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September, 1999 A “high-rise movement” is in the offing. Population explosion coupled with the hard fact that area of land available with us is fixed has changed the direction of “development arrow” from horizontal to vertical. Urbanisation is approaching its peak. There is a revolution in Information Technology with more and more citizens becoming “netizens” those having access to internet) too. Such a situation tends to break all restrictions and force its way to expansion. The available “earth-space” shrinking day by day, the only alternative left is “sky”, leading to springing up of skyscrapers all over the world. New York’s famous night-view makes one believe as if the high-rise towers are not scraping the sky but intruding into it. The 102-storeyed Empire State Building, inaugurated way back on August 30, 1929, still fascinates the onlookers. At that time, it could have been a case of giving shape to one’s dreams but today, high-rise structures have become a necessity. A glance at some picture showing a cluster of tall buildings may make one judge that it belonged to New York or Singapore but it may not be so easy in future when the skyline of almost every city will present a similar scene. In India, the VEB (Vertical Expansion Bug) has bitten the metros only. The population has touched a billion! Yet we are having four-canal houses, single-storeyed buildings, horizontal commercial centres and government offices opened in the old, dilapidated buildings. There is an urgent need to demolish all unsafe and old structures, to free the precious land, to utilise it in a judicious manner and to erect multi-storey tall buildings wherever possible. If we don’t act now on our own, soon we will be forced to do so. There is no alternative! Time is ripe to develop a high-rise science. So far as tall industrial structures are concerned, well defined written word is available. However, multi-storey commercial, residential and office towers are demanding ready availability of detailed guidelines that need to be followed as and when the VEB bites more and more cities. A few important factors are discussed here. Seismic forces assume greater significance with the increase in height of buildings and affect the structural design of the building in a big way. “Total deflection” at the top of the building increases with the increase in its slenderness ratio and this has to be taken care of. The architect, however, will not compromise over the services to be given to end-users of the building and will ask for wall free or column free floors where necessary. The ceilings too may be required to be flat and unhindered to accommodate AC-ducts and electrical fixtures above false-ceilings. Under such circumstances, the following guidelines may prove useful. (i) A tube-structure may be found highly effective in resisting seismic loads. Such a structure was first suggested by Owings and Merill, Chicago. In this structure, the core of the building is kept stiff while columns are provided along its periphery and are connected by spandel beams. A “Flat-slab” design is preferred for ceilings as it does away with the beams. (ii) The structural framework should be kept as highly redundant or indeterminate during design. Such a structure will provide better resistance to lateral earthquake forces. (iii) The mass of the buildings should be kept as low as possible. Lightweight materials should be brought under use. Lesser is the self-weight of the building, lesser will be the earthquake force affecting it. (iv) The seismic zone of the area having the building must be kept in view during design, along with the wind velocity in that area. (v) Deflection-diagram of the building should be studied and joints should be so designed that a cumulative effect of deflection does not occur in any member. (vi) Sub-soil investigations must be carried out in the field to ascertain the bearing capacity of the soil and other factors. The investigating agency must carry a high rating. Investigation results must be realistic and authenticated. Fire safety is the second most important factor to be kept in mind. We have not to give birth to “Towering Infernos”. The latest guidelines in this regard should include the following: (i) In case of fire, the main stairs of the high-rise buildings should get isolated from the rest of building by automatic closing of fire-doors and should further be pressurised with whiffs of fresh air. (ii) An automatic system should close the airconditioning system of the building thus stopping recirculation of air and smoke and at the same time should activate ventilation fans to suck in fresh air to all those floors that are not affected by fire. (iii) Provision of a computer-system loaded with software to analyse the fire-situation and make announcements over public address system should be mandatory. (iv) The electrical equipment and installations provided in the buildings must be of high standard. The building should be designed to carry an emergency power supply in addition to the main supply. The main supply should automatically switch off in case of fire. The emergency supply should turn on to run ventilation fans. (v) Safe exit-routes and escape stairs should be planned in the design of the buildings. Vertical transport system is another factor that must be counted while planning to raise a high-rise building. The following points should be given due consideration in this regard: (i) A “Traffic study” involving accurate assessment of building users must be made. Traffic flow measurements should tell the number of persons that ride the elevators in a five minute period. Peak demand hours should be identified. (ii) Elevators should be located in the central core of the building for the quickest and efficient carriage of vertical traffic. (iii) All elevators should operate under “Group control” system rather than independent control to avoid disproportionate loading. Under the “Group control” system, several cars respond to a call. Thus a centralised and group-controlled system responds maximum. (iv) All cars (elevators) should be fitted with overload devices. Such a device keeps the car-doors open, sounds a buzzer and switches on a warning light whenever the car-load exceeds 10% of rated capacity. (v) All cars should be provided with automatic rescue devices (ARD). These devices send the cars to nearest floors in case of power failures and even open the doors. Sears Tower in USA is a 110-storey building and is reckoned as the tallest office building in the world. It carries a 106-cab elevator system, including 16 double decker elevators. The top deck known as Skydeck rises 1353 feet above ground and two express elevators soar to this altitude in just over a minute-so efficient is the “vertical transport system”! Modern construction equipment should be put to use while raising tall building and skyscrapers if good quality work is to be ensured. The following specifications should be compulsorily adopted: (i) All concrete used be ready-mixed-concrete only. (ii) Use of super-plasticizers that are fully compatible with the cement under use should be made o maximum possible extent. (iii) Maximum concrete pouring should be done by use of concrete-pumps. Super-plasticisers will help in free flow of concrete through placer booms without increasing water-cement ratio. (iv) Sophisticated form-work systems such as slip-forms, hydraulic jump-forms, should be put to use wherever possible. This factor should be kept in mind at the time of building-design itself. A look at the world’s tallest twin towers in Kuala Lampur with a height of 1483 feet, the 1454-feet-high Sears tower in USA, 75-storeyed Interstate World Trade Centre, Los Angeles, and many other such structures make the necks bend at 90 and enthrall one and all. It is heartening to note that hundreds of tall super-structures in the USA have been designed and built by Indians with high-tech support, including most wonderful software packages becoming available in India, brilliant academic achievements galore and latest equipment arriving in plenty, there is nothing to hold us back. Now is the right time to touch the dizzy heights. We must not lose time any more as seizing opportunity is the name of the game.
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