Role of the Structural Engineer in Demolition
Rob Clarke, BEng, CEng, MICE, MIStructE
Keywords:
structural engineer, demolition, hazards, temporary works, sequence, collapse,
mechanism, pre-weakening, explosive, long-reach, pulverise
1.
Synopsis
Rob
Clarke has thirty years’ experience as a civil & structural engineer. After
a career with Buro Happold designing new structures, five years ago he joined
one of the UK’s most prominent demolition contractors, Controlled Demolition.
He is now practicing as a freelance structural engineer for the demolition
industry.
This
paper is intended to help other structural engineers as well as construction and
health & safety (H&S) professionals to appreciate some of the common
structural issues encountered during demolition. It also provides an insight
into the role of the structural engineer working for a demolition contractor.
2.
Introduction
“Although HSE statistics
show that demolition is a high-risk activity, it would appear that it is either
not given much consideration or is included at the end of the planning process
and given whatever time is left in the programme. The avoidance of accidents
depends on the quality and thoroughness of the Designer’s plan for the project.”
CDM Guidance for Designer, Construction Industry Council.
According
to the HSE Statistics Unit,
reportable injuries in demolition are twice as high as those in
construction. For the 12 month period 2007 – 2008 there were 10
reportable injuries for every 1000 demolition workers (of 18,000 total)
compared with 5 reportable injuries for every 1000 construction workers (of
500,000 total). Clearly, demolition is still a relatively dangerous industry to
work in.
Risks
associated with the industry do not only impact on the demolition contractor
and his staff, but can also affect the building owner, developer, local
authority, government agencies and the wider community.
The
content of this paper is equally relevant to refurbishment projects where
demolition is a necessary process but not always fully appreciated by a construction
industry that focuses on new-build.
The
Health & Safety and CDM regulations are an essential aspect of demolition
and much has been written from these perspectives. This paper focuses more on the
structural detail.
Role of the structural
engineer The
structural engineer can play a crucial part in reducing the hazards associated
with demolition, refurbishment, dismantling and decommissioning. From power
stations to tower blocks and from bridges to Victorian institutional piles.
From the robust and modern to the crumbling, damaged and ancient. From city
centre buildings trapped between other buildings to those located on greenfield
sites. The following text deals predominantly with buildings, however its
content can be related to many other types of structure.
Presenting
the structural risks clearly at the beginning of a project reduces accidents and
saves time and money. Good communication helps ensure that the potential hazards
are understood by the client team, site managers, supervisors and the workforce.
3. Demolition in practice
Demolition
may be viewed as the poor cousin
of construction, but an experienced demolition contractor will often know more
about the ultimate strength of materials and collapse mechanisms than many
structural engineers. During demolition the true strength of a structure and
its components are exposed. The demolition engineer has physically worked with,
manipulated and pulled apart more buildings than probably most structural
engineers will ever design in a lifetime. He will understand plastic and
elastic behaviour, serviceability and ultimate limit states, even though he
cannot recite the relevant formula.
The scenarios are often
complex; getting the demolition sequence right can be like a game of 3D chess,
thinking many moves ahead. The structural engineer must be able to visualise
the part-demolished structure.
Demolition
should not be thought of as de-construction. In construction, there is
relatively little choice in the methods and sequence available to build a
structure. In demolition there are always many alternative methods and
sequences that can be employed. Different contractors have different plant and
equipment, different skills and specialisms and different learned experiences.
These factors will greatly influence the cost and chosen method. With this variety
of methods there are varying hazards and degrees of risk to consider. There may
be a best solution in terms of programme or hazards but this may not
necessarily be the cheapest. Remote demolition, such as long-reaching or
explosives, is often safer because the number of man-hours working at height can
be considerably reduced.
In order to obtain a
better understanding of the demolition process it helps to be able to recognize
the potential hazards. These are not always obvious to those who are in a
position to influence decisions made on site. If they were obvious then
demolition would be a much safer industry.
The principle concern of
the structural engineer is uncontrolled collapse.
In
demolition only planned collapse is acceptable. An unplanned collapse of
elements greater than three tonne should be reported to the HSE as a dangerous occurrence.
Causes of collapse can
include:
· Collapse due to
overloading of floors by machines or debris.
· Collapse due to unexpectedly
weak connections.
· Collapse due to unexpected
voids and hidden basements.
