1. Introduction
1.1. Purpose
1.1.1. The purpose of these guidelines is to help design teams produce bridges of aesthetic value.
1.1.2. The document is intended for the common road bridges
1.1.3. The intention is to set down considerations and principles to eliminate the worst aspects of bridge design and encourage the best.
1.2. Aesthetics
1.2.1. Aesthetics is to be considered as an integral part of the design process
1.2.2. Good bridge engineering and good aesthetics are synonymous.
1.2.3. Beauty is not simply a matter of taste alone. Good use of qualities such as proportion, order and symmetry, give structures aesthetic value.
1.3. The designers
1.3.1. The designers are responsible for the look of bridges, and must consider appearance as a major design imperative along with strength, safety and cost.
1.3.2. Aesthetics must be an integral part of design and must be considered both in the general form and all the details that support it.
1.4. Perception of bridges
1.4.1. Bridges may be isolated objects in the landscape, part of a suite of engineered infrastructure or on a city street.
1.4.1.1. Views from all angles are considered
1.5. Terminology
1.5.1. Superstructure – that part of the structure which supports traffic and includes deck, slab and girders.
1.5.2. Transition pier – pier separating different superstructure types
1.5.3. Soffit – undersurface of the bridge superstructure.
1.5.4. Substructure – that part of the structure, ie piers and abutments, which supports the superstructure and which transfers the structural load to the foundations
1.5.5. Pile cap – A reinforced concrete mass cast around the head of a group of piles to ensure they act together and distribute the load among them.
1.5.6. Pile – a slender member driven into or formed in the ground to resist loads.
1.5.7. Pier – a part of the substructure which supports the superstructure at the end of the span and which transfers loads on the superstructure to the foundations
1.5.8. Safety / throw screen – protective fence to deter the launching of objects from the bridge onto the highway below.
1.5.9. Deck – bridge floor directly carrying traffic loads
1.5.10. Span – the distance between points of support (eg piers, abutment).
1.5.11. Abutment – the part of the structure which supports the superstructure at its extremities and retains earthworks
1.5.12. Spill through abutment – an abutment which allows fill to form a slope into the end span rather than retaining it with a face wall.
1.5.13. Traffic barrier
1.5.13.1. Parapet – low protective concrete wall at edge of bridge deck.
1.5.13.2. Railing – on top of parapet to restrict lateral movement of traffic
1.5.14. Plank bridges – bridges which utilise a simple concrete plank and cross support construction system.
1.5.15. Haunching – increase in the depth of a continuous beam at the point of support to withstand the increased moment of bending on the beam
1.5.16. Bearing – a component which supports part of the bridge and which transmits forces from that part to another part of the structure whilst permitting angular and/or linear movement between parts.
1.5.17. Pedestrian barrier – a railing placed on edges of bridge structure for pedestrian safety.
1.5.18. Pier Cap / Headstock – a component which transfers loads from the superstructure to the piers.
1.5.19. Beam / Girder – load bearing member which supports the deck.
2. The whole
2.1. Context sensitive design
2.1.1. Bridge type: Perhaps the most fundamental response to context is the choice of bridge structure.
2.1.1.1. This choice is affected by many contextual factors including the following.
2.1.1.1.1. The size of the span required
2.1.1.1.2. The topography either side of the span.
2.1.1.1.3. Local geology.
2.1.1.1.4. The load to be carried.
2.1.1.1.5. The nature of the load.
2.1.1.1.6. The nature of the land or water being crossed
2.1.1.1.7. The visibility or visual presence of the structure
2.1.1.2. Typical types of superstructure according to span lengths can be:
2.1.1.2.1. Short span (up to approximately 18m): pre-stressed concrete plank bridges.
2.1.1.2.2. Short to medium span (approximately 18-40m): pre-stressed concrete girders or pre-stressed concrete voided slabs
2.1.1.2.3. Medium span (approximately 40-80m): steel or post-tensioned concrete box girders or incrementally launched girders
2.1.1.2.4. Medium to long span (up to approximately 300m): balanced cantilever
2.1.1.2.5. Long span (up to approximately 800m): cable stay
2.1.1.2.6. Very long span (longer than 800m): suspension bridges
2.1.2. Bridges in the landscape: There are a number of ways to approach bridge design in landscape settings
2.1.2.1. Make the bridge as invisible as possible to hide it in the landscape.
2.1.2.2. Make the bridge as distinctive as possible to contrast and stand out in the landscape.
2.1.2.3. Make the bridge as simple and elegant as possible to complement the landscape
2.1.2.4. In areas of high scenic
2.1.2.4.1. The view from the bridge towards the surrounding landscape setting should be maximised.
2.1.2.4.2. Maximise views of the landscape through the bridge
2.1.2.4.3. The complexity of a bridge should be minimised in a natural landscape setting.
2.1.2.4.4. Natural vegetation should be protected and recovered. Some approaches to achieve this are:
2.1.3. Urban bridges: Designers should aim to ensure the bridge complements the local vernacular and benefits the local community with limited resources.
2.1.3.1. Creating a landmark structure which complements or contrasts with its visual catchment.
2.1.3.2. Maximising views from the bridge of the local urban setting.
2.1.3.3. Maximising views through the bridge from the urban setting.
2.1.3.4. Minimising visual impacts
2.1.3.5. Designing a well proportioned pleasing structure
2.1.3.6. Respecting locally valued structures and their curtilages
2.1.3.7. Complementing local styles and materials
2.1.3.8. Ensuring the spaces under the bridge are not dark, degraded and unsafe
2.2. Form
2.2.1. Proportion
2.2.1.1. Ratios
2.2.1.1.1. Common ratios can vary from five to 30. The ratio of five can result in a very chunky bridge although with appearance of strength while 30 can lead to very slender bridge.
