Transportation Infrastructure Needs and Developments

Dr. N. Subramanian, Consulting Engineer, Gaithersburg, MD, USA

Introduction

Mobility is fundamental to economic and social activities of any country. Mobility is provided by the transportation infrastructure and this has a huge impact on the development and welfare of the population. In several countries, lack of transportation infrastructure and regulatory controls are jointly impacting economic development. Moreover, transport systems are among the various factors affecting the quality of life and safety in a city. Though there are several modes of transport, like road, rail, air, and water, in many countries road networks cater to the majority of transportation needs. For example, in India, as per the National Highways Authority of India, about 65% of freight and 80% passenger traffic is carried by the roads. The National Highways carry about 40% of total road traffic, though only about 2% of the road network is covered by these roads. Rural areas have poor access 33% of villages in India still do not have all-weather road and remains cut-off during monsoon. Average growth of the number of vehicles has been around 10.16% per annum over recent years. (The Automobile industry in India is rapidly growing with an annual production of over 2.6 million vehicles.) Hence only roads and bridges are considered in this article.

Demand for freight and passenger transport, particularly by road, has typically grown 1.5 to 2 times faster than GDP in most developing and transition countries. Public investment in transport typically accounts for 2.0 to 2.5 percent of GDP and may rise as high as 4 percent or more in countries modernizing or building new transport infrastructure. GOI has raised the investment in infrastructure development from 4.7% to 8% of GDP in 11th five year plan. According to recent estimates by Goldman Sachs, India will need to spend $1.7 trillion on infrastructure projects over the next decade to boost economic growth, of which $500 billion is budgeted to be spent during the Eleventh Five-Year Plan [It may be of interest to compare it with the situation in USA: Complex calculations done by the American Society of Civil Engineers (ASCE), revealed that decaying roads, bridges, railroads, and transit systems are costing the United States $129 billion a year. ASCE's 2009 Report Card for America's Infrastructure graded the America's infrastructure a "D" based on 15 categories, and estimated that USA needs to invest approximately $2.2 trillion from 2009 – 2014 to maintain infrastructure in a state of good repair. The 2009 Report Card, gave grade "D-" for roads, and grade "C" for bridges (www.infrastructurereportcard.org). It noted that nearly one-third of roads in USA are in poor or mediocre condition, 25% of bridges either structurally deficient or functionally obsolete!]. With the need for such a large scale development of infrastructure in India, the way forward is to move to fast track construction mode, to upgrade quickly the design standards and specification to international standards, to modernize the construction techniques, to use new construction materials, and to use some innovative techniques..

The urban transport situation in large cities of India is deteriorating, leading to high transportation cost to road user. The deterioration is more prevalent in metropolitan cities where there is an excessive concentration of vehicles. Commuters in these cities are faced with acute road congestion, rising air pollution, and a high level of accident risk higher transport costs, but also delays rendering supply chain management unreliable. Many new technologies have been developed to tackle the deterioration of concrete due to corrosion.

Highway Bridges

Highway bridges are critical links in India's transportation network that should be maintained to remain safe and functional during their service lives to enable personal mobility and transport of goods to support the economy and ensure high quality of life. (Failure of any crucial bridge not only results in precious loss of lives, injury and huge property loss, but also affects the economy of the region). For example, it was found that the collapse of I-35W Mississippi River Bridge (which was used by more than 140,000 vehicles per day) resulted in huge economic loss to Minnesota –about $17 million in 2007 and $43 million in 2008 (more details about this bridge failure may be found from Subramanian 2008). It is also important to realize that lessons should be learnt from each failure, and improvements in the design result from these failures]. Both owners and users of bridges expect their bridges to have a service life of 50 to 100 years, with only routine maintenance. But demands on most of the bridges have been increasing annually because of growing traffic volumes, higher loads, and aggressive environments (e.g. deicing salts, frequent freeze- thaw cycles, etc.). These conditions, coupled with the inadequate funding allocated for maintenance, have led to the accelerated aging and extensive deterioration of these critical structures.


A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it.

