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04. TECHNICAL SPECIFICATION FOR FABRICATION OF STEEL STRUCTURES
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04.1.0 GENERAL
This specification shall apply to steelwork in buildings and general
structural work. For technological structures additional stipulations shall be
considered.
04.2.0 SCOPE OF WORK
The scope of work under fabrication includes, but not limited to, the
following :
a) Preparation and supply of material indents, bolt lists, bought out items
list.
b) Procurement and collection of all steel materials from stockyards/stores,
including loading, transportation, unloading and stacking and storing on skids
or supports.
c) Procurement and collection of all consumables like bolts, nuts, washers,
rivets, electrodes, paints, shims, packs, etc. including allowance for spares
and wastage and getting approval.
d) Preparation and submission of general arrangement drawings, fabrication
drawings, modification/ rectification sketches, as made drawings, erection
drawings, bill of materials,drawing office despatch lists/shipping documents.
e) Preparation and submission for approval of design calculation for
non-standard connections and temporary bracings.
f) Cold straightening of sections and plates whenever they are bent and
kinked.
g) Fabrication of all steel structural components covered under tender
drawings, design drawings and generally described under scope of the project.
h) Making arrangements for conducting tests, such as chemical analysis,
physical and mechanical tests on raw materials where specified/as directed by
the Engineer.
i) Making arrangement for providing all facilities for conducting ultrasonic,
x-ray or gamma ray tests on butt welds; getting the tests conducted by reputed
testing laboratories; making available test films/graphs, reports and
interpretation.
j) Assembly of steel structural components at shop, wherever required.
k) Preparation of steel structural surfaces for painting by power tools or
sand blasting as provided in the specifications/drawings.
l) Application of one primer coat of paint, at shop as specified in the
design drawing/specifications.
m) Loading, transportation from site of fabrication to site of erection,
unloading at site of erection, of all steel structural components/units
/assemblies.
04.3.0 DRAWINGS
04.3.1 The contractor shall prepare design drgs. showing general
arrangement/marking, fabrication drawings, erection drawings, bill of materials,
drawing office despatch lists/shipping documents, schedule of bolts and nuts.
04.3.2 All drawing work shall be in metric system and preparation of drawings
shall conform to iS:696 "Code of Practice for General Engineering
Drawings", Symbols for welding shall conform to IS:813 "Scheme of
Symbols for welding".
04.3.3 The fabrication drawings shall show full length layout with all
connecting members, and connections, marked thereon. The fabrication drawings
shall include all the necessary blown-up details required for the correct
fabrication of the structure to meet the design requirements. These drawings
shall be made in conformity with the best modern practices and with due regard
to speed and economy in fabrication and erection. Each erection piece shall be
clearly identified by an erection mark in these drawings. All the fabrication
drawings shall, wherever specified, have the approval of the Engineer before
commencement of fabrication. Approval of drawings will not absolve the
Contractor from his responsibility for the correctness and completeness of shop
drawings. The Contractor shall correct at his own expense all errors of any sort
in his drawings and cover all damages due to such errors, regardless of any
approval by the Engineer.
04.3.4 The preparation/detailing of fabrication drawing shall be complete in
all respects. In the case of bolted connections, the bolt diameter, the hole
diameter, the actual locations of bolt holes, co-ordinating scheme with
connecting/matching elements shall be clearly indicated. Where HSFG Bolts are
used, method of surface preparation shall be indicated.
04.3.5 In case of welded connections, the size and length of welds along the
relevant weld lines shall be distinctly marked. The length specified shall be
the effective length excluding end crates. For all butt-welds, details of
appropriate edge preparation shall be indicated.
04.3.6 Detailing of structural steel members subjected to dynamic loading
shall be such as to keep the stress concentration to a minimum. Cross-welding
shall be avoided as far as practicable. Welding across tension flange of crane
girders shall not be permitted.
For bolted connections subject to dynamic loading, a lock nut or spring
washer in addition to plain washers shall be used.
