Structural Steel Connection Design and Details: Featuring contributions from a team of industry-recognized experts, this up-to-date resource offers comprehensive coverage of every type of steel connection. The book explains leading methods for connecting structural steel components—including state-of-the-art techniques and materials—and contains new information on fastener and welded joints.
Structural Steel Connection Design and Details
Thoroughly updated to align with the latest AISC and ICC codes, Handbook of Structural Steel Connection Design and Details, Third Edition, features brand-new material on important structural engineering topics that are hard to find covered elsewhere. You will get complete details on fastener installation, space truss connections, composite member connections, seismic codes, and inspection and quality control requirements. The book also includes LRFD load guidelines and requirements from the American Welding Society.
Types of Bolts
There are two kinds of bolts used in steel construction. These are high-strength structural bolts (Fig. 1.1) and common bolts manufactured under ASTM A307 (Fig. 1.2). High-strength bolts are included in three separate American Society for Testing and Materials (ASTM) Specifications: F3125, F3043, and F3111. F3125 is an umbrella specification that includes four grades: A325, A490, F1852, and F2280. The AISC Specification divides high-strength bolts into three groups based on minimum tensile strength. Group A bolts have a minimum tensile strength of 120 ksi and include ASTM F3125 Grades A325, A325M, and F1852, as well as ASTM A354 Grade BC. Group B bolts have a minimum tensile strength of 150 ksi and
include ASTM F3125 Grades A490, A490M, and F2280, as well as A354 Grade BD. Group C bolts have a minimum tensile strength of 200 ksi and include ASTM F3043 and ASTM A3111. The various grades of F3125 are intended for general structural use, with the use of A354 and A449 fasteners intended only for conditions where the length or diameter limits of F3125 must be exceeded. F3034 and F3111 are probably best suited to heavily loaded connections. A449 bolts are also permitted to be used where the length and diameter limitations for A325 are exceeded. They are not included in Group A due to the multiple decreases in tensile strength based on diameter. A307 bolts, which were referred to previously as common bolts, are also variously called machine bolts, ordinary bolts, and unfinished bolts. The use of these bolts is limited primarily to shear connections in nonfatigue applications.
Structural bolts can be installed pretensioned or snug tight. Pretensioned means that the bolt is tightened until a tension force approximately equal to 70 percent of its minimum tensile strength is produced in the bolt. Snug tight is the condition that exists when all plies are in contact. It can be attained by a few impacts of an impact wrench or the full effort of a man using an ordinary spud wrench. Common bolts (A307) can be installed only to the snug-tight condition. There is no recognized procedure for tightening these bolts beyond this point.
Beam Shear Splices
If a beam splice takes moment as well as shear, it is designed with flange plates in a manner similar to the truss chord splice treated in Sec. 2.2.5.2. The flange force is simply the moment divided by the center-to-center flange distance for inside and outside plate connections, or the moment divided by the beam depth for outside plate connections. The web connection takes any shear. Two typical shear splices are shown in Fig. 2.54. These are common in cantilever roof construction. Figure 2.54a shows a four-clip angle splice. The angles can be shop bolted (as shown) or shop welded to the beam webs. The design of this splice is exactly the same as that of a double-angle framing connection. The shear acts at the faying surface of the field connection and each side is designed as a double-angle framing connection. If shop bolted all the bolts are in shear only; there is no eccentricity considered on the bolts. If shop welded, the
shop welds see an eccentricity from the location of the shear at the field faying surface to the centroids of the weld groups. This anomaly is historical. The bolted connections derive from riveted connections, which were developed before it was considered necessary to satisfy “the niceties of structural mechanics” according to McGuire (1968).
A second type of shear splice uses one or two plates in place of the four angles. This type, shown in Fig. 2.54b, has moment capacity, but has been used for many years with no reported problems. It is generally less expensive than the angle type. Because it has moment capability, eccentricity on the bolts or welds cannot be neglected. It has been shown by Kulak and Green (1990) that if the stiffness on both sides of the splice is the same, the eccentricity is one-half the distance between the group centroids, on each side of the splice. This will be the case for a shop-bolted–field-bolted splice as shown in Fig. 2.54b. A good discussion on various shear splice configurations and the resulting eccentricities is given in the AISC Manual of Steel Construction (2016).
Extended Single-Plate Shear Connections (Shear Tabs)
Single-plate shear connections can be very economical connections. In-fill beams can be drilled on the fabricator’s drill line with no further handling, since the beams will require none of the coping required for more traditional beam-to-beam connections. Beam-tocolumn-web connections are also made easier. Since the beam can be connected beyond the column flanges erection is greatly eased. Unlike double angle, end plate and sometimes single angle connections, there will be no common bolts at the support, so safety is also improved.
Maximum plate thickness: Due to the uncertainty related to the distribution of moments through the connection the plate and bolt group are sized such that yielding in the plate will preclude fracture of the bolts by redistributing the moments. It should be noted that this check uses the nominal bolt capacity without a factor of safety and discounts the 20% reduction in bolt shear strength assumed in the Specification to account for uneven force distribution in end-loaded connections. Since this is essentially a ductility check and not a strength limit state, this should not be considered a violation of the Specification.
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