There are six main types of structural forms in bridges: beam/frame bridges, cantilever bridges, arch bridges, suspension bridges, cable-stayed bridges and truss bridges (see also Fig. 1). These bridges may be built using a variety of materials and currently they are mainly built using reinforced concrete, prestressed concrete and steel (in India steel bridges are mainly built for the Railways). Longest bridges in each category are listed in Table 1 (it is of interest to note that the span lengths have reached their physical limits with today's materials). Fig. 2 shows the 5.6 km long Bandra-Worli Sea link in Mumbai, with its 8 lanes of traffic opened in March 2010, has two 250m long cable stayed spans. Note that the length of a bridge has a strong impact on its construction cost. In industrialized countries, labour costs can easily exceed half of the total construction cost of the bridge, unless highly mechanized erection methods used for the construction.


Bridges may also be classified as railroad, highway, or road and pedestrian bridges, depending on their use. In addition to the normal dead, live, wind and earthquake loads, they have to be designed for impact loads. The impact of moving vehicle loads is a complex phenomenon and depends on the speed of the moving vehicle, its mass relative to mass of the bridge, and the irregularities in the bridge surface and in the wheels of the vehicle.

Advances in deck technology are producing stronger, lighter decks. Orthotropic and exodermic decks are becoming increasingly popular on long-span structures as a means of reducing dead load. Bearings, joint systems, and seismic retrofitting components are becoming increasingly efficient as more large-scale testing facilities are built (Hill et al., 2004). Integral Bridges are growing in popularity for urban flyovers and for short to medium span bridges, which help in eliminating bearings and expansion joints all together.


The greatest area of concern with regard to cable-stayed bridge construction is protection measures for the stay tendons. The areas of focus include the use of epoxy versus grout, encased or non-encased stay cables, and a variety of issues regarding the protection of these key bridge elements. Other stay cable research topics are the effects of wind-induced vibrations, anchorage details, and determination of in-service stay tensions (Hill et al, 2004).

Construction Methods

Bridge construction is changing as the new millennium begins. New construction techniques and new materials are emerging. Such changes are not only required for long span bridges, but also for short- and medium-span bridges, which represent the vast majority of bridges constructed in India and abroad.

To meet the challenge of demand for infrastructural growth, construction time for these bridges will have to decrease, and traffic flow will need to be maintained during construction, often within a few feet of workers and equipment. Consequently, public agencies and contractors will seek new materials and methods that enable shorter construction times without compromising on the safety and durability of these bridges.


Segmental concrete bridges may be precast by either the long line or short line system. The segments may also be cast-in-place. They may be erected by the method of balanced cantilevers [see Fig. 3(a)], by progressive placement span by span, or by incremental launching method- launching the spans from one end. Almost any combination may be used to provide the most cost-efficient use of materials, labor, and equipment (Rosignoli, 2002).

In pre-cast bridges, the concrete segment may be constructed on the ground, and then transported and hoisted into place. As the new segment is suspended in place by the crane, workers may install steel reinforcing that attaches the new segment to preceding segments. Each segment of the bridge may be designed to accept connections from both preceding and succeeding segments. The process is repeated until the span is completed. Such a method adopted for Delhi Metro is shown in Fig.3(b).

Until year 2005, Indian codes did not cover design and construction of segmental superstructures. Now, a new document IRC: SP 65-2005 has been published. This document covers design and construction aspects of segmental bridges (Gupta 2009).

Innovations

The basic requirement of structural safety is that capacity should always exceed demand. Though new bridges are designed to satisfy the above condition, as they age their structural capacity decreases, but their demands increase over time. Assessing the current capacity of an aging structure to support growing demands is not an easy task.

With the emerging field of structural health monitoring, it is now possible to improve future estimates of structural degradation. Sophisticated sampling and analysis, better knowledge of how wires degrade over time and non-invasive testing of wires inside cables allow engineers to predict the rate of degradation and determine when cables require replacement in cable supported and cable stayed bridges. Several bridges in the world are now wired with sensors, which are monitored and the data intelligently processed by remote computer systems. For example, the I-35W Saint Anthony Falls Bridge, which replaced the collapsed I-35W Mississippi River Bridge, is made of high-strength concrete and has 323 sensors that regularly measure bridge conditions such as deck movement, stress, and temperature (the data is compiled and analyzed by the University of Minnesota).