04.3.7 Erection drawings may consist of line diagrams,showing every detailed
member in position with the respective erection mark. Erection marks shall
appear on the LEFT END of members AS DETAILED. All steel members shall be
erected with marks in the same relative position as shown in plan or elevation.
All loose members shall be either given part marks or wired on to the main
erection mark for despatch.
04.3.8 The erection clearances for cleated ends of members connecting steel
to steel should preferably be not greater than 1.5 mm at each end. The erection
clearance at ends of beams without web cleats should not be more than 3 mm at
each end but where for particular reasons greater clearance is necessary,
suitably designed seatings shall be provided.
04.3.9 The fabrication drawings shall be prepared in such a manner that
structures are despatched with maximum transportable length and work involved at
site is minimum. Steelwork shall be shop-fitted and shop-assembled as far as
practicable.
04.3.10 All edge preparations for welding shall conform to IS:9595 (latest).
04.4.0 MATERIALS
04.4.1 All steel and other materials used for steelwork and in association
with steelwork shall conform to the specifications shown on the drawings or
otherwise conform to appropriate Indian Standards. Only tested materials shall
be used unless written authority is obtained for the use of untested materials
for certain secondary structural members.
04.4.2 Structural steel shapes shall in general conform to IS:226(latest). In
case of welded fabrication with mild steel, steel plates shall conform to
IS:226(latest) or IS:2062(latest) according to suitability for welding. For
tubular structures, steel tubes shall conform to IS:1161(latest).
04.4.3 Mild steel electrodes used for welding shall conform to IS:814
(latest) and as specified in the specification /drawing. For welding in any
particular position the electrodes used shall be those recommended by the
manufacturer for use in that position. The current used shall be as per
electrode manufacturer's recommendations.
04.4.4 Black hexagonal bolts and nuts shall conform to IS:1363. Precision and
turned hexagonal bolts and nuts shall conform to IS:1363. HSFG bolts, nuts and
washers shall conform to IS:3757 Grades 8.8 and 10.9 or to ASTM specification
A325 and A490 or equivalent or as approved by the Engineer.
04.4.5 Certified mill test reports of materials used in the work shall be
made available for inspection by the Engineer upon request.
04.4.6 Approval for substitutions of structural steel sections shown in the
design drawing must be obtained in writing from the Engineer. This will not
normally be withheld in case of non-availability of design section. Payment for
such authorised changes shall be made on the basis of sections actually used.
04.4.7 All materials shall be straight and if necessary before being worked
shall be straightened and/or flattened by pressure including decoiling of plates
unless required to be of curvilinear form and shall be free from twists.
04.4.8 For utilizing the cut pieces and available lengths,the Contractor may
have to do full strength butt welded splices, at no extra cost to owner. The
design and location of such splices shall require prior approval of the Owner.
If plates/flats of required widths are not available, it will be necessary for
the Contractor to cut such sizes at no extra cost to Owner.
04.5.0 STRUCTURAL STEEL CONNECTION
04.5.1 The Contractor shall be responsible for the design and detailing of
all connections. The design of connections shall provide for adequate strength
for the transfer of force in the structural elements indicated on the design
drawings. For purposes of detailing the connections, the allowable stresses in
material, bolts and welds shall be as per IS:800 and IS:816 or as specified in
the design drawings.
04.5.2 Except where otherwise noted on the drawings, welding shall be used
for all shop connections, as well as field connections. Connections other than
those shown on the drawings,shall have prior approval of the Engineer.
04.5.3 For all full strength butt welding of plates and sections thicker than
or equal to 10 mm.,edge preparation shall be done and got approved by the
Engineer.
04.5.4 The use of ordinary bolts, HSFG bolts, shop and site welding shall be
as indicated on the drawings unless approved otherwise by the Engineer.
04.5.5 Two numbers of washers shall be used for all bolted connections, one
washer bearing against the head and other bearing against the nut.
