Innovation in Bridges Components and Materials

    Innovation In Bridges

    By Er. Vivek Abhyankar & Dr. N. Subramanian

    Engineering innovation in infra development

    The Infrastructure Industry is continuously evolving; new roads, elevated corridors, expressways, railways, dedicated corridors, metros, mono-rails are being constructed all the time. They also require constant maintenance and up-gradation. All of this involves huge capital investment and a manpower. Authorities such as NHAI, MSRDC, MCGM, KMDA, DMRC, Indian Railway, PWD and other state/central/private organizations are continuously engaged in the planning, monitoring and commissioning of the various infrastructure development projects as well as developing codes and standards for state-of-the art construction. Item-rated contracts have given way to BOT (build-operate-transfer), DBOT (design-build-operate-transfer), EPC (engineering-procurement-construction), and Turnkey contracts. The responsibility of the contractors has increased manifold, and to maintain or even to sustain the profit margin has become a challenge.

    Modern infrastructure development projects not only demand quality, safety, timely completion, ease of construction, functionality (efficiency/utility), and aesthetics from professionals, but also minimum cost. Such demands can only be fulfilled by engineered innovations. Often engineering innovation is confused with doing something ‘non-standard’ or ‘non-traditional’ or ‘non-routine’, and ‘cost optimization’ is also considered by a few as an innovation!

    Innovation In Bridges
    Figure 1: Perales Bridge in Spain - Foundation exposed due to scour (up to 4m depth) on left and additional forces acting on foundation due to scour (right)

    Real engineering innovation could involve a blend of a few traditional techniques with some innovative solutions for meeting the desired requirement / performance. Engineered innovations for bridges, for instance, involve suitable forms (shape/geometry), materials, and construction techniques/machinery to obtain the desired results. The engineered innovation is ‘purpose based’ or a ‘situation based’ treatment as no single bridge can be the same.

    Innovation In Bridges
    Fig ure 2 and 3: Interlocked concrete blocks used for scour protection

    This article is an attempt to explain engineered innovation through some case studies of bridges, which we hope will be of benefit to bridge planners, highway engineers and structural designers, as well as R&D professionals.

    Innovation in bridge foundations

    Innovation in Bridges
    Fig.4 Hammer head type pier (www.civildigital.com) Fig. 5 Cap and column pier (www.civildigital.com)
    The most uncertain and challenging part of a bridge design and construction is the ‘foundation’. During the design process, various aspects such as capacity of strata, its stability, seasonal variations, and adjoining structures’ foundations, have to be assessed (Heggade, 2017). But at the time of tenders, this information may not be available readily. At such a juncture, the structural engineer has to depend on his past experience and judgment and by conducting a local enquiry. Bridge foundations experience mainly three challenging situations:

    Deep foundation: When the load bearing strata is softer or when the loading itself is heavy (for long span bridges). Foundation in hard strata: When the foundation is placed in hard rocky strata (with N value > 100), then the depth of the foundation will be less; this requires proper anchoring of foundation in the hard rock.

    Foundation in deep waters: When the foundation is placed in deep rivers or seas.

    When the foundation of a bridge is in major rivers (type ‘a’ and ‘c’ together), the strata may be subjected to considerable scouring. The mean scour depth may be estimated as per IRC-78 clause 703.2. But the scour depth estimated could often be very high as the accuracy of the estimate depends on the accuracy of the geotechnical data and hydrological calculations of the flow. In such cases, use of scour protection blocks may be considered. Figure 1 shows a typical bridge foundation damaged /exposed due to scour. Fig.2 shows a foundation’s protection using ‘concrete inter-locked blocks’. Fig.3 shows a closer view of these scour protection blocks.

