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Facilitating Concept Design Skills

for

Cable Stayed Bridge Structures

Chandra Vemury

chandra.vemury@ncl.ac.uk

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

• 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

• 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

Sustainable

Engineering

System

Recycling

and Waste

Transport

Demand

Site

Investigation

Economics

and

Financing Geotechnical

Issues

Sustainability

Considerations

Environmental

Impact

Climate

Change

Reliability

and Risk Construction

Materials Structural

Design

Hydraulics

Health and

Safety

Project

Management

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

• 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

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 Concrete Deck

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

Span/Depth ratio for Continuous Steel Deck Elements

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?

• ………………….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?