STRUCTURAL
STEELWORK
SECTION I
: FABRICATION & TRANSPORTATION
1. GENERAL
The
members and bracing shall be of structural steel fabricated by electric arc
welding processes and connected in the field by means of bolts, welding and
connecting links. All workmanship shall be of first class quality in every
respect, the greatest accuracy being observed to ensure that all parts will fit
together properly on erection.
2.
MATERIALS AND TESTING
All steel
used shall be in accordance to BS EN 10025, BS EN 10210 or equivalent. Sections
rolled from mild steel shall conform to BS 4, BS EN 10056, BS EN 10210, BS EN 10219
or equivalent. Electrodes shall conform to the requirements of BS EN 440, BS EN
ISO 2560, BS EN 756, BS EN 1668. All black bolts, screws, nuts and washers
shall conform to B.S. 3692, B.S. 4190 & B.S. 4320. High strength Friction
Grip Bolts, nuts and washers shall be of approved manufacturer and shall comply
with the requirements of B.S. 4395. Manufacturer's Test Certificates for all
steel used for fabrication and for bolts for the work shall be supplied. These
shall include all the mechanical tests described in the appropriate
specification and also a chemical analysis. No materials shall be used in the
steel work until it has been identified with the tests and inspected or
otherwise approved by the Engineer, except in the case of minor parts or materials
for which this requirement may be waived by permission in writing from the
Engineer. All
steel shall be new and shall be free from cracks surface flaws, laminations,
rough
jagged or
imperfect edges and faces, slag inclusions and all defects.
3. SHOP
DRAWINGS
The
Contractor shall be responsible for the preparation of shop drawings which
shall give complete information necessary for the fabrication of the component
parts of the structure including the location, type, size and extent of all
bolt holes and welds and the electrodes to be used and the sequence of welding
which shall be controlled to minimize contraction stresses and distortion. The
drawings shall be submitted to the Engineer for approval not less than twenty
one (21) days before the fabrication of the steelwork is due to be commenced
and no
fabrication
shall be carried out until such approval is given. The instructions and directions
given on the drawings shall not be varied without further approval in writing. -
SS 1 - Approval by the Engineers of shop drawings shall indicate that the
general requirements of the structural design have been satisfied. Approval
shall not be taken to imply that the dimensions or the correct matching and
design of connections or joints have been checked and this will remain the
responsibility of the Contractor. Drawings submitted for approval shall be of
good standard and any drawing which clearly requires considerable amendment
will be returned for alteration without a detailed review of all the
corrections which may be required. The Contractor shall supply to the Engineer
two complete sets of shop drawings. After drawings have been submitted to the Engineer
for approval one (1) complete set shall be return to the contractor, each
drawing having been given one of the following classifications. Approved In
this case the drawing is satisfactory and fabrication may proceed. Approved
Subject In this case the drawing is to Amendment substantially satisfactory
except for small changes required. The drawing shall be amended by the
Contractor and submitted again for approval. However, fabrication need not be
held up pending final approval. Rejected In this case a drawing is considered
by the Engineer to require major alteration and must be re-submitted. Fabrication
shall not commence until the re-submitted drawing has been returned marked
"Approved" or "approved Subjected to Amendment". 4. WEIGHT
OF STEELWORK All sizes shown on the drawings are not sizes after machining and
the Contractor shall allow for the difference between this weight and the
actual gross weight required. 5. MEASUREMENT All measurement shall be made by
means of an approved steel tape. Dimensions of all steelwork given on the
drawings are to be assumed to obtain at a temperature of 720F/220
Celsius.
6. UNIVERSAL PLATES AND FLATS Universal lates
or flats with reasonable square and true rolled edges will be accepted as a
substitute for plates of flats with sheared flame cut or machined edges except
that such plates or flats shall not be used if the main stresses to which they
are subjected are other than in the direction of rolling. Where universal plate
or flat is to be fillet welded along its edges, the radius at the edge
shall not
exceed forty (40) per cent of the nominal fillet weld. -SS 2 - 7. STRAIGHTENING
Before any other work is done on them all plates shall be flattened and all
bars and sections straightened and made free from twist so that, when
assembled, adjacent surfaces shall be in close contact throughout. The method
adopted for the above work shall be such as not to injure or mark the material.
Lateral Variation of compression members shall be not greater than one
thousandth (1/1000) of the axial length between points of lateral support. For
other members lateral variation shall not exceed two thousandth (2/1000) of the
axial between supports. 8. CUTTING Unless otherwise specified, steelwork may be
cut by shearing, cropping, sawing or flame cutting. Surfaces produced by such
cutting shall be finished square (unless a beveled edge is called for) true and
smooth to the required dimensions. Finishing of surfaces shall generally be by
machining and/or grinding. In the case of flame cutting, surfaces having only slight irregularities may be lightly
ground only and allowance need not be made in
accordance with other relevant clauses provided that the finished edges
are substantially as straight, true, smooth and regular as those produced by
the finishing cut of a planning machine. Shearing will not be permitted on
plates in the main girder sections. Gusset plates and splice plates may,
however, be sheared in a direction perpendicular to the direction of their main
stresses. Ends of stiffeners shall be cut and finished to fit tightly to the
girder flanges after the flanges have been welded to the web plates and in
accordance with relevant clauses. The butting ends of the compression flanges
which are required to be part of the moment splice for erection or the butting
ends of other compression parts shall be faced after fabrication so as to be in
close contact.
