Unbalanced bascule bridge with concrete slab roadway

An unbalanced bascule bridge having an unbalanced bridge span including a pair of longitudinal girders with a low torsional stiffness interconnected at a pivoting end by a torsionally rigid cross-girder and interconnected along a longitudinal expanse of the longitudinal girders by a steel frame which forms a closely spaced lattice for supporting a relatively thin, lightweight concrete roadway deck. The bascule bridge span is raised and lowered by an actuator assembly including a plurality of hydraulic cylinders pivotally mounted on support columns and corresponding piston rods which apply a torque to the cross-girder through crank-plates welded to the cross-girder and pivotally interconnected to a base. The cross-girder isolates the longitudinal girders from all support and reaction forces while raising and lowering the bascule bridge span.

FIELD OF THE INVENTION 
The present invention relates to an unbalanced BASCULE bridge and more 
particularly to a novel unbalanced bascule bridge span comprising 
longitudinal girders interconnected at a pivoting end by a cross-girder 
and interconnected along an expanse of the longitudinal girders by a steel 
frame for supporting a lightweight concrete roadway. The bascule bridge 
span is raised and lowered by a powerful bridge actuator that applies a 
torque to the cross girder which isolates the longitudinal girders of the 
bascule bridge span from support and reaction forces. 
BACKGROUND OF THE INVENTION 
A conventional bascule bridge interconnecting sections of a roadway or 
thoroughfare generally comprises a single-leaf bascule bridge span formed 
of torsionally rigid box-section girders, which are expensive to construct 
and maintain, and a massive counterweight disposed on a relatively short 
lever arm or rearward extension located behind a pivot point. The 
counterweight reduces torque and power requirements of a machine that 
raises and lowers the bascule bridge span about the pivot point. In 
double-leaf bascule bridges, counterweights on opposing bascule bridge 
spans also reduce forces on an anchoring devices that secure the opposing 
spans in a lowered position. A bascule bridge span having a counterweight 
requires a large volume of space or a pit below the roadway, and often 
below a water surface, to accommodate the counterweight as it swings 
downward through an arc of travel when the bridge is raised. The pit 
however represents a significant expense in the construction of a 
conventional bascule bridge. The size of the counterweight may be reduced 
by extending the length of the lever arm on which the counterweight is 
disposed but this requires an even larger pit to accommodate the increased 
arc traveled by the extended lever arm. 
In the past, conventional bascule bridges have generally comprised a steel 
grating or steel plates disposed on the bascule bridge span as a roadway 
deck because it was thought that steel was lighter in weight than concrete 
and less susceptible to stress while raising and lowering the bascule 
bridge span. Steel grating however provides a rough roadway surface that 
is particularly noisy when traversed by motorized traffic and is dangerous 
to pedestrians who may easily loose their footing on the grated surface. 
Steel grating also allows drippings from vehicles to pass through the 
roadway deck onto water or land below which has an undesirable effect on 
the environment. It has been suggested to overcome these problems by 
filling the steel gratings with concrete. This proposed solution however 
eliminates the reduced weight benefit of the grating. Moreover, corrosion 
of the confined steel causes spalling and rapid deterioration of the 
concrete. Steel plate roadway decks have the disadvantage that they 
require installation of structural stiffeners which is labor-intensive and 
costly. Steel plate roadway decks also require an additional wearing 
surface to prevent corrosion and to improve traction. The wearing surface 
however must be bonded to the steel plate to ensure integrity during 
operation of the bridge and usually requires costly fabrication to ensure 
effective traction. There exists therefore a demonstrated need for an 
advancement in the art of bascule bridge design. 
It is an object of the present invention to provide a novel bascule bridge. 
It is also an object of the present invention to provide a novel bascule 
bridge having an unbalanced bridge span which eliminates the requirement 
for a large rearward structural extension to support a counterweight and a 
pit for receiving the counterweight. 
It is another object of the present invention to provide a novel bascule 
bridge that is economical to build and operate. 
It is a further object of the present invention to provide a novel 
unbalanced bascule bridge having longitudinal girders interconnected at a 
pivoting end by a cross-girder which isolates the longitudinal girders 
from support and operating forces. 
It is yet another object of the present invention to provide a novel 
lightweight concrete roadway deck that is economical to construct, has a 
improved durability and service performance, and requires minimum 
maintenance. 
