C-N5N5 Minimum requirements for inspection of structural steel buildings

N5.1 Quality Control

The welding inspection tasks listed in Tables N5.4-1 through N5.4-3 are inspection items contained in AWS D1.1/D1.1M (AWS, 2020), but have been organized in the tables in a more rational manner for scheduling and implementation using categories of before welding, during welding, and after welding. Similarly, the bolting inspection tasks listed in Tables N5.6-1 through N5.6-3 are inspection items contained in the RCSC Specification (RCSC, 2020), but have been organized in a similar manner for scheduling and implementation using traditional categories of before bolting, during bolting, and after bolting. The details of each table are discussed in Commentary Sections N5.4 and N5.6.

Typical model building codes, such as the 2021 International Building Code (IBC) (ICC, 2021) or NFPA 5000 (NFPA, 2021b), make specific statements about inspecting to “approved construction documents”—the original and revised design documents and specifications as approved by the building official or authority having jurisdiction (AHJ). Code of Standard Practice Section 4.2.1(a) (AISC, 2022a) requires the transfer of information from the contract documents (design documents and project specifications) into accurate and complete fabrication and erection documents; therefore, relevant items in the design documents and project specifications

that must be followed in fabrication and erection should be placed on the fabrication and erection documents or in typical notes issued for the project. Because of this provision, QC inspection may be performed using fabrication documents and erection documents, not the original design documents.

The applicable referenced standards in construction documents are commonly this Specification, the Code of Standard Practice, AWS D1.1/D1.1M, and the RCSC Specification.

N5.2 Quality Assurance

Code of Standard Practice Section 8.5.2 contains the following provisions regarding the scheduling of shop fabrication inspection: "Inspection of shop work by the inspector shall be performed in the fabricator's shop to the fullest extent possible. Such inspections shall be timely, in-sequence, and performed in such a manner as will not disrupt fabrication operations and will permit the repair of nonconforming work prior to any required painting while the material is still in-process in the fabrication shop."

Similarly, Code of Standard Practice Section 8.5.3 states, “Inspection of field work shall be promptly completed without delaying the progress or correction of the work.”

Code of Standard Practice Section 8.5.1 states, “The fabricator and the erector shall provide the inspector with access to all places where the work is being performed. A minimum of 24 hours notification shall be given prior to the commencement of work.” However, the inspector’s timely inspections are necessary for this to be achieved, while the scaffolding, lifts, or other means provided by the fabricator or erector for their personnel are still in place or are readily available.

IBC Section 2202.1 (ICC, 2021) states, “Identification of structural steel elements shall be in accordance with AISG 360 Where the steel grade is not readily identifiable from marking and test records, the steel shall be tested to verify conformity to such standards.”

Code of Standard Practice Section 6.1, Identification of Material, states, “The fabri-cator shall be able to demonstrate by written procedure and actual practice a method of material identification, visible up to the point of assembling members ”

Code of Standard Practice Section 8.2 states, “Material test reports shall constitute sufficient evidence that the mill product satisfies material order requirements. The fabricator shall make a visual inspection of material that is received from the mill, ” Code of Standard Practice Sections 5.2 and 6.1 address the traceability of material test reports to individual pieces of steel and the identification requirements for structural steel in the fabrication stage.

Model building codes, such as the IBC or NFPA 5000 (NFPA, 2021b), make specific statements about inspecting to “approved construction documents” and the original and revised design documents and specifications as approved by the building official or the AHJ. Because of these IBC provisions, the QAI should inspect using the original and revised design documents and project specifications. The QAI may also use the fabrication documents and erection documents to assist in the inspection process.

N5.3 Coordinated Inspection

Coordination of inspection tasks may be needed for fabricators in remote locations or distant from the project itself, or for erectors with projects in locations where inspection by a local firm or individual may not be feasible or where tasks are redundant.

The approval of both the AHJ and the engineer of record (EOR) is required for quality assurance to rely upon quality control, so there must be a level of assurance provided by the quality activities that are accepted. It may also serve as an intermediate step short of waiving QA as described in Section N6.

N5.4 Inspection of Welding

AWS D1.1/D1.1M requires inspection, and any inspection task should be done by the fabricator or erector (termed contractor within AWS D1.1/D1.1M) under the terms of clause 8.1.2.1, as follows:

Contractor's Inspection. This type of inspection and test shall be performed as necessary prior to assembly, during assembly, during welding, and after welding to ensure that materials and workmanship meet the requirements of the contract documents. Fabrication/erection inspection and testing shall be the responsibilities of the Contractor unless otherwise provided in the contract documents.

