Post 133 - by Gautam Shah
Buildings are demolished to place new structures, destroyed to dispose off the unsafe entities, and deconstructed to preserve or reuse valuable sub-components. Buildings also get devastated by natural calamities (floods, earthquakes, hurricanes, tsunamis, landslides etc.), man-made disasters (fires, explosions, wars, acts of mischief and terror), and through carelessness such as inadequate design, poor maintenance or repairs.
|Khobar Towers bombing in Dhahran, Saudi Arabia on 25 June 1996 Wikipedia image|
Buildings are conceived to be long-lasting assets. The execution of it takes time, and is a costly affair. A building has uncertainty about it. No one precisely knows how long it will last, and no one can predict how long it will remain functionally relevant and commercially valid. Buildings’ relevance or validity, are also dependent on external factors such as the neighbourhood, politics, styles, and social trends. Buildings are perpetuated so long as the structure is safe, and external services make it inhabitable. Buildings are doctored in may ways, like, restored, renovated, repaired, reformed, conserved, reinforced or retrofitted. These interventions make a building functional for some other purpose, if not the original.
|Planning for temporary stability during demolition Collapsed Cypress Street Viaduct in Oakland Wikipedia image by H.G. Wilshire, U.S. Geological Survey Permission (PD-USGOV-INTERIOR-USGS)|
The decision to demolish a building arises out of many considerations. Old buildings are removed, when safety and security are suspect without even waiting for the redevelopment plans or investors being readied. Old buildings are destroyed when there is a prospect of a new activity on the same site for new functions, for larger built-up volume, incorporation of newer technology for use-functions and for services, for implanting a new commercial or social image and for matching with the ethos of a current day neighbourhood. There is some resistance to demolition of public or private buildings with some historical linkage or metaphoric values. These necessitate stake-holders involvement in the process. Buildings being commercially replaced find few such problems.
|Flickr image by Colin Davis|
Demolitions incur costs of scavenging the structure for recyclable components and materials, pulling down a structure, carting away the debris removal, charges for environmentally safe disposal and costs of mitigating the risks. Demolition of buildings with recyclable materials such as wood, metals, stones and bricks, help to recover the cost of demolitions. Similarly buildings with antique components are highly valued. Older buildings are often built with massive materials, taller floor heights, and a new building at the same site is likely to be spatially leaner and minimalistic, and energy efficient, providing great advantage. Demolitions, require attention to several processes. These mandatory processes include permission for destruction, the methods of demolition, schedule, logistics of handling, loading and carting away the debris, recycling the removed material, and safe and adequate disposal of hazardous and other debris. In many localities one may need to indicate who-how the vacant plot will be maintained or used till an approved building system is regenerated.
|White house destruction for reconstruction 1950|
The methods of demolition depend on the scale of the building (number of stories, volume, footprint ) complexity of structure (assembled, framed and in-filled or fully integrated), locality, road access, debris carting route and allowable schedules, reaches of the demolition equipment, health hazardous conditions due to noise, vibrations, dust, etc. Building demolition occurs in a very tight schedule. The delaying factors are: scavenging for recyclable components and materials and the removal of the debris and the disposal management. Smaller buildings are pulled down using manual tools, but buildings of low heights and extensive footprints (plinth area) are demolished by ground-based equipment with deeper reach. Tall buildings require floor by floor demolition or use wrecking ball cranes. Buildings with bricks, precast blocks or stone masonry can be demolished in parts, but integrated structures like RCC frameworks, welded steel frames need careful planning about how the parts are destroyed and temporary support systems. Very large buildings are destroyed by implosion techniques so that debris falls within the premises.
WTC 3 debris Wikipedia image by Kafziel
Demolitions of large integrated structures are done after careful evaluations such as strength and behaviour of materials at near failure or collapse state, yield deformations, shear ruptures, mass versus weights factors. Demolition of disaster affected remnants of the buildings offer very little interim time for studying the buildings’ system.
|Stepped demolition Image by “LepoRello (Wikipedia)”.|
Options to demolitions are few. Displacements or relocations of the buildings have been tried, but involve a great expense and risk. Relocation of building is carried out in two basic ways. Buildings are deconstructed and reassembled, or transported as a whole to another location. The first approach requires building to be consisting of separable and re-unite-able parts, whereas the later one requires building to be an integrated entity. In reality buildings are exclusively neither of these.
Debris management is difficult for an individual site owner to handle. Paris once had no local government to handle it. The debris of demolished or falling off buildings was spread out or dumped into near by river or low areas. These resulted in many streets getting buried up to the first floor level. Some of the better options are, to reuse the old buildings, design buildings with greater life-span, and use components and materials that remain separable and recyclable.