To ascertain whether a building is safe or not in case of an earthquake is not an easy job. Even for a very big expert it is difficult to say by mere looking at a building whether it is safe or not. It is more difficult to say so in case of a concrete framed building for that we need proper examination and testing. Mere opinion is not valid in applied science, test and experiments must support it. Of course detail information of previous earthquake if preserved in archives are always very helpful.

We can of course specify a building as unsafe by sheer looking at it if it is of brickwalls with a reinforced concrete slab roof only, when (1) it is more than two storied; (2) it has different plans in covered floors; (3) it has cantilevers, arches or domes; (4) it has no tie above the lintel level or beneath the roof; (5) it has very big windows or openings. This building has more chance of collapsing in an earthquake jolt.

If we look at the old buildings constructed during British period, we will notice that most of the large buildings are two storied, symmetrical i.e. same plan in ground floor and 1st floor, thick walls (wall thickness as much as 2 to 3 ft) on wide foundations using lime mortars in all bonding layers. Some of these buildings lasted for many years and even great earthquake of 1897 and 1935 didn't destroy them. Later with advanced building knowledge, we started making three to four storied buildings with 10 inch wall in cement mortar and concrete slab roofs, often unsymmetrical in the top level plan with wall to wall wide open windows.

In the USA, frequent earthquake happens in California, same as Japan. There is the 'Standard for Structural Design of Masonry Construction "and" Japan Architectural Standard Specifications (JASS)". They specify that: (1) brick Buildings should not exceed 9 m. in height; (2) they should not have window opening exceeding 33 per cent of the wall area; (3) there should be tie at the plinth level, lintel level and under the roof slab; (4) there should be no cantilever or protruding windows or veranda; (5) domes and arches are more liable to collapse.

In order to avoid torsion, the upper level should be a symmetrical plan. Ordinary first class bricks are quite strong. They can easily withstand the compressive load of a five storied building but they can't withstand any tremor or shake up. Brickwalls lack ductility (quality to regain the former shape after the load removed) like reinforced concrete or steel. Unfortunately the cement mortar fails first and the crack pattern passes through the mortar totally separating the two parts of the brickworks. In the 1897 earthquake, the 33m high Shree Chaitanya Bijoy Stambha (Minar) of Joypurhat collapsed. The nine Ratnas (Minars) of the Great Kanta Temple of Dinajpur Maharaja shared the same fate but his palace made of small bricks in thick lime mortar was intact.

If one wants to live in safety please do follow the above rules. Make a two-storied house and if more stories are required then go for an RCC framed building designed and built as per codes. Walls of the ground floor should be made 15 inch thick. It will not only help in case of earthquake but it will also keep the floor cool. Follow the building codes carefully; they help to avoid any disaster. International codes are based on many years' of laboratory tests and experiments and the process is continuous. Therefore do not underestimate them. Do not make frequently holes on the brick walls as hammer blows will make the mortar crack and with a tremor the plaster will fall and the wall will collapse. Take good care of the buildings, as buildings both of brick and concrete need regular repair and maintenance.

Dr. M Harunur Rashid is a structural engineer trained in the USA and Canada, formerly Professor and Head of Civil Engineering, Engineering College Rajshahi now RUET.