FUTURE TRENDS IN DESIGN & CONSTRUCTION OFBRIDGES

Introduction Unprecedented developments both in the bridge technology as well as towards appearance. Technically, very long span bridges can be built with present-day materials. Spans are becoming bigger e.g. bridge on Chenab river in J & K, one of the longest arch span (480m) in the world. (Fig.1) Consideration of the entire life cycle justify driving the span upwards. Society increasingly willing to pay for the convenience and aesthetics of long span bridges. Cable-stayed bridges encroaching on the type of spans traditionally associated with suspension bridges. e.g. Longest cable stayed bridge constructed in the world in Japan (Tatara – 890m span). (Fig.2) Cable-stayed bridges encroaching on the type of spans traditionally associated with suspension bridges. e.g. Longest cable stayed bridge constructed in the world in Japan (Tatara – 890m span). (Fig.2) 1,000m barrier breached by Stonecutters bridge in Hongkong and Sutong bridge in China and 1,200m span already planned. Growth in smaller suspension bridges with spans of perhaps 100m to 500m.

Emerging trends in the design and construction of bridges Architectural Appearance Appearance plays a far greater role in bridge design today than it did a few years ago. Greater awareness of the importance of a bridge design that properly fits its setting e.g. Bow String Girder Bridge across Thane Creek in Mumbai region provides a visual treat to the rail commuters. (Fig.3) A client wants an artist to dictate the design, the architect to interpret, the engineer to make it work. The ‘wow’ factor can come with something that is both original and simple in concept e.g. much-praised Gateshead Millennium Bridge (Fig.4)

Emerging trends in the design and construction of bridges Security hazard Multi-hazard protection growing importance against blasts and earthquakes. Massive increase in armoury of tools to protect bridges. Developments in areas such as understanding of seismic activity, techniques for risk assessment, means of predicting seismic response.Solutions envisaged like wrapping columns with glass/carbon fiber, energy absorbing devices, structural fuses to dissipate energy. Earthquake not a force but a deformation. New concept to provide sufficient capacity in deformation and allow bridge to move instead of trying to resist force.

Emerging trends in the design and construction of bridges (contd.) Increased Span Developments in cable technology a key parameter to increasing the span. Significant progress made by reducing the size of strand systems,adding features such as helixes around the cables. Damping important for long spans.Solutions such as tuned mass dampers, cross-cables or ‘aiguilles’ as used on the cable-stayed Pont de Normandie bridge in France. (Fig. 5) Today’s spinning equipment is competitive with preformed parallel wire strand systems.

Emerging trends in the design and construction of bridges (contd.). Taller Bridges Equipment developed for handling and driving piles of large diameter upto 4m and length more than 100m. Improvements in drill hole stability while drilling huge diameter holes. Use of large diameter piles made it possible to position the pile cap further above the river bed. Larger piles can have a long unsupported length enabling the footing to be constructed far closer to the water surface.

Emerging trends in the design and construction of bridges (contd.) Getting stronger Introduction of a new material will only be successful if a new concept of structure can be developed to use that material e.g. use of stone to build arches. Steel made long span trusses box girders possible. High strength wires made suspension bridges possible. Together with concrete by way of prestressed concrete made long span concrete bridges possible. Ultra-high performance materials intoduced such as VSL’s cementitious material Ductal which is nearer steel than concrete.

Precast Components Pre-cast foundation, abutment, pier and superstructure units enable construction of bridges not in years but in months and weeks e.g. San Juan, Puerto Rico (Fig. 6)  erected from the ground up in just 21 consecutive hours Lake Ray Hubbard Bridge in Dallas, USA used pre-cast bent caps (Fig.7)  for all the 43 pier caps reducing construction time from 8-9 days to 1 day for each pier cap(Fig.8)   Pre-cast units eliminate costly field formwork as well as extend seasonal construction time. Emerging trends in the design and construction of bridges (contd.)

New materials Use of advanced composites started e.g. stainless steel. Different types of applications for composites e.g. use in post-tensioning, plates and strips, FRP decks, stay cables, wraps to provide seismic protection and enclosures to protect structures. For rehabilitation also e.g. composite rods to replace the top mat of steel reinforcement effectively increasing the cover to steel. FRP bridge decks gaining popularity in USA.

Emerging trends in the design and construction of bridges (contd.) Increasing durability Increased durability being demanded e.g. plastic ducts. Introduction of enhanced protection through use of electrically isolated systems. Change in the bridge deck design e.g. in the traditional design, there would normally be some kind of supporting structure generally topped by a concrete deck which could easily be replaced but now in the modern bridge, the deck is part of the structure and holding it up,its replacement could become more complex and expensive.

Emerging trends in the design and construction of bridges (contd.) Conclusion In India, so far one cable stay bridge constructed spanning across railway track near Bangalore. (Fig.9). Another one under construction at Chirayatand near Patna. Significant growth expected in demand for long span bridges.

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