Blueprint Reading and Layout

Lecture de Plans and Layout

Introduction to the Ironworker's Role in Reading Plans

The structural and ornamental ironworker is the first tradesperson on site after soil preparation. Your ability to read and interpret engineering drawings directly determines the safety, accuracy, and profitability of the installation. The Red Seal exam requires you to master not only symbol reading but also the transfer of dimensions from the plan to the ground or existing structure.

This chapter covers the essential elements: types of drawings, standardized symbols, scales, tolerances, layout with theodolite or laser level, and basic calculations for angles and slopes. Each section corresponds to tasks you will be required to perform during the practical and theoretical exams.

Types of Drawings and Their Use

General Arrangement Drawings (GA)

The general arrangement drawing shows the complete structure viewed from above (plan view) and in elevation. It indicates the position of each beam, column, bracing, and connection. For the ironworker, this document is used to:

Identify the mark numbers of each piece (e.g., C1 for column 1, B3 for beam 3).

Verify the finished floor levels (FFL) and structural steel levels (SSL).

Locate the anchor bolts relative to the structure's grid lines.

Golden rule: The general arrangement drawing never provides connection details. You must always consult the shop drawings for gusset plate dimensions, bolts, and welds.

Shop Drawings

These drawings are prepared by the detailer and show each individual piece with all its dimensions, holes, notches, and welds. The ironworker must:

Verify that the dimensions match the general arrangement drawing (maximum deviation of 2 mm for beam lengths).

Check the hole diameters (e.g., standard 22 mm hole for a 19 mm bolt – 3 mm tolerance).

Confirm the welding symbols according to CSA W59 (welding of steel structures).

Foundation and Anchor Bolt Plans

These plans, prepared by the civil engineer, show the exact position of the anchor bolts in the concrete footings. The ironworker must:

Verify the diameter, projection (length above the concrete), and spacing of the bolts.

Check the alignment relative to the structure's grid lines (tolerance of ± 3 mm from the theoretical axis).

Identify the leveling nuts and base plates.

Common trap: Foundation plans often use different coordinates than the general arrangement drawing. Always verify the reference system (grid lines A, B, C vs. north/south/east/west coordinates).

Standardized Symbols and Abbreviations

Welding Symbols (CSA W59)

The following table summarizes the basic symbols you must know by heart:

Weld Type	Basic Symbol	Typical Use
Fillet weld	Right triangle	Beam-to-column connections
Groove weld	Line with arrow	Full penetration butt joints
Plug/slot weld	Rectangle or oval	Reinforcement plates
Spot weld	Circle	Thin sheet metal

Reading rules:

The symbol is placed above the reference line if the weld is on the arrow side, below if it is on the other side.

The size of the weld (throat or leg) is indicated to the left of the symbol (e.g., 6 mm).

The length is indicated to the right (e.g., 100 mm).

A circle at the junction of the arrow and the reference line means the weld is all around.

Example: A symbol with an 8 mm triangle on the left and 150 mm on the right, placed above the line, means: 8 mm leg fillet weld, 150 mm length, on the arrow side.

Bolting Symbols

Standard bolt: solid circle (●) – hole 2 mm larger than the nominal diameter.

Oversized hole: circle with a dashed concentric circle – allows 6 to 8 mm of play.

Slot hole: rounded rectangle – used for thermal or fabrication adjustments.

High-strength bolt: circle with a cross (✚) – indicates controlled tensioning (specified minimum tension).

Common Abbreviations

Abbreviation	Meaning	Abbreviation	Meaning
CL	Centerline	FFL	Finished floor level
SSL	Structural steel level	TOS	Top of steel
BOM	Bill of materials	HSS	Hollow structural section
WT	Tee section	PL	Plate
Ø	Diameter	°	Degree (angle)
√	Square root	Δ	Delta (difference)

Scales and Measurements

Common Scales in Shop Drawings

Drawing Type	Horizontal Scale	Vertical Scale
General arrangement	1:100 or 1:200	1:100 or 1:200
Shop drawings	1:20 or 1:50	1:20 or 1:50
Connection details	1:5 or 1:10	1:5 or 1:10
Section profiles	1:1 or 1:2	1:1 or 1:2

Conversion rule: If the plan is at a scale of 1:50, each millimeter on paper represents 50 mm on the structure. To convert a measurement from the plan to the actual measurement, multiply by the denominator of the scale.

