US3794433A

US3794433A - Segmental precast concrete post-tensioned overpass bridges with cantilevered abutment

Info

Publication number: US3794433A
Application number: US00160707A
Authority: US
Inventors: M Schupack
Original assignee: SCHUPACK ASS
Current assignee: SCHUPACK ASS
Priority date: 1971-07-08
Filing date: 1971-07-08
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26
Also published as: ES404518A1; DE2233518A1; FR2145335A5; GB1398435A; IT960941B; CA996708A

Abstract

A bridge structure particularly adapted for construction in skewed orientation with respect to a lower, overpassed roadway comprises a bridge portion, end abutments, and an intermediate support column. The bridge portion is constructed by supporting a plurality of precast concrete open-topped box-beams and precast L-shaped parapet-sidewalk members on temporary falsework at the bridge site. Upstanding from the precast box beams are wooden flanges which are trimmed in place to provide temporary supports of desired heights for precast slabs forming a bed for the upper roadway. The variable-height supports are used to form a crown in the roadbed, or to form an inclined roadbed which may be part of a banked curve. The precast box-beams are joined together by formed-in-place concrete diaphragms which are poured simultaneously with a concrete roadbed, whereby a monolithic squared off bridge portion is formed. An intermediate support column engages one of the diaphragms, thereby eliminating an exposed transverse support beam. The bridge portion is post tensioned by means of longitudinal and transverse post tensioned tendons. The squared-off bridge portion extends between two abutments, and any skew angle between the upper and lower roadways is accommodated in the abutments by a diagonal rake or relief ''''chamfer'''' of the abutment corner closest to the roadway. The far side of the squared off end of the bridge portion engages the top of the unraked portion of the abutment wall at an expansion joint, and is supported thereon; the remainder of the end of the squared off bridge portion being supported in cantilever manner, projecting beyond the diagonally raked corner of the abutment. The diagonally raked portion of the base wall of the abutment is substantially parallel to the lower roadway, thereby providing adequate horizontal clearance therefrom. The top of the abutment provides the approach roadway for the bridge. The top of the abutment is supported on and integral with the base walls of the abutment, with a portion cantilevered outward beyond the raked portion of the base wall to meet the squared off bridge portion.

Description

United States Patent [191 Schupack SEGMENTAL PRECAST CONCRETE POST-TENSIONED OVERPASS BRIDGES WITH CANTILEVERED ABUTMENT Morris Schupack, c/o Schupack Associates, 2701 Summer St., South Norwalk, Conn. 06905 [22] Filed: July 8, 1971 [21] Appl. No.: 160,707

[76] Inventor:

[58] Field of Search 52/128, 174, 365, 79, 323, 52/227, 731, 223 R, 87, 335, 338; 14/17, 73, 75; 249/1; 94/1 A [56] References Cited UNITED STATES PATENTS 3,566,557 3/1971 Comolli 52/335 X 2,602,321 7/1952 Blair 14/75 X 3,367,074 2/1968 Vamich 52/174 X 3,570,207 3/1971 Launary.... 52/227 X 2,686,421 8/1954 Barron... 52/174 X 3,022,759 2/1962 McCall 52/223 R X 3,300,921 1/1967 Middendorf 52/227 3,253,288 5/1966 Nagin 14/73 3,295,276 l/l967 Rene 52/223 R X 3,555,753 1/1971 Magadini 52/227 3,302,348 2/1967 Pratt 52/223 R 731,595 6/1903 Mueser 52/174 FOREIGN PATENTS OR APPLICATIONS 1,279,303 4/1968 Germany 52/227 29,140 l/l909 Sweden 14/75 428,826 5/1967 Switzerland 14/16 OTHER PUBLICATIONS Engineering News Record, Box Members Distinguish Concrete Bridge, page 86, June 27, 1946 Primary Examiner-Henry C. Sutherland Assistant ExaminerCarl D. Friedman Attorney, Agent, or FirmMattern, Ware and Davis [57] ABSTRACT A bridge structure particularly adapted for construc- 1 Feb. 26, 1974 tion in skewed orientation with respect to a lower, overpassed roadway comprises a bridge portion, end abutments, and an intermediate support column. The bridge portion is constructed by supporting a plurality of precast concrete open-topped box-beams and precast L-shaped parapet-sidewalk members on temporary falsework at the bridge site. Upstanding from the precast box beams are wooden flanges which are trimmed in place to provide temporary supports of desired heights for precast slabs forming a bed for the upper roadway. The variable-height supports are used to form a crown in the roadbed, or to form an inclined roadbed which may be part of a banked curve. The precast box-beams are joined together by formed-inplace concrete diaphragms which are poured simultaneously with a concrete roadbed, whereby a monolithic squared off bridge portion is formed. An intermediate support column engages one of the diaphragms, thereby eliminating an exposed transverse support beam. The bridge portion is post tensioned by means of longitudinal and transverse post tensioned tendons.

