Analysis of Different Bascule Bridge Architectures
MOOTAZ E. ABO-ELNOR
Mechanical Engineering Department
MTC, Cairo, EGYPT
Abstract: - Bascule bridges are widely used nowadays to overcome the obstruction of ships passage as crossing
waterways and in some roadways to overcome transport vehicle height limitation. A Bascule bridge is a
movable bridge with a counterweight that continuously balances a span, or "leaf", throughout its upward swing
to provide clearance for boat or ship traffic. It may be single or double leafed. Balance Beam Bascule Bridge is
one of the famous bascule bridge architecture in which bridge span counter balance weight is attached to a
balance beam in the movable bridge operating mechanism. Although hydraulic cylinders is a particularly
common solution to power majority of modern bascule bridges, it is very important to understand the
kinematics and motion of the bridge leave for optimum operation of the bridge with prober counter balance
selection. In this study a review of two operating hydraulic actuators arrangements; push arrangement and pull
arrangement is carried out based on both design aspects and safety consideration. 3D model of the study
mechanisms are constructed and a kinematics of bridge leaf (span) opening mechanisms are developed for early
stage design configuration of bridge mechanism. kinematic analyses of bridge mechanism operation in both
push and pull arrangements based on rigid body consideration is performed and Numerical analysis using finite
element method is carried out in which stress distribution over tie rods is obtained. Some failure scenarios are
introduced. Results show that tension forces acting on tie rods in pull arrangement is lower than that in push
arrangement, work done by hydraulic cylinders (Actuators) in both arrangement is nearly identical and pull
arrangement is much better than push arrangement from safety point of view.
Key-Words: - Bascule bridge, beam balanced bridge, movable bridge, Bridge mechanism, bridge balance,
failure assessment.
Received: May 18, 2021. Revised: April 19, 2022. Accepted: May 20, 2022. Published: July 19, 2022.
1 Introduction
Movable bridges or partially movable bridges are
used widely where the bridge contradict waterways
and obstruct ships passage. Three basic types of
movable bridges are generally designed and built
today –bascule bridges, swing bridges and vertical
lift bridges. Bascule bridges mainly Rotates around
the horizontal axis while swing bridges Rotates
around the vertical axis. Regardless of the type of
movable bridge selected, span weight and balance
are critical issues. In order to minimize the size and
power requirements needed to operate a movable
bridge, movable spans for vertical lift and bascule
bridges are typically counterweighted to reduce a
balanced condition. This allows drive machinery to
be sized to only overcome small intentional
imbalances, rather than the full weight of the
movable span, in addition to frictional resistances,
and wind and ice loads. Counterweights are installed
in order to minimize the size of the mechanical
power transmission system components needed to
operate the bridge, and to provide a relative measure
of safety in the event of failure in the mechanical
system. The position of this counterweight depends
on the type of Bascule bridge. There are four main
types of bascule bridge [1] are depicted in Fig.1.
Fig. 1: Types of bascule bridges [1].
A new type for mobile stayed bridges: the
piston-stayed bridge is introduced [2]. The
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engineering design innovation of the piston-stayed
bridge lies in the use of one single element, i.e. the
piston stay, for actuation as well as support of the
mobile bridge section as shown in Fig.2. At the
design stage it is proposed to apply simulation
modeling in order to determine optimum law of
drive control.
Fig. 2: Piston-stayed bridge
Dynamics of power processes of hydraulic
lifting mechanisms upon motion of a single-wing
bascule bridge based on different algorithms for
automatic control is discussed [3] showing that the
coefficients of dynamicity significantly affected by
bridge mechanism dynamics. Based on appropriate
counter balance mechanism and proper material, a
comparative study is conducted between stainless
steel and structural steel used for construction of
Bascule Bridge considering stress and strain acting
on the bridge along with the total deformation
analysis [4]. Bridge structure health monitoring
along with operational parameters control is
introduced [5] in order to maintain proper operation
of the bridge and as extend including variable
operational parameter such as wind speed and
direction during bridge span rotation for proper
control of operation mechanism. Movable
components such as hydraulic cylinders, bridge
span and span lock for double leave Bascule
bridges are shown to be of the most critical
components [6].
