Structural Steel Detailing N5 Notes

Introduction

• This module covers civil and structural steelwork and the roles involved in construction projects.
• It also covers basic structural steel drawings, civil drawings with specifications, bolts, and welding.

Structural Steelwork

• Structural steel is commonly found in supermarkets and workshops.
• Steel is derived from iron.
• 'Structural steel' refers to sections, plates, and bars used to fabricate structural members like beams, girders, columns, struts, ties, and hangers.

Steel Profile Sections and Plates

• Steel is used in forms such as I-sections, H-sections, channels, angles, flats, bars, plates, sheets, cold-formed sections, and hollow sections.

Terminology

• Structural steel is produced in different strength grades, indicated in MPa (megapascal).
• Hot-rolled sections are made by heating steel ingots to 1200 °C and passing them through rollers.
• Standard hot-rolled sections are grades 43, 50, and 55; multiplying these by 10 gives the maximum tensile strength.
• Cold-rolled sections are formed by folding flat sheet steel into shapes.

Describing Steel Sections

• I- and H-sections: nominal depth (mm) × nominal width (mm) × mass (kg/m) e.g., 406 × 178 × 54 I and 305 × 305 × 118 H.
• Channel sections: nominal depth × nominal width: e.g., 200 × 75 (tapered flange channel) and 200 × 75 PFC (parallel flange channel).
• Angle sections: leg length × leg length × thickness: e.g., 70 × 70 × 6 L (equal angle) and 100 × 75 × 8 L (unequal angle).
• Tees: nominal depth × nominal width × mass: e.g., 229 × 191 × 34 T (cut from 457 × 191 × 67 I) and 76 × 152 × 12 T (cut from 152 × 152 × 23 H).
• Flat bars: width × thickness: e.g., 80 × 10 Fl.
• Square bars: width of side: e.g., 40 × 40 Sq.
• Round bars: diameter: e.g., 100 dia. round.
• Plates: width × thickness: e.g., 1 200 × 12 Pl.

Terminology of steel profile sections

• Angle profile sections: Indicated by the letter L: listed as long leg, short leg, thickness, the symbol L, and length e.g., 70 × 70 × 6 L × 2 100 mm and 100 × 75 × 8 L × 2 100 mm.
• Channel profile section: Similar to an I-beam trimmed on one side; indicated by RSC (rolled steel channel). Listed as depth, width, mass (kg/m), and length, e.g., 200 × 75 × 25,3 kg/m × 2 100 mm.
• I-profile section: Indicated by the letter I: listed as the symbol, depth (mm), width (mm), mass (kg/m), and length, e.g., I – 203 × 133 × 25 kg/m × 2 500 mm.
• H-profile section: Indicated by the letter H: listed as the symbol, depth (mm), width (mm), mass (kg/m), and length, for example, H – 305 × 305 × 97 kg/m × 2 500 mm.

Standard Steel Tables

• Used to obtain structural section sizes per the SA Institute of Steel Construction (SAISC).

Different Types of Steel Profiles

• Steel-rolling involves passing metal stock between rollers.
• Rolling is classified by metal temperature: hot-rolling (above recrystallization temperature) and cold-rolling (below recrystallization temperature).

Hot-Rolled Steel

• Begins as smelted iron ore melted, purified, and mixed with elements.
• Molten metal is poured into molds, cooled into slabs, and rolled into shapes while hot.

Hot-rolled sections:

• Produced by squeezing a heated billet between rollers into the final shape.
• Plates are made similarly using flat and wide rolls.
• Dimensions vary due to roller wear and possible misalignment.
• Used for load-bearing structural members: channel iron, joists, angle iron, rebars, girders, steel supports, roofing columns, and rails.

Cold-Formed Sections

• Made by bending a thin steel strip (not preheated) through rollers.
• Circular sections are seam-welded; rectangular sections undergo another cold-forming process.
• Used in light structures: wall partitioning, suspended ceilings, light steel roofing purlins, and cleats.
• Cold-formed steel sheeting is used for metal roofs, light-loaded beams, architectural applications, some car body parts, and steel cans and containers.

Open Cold-Formed Sections Specifications:

• Profile dimensions and angular accuracy measured at least 150 mm from the end.
• Offset should not exceed L/500 of length.
• Deviation of profile dimensions should not exceed ±2 mm or ±1.5%.
• Deviation from 90° angle should not exceed ±1° at corners.