The squared-off bridge portion extends between two abutments, and any skew angle between the upper and lower roadways is accommodated in the abutments by a diagonal rake or relief chamfer of the abutment corner closest to the roadway. The far side of the squared off end of the bridge portion engages the top of the unraked portion of the abutment wall at an expansion joint, and is supported thereon; the remainder of the end of the squared off bridge portion being supported in cantilever manner, projecting beyond the diagonally raked corner of the abutment. The diagonally raked portion of the base wall of the abutment is substantially parallel to the lower roadway, thereby providing adequate horizontal clearance therefrom. The top of the abutment provides the approach roadway for the bridge. The top of the abutment is supported on and integral with the base walls of the abutment, with a portion cantilevered outward beyond the raked portion of the base wall to meet the squared off bridge portion.

4 Claims, 12 Drawing Figures PAIENIEnrmemm' SHEETIBFY MATTERN WARE AND DAVlS v ATTORNEYS mdE SnEEI s or 7 Pmmmmzsmm FIG. ll

PAIENIEUrmzsmu I sum 7 or 7 SEGMENTAL PRECAST CONCRETE POST-TENSIONED OVERPASS BRIDGES WITH CANTILEVERED ABUTMENT SUMMARY OF THE INVENTION This invention relates to bridge structures, and more particularly to overpass bridge structures fabricated of modular members, said bridge structure also being easily oriented at any desired skew angle with respect to a lower, overpassed roadway.

BACKGROUND OF THE INVENTION The massive limited-access interstate highway program has necessitated the construction of thousands of overpass bridges, and many more thousands will be built in the near future. Generally, these bridges have been constructed by one of two methods. Both methods involve a substantial amount of custom designing and fabrication for each bridge, taking into account such factors as the skew angle of the upper roadway relative to the lower roadway, the length of the span, horizontal and vertical curves in the upper roadway, and the super-elevation transition to be accommodated by the bridge.

The first general method of constructing such a bridge comprises forming an abutment at each end of the bridge span, and constructing the bridge span of large steel beams supported at intermediate points by exposed transverse beams and associated columns. A bridge deck is then fabricated on the steel beams. If the bridge is skewed with respect to the lower roadway, a correspondingly skewed expansion joint is necessary at the ends of the bridge. A bridge of this type is expensive to fabricate, consumes a long construction time at the site, and requires regular maintenance.

The second general mehod of constructing overpass bridges comprises forming the bridge of cast-in-place concrete. This method requires on site construction of elaborate custom forms, which are generally used only once. The forms are custom-designed to provide for horizontal and vertical curves in the bridge deck, and the like. It appears at this time that the price of cast-inplace concrete has risen dramatically in the past several years because of the price of such form work. This method also requires extended on-site construction time with associated disruption of normal traffic flow.

It was therefore desirable that a unified scheme for constructing a plurality of overpass bridges be achieved. This was particularly important as several bridges located in one general area are often constructed by a single builder. It was recognized that the use of standardized uniform precast materials could result in substantial cost reductions and short construction times for such bridges.

OBJECTS OF THE INVENTION Accordingly it is a principal object of the present invention to provide a unified scheme for constructing bridges.

It is another object of the invention to provide a unitied scheme incorporating precast, modular members for constructing bridges.

It is an additional object of the invention to provide a unified scheme for economically constructing overpass bridges in skewed orientation with respect to a lower overpassed roadway.

It is a further object of the invention to provide an overpass bridge in skewed orientation with the lower overpassed roadway wherein the bridge abutment supports the squared off end of the bridge span and also provides adequate horizontal clearance from the lower overpassed roadway.

It is yet another object of the invention to provide an overpass bridge in skewed orientation with the lower roadway wherein the expansion joint for the bridge is not skewed, but extends transversely, perpendicular to the upper roadway.

A still further object of the invention is to provide a unified scheme for constructing overpass bridges wherein variations in the configuration of the bridge deck of a particular bridge are readily accommodated.

An additional object of the invention is to provide for constructing bridges with uniform minimum bridge deck thickness.

It is another object of the invention to provide an overpass bridge partially supported by an intermediate pier wherein no exposed transverse support beam is necessary.

It is yet another object of the invention to provide an attractive and safe overpass bridge.

It is an additional object of the invention to reduce the cost and construction time of overpass bridges.

Other and more specific objects will be apparent from the features, elements, combinations and operating procedures disclosed in the following detailed description and shown in the drawings.

THE DRAWINGS FIG. 1 is a fragmentary perspective view of an overpass bridge according to the invention, viewed from below;

FIG. 2 is a top perspective view of a precast opentopped box-beam used in constructing the bridge of FIG. 1;

FIG. 3 is a top perspective view of a precast slab used in constructing the bridge of FIG. 1;

FIG. 4 is a top perspective view of a precast sidewalkparapet member used in constructing the bridge of FIG. 1;

FIG. 5 is a top exploded perspective view of the abutment of the overpass bridge of FIG. 1;

FIG. 6 is a side elevation view of the overpass bridge of FIG. 1; partially constructed;

FIG. 7 is a top plan view, partially cut away of the overpass bridge of FIG. 1;

FIG. 7A is a top plan view of the skewed expansion joint of a prior art overpass bridge;

FIG. 8 is a cross-sectional view of the over-pass bridge of FIG. 1 taken along the line 88 of FIG. 7;

FIG. 9 is a fragmentary cross-sectional view partially broken away of the overpass bridge of FIG. 1 taken along the line 99 of FIG. 7;

FIG. 10 is an enlarged fragmentary view of the crosssection of the overpass bridge shown in FIG. 8; and,

FIG. 11 is a longitudinal, elevation sectional view, partially broken, of the overpass bridge taken along the line 11-11 of FIG. 7.

