Bridges with hinged spans after a centenary experience

Bridges with hinged spans after a centenary experience
Pier Giorgio Malerba(*), Dept. of Civil and Environmental Eng., Politecnico di Milano, Milan, Italy.
(*) piergiorgio.malerba@polimi.it

Malerba - Bridges with hinged spans after a centenary experience 2
CONTENTS
• LESSONS FROM THE PAST AND OBJECT OF THE PRESENTATION
• BRIDGES WITH HINGED SPANS - MAIN STATIC SCHEMES
• TYPES OF ARTICULATION
• IN-SERVICE BEHAVIOUR AND MAIN TYPES OF DAMAGES
• QUASI CONTINOUS BRIDGES (KINEMATIC CHAINS)
• CONTINUOUS BRIDGES
• INTEGRAL TYPE BRIDGES
• CONCLUSIONS

CONTENTS
• CONCLUSIONS

Introduction
Major drawbacks observed on medium-long span bridges of the last century can be resumed as:
• Surface wearing and steel corrosion
• Excessive deformability
• Sudden collapses, caused by breakage of some critical detail.
Surface wearing and steel corrosion are due to the aging of the construction, the original
characteristics of the materials and the lack of maintenance.
But, nowadays and on the basis of past experiences, we can realize that other causes could
have contributed to certain types of damage. In particular, some design criteria that appeared
reasonable in the past have resulted in a dangerous preconditioning of the following states of
the life of a structure.
Object of this presentation is a short exam of malfunctions triggered by:
• the initial choice of the static scheme.
• an incorrect use of prestressing in governing the static and deformed configuration of the
structure.

INTRODUCTION OF THE ARTICULATED STATIC SCHEMES
• End of nineteenth and beginning of twentieth century ( 1870   1960). At end of the
nineteenth and at the beginning of twentieth century, medium long distances were spanned
through trussed steel bridges.
At that time, trussed steel bridges reached the remarkable spans of 60÷80 m with simple
and statically determined schemes, obtained through the introduction of hinges in suitable
points along the spans.
In European Technical literature, these schemes are usually called “Gerber type” girders and
the mechanisms used for materializing the articulation are called “Gerber hinges”, “Gerber
corbels” or “articulations”.
• Advent of reinforced concrete. It is understandable that, when it became possible to span
the same distances with concrete girders, the same static schemes used for steel trusses
were assumed as a sound and tested reference.
• Advent of prestressing. After the end of the second world war, the diffusion of the
prestressing technology allowed the construction of concrete bridges spanning the same
lengths as the trussed steel bridges built at the end of the nineteenth century and during the
first half of the last one.

Another element that favoured the continuation of the use of articulated schemes was the
introduction of new erection systems.
In fact, prestressing forces concrete elements to work mainly in compression, counterbalancing
the tensile stresses due to huge negative moments.
This made it possible to build long cantilever spans, made of cast-in-situ or precast segments,
without using expensive temporary structures and scaffolding systems.
After the construction stage, cantilever beams must be interconnected to complete the final
structure.
The most common solutions are:
• Cantilever systems with suspended span, in which the ends of the two cantilevers are
connected by an independent suspended span. The final scheme results in a Gerber girder.
• Systems with hinged cantilevers, in which the ends are interconnected by a key central hinge.
• Systems made continuous, in which the adjacent cantilevers are completely connected and
then prestressed with cables all along the completed span.

CONTENTS
• CONCLUSIONS

RAILWAY & ROAD TRUSS BRIDGE WITH HINGE AND PENDULUM

A BASIC CLASSIFICATION
ARTICULATED BRIDGES
GERBER TYPE BRIDGES
CONTINUOUS BRIDGES
Ref.: Mathivat, J., 1983, “The Cantilever Construction of Prestressed Concrete Bridges”, J. Wiley & Sons, ISBN0471103438.
PARTIALLY ARTICULATED BRIDGES
KENTUCKY TYPE
NIAGARA TYPE

Malerba - Bridges with hinged spans after a centenary experience
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ARTICULATED BRIDGES – (Cantilever systems with suspended spans)
Description
• Cantilever beams are interconnected by independent suspended spans.
• One end of these spans is simply supported by a set of fixed hinges, while the other end lies on
sliding supports. This second set of supports allows the horizontal displacements due to changes in
length of the beams over time and to the temperature effects. Both supports permit rotations.
Advantages:
• Clear and simple static scheme (statically determined structure).
• Avoidance of spurious effect due to settlements of the foundations.
• Possibility of compensating potential differences in the cantilever ends levels.
• Reduction of bending moments at the supports, which may be reached through suitable choices of
hinges position and of girder sections.

