGE INVENTOR. Ross/ 7 M 0000:

it, %M/% l/IS A TTORNE)S.

Sept. 27, 1960 R. M. DODDS SPACE FRAME SUPPORT FOR SKEW BRIDGE 3 Sheets-Sheet 2 Filed July 1, 1958 INVENTOR.' ROBERT/l4 D0005 m .nilkl Sept. 27, 1960 R. M. DODDS 2,953,797

7 SPACE FRAME SUPPORT FOR SKEW BRIDGE Filed July 1, 1958 3 Sheets-Sheet 3 United States Patent 2,953,791 SPACE FRAME SUPPORT FOR SKEWBRIDGE Robert M. Dodds, 5270 Sherwood Drive, Pittsburgh 36, Pa.

Filed July 1, 1958, Ser. No. 745,996

18 Claims. (0]. 14-16) This invention relates to 'a support for the ends of bridge trusses which are skewed to their supporting pier, and more particularly, to a space frame support situated in the vertical space between the ends of the trusses and the top of the pier.

In the past it has been customary to construct bridges so that they lie perpendicularly to the flow of travel thereunder, and the supporting piers were accordingly constructed so as to lie longitudinally of the flow of the river or the flow of rail or highway traffic and perpendicular to the path of the bridge. The ends of the bridge trusses could then be evenly supported by the pier. With the increase in congestion now found in urban areas, it is not always possible to so construct a bridge that it will cross a river or a highway exactly perpendicular to it, and as a result, bridges are now being constructed to cross rivers, railroads, highways, etc., skew to or at an angle to the path of flow of the river, railroad, or highway thereunder. V

In order to accomplish structurally sound support for the bridge spans, it has been necessary to either skew the trusses, so that the ends thereof do not terminate opposite one another, or to skew the setting of the support piers so they lie perpendicular to the path of the bridge.

Both of these constructions have various disadvantages. When the trusses 'are skewed so that their ends are uneven, it is diflicult to structurally design, fabricate, and erect the bridge. Furthermore, this type of structure is expensive and uneconomical to construct and maintain and it does not produce a symmetrical appearance. When the piers are skewed in a river, navigation on the river is obstructed since the skewed pier presents'a broad front. In addition, the capacity of the river to carry flood dis charges, floating debris, ice, etc., is detrimentally hindered. When the skewed supporting pier is employed adjacent to a highway, such as at a cloverleaf, the skewed pier materially decreases the accessibility to the highway, and the potential width thereof.

An object of my invention has been to find a solution to the problem thus presented;

. Another object has been to provide an improved supporting structure for bridges which are to be constructed in a skewed relation;

A furtherobject of my invention is to provide an intermediate supporting structure between a supporting pier that is positioned longitudinally of a path of flow and the ends of the trusses of a skew bridge extending diagonally of the path of flow;

An additional object of my invention is to provide a space frame support between the ends of the trusses of a skewed bridge and the top of their supporting pier;

These and other objects of my invention will be ap parent to those skilled in the art from the following disclosure and drawings in which:

Figure 1 is a plan view showing a space frame construction of my invention for supporting the ends of bridge trusses;

'lce Figure 2 is an elevational end view of the construction taken along line II--II.of Figure 1; and

Figure 3 is a side elevational view of'the construction and showing two spans supported in the center by my space frame support and at the ends by standard rocker supports. a I

The elements or members of my space frame support carry the bridge loads diagonally downward from the trusses to the supporting pier. Resultant tensile forces are resisted by ties, one rigidly secured to or embedded within the top of the supporting pier and another extending transversely across the bridge structure and joining the trusses. As shown in Figure 2, the pier is preferably made of reinforced concrete or other masonry material. The elements of my supporting frame may be made of any suitable construction material, such as steel or other metal, reinforced concrete, wood, or any combination of these materials. The exact details of joining the elements together and the particular joints used are not a part of my invention, as they may be of any applicable design. Likewise, the cross sectional shape of the elements may be made of any structurally sound configuration.

Referring now to the drawings, A represents two bridge spans to be supported, B indicates a space frame support, C is a central supporting pier, and D represents rocker arm supporting structures. The center supporting end of the bridge span is represented by two trusses 11 and 12. These trusses may be plate girders, beams, tied arches, Vierendeel or any other type of truss which may be simply supported at its ends.

