QUESTION: (SUMMER2016) In National Building Code of Canada 2015, the period dependant Site Coefficient F(T), used for determination of seismic Design Spectral Accelerations, has replaced Site Coefficients Fa and Fv. CSA Standard S16-14, however, continues to reference Site Coefficients, Fa and Fv. Is S16-14 out of step with NBC 2015?

ANSWER: CSA S16-14 is compatible with NBC 2015. In S16-14, coefficients Fa and Fv, appear in two expressions: the short-period specified spectral acceleration ratio, IEFaSa(0.2), and the one-second specified spectral acceleration ratio, IEFvSa(1.0). Certain values of these quantities serve as triggers for more stringent requirements whereas other values set the conditions for relaxation. Although F(T) has replaced Fa and Fv for the purpose of determination of Design Spectral Accelerations in NBC 2015 the Code retains the expressions IEFaSa(0.2) and IEFvSa(1.0) as triggers. As defined in Sentence 4.1.8.4. (7) of NBC 2015, Fa = F(0.2) and Fv = F(1.0). Ideally, F(0.2) and F(1.0) should also replace Fa and Fv respectively in these trigger expressions. This was not possible in the 2015 code cycle for the following reason: In order to be considered for adoption by NBC 2015, CSA material design standards, S16, A23.3 etc., must be published in 2014. However, changes proposed for NBC, including the period dependant Site Coefficient F(T), could not be finalized in time to meet the publication schedule for the CSA standards.

QUESTION: (SUMMER2013) Is there a standard for anchor bolts?

ANSWER: Yes, ASTM F1554 covers three grades of anchor bolts: Grade 36 (248 MPa), Grade 55 (380 MPa) and Grade 105 (724 MPa).

The vast majority of anchor bolts (or anchor rods as defined in CSA S16-09) are used to position, level and secure base plates for concentrically loaded gravity columns. Fabricators have traditionally supplied these anchor rods manufactured from round bar stocks produced to ASTM A36 (or CSA G40.21 300W). Since the introduction of ASTM F1554, Grade 36 products fill this role.

Grades 55 and 105 are produced to meet higher specified strengths. In addition, when specified in the purchased order as a ‘supplementary requirement,’ they are supplied to meet specific Charpy notch-toughness with test values.

QUESTION: (SUMMER2013) What are the most common high-strength bolt products used in building construction?

ANSWER: Three-quarter-inch A325 bolts are still very common. Some fabricators/erectors prefer seven-eighth-inch A325 bolts, especially for large projects. A490 bolts are used increasingly in building construction. Typically, they are selected for connections resisting very large forces while A325 bolts may be used elsewhere in the structure. In such applications, care must be taken to prevent A325 bolts from being inadvertently installed in holes designed to receive A490 bolts. It is prudent to segregate them by size, typically, a quarter of an inch difference in diameter.

Practical combinations include:
a) 1˝ A490 bolts for heavy connections and ¾˝ A325 bolts elsewhere; and
b) 1⅛˝ A490 bolts for heavy connections and ⅞˝ A325 bolts elsewhere. Where pre-tensioned installation is required, twist-off type tension-control bolts (assemblies) have emerged to be viable options. ASTM F1852 and ASTM F2280 bolts (twist-off type) share the ultimate-limit-state resistances with A325 bolts and A490 bolts respectively. However, CSA S16-09 specifies smaller values for 5 per cent slip coefficients, c1, for these twist-off type bolt assemblies versus those of high strength bolts pre-tensioned to meet the turn-of-nut method of installation. For further discussion on ASTM F1852 and ASTM F2280, visit Q & A Column in Advantage Steel No. 38.

A490 and F2280 products shall not be galvanized. Use of metric bolts is still rare because they are unavailable unless a special order for a very large quantity is placed with advance notice.

QUESTION: (FALL2010) CISC/CPMA Standard 1-73a versus CISC/CPMA Standard 2-75: What do they have in common and what are the major differences?

ANSWER: These standards provide essentially the same laboratory requirements. The provision for surface preparation reflects the key difference. In addition to removal of grease and oil in accordance with SSPC Standard SP1, CISC/CPMA 2-75 requires steel cleaning in accordance with SSPC SP7, Brush-Off Blast Cleaning. Where CISC/CPMA 2-75 serves as a primer, it should be compatible with the top coat. CISC/CPMA 1-73a is a standard for one-coat paint, not a standard for primer.