· Collapse due to the incorrect
demolition sequence.
· Collapse due to ignorance
of stability issues.
· Collapse due to instability
in high winds.
· Collapse due to the
discontinuity of structure at movement joints.
· Collapse due to
over-stressed elements caused by an altered load path.
· Collapse due to excessive
commercial pressures leading to corner cutting.
· Collapse due to risk
taking individuals.
When
the structural issues are understood, collapses can be prevented as the
following examples demonstrate:
Cut lines. It is much better to pulverise
and munch up to a cut line rather than prop and diamond saw cut. Providing
lateral stability to the propped element can be difficult. Also, do not munch
up to the face of an in-situ column, leave a stub of reinforced concrete beam
protruding so as not to destroy the reinforcement anchorage.
When
working towards the end of a framed building i.e., an un-braced frame with no
shear walls, it is sensible to leave a minimum of two bays, which is much more
stable than one bay.
Long-reach demolition has now become common
place. The track-mounted plant with an extra long boom and dipper arm,
sometimes telescopic, can reach 40m easily and there are some giants that can
reach 90m high.
Long Reach
Sequence – working towards the stiff core to maintain stability.
When
long-reaching, it is good practice to follow a sequence that works back towards
the stiff core so that the lateral stability of the structure is always
maintained. The distance from the long-reach machine to the face of the
building should preferably be a minimum of half the height of the building so
that the operator is a safe distance from the falling demolition arisings.
Normally,
when long-reaching tower blocks, the floor slab will be able to safely carry
the demolition arisings from the floor above. If a floor is overloaded with the
demolition arisings from a number of higher storeys, a progressive vertical
collapse can occur. It is generally safer to long-reach bay by bay full height
rather than floor by floor. This prevents excessive debris built up on floors
and the potential for a progressive collapse.
The
large panel residential tower block system building can be at risk of a Ronan
Point type failure (the full height collapse of one structural bay)
during demolition. These buildings have pre-cast concrete floors, walls, stairs
and stair cores. The floors and walls are relatively slender and the fixity at
the slab/wall interface is poor compared to current practice. There is little slab
end bearing and limited slab continuity reinforcement connecting adjacent
pre-cast slabs across the wall support. Often remedial strengthening work was
undertaken in later years but the effectiveness of such work can be variable
and as-built records are hard to find. For this type of building the long-reach method
should be modified slightly. Extra care should be taken to limit the weight of
arisings on the lower slabs. As the building is reduced, a relatively wide
building base area should be maintained and the floors tiered back to preserve
the lateral stability of the building.
Weak
structure & high risk of collapse. Strong
structure & low risk of collapse.
Basements. The presence and
location of any basements should be identified in the pre-tender health and
safety plan. It is good practice is to keep a marked up drawing on site
recording the extent of the filled basement as the demolition front progresses.
Explosive Demolition. A ‘stand-up’ can present
a serious hazard if, after the charges have detonated, the structure does not
fall or collapse and break up. The risks associated with entering a partially
collapsed structure are high. Contingency measures for this should be provided
where possible, for example, having long-reach plant on stand-by. Pre-weakening
is required to help the structure break up under gravity. There is a fine
balance between carrying out enough pre-weakening to avoid a ‘stand-up’ and too
much pre-weakening, making the building unsafe to work in, especially during
high winds. The calculations which justify the extent of pre-weakening must also
consider accidental damage and over-break. The structural engineer has to work
closely with the demolition contractor to produce the most appropriate pre-weakening
arrangement. Special internal strengthening work can be designed to influence
the direction of fall in conjunction with the delay sequence for the charges.
“Commercial pressures imposed by the Client to expedite work often
impose severe limitations on the time available for a demolition contractor to
investigate the design and construction features in detail and then to plan the
demolition work carefully. Contracts tend to leave responsibility for
investigation of the existing structure to the demolition contractor and then
rely on cost penalties to enforce prompt completion. Contractual arrangements
framed in this way increase the risks to both the general public and site
workers, and limit fair competition.” 8th
SCOSS Report 1989. This was written 20 years ago and is still pertinent
today. The preparation time is so important that client pressures to reduce
this period should be resisted firmly.
Commercial pressures imposed by the demolition contractor can often
complicate the required demolition solutions. The competitive tender price can
necessitate imaginative solutions to avoid expensive methods. However, the
demolition contractor must be able to clearly demonstrate that all the
potential hazards have been considered and that the risk has been reduced to an
acceptable level. Compliance with the CDM regulations should prevent risk
taking or inexperienced contractors slipping through the net.