Example: A dimension of 42 mm measured on a 1:50 plan corresponds to 42 × 50 = 2100 mm = 2.1 m.

Trap: Shop drawings are often drawn at different scales for plan views and elevations. Never measure directly on the plan with a ruler – always use the written dimensions (dimension lines). Written dimensions are the legal reference, not ruler measurements.

Dimensional Tolerances (CSA S16 – Design of Steel Structures)

The following table gives fabrication and erection tolerances according to CSA S16:

Parameter	Tolerance
Beam length (≤ 10 m)	± 3 mm
Beam length (> 10 m)	± 5 mm
Column height	± 3 mm
Plate squareness	± 2 mm over 300 mm
Bolt hole alignment	± 1 mm between adjacent holes
Anchor bolt position	± 3 mm from grid line
Bearing level (elevation)	± 5 mm

Accumulation rule: Tolerances add up. If a column has a tolerance of ± 3 mm and the beam it supports has ± 3 mm, the total deviation can reach ± 6 mm. The engineer must validate any exceedance of the cumulative tolerance.

Layout: Principles and Procedures

Definition of Layout

Layout is the operation of transferring dimensions from the plan to the site by physically marking the positions of columns, anchor bolts, and bearings. It is done in three steps:

57.Establishing the grid lines (reference lines) from the surveyor's control points.

58.Marking the points (column centers, anchor bolts) on the concrete or ground.

59.Verifying distances, angles, and levels before installation.

Measuring Instruments

Instrument	Accuracy	Use
Steel tape (30 m)	± 1 mm / 30 m	Basic measurements, verification
Rotating laser level	± 1.5 mm / 30 m	Levels, elevations
Theodolite (total station)	± 2 seconds of arc	Angles, alignments, coordinates
Optical level	± 1 mm / 30 m	Level differences
Combination square	± 0.5 mm / 300 mm	Local verification

Temperature rule: A 30 m steel tape expands approximately 0.36 mm per degree Celsius above 20 °C. For spans over 30 m, apply the correction: ΔL = L × α × ΔT, where α = 0.0000116 /°C (coefficient of thermal expansion for steel).

Example: A 50 m span measured at 35 °C (ΔT = 15 °C): ΔL = 50 × 0.0000116 × 15 = 0.0087 m = 8.7 mm. The actual measurement at 20 °C would be 50.000 m – 0.0087 m = 49.991 m.

Triangulation Method

To lay out an inaccessible point (e.g., the center of a column on an existing wall), use triangulation:

66.Measure two known distances from two reference points (A and B).

67.Draw arcs with radii equal to these distances.

68.The intersection of the arcs gives the position of the point being sought.

Angle calculation: To verify a right angle between two grid lines, use the 3-4-5 rule. If the sides measure 3 m and 4 m, the diagonal must measure 5 m (√(3² + 4²) = √25 = 5). For larger dimensions, multiply by a common factor (e.g., 6-8-10, 9-12-15).

Anchor Bolt Layout

The typical procedure for laying out a column footing:

72.Locate the column grid line on the concrete footing using the theodolite.

73.Draw the perpendicular centerline (at 90°) using the 3-4-5 method.

74.Mark the column center at the intersection of the two lines.

75.Measure the distances from the center for each bolt (e.g., ± 150 mm in each direction for a 300 × 300 mm plate).

76.Verify the bolt projection (height above the concrete) with a laser level.

77.Check the squareness of the base plate relative to the bolts.

Critical tolerance: The deviation between bolts on the same footing must not exceed ± 3 mm. If the bolts are offset by more than 6 mm, oversized or slotted holes must be used – but this requires the engineer's approval.

Slope and Angle Calculations

Slope as Percentage and Degrees

The slope of a beam or rafter is calculated as follows:

Slope (%) = (vertical rise / horizontal distance) × 100

Angle (°) = arctangent (rise / horizontal distance)

Example: A roof beam rises 1.2 m over a horizontal span of 9.6 m.

Slope = (1.2 / 9.6) × 100 = 12.5%

Angle = arctan(1.2 / 9.6) = arctan(0.125) = 7.13°

Reverse conversion: To find the rise from an angle: rise = horizontal distance × tan(angle).