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1
Description
• The ends of the cantilevers are interconnected by a key
central hinge.
• The bending moment at midspan is zero.
• The central hinge transmits the shear forces.
• The hinge allows relative rotation between the two ends
of the cantilevers, and through a suitable design, allows a
free expansion of the girder.
PARTIALLY ARTICULATED BRIDGES – (Systems with hinged cantilevers)
Advantages
• Simple initial design (they are statically determined under the combined effects of self-weight and
prestressing).
• They become statically indeterminate only with respect to superstructures and additional loads once the
central hinge has been incorporated. At this second stage, the statically indeterminate forces for each span
are the vertical reactions transmitted by the hinges.
• These structures exhibit bending moments of constant sign. This simplifies the design of the prestressing
cables profile.

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2
CONTINUOUS GIRDERS - CANTILEVER SYSTEMS MADE CONTINUOUS
Of the three schemes (articulated, partially articulated and continuous), this represents the best solution.
In fact, many cantilever bridges built according to the other two schemes, have been over time modified and
rendered continuous.
Continuous bridges may be cast on scaffolding and then
prestressed.
In the case of a balanced cantilever construction, the
adjacent cantilevers are connected by concreting the central
segment and then prestressing the girder with cables acting
on its whole length, making the cantilever beams fully
collaborating and the girder continuous.

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CONTENTS
• TYPES OF ARTICULATIONS
• CONCLUSIONS

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ARTICULATIONS IN A RAILWAY & ROAD TRUSS BRIDGE

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TYPES OF ARTICULATIONS - GERBER TYPE SUPPORTS (R. Morandi Designer)
R. Morandi, Baia del
Banco Viaducts
(Cote d’Ivoire, 1977)
Ref. Boaga, G. , 1984, “Riccardo Morandi”, Zanichelli Ed.Ref. Radogna, E.F., 1966, “Un Ponte ad Arco sul
Bradano”, Rassegna dei Lavori Pubblici, n.11.
Reinforced concrete + link bearingReinforced concrete + roller bearing

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TYPES OF ARTICULATIONS - GERBER TYPE SUPPORTS (R. Morandi Designer)
Ref. Boaga, G. , 1984, “Riccardo Morandi”, Zanichelli Ed.
R. Morandi, Maracaibo Lagoon Bridge (Venezuela, 1957-62)
Introduction
of prestressing

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TYPES OF ARTICULATIONS SYSTEMS WITH HINGED CANTILEVERS
Key Central Connectors
• The bending moment at midspan is zero.
• The central hinge transmits the shear forces.
• The hinge allows relative rotation between the two
ends of the cantilevers, and through a suitable design,
allows a free expansion of the girder.

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CONTENTS
• TYPES OF ARTICULATIONS
• CONCLUSIONS

1
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IN SERVICE BEHAVIOUR - GERBER TYPE BRIDGES: KENTUCKY & NIAGARA BRIDGES
 
 
3
2 11 1
1
2 2 2 3
b
L



  

For the same geometry and loading conditions, articulated girders are statically equivalent to continuous
ones, if the articulations are placed at the sections with zero bending moment in the corresponding
continuous scheme.
 
 
3
2
11
1
2 2 3
a
l

 

 

KENTUCKY TYPE SCHEME NIAGARA TYPE SCHEME
l
L
 

2
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Articulated girders are very sensitive to the location of internal disconnections (hinges).
KENTUCKYNIAGARA
a=0.750 a=0.800 a=0.850
b=0.226
b=0.276 b=0.326
Briccola, D., (2017), “Sensitivity Analysis of Bridge structures to time-dependent effects”, PhD PHDSSGE Thesis, Milan.

