Rivet bolt connections12/2/2023 This is due to the equipment required for tensioning the bolts and the equipment or devices needed to measure and verify the pretension force. Bolt installation costs for connections requiring pretensioned bolts will be higher than for snug-tight connections. These cases are enumerated in the RCSC Specification. Only in certain cases is it required that bolts be installed to achieve a specified minimum pretension. Figure 1 – Typical Snug-Tight Building Column to Beam Connection This is the most economical bolted connection since bolt tensioning equipment is not required and the inspection of the completed connection is simple. Connections in buildings that not subject to cyclic live loads, stress reversals, or heavy rotating machinery are typically specified as snug-tight connections. Likewise, the tensile capacity of the bolt is not affected by bolt pretension. In connections that are specified to be snug-tight, neither the shear strength of the bolt nor the bearing capacity of the connected material are affected by the level of bolt pretension. The categories are identified and described in the paragraphs that follow: Structural connections using high strength bolts fall under three categories, whether the connection resists shear, tension, or a combination of shear and tension. While this standard is valuable resource, if structural bolting was a religion, its bible would be the “Specifications for Structural Joints Using High-Strength Bolts” published by the Research Council on Structural Connections (RCSC Specification). ASTM F3125 “Standard Specification for High Strength Structural Bolts, Steel and Alloy Steel, Heat Treated, 120 ksi (830 MPa) and 150 ksi (1040 MPa) Minimum Tensile Strength, Inch and Metric Dimensions” has a title that is quite a mouthful, and this standard consolidates and replaces six ASTM standards A325, A325M, A490, A490M, F1852, and F2280. However, there is a newer ASTM Standard for high strength bolts. Note the area of contact is not a variable in the equation only the clamping force and surface condition of the contact (or faying) surfaces.įor people of my advancing age, when you hear someone mention high strength bolts, you immediately think of ASTM A325 or A490 bolts. The force of friction is equal to the clamping force times the coefficient of friction (F f = mN). For the purposes of this article the normal force will be referred to as clamping force or pretension. The magnitude of the frictional force depends on the normal force and the coefficient of friction. As you may recall, friction is a force that resists motion or attempted motion and acts parallel to the contact surfaces. So what is the slip coefficient of a bolted connection? Quite simply, it is the coefficient of static friction (m) from elementary physics. The filling of the barrel of the hole and the clamping force provided better fatigue resistance and overall performance than other fasteners available at the time (e.g. Upon cooling, the rivet shrinks against the gripped material, thereby providing a force that clamps the connected parts or plies together. During this process, the shaft of the rivet completely (or nearly completely) fills the hole into which it was installed. Rivets were installed (either in a fabrication shop or in the field) by heating the rivet to a light cherry-red color (approximately 1000 oF to 1500 oF), inserting it into the holes of the parts being connected, and then applying pressure to the preformed head while at the same time squeezing the plain end of the rivet to form a rounded, flattened, or countersunk head. Undriven rivets are formed from steel bar stock with a cylindrical shaft and a head on one end. Rivets were the predominate fastener used in the early days of iron and steel construction. There are however some aspects of riveted connections that relate to the importance of slip coefficient for high strength bolted connections that should be mentioned. High strength bolts have for the most part replaced rivets as the principal method for making non-welded structural connections. This article is concerned with bolting, in particular high strength bolts. The other usual means is to use fasteners such as rivets or bolts. Welding is one such means and is quite effective. Nearly every structure is an assemblage of individual parts or members that must be fastened together, usually at the ends of the member, by some means.
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