The Rediff Special/ Ramesh Menon

As the tremors continue to shake Gujarat, the Earthquake Technical Assistance Cell of the City Managers Association of Gujarat has produced a ready-reckoner on how to repair your building after an earthquake. These FAQS were formulated by Ismet Khambhatta of the Environmental Planning Collaborative, an urban planning organisation.

When can I enter a quake-damaged building?

One should stay out out in the open immediately after an earthquake. Ideally, one should wait for the aftershocks to subside. But aftershocks can last for days or weeks. As building inspections take time, the United States Applied Technology Council and the US Geographical Survey offer the following tips and guidelines:

• The greater the magnitude of the earthquake and the stronger and longer the shaking, the greater the chances for strong and numerous aftershocks.
• If the damage after the main shock was heavy, the site is more likely to experience additional damage from the aftershocks.
• A main shock large enough to cause damage will probably be followed by several aftershocks within the first hour.
• Aftershocks decrease in number and magnitude over time. Generally speaking, the second day will have approximately half the number of aftershocks as the first day and one-tenth as many on the tenth day.
• Except for life-saving rescues, entry into seriously damaged buildings should be avoided during the first 24 hours following a main shock.
• If you have to enter a damaged building, the stay must be very, very brief.
• As a general rule, following a 6.5 or greater earthquake (on the Richter Scale), a period of at least three days should elapse before one enters a damaged building. Five more days should elapse before the building is occupied for fixed periods of time.

What should I do if my building is damaged?

• You must get a structural engineer to visit the building and assess the damage. Obtain a set of structural drawings of the building from the builder. This will help the structural engineer to make his assessment.
• Do not try to patch up cracks with plaster or cement as they will not strengthen the structure. In fact, it will only mislead the engineer who comes to assess the damage.
• Try to get an independent opinion, in addition to the opinion of the builder or contractor who has constructed the building.

Could you give me some tips that will help me understand how a building behaves during an earthquake? What kind of questions to I need to ask the engineer who examines my building?

• In Ahmedabad, for example, most multi-storied buildings are column-beam frame structures. This means they are composed of a system of columns and beams walls which are not load-bearing. Generally, load-bearing masonry (brick) walls are most susceptible to earthquakes. In all cases of damage, it may be unsafe to occupy the building. The good news, however, is that a lot of this damage can be repaired, depending on the quality and technological acumen with which it is done. Severely damaged buildings may have to be demolished. In all cases, it is advisable to get the opinion of a structural engineer.
• While trying to figure out how your building is doing, the first thing you should check are the columns at the lowermost level, on the ground floor. If your building has parking below, then these are completely visible to you. In case you don’t, then you should obtain the blueprint of the floorplan of your building, locate the columns and go through them with your neighbours. The most serious damage that a building can undergo is when its columns are damaged due to what is known as shear, which is the principal force exerted on any structure during earthquake. To give you a basic idea, shear is what happens when you try to bend two ends of a stick towards each other -- normally, the stick will break sideways. Structures are also subject to torsion shear: torsion is what you do to your wet clothes when you wring them to get the water out.
• The first thing you must look for is cracks which are at an angle of 45 degrees or more from the vertical, ie horizontal cracks, in the columns.
• If the cracks are closer to the ground, chances are that the foundation may also be damaged. Parts of the foundation may have to be dug out for inspection.
• Starting from the bottom, you should slowly move up, checking each inch of the structure carefully. Basically, the higher the cracks, the safer the building and the lower the cracks, the greater the damage. Of course, all cracks must be repaired. For instance, if there is a crack on the columns holding the water tank at the top of your stairs, these columns could actually collapse during a subsequent quake or aftershock.
• If the beams are cracked, this is relatively a less serious problem, since it affects only that particular floor at a local level and does not necessarily compromise the whole structure. On the other hand, it is pretty dangerous if there are cracks at the joint between the column and the beam and it shows on the sides. This means that the column itself may be cracked.
• It is not very dangerous for a structure if the walls have fallen down or are cracked. Basically, this doesn’t really matter as you can break the walls and rebuild them. In a column-beam structure, walls are not really an essential element. But if there is debris around a column from a broken wall, you should clear the wall area thoroughly and inspect damage to the columns. Don't worry if you find that the pipes have cracked; they have no structural strength.

• Yes. But this depends on the extent of the damage to the structure, which can be assessed only by a structural engineer. These repairs are called 'retrofitting' and help not only in making an existing building liveable, but also makes it strong enough to withstand a quake of a similar intensity in the future.
• Damaged concrete buildings, as revealed by cracks in beams and columns, can often be repaired after a quake. Small cracks can be repaired with injections of epoxy compounds. Damaged columns can be “jacketed” with steel cladding to prevent further deterioration or a larger column can be cast around them. Some buildings, however, might suffer serious damage and might require to be demolished, even if they are still standing after the quake.
• Do not undertake any repairs without the opinion of a structural engineer.

• Ask the builder for a full set of structural drawings (every resident or occupant of the building is entitled to a complete set of drawings). Get an independent structural engineer to review the drawings and give you a 'second opinion' -- just as you do with a doctor.
• If you are still a prospective buyer, ask for a complete list of specifications to ensure overall safety and sound construction.

Yes. Time tested practices like soaking bricks in water before use, washing aggregate and sand, limiting the height of the brickwork done at a time, vibrating and curing concrete sufficiently, filling each brick joint with mortar, using staggered brick joints are all 'sound' construction practices that have been neglected in the rush for 'quick' construction. This often results in weak structures that are then covered over with cement plaster. The plaster hides the flaws and gives an illusion of solidity and soundness.

If I renovate my flat or building, could I be making it unsafe for myself and my neighbours?

• Yes. Do not make any changes in the structure (like adding or removing a wall, enclosing balconies, making a terrace garden, an additional water tank, making openings in existing walls) without consulting a structural engineer. All buildings are designed to take only certain assumed loads distributed in a certain pattern. Any change to this pattern or an excessive increase in the load can prove extremely dangerous and will cause the structure to fall.
• If a Vastu consultant advises you to make changes to your house or office, do not rush to do so till you check with a structural engineer.

Design: Dominic Xavier

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