This invention is most applicable to trusses and tied arches which require vertical support at their end panel points, and which cannot easily be adapted to a shifted support as can beams and plate girders. For the sake of clarity, Figures 1 and 2 show only one span supported by my space frame. However, there will always be two spans supported at each center pier, as illustrated in Figure 3. It is immaterial whether one or both spansbear directly on the space frame, and if only one span bears on the frame, then the second span bears its lead on the first span. The particular type of joint employed between the spans may be a fixed pivoted, expansion, or any other suitable type of known joint.

My space frame is composed in part of four compression struts or

members

15, 16, 17, and 18 which extend from the truss ends diagonally downward to the pier ends. The

struts

15 and 16 and the

struts

17 and 18 are shown as a unitary construction in Figures 1 and 2. However, it is not necessary that these struts be unitary, as they may be formed as individual members.

A pair of

horizontal tension ties

13 and 14 extend laterally across the top and bottom, respectively, of my space frame support. The tension tie 13 connects the ends of the trusses 11 and 12, and the tie 14 extends later-ally across the top of pier C. The struts 15 and'16 are connected at their lower ends to one end of tie 14 at joint 23. The

struts

17 and 18 are connected at their lower ends to the other end of tie 14 at joint 26. The

struts

16 and 17 are connected at their upper ends to truss 12 at joint 24.

Struts

15 and 18 are connected at their upper end to truss 11 at joint 25. The

joints

23, 24, 25, and 26 are preferably of a universal pivot type of joint, to eliminate secondary stresses; however, they may be fixed joints, if desired.

Two compression struts, 19 and 20 extend from the ends of trusses 1'1 and 12, respectively, diagonally downward to the center of the pier C and are connected to the center of tie 14 at joint 27. The joint 27 may also be of a universal type. The

struts

19 and 20 reduce the required' strength and section of the

struts

15, 16, 17, and I-Sthat is necessary for supporting the span, and thus,

reduce the cost of their manufacture. However, the use of

struts

19 and 20 is optional, and they may be omitted if there is no center pier or central portion of a single pier available for these struts to bear upon, or if the load to be supported is relatively small. If desired, the

struts

15 and 17 may be omitted from the space frame when the

compression struts

19 and 20 are used. Although for purposes of illustration, the

struts

19 and 20 are shown integral with the trusses 11 and 12 and the tie member 13, it is obvious from the foregoing that they may also be made as separate members.

When the

struts

19 and 20 are used in the construction, the space frame is indeterminate and, therefore, is subject to conventional methods of structural analysis. In a simple preliminary design, it is possible to assume that struts 19 and 20 support the entire dead load and none of the other loads; and that the

supports

15, 16, 17, and 18 support live loads, wind loads, impact loads, earthquake loads and other accountable loads. When the

struts

19 and 20 are not used, the space frame is determinate and the

struts

15, 16, 17, and 18 support the dead load as well as the above enumerated loads. In both cases, the horizontal components of the compression stresses in all members are resisted by tension in the horizontal tension ties 13 and 14.

A vertical load applied by one of the truss ends to its corresponding space frame corner, results in a vertical reaction or opposing force in the pier, without any horizontal components. A transverse load applied by an end of a truss results in a transverse reaction plus a moment about the longitudinal axis of the bridge. This moment is imparted to the bridge due to the geometrical configuration of

struts

15, 16, 17, and 18. A longitudinal load applied by the truss ends to the space frame support, such as braking, acceleration, wind, earthquakes, etc., results in a tendency for the bridge to move longitudinally. The space frame, itself, will not resist this tendency to move longitudinally; however, it will act as a rocker for the entire span. Such a longitudinal movement will be accompanied by a rotation, of small angular movement, about the longitudinal axis of the bridge.

The rotation is imparted to the bridge due to the geometrical configuration of the

diagonal struts

15, 16, 17, and 18. When a longitudinal movement is produced in the bridge, as for example, in the direction of the arrow X of Figure 1, then the

struts

15 and 18, connected to truss 11 at joint 25, will move forwardly, and will accomplish this result by arcing downwardly. The

struts

16 and 17, connected to truss 12 at joint 24 will also be moved forwardly, but will are slightly upwardly. As a result, it can be seen that the longitudinal movement imparted to the bridge is relieved by a minute rotational movement about the longitudinal axis of the bridge.

