passerelle pedonali forma e struttura nuove tendenze passerelle ...

Lunedì 23 Maggio 2011
Presso lo Spazio Viterbi della Provincia di Bergamo
PASSERELLE PEDONALI FORMA E STRUTTURA
Prof. Ing. Bruno Briseghella
University of Fuzhou (PRC)
Prof. Ing. Enzo Siviero
Università IUAV di Venezia
Prof. Ing. Tobia Zordan
Tongji University (PRC)
NUOVE TENDENZE
PASSERELLE STRALLATE
PASSERELLE A NASTRO TESO

Footbridges can be special objects

What is the usual practice
for bridge engineers

Disappointing!
How can we improve our skills
in bridge design

What are bridges and footbridges
Are they just…
crossing devices

Are they just the result of the
application of codes’ requirements
Are they just the result of
the checking process
of repeated standard solutions

Hopefully not.
Proficiency in any art or science is not attained until its history is
known.
History is very fully taught in schools of architecture, but up to the
present , very little time or thought has been given in the engineering
school to history of engineering, which is certainly quite as worthy of
attention
- History of Bridge, 1911. H.G.Tyrrell

So what are bridges and footbridges
A FOOTBRIDGE CAN BE…

A FOOTBRIDGE CAN BE…
A FOOTBRIDGE CAN BE…

A FOOTBRIDGE CAN BE…THE MOST ENJOYABLE GAME FOR ENGINEERS!
BUY CAN ALSO REPRESENT A…PROBLEM FOR HUMANS AND LANDSCAPE

What makes you feel a bridge is
beautiful or ugly
Bridges are “naked” constructions
Bridges combine form with function.
Bridges are “sincere” constructions.
When Conceptual Design is wrong, the bridge will be a bad one and
designer and owner will have no chance to disguise it!
Generally bridges seem aesthetically more pleasing if they are
simple in form, the deck is thinner (as a proportion of its span), the
lines of the structure are continuous and the shapes of the structural
members reflect the forces acting on them.

" . . . a good looking bridge is one which responds most
gracefully to the structural requirements that it must meet."
David P. Billington
How do we sense bridges

How can we deal with
“perception”

Footbridge or…handle

Turbine or…footbridge
VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other

VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other
VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other

VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontality
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other
VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other

VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other
VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other

Girder cross seciton
The shadow created by the overhang reduces the dominance
of the girder. The deck overhang should be proportional to the
girder depth.
Girder cross seciton
Different girder cross sections can have different aesthetic
effects.
The cross sectional shape of the girder should be considered in
accordance with the following principles.
A right angled (90°) connection can catch the light and a
double line may be visible.
Maximizing the overhang will increase the shadow.

Girder cross seciton
An angled connection would minimize this effect
Girder cross seciton
A very acute angle provides a deep shadow nearly all of
the time.

Girder cross seciton
A curved soffit will provide a gradation of tone and minimize
a sharp line at the base of the beam.
VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other

VISUAL PERCEPTION – BRIDGE AND SOURROUNDINGS
Shaping parameters
Ratio elevation/background
Neighbouring objects
Rooting on the ground
Verticality vs horizontal
Trasparence vs Presence
Dynamic continuity
Lighting
Colors Material
Historical tradition
…… other
Some useful principles
to approach design

Understand context
Understand the natural, built and community context of that
would influence the design.
- Topography, water bodies and water courses.
- Other bridges in the area and along the road corridor.
- Soils and geology.
- Biodiversity.
- Views to and from the bridge location.
- Landscape and built character.
- History, tradition and culture of the place
Setting consistent design objectives
and goals
- Unobtrusive or landmark
- Integration (preferable) with landscape / Denial of surroundings.
- Proportions: symmetrical / non-symmetrical - slender / stocky.
- Simple / refined.
- Conform / not conform to suite of bridges along corridor.

Explore different possibilities
Understand and channel force flows
• Topological Optimization for Bridge Tower and Anchor
Y
MX Z X
Y
MX Z X

Understand and channel force flows
• Topological Optimization for Three-hinged Arch
Y
MX Z
X
MN
Y
MX Z
X
MN
Y
MX Z
X
MN
Sometimes a structure
is magnificently shaped
by the flow of forces…
under specified boundary
conditions and constraints so
that each single component
fulfill his task

J. Schlaich – Proposal for a pedestrian bridge
Sometimes this does not occur

But when this is the case
an observer might feel more
comfortable and harmony it’s
introduced in the design

Girder bridges
Truss bridges
Arch bridges
Cable stayed bridges
Suspension bridges
More variety can be found in
footbridges

Stress ribbon
Arch
+
Stress ribbon
Suspension
/
Stress ribbon
And even more…
MEMORIAL BRIDGE IN RIJEKA
Croatia, 2003

Trusses
Footbridge Alveiro University, Portugal

J. Da Fonseca – Aveiro bridge, Portugal
Last trends: new forms

BRIDGE AT THE ROYAL VICTORIA DOCK
London, UK, 1998

Pedestrian bridges
Cost per unit surface

New forms
Stess ribbon

Sacramento J. Strasky River Bridge, – stress Redding, ribbon California, footbridge USA

Grants Pass Bridge, Oregon, USA

Sacramento River Bridge, Redding, California, USA

Grants Pass Bridge, Oregon, USA
J. Schlaich – Northbridge, Rostock

J. Schlaich – In den Enzauen, Knoll
J.Conzett - Suransuns footbridge, 40m span, pre-stressed natural stone deck (h=6cm)
Switzerland

Stainless steel structural components, pre-stressed stone, and dry joints
are used for the deck

Stess ribbon supported by arch

Expressway R3508, Czech Republic
Expressway R3508, Czech Republic

Erection of footbridge: arch segments and deck segments
Possible different arrangements of partially or fully self-anchored
systems with the use of an arch
Arch fixed at the anchor blocks of the
prestressed concrete deck (tied arch)
The deck below the arch work as a
saddle for the stress ribbon scheme
of the side spans (tied arch with side
spans)
Side spans are stiffened by thicker
sections
Two spans stress ribbon suspended
on arch

PASSERELLE SIMONE DE BEAUVOIR
Paris, France, 2007

Self anchored supported by
lower suspension

J. Strasky - Johnson Creek Bridge, Portland, Oregon USA
Johnson Creek Bridge, Portland, Oregon, USA
Johnson Creek Bridge, Portland, Oregon, USA

Curved suspension
or cable stayed decks

Different layouts of curved cable stayed decks outer suspended
and their implications

Different layouts of curved cable stayed decks centrally suspended
and their implications
Radial uniformly distributed load
Radial uniformly distributed force H on
the edge
The principle is that highlighted by Boyle-Mariotte for a circular ring
subjected to a uniform pressure distribution. The tensile force in each
parallel (including that corresponding to the restraints) equals to:
N = H r a

J. Schlaich – footbridge in Kelheim over
Danube

J. Schlaich – footbridge in Deutsche museum in
Munich

J. Schlaich – Reedy river bridge, Greenville - USA

Structural Study
J. Strasky – proposal for a pedestrian bridge