18.1 General 18.1.1
18.1.1 Structural Structural steelwork steelwork should should be be used used for for multilevel multilevel plant plant structures, ovstructures, overheaderhead pipe racks, heavy girders, large span frames and for industrial buildings pipe racks, heavy girders, large span frames and for industrial buildings covering large areas by trusses or portal
covering large areas by trusses or portal frames and miscellaneous metal worksframes and miscellaneous metal works like platforms, stairs, ladders etc. as well as for equipment supports and like platforms, stairs, ladders etc. as well as for equipment supports and supporting structures, if not located
supporting structures, if not located at grade level.at grade level.
18.1.2
18.1.2 Normally, Normally, the structural the structural work work made of made of weldable weldable non-alloy, hot non-alloy, hot rolled rolled steelsteel sections is preferred over the other materials of construction due to the several sections is preferred over the other materials of construction due to the several factors as follows:
factors as follows:
a)
a) Ease Ease of of construction.construction.
b)
b) Speed of Speed of construction.construction.
c)
c) Ease of Ease of modifications modifications and and strengthening strengthening in in future.future.
d)
d) Ease Ease of of periodic periodic maintenance.maintenance.
e)
e) Reliability of Reliability of good good structural structural strength strength and and long long life.life.
f)
f) Highly Highly cost cost effective effective and and economical.economical.
18.2
18.2 Structural Structural FormForm 18.2.1
18.2.1 Structural Structural steelwork steelwork shall shall be be made made in in the the simpler simpler forms forms of cof construction onstruction for for easeease of fabrication and erection; as well as for ease of general maintenance and of fabrication and erection; as well as for ease of general maintenance and painting.
painting.
18.2.2
18.2.2 As As far as far as practicable, practicable, complex complex structural structural forms forms should should be be avoided; avoided; and and latticelattice type structures other than towers and roof trusses should preferably not to be type structures other than towers and roof trusses should preferably not to be used.
used.
18.2.3
18.2.3 Structural steelwStructural steelwork sork shall be hall be generally generally shop shop fabricated bfabricated by y welding, welding, and and fieldfield assembled and erected by bolting at Site. Or, they should be fabricated in assembled and erected by bolting at Site. Or, they should be fabricated in pieces and / or pre-assembled in a fabrication yard remote from the Site.
pieces and / or pre-assembled in a fabrication yard remote from the Site.
18.3
18.3 Design Design Conditions Conditions I I 2 2 II 18.3.1
18.3.1 The strucThe structure or ture or a paa part of rt of the sthe structure tructure shall shall be be designed designed to to resist resist all all applicableapplicable loads and worst load combinations within the deflection limits as specified in loads and worst load combinations within the deflection limits as specified in KOC-C-001
KOC-C-001 ““KOCKOC Standard for Basic Civil Engineering Design Data”Standard for Basic Civil Engineering Design Data”..
18.3.2
18.3.2 Structural Steel Structural Steel Design Design shall be shall be in accordain accordance with nce with the ANSI/AISC the ANSI/AISC 360360
““Specification for Structural Steel BuildingsSpecification for Structural Steel Buildings””, AISC 341, AISC 341 ““Seismic Provisions forSeismic Provisions for Structural Steel Building
Structural Steel Building”” and AISC 325 and AISC 325 ““Steel Construction ManualSteel Construction Manual””. The Load. The Load and Resistance Factor Design (LRFD) method in AISC shall not
and Resistance Factor Design (LRFD) method in AISC shall not be used in steelbe used in steel design and shall be fabricated with all the materials in compliance with the design and shall be fabricated with all the materials in compliance with the relevant technical specifications as specified in KOC-C-007
relevant technical specifications as specified in KOC-C-007 ““KOC Standard forKOC Standard for Structural Steel Work
-Structural Steel Work - Materials, Fabrication and Erection”.Materials, Fabrication and Erection”.
18.3.3
18.3.3 Normally, only Normally, only pinned colupinned column bases mn bases shall be shall be used in used in the design the design of steelof steel structures. However, to control the deflections for pipe racks and industrial structures. However, to control the deflections for pipe racks and industrial buildings etc., fixed base plates design shall be used with prior approval from buildings etc., fixed base plates design shall be used with prior approval from KOC.
KOC.