The space frame, however, may be rigidly attached to the pier, if desired, and in this case, longitudinal movement may be accommodated by simple rockers or rollers attached to the frame. If longitudinal movement must be resisted adjacent the center pier, then a pair of

brace members

21 and 22 are applied extending from trusses 11 and 12, respectively, diagonally downward to the pier (see Figure 3). Although the

brace members

21 and 22 are shown joined to the pier at joints 26 and 23, respectively, the location of their attachment to the pier is immaterial. It is important, however, that the upper ends of the

braces

21 and 22 be joined to the trusses 11 and 12, respectively, at points other than the ends of the trusses. When this type of construction is employed, the outer ends of the bridge spans are provided with rocker supports D, as shown in Figure 3.

In considering provision for thermal expansion, it is advisable for optimum results, that my pivotally mounted space frame support be used only on the immovable end of the span, and that the other end be supported on a normal pier with rocker supports, such as D. The reason for this preferred construction is the fact that longitudinal movement of the span at the space frame induces transverse tipping, if the entire space frame is used as a rocker. If both ends of the span must rest on skew piers, then the space frame at the movable end must be held relative to the pier, and rollers or rockers provided between the space frame and the trusses.

Whereas this invention is illustrated and described with respect to my now preferred embodiment, it is to be understoodthat various changes and modifications may be made therein and that other embodiments may be adopted on the basis of the teachings hereof, by those skilled in the art, without departing from the scope of the invention as defined by the following claims.

I claim:

1. In a bridge construction wherein at least one span is skew to a supporting pier and at least one end of the span is substantially perpendicular to the longitudinal axis of the bridge construction and lies in a vertical plane which intersects the longitudinal axis of the pier, a space frame supporting the one end of said span over the pier comprising, a plurality of diagonally-downwardly-extending rigid support members connecting a point on each side portion of one end of the span to spaced-apart points on the pier disposed substantially along a line parallel to said longitudinal axis of the pier.

2. In a bridge construction as defined in claim 1, a pair of brace members connected at one end to the pier substantially along said line and at their opposite end each to one of a pair of opposed side portions of the span at points spaced-apart from support member connections on the span.

3. In a bridge construction having at least one span which lies skew to its supporting pier and wherein at least one end of the span is substantially perpendicular to the longitudinal axis of the bridge construction and lies in a vertical plane which intersects the longitudinal axis of the pier, a space frame supporting the span in a vertically spatial relation above the pier comprising, a first pair of diagonally-extending rigid support members, both lying within one inclined plane and connected at their upper ends to a substantially common point of a side member on one side of the span and at their lower ends to spaced-apart points on the top of the pier which have a veitical plane intersecting the longitudinal axis of the span, a second pair of diagonally-extending rigid support members, both lying within a second inclined plane and connected at their upper ends to a substantially common point of a second side member on the other side of the span and at their lower ends to spaced-apart points on the top of the pier which have a vertical plane intersecting the longitudinal axis of the span, and a transversely-disposed tie member connecting end portions of the side members.

4. A supporting frame as defined in claim 3 wherein said first and second pair of diagonally-extending rigid support members are secured at their lower ends to common spaced-apart points which are adjacent the longitudinal ends of the pier.

5. A supporting frame as defined in claim 3 wherein said upper connections and said spaced-apart points are freely pivotable connection joints.

6. A supporting frame as defined in claim 3 wherein, a tension tie member is secured to the top of the supporting pier, and said spaced-apart points are attached to the longitudinal ends of said tie member.

7. In a bridge construction having side members of approximately equal length which terminate in transversely opposed ends to be supported by a pier positioned skew to the trusses, a space supporting frame supporting said side members comprising, a tension member secured to the top of the pier and extending longitudinally thereof, a transversely-extending tie member connecting the side members and disposed over said pier, a first pair of supporting members connected at their lower ends to one end of said tension member, one of said supporting members being connected at its upper end to one end of one of the side members, the other of said supporting members being connected at its upper end to a transversely-opposed end of the other of the side members; and a second pair of supporting members connected at their lower ends to the other end of said tension member, and one of said second supporting members being connected at its upper end to said one end of the one side member, and the other of said second supporting members being connected at its upper end to said transversely opposed end of the other side member.

