final-report-of-the-advisory-committee-on-falsework-bragg-report - Flipbook - Page 60
This test should be repeated where there is any change
in design, and when the model has been in production
for a few years.
For continuing assessment a proof test is needed.
This should be included in the initial assessment test
to form a reference for subsequent testing of production models and for equipment on site which is suspected of deteriorating or in some cases after repair
or refettling.
It has been suggested that a body should be set up to
investigate proprietary products and the relevant
literature and to give a mark of approval to products
which pass this body's examination.
Manufacturers' literature
Publications produced by manufacturers of proprietary equipment should not be confined to glossy sales
literature giving few details and little information on
permissible loadings.
The committee are convinced that adequate details
and information should be freely available to users.
It is important that erection sketches and photographs
should include all the necessary bracing and ties.
Data sheets should be available for all proprietary
equipment and should give the safe working loads
and the factors of safety. They should indicate whether
the information given is based on the yield or on the
collapse value of the unit, and whether the values
given are based on calculations or actual tests. The
mode and location of failure of units should be stated.
Full information of section properties, specifications
of materials used and boundary conditions of tests
should be given by the manufacturer.
In the interest of safety, where there is a danger of
wrong units being used, clear markings should be
incorporated in the design and manufacture of proprietary units.
The committee endorse the information to be supplied by the manufacturer of proprietary equipment
which is given in Appendix E of the report of the
Joint Committee.
Tolerances
Tolerances in permanent structural steel work have
not normally been specified since it is well known
that unless a certain standard of fabrication and
erection is maintained the components of the structure
will not fit together. In falsework, however, there is a
quite different set of circumstances. The joints are not
usually bolted through preformed holes and the level
and verticality have to be set out for each of many
members rather than for only a few.
To mechanical engineers the lack of specified tolerances on many falsework drawings is surprising. It is
readily agreed that the precise tolerances associated
with refined engineering projects such as aero engines,
machine tools or scientific instruments would be out
of place in the realms offalsework. We do recommend
however that the principle of indicating the acceptable
tolerances, e.g, ±20 mm should be followed on all
dimensioned drawings.
We are not stating that all props must be exactly vertical, but we do see the need for a consistently good
workmanship standard. The limits within which the
structure must be erected should be specified on the
design drawings and on the erector's detailed working
drawings.
Various draft standards have given guidance on
tolerances for verticality. For example, the Canadian
Standards Association specify at para 7.2.6.i of their
3rd Draft that vertical load-carrying members shall
be erected and maintained plumb within the following
limits:
Plumb lines through any two points on the centre
line of the member, and less than 10 feet apart
vertically, shall not be separated by more than
inch.
Plumb lines through any two points on the centre
line of the member shall not be separated by more
than 1 ½ inches.
The California rules for bridge falsework specify that
for steel shoring "the shoring shall be plumb in both
directions. The maximum deviation from true vertical
shall not exceed ¼ inch in 3 feet. If this deviation is
exceeded the shoring shall not be loaded until it is
readjusted within this limit". The first Draft British
Standard Code of Practice states that "plumblines
through any two points on the centre line of the vertical member shall not be separated by more than
25 mm except that, if the two points under consideration are less than 3 metres apart vertically, separation
shall not exceed 18 mm".
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