18.3.4
18.3.4 Where headroom Where headroom / / access access for for personnel personnel or or equipment equipment entry entry / / exit exit are are required,required, generally wind and other lateral loads on a steel structure shall preferably be generally wind and other lateral loads on a steel structure shall preferably be carried to the foundations
carried to the foundations through vertical through vertical X-bracing or X-bracing or K-bracing placed K-bracing placed in thein the transverse and longitudinal column lines of the structure. As a second choice, transverse and longitudinal column lines of the structure. As a second choice, wind and other lateral loads on a structure should be transmitted to the wind and other lateral loads on a structure should be transmitted to the foundations through moment resistant frames in one direction and vertical foundations through moment resistant frames in one direction and vertical X-braced or K-braced frames in the other direction. Structures that resist lateral X-braced or K-braced frames in the other direction. Structures that resist lateral load with rigid frame systems in two directions should be
load with rigid frame systems in two directions should be avoided.avoided.
18.3.5
18.3.5 Compression Compression bracing bracing for for steel steel structures structures shall shall normally normally be be designed designed with with widewide flange and structural tee shapes. For tension bracing, single angle or structural flange and structural tee shapes. For tension bracing, single angle or structural tees should be used. Double angle bracing, because of maintenance difficulties, tees should be used. Double angle bracing, because of maintenance difficulties, is not permitted for either compression or tension bracing. When using structural is not permitted for either compression or tension bracing. When using structural tees in compression, the design shall include bending induced by eccentrically tees in compression, the design shall include bending induced by eccentrically loaded connections.
loaded connections. Rods / Cables as bracing members shall not be permitted.Rods / Cables as bracing members shall not be permitted.
18.3.6
18.3.6 Braces Braces for structures for structures subject subject to vto vibration ibration from efrom equipment quipment shall shall be be designed designed asas compression members.
compression members.
18.3.7
18.3.7 Horizontal Horizontal bracing bracing shall shall be be provided provided in in the the plane plane of of a a floor, plafloor, platform, or tform, or walkway,walkway, when necessary to resist lateral loads or to increase the lateral stiffness of the when necessary to resist lateral loads or to increase the lateral stiffness of the floor, platform, or walkway. Floor grating shall not be assumed to resist lateral floor, platform, or walkway. Floor grating shall not be assumed to resist lateral loads in diaphragm action. Floor plate should be investigated before it is loads in diaphragm action. Floor plate should be investigated before it is considered to resist loads in diaphragm action.
considered to resist loads in diaphragm action.
18.3.8
18.3.8 In a In a floor syfloor system, beam stem, beam compression compression flanges flanges should should be be considered considered to to be be fullyfully braced when a concrete slab is cast to match the bottom face of the braced when a concrete slab is cast to match the bottom face of the compression flanges on both sides, or when checkered plate is welded to the compression flanges on both sides, or when checkered plate is welded to the compression flanges. Grating is normally clipped or bolted and therefore shall compression flanges. Grating is normally clipped or bolted and therefore shall not be considered as adequate compression flange bracing. In such cases, not be considered as adequate compression flange bracing. In such cases, additional horizontal bracing in the floor
additional horizontal bracing in the floor system shall be provided.system shall be provided.
18.3.9
18.3.9 Bar joist Bar joist floor and floor and roof syroof systems astems are genre generally erally considered considered to be to be too too light light forfor heavy industrial plant work. However, when approved by KOC, bar joist systems heavy industrial plant work. However, when approved by KOC, bar joist systems should be used on a project.
should be used on a project.
18.3.10
18.3.10 Steel Structures shall be Steel Structures shall be designed so designed so that the surfaces othat the surfaces of all parts wf all parts will be readilyill be readily accessible for inspection, cleaning and painting. Pockets for depressions which accessible for inspection, cleaning and painting. Pockets for depressions which would hold water shall have drain holes or be otherwise protected.
would hold water shall have drain holes or be otherwise protected.
18.3.11
18.3.11 The forces in truss members and all main bracing shall bThe forces in truss members and all main bracing shall be shown on thee shown on the engineering drawings with plus signs indicating tension and minus signs engineering drawings with plus signs indicating tension and minus signs indicating compression or as per the calculation note provided by Designer.
indicating compression or as per the calculation note provided by Designer.
