Have you ever wondered… how tall buildings are demolished within crowded urban areas?
With the growing and changing needs of today, as well as the limited design life of every building, demolition is a necessary undertaking, which requires due diligence and careful planning. While many of us think of dramatic implosions and wrecking balls, when we hear the word demolition, those methods are generally not permitted within built-up, heavily populated areas due to the associated concerns of noise, dust, safety, and proximity to other built assets. Hence, the disposal of tall buildings needs to be a carefully planned process that ensures safety and minimizes any impact on the surroundings.
Demolition in the middle of a heavily developed and densely populated area is highly complex and requires extreme care. Buildings in downtown urban districts have been, thus, manually dismantled in past projects to ensure the high level of prudence that is needed. In New York City, for instance, the 270 Park Avenue Building, which stood 216m high, is being demolished to make way for a newer and much taller 70-story JP Morgan Head Quarter building using the Deconstruction (or Reverse Building) technique. Through this method, buildings are carefully dismantled from top to bottom, floor by floor. After the approval of demolition plans and permits, contractors first remove any harmful substance or materials, such as asbestos, to avoid any possible contamination. The non-structural interior of the building is then unbuilt by the removal and stripping out of floor coverings, fixtures, doors, non-load bearing walls, wirings, pipelines, air-conditioning, lifts, and stairs, etc. The building is fully enclosed in protective fabric and scaffolding throughout all this, to minimize the impact of noise, debris and dust on the public and neighboring properties. With non-structural elements removed, and the tower stripped to its core superstructure, small excavators and handheld tools are employed to break up the concrete floor slabs and steel framings. Steel reinforcing bars are exposed by concrete removal, extracted, and recycled. All this process of deconstruction is repeated level by level until the building ceases to exist. For tall buildings, like skyscrapers, this disposal process can be divided into phases. During the demolition of 270 Park Avenue, for example, the demolition works are being done in four phases, with specific floors stripped out and modified to form the bracing levels that support the scaffolding for each of the sections above. Deconstruction and disposal are then repeated for each section. Hence, using this technique of Reverse Building, tall towers, wrapped in scaffold and nettings, are literally disassembled, in the order reversal in which they were first built.
Similar principles of the above-described approach have been employed, but with slight variations, in other projects around the world. The forty-story Grand Prince Hotel Akasaka in Tokyo, Japan, for instance, was demolished in a slow, yet careful process that involved a contained system of hydraulic framework. In this seemingly less dramatic of a demolition process, tall buildings can be dismantled from the top down or from the bottom up, unbeknownst to anyone outside the building. The work is hidden by a moving scaffold, with the entire structure being slowly jacked down. To a bystander, it may seem as if the building is slowly sinking into the ground over time. Non-structural elements and fixtures are first stripped out, following slabs, beams, and supporting columns in a floor by floor manner, similar to the deconstruction technique, and the debris is removed, while the temporary, computer-controlled hydraulic jack continues to lower the remaining building structure as works proceed. Hence, the skyscraper slowly disappears from the skyline in a slow and stealthy manner. This method is clean, efficient and does not disturb nearby buildings. In fact, during the Grand Prince Hotel demolition, the building was shrunk by about two floors every ten days. Whenever the two floors were removed, the roof and scaffold cap were gradually descended and columns subsequently lowered to new positions, before moving on to the next two floors.
While techniques to demolish such mammoth structures carefully and safely, in a densely packed locality, exist and have been successfully executed in past projects, such work is undoubtedly a significant undertaking, given the cost and efforts required. Demolition is, therefore, seen as the last resort among developers, during redevelopment projects. Other alternatives, like building adaptation, are growing to be favorable alternatives to the demolition process, through which skyscrapers are significantly altered to suit new needs, while the bulk of the superstructure is maintained. Nevertheless, the remarkable and ingenious ways in which such iconic building assets can be disposed of clearly demonstrate the endless opportunities possible due to engineering. What goes up can come down - slowly but surely!