C-51 Structural Steel exam questions, with answers

10 practice questions for the CSLB Structural Steel trade exam, each with the answer, a plain explanation and the source it rests on.

From our free C-51 test · Updated 14 October 2026

These are not real exam questions. CSLB does not release its test questions or answer keys, and nobody else has them. We write our own questions from the C-51 outline and the codes, standards and references CSLB lists for the exam. Each answer names its source so you can check it.

The C-51 exam has 5 sections. The questions below are grouped by section, with the share of the exam each one carries. Read the question, pick an answer, then open “Show the answer”. The other questions of the free test, scored section by section, are in the free 25-question C-51 test.

Planning and Estimating · 20% of the exam

Reviewing plans and specifications; conducting site visits; coordinating with other trades; estimating equipment and material.

1. The bracing schedule on a set of structural drawings calls for L 6 x 4 x 3/8 angles. In this standard angle callout, what does the 3/8 give?

  1. The thickness of both legs, in inches
  2. The thickness of the long leg only, in inches
  3. The weight of the angle, in pounds per foot
  4. The inside corner radius of the angle, in inches
Show the answer

Answer: A. An angle is called out by its leg dimensions in inches, wider leg first, and the third number is the leg thickness; both legs of a rolled angle have the same thickness. So L 6 x 4 x 3/8 has a 6-in leg, a 4-in leg and 3/8-in thick legs. Weight per foot is the second number only for shapes such as W-shapes and channels, not for angles.

Source: NAVEDTRA 14040, Chapter 7, Structural Shapes (angles), NAVEDTRA 14040 Blueprint Reading and Sketching, Chapter 7 Structural and Architectural Drawings (US Navy)

2. Before your crew sets the first columns on a new California building, you check the paperwork from the controlling contractor. Under 8 CCR 1710(c), the written notice must say that field-cured test samples show the footing and pier concrete has reached what share of its intended minimum compressive design strength (or enough strength to carry the erection loads)?

  1. 50 percent
  2. 66 percent
  3. 75 percent
  4. 90 percent
Show the answer

Answer: C. Section 1710(c)(2) bars a steel erector from erecting steel until it has written notice that the concrete in footings, piers and walls has reached 75 percent of its intended minimum compressive design strength, or enough strength for the erection loads, based on an approved test of field-cured samples. The other percentages do not appear in the rule.

Source: 8 CCR 1710(c)(1)(A) and (c)(2), Cal/OSHA Title 8, Section 1710 Structural Steel Erection

Job Preparation · 13% of the exam

Developing drawings; storing material; determining placement of material.

3. On an approved shop drawing, a welding symbol has a fillet weld symbol drawn only below its reference line, with nothing above the line. Under the AWS A2.4 convention as NAVEDTRA 14250 explains it, where is the fillet weld made?

  1. In the field, on the side of the joint the tail points to
  2. On the arrow side of the joint, where the arrow points
  3. On both sides of the joint, the same size on each side
  4. On the other side of the joint, opposite the arrow
Show the answer

Answer: B. A weld symbol on the lower side of the reference line means the arrow side; a symbol on the upper side means the other side, and symbols on both sides mean welds on both sides of the joint. A field weld is shown by a separate flag symbol, not by the position of the weld symbol.

Source: NAVEDTRA 14250, Chapter 3, Welding Symbols (arrow side and other side)

4. Your field crew keeps its high-strength bolt assemblies in a closed, dry storage box at the site. Under the RCSC Specification (2020), Section 2.10, how many assemblies should the crew take out of protected storage at the start of a shift?

  1. Enough for the next two shifts, so bolting never waits
  2. Only as many as they expect to install during that shift
  3. A full keg for each floor, left on that floor until used
  4. Any amount each shift, as long as bolts stay in the original keg
Show the answer

Answer: B. RCSC Section 2.10 requires bolting components at the site to be kept in protected storage, taken out only in the quantity expected to be installed during the work shift, and returned to protected storage at the end of the shift. Bolts left out on the floor pick up dirt and moisture, which changes how they tighten.

Source: RCSC Specification (2020), Sections 2.10.1-2.10.3, RCSC Specification for Structural Joints Using High-Strength Bolts (June 11, 2020)

Shop Fabrication · 18% of the exam

Processing material; creating holes and slots in material; cleaning and priming members; loading and transporting material.

5. Your shop receives W-shapes and plates for a job that requires material traceability, each lot with a mill test report (MTR). As the AISC Steel Solutions Center explains it under ASTM A6/A6M, what does an MTR for hot-rolled shapes and plates report?

  1. The grade, sizes, shop primer type, and the coating dry film thickness
  2. The heat number, grade, sizes, and tension and chemical test results
  3. The heat number, grade, sizes, and the fabricator's piece marks
  4. The grade, sizes, erection sequence, and the bolt grades to be used
Show the answer

Answer: B. An MTR comes from the producing mill and reports, among other items, the heat number, steel grade, nominal sizes, and the tension test and chemical composition results. Piece marks, primer, coating thickness and erection sequence are set later by the fabricator and erector, so they are not on the mill's report.

Source: AISC Steel Solutions Center FAQ 1.3.1 (ASTM A6/A6M Section 14)

6. Your shop is drilling bolt holes in girder splice plates for a Caltrans bridge contract under the 2025 Standard Specifications, Section 55. Within what limit must each finished bolt hole be perpendicular to the plane of the connection?

