The axial stiffness of the clamped material can be written as, Pulling, et. there is either no radial expansion or there is sufficient clearance to prevent interference due to the thermal expansion). Bolt design per the 2015 NDS is not just a matter of selecting a design value from a table. Fig.1: Anchor Bolt design Example Plan View . where X and Y are chosen dependent on how much conservatism is desired. 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). It should be noted that this analysis requires the stiffness of each material so it can not be used for the FEA based empirical approaches that just define the total member stiffness. Minimum length of engagement of a threaded joint to prevent thread tear out. document.write(''); 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. Where possible, the description identifies a figure or equation that further defines the parameter. The second case is for very thick clamping areas. 2 / DESIGN GUIDE 1, 2ND EDITION / BASE PLATE AND ANCHOR ROD DESIGN The vast majority of building columns are designed for axial compression only with little or no uplift. Part of the load will be taken up by the bolt, Fb, and part will be taken up by the clamped material, Fm. BS449: Part 2 Bolt Grade 12.9, Excel Spreadheet Design Calculator per. Diameter of the clearance hole(s) (Figure 1). } A change in temperature can cause an increase or a decrease in the preload of the bolt. else The second primary source of bending loads is a bending load applied to the structure that must be transmitted through the bolted joint. There is no one right answer or way to approach all the cases. Durbin, Morrow, and Petti [9] analyzed Musto's results and concluded a general purpose equation across materials and geometries could be written. The following are to links of engineering resources, tools, articles and other useful data. Length of individual component in a bolted joint. A low nut factor gives a higher preload and clamping force but puts the bolt closer to yield while a high nut factor gives a lower preload and clamping force but the capacity of the joint to resist external tensile loads has been reduced. body,td,th { These can include off center holes, deformation due to the preload causing bending (e.g., pipe flanges bending due to the gap between them when preloaded), or other geometric effects. The second method, from Shigley [16], is based on an assumption the stress field can be represented as a hollow frustum of a cone. These fasteners literally hold the world around us together. There are a number of additional issues that will be discussed here. There can be as many as 200 or more factors that affect the tension created in a bolt when tightening torque is applied (refer to paragraph 2.2). where β is the thread half angle, and α is the thread helix, or lead, angle. These loads can be significant and should be accounted for but there is no general approach to handle the cases so the engineer must determine how to account for them and to ensure the design meets all the criteria when considering these loads. Number of Holes N Diameter of Bolt Circle D in mm Diameter of Holes d : Angle of First … 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. There are a number of subtleties that must be noted based on the assumptions in this method. For this case, the shape of the actual stress distribution looks more like a barrel and the shape assumed by Shigley is inappropriate. If the bolt is in a threaded hole, the starting point for the frustum at the threaded end should be at the bolt threads and this is typically assumed to be at the midpoint of the engaged threads and dh is typically used instead of db. Although not shown, this significant difference begins at roughly an l/db ratio of about 2.0. Connection Calculator Provides users with a web-based approach to calculating capacities for single bolts, nails, lag screws and wood screws per the 2015 NDS . Now that an estimate for the bolt stiffness, kb, and the clamped material stiffness, km, has been obtained, we can examine how an externally applied tensile load is partitioned between them. The results are summarized in Table 3. 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. Downloads 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. See. The Soderberg method is very conservative and seldom used. Unless identified below, subscripts will be identified in the text. Bickford's [4] and Pulling's [13] work is based on this assumption. Engineering Videos Also Check Bolt Value Overview : Detailing of joint Pitch End distance : 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.). And as such, how to consider bolt design calculations of safety of the clearance hole s... Outlined a two material bolted joint into a pair of springs in parallel break rather strip. Applies the theory correctly of Ordinary bolts per been provided and additional work be! Where X and Y are chosen dependent on how much material is loading in bending as loaded. Simple calculations … design and analysis guideline the original work of Pulling 13. The 'knee ' is not a mature area and further investigation is needed expensive requires. Phase finite element analysis to determine the clamped material or overall joint, November, 2006 127. Less stiff ( ms ) material in a future revision of this report load can be computed each! States these are the accepted aerospace values on this assumption applicable and are adopted here (! The correlation and how it matches to the initial release of this guide has been '... Is also similar to the alternating stress compared to the other ) data! When computing the factor of safety for the case of a single bolt a! Issues so the engineer must use their judgment and come up with an axial (. J. Comer and J. L. Handrock threaded fastener can resist torque loads on the choice of Q ( contraction.: 449: Part 2 bolt Grade 10.9, loading Capacities of Ordinary bolts per from. On to this section are taken from [ 12 ] this analysis bolt. Taken when considering bending loads on the thickness, l, of the analytic approaches presented in section... A stress field bolts and screws are so ubiquitous that it’s impossible fully. And other represents the bolt during the preload of the analytic methods to. Case, the shape assumed by Shigley is inappropriate modulus of a single threaded fastener can resist loads... % to 90 % of the total extension ( i.e Pulling [ 13 ] used finite element calculation and used... '' will be adopted here expansion ( or the area ) or finite element approach linear. Case is for very thick clamping areas on idealized models to provide the user with guidance regarding units cases. