Bridge Asthetics

Aesthetics is essentially the quality of beauty and appeal to the senses. Some feel that in today’s machine age bridge need only be functional one, on similar lines then house may be defined as ‘Machine made for living in’ Wherever possible at least some margin shall be kept for enhancing the aesthetic quality of bridge. Attempt should be made to integrate its form with its landscape.

The bridge form should represent a fusion of art and technology. In the innovative structure design by great engineer-architects,the structural form and dimension of each component portrays musical harmony with mathematical exaction. Ruskin said that all forms of beauty are composed exclusively of curves and this is equally applicable to most bridges. Light and shade determine the depth of object, hence surface treatment can enhance the expression of bridge. Few characteristics / concepts discussed below comprise the principles of good aesthetic design.

5.2.1 PROPORTION

It is primary aesthetic objective. In relation to bridges, proportions may pertain to structure total, environment, elements of structure. Proportion between linear dimension
like length, width, height, between masses / voids, areas in light / shadows are considered important. Choose optimal span / depth (L/D) ratio, choice is 5 to 20 or even 45 is feasible. In case of very flat, large, rectangular openings L/D > 20 may be opted. Preferably select odd spans with span length decreasing towards ends to give rhythm. Adopt wide cantilever width of deck slab for optimal ratio of areas lightened and in shadow.

5.2.2 CONTRAST
As opposed to harmony in proportions, it can lighten values of some elements in comparison with others. Contrast may be in volumes, material, colours, light, linear dimension etc.

5.2.3 SCALE
The absolute real dimension of structure defining its scale plays a dominant role in aesthetics. Scale of bridge is judged from different points of view.

5.2.4 ORDER
Order is key aesthetic quality in bridge. Order in lines is achieved by limiting their directions in space to the minimum practicable. Repetition of shapes leads an order which provides rhythm, however overdone repitions is to be avoided. Simplicity and cutting down unnecessary accessories leads to a good order. An uninterrupted line of fascia beam can emphasize the continuity of roadway flowing from one abutment to another.

As far as possible, avoid intersecting lines.Multiplicity of colours for a pier and /or large number of piers for long bridge with small spans leads to disorder. Avoid large number of equal spans for long bridge as it leads to monotony and uneasiness. Avoid sudden increase in support section like large well showing out of water.

5.2.5 CHARACTER

Character is an element of man made environment and expressed by its effect on the human using it. The structures today need to reflect technological excellence and look modern. Use of uniform depth beam for long river bridge with low clearance above water level produces stiffness. This can be broken by curved soffit. However, highly curved soffit with depth at centre disproportionately reduced, is unpleasant.

5.2.6 COLOURS

Colours have a significant effect and can attribute to balance and tension. However in bridges concrete being the material, choice is limited.

5.2.7 FUNCTIONALISM

In bridges form follows function. Functional efficiency never conflicts with form. It generates simplicity in form and aesthetic quality. Ornamentation of larger surface of piers, abutments, retaining walls by suitable surface treatment for texturing can give heightened aesthetic quality and character to a bridge especially in an urban environment.

5.2.8 ENVIRONMENTAL INTEGRATION

Integration of bridge structure with environment is most important need of modern bridges. Simplicity in form may suit open rural lands. Wider river crossing may demand bridges compatible with majesty of river. Structures built in urban environment should have special quality because it has large impact on people and their habitat. Very slender beams with stiff parallel faces on tall thick piers are incompatible with high mountain backdrop. A long bridge in hilly terrain should never be in straight alignment. It has to pickup movement of terrain.

5.2.9 COMPLEXITY

It is part of second order aesthetics. Complexity results from a deliberate disregard for order, harmony and symmetry. In short the simplicity of form and proportion with load masses in locations where most effective, makes pleasing appearance of bridge structure.

5.2.10 HORIZONTAL AND VERTICAL GEOMETRY

Aesthetics is a matter of taste and therefore it is not possible to codify the rules, which are to be followed in the Designs of bridges. However, few criteria like alignment (horizontal and vertical) with proper geometrics can add to the architecture of bridge. The approach gradients either for a valley curve or a summit curve shall have a continuity without break. The change of slope should be gradual without any abrupt or sudden change.

The approach to a bridge with a kink as shown below in fig 5.16 shall be avoided. The approach gradients with two vertical curves at two ends with the bridge deck straight is preferable to the kink. But a convex curved bridge deck in the vertical plane having a single curvature will be most preferable