New Materials

Several new materials have been developed in the past to save the natural resources; solve the problem of corrosion in concrete bridges, provide quick erection, etc. Some of these solutions are presented below:

The first High Performance steel (HPS) bridge in the United States was opened to traffic in December 1997 in Snyder, Nebraska. Three grades of HPS are available now: HPS-345W, HPS-485W, and HPS-690W, out of which HPS 485W is widely used. The bridge in Tennessee is a two-span continuous structure located on state Route 53 over Martin Creek in Jackson County. This bridge consists of three continuous welded plate girders, fabricated from HPS-485W, 2 m deep and spaced at 3.2 m centers. These plate girders act compositely with a cast-in-place concrete deck slab of thickness 212.5 mm. The bridge is jointless, having integral, pile supported abutments.

Cost estimates prepared by the Tennessee Department of Transportation indicate that the steel weight was reduced by almost 25% compared to the original grade 345W design. Because HPS-485W costs slightly more than grade 345W steel, this resulted in a 16% net reduction in the total cost to fabricate and erect steel elements for this bridge.

Since steel reinforcements corrode and reduce the design life of structures, many new materials have been developed which will eliminate corrosion. The Beddington Bridge at Calgary, Alberta, Canada is the first smart highway bridge which is prestressed by carbon fiber reinforced polymer (CFRP) tendons in 1992. Taylor Bridge in Headingley, Manitoba, Canada is another example of smart long span highway bridge which uses CFRP for prestressing tendons and shear reinforcement for the bridge girders. In this bridge, CFRP was also used to reinforce part of the deck slab, while glass fiber reinforced polymer (GFRP) reinforcements were used in part of the barrier wall (Rizkalla et al, 1998). The Salmon River Bridge in Halifax, Nova Scotia, Canada is based on another innovative concept using polypropylene fibre reinforced concrete (thereby providing a reinforcement free concrete deck slab) and a new system of regularly spaced transverse steel straps which were welded to the top flange of the steel girders that provide lateral restraint to the girders. All these bridges were instrumented with optical fibre sensors monitored remotely from a central station through telephone lines, eliminating the need for costly site inspections (Mufti and Neale, 2008), as there are no code provisions for such innovative concepts, experimental tests were conducted at the University of Manitoba, Canada, to study their behaviour and also to validate the designs.

Engineered Cementitious Composites (ECC), developed by Prof. Victor C. Li, and associates at the University of Michigan, is a brittle matrix reinforced with randomly distributed short fibers and is designed based on the micromechanics of crack initiation, fiber bridging and steady-state crack propagation. Analogous to ductile metal where strain hardening is accompanied by dislocation damage to the material, ECC undergoes tensile strain-hardening accompanied by the formation of multiple micro-cracks (Li, 2011). Macroscopically, the brittle fracture mode of normal concrete is turned into a "plastic yielding"-like mode in ECC. The 972m long cable-stayed Mihara Bridge in Hokkaido, Japan employed a 38 mm thick continuous ECC overlay on a steel plate, and opened to traffic in 2005. In this application, the high tensile ductility of ECC was converted into higher flexural resistance with a thinner cross section of the bridge deck.


Traditional concretes used in bridge elements require vibration during construction in order for the wet concrete to fully fill the casting forms. Even with vibration, normal concrete structures require significant labour after deshuttering to fill 'bug' holes and improve the surface finish. Self-compacting concrete (SCC) was first developed in Japan in the 1980s to eliminate some of these construction problems. SCC is highly workable and flows through congested reinforcement areas under its own weight alone, filling formwork without the need for applied vibration and resulting in a structure free of voids. The highly flowable nature of SCC is due to very careful mix proportioning, usually replacing much of the coarse aggregate with fines and cement, and the addition of special chemical admixtures. Constructing bridge girders with SCC has the following advantages: (1) Low noise-level in the plants and construction sites, (2) Elimination of problems associated with vibration, (3) reduced labour for construction operation, (4)Faster construction, (5)Improved quality and durability, and (6) Higher strength. SCC is being used increasingly in a number of bridges in Japan, USA, Europe, and in India. More details about SCC in bridge construction are provided by Bartos, 2005.