  1. Within 1 in 20
  2. Within 1 in 30
  3. Within 1 in 40
  4. Within 1 in 50
Show the answer

Answer: A. Section 55-1.02E(6)(b)(i) lists the requirements for finished bolt holes: round within plus or minus 1/32 inch, perpendicular to the plane of the connection within 1 in 20, and clean cut without torn or ragged edges. The 1 in 30, 1 in 40 and 1 in 50 limits are not in the specification; the stated limit is 1 in 20.

Source: Caltrans Standard Specifications 2025, Section 55-1.02E(6)(b)(i) Bolt Holes, General

Field Erection · 25% of the exam

Erecting and securing material; installing beams and trusses; installing high-strength bolts; welding and finishing joints and connections.

7. Your connectors carry high-strength bolts and drift pins up to beam level while fitting up a steel frame on a California building. Under 8 CCR 1716(a)(1), how must those bolts and drift pins be kept while aloft?

  1. In containers that are secured against accidental displacement
  2. In the workers' pockets, a few at a time, to keep their hands free
  3. In containers set loose on the beam flange near the connection
  4. In containers that are secured only when working over 30 ft up
Show the answer

Answer: A. Section 1716(a)(1) requires containers for storing or carrying rivets, bolts and drift pins, and the containers must be secured against accidental displacement when aloft. Section 1716 sets no height threshold for this, and a loose bucket or pocketful can drop onto workers below; 1716(b)(1) adds that bolts or drift pins being knocked out need a means to keep them from falling.

Source: 8 CCR 1716(a)(1) and (b)(1), Cal/OSHA Title 8, Section 1716 Bolting, Riveting, Fitting-Up and Plumbing

8. Your crew is hoisting K-Series open web steel joists onto a roof frame one at a time. Under SJI 100-2025, Section 6.4 (Handling), where must the hoisting cables be attached to each joist?

  1. At the bottom chord quarter points, below the bridging rows
  2. At panel points, at locations picked to keep erection stresses low
  3. At the two bearing seats, so the chords carry none of the lift
  4. At midpanel spots on the top chord, between the web members
Show the answer

Answer: B. SJI 100-2025 Section 6.4 says hoisting cables shall be attached at panel point locations, and those locations shall be selected to minimize erection stresses. A panel point is where the web members meet the chord; a cable between panel points bends the chord locally and can damage the joist. The same section requires each joist to be braced laterally before any loads are applied.

Source: SJI 100-2025, Section 6.4 Handling, SJI 100-2025 Standard Specification for K-, LH- and DLH-Series Open Web Steel Joists and Joist Girders

Safety · 24% of the exam

Working in elevated areas; hoisting and rigging; correcting safety hazards; operating lift equipment; using personal protective equipment (PPE).

9. An ironworker who is not connecting is installing plumbing cables at a work point on the steel frame of a multistory California building, 22 ft above the floor below. Under 8 CCR 1710(m), what fall protection does this worker need?

  1. No fall protection yet, because the fall distance is not over 25 feet for this work
  2. A controlled decking zone, because the height is between 15 and 30 feet
  3. Personal fall protection, because the fall distance is greater than 15 feet
  4. No fall protection yet, because the fall distance is not over two stories or 30 feet
Show the answer

Answer: C. Section 1710(m)(2) says iron workers doing any work at a work point other than connecting shall be provided with and use personal fall protection where the fall distance is greater than 15 feet. The two-stories-or-30-feet threshold applies to connecting and moving between work points, and a controlled decking zone is only for initial placement of metal decking.

Source: 8 CCR 1710(m)(2) Work Other Than Connecting, Cal/OSHA Title 8, Section 1710 Structural Steel Erection

10. Your decking crew will place the initial metal deck on a roof level 38 ft above the floor below, and the foreman proposes a controlled decking zone (CDZ) instead of tie-off because he says tie-off is impractical there. Under 8 CCR 1710(n), is a CDZ permitted at that height?

  1. No; a CDZ is allowed only up to 15 feet above the lower level, not higher
  2. Yes; a CDZ is allowed at any height once the crew is trained in CDZ work
  3. No; a CDZ is allowed only over 15 and up to 30 feet above a lower level
  4. Yes; a CDZ is allowed up to two stories or 40 feet above a lower level
Show the answer

Answer: C. Section 1710(n)(1) permits a controlled decking zone only in the area of the structure over 15 feet and up to 30 feet above a lower level, and only when personal fall protection is shown to be impractical or a greater hazard. At 38 ft the deckers need personal fall protection; CDZ training is required but does not extend the height limit.

Source: 8 CCR 1710(n)(1) Controlled Decking Zone, Cal/OSHA Title 8, Section 1710 Structural Steel Erection

Where to go from here

How the license works, from experience to fees: how to get a C-51 license. Everything about the course: the C-51 exam page.

Questions from our free C-51 test, written from CSLB License Examination Study Guide, Structural Steel (C-51), form 13E-51 (03-2026), for examinations scheduled on or after March 1, 2025. CSLB notes that the percentages are approximate. Reviewed 14 October 2026. Study guidance only; we are not affiliated with CSLB or PSI.

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