2 Study Cases
In this study two different bascule bridge
architectures are considered based on lifting
mechanism hydraulic cylinders arrangements which
are: (1) Cylinders in push arrangement; in which
hydraulic cylinders are attached to the balance-beam
such and push the beam to rotate it around its pivot
and hence the balance-beam pull bridge leaf via tie
rods connecting the balance-beam and the bridge
leaf causing bridge span opening. This case is such
in Azmy Bridge, Port Said, Egypt [7] shown in
Fig.3.
Fig. 3: Azmy Bridge, Port Said, Egypt
(2) Cylinders in pull arrangement; in which
hydraulic cylinders are attached to bridge leaf and
pull the leaf around its trunnion for bridge span
opening. This case is such in Wolgast Bascule
Bridge in Germany shown in Fig.4.
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Fig. 4: Bascule bridge of Wolgast, Germany
Although hydraulic cylinders is a particularly
common solution and the majority of modern
bascule bridges and movable bridges are powered
by it [8], understanding kinematics and motion of
the bridge leave and the change in cylinder loadings
is important for prober design of bridge lift
mechanism.
3 Modeling and Analysis
In hydraulic operated balance-beam bascule
bridges; lift mechanism arrangement is a key factor
in optimum operation of the bridge (leaf rotates
during bridge span opening and closing) and in the
other hand lift mechanism should consider the
change of the moment required to lift the bridge
and withstand the fluctuation of wind pressure
during operation. At this point modeling and
simulation of designed mechanism operation at
design stage is one of the important steps in design
validation before production and construction
stages carried on. This step is not only important
for operating mechanism design but also in proper
design of hydraulic system operation control to
avoid overloads, dynamic effects and pressure
fluctuation. Mechanism kinematics based modeling
and simulation in the design stage can provide
informations about motion description including
forces acting on lifting mechanism during bridge
span rotation, proper operation velocity for power
considerations, dynamics of moving components
and corresponding stress acting on it during
operation.
3.1 Bridge Mechanism Kinematics
Fig. 5: Kinematics diagram of the bascule
mechanism
As long as this paper consider a comparative
analysis of two valid bascule bridges in a
qualitative manner and not a quantitative one; some
assumptions are introduced such as dealing with all
components as a rigid body and ignore effect of
elastic deformations. Also smooth operation
eliminating inertias and dynamics effect is
considered. Based on the previous assumptions;
bridge mechanism can be described in 2D (planar)
manner. The DOF of this mechanism can be
obtained using Gruebler’s formula [9] as follow;
(1)
Where:
d.. number of DOF in planar = 3
n.. number of links including the frame = 4
g.. number of joints = 4
.. DOF of joint i
As obtained by equation (1); the number of degrees
of freedom DOF of this mechanism is one. Loop-
Closure equations can be applied Using
trigonometric relations for the closed-loop
; forward kinematic relation of balance-beam lift
angle “” due to active link () bridge leaf
rotational (opening) angle “” is obtained as
follow:
(2)
(3)
(4)
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(5)
(6)
(7)
Set equation (7) in the form
(8)
Where;
=
=
(9)
Equation (9) describes bridge leaf opening angle
“” as a function of Balance-beam lift angle “”
and illustrated in Fig.6 which shows relatively
linear relation between balance beam rotation and
bridge leaf opening.
Fig. 6: Bridge leaf opening angle “” as a function
of Balance-beam lift angle “”
(a) Cylinders in push arrangement
(b) Cylinders in pull arrangement
Fig. 7: Kinematics diagram of operating hydraulic
cylinder
The relation between Balance-beam lift angle “”
and operating hydraulic cylinder length
““illustrated in Fig.7 (a) can be obtained using
trigonometric relations as follow:
(10)
Where:” “cylinder length at any time during
operation,” “angle of cylinder installation, “”
cylinder hub support vertical position and “”
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distance between balanced-beam pivot and cylinder
rod support point.
