BS 5975 2019 Extract - Flipbook - Page 62
BS 5975:2019
BRITISH STANDARD
13.3.4
The TWD should identify, from the design brief and associated information, the various loads that act
on the temporary works together with the combinations in which they are considered and with what
stiffness the temporary works should resist them.
13.3.5
Temporary works should be designed in accordance with recognized engineering principles (see
Section 3 or other recognized guidance). The design should take into account the variability of
materials, workmanship, site conditions and construction (erection) tolerances.
13.3.6
All temporary works should be designed using global or partial factors appropriate to the situation,
taking material quality, certainty of loading and standard of execution of the temporary works
into account.
NOTE 1 Issues that can affect material quality are use of second hand material and repeated use of components.
NOTE 2 PAS 8812 gives further advice on the application of European standards to the design of temporary works.
13.3.7
For permissible stress design the global factors incorporated into the allowable working loads given
in Section 3 should be used for general falsework and other temporary work design.
13.3.8
For limit state design of temporary works the loads should be in accordance with BS EN 1991-1-6 and
other relevant codes and industry best practice guidance.
NOTE 1 BS EN 1991-1-6 states that the supported loads are to be treated as variable actions (imposed loads) and
not as permanent actions (dead loads). In some situations geotechnical loads may be considered as permanent
actions instead of variable actions.
NOTE 2 The loads given in Section 3 are suitable as unfactored service loads for limit state design.
13.3.9
For the design of steel or aluminium elements of temporary works, the partial factor for material at
ultimate limit state should be a minimum of 1.1. Where temporary works are designed, manufactured
and assembled for a single use using similar details and execution standards as adopted for
permanent works then the designer may justify the use of a lower partial material factor.
NOTE The increased partial material factor for temporary works applications is used to take into account reuse
of equipment, increased tolerances, reduced stiffness at joints, reduced residual stiffness and reduced redundancy
compared with permanent works.
13.3.10
For each temporary works design, the designer should take into account:
a)
the structural strength and stiffness of the individual members and their connections to transmit
the applied forces safely including any p-delta or feedback effects;
b)
the lateral stability of both individual members and the structure as a whole;
c)
the resistance to overturning or rotational failure of the temporary works structure;
d)
positional stability; and
e)
the effects on the permanent works and its surroundings.
NOTE 1 Within these five considerations, subsidiary considerations might be necessary to allow for the different
phases of construction and the varying stability and restraint conditions applied, including the particular case
where falsework is designed as top-restrained.
NOTE 2 These five considerations apply to both limit state and permissible stress design.
13.3.11
Software should be used with caution to ensure all appropriate checks are carried out.
13.3.12
Temporary works systems should be designed with regard to ease and safety of erection and
dismantling. TWDs and suppliers should provide guidance on the implementation of their design.
13.3.13
Detailing of the temporary works structure should be such that any local failure within it does not
lead to the progressive collapse of the whole.
54#© THE BRITISH STANDARDS INSTITUTION 2019 3 ALL RIGHTS RESERVED