Hollow Sections Specifications:

• Produced to SANS 657: Part 1, with a yield stress of 300 MPa.
• Available in standard lengths of 6 m; some sizes in 9.144 m lengths.

The application of various steel profiles

• Steel profiles are used for roads, railways, infrastructure, appliances, and buildings.
• Steel skeletons support structures: stadiums, skyscrapers, bridges, and airports.
• Also used in office furniture, shipbuilding, pipeline transport, mining, offshore construction, aerospace, and heavy equipment.

Drawing of Various Sections

• Detailers must understand cross-sectional dimensions from structural steel tables (Table 1.2).

The Procedure for I- and H-Sections, Follow These Steps:

1. Construct horizontal and vertical center lines.
2. Construct flange and web thickness.
3. Construct the centers of the inside corner radii.
4. Insert the corner radii.
5. Darken the outlines with a heavier lead.
6. Clean up the construction lines.
7. Add the dimensions.

The Procedure for Channel Sections, Follow These Steps:

1. Draw the centre line.
2. Construct the outsides of the channel.
3. Construct the inside web and flanges and the inside radii.
4. Darken the outlines with a heavier lead.
5. Clean up the construction lines.
6. Add the dimensions.

The Procedure for Angle Sections , Follow These Steps:

1. Construct the outside dimensions.
2. Construct the web thicknesses.
3. Construct the internal radius.
4. Darken the outlines with a heavier lead.
5. Clean up the construction lines.
6. Add the dimensions.

Weight Variations for Similar Serial Sizes

• Steel mills consider factors during manufacture: recipe, carbon content, rolling speed, and steel temperature.
• Warping, twisting, and dimensional inaccuracy can occur during rolling or cooling, leading to slight variances.
• Rolling tolerance: Permitted limit of inaccuracy, specified by the SAISC.

Roles Involved in a Construction Project

• Structural steel detailing is essential for large, high-rise buildings and other industrial projects.
• Draughtspersons serve as intermediaries between designers and executors, translating intent into graphical instructions with clarity and accuracy.

Management and Technical Organization

• The architect and consulting engineer are appointed in commercial-type buildings, while the consulting engineer handles everything in industrial buildings.
• Government or public bodies may have their own architectural and engineering staff.

Role of the Structural Steel Detailer in Industry

• Structural steel detailers create detailed drawings for fabrication and construction, requiring relevant qualifications, awareness of international standards, communication skills, and CAD software proficiency.

Responsibilities of Detailers

1. The drawing office evaluates the consulting engineer’s drawings and specifications.
2. A list of steel materials is prepared for ordering.
3. Draughtspersons create steelwork detail drawings, scrutinized by checkers before fabrication.
4. The detail drawings go to the fabricating shop, and the drawing office prepares erection drawings.
5. Every component is given a distinguishing mark for easy identification, and drawings are updated with any revisions.

Knowledge and Fields of activity

• Detail draughtspersons can fill niches in consulting engineering practices, mining houses, and public utility companies, acquiring specialized knowledge and career advancement opportunities.

Abbreviations and Erection Marks

• Essential to understand abbreviations for drawings.
• Abbreviations: e.g., approx. (approximate), arrgt. (arrangement), AOE (as other end), assy. (assembly).
• Abbreviation Table (1.3) lists common abbreviations.

Erection Marks

• Each loose item from the workshop requires an erection mark for site identification.
• Marks consist of a prefix (drawing number) and component numbers; listed in Table 1.4.
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Steel Structures and Buildings

• Elevation, plan, and cross-section show steel framework for a warehouse-type building (Figure 1.15).

Types of Lines Used

• Three main line types: heavy, medium, and fine.
• Line thicknesses and pencil leads are related to each type, detailed in Table 1.5.

Types Of Outlines:

• Style in attractive appearance.
• Use lower-case lettering for general notation and upper-case for headings and titles.
• The minimum letter size for upper-case letters is 3 mm.

Leader Lines and Arrows

• Relate notes to objects; arrowhead points to the outline, or a dot for surface-specific notes.

Break Lines

• Denote imaginary cuts through objects when only a part is shown.

Reference Items

• Indicate position using short chain-dotted lines.

