Structural distress

Print edition : March 16, 2018

Arun Menon, along with other members of the expert committee formed to assess the damage to the Veera Vasantha Rayar Mandap, after their first meeting in Madurai on February 8. Photo: S. Krishnamoorthy

ARUN MENON, a structural engineer and conservation expert, is a part of the expert committee that assessed the damage caused by the fire at the Meenakshi temple in Madurai. A coordinator of the National Centre for Safety of Heritage Structures at the Indian Institute of Technology Madras, he has been involved in many conservation projects. A member of the International Council of Monuments and Sites, a non-governmental organisation promoting the application of theory, methodology and scientific techniques for the conservation of architectural and archaeological heritage the world over, Arun Menon was involved in preparing a Working Draft for the Hindu Religious and Charitable Endowments Department on the conservation and maintenance of temples.

This manual discusses various factors causing deterioration in heritage structures and focusses on typical distresses an ageing structure faces, diagnosis of structural distress that causes damage, and intervention highlighting techniques and methods.

In an exclusive interview to Frontline in Chennai, he explained the technical details of the mandap in the Meenakshi temple that was engulfed in fire, its age and the materials that were used to build it.

He said the Vasantha Rayar Mandap “is a hypostyle hall built in the trabeate (or post and lintel) construction technique with monolithic stone pillars, stone beams, brackets and stone slabs, all in granite. The hall spans an area of about 850 square metres. The structure has been damaged in the fire that raged on in the interior of the hall for hours before it could be completely put out. Large areas of the roof slab in the northern and southern aisles, on either side of the east-west oriented central corridor collapsed, owing to cracking of the stone slabs, which could no longer carry the weight of the heavy brick jelly, lime concrete weathering course.”

He said he was glad that the Thousand Pillar Hall, which houses a museum with rare sculptures, murals, highly sculptured pillars and other artefacts, was unaffected in the fire. The committee members were apprehensive that had a sudden collapse of the fire-affected structure occurred the exterior row of highly sculpted pillars would have suffered damage. “Hence, we have decided to focus on the first phase of post-disaster operations—to secure critical locations of the Vasantha Rayar Mandap so that any future risk to the Thousand Pillar Hall is mitigated. Our efforts have paid off. No visible damage can be noticed now,” he pointed out.

He further explained that there was an “apparent deterioration of the structural material [granite] in the most affected parts, particularly spalling or flaking of significant thickness of the stone surface in the pillars, and flexural cracking in the beams and the stone slabs”.

“A high-density material such as granite, an igneous rock, can be severely affected by fire. Scientific studies conducted at Britain’s Building Research Establishment have shown that building stones are affected not only by the temperature of the fire that the material is subjected to but also by the rate of increase of temperature,” he said.

“Up to about 250-300 °C, the effect of fire is reversible in granite, as long as the rate of temperature rise is around 1 °C per minute. Around 600 °C, irreversible changes are observed in the microstructure of granite owing to tensile and compressive strains leading to permanent deformation, spalling and cracking. Owing to its low porosity, granite suffers from differential thermal expansion much more than porous stones such as limestone and sandstone. At around 1,000 °C, stone is expected to melt,” he said, adding that the “initial visual examination in the temple fire had indicated that the temperature must have crossed 600 °C in the most-affected portions. This will, however, be verified in the detailed scientific investigation.”

Reconstruction and retrofitting measures have to be taken up for the restoration of the mandap since it is located inside a tangible heritage structure, the temple.

Ilangovan Rajasekharan

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