    Innovation in Bridges

    Interlocked concrete blocks can be used in small streams and rivers which are not perennial but have alluvial / weak soft strata (www.conteches.com). By using these blocks, the scour can be effectively controlled, leading to saving in the size of foundation and hence construction cost and time. However, in bigger perennial rivers like Ganga, Yamuna, Mahanadi, and Bramhaputra, the use of such blocks is difficult, but Indian clients / contractors should explore this as an effective option. (Ref. Vivek – 19, 22)

    Innovation in piers / pylons (substructure)

    Innovative design of the substructure of bridges is also possible (i.e. pier ad pier-caps). Selection of a type of pier depends mainly on the loads from superstructure, deck width, span length, pier heights, seismic zone, water / wind loads, and any underground utilities / roads.

    Innovation in Bridges

    Correct selection of pier type decides the success of a bridge project. Usually, in the case of river bridges, a wall type of pier is found to be very robust and is the most preferred. Wall piers offer minimal resistance to water and ice flows. Bridges in the olden days, constructed in stone masonry wall piers, are still standing. For wider bridges and also for the ‘integral-bridges’ (where the super-structure and the sub-structure are monolithic, without any bearings) a ‘pile bent type pier’ configuration is preferred. In the case of underlying road junction or some utility, where a regular pier may not be possible (due to heavy traffic the road cannot be stopped), a portal type pier is most appropriate.

    Innovation in Bridges
    Fig.10 Innovative Shape of Pylon of cable stayed bridge Fig.11 Innovative Shape of Steel Piers at Interchanges

    Tee type Hammer head piers should be considered for overpasses at high skews with tight alignment constraints. This type of pier provides an open appearance when supporting structures with long spans (see Fig. 4). It is more modern than the wall type and is commonly used when a taller pier is necessary. It consists of a rectangular or circular stem capped with a cantilever-type cap. It is cheaper to construct than a wall type pier because less concrete is used, and it is less intrusive to streams. It must be noted that two column piers are particularly vulnerable to collision damage because if one of the columns is destroyed, the remaining column will not be able to support the bridge, which will collapse. Hence, two column piers should be protected by a concrete barrier in front and a concrete grade beam installed between the columns to provide additional collision resistance and compensate for the lack of structural redundancy.

    Innovation in Bridges
    Figure 12 ‘V’ shaped piers in Woodrow Wilson Bridge over Potomac River, Maryland, Virginia (a seamless, box-girder bascule drawbridge) to reduce the bridge spans

    Multicolumn/pile bent or cap and column pier, as shown in Fig. 5, is commonly used, especially for highway overpasses. It consists of three or more round (1m diameter) reinforced concrete columns capped with a continuous pier cap (1 to 1.2m thick) forming a rigid frame. Note the use of concrete grade beam.

    Apart from the various regular options mentioned above (Figs 4 to 7), some innovative shapes of piers (in steel or concrete), as shown in Fig. 8 and 9 have been used. But these are mostly driven by the aesthetic requirements of piers rather than the utility or loadings. Other innovative shapes of pylons for a cable stayed bridge and at an interchange are shown respectively in Fig. 10 and 11.

    Innovation in Bridges
    Figure 13: Bridges with navigational clearance with pylon protection

    The ‘V’ shaped piers shown in Fig.12 are useful to reduce the unsupported span and hence ultimately useful to support longer spans (C/C length). Often in wider and deeper waterways the navigational clearance demands column-free space; also, the clearance below the bridge soffit is decided by the height of the maximum sized vessel used in the connected port. Normally, the vertical clearance required below road bridges is 5.5m, and in railway bridges up to 8m. However, in river bridges it could be more than 15m; this leads to taller bridge piers. In such taller river-bridge piers the vessel collision load becomes inevitable, and to avoid collision, a protection is provided all around the pier / pylon using armor stones / concrete blocks (tetrapod or acropods) as shown in Figs. 13 and 14 (see also Svensson, 2009).