9.
ALLOWANCE FOR MACHINING AND GRINDING
Where
plates are to be sheared or flame cut, the cutting shall permit of at least 3mm
of metal being removed from plates 12mm or less in thickness, and at least 6mm
of metal being removed from plates over 12mm in thickness.
10.
SURFACE FINISH OF MACHINED PARTS
The
surfaces to be finished by machining are indicated on the drawings. The
machining shall be of the highest quality workmanship and surfaces shall bear
to within 0.05 of a mm. Bearing surfaces shall, in addition, be flat to within
0.12 of 1mm. The bearing surfaces at each end of a girder shall be at right
angles to the vertical axis of the girder. - SS 3 -
11. HOLING
Finished
holes for bolts shall be not more than 2mm in diameter larger than the nominal diameter
of the bolt passing through them. Holes shall be drilled. Punching may be
permitted provided the holes are punched 2mm less in diameter than the required
size and reamed after assembly to the full diameter. The thickness of material
punched shall not exceed 15mm.
12.
ASSEMBLY
The
component parts shall be assembled in such a manner that they are neither
twisted or otherwise damaged. All hollow
sections shall be sealed so as to prevent the access of moisture to the
interior of the members.
13.
INSPECTION OF MEMBERS DURING FABRICATION & UPON COMPLETION
The
contractor shall make all necessary arrangements and meet all costs incurred by
the Engineer for the purpose of inspecting work and no work shall be erected
until it has been inspected and passed. Any work found defective or which is
not in accordance with the drawings or this specification may be rejected and
shall at once be made good. The Contractor shall supply free of charge all
labour, tools etc. required in connection with the inspection of the work.
14.
MARKING FOR ERECTION
Each part
shall be marked with approved destination marks and stamped with durable markings.
Two (2) copies of drawings correctly showing these markings shall be supplied free
of charge to the Engineer when the steelwork is despatched.
15. SUPPLY
OF BOLTS
(a) Black
Bolts
The
Contractor shall supply the full number of nuts, bolts washers, etc. required to
complete the work in the field. These shall have been dipped into hot boiled linseed
oil before delivery. All bolts and nuts shall have heads forged out of the
solid truly concentric and square with the shank, with hexagonal heads and nuts
of the sized set out in BS 916. Bolts shall be carefully screwed to BS 84
(using medium fit tolerances) and all nuts shall fit hand-tight to the bolts.
The bolt shanks shall be straight and true.
(b) High
Tensile steel Bolts
All high
tensile steel bolts, nuts and washers shall conform to BS EN 14399. Bolts and
nuts shall be washer-faced on the bearing surfaces of the head and nut. They shall
have been suitably protected before delivery. - SS 4 –
16.
PACKING AND MARKING OF FABRICATED STEELWORK
All bolts,
nuts, washers, plates under 30cm square, and small articles generally, shall be
packed separately to the satisfaction of the Engineer. Marking shall be
carefully stencilled on each piece in a conspicuous position.
17.
TRANSPORT AND HANDLING
Special
care shall be taken in the lifting, handling and transporting of structural
steelwork assembled before delivery to ensure protection from damage. In
particular, all open joints, gussets and other projecting parts shall be
protected to the satisfaction of the Engineer. The methods of transporting and
of handling the metalwork shall be subjected to the approval of the Engineer.
Any special precaution, safety measures or escorts which may be required for
the handling and transporting of large pieces shall be at the cost of the Contractor.
18.
DELIVERY AND CUSTODY OF STEELWORK
The
Contractor shall ensure the safe delivery of the whole of the steelwork. When
making delivery of the metalwork he shall bring immediately to the notice of
the Engineer any damage or defects therein and shall make good any such or
subsequent damage or defects at his own expense, to the entire satisfaction of
the Engineer.
19.
BOLTING
Where
necessary washers shall be tapered or otherwise suitably shaped to give the
heads and nuts of bolts a satisfactory bearing. The threaded portion of each
bolt shall project through the nut at least one thread. In all cases where the
full bearing area of the bolt is to be developed, the bolt shall be provided
with a washer of sufficient thickness under the nut to avoid any threaded portion
of the bolt being within the thickness of the parts bolted together. Where a
hollow section is drilled to take bolts or studs, provision shall be made to prevent
the access of moisture to the interior of the section. For example, a
transverse sleeve can be inserted where a bolt passes through a hollow section,
or grommets can be used under heads and nuts.