The same reference characters refer to the same elements throughout the several views of the drawings.

GENERAL DESCRIPTION The unified scheme for constructing overpass bridges according to this invention includes a squared-off elongated-rectangular monolithic bridge span constructed primarily of modular precast rectangular members. The basic precast modular members comprise precast open-topped box-beams incorporating longitudinal hollow tubes for receiving tensioning tendons; precast slabs for forming the top of the boxbeams and for spanning the spaces between spacedapart rows of box-beams to form the bottom portion of the bridge deck and to supply the positive reinforcing steel therefore, and precast L-shaped sidewalk-parapet members. All of the precast modular members include steel reinforcing rods, portions of which protrude for appropriate engagement linking the members.

The open-topped box-beams and sidewalk-parapet members are supported on temporary falsework at the bridge site. Temporary bridge slab form supports com prising wooden boards protruding upward from the box-beams are cut to proper elevation to support the precast slabs at accurate heights to assure the desired configuration of the bridge deck. Forms are placed to define transverse intermediate and end diaphragms joining the box beams, and the forms also include provisions for an intermediate support pier engaging one of the intermediate diaphragms in long continuous span bridges. Concrete is placed in situ to form the bridge deck and the diaphragms, linking the precast members into a monolithic bridge span. The bridge span is posttensioned by transverse and longitudinal tendon cables to supply the primary support.

The unified scheme also includes attention to abutments for accommodating the squared-off bridge span in bridges having a skewed orientation with respect to the lower roadway. The abutments comprise vertical walls and an integral cap. A first portion of the vertical abutment wall positioned transverse to the upper roadway engagingly supports over one-half of one end of the bridge span, and the remainder of the end of the bridge span protrudes outwardly being supported in cantilevered manner. A second portion of the vertical wall of the abutment is diagonally raked at an angle to the first portion, wherein the second portion is substantially parallel to the lower roadway to provide adequate horizontal clearance therefrom. The top of the abutment forms the approach to the bridge, and a portion of the top is cantilevered outward over the diagonally raked portion of the vertical abutment wall to meet the remainder of the squared-off end of the bridge span. An expansion joint is provided along the squared off end of the bridge span, whereby the expansion joint is as short and consequently as economical as possible.

SPECIFIC DESCRIPTION Referring now to FIG. 1, there is shown in perspective a portion of an overpass bridge according to the invention. The bridge overpasses a divided lower highway, and the bridge is skewed with respect to that lower highway. The bridge 10 generally comprises a bridge span 12 and an abutment 14.

The bridge span 12 is constructed primarily of precast modular members. These members include three rows of open-topped box-beams 20, precast slabs 22 which cover the open tops of the box-beams and span the distance between adjacent rows of box-beams, and L-shaped sidewalk-parapet members 24. The bridge span further comprises intermediate diaphragms 26 and heavier end diaphragms 28 joining the precast modular members into a unitary, squared-off bridge span.

The abutment 14 is custom-designed to adapt the squared-off bridge span 12 to various orientations skewed with respect to the lower, overpassed highway by means of a diagonal rake of the abutment corner closest to the lower roadway. The abutment l4 accordingly comprises a first unraked portion 30 of its vertical base wall, portion 30 being positioned transverse to the upper roadway and engagingly supporting more than one-half of the length of end diaphragm 28 and the associated bridge span 12. Expansion bearings 74 permits movement between the bridge span 12 and the abutment wall 30 to accommodate expansion and contraction of the bridge span caused by temperature changes. The remaining portion of end diaphragm 28 protrudes outward toward the overpassed roadway and is supported in a cantilevered manner. A second portion 32 of the vertical abutment wall is diagonally raked away from end diaphragm 28, and is preferably substantially parallel to the skewed lower roadway, providing ample horizontal clearance therefrom (See FIG. 7). The remaining

portions

31 and 33 of the vertical abutment wall extend parallel to the upper roadway to form the sides of the abutment.

An abutment top slab 34 with a cantilevered portion 36 forms the approach to the bridge. The triangular cantilevered portion 36 of the top slab extends outward beyond the diagonally raked portion 32 of the vertical abutment wall to meet the squared-off bridge span and complete the upper roadway. The abutment further comprises sidewalk-parapet members 38 cantilevered outward from the abutment cap 34. An expansion space 40 adjacent to expansion bearings 74 remains between the bridge span 12 and the abutment cap 34 to accommodate dimensional changes due to temperature variation. (See also FIG. 11).