18.3.12
18.3.12 Gusset plates sGusset plates shall not be hall not be thinner than the thinner than the members to members to be connected, be connected, and shalland shall have a thickness of at least 10 mm.
have a thickness of at least 10 mm.
18.3.13
18.3.13 Contractor shall note Contractor shall note that the minimum thickness that the minimum thickness of any plate oof any plate or rolled sectionr rolled section for use as a structural element should not be less than 6mm.
for use as a structural element should not be less than 6mm.
18.3.14
18.3.14 All bracing shall be arranAll bracing shall be arranged to minimize torsion ged to minimize torsion and where practicable, band where practicable, bee arranged concentrically about the resultant line of force. The connections arranged concentrically about the resultant line of force. The connections wherever possible, shall be arranged so that their centroid lies on the resultant wherever possible, shall be arranged so that their centroid lies on the resultant of the forces they are intended to resist.When the condition cannot be achieved, of the forces they are intended to resist.When the condition cannot be achieved, the members and connections shall be designed to resist any local bending due the members and connections shall be designed to resist any local bending due to the eccentricity of the force.
to the eccentricity of the force.
18.3.15
18.3.15 Bracings located Bracings located within the fireproofing zowithin the fireproofing zone shall alsne shall also be fireproofed o be fireproofed similar tosimilar to other members as bracings are part of structural stability. Fireproofing loads other members as bracings are part of structural stability. Fireproofing loads shall be considered under dead loads in the structural design. For detail of shall be considered under dead loads in the structural design. For detail of Passive Fire Protection of Structural Steel refer clause no. 18.5 of this RP.
Passive Fire Protection of Structural Steel refer clause no. 18.5 of this RP.
18.3.16
18.3.16 Structural steelworks Structural steelworks generally shall generally shall be fabricated by be fabricated by welding. Stitch welding. Stitch welds andwelds and one side welding are not accepted. Welds shall not be less than 6mm one side welding are not accepted. Welds shall not be less than 6mm continuous fillet welding.
continuous fillet welding.
18.3.17
18.3.17 All load bearing sAll load bearing structural steel members shall tructural steel members shall be hot rolled. Built-up steelbe hot rolled. Built-up steel sections shall not be allowed unless approved by the KOC in writing. If built-up sections shall not be allowed unless approved by the KOC in writing. If built-up steel sections are allowed by the KOC, minimum thickness of web and flange steel sections are allowed by the KOC, minimum thickness of web and flange shall be 6 mm and 8 mm respectively and the flange shall be proportioned to shall be 6 mm and 8 mm respectively and the flange shall be proportioned to provide a compact section.
provide a compact section.
18.3.18
18.3.18 Purlins, girts, fly Purlins, girts, fly bracings and bracings and sheetings shsheetings shall not be all not be considered as part considered as part of theof the bracing system for reducing the unsupported length or the buckling length of bracing system for reducing the unsupported length or the buckling length of steel sections. Only a well-braced system shall be considered as effective in steel sections. Only a well-braced system shall be considered as effective in providing restraint to the compression flange of the steel sections. The roof and providing restraint to the compression flange of the steel sections. The roof and the side structure shall be adequately braced in its
the side structure shall be adequately braced in its plane.plane.
18.3.19 The slenderness ratio for all the structural steel members in compression 18.3.19 The slenderness ratio for all the structural steel members in compression
(including bracings) shall be less than 200.
(including bracings) shall be less than 200.
18.3.20
18.3.20 Lifting / Lifting / transportation calculationstransportation calculations, drawing, drawings and s and Method statement Method statement shall beshall be provided to KOC if the structural components / modules are planned to be provided to KOC if the structural components / modules are planned to be installed by lifting.
installed by lifting.
18.3.21
18.3.21 Guardrail configuration sGuardrail configuration shall confirm to the hall confirm to the IBC and IBC and OSHA requirements OSHA requirements as aas a minimum.
minimum.
18.3.22 Workplace walking and working surfaces shall conform to the safety 18.3.22 Workplace walking and working surfaces shall conform to the safety
requirements of ASSE A1264.1.
requirements of ASSE A1264.1.
