- Arul Jayachandran, Professor, Dept. of Civil Engineering, IIT Madras
- Saravanan A, Director – Operations, SPL Infrastructure Pvt Ltd, Chennai
They stand tall. They stand together. And they are a testimony to the excellence of an innovative construction design. The steel flyovers at Marthandam and Parvathypuram in Kanyakumari district of Tamil Nadu have a special place in India’s construction scene. They were a first for South India, and the second of its kind for the country. And they have eased traffic congestion on NH-47 that bypasses these business hubs while connecting Kanyakumari with Thiruvananthapuram.
These flyovers were built at a cost of Rs 314.02 crore, and completed within a record 20 months. E 410, a special grade structural steel plate was used to achieve the optimized design build of steel components. Prefabrication of the structural steel members is the key feature for the successful launch of these steel flyovers.
The super-structure is entirely made of structural steel and connected to the concrete pile-foundation through a specially-designed anchor bolt system. This construction methodology was employed both for the 109-span Marthandam flyover and 51-span Parvathypuram flyover. Technical aspects involved in the effective launch of both flyovers are listed here.
A flyover was proposed to ease the traffic congestion from Km: 604+252 to Km: 607+060 at Marthandam and from Km: 630+116 to Km: 631+650 in NH-47 at Parvathipuram and from Km:
0+000 to Km: 0+380 in the NH-47(B) Alignment of Parvathipuram. What led to this proposal was the complexity in land acquisition in this locality, and the need to reduce the construction time taken for conventional concrete flyovers.
An aerial view of the completed flyover surrounded by dense structural utilities at Marthandam is shown in Fig. 1. This type of steel flyover is the second of its kind in India, the first being in Kolkata built by Japanese designers. This technology is totally new for South India.
The flyovers were designed by M/s Samarth Infra Engg Technocrats Pvt. Ltd, Hyderabad, and proof- checked by M/s Pragati Consultants, Hyderabad, and construction was undertaken by EPC contractor M/s SPL Infrastructure Pvt. Ltd, Chennai. The Indian Institute of Technology (IIT), Madras, provided technical assistance for this project at all stages. Construction of the 2.687 km stretch fl yover at Marthandam commenced on August 20, 2017, and completed by December 19, 2018, while the 1.409 km stretch at Parvathypuram that began on January 5, 2018, also was completed by December 19, 2018. The total time taken for construction of the twin fl yovers was 20 months, which is a remarkable achievement compared to conventional construction.
The construction of the two flyovers required 12,000 tonnes of special grade E410 structural steel plates, and the fabrication of these steel structural components was executed by five reputed steel fabricators and 150 skilled labourers who worked in two shifts.
Around 200 MIG welders also worked in two shifts to supplement robotic welding to enhance the work efficiency. Steel grid blasting / metallization was performed at 600°C (85% zinc 15% aluminum) and 200 workers were engaged in this activity. In spite of this humongous task force, the rate of work done was only 20 to 25 Sqm per hour due to the high temperature. Metallization is done in three layers of 50 microns and two coats of epoxy (PUC) of 50 microns to enhance the life of the structure.
Metal decking sheets were used to avoid shuttering and staging works in the construction of concrete bridge deck. It was the first time in the country that such a method was used for a long stretch flyover project, and it saved quality construction time. The metal deck was filled with concrete layer, and around 1.95 lakh numbers of shear studs were used. However, the advantage of steel-concrete composite action was not considered in the deck design.
In addition to structural steel, other building materials like concrete of 66,000 CUM and reinforcement of 8,000 MT were used, mostly for the construction of the sub-structure (pile and pile cap). The piers in the flyover were connected to the pile cap through specially designed 4,500 anchor bolts of 2.3 m length and 75/85 mm diameter). Around 1.97 lakh HSFG bolts and nuts with washer were used for connecting various structural steel elements, and 4.75 lakhs running meters of welding was consumed. Forty types of spherical bearing were installed between the pier cap and the bridge girders, and 45 expansion joints were deployed at every 500 m stretch along the length of the flyover. Photos of the site before and after the construction at Marthandam and Parvathypuram are shown in Figs. 2 and 3, respectively. Structural details of the twin steel flyover are listed in Table 1.
This project is distinctively different from other conventional flyover projects mainly due to the innovative building technologies adopted at the design and construction stages. At design level, box type pier and pier hammer head, a Japanese technology, was applied with technical assistance from IIT, Madras. The structural steel was pre-fabricated using robotic welding technology to ensure the required quality of work (Fig. 4). Most of the fabrication work was performed at the yard, and erected at site during non-peak hours to minimize traffic hindrance. Steel girder of ordinary and obligatory spans fabricated at the yard is shown in Fig. 5. Erection of obligatory span was a challenging task because of the associated structural instabilities. Metal decking and specially-designed embedded anchor bolt system are the other inventories in the list of innovative techniques adopted for this construction. Real time load and vibration test was also performed to certify the structural adequacy in the interest of public safety.
The effective use of building materials and innovative construction technology along with high-end design principle makes this project different from other conventional works. It also paves the way for better implementation of flyover projects in the future in an urban terrain. Recommendations for the construction of steel flyovers based on this project are:
• Use of special grade E410 structural steel plates for an optimized steel design. It reduced steel consumption by 20% compared to conventional structural steel
• Pre-fabrication of structural steel members and the employment of robotic welding ensured an erection precision within 1 mm tolerance limit.
• Effective shuttering technique adopted for pile cap and profiled sheet deck allowed regular traffic movement and reduced the construction time-period.
• Specially designed anchor bolt frame adopted to connect the steel pier to the concrete pile cap ensured safe transfer of load from the steel super-structure to the concrete sub-structure.