Bridge engineering

Learning Objectives

To gain a comprehensive understanding of bridge loading To develop a critical appreciation and comprehensive

understanding of methods of structural Idealisation and analysis of bridge structures.

To develop a critical awareness of bridge inspection and assessment.

Lecture-1

Bridge Definition

Types of Bridges

Bridge Components

Aesthetic in Bridge Design

Selection criterion of a Bridge Type

Quiz

What is a Bridge?

Bridge is a structure which covers a gap

Generally bridges carry a road or railway across a natural or artificial obstacle such as, a river, canal or another railway or another road

Bridge is a structure corresponding to the heaviest responsibility in carrying a free flow of transport and is the most significant component of a transportation system in case of communication over gaps for whatever reason such as aquatic obstacles, valleys and gorges etc.

Bridge is the KEY ELEMENT in a Transportation System

What is a Bridge?

Structures for Transportation

Beauty can be expressed in the

structural efficiency, simplicity, and

repetition of a bridge.

Millau Viaduct, France

SubstructureFoundation (Pile/Spread footing)Pier (Column)Abutment

SuperstructureAny structure above bearingWearing surface

Bridge Components

Bridge Components

Bridge Planning

Traffic StudiesHydro technical StudiesGeotechnical StudiesEnvironmental ConsiderationsAlternatives for Bridge TypeEconomic Feasibility Bridge Selection and Detailed Design

Span>6m BridgeSpan<6m Culvert

Short span : 6-30mMedium span: 30-100mLong span: >100m

Bridge Span Length

Steel Concrete Timber Hybrid Stone/Brick FRP

Pedestrian Highway Railroad

Short Medium Long

Slab Girder Truss Arch Suspension Cable-Stayed

MaterialMaterial

UsageUsage

Span

Structural form

Types of Bridges

Material and FabricationMaterialsMasonry (brick, rock)

Timber

Reinforced Concrete

Prestressed Concrete

Iron

Steel

Composites

FabricationPrecast (RC, PC)

Cast in place (RC, PC)

Pre tensioned (PC)

Post tensioned (PC)

Prefabricated (Steel)

Rivet (steel)

Bolted (steel, timber)

Types of Bridges

Bristol Bridge, Bristol, UK

Highway Bridges

Electric Wharf Footbridge, UK

London Millennium Footbridge, UK

Pedestrian Bridges

The Forth Railway Bridge, Scotland

Thames Ditton Railway bridges

Railway Bridges

Basic types based on structural form:

ArchBeamCantileverTrussCable StayedSuspension

Types of Bridges

Types of Bridges

Arch BridgeArch bridges are one of the oldest types of

bridges and have great natural strength. Instead of pushing straight down, the weight

of an arch bridge is carried outward along the curve of the arch to the supports at each end.

These supports, called the abutments, carry the load and keep the ends of the bridge from spreading out.

Forces

When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

Beam/Girder BridgeThe most basic type of bridge

Typically consists of a beam simply supported on each side by a support and can be made continuous later

Typically inexpensive to build

Types of Bridges

Beam/Girder BridgeCurrently, most of the beam bridges are precast (in case of RC and PC) or prefabricated

Most are simply-supported

Some are made continuous on site

Simply supported

Cantilever

Continuous

Types of Bridges

Cantilever BridgeIn a cantilever bridge, the roadway is constructed out from the pier in two directions at the same time so that the weight on both sides counterbalance each other

Notice the larger section at the support to resist the negative moments

Firth of Forth Bridge, Scotland521m span

Types of Bridges

Truss BridgeAll beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.

Typical Span lengths: 40m-500m

Types of Bridges

Suspension bridge needs to have very strong main cables

Cables are anchored at the abutment

Suspension Bridges

London Tower Bridge (1894),UK

Types of Bridges

Types of Bridges

Cable-stayed Bridge

All the forces are transferred from the deck through the cables to the pylon

Roadway deck can be : (prestressed) Concrete Box Deck Steel Box Deck Steel Truss Deck

Consider the following:Span length

Bridge length

Beam spacing

Material available

Site conditions (foundation, height, apace constraints)

Speed of construction

Aesthetics

Cost

Access for maintenance

Which Type Should I Use?

Selection of a Bridge Type by Span Lengths

An ugly bridge, however safe, serviceable and inexpensive, is not a good bridge

Long span bridge over a river can be a land mark: thus aesthetics should be an important factor

Bridge should blend with the environment

Smooth transition between members

Determinant of bridge’s appearance (in order of importance)

•Vertical and Horizontal geometry relative to surrounding topography and other structures

•Superstructure type and shape

•Pier/abutment placement and shape

•Color, surface texture, Signing, Lighting & landscaping

Aesthetics : What it means?

Aesthetics : What it means?