20.
WELDING - GENERAL
Welding
shall be in accordance with BS 5950, BS EN 1011, all appropriate clauses of these
standards shall be taken as being incorporated herein with details of the
proposed welding procedure. The tests of welding shall be carried out to BS EN
875, BS 709. All welding shall be carried out under the immediate and
continuous supervision of a person who, in the opinion of the Engineer, has had
suitable training and practical experience in the execution of this form of
construction.
- SS 5 -
Plates and
sections shall be reasonably free from slag, oil, grease, paints, rust or heavy
scale or any substance which might affect the quality of the weld. A light film
of linseed oil may be disregarded. Where a weld is to be deposited on a flame
out surface, the surface shall be rendered reasonably free of scale before
welding. Portions of plates or sections which are to be welded by a machine
welding process shall be completely free of scale and rust for a width of at
least 13mm on each side of the weld edge. The landing edges of plate sections
to be welded shall be closed by service bolting, cramping, jigs or tack welds.
When the work is liable to distortion during the welding, it shall be held in
approved frames or jigs. The completed work shall be straight, square and free
from twists, bends and open joints, particular care being taken to secure the
correct dimensions. Due allowance shall be made for loss of dimensions by
shrinkage of welded parts. Wherever possible, or considered to be necessary by
the Engineer, the welding shall be carried cut in a manner to minimize
distortion and contraction stresses by applying the welding in intermittent
stretches and by back-step welding. Where members are cut or machined to
finished length after welding, welding shall proceed from the centre towards the
ends or outside edge. No member at any time during fabrication shall depart
from the straight by more than one in five hundred (1/500) of its length nor
shall the longitudinal profile of any girder
vary from
that shown on the drawings by more than 3mm. All slag shall be removed and the
weld thoroughly cleaned before a run of welding may be superimposed on a
previous run. The welding shall be deposited in runs of good clean metal free
from slag inclusions and porosity. Tamping or hammering of the metal shall be
prohibited, but the slag may be chipped from the metal with a light hammer. The
weld shall show a good even contour, and on a cut specimen shall indicate a
good fusion with the parent metal. Slag inclusions or welds showing porosity
shall be cut out and re-welded. When the V of single V or the first V of double
V butt welds is filled with weld metal the plates shall be turned over and any
slag remaining on the back of the first run removed before a welding is
undertaken on the other side. All butt welds shall be reinforced so that the
section at the weld is ten (10) per cent greater in thickness than the adjacent
metal. Flange butt welds shall be subjected to full X-ray examination where
required by the Engineer, and the Contractor shall allow for the cost of such
examination on at least 50% of flange butt welds. Such cost or the portion
thereof shall be deducted from the monies due to the Contractor if all or some
of the tests have not been carried out. - SS 6 - The Engineer shall require
examination by X-ray, fluorescent links and penetrant dyes of the weld between
flange and web until such times as a uniform and satisfactory procedure is
established. The cost of these shall be borne by the Contractor.
21. FILLET
WELDS
The throat
thickness of fillet shall be not less than seventy percent (70%) of the nominal
size of the weld and each surface of contact shall be not less than the nominal
size of the weld. Surfaces of fillet welds shall junction as smoothly as
practicable with the parent metal and welds showing excessive bulging shall be
cut out and re-welded. Where shown on the Drawings or directed by the Engineer,
fillet welds shall be ground to a smooth, slightly concave finish. 22.
22.WELDING
DETAILS
Particular
care shall be taken that in connection the leg of a stiffener to the flange
plate, no welding transverse to the tension flange shall take place. In the
case of bearing stiffeners over the piers, these shall be carefully fitted to
bear against the bottom flange and welded direct thereto.
23.
PROTECTION OF STEELWORK AND PAINTING
All
steelwork shall be thoroughly cleaned of all loose scale, rust, oil and grease
etc. and then be painted with
• one coat
alkyd-based anti-corrosion primer
• one coat
alkyd enamel undercoat (SS34)
• two coats
alkyd enamel gloss topcoat (SS7)
or
equivalent prior to delivery to the site. Steelwork shall be mechanically wired
brushed. Any coat that has become damaged or defective in any way shall be made
good before application of the subsequent coat. Contact surfaces of High
Strength Friction Grip (H.S.F.G.) bolted connections shall be unpainted except
that the first shop priming coats may extend onto the interface a maximum
distance of 13mm. Subsequent coats shall be thoroughly cleaned by hand wire
brushing before assembly. Painting shall be carried out by brush or roller
generally in accordance with Singapore Standard SS 542. Surfaces to be welded
shall not be painted or metal coated within a reasonable distance of any edges
to be welded. if the paint or metal coating specified will impair the quality of
the weld. Welds and adjacent parent material shall not be painted prior to
de-slagging inspection and approval. Parts
to be encased in concrete shall not be painted or oiled. - SS 7 –