This is further clarified in clause 8.1.3.3, which states the following:

Inspector(s). When the term inspector is used without further qualification as to the specific inspector category described above, it applies equally to inspection and verification within the limits of responsibility described in 8.1.2.

The basis of Tables N5.4-1, N5.4-2, and N5.4-3 are inspection tasks, as well as quality requirements, and related detailed items contained within AWS D1.1/D1.1M. Commentary Tables C-N5.4-1, C-N5.4-2, and C-N5.4-3 provide specific references to clauses in AWS D1.1/D1.1M. In the determination of the task lists, and whether the task is designated “observe” or “perform,” the pertinent terms of the following AWS D1.1/D1.1M clauses were used:

8.5 Inspection of Work and Records

8.5.1 Size, Length, and Location of Welds. The Inspector shall ensure that the size, length, and location of all welds conform to the requirements of this code and to the detail drawings and that no unspecified welds have been added without the approval of the Engineer.

8.5.2 Scope of Examinations. The Inspector shall, at suitable intervals, observe joint preparation, assembly practice, the welding techniques, and performance of each welder, welding operator, and tack welder to ensure that the applicable requirements of this code are met.

8.5.3 Extent of Examination. The Inspector shall examine the work to ensure that it meets the requirements of this code Size and contour of welds shall be measured with suitable gages.

TABLE C-N5.4-1

Reference to AWS D1.1/D1.1M (AWS, 2020) Clauses for Inspection Tasks Prior to Welding

“Observe” tasks are as described in clauses 8.5.2 and 8.5.3. Clause 8.5.2 uses the term “observe” and also defines the frequency to be “at suitable intervals.” “Perform” tasks are required for each weld by AWS D1.1/D1.1M, as stated in clause 8.5.1 or 8.5.3, or are necessary for final acceptance of the weld or item. The use of the term “perform” is based upon the use in AWS D1.1/D1.1M of the phrases “shall examine the work” and “size and contour of welds shall be measured”; hence, “perform” items are limited to those functions typically performed at the completion of each weld.

The words “all welds” in clause 8.5.1 clearly indicate that all welds are required to be inspected for size, length, and location to ensure conformity. Chapter N follows the same principle in labeling these tasks “perform,” which is defined as “Perform these tasks for each welded joint or member.”

The words “suitable intervals” used in clause 8.5.2 characterize that it is not necessary to inspect these tasks for each weld, but as necessary to ensure that the applicable

TABLE C-N5.4-2

Reference to AWS D1.1/D1.1M (AWS, 2020) Clauses for Inspection Tasks During Welding

requirements of AWS D1.1/D1.1M are met. Following the same principles and terminology, Chapter N labels these tasks as “observe,” which is defined as “Observe these items on a random basis.”

The selection of suitable intervals as used in AWS D1.1/D1.1M is not defined within AWS D1.1/D1.1M, other than the AWS statement “to ensure that the applicable requirements of this code are met.” The establishment of “at suitable intervals” is dependent upon the quality control program of the fabricator or erector, the skills and knowledge of the welders themselves, the type of weld, and the importance of the weld. During the initial stages of a project, it may be advisable to have increased levels of observation to establish the effectiveness of the fabricator’s or erector’s quality control program, but such increased levels need not be maintained for the duration of the project, nor to the extent of inspectors being on site. Rather, an appropriate level of observation intervals can be used that is commensurate with the observed performance of the contractor and their personnel. More inspection may be warranted for weld fit-up and monitoring of welding operations for complete-joint-penetration (CJP) and partial-joint-penetration (PJP) groove welds loaded in transverse tension, compared to the time spent on groove welds loaded in compression or shear, or time spent on fillet welds. More time may be warranted observing welding operations for multi-pass fillet welds, where poor quality root passes and poor fit-up may be obscured by subsequent weld beads when compared to single pass fillet welds.

TABLE C-N5.4-3 Reference to AWS D1.1/D1.1M (AWS, 2020) Clauses for Inspection Tasks After Welding

The terms “perform” and “observe” are not to be confused with the terms “periodic special inspection” and “continuous special inspection” used in the IBC for other construction materials. Both sets of terms establish two levels of inspection. The IBC terms specify whether the inspector is present at all times or not during the course of the work. Chapter N establishes inspection levels for specific tasks within each major inspection area. “Perform” indicates each item is to be inspected and “observe” indicates samples of the work are to be inspected. It is likely that the number of inspection tasks will determine whether an inspector has to be present full time but it is not in accordance with Chapter N to let the time an inspector is onsite determine how many inspection tasks are done.

