Developers and demolition experts look at several factors when deciding how to demolish a building. Among other concerns, they consider the area where the building is located, the primary building materials, the purpose of the demolition, and how to dispose of the debris. Demolition methods can range from one devastating blast to careful, piece-by-piece dismantling, but in a crowded urban setting, any technique must be safe for the demolition crew and the surrounding buildings and public areas.
Implosion is by far the most dramatic way to demolish a building. It involves using explosives to knock out a building's primary vertical supports, causing the building to collapse onto itself from the inside out. The placement of the explosive charges and the sequence of detonation are critical to a successful and safe demolition. Implosion is often used to demolish large structures in urban areas.
For a successful demolition, blaster crews analyze a complete set of structural blueprints to identify the main components of the building and determine whether other areas need to be blasted in addition to those identified on the blueprints. They then determine the type of explosives to use, where to position them in the building, and how to time their detonation.
High Reach Arm
Demolition with a high reach arm is an alternative to implosion and is typically used on buildings reaching a height of more than about 66 feet. This method involves a base machine, such as an excavator, fitted with a long demolition arm consisting of three sections or a telescopic boom. A demolition tool, such as a crusher, shears, or a hammer, is attached to the end of the arm and is used to break up the building from the top down. The machine removes large pieces of the structure, and a special grounds crew breaks down the pieces and sorts them for disposal.
High reach arm demolition is used on reinforced concrete, masonry, steel, and mixed-material structures and is considered to be safer than traditional wrecking ball demolition for removing tall buildings.
Wrecking ball demolition, or crane and ball demolition, is one of the oldest and most common methods of building demolition and is typically used for concrete and other masonry structures. The wrecking ball—weighing up to 13,500 pounds—is suspended on a cable from a crane or other heavy equipment. The ball is either dropped onto or swung into the structure, simply crushing the building with repeated blows.
Highly skilled and experienced crane operators must perform wrecking ball demolition. Smoothness in controlling the swing of the ball is critical, since missing the target may tip or overload the crane. The size of the building that can be demolished with this method is limited by the crane's size and the working room, including proximity to power lines. Wrecking ball demolition creates a great deal of dust, vibration, and noise.
Also known as strip-out, selective demolition is gaining popularity because it allows builders to reuse or recycle the building's materials. Selective interior and exterior demolition of wood, brick, metals, and concrete allow for recycling and future use in new structures, blending the old with the new. The main goal of this method is to recover the maximum amount of primary (reusable) and secondary (recyclable) material in a safe and cost-effective procedure. However, the process is labor-intensive and can be very difficult to achieve in a timely and economical manner for light-framed buildings.