The
Code of Practice for Demolition (BS 6187) is an extremely good reference
document providing an overview of the demolition process. However, the BS
cannot be too prescriptive because every structure is different. That said,
there are some regularly occurring situations where the following advice may be
useful:
|
Plant |
Small plant are used wherever possible to
avoid hand and arm vibration (HAV) caused when using hand held tools. When
considering the safe size of small demolition plant to work on suspended
floors, a starting guide is: ·
Residential - 1 tonne ·
Offices - 2 tonne ·
Shops - 3 tonne In the right situations these weights can be increased using
back-propping with calculations to prove the strength of the floor. |
|
Debris |
Getting the debris away efficiently to avoid a back-log of material
which can overload floors is often
the key to safe and successful demolition. This is particularly important on
constrained city centre sites when internal drop zones and openings through
structural walls are often necessary to create a route to get the demolition
debris material out of the building. Strengthening masonry walls to turn them
into deep beams can allow new openings to be created underneath. |
|
Scaffolding |
A fully enclosed scaffold with reinforced plastic sheeting is used to
surround a building during demolition when it is necessary to protect the
public from any debris escape. A demolition scaffold is typically fully
boarded with no gaps, sheeted or debris netted and carries 2kN/m2 at the top
level. It is important for the structural engineer to consider the scaffold
tie back fixings to the existing structure, which may be weak. The vertical
cantilever must not be allowed to become too high as the demolition
progresses. |
|
Pre-stressed concrete |
When working with pre-stressed concrete, the stressed tendons should
never be cut. Generally there is no need. These elements can be demolished
quite safely by destroying the concrete around the stressed tendons.
Immediately the concrete fails and crushes the tendons relax and become
de-stressed. This is true for grouted and un-grouted ducts. |
|
Deep RC beams |
Deep RC beams can be very difficult to demolish, particularly at
height. One practical solution is to gradually reduce the beam’s
cross-section along its entire length with a hammer attachment. This can be
much less hazardous than cutting and lifting. |
|
Party walls |
Demolition against a party wall is one of the most complex operations.
Sometimes pre-weakening the structure to allow hinges to develop whilst
long-reaching can be used to fold the frame away from the retained building. |
It
should be noted that every situation is different and should be individually
checked and assessed.
4. Survey and Inspection
Surveys
and inspections form an essential part of a preventative safety system,
particularly at the planning stage for demolition operations.
Structural
surveys are a form of detective work; the structural engineer has to read the
clues to determine how the structure
was actually constructed. He has to look for tell tale signs and evidence about
connection strength and the general quality of workmanship and attention to
detail.
The
importance of the Structural Survey cannot be underestimated. Serious hazards
are created if, for example, a movement joint or a narrow bearing detail is
missed.
A
detailed structural assessment should identify any weak elements, supports,
connections or structural features which are stability sensitive. Overall
stability throughout the demolition process to avoid the danger of an unplanned
collapse should be considered. Load paths must be identified and it is
important to identify the potential for hazards associated with hangers, ties,
cable stayed roofs, barrels, arches and domes, space frames, retained facades,
pre-stressed components, structures retained by ground anchors and structures that
have been modified.
There
are three main opportunities for the demolition contractors to carry out a
structural survey:
Pre-demolition survey. A good time to carry out the first survey is
during the Type 3 asbestos survey work when intrusive work is acceptable.
Usually after the building is vacated and before the soft-strip starts.
The
Pre-demolition building survey should include:-
1. Structural form and movement joint locations.
2. A description of how lateral stability is maintained.
3. Any pre-stressed or post-tensioned elements.
4. Novel forms of construction.
5. Gross structural defects, cracks and signs of movement.
6. Hangers and ties.
7. A search for any existing drawings and calculations, noting that
actual details may vary.
8. The building age and
typical details to expect.
9. Recommendations for any local exploratory work.
A
good pre-tender H&S plan will have a pre-demolition structural survey.
During soft-strip. Often the structure is not properly exposed until
the soft-strip operation is completed. The original demolition method may then need
to be revised. Much of the floor and ceiling finishes will have been removed,
exposing the structure to provide a fuller understanding of the building. Early
investigation work can now be confirmed. Signs of poor workmanship may be
exposed. More intrusive work can be carried out to expose connections and
joints and locally check slab reinforcement.