8. In a bridge construction as defined in claim 7, a pair of diagonally-inclined compression members are connected to a common point within a center portion of the pier and extend diagonally upwardly in opposed directions and connected to the side members.

9. In a bridge construction as defined in claim 7, a pair of brace members are connected at one end to the pier and at their opposite end each to one of the side members at points spaced-apart from the ends thereof.

10. A supporting frame for structurally supporting a bridge extending diagonally of the longitudinal extent of its central supporting pier, the bridge having left and right side trusses of about equal longitudinal length terminating in evenly opposed ends which comprises, a tie member connecting the ends of the trusses together and disposed over said pier, a tension member secured to the central pier and extending longitudinally thereof, a downwardly-diagonally-extending strut connected between one end of the right side truss and one end of said tension member, a second downwardly-diagonally-extending strut connected between said one end of the right side truss and the other end of said tension member, a third downwardly-diagonally-extending strut connected between the opposed end of the left side truss and said one end of said tension member, and a fourth downwardly-diagonally-extending strut connected between said opposed end of the left side truss and said other end of said tension member.

11. A supporting frame as defined in claim wherein said struts are connected to said trusses and said tension member with pivot joints.

12. A support frame as defined in claim 10 wherein, a first downwardly-diagonally-extending compression member is connected between the right side truss and a center portion of the supporting pier, and a second downwardly-diagonally-extending compression member is connected between the left side truss and a center portion of the supporting pier.

13. A supporting frame as defined in claim 10 wherein a first brace member is connected between a point on the supporting pier and the right side truss at a point remote from the ends thereof, and a second brace member is connected between a point on the supporting pier and the left side truss at a point remote from the ends thereof.

14. A space frame for supporting a bridge which lies skew to the longitudinal extent of its supporting pier wherein the bridge has left and right side members of about equal longitudinal length terminating in evenly opposed ends which comprises, a tie member connecting the ends of said members together and disposed over said pier, a downwardly-diagonally-extending strut member connected at its upper end to one end of the left side member and at its lower end to the supporting pier adjacent a longitudinal end thereof, a second downwardlydiagonally-extending strut member connected at its upper end to the evenly opposed end of the right side member and at its lower end to the supporting pier adjacent the other longitudinal end thereof, a first downwardly-diagonally-extending compression member connected at its upper end to said one end of the left side member and at its lower end to the top of the supporting pier adjacent an intermediate portion thereof, and a second downwardly-diagonally-extending compression member connected at its upper end to said opposed end of the right side member and at its lower end to the top of the supporting pier adjacent an intermediate portion thereof.

15. A space frame as defined in claim 14 wherein, a longitudinally-extending tension member is secured to the top of the pier between longitudinal ends thereof, said downwardly-diagonally-extending strut members are connected at their lower ends to opposite ends of said tension member, and said downwardly-diagonally-extending compression members are connected at their lower ends to an intermediate portion of said tension member.

16. A support frame as defined in claim 15 wherein said strut members and compression members are connected to the side members and said tension member with pivotal joints.

17. A support frame as defined in claim 14 wherein, a first brace member is connected at its upper end to the left side member at a point remote from said one end thereof and is connected at its other end to the supporting pier, and a second brace member is connected at its upper end to the right side member at a point remote from said opposed end and is connected at its lower end to the supporting pier.

18. A support frame as defined in claim 14 wherein said downwardly-diagonally-extending strut member connected at its upper end to one end of the left side member is connected at its lower end to the supporting pier adjacent a corresponding left end thereof, and said second downwardly-diagonally-extending strut member connected at its upper end to the evenly opposed end of the right side member is connected at its lower end to the supporting pier adjacent a corresponding right end thereof.

References Cited in the file of this patent UNITED STATES PATENTS Re. 18,973 Wichert Oct. 24, 1933 89,948 Smith May 11, 1869 499,631 Hawes June 13, 1893 OTHER REFERENCES Elementary Structural Analysis, Wilbur and Norris, McGraw-Hill Book Co., Inc., 1948, page 201.