Earthquake resistant construction system with reinforced hollow concrete block masonry - An ideal reconstruction strategy for Gujarat :   A technical paper presented at the national seminar on "Earthquakes in built environment", at the Indian building congress (IBC), New Delhi, in May 2001.

This paper was presented by Sri N.G.Bhagavan, stating that his presentation would be on a simple technology for earthquake resistant construction system that is adaptable in Indian environment, namely reinforced hollow concrete block masonry construction system which is based on the work done at SERC on the sponsorship of BMTPC.

He further stated that since earthquakes cannot be predicted nor they can be prevented, we have to go for good alternative construction systems. A construction system that gives a real three dimensional stable structure like a bus / rail coach which is subjected to artificial earthquakes and random vibration in its service life but it still does not collapse. The structure should have wider base, e.g. Pyramids in Egypt though made of very brittle material, about 4500 years back, and they being tallest, largest and heaviest man-made structures, but which have withstood so many natural calamities. They are still intact because they have a large base - an important stability criteria for any structure. Other equally important craters are ductility and damping capacity.

Pointing out that shear wall structural system which has performed very well in many parts of the world during earthquakes, is not feasible and will be a costly affair in Indian conditions, Dr. Bhagavan said that the best system would be reinforced masonry like multi-width wall systems in which there are two layers of brick masonry or stone walls and in between RCC is sandwiched with both horizontal and vertical reinforcement or a confined masonry system. But these are costly. As an alternative, therefore, SERC has recommended the reinforced hollow concrete block masonry i.e., make use of hollow concrete block as a structural wall and put the reinforcement and grout it at critical locations and make it a shear wall.

Construction process of the hollow concrete block masonry was explained with the help of slides and sketches. In these blocks the reinforcement can run through the masonry both horizontally and vertically, right from foundation through the wall and gets bent into the RCC slab giving an excellent diaphragm shear wall structural system. In terms of cost, it compares well with other structures.

Dr. Bhagavan further elaborated the advantages like increased floor area (8" wall instead of conventional 9" wall) dead weight reduction as compared to conventional, masonry system and RCC framed structures. Showing some photographs on full scale testing of this technology n conclusion, Dr. Bhagavan stated that reinforced hollow concrete block masonry system is superior structural system, is not costly and hence is highly recommended for construction in Gujarat or elsewhere in the country.

Referring to the Hon'ble Minister's speech, Dr. Bhagavan suggested that to make the built environment safe from CDEF syndrome, one is to go for ABCD system i.e. Anchorage to the building, i.e. strong foundation, Bracing for excellent connectivity between different structural elements, Continuity so the structure is three dimensional and Ductility.

Discussions - Reply by Shri N.G. Bhagavan

Reacting to the question from Shri V. Choubey of Western Railway, Ahmedabad, as to whether hollow blocks should be used as a building material, particularly when they have failed in Gujarat and to what height of the structure it may be cost effective to go in for reinforced concrete block masonry and by Shri Yogesh K. Singhal as to whether SERC has taken any initiative in implementing this technology in Gujarat and the remarks of the Co-Chairman that his experience in Iran had been of hollow blocks construction having failed miserably and people were not ready to use these blocks, Shri Bhagavan clarified that one should go for structural grade hollow blocks which are available in different grades. In addition reinforcement is to be used with hollow block masonry which takes care of the problems mentioned in the question. Regarding the number of storeys, Shri N. G. Bhagavan mentioned that for Indian conditions one can go up to 10 stories whereas tallest buildings constructed so far is in United States, having 28 storeys and finds a place in Guinness Book of World Records. Regarding cost, he emphasised that this technique is cost effective as compared to conventional methods if various design parameters like resistance to earthquakes etc. is taken into account.