Visakhapatnam Airport is the largest and one of the busiest airports in the state of Andhra Pradesh. The Airport is located about 7 KM from the city of Visakhapatnam popularly known as Vizag. The airport began its civilian operations in 1981 with a couple of flights per day. However, today it is the busiest Airport in the state handling both, international and domestic flights.
In 2009, due to increasing air traffic, the Airports Authority of India (AAI) constructed a new passenger terminal at the airport and converted the old terminal into a cargo complex. The new terminal handles both, the international and domestic passengers. The new integrated passenger terminal covers an area of 20400 sq. meters and can handle 300 passengers on arrival and 700 passengers on departure at a time.
The new integrated passenger terminal is covered by a massive steel roof. The terminal roof structure consists of arched and flat steel 3D triangular space truss made of circular steel tubes and mounted on RCC columns. The roof structure is divided in to 3 main sections which are mounted at 3 different elevations. The roof truss facing the runway is mounted at a height of 14.72m. The city side roof truss us mounted at a height of 4.94m.
The roof truss between the runway-side and city side canopy is mounted at a height of 11.42m. The depth of the space truss in the runway-side and the middle section is 2m whereas the depth of the roof truss at the city side is 1.061m. The maximum length of the roof structure is 182m and extends to about 100m from the runway side to city side.
Best Out of Left-Over
On 12th October 2014, a very severe cyclonic storm Hudhud made landfall in the coast of Andhra Pradesh over Visakhapatnam. During landfall, the cyclone had a maximum sustained wind speed of 180 kmph. The cyclone also caused heavy rainfall with strong gale winds leading to large scale structural damage over Visakhapatnam and along the cost of Northern Andhra Pradesh and adjoining Orissa. The strong gale winds caused heavy damage to the terminal roof and adjoining buildings.
Although the terminal roof was designed for such heavy wind pressures, the entire roofing sheet of the terminal was blown away. This was largely because the roof at the time was made of thin GI roofing sheets and the connections between the roofing sheet and the roof purlins were not designed or sufficiently enough to resist the extreme gale forces. As a result, the connection between the roofing sheet and the purlins failed and sheets was blown off. Subsequently, the roof insulation, false ceiling and HVAC installments got exposed to very severe wind and rain causing these items to be completely blown away. However, once the roofing sheet failed and was blown off, the wind fore on the roof truss reduced considerably and therefore the roof truss was largely intact and undamaged.
Since the terminal roof frame was virtually damaged and replacing the entire roofing frame will take considerable amount of time, the authorities decided to install a new roofing sheet on the existing roof truss. Also, replacing the roof truss will severely affect the daily operations at the airport during the construction and will leave most part of the terminal exposed to the elements of nature for several weeks or months.
Hence, the best viable option was to make use of the existing frame work. However, to do so, the roof frame should be verified for its strength and stability. Further the region being cyclone prone, the roof should be checked and certified to resist cyclonic winds and to satisfy functional requirements and ensure structural integrity of the structure as envisaged in the applicable safety standards.
Engineers at Mission
IIT Madras was tasked with the responsibility of certifying the structural integrity and safety of the existing steel roof frame. The role of Marvel in this project was to assist IIT Madras by doing an independent analysis and design verification of the roof frame with updated loads as per the latest Indian standards.
Marvels’ engineering team did a rigorous and thorough analysis of all the steel sections, their joints and connections and certified the safety of the existing roof frame for both, strength and stability for these updated loading conditions. A team from IIT Madras also visited the site and did a thorough inspection of the structural integrity of the roof frame and their joints and connections. Marvel also submitted a set of recommendations and design upgrades for better performance of the roofing system during high wind loads.
Marvel’s engineering team modeled the entire roofing system in STAAD Pro and did an independent analysis of the steel truss system. For the refurbished terminal roof, AAI proposed the use of rock wool insulated sandwich roof panel instead of previously used thin walled roofing sheets. These panels were heavier and sturdier than the roofing sheets used and their extra weight had to be incorporated in to the analysis. Further, taking in to account of the topography of the Airport site, the roof frame was analyzed for a design wind speed of 192 kmph.