Actual Length of an Inclined Beam

The actual length (hypotenuse) is calculated using the Pythagorean theorem: L = √(H² + V²), where H is the horizontal distance and V is the vertical rise.

Example: H = 9.6 m, V = 1.2 m → L = √(92.16 + 1.44) = √93.6 = 9.67 m.

Trap: Plans often give the horizontal length (projection) rather than the actual length. The detailer calculates the actual length for cutting, but the ironworker on site must verify that the delivered beam matches the actual length, not the projection.

Cut Angles for Inclined Connections

For a connection between an inclined beam and a vertical column:

Cut angle = 90° – beam inclination angle.

Gusset cut angle = inclination angle / 2 if the gusset is symmetrical.

Example: beam inclined at 30° → cut angle = 60° from the horizontal. The gusset will have a 15° angle on each side.

Plan Verification: Systematic Procedure

Before starting the installation, the ironworker must perform a cross-check of the documents:

101.Compare the general arrangement drawing with the shop drawings: each mark number must appear in both documents with the same dimensions.

102.Verify the levels: the SSL (structural steel level) must correspond to the FFL (finished floor level) minus the floor thickness (slab, joists, etc.).

103.Check the loads: the loads indicated on the plans (dead load, live load) must be compatible with the connection capacities.

104.Identify conflicts: pipe passages, electrical conduits, other trades – report any overlaps to the engineer.

105.Verify revisions: plans carry a revision number (Rev. A, B, C). Always use the latest revision and confirm that changes are clearly marked (revision bubbles).

Communication rule: Any discrepancy between plans must be reported in writing (RFI – Request for Information) before proceeding. Never improvise on site.

Traps to Avoid

109.Measuring on the plan with a ruler: scales can be distorted by photocopying or folding. Always use the written dimensions.

110.Confusing the arrow side and the other side for welding symbols: the symbol above the reference line = weld on the arrow side; below = the other side.

111.Ignoring cumulative tolerances: a 3 mm error on each column can become 30 mm over a row of 10 columns.

112.Forgetting the temperature correction for long spans: at 35 °C, a 50 m span is 8.7 mm longer than at 20 °C.

113.Using a fiberglass measuring tape for precision measurements: it stretches and gives errors of 5 to 10 mm over 30 m.

114.Not verifying the perpendicularity of grid lines: a 1° deviation over a 20 m span gives a 349 mm offset at the end.

115.Confusing levels: SSL (structural) vs. FFL (finished) – a 150 mm thick slab can cause a 150 mm level error.

116.Assuming anchor bolts are perfectly placed: always verify the actual position before ordering base plates.

117.Ignoring general notes on the plans: they often contain critical requirements (surface preparation, bolt type, torque specifications).

118.Not documenting deviations: if you must force a piece into place, note it and report it – this protects your professional responsibility.

Summary

Reading plans is the ironworker's fundamental skill: it transforms drawings into a real structure with millimeter precision.

Three types of drawings are essential: general arrangement drawings (positioning), shop drawings (fabrication), and foundation plans (anchor bolts).

Welding symbols follow CSA W59: symbol position (above/below) indicates the weld side.

Tolerances according to CSA S16: ± 3 mm for beam lengths, ± 3 mm for anchor bolts, ± 5 mm for levels.

Layout is done by triangulation, the 3-4-5 method, and verification with a theodolite or laser level.

Slope calculations use trigonometry: slope (%) = (rise / horizontal) × 100, angle = arctan(rise / horizontal).

The actual length of an inclined beam is calculated using Pythagoras: L = √(H² + V²).

Systematic plan verification (revisions, conflicts, levels) is mandatory before any installation.

Written communication (RFI) is the standard procedure for reporting discrepancies – never improvise.

For the Red Seal exam: focus on rapid symbol reading, scale conversions, slope calculations, and tolerances. Typical questions include: "What is the actual length of a beam with a horizontal span of 12 m and a 15% slope?" (Answer: √(12² + 1.8²) = √147.24 = 12.13 m) or "What is the maximum allowable deviation for an anchor bolt?" (Answer: ± 3 mm).

Precision is your trademark. An ironworker who reads plans correctly and lays out accurately saves thousands of dollars in corrections and protects the safety of all workers.