1.8 FABRICATION
1.8.1 General
1.8.1.1 Fabrication shall in general be carried out in accordance with BS 5950: Part 2 and
BS 5400: Part 3 and Part
6 for
bridges unless otherwise specified by SCI.
1.8.1.2
All steelworks shall be fabricated from new sections free from rust and pitting and in
such manner that they are not bent,
twisted or damaged.
1.8.1.3 Start of Fabrication
The Contractor shall obtain authorisation from the S.O. to start fabrication.
Such authorisation will not normally be given before all shop drawings have been checked
and approved.
1.8.1.4 Accuracy of Fabrication
All steelworks shall be fabricated to an accuracy so as to
enable erection to the specified tolerances
to take place without introducing permanent erection stresses
into the structures. Due account shall be taken of the effects of temperature on the dimensions of the
fabricated steelworks and measuring instruments when the temperature at the
time of steelwork fabrication is different from the
temperature
of the structural steelworks under service conditions. In addition each fabricated
member after fabrication shall individually comply with the following tolerances.
(1) Cross Section:
Hot Rolled Sections
The tolerances on cross sections of hot rolled sections shall be as specified in BS 4 or
BS
4848 as appropriate.
(2) Length
The length of a member shall not deviate from its specified length by more
than
+/- 3 mm.
(3) Straightness
Unless required to be any
other shape, the deviation of a member from a
straight line drawn between adjacent points of subsequent effective lateral
restraint
shall not exceed:
(a) For all non-hollow sections used as beams or
compression
members:
-
3 mm or S/1000 whichever is the greater where S is the distance between restraints (in mm)
(b) For all other sections:
- S/500, but not greater than 25 mm where S is the distance between
restraints (in mm)
1.8.1.5 Accuracy of Fabrication (Cont’d) (4) Built-Up Members
(a) Tolerance on cross section to comply with Clause 7.2.2 of BS 5950:
Part 2
(b) Tolerance on web plates to comply with Clause 7.2.3 of BS 5950: Part
2
(c) Tolerance on shape of built-up sections to comply with Clause 7.2.4 of
BS 5950: Part
2
(5) Squareness
The deviation from squareness of all ends relative to the axis of the
member shall be such that when the
members are finally positioned and connected they
are
true to their intended line
(within the
tolerances
specified for erection) without excessive deflection or stresses being induced
in them or in
any associated components.
(6) Flatness For Milled Surfaces And Contact
Bearing
Where a "milled surface" is specified at the
ends of compression members at
splices, or the faces of steel packing where required, which are dependent on contact for transmission of compressive stress, the flatness shall be such
that
when measured against a straight edge laid against the full length of
bearing surface in any direction the abutting faces are in full contact except
for 5% of the length they have clearances not exceeding 0.15 mm.
The abutting faces are at right angles to the axis of the member or such other
angle as may be indicated.
(7) Camber
The structural steel members shall be fabricated
with cambers shown on the drawings. The cambers shall be measured at the mid-span of the members in
the
absence
of
the influence of
its
self-weight
and
shall
be within
a
tolerance of +/- 5 mm.
1.8.1.6
Thermal
Cutting
All thermal cutting shall
be
subject to approval.
Manual thermal
cutting of edges to be welded shall
not be permitted.
The edges of all plate cut by
flame and subsequently 0welded shall be machined prior to welding. The amount of metal to be removed shall be subject
to
approval.
1.8.1.7 Heat
Treatment
Details of all heat treatment shall be submitted for approval prior to the
commencement of fabrication.
1.8.1.8 Machining
Machining of ends shall normally be carried out with angle cleats, gussets and other end
fittings fixed in their
permanent positions.
Angles and flats used as bearing stiffeners shall be cut and ground so as to ensure a tight fit along edges in contact with flanges or end plates.
1.8.1.9 Holing
Round holes for fasteners shall
only
be drilled. All
matching holes for fasteners shall
register with each other so that the fasteners can be inserted
freely through the assembled members in
a direction at right angles to the
faces in contact. No site
drilling of holes is permitted.
For black and HSFG bolts not exceeding 24 mm diameter, holes shall not be more than 2 mm greater in diameter than the bolt, and for bolts over 24 mm diameter, holes shall
not be more than 3 mm greater
in
diameter
than
the bolt.
1.8.1.10 Burrs
Burrs and sharp arrises shall be removed by grinding.
1.8.1.11 Checking Before and After Making Permanent Connections
Before and after making permanent connections in structural steel members, which
are
assembled before delivery to Site, the
fit and profile shall be checked by the
Contractor for accuracy.
1.8.1.12 Despatch from Works
The Contractor shall advise SCI of intended dates of despatch to site of steelwork and accessories in such a way that inspection can take place prior to despatch.
1.8.1.13 Notice for Inspection
The Contractor shall give a minimum of 3 working days notice for any inspection but SCI and his appointed representatives shall
have the right to visit the Contractor's or his suppliers' works at
any
reasonable time for the purposes of inspection.
1.8.1.14 Marking
At all stages of fabrication, structural steel members shall be positively identified by
a suitable marking scheme.
For the purpose of marking for erection and inspection, all steel
shall be marked with
a durable and distinguishing identification mark in such a
way
as not to damage the material. The
marks shall be in positions, which are not masked by
other material
after erection and shall correspond to that
given on the shop drawings and erection drawings related to the specific structural steel members.
1.8.2 Templates
1.8.2.1 Full size templates necessary for fabrication when required shall be prepared by the
Contractor and subject
to
SCI’s approval.
1.8.3 Cutting
1.8.3.1
Cutting of
steelworks may be by shearing,
cropping, sawing or
machine flame
cutting.
All cut edges shall be dressed to a neat workmanlike finish, and shall be
free
from distortions.
1.8.4 Tolerances
1.8.4.1 Members
and
components
of rolled and built-up
sections shall
be
checked for tolerances in
accordance with BS
5950 unless otherwise specified
or
approved by SCI.
1.8.5 Protection of Hollow Section
1.8.5.1
Unless special protection is provided for by other means, the interior of any
hollow members, whether a structural hollow section or a fabricated member, shall be
sealed to prevent ingress of water.