    As mentioned earlier, in river bridges, a wall type pier is given preference over a column or portal type pier due to the robustness. In column type piers located in deep vigorous rivers in higher seismic zones like western Maharashtra (Konkan region), Jammu-Kashmir, and Himachal Pradesh, the issue of ductile detailing of piers become important, and the identification of the location of plastic hinges plays a vital role. Apart from ductility, the natural time period of vibrations of these piers and the resulting response reduction factor R varies significantly (see also Goswami and Murty, 2005).

    Innovation in Bridges

    Apart from the various shapes covered above, their aesthetics and structural considerations (loading, geometry etc), the green initiative deployed by Bangalore metro is the Vertical Gardening on the piers (Fig. 15). This was first carried out in the Mexico City in 2012. The plants grow around the metal frames, which are buffered against the piers with fabric to avoid damaging the highway structure. Vertical gardens serve as air filters and regulate heat, reducing temperature by as much as eight degrees and can reduce almost 10 decibels of noise pollution. Hydroponics is a technique of growing plants by using all required nutrients through water, and without soil. It requires minimum investment, maintenance, and consumes minimum resources.

    Table 1 Span of bridge and choice of super structure

    Typical Span Length Choice for Super structures*
    Up to 10m RCC solid slabs
    10m – to – 15m RCC solid slabs / Inverted Tee beams with top concrete (composite solid slab)
    15m – to – 20m RCC slabs / RCC I-Girders
    20m – to – 25m RCC / PSC I-Girders; voided slabs
    25m – to – 30m RCC / PSC I-Girders; PSC Box Girders; PSC-Voided slabs
    30m – to – 40m PSC I-Girders; PSC Box Girders; PSC – U, Steel I-Girders
    40m – to – 50m PSC Box Girders / Steel Trusses, spine-wing type deck
    50m – to – 60m PSC Box Girders / Steel Trusses / Bow string spans
    70m – to – 100m Balance Cantilever, Arch bridges / Bow string
    100m – to – 300m Extra dosed, Arch bridges
    300m – to – 600m Cable Stayed
    > 600m Suspension cable spans
    (N.B. - * choices shown above are general and based on current practices in the industry). It may be noted, that in India, bridges over railway lines (ROB) are permitted only with steel girders

    Aesthetics and utility in super structures

    The superstructure for a bridge is chosen mainly as per the loading and aesthetic requirements as listed in Table 1.

    It may be noted, that in India, bridges over railway lines (ROB) are permitted only with steel girders.

    Innovation in Bridges
    Figure 16: Foldable bridge spans (right – bascule Woodrow Wilson bridge, USA)

    Often, if the navigational clearance is not planned / provided, then the ‘foldable’ or ‘bascule’ bridge decks (Fig.16) are planned. The foldable bridge can reduce the initial investment in the structure but cannot be used in busy arterial roads. Even the mechanism of folding / rotating needs routine maintenance. Some different types of rotating bridge decks / superstructure can be seen in Figs. 17 and 18.

    Often, if the navigational clearance is not planned / provided, then the ‘foldable’ or ‘bascule’ bridge decks (Fig.16) are planned. The foldable bridge can reduce the initial investment in the structure but cannot be used in busy arterial roads. Even the mechanism of folding / rotating needs routine maintenance. Some different types of rotating bridge decks / superstructure can be seen in Figs. 17 and 18.

    Innovation in Bridges
    Figure 17: A foot-over bridge deck in closed and open position

    Toughened glass is used in the deck of Zhangjiajie Grand Canyon footbridges in Sanguansixiang, Hunan, China, designed by Israeli architect Haim Dotan. It is suspended about 260m above the ground (Fig. 20) and has a span of 430m. The bridge that opened in 2016 (www.xinhuanet.com), is made of a steel frame with more than 120 glass panels. Each of these panels is 3-layered, 50 mm thick slab of tempered transparent glass. The glass deck is 15m wide at the ends and narrows to only 6m in the center. This depth to span ratio of 625:1 is greater than any other stiffened deck suspension bridge in the world. The 2,200-ton steel and glass deck was tested at Hunan University in Changsha to support the weight of 800 people at a time, and withstand wind speeds of 200 km/hour. Fifty glass balls, each weighing around 500 kg, have been placed on the surface of the bridge to resist vibrations. Two large water reservoirs suspended beneath the span further dampen any movement.

