AD 435: Beams supporting precast planks:
checks in the temporary condition
The purpose of this note is to remind designers
of their responsibility for basing their design on
a safe method of erection. This is particularly
necessary if structural stability in the part-erected
condition is not evident.
The CDM (2015) regulations consider this in
Regulation 11 where “(1) The principal designer
must … ensure that, so far as is reasonably
practicable, the project is carried out without risks
to health or safety. …
“In fulfilling the duties in paragraph (1), the
principal designer must identify and eliminate
or control, so far as is reasonably practicable,
foreseeable risks to the health or safety of any
(a) carrying out or liable to be affected by
construction work; …”.
BS EN 1090-2:2018 addresses this issue more
directly in paragraph 9.3.1 which states that the
design basis method of erection shall consider
amongst other things the following: “d) stability
concept for the part-erected structure including
any requirements for temporary bracing or
SCI publication P401: Design of composite
beams using precast concrete slabs in accordance
with Eurocode 4 states in Section 3.6 “The stability
of the steel beams during the erection of the
floor units and the placement of the structural
topping must be considered. The designer
should take due account of the floor erection
process (which will usually require erection in
‘bays’ to avoid excessive re-siting of the crane).
Should a particular sequence of erection or
temporary support be necessary, this should be
noted in the specification and on the drawings.
The placement of the precast concrete units
should be carefully controlled in order that out
of balance construction loads are kept within the
limits assumed in the beam design …”.
Section 4 of the publication discusses the
checks for torsion which should be carried out in
the event that an out-of-balance load results from
the assumed erection sequence. Such conditions
may result from:
1. The assumed erection sequence;
2. Unequal plank spans on either side of the
3. Planks spanning in different directions on
either side of the beam;
4. The sequence of placing the in-situ topping.
Other relevant issues are the effectiveness
of the lateral restraint provided by the precast
planks and the specification of additional restraint
if the planks are inadequate by themselves. (See
P401, Section 3.6).
Contact: Richard Henderson
Tel: 01344 636555