AWS D1.1/D1.1M, clause 8.3, states that the contractor’s (fabricator’s and erector’s) inspector is specifically responsible for the welding procedure specifications (WPS), verification of prequalification or proper qualification, and performance in compliance with the WPS. Quality assurance inspectors monitor welding to make sure QC is effective. For this reason, Tables N5.4-1 and N5.4-2 maintain an inspection task for the QA for these functions. For welding to be performed, and for this inspection work to be done, the WPS must be available to both welder and inspector. A separate inspection for tubular T-, Y-, and K-connections was added to recognize the separate fit-up tolerances for these joints in AWS D1.1/D1.1M, Table 10.7, and their importance to achieving an acceptable root.

Material verification of weld filler materials is accomplished by observing that the consumable markings correspond to those in the WPS and that certificates of compliance are available for consumables used.

AWS D1.1/D1.1M does not require a welding personnel identification system. However, the inspector must verify the qualifications of welders, including identifying those welders whose work “appears to be below the requirements of this code.” Also, if welds are to receive nondestructive testing (NDT), it is essential to have a welding personnel identification system to reduce the rate of NDT for good welders and increase the rate of NDT for welders whose welds frequently fail NDT. This welder identification system can also benefit the contractor by clearly identifying welders who may need additional training.

Table N5.4-3 includes requirements for observation that “No prohibited welds have been added without the approval of the engineer of record.” AWS D1.1/D1.1M, clause 7.17, includes specific provisions for tack welds incorporated into final welds, tack welds not incorporated into final welds, and construction aid welds.

The footnote in Table N5.4-3 was revised to clarify the use of stamps to identify welders and when used by inspectors. AISC does not mandate the use of stamps to identify a welder’s or inspector’s work; however, if stamps are used as a system of identification on cyclically loaded members, they must be the low-stress type and the EOR must grant approval for use.

AWS D1.1/D1.1M, clause 9 on stud welding, includes requirements regarding the stud welding materials and their condition, base metal condition, stud application qualification testing, pre-production welding inspection and bend testing, qualification of the welding operator, visual inspection of completed studs and bend testing of certain studs when required, and the repair of nonconforming studs. For manually welded studs, special requirements apply to the stud base and the welding procedures.

The proper fit-up for groove welds and fillet welds prior to welding should first be checked by the fitter or welder, as applicable. Such detailed dimensions should be provided on the fabrication or erection documents, as well as included in the WPS. Fitters and welders must be equipped with the necessary measurement tools to ensure proper fit-up prior to welding.

AWS D1.1/D1.1M, clause 8.2 on inspection of materials and equipment, states that “The Contractor’s Inspector shall ensure that only materials and equipment conforming to the requirements of this code shall be used.” For this reason, the check of welding equipment is assigned to QC only and is not required for QA.

N5.5 Nondestructive Testing of Welded Joints

N5.5a Procedures

Buildings are considered to be subjected to static loading unless fatigue is specifically addressed as prescribed in Appendix 3. Section J2 provisions contain exceptions to AWS D1.1/D1.1M.

N5.5b CJP Groove Weld NDT

For statically loaded structures, AWS D1.1/D1.1M and this Specification have no specific nondestructive testing (NDT) requirements, leaving it to the engineer to determine the appropriate NDT method(s), locations, or categories of welds to be tested, and the frequency and type of testing (full, partial, or spot), in accordance with AWS D1.1/D1.1M, clause 8.15.

The Specification implements a selection of NDT methods and a rate of ultrasonic testing (UT) based upon a rational system of risk of failure. If based upon a model building code, such as the International Building Code (ICC, 2021) or NFPA 5000 (NFPA, 2021b), the applicable building code will assign every building or structure to one of four different risk categories. Where there is no applicable building code, then Section A1 requires that the risk category be assigned in accordance with ASCE/SEI 7 (ASCE, 2022).

Complete-joint-penetration (CJP) groove welds loaded in tension applied transversely to their axis are assumed to develop the capacity of the smaller steel element being joined, and therefore, have the highest demand for quality. CJP groove welds in compression or shear are not subjected to the same crack propagation risks as welds subjected to tension. Partial-joint-penetration (PJP) groove welds are designed using a limited design strength when in tension, based upon the root condition, and therefore, are not subjected to the same high stresses and subsequent crack propagation risk as a CJP groove weld. PJP groove welds in compression or shear are similarly at substantially less risk of crack propagation than CJP groove welds.

Fillet welds are designed using limited strengths, similar to PJP groove welds, and are designed for shear stresses regardless of load application, and therefore, do not warrant NDT.

