|
1.0 General
1.1 This specification shall apply to steelwork in building and general
structural work. For technological structures additional stipulations shall be
considered.
Go back
SECTION-1 FABRICATION OF STEEL STRUCTURES
Go back
2.0 SCOPE OF WORK
2.1 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,
electrodes, paints, shims, packs, etc., including allowance for spares and
wastage.
d)Preparation and submission of fabrication drawings, modification
/rectification sketches, as made drawings, erection drawings,bill of
materials, bolts lists and shipping documents for approval of purchaser.
e) Preparation of design calculations fornon-standard connections,
temporary bracings etc. for approval of purchaser.
f)Cold strightening of section 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 the scope of the
project.
h)Making arrangements for and conducting tests, such as chemical analysis,
physical and mechanical tests on raw materials where specified/as directed by
the purchaser.
i)Making arrangements for providing all facilities for conducting
ultrasonic, X-ray or gamma ray tests of welds; getting the tests conducted by
reputed testing laboratories making available test films / graphs, reports and
interpretation.
j)Control Assembly of steel structural components at shop, wherever
requiured.
k) Preparation of steel structural surfaces for painting as provided in the
specifications / drawings.
l)Application for one primer coat of painting at shop, as specified in the
design drawing/specifications.
m) Loading, transportation from fabrication workshop to site of erection
and unloading of all steel structural components / units / assemblies.
n)Preparation of "As-built" drawings.
3.0 PREPARATION OF FABRICATION AND ERECTION DRAWINGS
3.1 Fabrication drawings shall be prepared based on design drawings of
steel structures.
3.2 Drawing shall be prepared in metric system as per IS:696-1972 and
IS:813-1986. The fabrication drawings shall specify the following details:-
(a) Type,size and length of welds in case of welded connections,(specifying
clearly shop or site weld). Length of weld specified shall be effective length
(excluding end crates).
(b) In case of bolted joints,arrangement of bolts and specification of
bolts, nuts etc.(specifying clearly shop and site bolts).
(c) Specification of electrode/wire flux.
(d) If required special provision to be mentioned in the drawings for
handling of structures during and after fabrication.
(e) Specification of paint and corresponding surface preparation for
painting.
(f) General arrangement/marking plan.
(g) Reference to design drawings.
(h) Material list indicating mark number-wise material requirement giving
size, weight, material specification,identification number of each items,
number of pieces required etc.
(i) Layout with all connecting members with blown up joint details wherever
required, in order to specify clearly various fabrication and erection
requirements as per design drawings.
(j) Specification of preparation of mating surfaces in case of connection
by HSFG bolts.
(k) Appropriate edge preparation in case of butt/groove welds in accordance
with IS:9595-1980, for all plates and sections having thickness greater than 8
mm.
(l) Erection clearances in order to facilitate smooth erection at site (ref
clause no.11.2.2.of IS: 800-1984).
(m) Each erection piece shall be clearly identified by an erection mark in
these drawings. All loose members shall be given part mark, which shall be
'wired on' the main erection piece for despatch.
3.3 Fabrication drawings shall be prepared in such a manner that Structures
can be despatched from fabrication shop to erection site with maximum economic
transportable size, so as to reduce work involved at site to a minimum.
3.4 Bracings shall be connected for 50% of the capacity of the member or
the force specified in the design drawing, whichever is more.(for single angle
bracing member, consider full area as effective for this purpose).
3.5 Standard simple beam connections, unless otherwise stated in the
drawings, shall be designed and detailed for 60% beam shear / moment carrying
capacity.
3.6 Wherever there is risk of nuts becoming loose due to vibration, lock
nuts shall be provided, or nuts shall be welded after alignment and
tightening.
3.7 For all connections by permanent bolts, two nos. of washers shall be
used. One washer bearing against the head and the other bearing against the
nut.
3.8 Detailing of structural steel members subject to dynamic loading shall
be such as to ensure smooth transition of load, as well as best behaviour
under stress due to fatigue. Welding across tension flange of crane girders is
not permitted.
3.9 For detailing connection, the allowable stress for materials, welds,
bolts etc, shall be as per IS:800-1984 and IS:816-1969, or as specified in the
drawing.
3.10 The contractor shall be responsible for design and detailing all
connections. The design ofconnection shall provide adequate strength for
transfer of force in the structural elements, as indicated on design drawings.
Detailing shall be such that erection shall be convenient and free from all
interfaces, drilling and cutting at site.