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Time-dependent effects magnify deflections irregularities and kinks between the two sides of the
hinges, causing distresses in the joints both with respect to functionality and durability.
Joint drawbacks cause severe washing effects on bearing devices and supporting structures.
KENTUCKYTYPEBRIDGE
DEFLECTIONS
ROTATIONS

2
2
IN SERVICE BEHAVIOUR AND MAIN TYPES OF DAMAGES

2
3
EXCESSIVE DEFLECTIONS AND PLATFORM DISCONTINUITIES
NIAGARA TYPE BRIDGE
KINK POINTS
KINK POINT
HINGED CANTILEVER BRIDGE
Kink effects are progressively increased by time-
dependent effects.

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CUMULATED DAMAGE EFFECTS
JOINT & DRAINAGE
DYSFUNCTIONS
CUMULATED EFFECTS

2
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Disadvantages of the Articulated Schemes
• The systematic use of internal bearing supports and joints causes slope discontinuities of the road
profile.
• Under permanent loads, such kinks are progressively increased the time-dependent effects.
• Local discontinuities foster dynamic effects in the proximity of hinges, reduce the ride comfort and
cause severe damages both at these devices and at their interfaces with the main structure.
• Lower ultimate strength than in a continuous structure (each hinge behaves as a plastic hinge with a
zero moment of resistance);
• Hinges and joints are difficult to place (and replace) and remain vulnerable and expensive devices,
characterized by a life cycle very short with respect to that of the bridge.
• In systems with hinged cantilevers the negative bending moments, deflections and the relative
rotations at the key joints increase, fostering the effects already described.

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a: aggressive attack from one side only.
b: aggressive attack from two sides.
c: interior reinforcement bars (protected)
Problems concerning R. C. Gerber corbels
Articulated Schemes and Repairing Problems
a, b, c: Sequence of activation of the corrosion effects.
The bars close to lateral surfaces are more vulnerable.
Internal bars are an important reserve of strength.
b

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Problems concerning R. C. Gerber Corbels
Articulated Schemes and Repairing Problems
• Gerber Corbels robustness depends on their dimensions and on the internal arrangement of its
reinforcing bars.
• The stress diffusion effects assumed in the assessment models (S&T Models), are reliable if the
struts dimensions are sufficiently higher with respect to the actual dimensions of the aggregates,
of the bars and of their bend radius.
• The bearing supports must rest on an area suitable to activate a correct loading diffusion (far
from the end of the corbel and engaging the kernel of the strut).

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CONTENTS
• CONCLUSIONS

2
9
A so-called “tied-deck girder” or “kinematic chain girder” is a viaduct composed of a
train of simply supported decks, longitudinally connected through short and flexible
continuity slabs.
QUASI-CONTINUOUS BRIDGES (KINEMATIC CHAINS))

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By avoiding joint devices between the spans, such scheme makes the carriageway
continuous and improves riding comfort.
BUT (*), (**)
• Dealing with long span continuous or tied-deck-girder bridges, time-dependent effects
(shortening) and temperature excursions, cause longitudinal displacements which
increase from the fixed point towards the free ends.
• Movements are allowed by the relative displacement between the upper and lower
plates of the bearing devices. The upper plate follows the superstructure in its movements.
The lower one is built in the head of the piers or the abutments.
(*) Malerba, P., G., Quagliaroli, M., Scaperrotta, D., (2016), “A Collapse induced by shortening in a Multispan
Viaduct”, IABMAS2016 8th Int. Conf. on Bridge Maintenance, Safety and Management, June 26 - 30, 2016
Foz do Iguaçu Brazil.
(**) Malerba, P. G., (2016), “Conceptual Design: From Abstract Reasoning To Consistent Details”, 5TH Int.
Workshop on Design in Civil and Environ. Eng., Rome, La Sapienza University of Rome, Italy, Oct. 6-8.
KINEMATIC CHAINS

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Distance of the edge of the beams from the axis of the bearing supports:
(a) in the design configuration; (b) after 20 years.
Shortening (Theoretical): 467.8 mm
(a) (b)
KINEMATIC CHAINS

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a) situation at the maximum displacement;
b) local detail of the reinforcement;
c) local pressure distribution;
d) spalling of the concrete cover;
e) contact surface reduction due to spalling;
f) buckling of the bars;
g) rotation of the upper plate;
h) final situation.
CHANGES IN THE LOCAL DIFFUSIVE EFFECTS

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CONTENTS
• CONCLUSIONS

3
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CONTINUOUS BRIDGES
With respect to previous schemes, the design is more complicated.
Nowadays there are many new tools for linear, non-linear and time-dependent structural
analyses.
There are new construction systems, prestressing techniques and specialized devices aimed to
solve or, at least, mitigate many of the aforementioned problems.

