LearningObjectives • To gain a comprehensive understanding of bridgeloading • To develop a critical appreciation and comprehensive understanding of methods of structural Idealisation and analysis of bridgestructures. • To develop a critical awareness of bridge inspection and assessment.
Lecture-1 • Bridge Definition • Types of Bridges • Bridge Components • Aesthetic in BridgeDesign • Selection criterion of a BridgeType • Quiz
What is aBridge? • Bridge is a structure which covers agap • 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 gorgesetc.
Structures forTransportation Beauty can be expressed in the structural efficiency, simplicity, and repetition of abridge.
Superstructure • Substructure • Foundation (Pile/Spread footing) Any structure abovebearing • Wearingsurface • Pier(Column) • Abutment
BridgePlanning • TrafficStu • Hydrotec • Geotechn • Environme • Alternativ • Economic • BridgeSel dies hnicalStudies ical Studies ntal Considerations es for Bridge Type Feasibility ection and DetailedDesign
Shortspan : 6-30m • Medium span:30-100m • Long span: >100m Span>6m Span<6m Bridge Culvert
Material HSteel Concrete TimberP ybrid Stone/Brick FR Pedestrian Highway Railroad Usage Short Medium Long Span Structural form Slab Girder Suspension Truss Arch Cable-Stayed
Material andFabrication • Materials • Masonry (brick,rock) • Timber • ReinforcedConcrete • PrestressedConcrete • Iron • Steel • Composites • Fabrication • Precast (RC,PC) • Cast in place (RC,PC) • Pre tensioned(PC) • Post tensioned(PC) • Prefabricated (Steel) • Rivet(steel) • Bolted (steel,timber)
London Millennium Footbridge,UK Electric Wharf Footbridge,UK
Thames Ditton Railwaybridges The Forth Railway Bridge,Scotland
Basic types basedon structuralform: • Arch • Beam • Cantilever • Truss • CableStayed • Suspension
Types ofBridges • ArchBridge • Arch bridges are one of the old bridges and have great naturals • Instead of pushing straight down, the weight of an arch bridge is carriedout • curve of the arch to the support • These supports, called the abu the load and keep the ends oft spreading out. est typesof trength. ward alongthe s at eachend. tments, carry he bridgefrom
Beam/GirderBridge • The most basic type ofbridge • Typically consists of a beam simply supported on each side by a support and can be made continuouslater • Typically inexpensive tobuild • Forces • When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulledapart.
Beam/GirderBridge • Currently, most of the beam bridges are precast (in case of RC and PC) or prefabricated • Most aresimply-supported • Some are made continuous onsite Simplysupported Cantilever Continuous
CantileverBridge • In 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 negativemoments Firth of Forth Bridge, Scotland 521mspan
TrussBridge • All 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 greatdistances. • Typical Span lengths:40m-500m
SuspensionBridges • Suspension bridge needs to havevery strong main cables • Cables are anchored at theabutment London Tower Bridge(1894),UK
Types ofBridges • Cable-stayedBridge • All the forces are transferred from the deck through the cables to the pylon • Roadway deck can be : • (prestressed) Concrete BoxDeck • Steel Box Deck • Steel Truss Deck
Consider thefollowing: • Span length • Bridgelength • Beamspacing • Materialavailable • Site conditions (foundation, height, apaceconstraints) • Speed ofconstruction • Aesthetics • Cost • Access for maintenance
An ugly bridge, however safe, serviceable and inexpensive, is not a goodbridge • Long span bridge over a river can be a land mark: thus aesthetics should be an importantfactor • Bridge should blend with theenvironment • Smooth transition betweenmembers • Determinant of bridge’s appearance (in order ofimportance) • Vertical and Horizontal geometry relative to surrounding topography and otherstructures • Superstructure type and shape • Pier/abutment placement andshape • Color, surface texture, Signing, Lighting &landscaping
Context • Comprehensive • Cost • Constructability • Adaptedfrom “Restore Aesthetics as Design Priority” by JefferyGrob
Context • All 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 islocated. • Comprehensive • The designs that work best are those that take aesthetics in to account right fromstart.
Cost • No discussion of design considerations can be conducted realistically without asking “How much is it going tocost?”. • Constructability • No discussion of aesthetics is complete without consideringconstructability.
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 beautifulstructure • Function • Proportion • Harmony • Order &Rhythm • Contrast &Texture
For a bridge design to besuccessful, it must always safely perform its • function. • For example, a bridge is designed that fulfills every requirements of aesthetic consideration and other requirements constructability such etc. as economy, but is somehow • unable to perform the function for which it was designed, then however beautiful it is, it won’t beappealing. • The very first notion of beauty in a bridge is that it performs its function efficiently and people using it are satisfied.
Good proportions are fundamental to achieving an aesthetically pleasing bridgestructure • 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 thevalley. • 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 aestheticpleasure • The proportions of parapet, spandrel, arch etc. are very important on suchbridges. • Runnymede Bridge, River Thames(1962)
Slender girders can be achieved if the superstructure is made continuous. In fact, the superstructure continuity is the most important aesthetic consideration • Byker Viaduct, Tall, • slender divided piers, straight haunches and a shallowdeck. Athlone Bypass Bridge,Ireland A shallow deck, straight haunches extended into piers and broad ,shallow cutwaters combine to give a strong and distinctiveeffect.
Harmony between the elements of abridge: • It depends on the proportions between the span lengths and depth of girders, height and size of piers, and negative spaces and solidmasses. • Harmony between the whole structure and itssurroundings • The scale environment. • Dornoch and size of a bridge structure should be relative to its A9 Firth Bridge, Scotland. Constant depth box on simple supports, alow key suiting shallow solution a estuarial crossing. River Camel Viaduct, Wadebridge, Cornwall: Simple constant depth girder viaduct with clean and neatlines.
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.
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 thelandscape” • 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 behorizontal. G-Mex bridge, Manchester Metrolink. The steel structure contrasts boldly with itssurroundings. Avon Bridge, M40,Warwick A lack of much detailing gives ‘wallpaper’effect
Establishrequirements Understandcontext DesignRefinement Setting designobjectives andprinciples ImplementationPlan Developdesign Analysis ofdesign
Bridge DesignProcess • Function (To bridge or not? Replace orremove?) • Who is User? • Manydecisions. • Project Funding and Scopefinalized. • Where is bestspot? • Plans, Estimates. Specs,
Quiz Question1: What are the oldest type ofBridges? Beam Arch Cable-stayed Suspension
Quiz Question2: Which type of bridge is normally the longesttype? Beam Arch Cable-stayed Suspension
Quiz Question3: Which type of bridge is thecheapest? Beam Arch Cable-stayed Suspension
Quiz Question4: Which Quality of Aesthetic Design is the most important? Rhythm Function Proportion Harmony
Quiz Question5: During this step, the designs are studied based on their merit in relationship to strength, cost, market appeal, andmanufacturability. IdentifyProblems Modify the Implementation DetermineConstraints Analysis of Design