Accordingly, the present invention is directed toward a novel unbalanced 
bascule bridge having an unbalanced bridge span including a pair of 
longitudinal girders with a low torsional stiffness interconnected at a 
pivoting end by a torsionally rigid cross-girder and interconnected along 
a longitudinal expanse of the longitudinal girders by a steel frame which 
forms a closely spaced lattice for supporting a relatively thin, 
lightweight concrete roadway deck. The bascule bridge span is raised and 
lowered by an actuator assembly including a plurality of hydraulic 
cylinders pivotally mounted on support columns and corresponding piston 
rods which apply a torque to the cross-girder through a corresponding pair 
of crank plates welded to the cross-girder and pivotally interconnected to 
a base by corresponding main trunnions. When the bascule bridge span is in 
a cantilevered or raised position, all support forces including the forces 
of the main trunnions and support members act on the cross-girder through 
the crank plates and all reaction forces including the forces of the 
longitudinal girders act directly on the cross-girder. Consequently, the 
cross-girder effectively isolates the longitudinal girders from the 
support and operating forces some of which may be non-uniform due to lack 
of symmetry in the forces applied by the plurality of piston rods, 
possible bearing or trunnion misalignment and unequal weight distribution 
by absorbing the non-uniform effects thereby ensuring proper support and 
alignment of the longitudinal girders. 
These and other objects, features and advantages of the present invention 
will become apparent upon consideration of the following Detailed 
Description of the Invention with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is an elevation view of an unbalanced bascule bridge 10 of the 
present invention generally comprising a single-leaf unbalanced bascule 
span 100 interconnecting sections of a roadway or an approach span 20 
which traverse a waterway. The unbalanced bascule span 100 is pivotable at 
a pivoting end by a bridge actuator assembly 200 which raises and lowers 
the unbalanced bascule span to permit, in the exemplary embodiment, 
passage of a vessel navigating the waterway. An opposing end of the 
bascule bridge 100 may be supported by a support member 50 when the 
bascule bridge span 100 is in a lowered roadway interconnecting position. 
The invention is equally applicable to an unbalanced bascule bridge 
comprising a double-leaf unbalanced bascule span which traverses a 
waterway or other obstacle. 
FIGS. 2a and 2b are partial perspective views of the unbalanced bascule 
span 100 generally comprising two parallel longitudinal girders 110 
interconnected, by a weld, at one end by a cross-girder 120 and 
interconnected along a longitudinal expanse of the girders 110 by a steel 
frame 130 which supports a roadway deck 140. The longitudinal girders 110 
have a low torsional stiffness or strength and comprise welded steel 
plates forming a top flange 112 and a bottom flange 114 interconnected by 
a plurality of sections 116 and a plurality of transverse flanges 118 
giving the longitudinal girders 110 an I-shaped cross-section. 
Longitudinal girders with alternative geometries having comparable 
structural characteristics may be used as an equivalent. The cross-girder 
120 is torsionally and flexurally rigid steel of circular cross-section 
and comprises a central girder portion 122 and two end portions 124 
extending beyond a separation width of the longitudinal girders 110. A 
plurality of D-shaped crank plates 126 each having an upper hole 127 and a 
lower hole 128 are arranged in pairs and welded to the central and end 
girder portions 122 and 124. The steel frame 130 comprises a plurality of 
transverse floor beams 132 rigidly connected to the longitudinal girders 
110 and a plurality of longitudinal stringers 134 which extend along the 
longitudinal expanse of the longitudinal girders 110 and interconnect the 
transverse floor beams 132 to form a steel frame 130 having a closely 
spaced lattice structure. The low torsional stiffness of the longitudinal 
girders 110 make possible the rigid connection of the transverse floor 
beams 132 to the longitudinal girders 110 without risk of generating 
excessive stress in the floor beams, connections and longitudinal girder 
components. 
The roadway deck 140 comprises a steel reinforced concrete slab that is 
fastened to the transverse floor beams 132 and the longitudinal stringers 
134 of the steel frame 130 by stud shear connectors 142. The weight of the 
concrete deck 140 is minimized by using a lightweight concrete having a 
small slab thickness in combination with the closely spaced lattice 
structure steel frame 130 which forms a structurally composite unit. The 
concrete deck 140 is supported well below the top flange 112 of the 
longitudinal girders 110 by the steel frame 130 to reduce stress in the 
concrete deck 140 when the bascule bridge span 100 is raised and lowered. 