18.4
18.4 Design Design Stress Stress LevelsLevels Allowable
Allowable design design stresses stresses for for the the selected selected structural structural steel steel sections sections (rolled (rolled //
hollow) conforming to BS EN 10025 Grade S275JR / S275 JOH or hollow) conforming to BS EN 10025 Grade S275JR / S275 JOH or ASTM A36/A36M
ASTM A36/A36M or equivalent or equivalent shall be shall be used in used in accordance with the accordance with the applicableapplicable National codes and standards given in clause 4.2 of this RP. However, National codes and standards given in clause 4.2 of this RP. However, reduction in the allowable design stresses should be considered necessary as reduction in the allowable design stresses should be considered necessary as safety measures for the f
safety measures for the following conditions.ollowing conditions.
18.4.1 Fatigue 18.4.1 Fatigue
a)
a) Special structures, Special structures, such such as as gantry gantry girders girders with with heavy heavy moving moving loads loads fromfrom the crane(s), tall free-standing towers and guyed masts which are prone the crane(s), tall free-standing towers and guyed masts which are prone to fatigue due to cyclic loading, should consider in design, the to fatigue due to cyclic loading, should consider in design, the appropriate safety factors and reduced stress levels in order to limit the appropriate safety factors and reduced stress levels in order to limit the allowable material stresses.
allowable material stresses.
b)
b) Structural details, Structural details, which which should should give give rise rise to to high high local local stress stress in in thesethese fatigue prone structures, should be avoided.
fatigue prone structures, should be avoided.
18.4.2 Fire 18.4.2 Fire a)
a) Structural steel Structural steel can can withstand withstand temperature temperature up up to to 200200C (392C (392F) withoutF) without any significant reduction in the allowable stresses and can retain its any significant reduction in the allowable stresses and can retain its integrity without change in its strain levels. But its loss of strength starts integrity without change in its strain levels. But its loss of strength starts then at an increasingly faster rate, up to a temperature of about 750 then at an increasingly faster rate, up to a temperature of about 750CC
(1382
(1382F) with increased strain levels causing serious inelasticF) with increased strain levels causing serious inelastic deformations as per BS EN 1993-1-2.
deformations as per BS EN 1993-1-2.
b)
b) If If the the critical critical temperature temperature for for structural structural steel steel is is intended intended to to describe describe thethe steel temperature at which its strength reduces to such an extent that steel temperature at which its strength reduces to such an extent that collapse is impending, this temperature should be judged with collapse is impending, this temperature should be judged with reasonable approximation in the range of 538
reasonable approximation in the range of 538C (1000C (1000F).F).
c)
c) Where the Where the structure structure supports supports equipment equipment containing containing or or handlinghandling flammable materials and where high risk of potential fire exists, suitable flammable materials and where high risk of potential fire exists, suitable reduction in the allowable stresses should be considered in design as an reduction in the allowable stresses should be considered in design as an additional protective measure other than encasing the structure with additional protective measure other than encasing the structure with selected fire proofing material.
selected fire proofing material.
18.5
18.5 Passive Passive Fire Fire ProtectionProtection 18.5.1
18.5.1 The pasThe passive sive fire protection fire protection of steel of steel structures structures as as needed needed shall shall be be establishedestablished for the requisite fire rating, wherever fireproofing requirements are specified by for the requisite fire rating, wherever fireproofing requirements are specified by KOC or by the designer / contractor; and shall be provided in accordance with KOC or by the designer / contractor; and shall be provided in accordance with KOC-C-027
KOC-C-027 “KOC Standard for Fireproofing of Structural Steelwork”“KOC Standard for Fireproofing of Structural Steelwork”..
18.5.2
18.5.2 The The materials materials shall shall be be fire rafire rated ted to to maintain maintain the the temperature temperature of of 538538C (1000C (1000F)F) on the steel substrate to a specified period of fire resistance, which should in on the steel substrate to a specified period of fire resistance, which should in general vary from minimum one (1) hour to maximum four (4) hours to provide general vary from minimum one (1) hour to maximum four (4) hours to provide the breathing time for the required fire fighting response. Accordingly, the the breathing time for the required fire fighting response. Accordingly, the material properties and thickness should be selected and verified by the fire material properties and thickness should be selected and verified by the fire tests certificates for suitability as per BS 476 Parts 20 and 21.
tests certificates for suitability as per BS 476 Parts 20 and 21.
tests certificates for suitability as per BS 476 Parts 20 and 21.