Facilitating Concept Design Skills
for
Cable Stayed Bridge Structures
Chandra Vemury
[email protected]
A bit about me
• Teaching Fellow in Civil Engineering at Newcastle
University
• Aspiring to get chartered with CIHT in 2013.
• First degree in Civil Engineering from Osmania
University, India. Masters degree in Structural
Engineering from University of Dundee.
• Fellow of the Higher Education Academy, UK.
• Tyneside Meetings Secretary and ETRO for Northern
Regions committee of IStructE.
Presentation Overview
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Context for this work
What is a bridge?
Preliminary design
Aesthetics
Cable stayed bridge elements
Preliminary sizing
A good bridge
Context for this work
• Teaching ‘CEG2001 Design of Sustainable
Engineering Systems’ to 2nd year UG students at
Newcastle University.
• Interdisciplinary project aimed at developing
sustainable design concepts.
• My roles: deputy to module leader (Dr. Neil Thorpe);
facilitator of preliminary structural design skills for the
bridge structure.
Brief
• a suitable location where a new bridge or tunnel crossing
will be feasible in engineering terms;
• a suitable location to meet likely traffic demands that may
relieve pressure on existing crossings and promote
environmentally friendly modes of transport;
• an acceptable solution environmentally;
What is a bridge?
bridge carries a different meaning for different people
• A means that shortens distances
• A link between neighbourhoods
• One that opens up new markets and
expands commerce
• A confluence of nature and manmade
beauties as seen by an artist
• Something that helps one (symbolically)get
to the better side (could be God)
Preliminary Design of Bridges
One prime objective is to select and refine various
schemes (design layouts) in order to select the most
appropriate one. This is based on the designer’s
experience and the requirements as dictated by the
project.
• Visualisation of the scheme (project)
• Rationale, applicability
• Economy
• Analysis of forces, moments and displacements
• Design calculations
Factors - Bridge type
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Aesthetics
Function (highway/railway/pedestrian)
Economy
Safety
Construction experience
Traffic control
Soil conditions
Seismicity & environmental loads
Aesthetics
• It is the science or study of the quality of beauty of
an object as perceived by our senses. As the
adage goes ‘beauty lies in the eyes of the
beholder’.
• The society holds engineers responsible for not
just the quality of the work but also its aesthetic
appeal.
• Engineers must include visual quality as a
fundamental criterion along with a structure’s
performance, cost and safety.
Sunshine Skyway Bridge
Milau Viaduct
Recycling
and Waste
Climate
Change
Construction
Materials
Structural
Design
Hydraulics
Transport
Demand
Health and
Safety
Sustainable
Engineering
System
Site
Investigation
Economics
and
Financing
Reliability
and Risk
Geotechnical
Issues
Sustainability
Considerations
Project
Management
Environmental
Impact
Bills of
Quantities
A river crossing………
• Awareness of transport, socio-economic and
socio-political consequences to the
surrounding region(s)
• Impact on river life
• Implications on river-navigation systems
• Cost of construction
• Overall environmental impact
• Ease of construction (‘buildability’)
Design elements in a CS bridge
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Cable Configuration
Tower / Pylon
Superstructure (bridge deck)
Cables
Foundations
Abutments
Cable Configuration
Dame Point Bridge across St. Johns River in Florida
Barrios de Luna Bridge, Spain
Back Stay
cables
Types of Tower shapes
• A shaped: most suitable for regions with strong
winds and very long spans.
• H shaped: must use transverse bracing between
the tower shafts for tall towers to protect from
winds.
• Inverted Y shaped
• Choice of materials : reinforced concrete, precast
concrete elements, steel
Tower Design
• The tower may be hinged or fixed at the base. This
decision must be based on the knowledge of the
magnitude and relationship between the horizontal
and vertical forces acting on the bridge.
• The height of the tower must be decided on the
basis of several considerations, such as tower
height to span length, type of cable arrangements
and the general aesthetics of the bridge.
Talmadge Bridge
Sutong Bridge
Force Distribution
Preliminary Sizing of Members
Span/Depth ratio for Continuous Concrete Deck
Table 2.5.2.6.3-1 AASHTO specifications
Bridge Type
Typical Span/Depth ratio
Nonprestressed slabs
20-24
Nonprestressed T-Beam
15
Nonprestressed Box-Girder
18
Prestressed cast-in-situ slab
24-40
Prestressed and Precast
25-33
Prestressed Box Girder
25-33
Precast I-Beam
20-28
Span/Depth ratio for Continuous Steel Deck Elements
Table 2.5.2.6.3-1 AASHTO specifications
Bridge Type
Typical Span/Depth ratio
Composite I-Beam
35
Composite Welded Girder
22
Structural Steel Box
22
Typical Pylon Height
A pylon height is deemed optimum when it is in the range
of 20-30 % of the main span (not the total span).
Important Note
• The preliminary sizing information is aimed at
giving a starting point in your design.
• Your final member dimensions will be different to
your initial sizes as these values are just a rough
guide and do not take into account the loading
conditions and material properties.
• You must also note that the member dimensions
are also governed by various requirements listed
in the client's brief.
What is a good bridge design?
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………………….highly subjective argument
Functionality
Structural soundness
Economy
Aesthetic appeal
Durability
Final word
• Designing bridges involves sound engineering and
creativity.
• Novel designs add value to the lives of their users………
Thank you, any Questions?