Cross-Hatching and Shading

• Used within the section profile to indicate that the item has been cut.
• Conventions for timber, concrete, brickwork, and grout are used.

Opposite-Hand Components

• Mirror images; detail only one with the notation ‘One required as drawn. One to opposite hand’.

Indication of Bolts and Bolt Holes

• Shown with symbols (Table 1.6); HSFG bolts must be indicated clearly.

Indication of Welding

• Indicated with standard symbols and not shown graphically, unless there's a specific reason to show a convention is used.

Machining Symbols

• Machining of a steel surface is indicated by machining symbols.

Elevation and Section Arrows

• Various styles; drawing number in the lower half indicates the view appears on a different drawing.

Drawing Scales

• Involve scaling down true size with consistent proportions; common scales: 1:5, 1:10, 1:20, 1:50, 1:100, and 1:200; 1:15 is also frequently used.

Dimensions of Orthographic Projection Drawing

• Three-dimensional objects are represented in two dimensions using orthographic projection.

Shape description

• Most objects in the world today are created in three dimensions and shape description is how they're described.

Third-angle orthographic projection

• Third-angle orthographic projection of I-profile section beam enable a beam to be made to specification, it is necessary for the detailer to depict it accurately and to indicate its size.

Dimensioning

• The detailer indicates its size with enough dimensions defining every part.
• Projection lines should be thin and should cross as few other lines as possible.
• The outermost line on an object is used for the dimensioning and dimensions are given in millimetres.

Welding Symbols and Joints

• A structural steelwork detail draughtsperson (detailer) must be able to identify and explain various welding connections on their drawings.
• The detailer must understand welding symbols and know how to convey information about the configuration of the joint members to be welded.

Important terms:

• Arrow: identifies the location where the welding operation is to be performed
• Arrowhead: Symbol that indicates the extent of a dimension
• Base metal: Material to be welded.
• Butt joint: Weld joint formed when two joint members, located approximately in the same plane, are positioned edge to edge Concave

Welding Symbols

• Basic welding symbols are in Table 1.7.
• Reference line direction and information placement.
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Complete basic and welding types

• Fillet, square butt, single V-butt, and double V-butt.
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Information contained in basic welding symbols

• Arrow, the reference line, the weld symbol, the dimensions, the tail.
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Supplementary welding symbols

• weld-all-round symbol, the site- / field-weld symbol, the melt-through symbol, the consumable-insert symbol, the backing symbol, the spacer symbol, and the contour symbol.
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Weld joint

• The physical configuration of the joint members to be joined. Different weld joints are used on a fabrication to meet design requirements.
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Filler metal

• The metal deposited during the welding process. Filler metal in the weld joint is usually matched to the strength of the base metal.
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Different types of welding joints

• Butt joints, T-joints, corner joints, lap joints edge joints
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Welding processes

• Manual metal arc, automatic with continuous coated electrode, gas shielded arc, submerged arc and electro slag
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Different weld types

• Groove welds, fillet welds, plug welds slot welds, stud welds, spot welds, projection welds, seam welds, back and backing welds, surfacing welds and flange welds
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Bolts in structural steelwork

• Bolting is a common method for joining components in structural steelwork.
• Bolts transfer force from one member to another not only holds the beam in
  relation to the column. All bolts have hexagonal heads and nuts, and parallel shanks with threads cut or rolled into them . All bolts have hexagonal heads and nuts, and paralle The commercial bolt is commonly used in diameters: M 12 (purlin and girt applications), M 16 (relatively lightly loaded cleats and brackets), M 20 (general structural connections and holding-down bolts),M 24 (general structural connections and holding -down bolts), M 30 (holding-down bolts), and M36 (holding-down bolts).
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Three types of bolts are

• 1. Grade 4.8 ordinary bolts (also known as black bolts),
• 2. Grade 8.8 precision bolts (also known as close tolerance bolts) and
• 3.HSFG bolts (also known as high strength friction-grip bolts)
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Bolts and bolt hole symbols

• Shop bolts, site bolts, plain holes, countersunk near side and countersunk far side
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Drawings of structural bolts

• Conventional and construction methods of structural bolts
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Bolt holes

• The holes for the bolts are usually punched or drilled.

Steel List and Calculations

• The detail drawings provide the data needed to develop the materials requisition list, the bolt list, cutting and item numbers and to calculate the mass for the structure