(a) Cylinders in push arrangement
(b) Cylinders in pull arrangement
Fig. 8: Bascule mechanism operation relations
In the same way; the relation between Balance-beam
lift angle “” and operating hydraulic cylinder
length ““in pull arrangement illustrated in Fig.7
(b) can be obtained as follow:
(11)
Where:” “cylinder length at any time
during operation,” “angle of cylinder installation,
“” cylinder hub support vertical position and “”
distance between bridge leaf pivot and cylinder rod
support point. Geometrical parameters of presented
bascule bridge mechanism shown in Fig.5 and Fig.7
are listed in Table 1.
Table 1. Geometrical Parameters
Based on equation (9) and equation (10) the relation
between bridge leaf opening angle “” and
operating hydraulic cylinder length ““in push
arrangement is obtained and illustrated in Fig.8 (a)
and based on equation (11) the relation between
bridge leaf opening angle “” and operating
hydraulic cylinder length ““in pull arrangement is
obtained and illustrated in Fig.8 (b). These
relations are important in conceptual design stage
for bridge operating hydraulic control system design
and selection.
3.2 Bridge Mechanism Modeling
(a) Push arrangement
(b) Pull arrangement
Fig. 9: Bascule bridge mechanism model
For the sake of comparative analysis of bascule
bridge mechanism using hydraulic system arranged
in both push and pull architectures , a 3D model of
bridge system is created such that bridge leaf is 22m
long and 15m wide and weighted 250 ton is attached
to balance beam through two tie rods. Counter
balance weight of 240 ton is attached to the balance
beam. Fig.9 illustrates the bascule bridge
mechanism model in both push and pull
architectures.
Forces acting on tie rods and hydraulic cylinders
(actuators) of the bridge mechanism during bridge
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leaf opening in both push and pull arrangement are
illustrated in Fig.10.
(a) Push Arrangement
(b) Pull Arrangement
Fig. 10: Forces acting on tie rods
In push arrangement forces exerted by hydraulic
cylinders is acting on balance-beam which rotates
pulling the tie rods and hence bridge leaf open. In
this case moment applied by balance beam counter
balance and hydraulic cylinders acting on bridge
leaf via the tie rods in tension while in the case of
pull arrangement case the tie rod affected by tension
force due to the effect of balance beam counter
balance and compression force due to pulling action
of the bridge leaf by the hydraulic cylinders. This
explains the difference of tie rods forces shown in
Fig.10 (a) and Fig.10 (b). This note can be stated as
the first advantage of pull arrangement over push
arrangement. Fig.10 shows that forces acting on
both right and left actuators (cylinders) are behave
same manner as the system explained by rigid body
motion as mentioned before in the assumptions and
they will appear as a single line in most of the
coming results figures. Concerning forces required
by actuators (hydraulic cylinders); Fig.10 shows
significant difference between actuators forces in
push and pull arrangement. This difference is due to
distance between actuator and active pivot for each
case and as a result both actuators has different
stroke length for the bridge mechanism to set the
bridge leaf to the opening position.
(a) Actuators stroke
(b) Work done by actuators
Fig. 11: Actuators configuration and work done to
rotate bridge leaf
The relation between actuators stroke in both push
and pull arrangement and bridge leaf opening angle
is illustrated in Fig.11(a) in the other hand work
done by each actuator in both push and pull
arrangement is illustrated in Fig.11(b). As shown in
Fig.11 (b) work done by hydraulic cylinders
(Actuators) in both arrangement is nearly identical.
4 Discussion of Failure Scenarios
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Some failure scenarios are introduced and behaviour
of both push and pull arrangement mechanism
architecture is discussed.
First scenario is that both tie rods fail and both
actuators fail: in this case bridge leaf will fell as
illustrated in Fig.14.