It
should be noted that it is quite often difficult for the demolition contractor
to supply a set of complete method statements before the structure is fully
exposed, although this is often requested. The contractor needs to be given the
flexibility to modify his methods in the light of new found information.
During demolition. Site inspections by the structural engineer during demolition are a
sensible precaution. This is an important opportunity, for example, to spot
hidden ties which hold a mansard roof together or to inspect a wall which is
being subjected to high lateral loads from a rubble pile. Often the temporary
works structural engineer is only commissioned to design the temporary works
and not inspect progress. A temporary works design needs to be very clear so
that it cannot be misinterpreted. Any potential hazards should be brought to
the attention of the site manager immediately.
The
condition of brickwork and timber is particularly important in refurbishment
work. The mortar can vary from rock-hard and fully bonded to a loose sand that
flows out of the joints with the slightest disturbance. It can also be patchy, depending
on work carried out at different times or work by different gangs. Removing the
plaster during refurbishment of old buildings from all faces is recommended to
help determine the masonry condition.
5. Design
During
the appraisal of an existing building there are a few basic questions the
structural engineer should ask:
Strength and robustness It is a good idea to ask
oneself how one would have designed the original structure, considering the
site restrictions, the use of the structure and any change of use. Historical
plans and a knowledge of historical codes of practice can be of help. Then
whilst surveying the building any deviations from your expected design can be
further investigated to check for potential difficulties later. When
considering the robustness of a structure, the strength and rotational
stiffness of connections is key to how the building will behave.
Collapse mechanisms. The Structural Engineer
needs to think carefully about how the structure will behave during planned
collapses as well as any unplanned collapses. What will be the exact mode of
failure: bending, shear, or excessive deflection? Will the failure be slow or
sudden? Will there be any warning? Imagine the collapse second by second, in
slow motion. How much of the structure will be affected? There are many
instances where a load-bearing wall can be removed with no effect because of
redundancy in the structure and alternative load paths. One must also consider
the possibility of accidental impact by moving plant. What are the key elements
which, if damaged, could cause a progressive collapse or catastrophic failure?
Building design details are often simplified to
assist construction. For example, reinforcement or bolted connection details
may be standardised. This can provide extra load carrying capacity which the Structural
Engineer can take advantage of, even if this only increases factors of safety.
Strength of elements When assessing the strength of elements such as reinforced
concrete slabs and beams, shear is often the most important failure mechanism
to consider because shear failures are generally sudden and without warning.
Member stiffness and deflection is less important. Justifying the safe bending
capacity can be difficult because the reinforced concrete code limits crack
width for durability which is not important during demolition. In the right
circumstances the demolition contractor will sometimes safely overload a slab
or beam until it fails and the ultimate load can be many times greater than the
predicted factor of safety would suggest.
Adjacent buildings An understanding of the sensitivity of any adjacent
buildings, their structural frame and stability provision are important.
A
structural engineer with the appropriate experience will provide the following
services for a demolition contractor:-
Planning
·
Feasibility studies considering alternative demolition options and
methods with recommendations that cause least risk to human life and least
disturbance to neighbours.
·
Advising on the most suitable methods for dealing with pre-stressed and
post-tensioned structural elements and other ‘special structures’.
·
Calculate the strength of existing floors and advise on the size, type
and number of demolition plant that can be safely used. If necessary, advising
on back-propping, type and layout.
Small plant
demolishing a multi-storey office block.
Remotely
controlled breaker.
·
Assist in the planning of demolition sequences and the preparation of
detailed method statements and risk assessments. This is particularly important
for complex structures and refurbishment schemes. The demolition of simple
structures can be made complex due to close proximity to adjacent buildings. Where
noise or vibration cannot be tolerated or where access for the removal of
materials is particularly restricted.
·
Work with the demolition contractor on alternative methods to pre-weaken
a structure. The engineer will demonstrate by calculation the safety of a
pre-weakened structure during its pre-weakened and part demolished condition.
pre-weakening for explosive demolition (steel). Each column has 5 cuts.
pre-weakening for explosive demolition (concrete)
·
Work with the demolition contractor to design safe, efficient and
effective collapse mechanisms such
as hingeing, launching, pulling or the controlled use of explosives and
combinations of these.