04.5.6 The magnitude of forces shown on design drawings shall be used at face
values with no reductions for connections.
04.5.7 All bracing shall have a nominal draw of 1 mm for each 1500 mm length.
04.5.8 Bracing shall be connected for 50% of the capacity of the member in
tension (for single angle bracing member consider full area as effective) or the
forces indicated on the drawings whichever is greater, unless otherwise noted.
04.5.9 Sliding, rolling, hanging or slotted hole connections as specified in
the design drawing shall be designed to allow for necessary amount of movement
at joints. Joints with slotted hole connection shall have slotted holes as
specified on the design drawing. The bolts shall have two nuts, the outer being
tightened against inner with a clearance of 2 mm between the inner nut and the
connected material.
04.5.10 All penetration for piping, conduit, cable trays, etc., through
grating or plate flooring shall be cut and suitably banded in the field, except
when such penetrations are dimensioned in the drawings,in which case they shall
be shop cut and banded.
04.6.0 FABRICATION & DELIVERY
04.6.1 Fabrication of all structural steelwork shall be in accordance with
IS:800 (latest) unless otherwise specified, and in conformity with various
clauses of this specification.
04.6.2 Wherever practicable and wherever perfect matching of parts is
required at site, members shall be shop assembled before despatch to minimise
site work. Parts not completely assembled in the shop shall be secured, to the
extent possible, to prevent damage during despatch.
04.6.3 All pieces shall be properly identified and bundled for transportation
to work site. Care shall be exercised in the delivery, handling and storage of
material to ensure that material is not damaged in any manner. Materials shall
be kept free of dirt, grease and foreign matter and shall be protected from
corrosion. All materials shall be stored properly on skids above the ground
which shall be kept clean and properly drained. Girders and beams shall be
placed upright and stored. Long members such as columns and chord members shall
be supported on skids placed near enough to prevent damage due to deflection.
04.6.4 Bolts shall be furnished according to bolt lists showing the location
of their use and additional bolts shall be supplied to cover wastage.
04.6.5 All fabricated pieces shall bear erection mark numbers painted/punched
according to appropriate erection and shop drawings at a prominent location on
the structure for easy identification.
04.6.6 All workmanship shall be in accordance with the best practice in
modern structural shops. Greatest accuracy shall be achieved in the manufacture
of every part of the work and all identical parts shall be strictly
interchangeable.
04.6.7 Templates used throughout the work shall be of steel/ steel bushed, in
such cases as the Engineer may consider necessary. In cases where actual
materials have been used as templates for drilling similar pieces the Engineer
shall decide whether they are fit to be used as parts of the finished
structures.
04.6.8 All smithy work shall be accurately made to the dimensions shown on
the drawings and shall be clean and sound. The metal shall not be burnt or
injured in any way. All joggles shall be formed by pressure. Crankedsections and
knees may however be formed by cutting and welding unless otherwise indicated in
the design drawings.
04.6.9 Shearing or flame cutting may be used at the Contractor's option
provided that a mechanically controlled cutting torch is used for flame cutting
and that the resulting edges are clean and straight. Unless clean square and
true to shape all flame cut edges shall be planed/cleaned by chipping or
grinding. Where machine flame cutting is permitted for high tensile steel,
special care shall be taken to leave sufficient margin and all flame hardened
material shall be removed by machining/edge planing.
04.6.10 Wherever shearing is used for cutting to size, sheared members shall
be free from distortions at sheared edge.
04.6.11 The ends of all girder stiffeners shall be in contact with the
compression flange and shall be planed or ground to fit tightly against flange
plates unless otherwise stated on the drawings. Care shall be taken to ensure
full bearing of the stiffeners at the supports by machining the contact surfaces
of both bearing stiffeners and bearing plates. The ends shall not be drawn or
caulked.