PRECAST MEMBERS One of the precast open-topped box-beams 20 is shown isolated from the bridge span in FIG. 2. It comprises a bottom plate 42, end webs 44, and side webs 46. Wooden boards 48 upstanding from the top of the box-beam 20 by a distance of several inches to one foot, along the inside of end webs 44 and flanking each of the side webs 46. The wooden boards 48 are secured to the box beams by bolts 47, and flanges of greater height can be easily substituted if necessary for the particular application. These flanges are cut to desired heights at the construction site, using a portable power saw for example, adapting them to support the precast slabs 22 in positions and altitudes corresponding to the desired configuration of the bridge deck surface.

The box-beam 20 further includes steel reinforcing rods for added strength. The steel reinforcing rods preferably protrude from the box-beam for engagement with adjacent steel reinforcing rods protruding from the other precast members, and for engaging with the cast in situ concrete intermediate and end

diaphragms

26 and 28. The steel reinforcing rod stirrups 52 preferably terminate in loops protruding along the tops of end webs 44 and side webs 46, and preferably terminate in longitudinal protrusions 54 from the ends of box-beam The box-beam 20 also has formed therein several elongated longitudinal tubes 56 for receiving longitudinal post tensioning tendon cables. The positioning of these tendon tubes may be varied in the plurality of box-beams, so that the openings at the end of each boxbeam are aligned with the openings in the end of the adjacent box-beam to form generally sinusoidal conduits extending the entire length of the bridge span 12, the conduits in elevation resembling the catenary sag of suspension bridge cables, with high points at the ends of the bridge span and at the intermediate support columns, and with low points strengthening the lower fibers of the bridge for tension loading at the centers of the unsupported portion of the span. This configuration of post tensioning cables is well known in the art. However, this well known method of positioning post tensioning tendons has the disadvantage of necessitating the non-uniform positioning of tubes in each box-beam such that the overall assembly comprises sinusoidal tubes. In addition to the individual specialized placement of the tube form in each precast member, it is required that each member be preplanned for its particular position in the bridge span, labeled to indicate that position, and placed in that position at the bridge site.

The disadvantages noted above are overcome in bridges constructed of precast segments as disclosed herein by utilizing a new configuration for the post tensioning tendon cables. Referring now to FIG. 6, in this configuration the cables are also high at the end abutments and at the intermediate support columns, and low adjacent to the centers of the unsupported portion of the span. However, the transition between the high and low portions of the tendon occurs entirely in the box-beams a and 20c positioned adjacent to the abutments and adjacent to the center support column 84. The tendon tubes now run in a straight line along the lower edge of the remaining box-beams 208. Thus only three different types of box-beams are required. Box-beams 20a have tubes in parabolic transition between the low tendon position and a high, tendon anchorage position. Box-beams 20c have a generally half sine wave tube configuration providing transition upward from the low tendon position and to a high tendon position, and providing a smooth transition across central diaphragm 26a. Both box-

beams

20a and 200 are reversible. This tube configuration greatly simplifies the procedure in precasting the box-beams, and also greatly simplifies organization of the boxbeams at the bridge site.

In addition to the great ease of construction achieved by this configuration of the tendon cables, it has also been found that this configuration gives greater structural strength than the well-known sinusoidal configuration.

The open-topped box-beams 20, including the upstanding wooden boards 48, the internal reinforcing steel, and the longitudinal tubes 56, may be readily and inexpensively fabricated in a concrete yard, and transported to the bridge site on trucks. An elongated U- shaped steel form may be used to form the outside of the precast box-beams with a smooth, even finished appearance. Movable end plates within the U-shaped steel form permit easy adjustment for forming boxbeams of various lengths, and a 'wooden or steel form may be positioned in the form to form the hollowed-out center portion of the box-beams. The tension cable tubes and steel are then placed, and subsequently the concrete forming the box-beams is placed in the form. Different web heights are achieved by using adjustable height inside forms to permit filling the forms to a desired level. Casting of the box-beams can also be easily accomplished at the bridge site if so desired, and size limitations caused by trucking capabilities are thereby avoided.

Referring now to FIG. 3, there is shown a precast slab 22 used in constructing the bridge span 12. The slab 22 has internal reinforcing steel rods serving as the positive bridge deck reinforcing steel, which protrude as shown at 58 for engaging with the reinforcing steel of the box-beam 20 and for engaging with concrete subsequently placed over and around the slabs. The slab 22 is generally rectangular, having dimensions such that it can be positioned with its peripheral edges resting on the inboard wooden boards 48 upstanding from the box-beam 20, and wherein steel reinforcing rods 58 protruding from the edge of the precast slab engage the loops of stirrups 52 upstanding from the webs of boxbeam 20. Slabs 22 having longitudinal dimensions of over 20 feet are somewhat flexible, and readily conform to the cut edges of the wooden boards even if they do not lie precisely in the same plane. Precast slab 22 may have a slight crown, as indicated at 60, whereby the slab is strengthened in its central, unsupported portions. A plurality of slabs 22 are used in constructing the bridge span 12, some of which cover the tops of box-beams 20, and some of which span the distance between the three rows of box-beams as can be seen in FIGS. 1, 7 and 8, thereby comprising the bottom portion of the bridge deck.

