Demolition - Summary

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General

All demolition should be planned & carried out by competent practitioners and organisations.

Mechanical equipment is favoured to hand demolition techniques.

Coordinated approach is vital to ensuring total safety & efficiency with multiple operations running concurrently.

Dangerous Structure - Any bolt structure which could by its condition endanger the public.

Demolition is a dangerous and complex activity.

Requires sound knowledge of various legal procedures, construction technique & their associated demolition methods.

Construction (Design and Management) Regulations 1994 requires demolition to be considered during the design stage of a project & fed into the O&M manuals.

General sequence of demolition is from top down.

Criteria for a Successful Demolition

Safety - may require decontamination works prior to work - keep flying debris to a minimum.

Thorough investigation - prior to demolition to identify potential problems such as weak sections, hazardous materials...

Good neighbour policy - adjacent owners/occupiers should be notified at all stages of the demolition process.

Avoid damage & operational problems - protect other parts of the building and adjacent properties through temporary screening.

Proper disposal - dispose in proper bags and appropriate/licensed sites.

Maximise recycling - utilise materials that are directly useable (windows, roof slates, doors, sanitary ware, glass...)

Reasons for Demolishing a Structure

Structural failure

Progress of society - change in use, new legislation, redevelopment.

Economic factors - repairs costs, land use & end of useful life.

What Makes a Building Dangerous?

Poor maintenance

Fire

Storm

Vehicle impact or explosion

Section 80 of the Building Act 1984

Requires person undertaking the demolition to give a 'demolition notice' to the following:

Occupiers of all adjacent buildings

The local gas & electricity suppliers.

The health and safety executive.

Initial Procedures for Demolishing a Structure

Obtain necessary statutory consent, licences, permissions...

Disconnect or cap off redundant services.

Protect remaining elements.

Safety/security check to ensure no on is inside the building.

Soft stripping - removal of non-load bearing parts of the building and salvageable materials first (partitions, windows, doors...)

Pre-weakening - cutting holes in walls or other elements prior to using a pusher arm to topple the remaining elements.

What Determines the Method of Construction?

Type of structure

Type of construction

Location of site

Methods of Demolition

Category 1 - Piecemeal

By Hand Using a Sledgehammer - least damaging & disruptive option (commonly used in adaption work)

Pusher Arm - suitable for low-rise redundant extensions.

Mechanical Demolition - use of crane with ball & chain - limited use due to the risk of collateral damage.

Hydraulic Splitter - used to pre-weaken or remove masonry or concrete elements.

Thermal Lance - used to remove difficult concrete elements.

Category 2 - Deliberate Collapse

Controlled Using Non-Explosive - used to pre-weaken walls & burn timber wedges & other temporary supports.

Controlled Using Explosives - limited use in adaption work due to risk of collateral damage.

Techniques for Demolition

By Hand

Used when inaccessible to machines, high level work or materials need to be retained.

Time consuming & labour intensive method.

Wire Rope

Commonly used to pull down masonry & brick structures.

Not to be used on buildings over 20m high & length of rope must be at least 2x the height of the building.

Demolition Ball

Used for large brick and concrete structures.

Requires high level of supervision as crane driver has restricted view of the building.

Pusher Arm

Used on low level masonry structures.

Deliberate Collapse

Used when certain structural members support the whole building.

Dangerous method & care must be taken to ensure site personnel are a suitable distance away.

Explosives

Used on large structures where materials don't have to be retained.

Fast & economical method but there's safety implications.

Hydraulic Or Gas Expansion Burster

Used for reinforced concrete structures.

Holes are drilled into the concrete & a steel tube is placed into each of them.

Hydraulic pressures Or gas force pistons out the tube to break the concrete along each tube line.

Slow but quiet method.

Thermal Lance

Developed in 2nd World War - primarily used for reinforced concrete structures.

Steel tube with internal steel rod has its end heated before passing oxygen down it.

Resultant 3,500 degree temp. melts away concrete & reinforcement.

Disadvantages - can damage surrounding members through expansion & hot slag is produced.

Suitable Demolition Methods for Various Building Elements

Masonry - Demolition ball, hand demolition or pusher arm is usually applied.

Roof Trusses - Trusses are lifted out and lowered by a crane after removal of the purlins.

Steelwork - Cranes usually used to lower steel members to ground.

Reinforced Cast In-Situ Concrete

Expensive to demolish as equipment required is costly.

Slabs usually cut out with hydraulic bursters in small sections.

Reinforcement is cut at one end and the beams are lowered to the ground.

Columns are supported by ropes then pulled over after reinforcement is cut.

Pre-Stressed Concrete Structures

Most difficult form to demolish.

Mistakes may cause reinforcement bars to shoot out the beams.

Expert advice should be sought.

Shoring

Shoring is a supporting framework used to provide temporary support to structures.

2 Types:

Raking Shores - shores that lean against the exposed wall of the building requiring support.

Flying Shores - shores that span between two close buildings up to a distance of 9m.

Demolition Method Statement

Complete a detailed H&S method statement before work starts - should include a full risk assessment. Should be easy to understand & agreed by all levels of management & supervision. Must include:

Sequence and method of demolition or dismantling.

Details of personnel access, working platforms & machinery requirements.

Design of any temporary structures required.

Details of any pre-weakening required & areas to be pulled down or demolished with explosives.

Arrangements for personnel protection & public and the exclusion of unauthorised people.

Details of areas outside the site boundary requiring control to improve safety during critical stages.

Details of removing/making safe services.

Details of temporary services available and required by contractor.

Details & methods for detailing with flammable materials & gases found.

Details of methods to identify hidden or other hazardous substances, the methods for disposal & what protective equipment is required.

Arrangements for the control of site transport to be used for removing demolition debris.

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