04.6.12 Column splices and butt joints of struts and compression members
depending on contact for stress transmission shall be accurately machined and
close-butted over the whole section with a clearance not exceeding 0.1 mm
locally at any place. In column caps and bases. the ends of shafts together with
the attached gussets, angles, channels etc., after welding together, should be
accurately machined so that the parts connected butt over the entire surface of
contact. Care should be taken that these connecting members are fixed with such
accuracy that they are not reduced in thickness by machining by more than 1.0
mm. Where sufficient gussets and welds are providedto transmit the entire
loading, the column end need not be machined.
04.6.13 Holes for permanent black bolts shall not be more than 1.5 mm larger
than the nominal diameter of the black bolts unless specified otherwise. All
holes for turned and fitted bolts shall be sub-punched or drilled and reamed at
site under assembly of connected parts to a tolerance of plus 0.3mm unless
specified otherwise.
04.6.14 Holes in purlins, side sheeting runners, packing plates and lacing
bars may be punched full size. Holes in light framing with the exception of
joint holes, may be punched full size.
04.6.15 All punching and sub-punching shall be clean and accurate and all
drilling free from burrs. In block/batch drilling, parts shall be separated
after drilling and the burrs removed.
04.6.16 No hole shall be made by gas cutting process.
04.6.17 The component parts shall be so assembled that they are neither
twisted nor otherwise damaged and specified cambers, if any, shall be provided.
04.6.18 No drifting of hole shall be permitted except to draw the parts
together. Drifts used shall not be larger than the nominal diameter of bolt.
Drifting done during assembly shall not distort the metal or enlarge the holes.
04.6.19 Sufficient trial assembly shall be carried out in the fabrication
works to prove the accuracy of workmanship and the number of such trials
required will be at Inspector's discretion.
04.6.20 Where necessary, washers shall be tapered or otherwise suitably
shaped to give the heads of bolts a satisfactory bearing.
04.6.21 The threaded portion of each bolt shall project through the nut at
least one thread.
04.6.22 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 so as to avoid any threaded portion of the bolt being within the
thickness of the parts bolted together.
04.6.23 Ends of structural members and portions of gussets receiving welding
at site shall be left unpainted.
04.6.24 The welding and the welded work shall conform to IS:816 and other
relevant codes unless otherwise specified.
04.6.25 Welding shall be done by the electric arc process. Automatic welding
shall be employed for important structures as specified in the drawings.
04.6.26 Generally, submerged arc, automatic & semi-automatic welding
shall be employed. Only where it is not practicable, manual arc welding may be
resorted to. In case of manual arc welding, recommendations of electrode
manufacturer is to be strictly followed.
04.6.27. Welding shall not be done under such weather conditions which might
adversely affect the efficiency of the welding and where necessary, effective
protection or other safeguards shall be provided.
04.6.28 Only qualified welders suitable for the job shall be employed. The
engineer at his discretion can order periodic tests in accordance with IS:817 of
the welders and/or of the welds produced by them.
04.6.29 Welds shall be made using requisite jigs and fixtures to avoid
distortion or damage to members during/after welding. Welds on exposed work
shall be finished uniformly smooth to present a neat appearance.
04.6.30 As much work as possible shall be welded in shops and the layouts and
sequence of the operations shall be arranged so as to eliminate distortion and
shrinkage stress to the satisfaction of the Inspector.
04.6.31 Welding work shall be under constant supervision of competent welding
supervisor and shall be done in a properly organised manner with the approved
quality welding sets and with automatic welding machines. Details of welding
procedure shall be agreed upon with the Engineer before fabrication is
commenced.
04.6.32 Welding procedure shall include the following :-
i) Type and size of electrodes.
ii) Current and arc voltage.(for automatic welding)
iii) Length of run per electrode, or (for automatic welding) speed of travel.
iv) Number and arrangement of runs in multirun welds.
v) Position of welding.
vi) Preparation and set-up of parts.
vii) Welding sequence.
viii)Pre or post-heating.
ix) Any other relevant information.