Using a precast slab containing positive reinforcing steel as the lower portion of the bridge deck greatly reduces the possibility of the bridge deck surface cracking. When the lower positive reinforcing steel and the upper negative reinforcing steel are placed and the entire bridge deck formed in situ, there has been a tendency for pockets to develop along the underside of the negative reinforcing steel. These pockets develop because of settlement of the materials in the concrete mix away from the lower side of the negative reinforcing steel. When the bridge is in use, very fine cracks develop extending downward from the bridge deck surface to the negative reinforcing steel. Water and road salt seeping down the cracks collect in the pockets under the negative steel, and freezing of the water can cause the bridge deck surface to become pitted and extensively cracked, requiring expensive repairs.

By forming the lower portion of the bridge deck of precast slabs, a much thinner portion of the bridge deck remains to be cast-in-place. The settlement problem is minimized in a thinner cast-in-place portion, and consequently pockets below the negative reinforcing steel do not form. Without these pockets, the bridge deck is far less susceptible to pitting and cracking. The result is a higher quality bridge deck requiring minimum maintenance.

The third precast member utilized in constructing the bridge span 12 is the L-shaped sidewalk-parapet member 24, shown isolated from the bridge span in FIG. 4. The sidewalk-parapet member preferably has a longitudinal dimension approximately equal to that of boxbeam 20. The sidewalk portion 62 is relatively thin, wherein utility conduits 86 (See FIG. 10) for telephone and electric lines and the like may be positioned thereon. As described below, additional later-placed concrete 87 is cast over the sidewalk portion 62, encasing the utility conduits and further strengthening and anchoring the sidewalk-parapet 24 firmly in its cantilevered position. The parapet, or guardrail portion 64 has the thickness desired for the final bridge structure.

The L-shaped sidewalk-parapet member 24 further comprises steel reinforcing rods, portions of which protrude for engagement with adjacent steel reinforcing rods and the later placed concrete. The steel reinforcing rods include longitudinal reinforcing rods which do not protrude, and transverse reinforcing rods protruding at 68. The steel reinforcing rods also comprise L- shaped protrusions 70, which are anchored in the parapet portion 64, and which are later enclosed in the concrete 87 placed over the sidewalk portion 62 to aid in securing the sidewalk parapet member into the bridge span in cantilevered manner. FIG. 10 shows a typical internal configuration of the steel reinforcing rods.

All of the above described members are preferably precast in a concrete yard, and transported to the bridge site on heavy equipment. Cranes, trucks and other equipment capable of handling precast members weighing up to 60 tons are readily available. Box-beams and sidewalk parapet member 24 having lengths of 40 to 50 feet are'within this 60 ton limit.

ABUTMENT WALLS The first step in constructing the bridge is to construct transverse portion 30 of the vertical abutment walls. The remaining portions of the vertical abutment walls may also be constructed at this time; however, construction of the abutment cap may be deferred to provide clearance for jacks used in post-tensioning until the bridge span is completed. Referring now to FIG. 5, a perspective view of the vertical abutment walls is shown. They comprise the transverse portion 30 which is relatively thick for engagingly supporting the transverse end diaphragm 28 of the bridge span 12. The second diagonally raked portion 32 of the vertical abutment wall is disposed at an angle to the first portion 30, portion 32 being substantially parallel to the lower divided highway 72. A large clearance width W is thereby provided between the vertical abutment wall and first roadway 72a of the divided highway 72. (See FIG. 7). Such horizontal clearance would not be provided if transverse portion 30 of the vertical abutment wall were extended to the full width of the abutment. The vertical abutment walls further comprise rearward extending

walls

31 and 33.

Similar vertical abutment walls are constructed for the other end of bridge span 12, the second abutment being appropriately reversed as can be seen in FIG. 7, to provide adequate horizontal clearance W from the second roadway 72b comprising the lower divided highway.

The expansion bearings 74 are positioned on the top of transverse portion 30 of the vertical abutment wall. Referring now to FIG. 11, the expansion bearing 74 comprises a lower steel plate 76 engaged with the top of transverse portion 30 of the vertical abutment wall. The expansion bearing 74 further comprises an upper steel plate 78, and an elastomer material 80 which may be compressed rubber, positioned between the two steel plates permitting sliding movement therebetween. Such expansion bearings are commercially available and are well known in the art.

CONSTRUCTION OF THE BRIDGE SPAN In the embodiment of the bridge disclosed herein, the span comprises three parallel, spaced-apart rows of box-beams 20, each row comprising eight box-beams having their adjacent end faces aligned and spaced apart to accommodate intermediate diaphragms. Wider spans can be constructed using additional rows of box-beams, and narrower spans may comprise as few as one row of box-beams.