    Innovation-in-Bridges
    Fig.18 Barton Swing Aqueduct, Manchester England (www.friargatebridge.blogspot.com)

    Wildlife-Crossing Structures

    Since wild animals crossing roads could disrupt traffic, wildlife-crossing structures have been successfully introduced throughout Europe and in various locations in Asia, Australia, and North America. These structures include both underpasses (culverts, eco-passages, tunnels) and overpasses (bridges),in a variety of sizes and designs and are highly effective (Lister et al. 2015). The surrounding of Wildlife Overpasses (WOP) should be so designed as to not lead a noise pollution as well as a hostile environment (see Fig. 21).

    Innovation-in-Bridges
    Figure 19: The Gateshead Millennium Bridge (a pedestrian and cyclist tilt bridge on River Tyne, England)

    In India there is a need for more proper guidelines towards design of a WOP landscape. While India may soon construct its first wildlife overpass in a section of the NH7 passing through Madhya Pradesh, a similar wildlife overpass over the same NH7 stretch in Gangaikondan, in Tamil Nadu, where spotted deer are being run over by speeding vehicles, is yet to get approval.

    Geometric design (curvature)

    Road geometrics are designed as per the available land and surrounding geological features. In tall bridges, the approaches are also long due to the gentle gradient. In such cases, the land required may not be available (especially in busy cities), which calls for innovative solutions like spring / coil type ramp or even speed restrictions.

    Innovation in Bridges
    Fig.20 Zhangjiajie, foot-bridge with glass deck, China [www.highestbridges.com]

    A roundabout, also called a traffic circle, is a circular intersection or junction in which road traffic flows almost continuously in one direction and around a central island. A "modern roundabout" is a type of looping junction in which road traffic travels in one direction around a central island and priority is given to the circulating flow. Signs usually direct traffic entering the circle to slow down and give way to traffic already on it. The fundamental principle of modern roundabouts is that entering drivers give way to traffic within the roundabout without the use of traffic signals. Roundabouts have been found to reduce carbon monoxide emissions by 15 - 45%, nitrous oxide emissions by 21- 44%, carbon dioxide emissions by 23 - 37% and hydrocarbon emissions by 0 - 42 percent. Fuel consumption was reduced by an estimated 23 – 34 percent. (More information may be found in NCHRP Report 672, 2010). Fig 22 shows elevated roundabouts.

    Innovation in Bridges
    Figure 21: The EcoLink overpass in Singapore built to protect animals from traffic

    Sustainable and smart concrete

    To alleviate problems of scarcity of natural materials and to reduce green-house gases, alternate materials such as Manufactured Sand (M-sand) and iron, steel and copper slag aggregates have been suggested and also included in national codes of practices (IS 383:2016). The production of cement leads to emission of 5-7% of greenhouse gases such as CO2, throughout the world, and which are responsible for climate change and melting of polar ice caps and glaziers, which will in turn, accelerate global warming and submerge large parts of our continents and islands (8 tiny Pacific islands belonging to Solomon Islands have already disappeared due to the effect of rise in sea levels, which average 3mm per year globally and up to 12mm per year in the western Pacific, in recent decades).

    Innovation in Bridges
    Figure 22: (a) Elevated junction of the West Cross Route and Westway at White City, London and (b) A pedestrian bridge in Shanghai, China in the form of another raised roundabout

    Several attempts have been made to reduce the environmental effect of concrete, which is used in volumes, second only to water. Attempts include use of industrial by-products called supplementary cementing materials (SCMs), like fly ash, slag cement [formerly referred to as ground granulated blast-furnace slag (GGBS)], silica fume, rice husk ash, and natural pozzolans (metakaolin and calcined shale). These can be used individually with Portland or blended cement or in different combinations. Additions of SCMs not only make concrete mixtures more economical, but also reduce heat of hydration and permeability, increase strength, and influence other concrete properties. SCMs are compared in Table 1.