10.0 INSPECTION & TESTING
10.1 The purchaser/Inspector shall have free access at all times to those parts of
Contractor's or his Sub-Contractor's works which are concernedwith the fabrication of
steel works and shall be afforded all reasonable facilities at all stages of preparation,
fabrication and trial assemblies for stisfying himself that the fabrication is being
undertaken in accordance with the provisions of relevant specification.
10.2 All gauges and templates,tools, apparatus, labour and assistance for checking
shall be supplied by the contractor free of charge. The purchaser /Inspector may at his
discretion, check the test results obtained at the Contractor's works,by independent test
at the Goernment Test House or elsewhere, and should the material so tested be found to be
unsatisfactory, the cost of such such test shall be borne by the Contractor.
10.3 Contractor shall make all necessary arrangements for stage inspection by
purchaser/Inspector during the fabrication at shop and incorporate all on-the-spot
instructions/chnages conveyed in writing to the Contractor.
10.4 Material improperly detailed or wrongly fabricated shall be reported to the
Purchaser/Inspector and shall be made good as directed. Minor misfits which can be
remedied by moderate use of drift pins, and moderate amount of reaming and slight chipping
may be corrected in that manner, if in the opinion of the Purchaser/Inspector the strength
or appearance of the structure will not be adversely affected. Inthe event the
Purchaser/Inspector directs otherwise, the items will be rejected and a completely new
piece shall be fabricated. The cost of correcting errors shall be to the account of the
Contractor.
10.5 i) The Purchaser/Engineer shall have the power:
a) To certify, before any structure is submitted for inspection, that the same is not
in accordance with the contract, owing to the adoption of any unsatisfactory method of
fabrication.
b) To reject any structure as not being in accordance with specifications &
drawings.
c) To insist that no structure or parts of the structure once rejected is resubmitted
for inspection/test, except in cases where the Purchaser / Inspector authorised
representative considers the defects as rectifiable.
ii) If, on rejection of structure by the Purchaser/Inspector the Contractor fails to
make satisfactory progress within the stipulated period, the Purchaser/Inspector shall be
at liberty to cancel the contract and fabricate or authorise the fabrication of the
structures at any other place he chooses, at the risk and cost of the Contractor, without
prejudice to any action being taken in addition to terms of General Conditions of
Contract.
iii)The Purchaser / Inspector's decision regarding rejection shall be final and binding
on the Contractor.
iv) The specifications prescribe various tests at specified intervals for ascertaining
the quality of the work done. If the tests prove unsatisfactory, Purchaser/Inspector shall
have liberty to order the Contractor to re-do the work, done in that period and/ or to
order such alterations and strengthening that may be necessary at the cost of the
Contractor and the contractor shall be bound to carryout such orders failing which the
rectification/redoing will be done by the Purchaser through other agencies and the cost
recovered from the Contractor.
v) Notwithstanding any inspection at the workshop the Purchaser/Inspector shall have
the liberty to reject, without being liable for compensation any fabricated members or
materials brought to site that do not conform to specifications / drawings.
vi) All rejected materials shall be removed from the site of fabrication by the
Contractor at his own cost and within the time stipulated by the Purchaser/Inspector.
11.0 CONTROL IN WELDING
11.1 The extent of quality control in respect of welds for structural elements for both
statically and dynamically loaded structures shall be as follows and shall be conducted by
the contractor at his own cost:-
a) Visual Examination - All welds shall be 100% visually inspected to check the
following:
i) Presence of undercuts
ii) Visually identifiable surface cracks in both weldsand base metals.
iii) Unfilled craters
iv) Improper weld profile and size
v) Excessive reinforcement in weld
vi) Surface porosity
Before inspection, the surface of weld metal shall be cleaned of all slag,spatter
matter, scales etc. by using wire brush or chisel.
b) Dye Penetration Test (DPT) - This shall be carried out for all important fillet
welds and groove welds for both statically and dynamically loaded structures to check the
following :
i) Surface cracks
ii) Surface porosities
Dye Penetration Test shall be carried out in accordance with American National Standard
ASTM E165.
c) Ultrasonic testing
Ultrasonic test shall be conducted for all groove welds and heat affected zone in
dynamically loaded structures and for other important load bearing butt welds in
statically loaded structures as desired by purchaser, to detect the following :
i) Cracks
ii) Lack of fusion
iii) Slag inclusions
iv) Gas porosity
Ultrasonic testing shall be carried out in accordnce with American National Standard
ANSI/AWS D1.1-96 Chapter -6: Part F.
