Demo design and sequencing

Demolition Techniques

Demolition work can be considered as falling under two broad categories:
  • progressive demolition; 
  • deliberate collapse mechanism

Progressive demolition is the most common with most partial demolition works undertaking progressive demolition work.

Progressive demolition

This involves the controlled removal of portions of the structure whilst ensuring the remaining structure remains stable. In general terms the demolition is carried out working from the top to the bottom of the structure, usually working towards the structural core to ensure that stability is maintained. Partial demolition of a structure will follow similar constraints. However, the works will not necessarily be from top to bottom. Progressive demolition can be further subdivided into three broad methods based on the plant used for the works. It is not uncommon for a combination of all three methods to be used on a single project.

Top down demolition

If access to the structure is limited by adjoining properties, roads or railways then top down demolition work will be undertaken. The plant will be lifted onto the roof, the structure will then be demolished floor by floor; generally leaving the core as the last section on each floor to be demolished, thereby ensuring stability. Rubble is generally cleared by skid steers.
As with most forms of engineering, the success of the project comes down to the Engineer’s understanding of the structure. The more information provided to the Engineer the better the assessment of the structure will be. 

High reach demolition

A high reach excavator on a suitable working platform is used to demolish the structure in a controlled manner. A number of floors will be tackled at the same time leaving a staggered profile when viewed from the side. This allows the high reach machine driver to see the work being undertaken and reduces the likelihood of rubble falling onto the machine.

Dismantling

Typically, the structure will be dismantled using cranes with cutting techniques to release suitably sized sections. In some cases, it may be possible to simply reverse the original construction methodology by undoing bolts, or in the case of precast sections simply breaking out in-situ concrete to release.

Deliberate Collapse Mechanism

See hyperlink to page on pull down/blow down of structures for more information.
The sequencing of the demolition works will generally be undertaken in conjunction with the demolition contractor, and will be influenced by safety, the programme, and available plant. We will provide clearly laid out and annotated drawings which show the intended sequence, alongside any identified hazards. The sequence will identify any propping or other temporary works if required.

Have a demolition project that requires specialist design support?