Upon completion of the vertical abutment walls and installation of the expansion bearings as described above, construction of the bridge span 12 is begun by supporting the box beams 20 in the three rows on temporary falsework 82. (See FIG. 6). The temporary falsework comprises wooden or steel pier structures and each can be used to support the adjacent ends of two box-beams and the forms for the diaphragms. Two temporary falsework piers are provided flanking the location of the center support pier 84, wherein clearance for forming this pier is provided.

It is very important that the thickness of the bridge deck be uniform, as any unnecessarily thick portions can result in substantial amounts of extra weight. Therefore, crown or twist variations in the configuration of the bridge deck are primarily accommodated in positioning the box-beams. Referring now to FIG. 8, the bridge deck shown has a crown for the purposes of drainage. The central row of box-beams is elevated on the temporary falsework with respect to the outside rows by a distance approximating the desired crown. If it were desired to form a banked bridge deck, one of the outside rows of box-beams would be supported at a greater relative height.

Referring now to FIGS. 8 and 10, the

wooden boards

48a and 48L along the outside edge of bridge span 12 are cut to the height desired for engaging and supporting lower peripheral edges of sidewalk-parapet members 24. The sidewalk-parapet members are then temporarily supported in the cantilevered manner shown by additional temporary falsework, not shown, extending upward from falsework 82.

The next step in constructing the bridge span 12 comprises positioning the precast slabs 22 to form the bottom portion of the bridge roadbed. This is accomplished by first cutting the wooden boards 48b-k upstanding from the box-beams to desired heights for engagingly supporting the peripheral edges of the slabs 22. The height or grade to which the boards 48b-k are cut is also determined by the desired configuration of the bridge deck, and by the necessity of maintaining a uniform bridge deck thickness. In the crowned bridge deck shown, board 48c is cut at a slightly greater height than board 48b to tilt precast slab 22a in accordance with the crown, thereby providing fine adjustment of the bridge deck thickness.

As mentioned above, precast slabs having longitudinal dimensions of 20 feet or more are somewhat flexible, and therefore the wooden boards may be cut to define complex surfaces having more than one radius of curvature, and the precast slabs position on the boards will conform thereto. The wooden flanges 48 also compensate for minor irregularities in the positioning of the box-beams 20. This is accomplished by cutting the flanges in accordance with measurements obtained by means of a level or other surveying equipment, rather than measuring upward from the precast box-beam.

Vertical curves in the bridge deck are accommodated in a similar manner. The precast box-beams are raised near the high point of the curve, and the wooden boards are cut to support the precast slabs in positions accurately defining the vertical curve.

The precast slabs can be eliminated from the bridge structure, and the bridge deck cast entirely in situ. The wooden boards 48 are also useful when this method of construction is chosen. The wooden boards are cut to the proper heights defining the bottom of the bridge deck, and metal joist hangers are then attached to the boards to support joists on which plywood form boards are supported covering the tops of the box-beams and spanning the space between the rows of box-beams. The reinforcing steel and the concrete for the bridge deck are then placed. After the concrete has hardened, the joists, joist hangers, form boards, and temporary wooden boards 48 are removed where visible to present an uncluttered, attractive underside of the bridge span. Utilizing the wooden boards to temporarily support such forms is much simpler than prior art methods of supporting such forms.

In the bridge disclosed herein five rows of precast slabs are positioned on the box-beams. Referring now to FIG. 7, the first row of precast slabs 22a covers the top of the first row of box-beams, the second row of precast slabs 22b spans the open space between the first and second row of open topped box-beams, the third row of precast slabs 22c covers the tops of the central row of box-beams, and the like.

As described above, the precast box-beams are supported on temporary falsework 82 with a space remaining between their facing end webs 44. This space accommodates any minor variations in the length of the precast box-beams, and also accommodates the protruding steel reinforcing rods 54. The sidewalk-parapet members 24 are approximately the same length as the box-beams 20, and an open space 66 remains between adjoining sidewalk-parapet members when they are positioned on the temporary falsework.

The next step in constructing the bridge is to place forms for the end diaphragms 28, the intermediate diaphragms 26, and for the central support pier 84. The forms for the intermediate diaphragms 26 primarily bridge the space between the positioned box-beams, and the forms for the end diaphragms 28 are merely a box enclosure partially supported on abutment wall 30 and partially supported by falsework. The space .66 between the sidewalk-parapet members is left open. Consequently, these diaphragm forms are relatively simple, and represent a small amount of labor and time.

The form for the central pier 84 is merely a vertical tube or elongated box upstanding from a footing 83, and opening into the form for the central intermediate diaphragm 26a, which is preferably somewhat wider than the other intermediate diaphragms.

The upstanding wooden boards 48 supporting the slabs 22 also act as haunch forms, preventing any concrete poured on the slabs from filling the box-beams or escaping through the bottom of the bridge span.