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5
PRESTRESSING A CONTINUOUS GIRDERPRESTRESSING A CONTINUOUS GIRDER

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PRESTRESSING A CONTINUOUS GIRDER
CANTILEVER TENDONS designed to balance the negative moment distribution and control the tip deflection.
MIDSPAN TENDONS designed to bear positive bending moments in the central part of the span
SIDE-SPAN TENDONS designed to bear positive bending moments towards the end supports.
After : Krístek,V., Bažant Z.P., Zich, M. Kohoutková, A., (2006), “Box Girder Bridge Deflections”,
ACI Concrete International, Vol. 28(1), Jan., 55-63.

3
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PRESTRESSING OF CONTINUOUS SYSTEMS
Prestressing may be modelled as: (a) a system of equivalent forces; (b) a distribution of imposed distortions.
The effects of prestressing on the vertical displacements may be assessed by using influence lines (I.L.)
*
*
M
Pv M
F

 
*
*P
M
v
F

 
*
*
F
P
v
v F
F
 
I.L. of vP due to F. (Maxwell Th.)
I.L. of vP due to M. (Maxwell Th.)
I.L. of vP due to . (Volterra Th.)
Briccola, D., (2017), “Sensitivity Analysis of Bridge structures to time-dependent effects”, PhD PHDSSGE Thesis, Milan.

3
8
PRESTRESSING OF CONTINUOUS SYSTEMS
vP is computed through superposition of the effects
1 1 1
( ) ( ) ( )
S
R
x
F F M M
P P R P R S P S
x
v x p x v dx M v x M v x  
     
1
( )
S
R
x
F
P P
x
v x x v dx
 
 
*
*
M
Pv M
F

 
*
*P
M
v
F

 
*
*
F
P
v
v F
F
 I.L. of vP due to F. (Maxwell Th.)
I.L. of vP due to M. (Maxwell Th.)
I.L. of vP due to . (Volterra Th.)
(b) prestressing as a distribution of angular distortions:
(a) prestressing as a system of forces and moments:
p N r
( ) ( )N x e x
EI



R RM N e  S SM N e 

3
9
Slight changes in the position of the tendon can affect the deflection at midspan either way.
EXAMPLE OF USE OF I.L.: EFFECTS OF A STRAIGHT HORIZONTAL TENDON - s = Lenght of the tendon
N e
EI



The vertical displacement vP is given by the product of (Ne/EI) by the area subtended by the influence line.
Imposed distortion

4
0
Length and position of the tendon may be arranged to obtain the expected effects in term of vP.
EXAMPLE: EFFECTS OF A STRAIGHT HORIZONTAL TENDON - s = Length of the tendon
Total area A=0 Total area A>0 Total area A<0
vP.= 0 vP.  vP 

4
1
Past experiences suggest a set of hints in order to deal with the aforementioned effects (*).
In particular:
• search for a tendon layout optimizing curvature and deflections;
• proceed to prestressing of the structure only after a suitable curing time and after having
reached adequate strength characteristics;
• in the design stage, prearrange empty ducts for additional cables, to be used in contrasting
unfavourable time depending effects;
• although auxiliary cables could be activated after decades after the building stage, it is
important to design their layout according to a set of possible diverging schemes;
PRESTRESSING A CONTINUOUS GIRDER - CONCLUSIONS
(*) Krístek,V., Bažant Z.P., Zich, M. Kohoutková, A., (2006), “Box Girder Bridge Deflections” ,
ACI Concrete International, Vol. 28(1), Jan., 55-63.