The selection of joint type and thickness ranges for ultrasonic testing (UT) are based upon AWS D1.1/D1.1M, clause 8.19.1, which limits the procedures and standards as stated in Part F of AWS D1.1/D1.1M to groove welds and heat-affected zones between the thicknesses of 5/16 in. (8 mm) and 8 in. (200 mm), inclusive. The requirement to inspect 10% of CJP groove welds is a requirement that the full length of 10% of the CJP groove welds be inspected.

N5.5c Welded Joints Subjected to Fatigue

CJP groove welds in butt joints so designated in Sections 5 and 6.1 of Appendix 3, Table A-3.1, require that internal soundness be verified using radiographic testing (RT) or ultrasonic testing (UT), meeting the acceptance requirements of AWS D1.1/ D1.1M, clause 8.12.2 or 8.13.2, as appropriate.

N5.5e Reduction of Ultrasonic Testing Rate

Reduction of the rate of UT from 100% is permitted for individual welders who have demonstrated a high level of skill by satisfying the requirements of this section.

N5.5f Increase in Ultrasonic Testing Rate

For risk category II, where 10% of CJP groove welds loaded in transverse tension are tested, an increase in the rate of UT is required for individual welders who have failed to demonstrate a high level of skill, established as a failure rate of more than 5%, after a sufficient number of their welds have been tested. To implement this effectively, and not necessitate the retesting of welds previously deposited by a welder who has a high reject rate established after the 20 welds have been tested, it is suggested that at the start of the work, a higher rate of UT be performed on each welder’s completed welds.

N5.6 Inspection of High-Strength Bolting

The RCSC Specification (RCSC, 2020), similar to AWS D1.1/D1.1M, defines bolt- ing inspection requirements in terms of inspection tasks and scope of examinations. The RCSC Specification uses the term “routine observation” for the inspection of all pretensioned bolts, further validating the choice of the term “observe” in this chapter of the Specification.

Table N5.6-1 includes requirements for observation of “Fasteners marked in accordance with ASTM requirements.” This includes the required package marking of the fasteners and the product marking of the fastener components in accordance with the applicable ASTM standard. As an example, ASTM F3125/F3125M Grade A325 or A325M requires the following items for package marking: ASTM designation and type; size; name and brand or trademark of the manufacturer; number of pieces; lot number; purchase order number; and country of origin. ASTM F3125/F3125M Grade A325 or A325M also requires manufacturer identification and grade identification on the head of each bolt.

Snug-tightened joints are required to be inspected to ensure that the proper fastener components are used and that the faying surfaces are brought into firm contact during installation of the bolts. The magnitude of the clamping force that exists in a snug-tightened joint is not a consideration and need not be verified.

Pretensioned joints and slip-critical joints are required to be inspected to ensure that the proper fastener components are used and that the faying surfaces are brought into firm contact during the initial installation of the bolts. Pre-installation verification testing is required for all pretensioned bolt installations, and the nature and scope of installation verification will vary based on the installation method used. The following provisions from the RCSC Specification serve as the basis for Tables N5.6-1, N5.6-2, and N5.6-3.

9.2.1. Turn-of-Nut Method Pretensioning

The Inspector shall:

• (1) Observe the pre-installation verification testing required in Section 7;
• (2) Verify by routine observation that the snug-tight condition has been achieved in accordance with Section 8.1; and
• (3) Verify by routine observation that the bolting crew subsequently rotates the turned element relative to the unturned element by the amount specified in Table 8.1.

Alternatively, when bolting assemblies are match-marked after snug-tightening of the joint but prior to pretensioning, visual inspection after pretensioning is permitted in lieu of routine observation. No further evidence of conformity is required.

A pretension that is greater than the value specified in Table 5.2 shall not be cause for rejection. A rotation that exceeds the required values, including tolerance, specified in Table 8.1 shall not be cause for rejection.

9.2.2. Calibrated Wrench Method Pretensioning

The Inspector shall:

• (1) Observe the pre-installation verification testing required in Section 7;
• (2) Verify by routine observation that the snug-tight condition has been achieved in accordance with Section 8.1; and
• (3) Verify by routine observation that the bolting crew subsequently applies the calibrated wrench to the nut. No further evidence of conformity is required.

A pretension that is greater than the value specified in Table 5.2 shall not be cause for rejection. The use of a torque greater than the minimum installation torque shall not be cause for rejection.