Bridge piers often require seismic or regular repair, rehabilitation and/or strengthening. Repairs may be necessitated by corrosion of reinforcing steel and general deterioration of materials. Strengthening may be necessary to resist larger shear forces and confine the column so that it can safely resist larger loads. Design and construction with conventional materials lead to expensive and time-consuming solutions. A novel approach developed by Prof. Ehsani that uses carbon or glass Fiber Reinforced Polymer (FRP) wraps that are applied like wallpaper, reach three times the strength of steel in 24 hours and leads to significant construction savings in time and materials (Saadatmanesh et al 1997).

Bridges of the Future

The inflatable bridge system developed at the University of Maine, by Dr. Habib Dagher and associates could be used to repair or replace any existing deteriorating bridge, faster and cheaper. This bridge nick named as a bridge in the back-pack, consisting of carbon-fibre tubes can be rolled and transported to any site, inflated and hardened with resins to produce sturdy arches, and filled with concrete. It may be covered with sand and asphalt and used (see Fig. 5). In 2009, an 8.5m long bridge of this type was first built by Advanced Infrastructure Technologies in Maine in just 11 days, instead of the usual 2 months, and has an expected life of 100 years. The "Bridge in a Backpack" serves three purposes: it is a stay-in-place form for poured concrete; provides exoskeleton reinforcement for existing bridges; and serves as a protective layer for concrete. This bridge is agreener alternative to concrete and steel construction and saves money, reduces fabrication timelines, lessens transportation costs, accelerates bridge construction, and dramatically reduces lifetime maintenance costs.


Another innovative concept called the Hybrid-Composite Beam (HCB) is structural member akin to a prestressed concrete or steel beam, and is shown in Fig. 6. The FRP (Fiberglass Reinforced Polymer) outer shell provides shear strength and encapsulates the tension and compression elements.The compression element is a concrete arch. The tension element is steel reinforcement that runs longitudinally the length of the beam and ties the two ends of the concrete arch together. Essentially the HCB is a tied arch in a fiberglass box where 90% of the strength is provided by steel and concrete. The encapsulating FRP shell provides maximum protection from the elements for the steel and concrete ensuring an extended service life and minimal maintenance.

Sustainability of Bridge Construction

Sustainability is now recognized as a key issue which must be addressed in the design, construction and life long maintenance of bridges. A sustainable bridge may be designed as a structure that has been built quickly but efficiently to last a long time with an optimal use of resources, as well as minimal disruption of the surrounding environment and zero tolerance for wasted materials. Hence we should give more importance to the 'life time cost'/'life time energy use' than to the 'initial cost'. In this context, life cycle cost analysis and energy use analysis assumes significance, though there are no straight forward methods to access them. Since corrosion is the main cause for the deterioration of concrete bridges, integral bridges with protective coatings in the form of silane or 'Pavix' may provide maximum resistance to chloride penetration, and result in less life time cost. In the United States, there is currently no national standard to rank sustainable bridges like the U.S. Green Building Council's (USGBC) benchmark LEED^® ((Leadership in Energy and Environmental Design) standard for buildings. However, Whittemore recently showed that the LEED concepts could be extended to Bridges also, except the category on Indoor Environmental Quality (Whittemore, 2010)

Bridge Aesthetics

Bridges dominate our freeway landscape and the public is becoming aware of the appearance of bridges and the effects they have in the visual environment of their communities. The consensus on bridge aesthetics over the years has emphasized the following basic criteria: (1) Simplicity, (2) Good proportions of the various elements with an emphasis on thinness, (3) the bridges ability to match its surroundings, and (4) their demonstration of how the structure works. The largest parts of the bridge – the superstructure, piers and abutments – have the greatest impact followed by surface characteristics (color/texture) and finally the details (http://www.bridgeaesthetics.org/). More details on bridge aesthetics may be found in Subramanian, 1987 and Leonhardt, 1982.