(a) Push – both rods fail- Bridge Fell
(b) Pull – both Rods and actuator fail – Bridge
Fell
Fig. 14: Forces in first failure scenario
Second failure scenario is that both tie rods fail
but actuators can withstand the jump applied load as
shown in Fig.15. Fig.15 (a) illustrate bridge leaf
opening with respect to time as the bridge
mechanism operates. At angle 22o tie rods fail and
bridge leaf starts to close down to bridge span
support. In this case if the system designed to
withstand this load jump; bridge leaf will subjected
to hydraulic actuators pull forces only and
hydraulic system safety valves will blocking the
cylinders at this pressure to insure save close to the
bridge leaf avoiding sever damage.
(a) Bridge leaf opening
(b) Actuators and tie rods forces
Fig. 15: Second failure scenario
(a) Push – both actuator fail – Bridge Fell
(b) Pull – both actuator fail – Bridge Fell
Fig. 16: Forces in third failure scenario
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Third failure scenario is that both actuators fail
while tie rods still active: As shown in Fig.16 during
normal operation of bridge leaf opening and at angle
of 26o hydraulic actuators fail and hence the bridge
supported only by the counter balance moment
acting on tie rod. As bridge leaf weight moment is
higher than the counter balance moment; bridge leaf
rotates back to the close position.
(a) Push– single actuator fails
(b) Pull – single actuator fails
Fig. 17: Forces in forth failure scenario
Forth failure scenario is that one of the hydraulic
actuators fails while the other is still active along
with tie rods. In this case a jump of actuator force is
occurred as shown in Fig.17 (a) and Fig.17 (b)
which illustrate the behavior of actuators load if
failure of right actuator is introduced in both push
and pull arrangement.
Failure of tie rod or hydraulic system may be
occurred due to non-accurate design, low production
quality control, improper selection of hydraulic
system and extreme operation conditions that not
considered in design stage. If such failure occurs
during operation; bridge leaf may fall down striking
bridge support and hence bridge sector may be
damaged. A comparison of impact impulse of bridge
leaf and bridge span support is carried out for the
first three failure scenarios where bridge leaf fell
and strike bridge span support. Results of impact
impulse are illustrated in Fig.18.
Fig. 18: Bridge leaf impact impulse for failure
scenarios no. 1, 2 and 3
As shown in the figure; both push and pull
arrangements shows similar impact impulse trend in
the first and third failure scenario while pull
arrangement shows interested behavior in the
second failure scenario when tie rods fail and
hydraulic system withstand the jump applied load.
5 Finite Element Results and Analysis
Stress analysis of both bascule bridge mechanism
architecture is carried out using finite element
modeling.
(a) Push Arrangement
(b) Pull Arrangement
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Fig. 12: Stress of Tie rods-both rods active
Von Misses stress distribution of tie rods
considering both rods active is illustrated in Fig.12
and that of tie rods considering single rod active is
illustrated in Fig.13 for both push and pull
arrangements. The finite element results shows
slight difference between the two architecture
analysis cases in which both tie rods of the Bascule
mechanism are active and transmit bridge span load
to support beam structure as shown in Fig.12.
(a) Push Arrangement
(b) Pull Arrangement
Fig. 13: Stress of Tie rods- single rod active
While Left rod fail scenario is introduced during
bridge opening procedure; finite element
results shows significant difference between push
and pull arrangement as stress acting on the active
tie rod in pull arrangement is much lower than
that in push arrangement as shown in Fig.13.
6 Conclusion
Stress distribution on tie rods shows lower
stresses on pull arrangement rather than
in push arrangement. Bridge leaf opening
mechanism in pull arrangement show advantage
that when tie rod fail during bridge leaf opening
with caution design of the hydraulic control system
bridge leaf return back to its horizontal position
with relatively low impact impulse at bridge
support.
As a conclusion bridge leaf mechanism in pull
arrangement architecture provide redundant safety
in design and operation with lower stress of
operating structure components and this is an
advantage over the push arrangement architecture
one.
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Contribution of Individual Authors to the
Creation of a Scientific Article (Ghostwriting
Policy)
The author contributed in the present research, at
all stages from the formulation of the problem to
the final findings and solution.
Sources of Funding for Research Presented in a
Scientific Article or Scientific Article Itself
No funding was received for conducting this study.
Conflict of Interest
The author has no conflict of interest to declare.
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