structural steel 2009

8/11/2019 Structural Steel 2009

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Structural Steel Work

This training module is designed to give studentsa good appreciation on the use of structural steelas a construction material and the good practicesof structural steel work construction.

Building & Construction Unit, IC

(Notes can be downloaded from BCU

Web page)httphttp:://www//www..icic..polyupolyu..eduedu..hk/bcu/hk/bcu/$$TrainingTraining--materialsmaterials..htmhtmPasswordPassword :: 1234512345

Learning Objectives:

State the characteristics of structural steel asconstruction material, and the commonly usedsteel sections

Read and interpret the construction details ofstructural steel elements of a building structurein drawing format

Participate in fabrication of a simple steel buildingframe; use of cutting and drilling tools;connection practices including bolt and nuts and

welding Recognize protective coatings of structural steel

structures: painting & hot-dip galvanizing Conduct inspection on the fabricated frame and

simple NDT for the welding connections


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Terminology

Steel framed structures are usually madeup of the following structural elementsconnected by bolts or welding :

beams

girders (large steel beams)

trusses

stanchions (columns)

bracing

Shapes and Properties of hot rolled steel

Shapes of commonly used steel sections in Hong Kong based on product information ofBritish Steel: UB, UC, EA, UA, PFC, CHS, RHS, SHS and Joists

Standard Length of Steel Component: 12m

e.g UC - Universal Column UB - Universal Beam

EA - Equal Angle

UA - Unequal Angle

PFC- Parallel Flange Channel

RHS - Rectangular CHS Circular Hollow SectionHollow Section

SHS - SquareHollow Section


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Standard and grade of steel

BS EN 1993 is the standard for the design,fabrication and erection of structural steelwork(These were formerly referred to BS 5950).

BS EN 10025 is the standard for materialstrength is specified in relation to steel grade. Itdependent on yield stress. Stresses are given forthree grades of steel called S275, S355 & S460(These were formerly referred to BS 4360 asGrades 43, 50 and 55) is commonly used, except

for bridges Structural steel for bridgework according to BS

5400

Standard and grade of steel

Source: Code of Practice for the Structural Use of Steel 2005


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Typical examples of structural steel worksconnections method:

Beam-to-column connections: Boltedendplate + welded connections

Beam-to-beam connections: Endplate typebeam splice (plate-to-plate connection).

Column bases: Bolted base plateconnection.

Column-to-Column: Splice plate + welded

connections

Connection Methods

Example of beam-to-column connections:Extended End Plate Moment Connection

This connection is the end plate moment connection. It is made byshop-welding a plate to the end of a beam and field-bolting it to acolumn or to another beam. The four bolts around the tension flangetransmit the flange force into the column. Additional bolts may be neededin deeper sections. A bolt may also be added near the neutral axis of thebeam to prevent gaps between the plates.

Source: http://wwweng.uwyo.edu/connections/


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Example of Beam-to-beam connections:Beam Splice Moment Connection

This is a beam splice moment connection. The flange plates andbolts in this beam splice must be capable of transferring all theflange force from one side to the other. The web plate and bolts may

help to resist moment, but their primary function is to transfer shearacross the splice.This moment connection has flange plates on the outside only.In some connections it may be necessary to have plates inside theflanges as well.


Example of Column bases: Pipe ColumnBase Plate

A round pipe column sits atop a wide flange and is fastenedwith a rectangular end plate having four bolts. Even though all thebolts lie outside the round section, this is generally designed as apinned connection. The column delivers a concentrated load to thebeam and a bearing stiffener is used on the web.



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An all-welded column splice. The web plate is shop-welded to

the lower column, then the upper column is lowered into theconnection and field-welded. The web bolts are just for fit-upand erection.

Example of Column-to-Column: WeldedColumn Splice

Structural Steelwork Fabrication Processes

1. Measurement / Marking

2. Cutting and Drilling

3. Welding/Plating Components

4. Painting/Galvanizing

5. Quality Control

6. Handover


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Cutting and Drilling

Use of common hand tools or equipmentsincluding cutting machine, grinder, hammer,dividers, steel rule, and drilling machine etc.

Holes in steel sections and plates shall beformed to the following sizes:

For ordinary bolts and high strength friction grip bolts:

Not exceeding 24 mm diameter - 2 mm greater than the bolt diameter.

Greater than 24 mm diameter - 3 mm greater than the bolt diameter.

For holding down bolts:

6 mm greater than the bolt

diameter or with sufficient

clearance to ensure that a bolt,

whose adjustment may cause

it to be out of perpendicular,

can be accommodated

through the base plate.

