1.4 Structural Safety

Question 1

Buildings must be strong enough

to deal with three main types of loads, known as

Answer 1

static, dynamic, and hidden loads.

Question 2

Signs of damage to building structure

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Answer 2

  Sagging along the roof line (ridge) 
  Missing roof timbers and roof coverings 
  Walls  and  quoins  (corners)  out  of 
plumb (vertical alignment) 
  Cracked  and  spalling  (peeling  off) 
render 
  Missing or collapsed masonry 
  Broken gutters and downpipes 
  Collapsed or damaged arches or lintels 
at doorways and other openings. 
  Signs  of  corrosion  on  concrete 
(from reinforcement) 
  Cracks  through  structural  block 
work, brick work or masonry 
  Dampness – mould growth 
  Signs of wet or dry rot 
  Signs  of  insect  infestation 
(woodworm).

Question 3

Causes of damage to building structure

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Answer 3

Adverse weather conditions  
Overloading of structures 
Hot and corrosive atmospheres 
Vibration
Alteration to structural members 
Subsidence
Deterioration of building materials 
Excavations
Unauthorised modifications to buildings

Question 4

Structural collapses can occur for a variety of reasons. They can result from a major
structural fault but any seemingly minor faults can contribute to a chain of events that
inevitably may lead to a collapse, which can be classified under three categories:

Answer 4

 Localised collapse relates to collapses that are confined to a small part of the
building, without any induced damage occurring on other parts.
 Progressive collapse occurs when a key member, or members of a structure
fails. The isolated failure of the key member or section initiates a sequence of
events, causing failure of the entire structure.
 Disproportionate collapse occurs if removal of one supporting member causes
damage disproportionate to the cause of the damage, for example: where the
remaining load bearing elements (walls, floors and roofs) are not strong enough
or adequately strengthened, to resist the loads overstress and collapse.

Question 5

Some of the major causes of structural collapse during refurbishment are:

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Answer 5

 failure to determine structural integrity
 inappropriate weakening of structures
 accumulation of smaller weaknesses in structures
 activity induced (example: poor weakening)
 load induced failures (example: debris, climatic)
 spontaneous failures of structures (deterioration and sunlight)
 remote activity (example: vibration) during partial demolition/removal of any
structural element and/or structure
 lack of or inadequate method statements for the erection and safe removal of
structural elements
 lack of appropriate temporary support
 early removal of formwork/temporary supports
 misunderstanding of load paths
 differential settlement (example: liquefaction of soil) of the foundation.