PROJECT BRIEF
Everest executed a prestigious project of a commercial airplane hangar with a clear span of 93 m in one of India’s leading metros. Indigo, the end user and consultant had specific limitations of floor area usage strictly imposed by the authorities that were making the design of airplane hangar impossible by conventional methods – called as “fixed base” design.
INNOVATION & SOLUTION
The design and engineering team of Everest worked with the consultant and understood the reason for the limitations in space. Once the same was acknowledged as non-negotiable, the design team from Everest revisited the design concept, and successfully performed the design using the “pinned base” philosophy.
In a fixed base design, the vertical columns that support the structure transmit both the imposed loads as well as the moment to the base via their base plates. Since the size of the base plate has a direct bearing on the size of the concrete pedestal where anchor bolts are cast, this directly causes the civil work sizes to increase in the form of a heavier pedestal.
In a pinned base design, the moments are absorbed and compensated at the joint between the column (vertical member) and rafter (horizontal member). This means that the coupler between the column and rafter (called “haunch”) is designed to be much heavier and rigid.
CHALLENGES
The key challenges in a pinned base design include heavier haunches and iterative designs, including the use of kicker elements (plates provided at the haunch) to the higher loads and higher deflections at the center of the rafters. These require an intimate compensation understanding of the interplay between the various forces and the sensitivity of members to each. ESBS design team is very well versed in these complexities and could easily handle this complex design without compromising the integrity or safety of the hangar.
OUTCOME
By using a pinned base, the area of the base plate was reduced by nearly 70 percent and an overall saving of 10 percent was affected in the weight. In addition, the inside-to-inside and outside-to-outside dimensional limitations of the hangar were also maintained.
This is the first case where a pinned base has been used for a large clear-span building of over 90 meters, thus pioneering the implementation of this concept as per customer requirements.