Precaution of holes drilling

Source: General Specification for Building 2007 Edition


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Welding/Plating Components

A weld is defined as a localized coalescence ofmetals wherein coalescence is produced byheating the metal to suitable temperatures, withor without the application of pressure andwithout the use of any filler metal.

Butt welds and fillet welds are included in thesection of welded connections. Butt welds arenormally used for in-line jointing in plates or

sections and fillet welds are used for tee or lapjointing.

Source: Explanatory Materials to Code of Practice for the Structural Use of Steel 2005

Welding/Plating ComponentsTack weld

Functions of tack weld hold up the correct alignment andconnection of two components before permanent welding.

The minimum length of the tack shall be the lesser of 4times the thickness of the thicker part or 50 mm.

If the permanent weld joint is required for the any x rayinspection. The tack weld cannot be connected on the jointdirectly. Such (b) and (c) as below:


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Butt Weld

Full penetration welds

A full penetration weld is a butt that has complete penetration and fusionof weld with parent metal throughout the thickness of the joint. In the useof matching welding consumables, which have all mechanical propertiesequivalent to, or better than, those specified for the parent metal, thedesign strength of full penetration butt weld can be taken as equal to theparent metal. If parent materials are of different grades, the lower gradesteel should be assumed for all connected plates. However, the electrodefor the highest grade should be used. Two common types of butt weldsare available as U and V butt joints. U butt joint has a depth of penetrationequal to the depth of weld penetration and V butt joint has a depth 2 mmless than the depth of weld penetration.

Partial penetration weld

When connecting strength is not required to be as high as the strength ofthe capacity of the connection components, a partial penetration butt weldcan be used.




Fillet welds

Fillet weld is more commonly used because itscost is lower than full penetration weld.

Fillet weld does not require end preparation ofthe element to be welded and the size or leglength is smaller. The amount of testing required

for fillet weld is also smaller.



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Source: http://www.engr.mun.ca/~dfriis/cadkey/program/textappi.html

Symbols indicating fillet welds

Symbols for different butt weld notches

Steel materials is easily rust without protectivecoating. Because the rust on steel materials maycause malfunction or weaken the strength of ownstructure. So, we must provide some competentcoating to prevent any rusting reaction occur.

Coating System - Painting


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Painting is the principal method of protectingstructural steelwork from corrosion. Paints areusually applied one coat on top of another andeach coat has a specific function or purpose.

Primers for steel are usually classified according to the maincorrosion

Iron-oxide (Generally red or yellow)

Zinc Phosphate

Hot-Dip Galvanized (BS EN ISO 1461)

Finished coating - A high performance, two, componentschemically-cured aliphatic urethane gloss enamel for use inareas where maximum gloss & colour retention are required.

For use on properly prepared and primed / galvanized steel



Zinc Phosphate Primer (Type of Primer)


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Red or Yellow Oxide Primer (Type of Primer)


Micaceous Iron Oxide (Type of Undercoat)


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Gloss Enamel (Type of Finishing Coat)


Common thickness of each coating

Primer: dry film thickness = 35 m

Undercoat: dry film thickness = 35 m

Finishing coat: dry film thickness = 30 m

Minimum overall dry film thickness = 100 m

Checking with thickness of coating we use elcometer



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Coating System - Hot Dip Galvanizing

Hot Dip Galvanizing is a factory controlled metallurgicalcombination of zinc and steel that provides corrosionresistance in a wide variety of environments. It protectssteel from corrosion in two ways. It provides cathodicprotection and barrier protection.


1. Degreasing

2. Pickling

3. Fluxing

4. Galvanizing

5. Finishing

6. Quenching

7. QC Inspection


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Hot Dip Galvanizing Process

Surface Preparation

The most important step in the application of any coating. In mostinstances, where a coating fails before the end of its expected service lifeit is due to incorrect or inadequate surface preparation. With galvanizing,the surface preparation process contains its own built-in means of qualityassurance and quality control in that zinc will simply not react with a steel

surface that is not perfectly clean.

Caustic Cleaning Acid Pickling Fluxing

Source: http://www.gscsteel.com/galvanizing.html /


Galvanizing - In this step, the material is completely immersed in a bathof a minimum of 98% pure molten zinc. The bath temperature ismaintained at about 450 C. Fabricated items are immersed in the bathlong enough to reach bath temperature. The articles are slowly withdrawnfrom the galvanizing bath , and the excess zinc is removed by draining,vibrating, and/or centrifuging. The steel then goes into a dilute chromatequench giving your product a longer lasting luster.



