Bridge Construction
Bridges are not only a functional part of transportation but also an identity of the place where it is built. We can see numerous examples of Smart Bridge Construction around us. Golden Gate Bridge (California), Tower Bridge (London), Sydney Harbor Bridge, Brooklyn Bridges are some of the examples. All those bridges are constructed during a time of limited technologies and machinery.
In today’s context, from the design to construction the entire concepts of bridges has been changed and it’s mainly because of the advancement in technology and availability of new construction materials etc. Nowadays, designers are always eager to introduce a symbolic aesthetic architecture or a unique touch to the bridge design to get people an emotional touch with it. In light of advanced technology, the concepts of bridge design got evolved so far and we are discussing some of that;
Low Hindrance Bridge Replacement
Most of the conventional highway bridges are statically indeterminate three or four-span concrete plate bridges. While using it as an overhead highway bridge, most of the case the bridge takes more time, space, and cost in construction of pillars. As you can see in the figure below, without the piers the bridge would be more advantageous.
To tackle this problem new concept has been derived which is replacing the statically indeterminate bridge with a single-span bridge. The challenges that arise due to adopting this method can be solved by using innovative materials like steel, steel-concrete composite structures, precast structures, or high-performance prestressed concrete plates. This makes the necessity of exploitation of Advanced Cementitious Materials (ACM) with other innovative construction materials.
Smart Bridge Construction Concepts
Smart Bridge Concepts is a new concept that is focused on the utilization of advanced technologies and design parameters in bridge engineering to meet current and future demands (also address the shortcomings like durability, low maintenance, short construction time etc.). The smart bridge concepts basically stand on three fundamentals. ACM (Advanced cementitious materials), ABC (Accelerated bridge construction) and Advanced design tools. Finally, it’s all linked to detailed Structural Health Monitoring (SHM).
Advanced Cementitious Materials (ACM):
As mentioned earlier ACM primarily used to obtain slender bridge. Most of the case Ultra-High-Performance Concrete (UPHC) is preferred. UPHC is a kind of Advanced Cementitious Material that has been used in prestressed concrete. girder simple span bridge, precast concrete deck and precast bridge components etc. UHPC holds up a compressive strength of 120Mpa also have good tensile strength, toughness and ductility.
But the more application of ACM is limited here and this is mainly because of the absence of technical and economic feasibilities. But many highway projects which are based on UHPC had been carried out in Malaysia over the years and this mainly because of its durability and low maintenance in remote areas. Now UHPC is getting wild recognition across the globe especially in the construction of the long single-span bridges.
Accelerated Bridge Construction (ABC)
Accelerated Bridge Construction technique is developed to reduce the construction time and minimize traffic conjunctions faster. This ABC technique only adopted in regions that experience low seismic activity. Regions having high seismic activity, ABC is limited because of the concern over the strength performance of precast components and their connections.
An illustration of ABC is given below. Self-Propelled Modular Transporters (SPMT’s) is used to transport the precast bridge deck. The high slenderness and reduced self-weight are very important for lifting and halting the component in position. Figure b is the replacement project which is the I-84 bridges over Marion Avenue in Southington Us. The work duration would have crossed months if it is followed by traditional construction practices. Here they followed SMPT’s method and the work is completed within four days.
Structural Health Monitoring Techniques in Bridge Construction
Structural Health Monitoring system is very crucial in the Smart Bridge concept. The stability analysis of the bridge is extremely based on the data from this. Currently, there are different types of equipment are available to carry out the analysis such as strain gauge, fibre optics, strain sensors, vibration monitoring, image analysis etc. a common challenge in this system is in the conversion of collected data into useful information. S
HM contributes huge support in innovative bridge design and construction whether there is no specific design codes are available. This system helps us to monitor the behaviour of bridge in various environmental conditions and suitable action can be taken effectively.
3 types of Bridges Proposed for Smart Bridge Construction
The basic principle of the Smart Bridge concept is to replace the multi-span with single-span structures made of UHPC with minimum foundation requirements and alignments. The precast industry now brings up many innovative ideas on bridge design, especially in the slender bridge. The figure is the design examples of precast slender bridges.
The left one is which the deck is comprised of a prestressed girder box arranged in parallel. The middle one is a post-tensioned UHPC modular segmental girder bridge. The last one is UHPC load-bearing girder on which the deck is hanging. In Netherlands these kinds of bridges widely used in the construction of short and medium span bridge construction.
Multiple girders placed adjacent to each other and connecting post-tensioning in a transverse direction making it faster in construction and economical. Here two UHPC girders with deck hanging (the last one in the figure) possess good stiffness and load-carrying capacity.
Energy Dissipation in Bridges
Energy Dissipation device is a kind of damping device which absorb the input energies due to vibrations, earthquake, wind and helps to maintain the stability. Mostly this is provided in DCR (Dissipative control Rocking) System.
The figure below shows the working of internal and external energy dissipators in bridges. In internal dissipators, the mild steel bars are grouted into the duct of precast duct element and also it is unbounded to a certain limit to prevent premature yielding due to seismic load. Sometimes the bar is fused by reducing its diameter to maintain inelastic deformation.
In the case of external dissipators, there is a wide range of devices are available. Buckling Restrained Bracings, Viscous Dampers, Friction Dampers, High Force to Volume Dampers. The working principle is shown in the above figure.
Future Bridges
There are different statements are floats around us based on Future Bridge and their appearance. Will it same as today or will new big changes occurs in bridge engineering. As we go through the detailed analysis, there might not be a big change that can happen in bridge design, but the construction practices and use of materials may evolve slowly in a better direction.
In US, most of the bridges are 50yr old and still doing well. i.e. here just only needed periodic maintenance. Fast developing countries like China are currently working on innovative bridge construction. They have constructed 689400 highway bridges with a total length of 33000 km.
The effort of maintaining and life cycle approach towards the bridge is changing drastically. I.e. many new concepts are popping up in bridge robustness and resilience and it is appearing on design codes and practices for the construction of safer and durable bridges. And it is mostly because of the rise in concern of change in climate and natural hazards etc.