Utility conduits 86 are placed above the sidewalk portion 62 of the sidewalk parapet member 24, as is best seen in FIG. 10. The conduits 56 are joined and secured between adjacent box-beams to avoid infiltration of concrete and provide a complete through conduit for the longitudinal post tensioning tendons. Additional steel reinforcing rods may be placed above the precast slabs. Granite sidewalk curbs 88 may be positioned if desired, as can also be seen in FIG. 10, or forms for sidewalk curbs may be placed. Conduits with tendons 45 for transverse post tensioning are placed at the central intermediate diaphragms 26a, and end diaphragms 28, as can be seen in FIG. 9.

After the elements described above have been positioned in the bridge span l2, concrete is placed to form the support pier 84, the intermediate diaphragms 26, the end diaphragms 28, a roadbed surface 89, and the sidewalk 87. The concrete flows under the edges of the precast slabs up to the wooden boards to provide permanent support of the bridge deck, the wooden boards thereby acting as haunch forms. The concrete links all of the precast members and other elements of the bridge span into a single, unitary, monolithic structure.

When the concrete has hardened, the longitudinal tensioning cables 55 are pulled through conduits 56. Hydraulic jacks are used to tension the tendons, and the tendons are held in tensioned condition by anchorages 97 which are then preferably grouted (See FIG. 11). Referring now to FIG. 9, anchorages 47 holding transverse tendons 45 in tension condition are shown at the central diaphragm 26a, the transverse tensioning tendons for the end diaphragms 28 being similar. The order of tensioning these cables is determined for each particular bridge.

The bridge span 12 may be given an attractive finished appearance by adding raised concrete portions 17 at the ends of the intermediate diaphragms 26, as can be seen in FIG. 1, and a screen fence 19 or rail may be provided above the parapet portion 64 of the sidewalk parapet member 24, as can be seen in FIG. 6. The exposed wooden boards may also be removed, as the temporary support they provided is no longer necessary.

ABUTMENT CAP The abutment cap 34 is now formed above the vertical base walls of the abutment. Referring now to FIG. 5, the space 37 surrounded by the vertical abutment walls is filled with suitable fill material, and forms for the abutment cap 34 are placed. The cap 34 is shown exploded upward in FIG. 5, but is actually formed directly on top of and integral with the abutment walls. Appropriate steel reinforcing rods are laid in the form, and appropriate extra steel reinforcement 92 is placed in the area of the triangular cantilevered portion 36. The amount and positioning of the reinforcing steel in the abutment cap is chosen to tune the cantilevered portion of the cap with the cantilevered portion of the end of the bridge span. These two portions are tuned if they remain aligned with each other throughout varying load and temperature conditions. This is necessary in order that a bump does not exist at the transition between the abutment cap and the bridge deck. Additional sidewalk parapet members 38 are placed along the vertical abutment sidewalls 31 and 33 (See FIG. 1), additional sections of utility conduits 86 are laid along the sidewalk portions, and curb members are placed. Concrete is then placed in the forms to comprise the abutment cap; including the cantilevered triangular portion 36 thereof, and the sidewalks lying therealong.

Referring now to FIG. 11, an expansion space 40 is left between the end diaphragm 28 and the abutment cap 34, this space accommodating expansion .of the bridge span 12. A suitable expansion joint 92 is placed to span the gap 40 and provide a smooth transition between the abutment cap and the bridge span 12. A final road upper surface 95 of asphalt may be laid on the surface of the bridge span and on the abutment cap.

The expansion joint 92 is an expensive portion of the bridge, often costing more than a hundred dollars per linear foot. Referring now to FIG. 7, in the bridge disclosed herein the expansion joint 92 of length Ljoining the squared off end of the bridge span and the abutment is transverse to the bridge span, and consequently as short as possible. In prior art bridges wherein the end of the bridge span is skewed and mates with a correspondingly skewed abutment, as is shown in FIG. 7A, a much longer expansion joint 92A of Length L is required. The substantial savings achieved in the short expansion joint of the bridge disclosed more than offsets the expense of cantilevering a portion of the abutment cap.

The modular bridge span disclosed herein may also be used with substantial cost reductions in bridges which are not skewed with respect to the lower roadway. In such a bridge, the abutment wall 30 may extend the width of the bridge span, supporting the end diaphragm 28 along its entire length thereon. Thus, no cantilevered portions of either the bridge span or the abutment cap are necessary.

Substantial savings realized in constructing bridges according to the scheme disclosed herein also stem from a reduction of on-site construction time and labor costs. Bridge members which are precast generally cost less than formed-in-place concrete, primarily because of the extensive on-site formwork required in the latter method. By placing all of the positive reinforcing steel for the bridge deck in the precast-slabs, the need for specialized workers to lay such steel at the bridge site is minimized. Savings in architectural and bridge designer fees are also achieved, in that the unified scheme may be easily modified to construct bridges of varying width and length.

Bridges constructed according to this scheme also have aesthetic and safety advantages. Using a transverse support beam integral with the bridge deck, a center column is permitted which gives-the bridge a great feeling of airiness and minimizes the tunnel effect of a protruding skewed support beam. The aesthetics of a single pier column supporting a -foot wide bridge is striking, and also affords extra visibility and consequent safety. The wide box members and the large cantilevered sidewalk parapet members which shadow the outside box-beam minimizes the massiveness of the elevation view, and results in an extremely attractive appearance.

