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--> | Contact, Home Various angles, α, have been used. These include better guidelines for choosing a pre-computed nut factor or using a method to compute a more accurate nut factor, bending effects (both globally applied that result in axial loads on the bolt and local bending on the bolt due to geometric effects such as bolting a pipe flange that has a gap between materials), fatigue analysis, extending the DMP method [9] to more than two materials and how to include thermal effects with it, and guidelines on designing bolted joints to carry shear load (including frictional capacity, shear pins, shear load applied to the bolts, etc.). If the analytic/empirical approaches above are not applicable or additional accuracy is required, then the recommended approach is a finite element analysis of the joint. The down side is that it is only applicable for two layer joints and only applies in certain ranges of geometries (although it should be noted the range is relatively broad and likely to cover most engineering applications). The methods produce very similar results. For this case, the shape of the actual stress distribution looks more like a barrel and the shape assumed by Shigley is inappropriate. The first is a method based on an assumed cylindrical stress field. A bolted joint is constrained so the actual change in length will be the natural extension plus some amount (which can be zero) due to the constraints. A table of nut factors was given in Table 4. The second method, from Shigley [16], is based on an assumption the stress field can be represented as a hollow frustum of a cone. At this point, the recommended method is to use a pre-computed nut factor from Table 4 until the analytic methods are better understood, compared to the known methods, and confidence is gained in the accuracy of the method. Calculation Example – Design bolted connection of tension plates (EC3) Create a free account and view content that fits your specific interests in structural engineering Learn More. Bolt capacity 4. The following design resources are for design screws and bolts for the proper torque, stress, strain, preload and other engineering critical design parameters. { Thickness of clamped material. As is typical with bolted connections subjected to shear, the load is … Young's modulus for the less stiff (ls) material in a two material bolted joint. The thermal load that reduces the tensile load will be subtracted from the minimum preload when computing the factor of safety for joint opening. Due to flexibility in the bolt or washer, the correct value of dh will be less than the bolt head (or washer) diameter and the degree to which it is less depends on the relative stiffness of the materials involved. In many cases, additional work will be needed to assess the quality of current practices and provide guidance. While there are subtleties to applying the method, it has been used successfully since the 1960's for designing and analyzing bolted joints and it is general enough to apply to any axisymmetric geometry (although the accuracy is unknown at best or questionable at worst for anything but simple geometries). Bickford [4] noted that spheres, cylinders and frustums could all be used. His equations are modified here to account for qi so that it can be compared to the work of Pulling [13]. document.write(' ') It consists of a bolt, two washers, two materials, and a nut. Sample Design Calculations. Although not shown, this significant difference begins at roughly an l/db ratio of about 2.0. First, there must be 'symmetric' frustums across the entire joint regardless of the number of materials (otherwise static equilibrium would not be met). For the case of a bolted flange of a pipe with the bending applied to the neutral axis of the pipe, the actual load on the bolt will be more like an axial load and less like a bending load. floodproofing, and construction of a floodwall in a … The correlation has a standard error of 0.065. BS449: Part 2 Bolt Grade 8.8, Loading Capacities of Ordinary Bolts per. When considering factors (or margins) of safety for bolted joints, it must be realized that part of the load on the joint (the preload and resulting clamping forces) should NOT be scaled by the applied loads to account for the factors of safety, they are fixed. BS: 449: Part 2, GD&T Training Geometric Dimensioning Tolerancing. This section outlines how to account for the thermal loads. The method is the easiest to apply and has been 'verified' since it was based on finite element calculations. They are here to give some perspective to what goes into the nut factor. In these cases, any analysis should be done using a range of nut factors to bound the results. For ductile steels, the Morrow line predicts less sensitivity to mean stress. NASA [11] allows using either pre-computed nut factors or computing the preload (without considering the uncertainties here but which must be accounted for later) as, where Ro is the effective radius of the thread forces (approximately half the basic pitch diameter of external threads), α is the thread lead angle, μt is the coefficient of friction between the threads, β is the thread half angle, μb is the coefficient of friction between the nut and the bearing surface, and Re is defined as, where Ro is the outer radius of the torqued element (nut of head) and Ri is the inner radius of the torqued element.