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View Full Version : 1.25 wind brace capacity increase when considering wind



SE1006
18th July 2012, 10:32 AM
Hi guys, just after a bit of info:

Some years ago i inherited, and have used since, an increasing factor of 1.25 for wind brace capacities when considering resistance to wind loads.

Could anyone advise from which standard it originates?

Thanks in advance

BMB
18th July 2012, 01:18 PM
BS 5975:2008 + A1:2011 cl. 19.4.2.1 page 117... however you will need to read the preceding criteria.

As far as I know, this is the only place this is mentioned in current codes of practice.

B.

Alan Reade
18th July 2012, 02:52 PM
You will also find it as far back as BS5873 1993 39:19:2:3 however I think this is now omitted from TG20. However as Ben has stated it is in 5975 but does com with a preamble!

Alan Reade
19th July 2012, 03:44 AM
19.4.2.1 General
The proposed falsework structure should be analysed to find the
parameters that need to be taken into account in the selection of
the individual elements. These parameters include the relevant axial
loads, bending moments, shear forces, bearing stresses and deflection
characteristics.
When considering the reactions on vertical members account should
be taken of any effects of continuity, see 19.3.3.2. Where specific
conditions can be identified, such as beams on three supports, a more
detailed analysis may be justified.
Wherever possible, when detailing the individual elements, the
maximum tolerances permitted for workmanship on site as described
in Clause 20 should be adopted and allowed for in the element design.
For items listed in 20.3.2, the allowable safe working stresses used in
conformity with the recommendations of this code will be adequate.
Where the eccentricity at the point of transfer of loads between
components exceeds the tolerances recommended in 20.3.2, the
connection and the resulting forces should be evaluated and provisions
made for them. Particular care is required when the falsework supports
a soffit with longitudinal and/or transverse crossfalls and where base
plates are supported on a sloping foundation (such as a concrete slab
with a crossfall). Refer to 19.7.7.
Where high concentrations of loading occur on relatively light members,
any problems of local instability due to web crushing and buckling
become more critical. The methods of analysis are outlined in Annex J.
The allowable stresses recommended in this section may be exceeded
by 25% in cases where an increase in stress is solely due to wind forces,
provided that the sections should be not less than those needed if the
wind stresses were neglected.

SE1006
31st July 2012, 03:50 PM
... that's the badger! Many thanks gents