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There are two obvious examples when this falls apart. nd is used to denote non-dimensional quantities. the surrounding joint contains material to at least three times the bolt diameter). color: #000000; If this is done, a hand calculation of the shear load on the bolts can done and that load added directly into the loads on the bolt (it is desirable to have the shear load taken by frictional capacity in which case the actual load the bolt would see is zero). This section outlines how to account for the thermal loads. As will be shown by comparing the different methods in a later section, the value of Q is variable and depends on the geometry of the joint. They implemented an iterative solve for Q and incorporated that into an updated spreadsheet based on the original work of Pulling [13]. As can be seen in Figure 8 the methods produce very similar results for "thin" clamped joints. 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. There are N equations of the type of Equation (32) (one for each layer). where dbmm is the minimum major diameter of the external threads, di is the maximum pitch diameter of the internal threads. If we have N layers of clamped materials, we have 2*N+2 unknowns (N+1 forces and N+1 extensions, the +1 is for the bolt). It consists of a bolt, two washers, two materials, and a nut. They assumed that the same material is loading in bending as was loaded axially. al. There is no one right answer or way to approach all the cases. Guidance is provided for general bolted joint design, computation of preload uncertainty and preload loss, and the calculation of the bolted joint factor of safety. how much material is being clamped) relative to the bolt diameter. BS449: Part 2 Bolt Grade 8.8, Loading Capacities of Ordinary Bolts per. Due to the complexity of this type of analysis, it should only be done by experienced analysts. Usually subscripted. Although not shown, this significant difference begins at roughly an l/db ratio of about 2.0. This data is shown in Figure 7. This can range from a relatively simple axisymmetric linear elastic finite element model to a fully nonlinear three dimensional finite element model incorporating geometric nonlinearities and frictional contact. Otherwise, the Shigley method is recommended. A preloaded joint must meet, as a minimum, the following three basic requirements: Bolt strength is checked at maximum external load and maximum preload, and joint separation is checked at maximum external load and minimum preload. He also notes that stress concentration factors for cut threads are much higher. Subscripts not specifically identified in these tables will be addressed during discussions in the appropriate text. Engineering Book Store One method recommended in this reference will be explicitly noted because it comes from an ASTM standard and is called Rainflow counting [2]. A clearance between the bolt and the clamped materials can be accounted for, however, the methodologies presented here assume a single clearance that applies to all the layers. Subscripts will be described in the text. A critical component of designing bolted joints is not only determining the number of bolts, the size of them, and the placement of them but also determining the appropriate preload for the bolt and the torque that must be applied to achieve the desired preload. The following are to links of engineering resources, tools, articles and other useful data. 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). Using it incorrectly can result in very large errors (due to the fact that Q varies dramatically depending on the joint and materials and any errors in it are at best squared, amplifying the error). The accuracy of this method is highly dependent on the choice of Q. It is planned for follow on work to extend the work of Morrow [9] to cases of more than two materials and perhaps to expand the range of geometries that it is applicable to. They are here to give some perspective to what goes into the nut factor. al. His equations are modified here to account for qi so that it can be compared to the work of Pulling [13]. the two "plates"). The first is a method based on an assumed cylindrical stress field. That assumption is valid throughout this section as well given that the expansion (or contraction) is only axial (i.e. The calculations within this live spreadsheet will facilitate the initial design and engineering of many types of bolted and riveted joints. This is the value Shigley used in the 1st edition of Mechanical Engineering Design. This gives 2*N+2 equations in 2*N+2 unknowns which is easily solvable. The method is the easiest to apply and has been 'verified' since it was based on finite element calculations. there is no rotation constraint posed by the material beyond that considered loaded). DFM DFA Training 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. ΔLconstrained is the extension that will result in load being generated in the joint. An unconstrained object will expand due to a change in temperature as, where ΔL is the change in length due to thermal effects, αL is the coefficient of thermal expansion, L is the length, and ΔT is the change in temperature. This report provides a guideline for designing and analyzing bolted joints. They concluded that there is not significant degradation of the joint until the edge or corner effect is within 1.5 bolt diameters of the hole. For example, in the design of bolted … The data was generated assuming a 5/8" diameter bolt, d, with a bolt head diameter of 15/16" (1.5 time the bolt diameter), dh. This was the original assumption made by Shigley in his first edition mechanical engineering design book [8] and is what is chosen by Bickford [4]. As can be seen by examining the data, there can be large ranges of potential nut factors and as such, it is recommended in the Standard Handbook of Machine Design [15] to only use nut factors when approximate preload is sufficient for the design. As can be seen, Q is squared (or raised to the 4th power for bending), and therefore any errors in Q are magnified. Several methods for the design and analysis of bolted joint connections are presented. Calculations must use exact lengths of both the unthreaded portion of the bolt and the remaining length of the unengaged threaded portion of the bolt … The nonlinearities that can be modeled include geometric non-linearities, frictional sliding contact, and material non-linearities (including plastic yielding) so a high degree of accuracy can be obtained if appropriately used. Figure 8 shows the results for an l/db ratio of 0.75 (this represents a "thin" clamped joint) and Figure 9 shows the results for an l/db ratio of 5.0 (this represents a "thick" clamped joint). Nonetheless, these methods constitute the first tool available to an engineer looking at bolted joints. Green, "Computation of Member Stiffness in Bolted Connections," ASME J. Mech Des., December, 1991, 113, pp. One spring represents the bolt and other represents the clamped material. Usually subscripted. [9] compared this equation to the one derived for the Q-factor method and noted the only unknown between the two equations is Q. An overview of the current methods used to analyze bolted joint connections is given. Concrete tension breakout A Nc = 1215 in 2, ... PIP STE05121 Anchor Bolt Design … steel in this case). Using it implies the need to have a very accurate solution due to small margins, designing into the non-linear regime, and/or other non-traditional design spaces. --> { The reasons for recommending the DMP method are 1) it matches very well with finite element analysis and Shigley's frustum approach for standard cases, 2) it doesn't have the subtleties and the unknown accuracy for differing materials with different thickness (but matches extremely well for identical thicknesses where Shigley is known to be accurate) and 3) it is the easiest to apply and gives the same results in cases where both are equally applicable. The third method is based on using finite element analysis of bolted joints and fitting the results with empirical equations. 45 degrees is often used but this often over estimates the clamping stiffness. In summary, three approaches to calculating joint stiffness have been presented. 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