    Table 1 General strengths and weaknesses of supplementary cementing materials
    Material Strength Weakness
    Fly ash

    Low cost (currently)
    Largest reserves

    Inconsistent properties (Class C and F)

    Diminishing supplies due to switchover from coal to renewable energy plants
     

    Best availability (though variable)

    Well tested
     
    Slag cement

    Best availability (though variable)

    Well tested

    Geographically limited supply

    Requires more attention to curing
    Silica fume Consistent performance Cost
    Natural pozzolan

    Consistent performance

    Cost competitive with fly ash

    Limited experience with use
    Geographically limited supply

    Range of performance

    Although codes permit use of abundant natural materials such as stones and bricks in bridges, construction professionals are reluctant to use these traditional materials in modern bridges. Great Roman bridges such as the Alcántara Bridge (also known as Puente Trajan at Alcantara) and Pont du Gard, are stone arch bridges having semicircular arches with rise equal to one-half the clear span, and are in service even today (Fig.23).

    Innovation in Bridges
    Figure 23: Alcántara Bridge at Alcántara, Spain built between 104 and 106 AD by an order of the Roman Emperor Trajan (Source wikipedia.org)

    Innovations in Concretes

    Innovation in BridgesFigure 24: World’s First UHPC Cable Stayed Bridge-Jobal Grand Bridge, Korea (www.cor-tuf.com)
    Several new types of concretes developed include self-compacting concrete (SCC), High performance concrete (HPC), Fibre reinforced concrete (FRC), and Ultra High-performance concrete (UHPC). This is a high-strength, high stiffness, self-consolidating, ductile material, formulated by combining Portland cement, silica fume, quartz flour, fine silica sand, high-range water reducer, water, and steel or organic fibers]. Each of these materials have their own advantages and can be used judiciously by utilizing their advantages (FHWA-HRT-13-060, 2013 and Subramanian, 2018).

    To reduce the self-weight of the decks of long-span cable-stayed bridges, a 60mm deep slab with prestressed ribs of fibre-reinforced UHPC was developed at the Korean Institute of Construction Technology (KICT). The centre-to-centre spacing of the ribs is 600mm. Using this technology, a cable-stayed bridge with three 90-m high pylons and a main span of 200m was designed in 2011 to link the town of Jobal with Dunbyung Island on Korea’s south coast (Fig. 24). This resulted in reduced cost of construction and maintenance by 20% and extended the service life of the main structural elements up to 200 years. (Also see China bridge in Fig. 20 above).

    Innovation in Bridges
    Figure 25: Use of self-healing material to block the cracks in concrete (various stages seen in photo – before and after healing of cracks)

    Smart materials are engineered to respond to cracks, excessive stress, or environmental effects such as temperature, pressure, and the presence of oxygen. A new type of smart concrete called self-healing concrete contains dormant bacteria spores and calcium lactate in self-contained pods. When these pods come into contact with water, they create limestone, filling up the cracks (see Fig. 25). Self-healing concrete is estimated to save up to 50% of concrete’s lifetime cost by eliminating the need for repairs. Smart concrete is still being tested in laboratories to determine how long the bacteria sustains itself, but researchers are hopeful that it will be introduced in the construction industry very soon.

    Shape Memory alloys

    Another smart material is the shape-memory alloy (SMA), which has two unique characteristics: a shape-memory effect and super-elasticity. The shape-memory effect is the ability of the alloys to revert to their initial shape upon being heated, until they enter their phase transformation temperature. Super-elasticity is the property of alloys that exhibits comparatively large recoverable strain. The maximum recoverable strain these materials can hold without permanent damage is up to 8% for NiTi alloys. Compared to this, the maximum strain that can be sustained by conventional steels is only 0.5% (Chang, and Araki, 2016).