9.2.3. Twist-Off-Type Tension Control Bolt Method Pretensioning

The Inspector shall:

• (1) Observe the pre-installation verification testing required in Section 7;
• (2) Verify by routine observation that the snug-tight condition has been achieved in accordance with Section 8.1 and that splined ends are intact after snug tightening; and
• (3) Verify by routine observation that the splined ends are subsequently twisted off during pretensioning by the bolting crew. No further evidence of conformity is required.

A pretension that is greater than the value specified in Table 5.2 shall not be cause for rejection.

9.2.4. Direct Tension Indicator Method Pretensioning

The Inspector shall:

• (1) Observe the pre-installation verification testing required in Section 7.
• (2) Verify by routine observation that the snug-tight condition has been achieved in accordance with Section 8.1, that the appropriate feeler gage is accepted in half or more of the spaces between the protrusions of the direct tension indicator, and that the protrusions are properly oriented away from the work. If the appropriate feeler gage is accepted in fewer than half of the spaces, the direct tension indicator shall be removed and replaced.
• (3) After pretensioning, verify by routine observation that the appropriate feeler gage is refused entry into more than half of the spaces between the protrusions. No further evidence of conformity is required.

A pretension that is greater than that specified in Table 5.2 or feeler gage refusal in all locations shall not be cause for rejection..

9.2.5. Combined Method Pretensioning

The Inspector shall:

• (1) Observe the pre-installation verification testing required in Section 7;
• (2) Verify by routine observation that the bolting crew applies to the nut the initial torque used in pre-installation verification testing, that the plies have been brought into firm contact, and that the requirements of Section 8.1 have been met; and
• (3) Verify by routine observation that the bolting crew properly rotates the turned element relative to the unturned element by the amount specified in Table 8.2. Alternatively, when bolting assemblies are match-marked after the initial application of the torque, but prior to pretensioning, visual inspection after pretensioning is permitted in lieu of routine observation. No further evidence of conformity is required.

A pretension that is greater than the value specified in Table 5.2 shall not be cause for rejection. A rotation that exceeds the required values, including tolerance, in Table 8.2, shall not be cause for rejection.

The presence of the inspector is dependent upon whether the installation method provides visual evidence of completed installation. Turn-of-nut installation with matchmarking, installation using twist-off bolts, and installation using direct tension indicators provides visual evidence of a completed installation, and therefore, “observe” is stated for these methods. Turn-of-nut installation without matchmarking and calibrated wrench installation provides no such visual evidence, and the inspector is to be “engaged” onsite, although not necessarily watching every bolt or joint as it is being pretensioned.

The inspection provisions of the RCSC Specification rely upon observation of the work, hence all tables use “observe” for the designated tasks. Commentary Tables C-N5.6-1, C-N5.6-2, and C-N5.6-3 provide the applicable RCSC Specification references for inspection tasks prior to, during, and after bolting.

N5.7 Inspection of Galvanized Structural Steel Main Members

Cracks have been observed on the cut surfaces of rolled shapes, plates, and on the corners of hollow structural sections (HSS) that have been galvanized. The propensity for cracking is related to residual and thermal stresses, geometric stress concentrations, and a potential for hydrogen or liquid metal assisted cracking. These characteristics can be modified, but no provisions have been found that eliminate all potential for cracking. Inspection should be focused near changes in direction of the cut surface, at edges of welded details, or at changes in section dimensions. In HSS, indications may appear on the inside corner near the exposed end. The word “exposed” in this section is intended to mean the cut surface that is not covered by a weld or a connected part.

TABLE C-N5.6-1 Reference to RCSC Specification (RCSC, 2020) Sections for Inspection Tasks Prior to Bolting

TABLE C-N5.6-2 Reference to RCSC Specification (RCSC, 2020) Sections for Inspection Tasks During Bolting

TABLE C-N5.6-3 Reference to RCSC Specification (RCSC, 2020) Sections for Inspection Tasks After Bolting

Inspection Tasks After Bolting: Document acceptance or rejection of bolted connections Sections: not addressed by RCSC

N5.8 Other Inspection Tasks

IBC requires that anchor rods for steel be set accurately to the pattern and dimensions called for on the plans. In addition, it is required that the protrusion of the threaded ends through the connected material be sufficient to fully engage the threads of the nuts, but not be greater than the length of the threads on the bolts.

Code of Standard Practice Section 7.5.1 states that anchor rods, foundation bolts, and other embedded items are to be set by the owner’s designated representative for construction. The erector is likely not on site to verify placement; therefore, it is assigned solely to the quality assurance inspector (QAI). Because it is not possible to verify proper anchor rod materials and embedment following installation, it is required that the QAI be onsite when the anchor rods are being set.