Since the foregoing description and drawings are merely illustrative, the scope of the invention has been broadly stated herein and it should be liberally interpreted to secure the benefit of all equivalents to which the invention is fairly entitled.

I claim:

1. A bridge for skewed orientation with respect to a lower overpassed roadway or the like comprising A. a rectangular bridge span having transverse ends perpendicular to its longitudinal axis and having .1. longitudinal beams longitudinally spaced supporting a bridge deck,

2. transverse diaphragms connecting longitudinally spaced pairs of said longitudinal beams 3. transverse end diaphragms supporting terminal ones of said longitudinal beams and each forming a perpendicular transverse end of said bridge span and incorporating end anchorage means for receiving post-tensioning tendons of the bridge span, accomodating tendon cable ends for convenient non-skewed post tensioning,

B. an abutment for supporting the end of the rectangular bridge span and having l. a first support wall transverse to the bridge span axis and engagingly supporting a major portion of the transverse end diaphragm of the bridgespan, said first support wall having a first end adjacent to a first bridge span corner furthest removed from the lower roadway, and a second end positioned between the longitudinal axis of the bridge span and the adjacent bridge span corner closest to the lower roadway,

C. a second wall positioned substantially parallel to the lower roadway and extending diagonally from said second end of the first support wall to a point adjacent to the outside edge of the upper roadway; and

D. a cantilevered abutment slab supported by the second wall and having a portion thereof cantilevered outward from said second wall in juxtaposed relation with the transverse end diaphragm of the bridge span extending beyond said first support wall in cantilever fashion to form an approach to the bridge span.

2. An abutment as defined in claim 1 and further comprising:

D. expansion bearings positioned between the first support wall and the transverse end diaphragm of the bridge span supported thereon permitting movement of the bridgespan relative to the abutment.

3. A bridge span as defined in claim 2 and further comprising:

B. an expansion joint joining the transverse end diaphragm of the bridge span and the abutment slab adjacent thereto, said expansion joint'thereby lying transverse to the bridge span and consequently being of minimum length.

4. An abutment as defined in claim 1 wherein the cantilevered portion of the abutment slab is provided with reinforcing steel dimensioned and positioned to provide load deformation characteristics substantially matching those of the adjacent transverse end of the bridge span, whereby theslab is designed for load deformation movement corresponding to similar movement of the cantilevered portion of the bridge span under varying load conditions.

Claims

1. A bridge for skewed orientation with respect to a lower overpassed roadway or the like comprising A. a rectangular bridge span having transverse ends perpendicular to its longitudinal axis and having 1. longitudinal beams longitudInally spaced supporting a bridge deck, 2. transverse diaphragms connecting longitudinally spaced pairs of said longitudinal beams 3. transverse end diaphragms supporting terminal ones of said longitudinal beams and each forming a perpendicular transverse end of said bridge span and incorporating end anchorage means for receiving post-tensioning tendons of the bridge span, accomodating tendon cable ends for convenient non-skewed post tensioning, B. an abutment for supporting the end of the rectangular bridge span and having 1. a first support wall transverse to the bridge span axis and engagingly supporting a major portion of the transverse end diaphragm of the bridge span, said first support wall having a first end adjacent to a first bridge span corner furthest removed from the lower roadway, and a second end positioned between the longitudinal axis of the bridge span and the adjacent bridge span corner closest to the lower roadway, C. a second wall positioned substantially parallel to the lower roadway and extending diagonally from said second end of the first support wall to a point adjacent to the outside edge of the upper roadway; and D. a cantilevered abutment slab supported by the second wall and having a portion thereof cantilevered outward from said second wall in juxtaposed relation with the transverse end diaphragm of the bridge span extending beyond said first support wall in cantilever fashion to form an approach to the bridge span.

2. transverse diaphragms connecting longitudinally spaced pairs of said longitudinal beams

2. An abutment as defined in claim 1 and further comprising: D. expansion bearings positioned between the first support wall and the transverse end diaphragm of the bridge span supported thereon permitting movement of the bridgespan relative to the abutment.

3. transverse end diaphragms supporting terminal ones of said longitudinal beams and each forming a perpendicular transverse end of said bridge span and incorporating end anchorage means for receiving post-tensioning tendons of the bridge span, accomodating tendon cable ends for convenient non-skewed post tensioning, B. an abutment for supporting the end of the rectangular bridge span and having

3. A bridge span as defined in claim 2 and further comprising: E. an expansion joint joining the transverse end diaphragm of the bridge span and the abutment slab adjacent thereto, said expansion joint thereby lying transverse to the bridge span and consequently being of minimum length.

4. An abutment as defined in claim 1 wherein the cantilevered portion of the abutment slab is provided with reinforcing steel dimensioned and positioned to provide load deformation characteristics substantially matching those of the adjacent transverse end of the bridge span, whereby the slab is designed for load deformation movement corresponding to similar movement of the cantilevered portion of the bridge span under varying load conditions.