    Innovation in Bridges
    Figure: 26 Spin-Wing and Strutted Box type bridge deck

    The three main types of SMA are copper-zinc-aluminum, copper-aluminum-nickel and nickel-titanium (NiTi) alloys. Although iron-based and copper-based SMAs such as Fe-Mn-Si, Cu-Zn-Al and Cu-Al-Ni are commercially available and cheaper than NiTi, SMAs using NiTi are preferable for most applications due to their stability, practicability, and superior thermo-mechanic performance. NiTi alloys were first developed in 1962-1963 by the US Naval Ordnance Laboratory and commercialized under the trade name Nitinol (an acronym for Nickel Titanium Naval Ordnance Laboratories). Their remarkable properties were discovered accidentally: when a sample which was bent out of shape many times, and presented at a meeting, one of the associate directors, Dr. David S. Muzzey, applied heat from his pipe lighter to the sample. To everyone's amazement, the sample stretched back to its original shape.

    In civil structures, SMAs can perform as passive, semi-active or active components to reduce damage caused by environmental impacts or earthquakes. The passive structural control may utilize SMA’s damping property to reduce the response and consequent plastic deformation of structures subjected to severe loadings. SMAs can be effectively used for this purpose via two mechanisms: ground isolation system and energy dissipation system (Song et al.,2006).

    Innovation in Bridges
    Figure 27: Internally strutted box type bridge deck
    Active tuning of structural natural frequency using martensite SMA wires for vibration suppression is an example of semi-active control of civil structures. Structural self-rehabilitation using stranded martensite SMA wires for post-tensioning is an example of active structural control. By monitoring the electric resistance change of the shape memory alloy wires, the strain distribution inside the concrete can be obtained. When cracks appear due to explosions or earthquakes, the SMA wire strands can be heated electrically, thus contracting them to reduce cracks. This self-rehabilitation can handle macro-sized cracks. The concrete structure is intelligent since it can sense and has the ability to self-rehabilitate (Song et al., 2006). Companies like Shape Change Technologies LLC (www.shapechange.com) produce products of SMAs.

    Strutted deck, spine-wing construction

    Anther innovation in deck system is the ‘strutted deck’ and ‘spine-wing’ type of construction. This system is a perfect example of use of triangulation for a bridge deck, yet making it lightweight and aesthetically pleasant. Figure 26 shows a typical spin-wing deck (on left) and a strutted box deck (right) in Goa’s cable stayed bridge. For wider bridge decks, struts are used from inside, and in some projects, struts are not allowed to be visible / exposed by the client. In such cases, inner struts may be used as shown in Fig.27 (ref. Vivek, 20).

    Acknowledgements

    The authors wish to acknowledge that the images used in this paper have been extracted from several internet resources.

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    About the Authors

    Vivek G. Abhyankar – C.Eng (Ind), DGM (Design), L&T TIIC, has over 19 years of experience in planning and design, detailing of various enabling and permanent works in concrete and steel. He was visiting faculty for Structural Engineering at VJTI, SPCE, a certified structural engineer of MCGM, and life member of various professional bodies. He has written more than 25 technical papers and 3 chapters in books and guided more than ten M.Tech, AMIE projects.

    Dr. N. Subramanian, a PhD from IIT Madras, has worked in Germany as Alexander von Humboldt Fellow and has served as National Vice-President of ICI and ACCE (I). He has 40 years of experience, including teaching, research, and consultancy and has authored 25 books and over 240 technical papers. He has won the Lifetime Achievement Award from the Indian Concrete Institute (ICI), the Tamil Nadu Scientist award and the ACCE(I)-Nagadi best book award for three of his books.

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