Bickford [5] uses these same equations for the case where the internal threads are stronger than the external, and this is the practice recommended here. They implemented an iterative solve for Q and incorporated that into an updated spreadsheet based on the original work of Pulling [13]. The next comparison that can be made is using two materials for Shigley's method [16] and the extension of Wileman [17] by Musto [10] and then Morrow [9]. For cases where a high degree of accuracy is required, the geometries and/or materials don't match the assumptions of these analytic methods, the loading is complicated, or the margins are very small, it is recommend that a finite element analysis be performed on the joint. The methods of Pulling [13], and the associated Excel spreadsheet, can still be used and reasonable results obtained, but it is important to understand the theory, the limitations, and the deficiencies in it. In contrast, a complicated joint or one with small margins may require additional analysis. These equations apply for both yield and ultimate strength factor of safety calculations. Usually subscripted. This is overly conservative and in general the NASA values should be sufficient. The following design resources are for design screws and bolts for the proper torque, stress, strain, preload and other engineering critical design parameters. As such, small errors in Q become large errors in the member stiffness. Advertising Center The type of connection designed has an influence on member design and so must be decided even prior to the design of the structural system and design of members. Young's modulus for the more stiff (ms) material in a two material bolted joint. Bickford's [4] method is dramatically different than the other 2 and in comparison will produce much lower clamped material stiffness. In this method, the stiffness in a layer is obtained by assuming the stress field looks like a frustum of a hollow cone (See Figure 5). Wileman [17] used finite element analysis to determine the clamped material stiffness for two "plates" made of the same material. - You can calculate the shear strength or the tensile strength of a bolt • Simple connection: If the line of action of the force acting on the connection passes through the center of gravity of the connection, … The book is intended to provide a comprehensive source of information on bolted and riveted structural joints as well as an explanation of their behavior under various load conditions. al. For variable amplitude loading, Miner's rule can be used to estimate fatigue life [1]. 1357-1360. 1. Preliminary analysis indicates a joint with a single threaded fastener can resist torque loads on the order of the applied preload torque. For rolled threads, he suggests an average stress concentration factor of 2.2 for SAE grades 0 to 2 and a factor of 3.0 for SAE grades 4 to 8. For ductile steels, the Morrow line predicts less sensitivity to mean stress. where Le is computed in the previous section. Engineering Book Store The NASA guide states these uncertainties should be used for all small fasteners (defined as those less than 3/4"). He then proposed the clamped material stiffness to be, and computed valued of m and b based on different materials stiffness ratios between materials and ratios of bolt diameter to clamped material length. The actual point of where one frustum begins and the other ends must be computed for each layer. With these assumptions, the bending stiffness for each layer can be computed to be, The moment of inertia, I, for the ith layer can be computed as, Once again assuming each layer is represented by a spring in series, the bending stiffness of the clamped material can be computed as. This implies a Q factor of, For the case where the joint "diameter" is greater than three times the diameter the of the bolt (or washer), the area that should be used is, Again it can be seen that the equation above accounts for the materials under the bolt plus additional material that is dependent on the thickness of the joint. color: 333399; [13], went on to define a bending stiffness for the clamped material using the same methodology. The thermal load that reduces the tensile load will be subtracted from the minimum preload when computing the factor of safety for joint opening. As can be seen in Figure 8 the methods produce very similar results for "thin" clamped joints. The primary focus of this guide has been on analytic/empirical methods for analyzing axial and thermal loads. Thread Stress Area Calculator and Equation Bolt Threads, Grade, Bolt Strength, Excel Spreadsheet Calculator… There is no one right choice for the preload or torque. Axial loads, shear loads, thermal loads, and thread tear out are used in factor of safety calculations. It is preferable to have the bolt break rather than strip out the threads if a joint is going to fail [12]. Shigley [16] used a similar methodology but made a different assumption about the shape of the stress field to better correlate with experimental data. Miller, Keith, private conversations, 2007. To do this, a conservative estimate of the maximum and minimum preloads must be made, so that no factors of safety are required for these preloads. If the bolted joint of interest does not meet these assumptions (and the additional assumptions of the approaches below) then it is recommended that a finite element analysis be used for the joint. } Design of bolted beam-column connections Bolt capacity of force resistance needs to be calculated in most of the connections except some seated connections as shown in The general procedure of bolted beam-column connection design is: Fig.2.4 and Fig.2.5 (bolts … The following are to links of engineering resources, tools, articles and other useful data. Bending loads can come from two primary sources. Register . It consists of a bolt, two washers, two materials, and a nut. First, there must be 'symmetric' frustums across the entire joint regardless of the number of materials (otherwise static equilibrium would not be met). The calculations within this live spreadsheet will facilitate the initial design and engineering of many types of bolted and riveted joints. Although not shown, this significant difference begins at roughly an l/db ratio of about 2.0. Both lateral (single and double shear) … Green, "Computation of Member Stiffness in Bolted Connections," ASME J. Mech Des., December, 1991, 113, pp. The joint must demonstrate a separation factor of safety at limit load.