·
Produce lifting plans.
·
Review demolition methods and sequences providing an expert opinion and
confirmation that the proposals are safe.
Temporary Works
·
Temporary works design for floor strengthening for machine and debris
loads or for breaking-out of temporary openings to allow debris removal and
machine access.
·
Temporary works design for shoring basement walls and under-pinning.
·
Temporary works design for propping and needling for wall removal or for
temporary bracing systems for stability in refurbishment and demolition.
·
Design of working platforms for tracked plant (typically a compacted
hardcore embankment, several storeys high, which will allow a long-reach machine
to reach the top of the building). These are most commonly constructed using the
demolition arisings. Loose and compacted pulverised brick and concrete has a
very high angle of internal friction and there is no problem maintaining 45
degree slopes in this material.
·
Design of temporary ramps for moving plant from floor to floor inside
buildings.
·
Provide advice and assistance on site during complex procedures.
To
give an example of temporary works design for demolition, a long-span trussed
roof in a city centre location
requires a 500 ton crane to lift down each truss to ground level and all
the associated working at height cutting and slinging operations. The
alternative was to prop the trusses so that each truss could be safely
long-reached in-situ.
Temporary steel props enable long-reach cutting operation
6. Communication
Collapses
are often the result of failure to use information that is available somewhere.
Unless
you are used to demolition it can be difficult to visualise what a structure
will look like during the demolition process. Providing structural engineering
advice is a waste of time if it cannot be understood. A simple sketch can
replace sides of A4 text, which in reality, few people take the time to read.
The sketch can also be easily copied into method statements.
The 3D sketch
also helps design development. 3D
Collapse simulation movie in real time.
Preferably nothing should
be so complicated that it cannot be explained to non-experts. If it is that
complicated, one should try to make it simpler. There is much more risk of an
incident occurring because, for example, a machine operator or scaffolder has
not understood. Also approvals will be easier to obtain. Explaining the reasons
behind methods can make them easier to understand and easier for others to
remember. This also allows methods to be improved upon and developed by others
in the chain.
There
are three levels at which communication is important:-
The client’s team need to
communicate their views on any assumed demolition sequence to the contractor.
They should highlight known hazards and any assumptions made about the existing
building that will need to be confirmed by the contractor.
The contractor has to
communicate his demolition sequence proposals to the client’s team for
approval.
The contractor has to communicate the approved method and sequence to
the workforce.
3D
drafting software such as Revit and Tekla are being used increasingly to
clearly demonstrate complicated demolition sequences, for which they are
invaluable tools, particularly where there are a number of different
sub-contractors working in the same area at different stages.
3D
collapse simulation software such as Extreme Loading from ASI is an impressive tool
that is going to become more prevalent, particularly for ‘pulling’ structures (this
is where a structure is weakened and pulled to the ground) and for ‘blowdowns’
(demolition by the controlled use of explosives). ASI’s Applied Element Method (AEM) based technology is the
only analysis method for accurately analysing the behaviour of a structure
during a critical failure and the resultant progressive collapse. The software
will analyse and predict the linear, nonlinear, and failure modes of structures
in a 4D environment. It will analyse and play out different ‘key element’
removal scenarios. Collapse simulation is an excellent way to demonstrate to
clients exactly what to expect and it can be used during the demolition design process
to check and refine collapse mechanisms.
The position of structural
engineer can be immensely satisfying when, through good communication, one is
able to combine the knowledge of experienced construction and demolition
professionals to produce innovative, simple and safe solutions to complex and
difficult problems.
7. Sustainability Considerations
Designing
attractive high quality new buildings that are built to last and can easily be
adapted for change of use will produce the most sustainable buildings because
they will not need to be demolished.
Demolition
contractors have always been efficient at recycling because it makes commercial
sense to sell and re-use as much material as possible. Typically 90% of the
demolished building is recycled. The 10% that goes to landfill is generally
carpets, curtains, blinds, false ceilings and roofing felt.
Water
and air pollution is controlled by good site practice, the contract
specification and legislative requirements.
When
considering the reduction of carbon emissions during demolition operations, diesel
fuel is by far the largest single contributor to the quantity of carbon dioxide
emissions that are produced. Every 100 litres of diesel fuel consumed results
in 268kg of CO2 being produced. It is in everybody’s interest to
reduce this as much as possible and there are various methods by which this can
be achieved:
· Using modern and well-maintained demolition plant and
choosing plant with low fuel consumption rates will save fuel. So will reducing
transport distances, including plant to site, waste to the processor and
operatives commuting distances.