Roads and Pavements

India has a network of National Highways connecting all the major cities and state capitals, forming the economic backbone of the country. As of 2005, India had a total of 70,934km of National Highways, of which 200km are classified as expressways. According to 2009 estimates, the total road length in India is 3,320,410 km, making the Indian road network the third largest road network in the world. At 0.66km of highway per square kilometre of land the density of India's highway network is higher than that of the United States (0.65) and far higher than that of China's (0.16) or Brazil's (0.20). Fig 7 shows the Mumbai-Pune Expressway, India's first expressway.

Innovations in Roads

Roads are often constructed using asphalt (specifically, asphalt concrete) and concrete. Cement concrete roadways are typically stronger and more durable than asphalt roadways. They can easily be grooved to provide a durable skid-resistant surface. Disadvantages are that they typically have a higher initial cost and are perceived to be more difficult to repair than asphalt roads.

Asphalt (bitumen) Emulsion

A number of new technologies allow asphalt to be mixed at much lower temperatures. These involve mixing the asphalt with petroleum solvents to turn the asphalt into an emulsion. Asphalt emulsions contain up to 70% asphalt and typically 2.5% to 5% (by weight of residual asphalt content) of polymer. SBS (Styrene-Butadiene-Styrene) and SBR (Styrene-Butadiene Rubber) are the most commonly used polymers, and they generally yield the best performance. Polymers can dramatically improve the performance of emulsions when used properly.

Asphalt emulsion surface treatment is a broad term used to denote several types of asphalt and asphalt- aggregate applications, usually less than 25 mm thick and applied to any kind of road surface. The road surface may be a primed granular base, or an existing asphalt or Portland cement concrete (PCC) pavement.

A single surface treatment, commonly called a chip seal, involves spraying asphalt emulsion and immediately spreading and rolling a thin aggregate cover. In the United States, chip seals are typically used on rural roads carrying lower traffic volumes. In Australia and New Zealand, chip sealing is referred to as a "sprayed seal" or "tarseal" and is used on a larger percentage of roads, both rural and urban. For multiple surface treatments, the process is repeated a second or even a third time with the aggregate size becoming smaller with each application. A sandwich seal is a relatively new technique in which a large aggregate is placed first, asphalt emulsion (normally polymer modified) is sprayed onto the aggregate, and immediately followed by an application of smaller aggregate on top that locks in the seal. A Cape seal is a single surface treatment followed by a slurry seal or micro-surfacing to fill in the voids between large aggregates.

A slurry seal is a mixture of dense graded aggregate, asphalt emulsion, fillers, additives and water. The slurry seal is applied as a thin surface treatment using a specially designed slurry seal machine. Microsurfacing is much like slurry seal, but through the addition of polymers and the use of specialized design techniques, micro-surfacing provides greater durability and can be placed thicker.

Cold mixed asphalt can also be made from asphalt emulsion to create pavements similar to hot-mixed asphalt. Cold mix asphalt Paving is eco-friendly, used at ambient temperatures, and reduces harmful emissions, fumes and energy needs. It can be easily recycled and maintained, minimizes transportation and material costs, and is cost-effective for upgrading rural roads.

Bio-asphalt

For millions of people living in and around cities, the phenomenon of heat island is of growing concern. Due to this urban and suburban temperatures are about 1 to 6°C hotter than nearby rural areas. Elevated temperatures can impact communities by increasing peak energy demand, air conditioning costs, air pollution levels, and heat-related illness and mortality. These concerns prompted the development of Bio-asphalt, which is an alternative to regular asphalt, made from non-petroleum based renewable resources. Such bio-asphalts can be colored, reducing the temperatures of road surfaces and subsequently urban heat islands. It also produces negligible levels of fumes during the laying and can be stored and transported at room temperature.

Shell Oil Company paved two public roads in Norway in 2007 with vegetable-oil-based asphalt and a bicycle path in Des Moines, Iowa, was paved with bio-oil based asphalt in 2010.