Tensile stress in the concrete deck 140 is further reduced by fastening 
the concrete deck 140 to the steel frame 130 when longitudinal girders 110 
and steel frame 130 of the bascule bridge span 100 are in a cantilevered 
or raised position whereby the concrete deck 140 is in a "neutral" 
condition when the bascule bridge span 100 is raised and the concrete deck 
140 is in a "prestressed" condition when the span 100 is lowered. The 
bascule bridge span 100 is interconnected to the roadway 20 by a trap door 
160 which is pivotally interconnected to a portion of the roadway 20 by a 
hinge 162 at a first end and further comprises a roller assembly 164 at a 
second end which may include a bevelled surface 166 that provides a smooth 
interface with the roadway deck 140. Additional structure like a 
pedestrian walkway and handrail may also be supported by the longitudinal 
girders 110 and the steel frame 130. In the alternative, the roadway deck 
140 may be configured for rail traffic by disposing rails over the steel 
frame 130 in addition to or in place of the concrete roadway deck 140. 
FIGS. 3 and 4 are partial sectional views of the unbalanced bascule bridge 
10 showing both the bascule bridge span 100 and the bascule bridge 
actuator assembly 200 mounted on a concrete base or foundation 30 which in 
the exemplary embodiment of FIG. 1 is a pier 40 comprising a base 42 
supported by a plurality of caisson foundations 44 piled or supported in 
the river bed 46. FIGS. 5a and 5b are partial sectional views of FIG. 3 
illustrating, in part, a plurality of trunnions 150 extending through the 
lower holes 128 of corresponding pairs of crank plates 126 of the bascule 
bridge span 100 to pivotally interconnect the pairs of crank plates 126 to 
a corresponding support member 152 permanently mounted on the base 30. A 
bumper block 136 may be disposed on the base 30 below end portion 119 of 
the longitudinal girders 110 to damp excessive rotation or pivoting action 
of the bridge span 100 although the bascule bridge span 100 is not 
designed to rest on the bumper blocks during operation as further 
discussed below. The actuator assembly 200 generally comprises a plurality 
of hydraulic cylinders 220 having a hydraulically actuated piston rod 224 
with a piston rod eye 226 pivotally interconnected by corresponding rod 
trunnions 232 to the upper holes 127 of a corresponding pair of crank 
plates 126. A cylinder trunnion 230 pivotally interconnects each hydraulic 
cylinder 220 to a corresponding cylinder support column 228 permanently 
mounted on the base 30 and at least one static strut 234 extends from each 
support column 228 to each support member 152. 
In operation, the unbalanced bascule bridge span 100 is raised from its 
lowered position in which the span 100 interconnects the sections of 
roadway 20 by actuating the plurality of bridge actuators 200 by 
retracting the piston rods 224 into the hydraulic cylinders 220 which 
pivots the crank plates 126 and the bascule bridge span 100 in a 
counter-clockwise direction about the main trunnions 150 and at the same 
time pivots the hydraulic cylinders 220 about the cylinder trunnions 230 
as shown in FIGS. 1 and 4. As the bascule bridge is raised, the roller 
assembly 164 moves along the bascule bridge span 100 pivoting the trap 
door 160 in a counter-clockwise direction about the hinge 162 to remove a 
portion of the roadway comprising the trap door 160 that would otherwise 
obstruct the pathway of the pivoting bascule bridge span 100 as shown in 
FIG. 4. When the bascule bridge span 100 is in a cantilevered or raised 
position, all support forces including the forces of the main trunnions 
150 and support members 152 act on the cross girder 120 through the crank 
plates 126 and all reaction forces including the forces of the 
longitudinal girders 110 act directly on the cross girder 120. 
Consequently, the cross-girder 120 effectively isolates the longitudinal 
girders 110 from the support and reaction forces some of which may be 
non-uniform due to lack of symmetry in the forces applied by the plurality 
of piston rods 224, possible bearing or trunnion misalignment and unequal 
weight distribution by absorbing the non-uniform effects thereby ensuring 
proper support and alignment of the longitudinal girders 110. The bascule 
bridge span 100 is lowered from its raised or cantilevered position by 
actuating the plurality of bridge actuators 200 to extend the piston rods 
224 from the hydraulic cylinders 220 which pivots the crank plates 126 and 
the bascule bridge span 100 in a clockwise direction about the main 
trunnions 150 and at the same time pivots the hydraulic cylinders 220 
about the cylinder trunnions 230 as shown in FIGS. 1 and 3. As the bascule 
bridge is lowered, the roller assembly 164 moves back along the bascule 
bridge span 100 pivoting the trap door 160 in the clockwise direction 
about the hinge 162 to position the trap door 160 between the roadway 20 
and the bascule bridge span 100 which maintains a continuous interface 
between the roadway and the bascule bridge span 100 as shown in FIG. 1 and 
3. 
The foregoing description will enable one of ordinary skill in the art to 
make and use the preferred embodiments of the present invention and it 
will be understood that there exists variations, modifications and 
equivalents to the embodiments disclosed herein. The present invention 
therefore is to be limited only by the scope of the appended claims.