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Inspection/Finishing The most important method ofinspection for galvanized articles is visual. A variety ofsimple physical and laboratory tests may be performed for:

Thickness, Adherence of the coating, Uniformity of the coating, Appearance


Inspection and checking occurs at each stage in the

fabrication process and after final assembly.

These checks are usually carried out examine for:

Straightness

Flatness

Inherent defects

Dimensions

Connections

Alignment of holes

Welding

Finishes/cleanliness

Inspection and Quality Control


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Material testing

Samples of steel shall be provided from eachbatch of steel within 3 days after delivery of thebatch to the fabricators works or to the Site.The rate of sampling and the position anddirection of the samples shall be in accordancewith BS EN 10002-1 and BS EN 10045.

Test for material of steel

Impact test (BS EN 10045-1)

Tensile test (BS EN 10002-1)

Charpy 'V-notch' Impact test (BS EN 10045-1)

Consists of striking a notched test piece with a hammer andmeasuring the energy required to cause fracture. The energy isindicated on the dial of the test machine and the force is producedby a swinging mass. Energy to fracture specimen .

Material testing


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Material testing

Tensile test (BS EN 10002-1) Testing machines are used to determine the mechanical properties of

materials under tension, compression, bending, shear and torsion. Astandard test piece is gripped at either end by suitable apparatus in atesting machine which slowly exerts an axial pull so that the steel isstretched until it breaks. The test provides information on proof stress,yield point, tensile strength, elongation and reduction of area.

Inspection and Quality Control

All welds shall be inspected and tested according to the

requirements.

NDT inspection has become important in different industries.Also, the inspection is widely used and requires expensiveequipment and special technologies.

Final inspection of welds a. Visual examination

b. Non-destructive testing Dye Penetrate Testing

Magnetic Particle Inspection

Ultrasonic Testing

X-ray


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Non-destructive testing

Dye Penetrate Testing Utilized to detect open or surface cracks

or defects in materials. Red dye orfluorescent penetrants are utilized aswell as various types of wet and drydevelopers.

1. Pre-treatment by cleaner

2. Penetration of red penetrate

3. Remove red penetrate completely with cleaner before inspection

4. Applied white developer

5. As it dries, red penetrate in flaw areais absorbed and appeared

Non-destructive testing

Magnetic Particle Inspection An articulated leg magnetic yoke providing a portable means of

creating magnetic fields for detection of surface cracks.ferromagnetic materials to detect surface and slight subsurfacediscontinuities.


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Acceptance of Welds

Weld Type Weld Size Approval of WeldingProcedure

Butt weld < or = 4 mm Not necessary

Ditto > 4 mm By qualified weldinginspector

Fillet weld < or = 4 mm Not necessary

Ditto > 4 mm By qualified weldinginspector


Acceptance of WeldsWeld Type Frequency of Non-destructive

Testing

All types of butt welds 100% ultrasonic examinationand magnetic particle inspection

Fillet welds with leglength exceeding andincluding 10 mm

20% ultrasonic examination andmagnetic particle inspection

Fillet welds with leg

length not exceeding 10mm

20% magnetic particle

inspection

Secondary attachmentwelds, e.g. for fixingpurlins, side rails

5% of attachments by magneticparticle inspection and ultrasonicexamination if leg lengthexceeds and includes 10 mm



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Acceptance of Welds


Acceptance of Welds



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Each part of the structure shall be aligned assoon as practicable after it has been erected.

Any temporary bracing or temporary restraintshall be left in position until erection issufficiently advanced to leave the remainingstructure in a stable and safe condition.

Common Practice

Code of Practice for the Structural Use of Steel 2005, Building Department,HKSAR.

Connections From Steel Sculpture, College of Engineering and AppliedScience, University of Wyoming, Denver, US, Online[http://wwweng.uwyo.edu/connections]

Section 15, Structural Steel Work, General Specification for Building ( 2007Edition ), Architectural Services Department, HKSAR.

Section 21, Painting, General Specification for Building ( 2007 Edition ),Architectural Services Department, HKSAR.

Explanatory Materials to Code of Practice for the Structural Use of Steel

2005 , Building Department, HKSAR. Appendix I, Symbols Used in Engineering Drawings, Engineering - 1502;

Engineering Design I (Computer Graphics), Faculty of Engineering andApplied Sciences, University of Newfoundland, Canada. Online[http://www.engr.mun.ca/~dfriis/cadkey/program/textappi.html]

Galvanizing Process, Goodluck Steel Co, India. Online[http://www.gscsteel.com/galvanizing.html]

Reference

structural steel 2009

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