C-5.25.2 material properties

5.2.1 Determination of Required Tests

The extent of tests required depends on the nature of the project, the criticality of the structural system or member evaluated, and the availability of records pertinent to the project. Thus, the engineer of record has the responsibility to determine the specific tests required and the locations from which specimens are to be obtained.

5.2.2 Tensile Properties

Samples required for tensile tests should be removed from regions of reduced stress, such as at flange tips at beam ends and external plate edges, to minimize the effects of the reduced area. The number of tests required will depend on whether they are conducted to merely confirm the strength of a known material or to establish the strength of some other material.

It should be recognized that the yield stress determined by standard ASTM methods and reported by mills and testing laboratories is somewhat greater than the static yield stress because of dynamic effects of tensile testing. Also, the test specimen location, for example, specimens removed from the flange of a shape versus specimens removed from the web, may have an effect on test results. These effects have already been accounted for in the nominal strength equations in the Specification, and as a result, no adjustments for specimen location and for dynamic effects of tensile test results are necessary when using nominal strength equations.

However, where strength evaluation is accomplished by load testing, the effects on yield strength of dynamic tensile testing should be accounted for in load test planning because yielding during the load test, where test loads are applied to the structure in a quasi-static manner, will tend to occur earlier than otherwise anticipated on the basis of a dynamic test yield strength. The static yield stress, $F_{y s}$, can be estimated from the specified minimum yield stress determined by routine application of ASTM methods, $F_{y}$, by the following equation (Ziemian, 2010):

(C-A-5-1)

$F_{y s}=R\left(F_{y}-27\right)$

(C-A-5-1M)

where

$F_{y}=$ reported yield stress, ksi (MPa)

$F_{y s}=$ static yield stress, ksi (MPa)

$R=0.95$ for tests taken from web specimens

= 1.00 for tests taken from flange specimens

The $R$ factor in Equation C-A-5-1 and Equation C-A-5-1M accounts for the effect of the coupon location on the reported yield stress. Prior to 1997, certified material test reports for structural shapes were based on specimens removed from the web, in accordance with ASTM A6/A6M. Subsequently, the specified coupon location was changed to the flange.

5.2.3 Chemical Composition

Where a structure is to be repaired or modified by welding, chemical composition provides information that is used when preparing the weld procedure specification (WPS). This Specification requires determination of chemical composition because some older and pre-standardized structural steels may exhibit elevated levels of phosphorus or sulfur, among other chemical constituents, that may affect requirements to be specified in the WPS. Additionally, where the structural steel to be welded is an obsolete or pre-standardized structural steel, particularly those steels manufactured prior to approximately 1950, consideration should be given to use of metallographic examination to assess possible unsound features in the steel. Physical features that may adversely affect the soundness of structural steel to be welded include nonmetallic inclusions, stringers, voids of various shapes, tears, and segregation, among others. These unsound features are of concern because their presence may potentially lead to lamellar tearing in the steel at the completed weld. An experienced welding metallurgist should be consulted for the metallographic examination and for guidance with selection of weld joint details where unsound features are observed to be present in the steel to be welded.

5.2.4 Base Metal Notch Toughness

The engineer of record should specify the location of samples. Samples should be cored, flame cut, or saw cut. The distance from the edge of flat tension specimens (generally, specimens 1/2 in. (13 mm) thick or less) need to be made only large enough to obtain the grip width. The distance from the center of a cylindrical tension specimen to either of the thermally cut edges should be 1 in. (25 mm) or larger. The engineer of record is responsible for determining if remedial actions are required to repair the sampling location, such as the possible use of bolted splice plates.

5.2.5 Weld Metal

Because connections typically have a greater reliability index than structural members (see Commentary Section B3.1), strength testing of weld metal is not usually necessary. However, field investigations have sometimes indicated that completejoint-penetration groove welds, such as at beam-to-column connections, were not made in accordance with AWS D1.1/D1.1M (AWS, 2020). The specified provisions in AWS D1.1/D1.1M provide a means for judging the quality of such a weld. Where

feasible, any samples removed should be obtained from compression splices rather than tension splices, because the effects of repairs to restore the sampled area are less critical.

5.2.6 Bolts and Rivets

Because connections typically have a greater reliability index than structural members (see Commentary Section B3.1), removal and strength testing of fasteners is not usually necessary. However, strength testing of bolts is required where they cannot be properly identified otherwise, such as by observation of grade markings on bolt heads. Because removal and testing of rivets is difficult, assuming the lowest-strength rivet steel grade simplifies the investigation. Rivet grades can often be determined by referring to Section 1.3 of AISC Design Guide 15, Rehabilitation and Retrofit (Brockenbrough and Schuster, 2018.)