ContextComprehensiveCostConstructability

Adapted from “Restore Aesthetics as Design Priority” by Jeffery Grob

The Four “C’s” of Bridge Aesthetics

ContextAll projects from a simple creek bridge to the longest multi span water crossing must first be considered with a view to the context in which it is located.

ComprehensiveThe designs that work best are those that take aesthetics in to account right from start.

The Four “C’s” of Bridge Aesthetics

CostNo discussion of design considerations can be conducted realistically without asking “How much is it going to cost?”.

ConstructabilityNo discussion of aesthetics is complete without considering constructability.

The Four “C’s” of Bridge Aesthetics

There are not HARD & FAST rules or formulas for aesthetics of bridge design. It finally gets down to the responsibility of each designer on each project to make personal choices that will lead to a more beautiful structure

Function

Proportion

Harmony

Order & Rhythm

Contrast & Texture

Qualities of Aesthetic Design

For a bridge design to be successful, it must always safely perform its function.

For example, a bridge is designed that fulfills every requirements of aesthetic consideration and other requirements such as economy, constructability etc. but is somehow unable to perform the function for which it was designed, then however beautiful it is, it won’t be appealing.

The very first notion of beauty in a bridge is that it performs its function efficiently and people using it are satisfied.

Function

Good proportions are fundamental to achieving an aesthetically pleasing bridge structure

It is generally agreed that when a bridge is placed across a relatively shallow valley, the most pleasing appearance occurs when there are an odd number of spans with span lengths that decrease going up to the side of the valley.

The bridge over a deep valley again should have an odd number of spans, but should be of equal length. Slender girders and the tall, tapered piers can add to the aesthetic pleasure

Runnymede Bridge, River Thames (1962)

The proportions of parapet, spandrel, arch etc. are very important on such bridges.

Proportion

Slender girders can be achieved if the superstructure is made continuous. In fact, the superstructure continuity is the most important aesthetic consideration

Athlone Bypass Bridge, IrelandA shallow deck, straight haunches extended into piers and broad ,shallow cutwaters combine to give a strong and distinctive effect.

Byker Viaduct, Tall, slender divided piers, straight haunches and a shallow deck.

Proportion

Harmony between the elements of a bridge:

It depends on the proportions between the span lengths and depth of girders, height and size of piers, and negative spaces and solid masses.

Harmony between the whole structure and its surroundings

The scale and size of a bridge structure should be relative to its environment.

A9 Dornoch Firth Bridge, Scotland.Constant depth box on simple supports, a low key solution suiting a shallow estuarial crossing.

River Camel Viaduct, Wadebridge, Cornwall: Simple constant depth girder viaduct with clean and neat lines.

Harmony

Developing a rhythm to the bridge is also important. For example, spans should match where possible or at least demonstrate a consistent order.

The cumulative effect of all bridge elements including lighting columns, barrier support and pier should be considered.

For example, outer spans of this bridge are not the same dimension and the symmetry of the bridge is affected.

Order and Rhythm

All bridges do not have to blend in with their surroundings. “ when a bridge is built in the middle of the country, it should blend in with the country side, but very often, because of its proportions and dynamism, the bridge stands out and dominates the landscape”

Avon Bridge, M40,Warwick A lack of much detailing gives ‘wallpaper’ effect

For Example: When the deck line is not expressed, the scale looks odd due to paucity of detail. Also the coursing of the stone or brick then follow neither the arch, the deck nor the parapet, so invariably it tends to be horizontal.

G-Mex bridge, Manchester Metrolink. The steel structure contrasts boldly with its surroundings.

Contrast, Texture & Finishes

Establish requirements

Understand context

Setting design objectives and principles

Develop design

Engineering Process

Analysis of design

Design Refinement

Implementation Plan

Project Scope

Location/Survey

Final Design

Construction

Preliminary Design

Bridge Design Process

•Function (To bridge or not? Replace or remove?)

•Who is User?

•Where is best spot?•Many decisions.

•Project Funding and Scope finalized.

•Plans, Specs, Estimates.

Quiz

Question 1:What are the oldest type of Bridges?A. BeamB. ArchC. Cable-stayedD. Suspension

Quiz

Question 2:Which type of bridge is normally the

longest type?A. BeamB. ArchC. Cable-stayedD. Suspension

Quiz

Question 3: Which type of bridge is the cheapest?A. BeamB. ArchC. Cable-stayedD. Suspension

Quiz

Question 4: Which Quality of Aesthetic Design is the most

important?A. RhythmB. FunctionC. ProportionD. Harmony

Quiz

Question 5: During this step, the designs are studied based on

their merit in relationship to strength, cost, market appeal, and manufacturability.

A. Identify ProblemsB. Modify the ImplementationC. Determine ConstraintsD. Analysis of Design