2.2.1.1.2. The setting and scale of the bridge can influence whether slenderness or ‘chunkyness’ is appropriate
2.2.1.2. Guidelines
2.2.1.2.1. Using excessively imbalanced proportions between significant elements should be considered carefully.
2.2.1.2.2. Repeating similar proportions or ratios throughout a structure can lead to a harmonious structure.
2.2.1.2.3. The proportion between depth of superstructure and bridge spans is an important ratio. It is referred to as the slenderness of the bridge
2.2.2. Symmetry
2.2.2.1. Symmetrical bridges are often more aesthetically pleasing
2.2.3. Order and rhythm
2.2.3.1. Spans should match where possible or at least demonstrate a consistent order.
2.2.3.2. A designed order to individual bridge elements can look more pleasing than chaotic randomness.
2.2.4. Contrast and harmony
2.2.4.1. Natural features such as vegetation, stone or landform can create a good contrast with the order, precision and simplicity of a bridge
2.2.5. Simplicity
2.2.5.1. Refinement of design should generally be pursued
2.2.5.2. Honesty of form and design integrity
2.2.5.3. There may be good reasons for avoiding total refinement based upon local context.
2.2.6. Unity of design
2.2.6.1. A bridge is a whole not an assemblage of parts. The landscape design, the approach road design, and all the associated signage contribute to the bridge design as a whole.
2.2.7. Consistency along the corridor
2.2.7.1. There should be a relationship between elements in terms of materials, proportion, colour or details. This aesthetic aspect is very important when the bridge structure is but one element in a road corridor and a degree of consistency is desirable along the corridor.
2.2.8. Detail
2.2.8.1. Good detailing is essential to good bridge design and lack of attention to detail can spoil an otherwise beautiful bridge. Careful consideration of interrelationship of each element, and their relationship with the whole.
3. Design Approaches
3.1. Design values
3.1.1. Commitment to aesthetics
3.1.1.1. A commitment to aesthetics is needed from both the client and contractor.
3.1.1.2. The commitment must be carried through the implementation process
3.1.2. Context sensitive design
3.1.2.1. The aesthetic value of a bridge is dependent on its context. Valued bridges are produced when the design process starts after natural, built and community context is understood and significant constraints identified.
3.1.2.1.1. The appearance and proximity of other bridges is an important contextual factor. relationship. New bridges should respect the role, form and design of the existing bridges.
3.1.2.1.2. Visibility of the bridge is also an important contextual factor.
3.1.3. Comprehensive design process
3.1.3.1. Aesthetics is the final product of the planning, design and procurement process, from initial route selection, through environmental assessment, to detail design and construction. It can not be added at the end.
3.1.4. Collaboration in the design team
3.1.4.1. A lack of collaboration in the design process will affect the aesthetic outcome. Those concerned with the visual qualities of a bridge must work alongside those concerned with the engineering and economic aspects of a bridge.
3.1.4.2. A balance must be achieved between the requirements of the road engineers and the bridge engineer.
3.1.5. Cost and aesthetics can be complementary
3.1.5.1. Bridges of aesthetic merit are not necessarily more expensive. Cost and aesthetics as driving forces in the design process need to be balanced.
3.1.5.2. Designers should not aim to place the maintenance burden on the future custodians of the bridge. Simple, elegant and refined bridges are likely to be sustainable and self-reliant also.
3.2. Design methodology
3.2.1. The following process and checklists should be addressed in the methodology of designing a bridge.
3.2.1.1. Establish requirements
3.2.1.1.1. The level of flexibility in the vertical and horizontal road alignment.
3.2.1.1.2. The span and load requirements and considerations of most appropriate superstructure type.
3.2.1.1.3. Signage and lighting requirements.
3.2.1.1.4. Safety barrier criteria
3.2.1.1.5. Traffic volumes and speeds.
3.2.1.1.6. Pedestrian cyclist and public transport requirements.
3.2.1.1.7. Environmental requirements.
3.2.1.1.8. Political issues
3.2.1.2. Understand context
3.2.1.2.1. Topography, water bodies and water courses.
3.2.1.2.2. Other bridges in the area and along the road corridor.
3.2.1.2.3. Soils and geology.
3.2.1.2.4. Biodiversity
3.2.1.2.5. Views to and from the bridge location
3.2.1.2.6. Local vernacular.
3.2.1.2.7. Landscape and built character
3.2.1.3. Setting design objectives and principles
3.2.1.3.1. Unobtrusive or landmark
3.2.1.3.2. Integration with landscape.
3.2.1.3.3. Proportions: symmetrical slender / stocky
3.2.1.3.4. Simple/refined.
3.2.1.3.5. Conform to suite of bridges along corridor.
3.2.1.4. Develop design
3.2.1.4.1. Plans of the bridge approaches and bridge in context.
3.2.1.4.2. Elevations of the bridge illustrated with background context.
3.2.1.4.3. Cross sections, axonometrics and models illustrating three dimensional shape and proportions of piers, pile caps, abutments, parapets, beams.
3.2.1.4.4. Typical details illustrating barriers connections between barriers, jointing, lighting, signage and landscape.
3.2.1.4.5. Artist illustrations and photomontage of the bridge structure as seen from the highway and surrounding key viewpoints.