Effective use of pull down or blow down demolition techniques can shorten demolition timelines compared to progressive or top down demolition approaches. This approach requires sufficient space to implement. Andun have designed and sequenced this type of demolition for a number of high profile projects including Tottenham Hotspur’s White Hart Lane redevelopment.
Many people mistakenly believe that an explosive actually blows the structure apart; in reality, it is used to trigger the collapse of the structure by weakening or removal of key structural elements, allowing gravity to do the rest. The mechanism for triggering the collapse can be either explosive charges or by pulling with a wire/chain attached to an excavator.
Planning the deliberate collapse of a structure requires an Engineer to have a very good understanding of the structure and experience of how structures behave in extreme conditions. Steel and concrete structures require different approaches.
To prepare concrete structures key structural elements are weakened. Explosives are typically placed in holes pre-drilled into the key elements that are to be fragmented. Once detonated the solid explosive converts instantly to a gas of much higher volume which effectively blows the concrete off the reinforcement and gravity does the rest.