Whisper Concrete Pavements

Exposed Aggregate Concrete Surface (EACS), formerly known as 'whisper concrete', can provide a long life road surface with lower traffic noise than traditionally surfaced roads, offering comparable skid resistance. The exposed aggregate top surface forms a matrix of interconnected path below the plane running surface through which water can pass, to maintain a high speed skidding resistance, and assist in reducing tire/road surface noise. EACS was first used in Denmark and later developed in Belgium. The Austrians refined the Belgian process, discovering that by reducing the size of the coarse aggregate at the road surface, the tire/road noise levels could be substantially reduced (Descornet, and Fuchs,1992). Two layer construction was chosen to produce an economic solution, though it may be 10% costlier than regular pavements. A suitable retarder should be used which will retard sufficiently the action of the cement at the surface of the top layer so that the target texture depth can be achieved by the brushing operation.

Pervious Concrete Pavements

The latest solution to rain water runoff and associated water pollution problems is pervious concrete pavements. Pervious concrete has a 15-25% void structure, allowing for 120-320 liters of water per minute to pass through each square metre, with typical flow rate of 3.4 mm/s (200 L /m2/min) or more (see Fig.8).

Pervious concrete is a performance-engineered concrete made with controlled amounts of cement, coarse aggregates, water, and admixtures to create a mass of aggregate particles covered with a thin coating of paste. A pervious concrete mixture contains little or no sand, creating a substantial void content. Pervious concrete has been used in the United States for almost 40 years, Australia, Europe, and in many Olympic venues in and around Beijing. Increased awareness of environmental issues, however, has recently given much importance to pervious concrete as a solution to pollution and erosion associated with pavement runoff. More details about pervious concrete may be found in www.perviouspavement.org & Subramanian 2010.

Green Highways

Recycling industrial by-products and construction materials in highway construction can help generate "green highways" where use of virgin materials and large amounts of energy is avoided. A green highway integrates transportation functionality and ecological sustainability. The technologies that are used in green highways are: (1) Bio-retention, (2) previous pavement, (3) Environment-friendly concrete pavement and use of industrial by-products in sub-base, and embankments, (4) Development of Riparian forest buffers, (5) Wetland Restoration by passive or active approaches, (6) Stream restoration, (7) Development of Wildlife crossings, and (8) Soil amendments. More details about Green Highways may be found in www.greenhighways.org & Subramanian, 2011.

Summary

Transportation infrastructure is necessary for the movement of goods and people across the country. Development of such a network of roads and bridges is expensive and needs to be maintained. Failure of bridges or roads will affect the local economy significantly. The span length of different types of bridges has increased considerably in the recent past; however we have reached their limits with the present day materials. Several innovative materials and methods have been invented to extend the life span of bridges and to keep their maintenance cost low. In future, more bridges will be provided with sensors, which can be remotely monitored for defects. Sustainability of bridges requires careful life cost and energy use analysis. Similar innovations in materials and techniques in road and pavements have been developed. Pervious pavements and other sustainable measures such as recycling are necessary to develop green highways.

References

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Dr. N. Subramanian, a consulting engineer living in Maryland, USA, is the former chief executive of Computer Design Consultants, India. A doctorate from IITM, he also worked with the Technical University of Berlin and the Technical University of Bundeswehr, Munich for 2 years as Alexander von Humboldt Fellow. He has more than 35 years of professional experience which include consultancy, research, and teaching. Serving as consultant to leading organizations, he designed several multi-storey concrete buildings, steel towers, industrial buildings and space frames. A reputed author of more than 200 technical papers in National and International journals & seminars, Dr Subramanian has also published 25 wide selling books. He has also been a reviewer for many Indian and international journals. He is a Member/Fellow of several professional bodies, including the ASCE, ACI, ICI, ACCE (India) and Institution of Engineers (India) and a past vice president of the Indian Concrete Institute and Association of Consulting Civil Engineers (India). A mentor in Structural Engineering Forum of India, he is a recipient of several awards including the Tamilnadu Scientist award.