4
2
CONTENTS
• CONCLUSIONS

4
3
INTEGRAL TYPE BRIDGES
Main characteristics of an Ideal Integral Bridge:
• Suitable for (Medium) - Short Spans
• No Articulations
• No Bearing Supports
• No Joints
AN EXAMPLE: THE TWO INTEGRAL BRIDGES CONNECTING THE RUNWAYS OF THE MILANO
MALPENSA AIRPORT (*)
(*) Malerba, P., G., Comaita, G. (2014), “Design and Construction of two integral bridges for the runway of Milan
Malpensa Airport”, Structure and Infrastructure Engineering, 2014, Vol.0 , No. 4, pp. 1-15, (Published online).
DOI: 10.1080/15732479.2014.951862.
BRIDGES WITHOUT ARTICULATIONS - INTEGRAL TYPE BRIDGES

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4
MAX LOAD: AIRBUS A380
• Structure shaped like a portal frame
• Abutments working as retaining walls
• Lack of bearing supports and joints
BRIDGES WITHOUT ARTICULATIONS

4
5
COMPOSITION OF THE SLAB
• West Bridge deck 73 precast, prestressed beams, with 22,30 m span.
• East Bridge deck: 67 beams, spanning 20,30 m.
• All beams have a constant depth of 1,65 m.

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6
MAIN RESULTS
With regards to the structural behaviour, the self weight and the permanent loads give rise
to cylindrical flexure and, as a consequence, to axial forces, shears and moments typical
of a portal frame.
The loads due to the aircraft are exerted on very localised areas, thus inducing the
deformed shapes distributions shown in Figure.

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ABUTMENTS
• Backwalls made of diaphragms, 1,50 m thick and 8,00 m wide,
flanked adjacent to each other for the entire length of the deck.
• At the base they are fixed to the foundations.
• At the top they are clamped to the transverses.
• Diaphragms separated by vertical joints, in order to prevent the
shear action that would arise from possible differential settlements.

4
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ABUTMENTS . . .
In case of continuous walls the flexural stiffness in the transverse direction is that of the
whole section.
In this case, due to the segmentation, the inertial coupling between the upper and the
lower part of the structure is avoided, thus resulting in a reduced flexural stiffness.
The advantages of providing vertical joints can, therefore, be summarized as follows:
• more flexibility in the transverse direction;
• reduction of the onset of cracks which tend to appear on continuous walls due to
concrete shrinkage and delayed differential settlement.

4
9
CONTENTS
• CONCLUSIONS

5
0
CONCLUSIONS
• Initial concepts in defining the bridge characteristics are the bases for a sound and reliable design.
• Chose the best scheme according to location, soil characteristic, costs and time of expected for execution.
• Avoid articulated Gerber type decks and favour continuous structural schemes;
• In continuous prestressed systems, the final value of the deflections is the difference of two large and
opposite numbers (downward and upward deflections), strongly depending on the several uncertainties
involved.
• Consider the role of uncertainties on the time dependent behaviour. For the case of a prestressed cantilever
bridges, the uncertainties in the pretensioning forces and in the concrete strength may cause relevant
variance of the tip deflections. (*), (**).
• In the design stage, prearrange solutions to recover potential drawbacks due for instance to
dysfunctionalities of the special devices (drainage systems, joints, bearing supports), environmental
damages, creep and shrinkage, . . .
(*) Malerba, P.G.,(2012): “Stable and Diverging Time Dependent Behaviours in some types of Bridge Structures”, Keynote,
ASEM11+, The 1th World Congr. on Advances in Struct. Eng. and Mech., Seoul, Sept., 18-23, 2012.
(**) Briccola, D., (2017), “Sensitivity Analysis of Bridge structures to time-dependent effects”, PhD PHDSSGE Thesis, Milan.
CONCLUSIONS

5
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THANK YOU FOR YOUR KIND ATTENTION
Bridges with hinged spans after a centenary experience
Pier Giorgio Malerba(*), Dept. of Civil and Environ. Eng., Politecnico di Milano, Milan, Italy.
DCEE 2017 - 6TH Int. Workshop on Design in Civil and Environmental Engineering
University of Cagliari – November 9-10-11, 2017

Bridges with hinged spans after a centenary experience

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