· Separating and re-cycling the elements of the
demolished building reduces the carbon footprint. Every 0.34 tonnes of waste
that is re-cycled and not sent to landfill will save the greenhouse gas
equivalent of 1.0 tonne of carbon dioxide production.
·
Recycling can be made more efficient if building designers consider
material separation. For example, specifying dry linings rather than wet
applied plaster which is difficult to separate from masonry.
· Comparing alternative demolition methods, for example,
the controlled use of explosives can reduce the contract period, the amount of
demolition plant required and, most importantly, the amount of diesel consumed.
A typical 20-storey tower block blow-down process will produce 15 tonnes of
carbon dioxide emissions. The same block demolished by traditional work-down
methods using 5 or 7-ton machines over the longer period will produce 80 tonnes
of carbon dioxide. The blow-down method will save 65 tonnes of carbon dioxide
from being discharged to the atmosphere.
8. Design for future demolition and refurbishment
The
more as-built information there is available the closer demolition tender sums
will be and there will be less opportunity for claims through unforeseen
difficulties. CDM health and safety files and operation manuals for new
buildings should improve this aspect and help reduce hazards for future
generations.
The
following design considerations may not be at the top of most designer’s or
client’s to-do list, however, they will make future demolition safer and the
provisions do assist the creation of robust and adaptable buildings:-
1.
Stiff connections and built-in redundancy allow alternative load paths and
will make demolition safer, with fewer uncontrolled collapses. Recent revisions
to design codes have improved continuity ties for in-situ concrete and precast
concrete design.
2.
Adopting a robust minimum size bolted end connection detail for steelwork.
3.
Providing a 50mm air gap at party wall junctions, instead of 10 or 20mm.
4.
Wider staircases and landings, 1500mm to avoid the necessity for cranes
to lift small plant onto the upper floors will allow small plant to access all
levels without the need for a crane.
5.
Avoid designing massive structures carrying heavy plant and tanks on the
top floor of multi-storey office blocks and flats. (It’s difficult getting a 20
tonne machine onto the roof) Dealing with these roof top structures is often
the most hazardous operation.
6.
Use a design live load allowance of 4kN/m2 which is adequate
to support two or three tonne demolition plant and provides the added bonus of
reasonable flexibility for change of use and refurbishment to extend the useful
life span of a building.
9. Conclusion
The structural engineer
combines technical knowledge with management and communication skills.
With a knowledge of the
demolition industry and its practices, the structural engineer can contribute
and add value to demolition works from all perspectives – whether the client
is a contractor, building owner, developer, local authority or government
agency.
Demolition, like most
other branches of engineering, is becoming increasingly complex due to factors
such as commercial pressures, health & safety, sustainability, community
interest/concern, new technologies, new materials and new construction
processes. The structural engineer can help clients address these issues
and
help the demolition contractor improve productivity and
health & safety outcomes through engineering analysis and design.
Engineering analysis and
visualisation with CAD provide an opportunity for demolition contractors to
improve record keeping and knowledge management, so that practical experience
can be passed on to junior staff.
The structural engineer
can assist with communication with stakeholders and regulatory authoritories.
Cost efficient, safe and
sustainable demolition depends on:
· A good quality
pre-demolition survey.
· Good communication between
all parties involved.
· Much depends on the assessment
of the strength of connections and continuity ties.
· Identification and
communication of stability and robustness systems and assumptions.
· As with construction,
access to move materials can be crucial to the success of a project.
· Most importantly, keep it
simple.
Employ expert advice every
time. Early input will reduce costs, financial and H & S risks, contract
duration and improve sustainability.
10. Useful links and references
Institution of Civil Engineers: www.ice.org.uk
(Demolition Protocol 2008.pdf)
National Federation of Demolition Contractors:
www.demolition-nfdc.com
Health & Safety Executive: www.hse.gov.uk
Institute of demolition engineers: www.demolitionengineers.net
Confidential Reporting on Structural Safety (CROSS)
scheme: www.scoss.org.uk
Corporation of London: www.cityoflondon.gov.uk
(Demolition-control_and_advice)
BS 6187-2000 – Code of Practice for
Demolition