Date post: | 13-Sep-2014 |
Category: |
Documents |
View: | 8,514 times |
Download: | 44 times |
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