04.6.33 The welding procedure shall be arranged to suit the details of the
joints as indicated on the drawings and the positions in which the welding is to
be carried out. The welds shall meet the requirements of quality specified.
04.6.34 All electrodes for use in the work to which this specification
relates shall be kept under dry conditions. Electrodes which are damaged by
moisture shall not be used unless it is stated by the manufacturer that when it
is properly dried there will be no detrimental effect. Any electrode which has
part of its flux coating broken away or is otherwise damaged shall be discarded.
04.6.35 The Contractor shall prepare the edges with an automatically
controlled flame cutting torch followed by grinding correctly to the shape, size
and dimensions of the groove, prescribed in the design and shop drawings. In
case of U-groove joint, the edges shall be prepared with an automatic flame
cutting torch in two passes following a bevel cut with a gouging pass, or by
machining.
04.6.36 The welding surfaces shall be smooth, uniform and free from fins,
tears, notches or any other defect which may adversely affect welding. The
welding surfaces and the surrounding surfaces within 50 mm of weld shall be free
of loose scale, slag, rust, grease, paint, moisture or any other foreign
material.
04.6.37 Pre-bending of plates for three plate welded sections shall be done
where found necessary.
04.6.38 Manipulators shall be used where necessary and shall be designed to
facilitate welding and to ensure that all welds are easily accessible to the
operators.
04.6.39 Where full strength butt-welds are specified, run-on and run-off
pieces shall be used.
04.6.40 The welding shall be such that the face of weld deposit shall at all
places be proud of the surfaces of the parent metal by 1 to 1.5 mm. Where a
flush surface is required, the surplus weld metal shall be ground and dressed
off.
04.6.41 After completing each run of weld, all slag shall be thoroughly
removed, and the surface cleaned before starting the next run of weld.
04.6.42 Stress relieving after welding shall be done,if specifically called
for in the drawing.
04.6.43 The weld metal, as deposited (including tack welds if to be
incorporated) shall be free from cracks, slag inclusions, gross porosity,
cavities and other deposition faults. The weld metal shall be properly fused
with the parent metal without serious undercutting or over-lapping at the toes
of the weld. The surfaces of the weld shall have a uniform and consistent
contour and uniform appearance.
04.6.44 All weld runs found defective shall be cut by using either chipping
hammer, gouging torch, or suitable grinding wheel in such a manner that adjacent
material is not injured in any way.
04.6.45 Peeling of the welds involving deformation of the weld surface either
during deslagging or thereafter shall not be allowed.
04.6.46 Column bases and caps, if applicable, shall be in one solid piece,
and except when cut from plates with true surfaces, shall be accurately machined
over the bearing surfaces, and shall be in effective contact over the whole area
of the machined end of the stanchion.
04.6.47 Each piece shall be distinctly marked before delivery, in accordance
with an approved marking diagram and shall bear such other marks as will
facilitate erection. For easy identification at site,a small distinguishing mark
for each building shall be painted at each end of every member before despatch
from fabrication shop. The fabricated steelwork shall be despatched in sequence
as per agreed programme and for such portion as may be found convenient for
erection or as ordered by the Engineer.
04.6.48 The Contractor shall provide suitable packing wherever necessary to
guard against damage during handling and transportation to site. All fabricated
parts shall be adequately braced to prevent damage during transit.
04.6.49 The tolerances for fabrication of steel structures shall generally
conform to IS:7215, unless otherwise specified in this specification or
drawings. (Refer Table I to Table III).
04.6.50 Any fabrication or erection work which is considered not to be
keeping with the Technical Specification forming the Contract, or in the absence
of Technical Specification with recognised good practice, shall be
rectified/replaced/corrected at the Contractor's expense as directed by
Engineer.
04.6.51 Site fabrication work shall also conform to all specifications,
stipulations, terms andconditions applicable for shop welded structures as
mentioned above.
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