Before ultrasonic test is carried out, any surface irregularity like undercuts,sharp
ridges etc. shall be rectified. Material surface to be used for scanning by probes must
allow free movement of probes. For this purpose, surface shall be prepared to make it
suitable for carrying out ultrasonic examination.
d) Radiographic Testing
(X-ray and Gamma-Ray Examination) :- This test shall be limited to 2% of length of
welds for welds made by manual or semi- automatic welding and 1 % of length of weld if
made by automatic welding machines . The location and extent of weld to be tested by this
method shall be decided by purchaser to detect the following defects :-
i) gas porosity
ii) slag inclusions
iii) lack of penetration
iv) lack of fusion
v) cracks
Radiographic testing shall be conducted in accordance with American National Standard
ANSI/AWS D1.1-96 Part E.
Any surface irregularity like undercuts, craters, pits etc. shall be removed before
conducting radiographic test. The length of weld to be tested shall not be more than 0.75
x focal distance. The width of the radiographic film shall be width of the welded joint
plus 20 mm on either side of the weld.
12.0 ACCEPTABLE LIMITS OF DEFECTS IN WELD
12.1 Limits of Acceptibility of welding defects shall be as follows : -
a) Visual inspection & Dye Penetration Test - The limits of acceptibility of
defects detected during visual inspection and Dye Penetration Test shall be in accordance
with clauses 6.9 & clause 6.10 of American National Standard ANSI/AWS D1.1-96 for
statically as well as dynamically loaded structures respectively.
b) Ultrasonic Testing - The limits of acceptability of defects detected during
ultrasonic testing shall be in accordance with clause 6.13.1 & clause 6.13.2 of
American National Standard ANSI/AWS D1.1-96 Chapter 6 : Part C for statically and
dynamically loaded structures respectively.
c)Radiographic testing - The limits of acceptability of defects detected durging
Radiographic testing shall be in accordance with clauses 6.12.1 & 6.12.2 of American
National Standared ANSI/AWS D1.1-96 Chapter 6 : Part C for statically and dynamically
loaded structures respectively.
13.0 RECTIFICATION OF DEFECTS IN WELDS
13.1 In case of detection of defects in welds , the rectification of the same shall be
done as follows :
i) All craters in the weld and breaks in the weld run shall be throughly filled with
weld.
ii) Undercuts, beyond accptable limits, shall be repaired with dressing so as to
provide smooth transitionof weld to parent metal.
iii) Welds with cracks and also welds with incomplete penetration, porosity, slag
inclusion etc. exceeding permissible limts shall be rectified by removing the length of
weld at the location of such defects plus 10 mm from both ends of defective weld, and
shall be re-welded. Defective weld shall be removed by chipping hammer,gouging torch or
grinding wheel. Care shall be taken not to damage the adjacent material.
14.0 ACCEPTANCE CRITERIA OF MACHINING SURFACE
14.1 Standard of acceptance for machined surfaces, wherever specified by designer,
(eg.
in column cap plates, base plates and column shafts etc.)shall be as given as per clause
14.2 & 14.3.
14.2 Maximum surface unevenness on bearing surface of cap/ base plate shall not exceed
0.5 mm.
14.3 When assembled, there must be physical contact for atleast 75% of the contact
surface.(The checking shall be carried out with 0.2mm guage . Care should be taken that
these connecting members are fixed with such accuracy that they are not reduced in
thickness during machining by more than 1.0 mm.
15.0 DESPATCH INSTRUCTIONS
Each despatchable structure shall bear mark no. along with reference drawing number at
two prominent locations (e.g. on flange and bottom of base plate of a column).
15.1 "As built" drawing shall be prepared after fabrication is completed to
indicate additions / alterations made during the process of fabrication. (Refer clause
4.1.2 & 4.1.3.)
15.2 Control assembly of important structures shall be done in the shop floor before
despatch to avoid mismatching. For all such important structures, match marking shall be
given at the control assembly stage in the shop floor and such match markings shall be
made clearly visible while assembling the structures at site.
15.3 Centre lines of column flanges and both sides of web shall be punched, preferably
at top and bottom to facilitate alignment after erection.
16.0 COMPLETION DOCUMENTS
16.1 On completion of work,the Contractor shall submit to the Purchaser the following
documents :-
a) The technical documents according to which the work was carried out.
b) Copies of the "As built" drawings showing thereon all additions and
alterations made during the fabrication.
c) Manufacturer's test certificates
d) Certificates/documents on control checking
e) Test of welds
16.2 Inspection Certificates shall be issued to the contractor for the structures found
acceptable in all respects by the Purchaser/Inspector.
| 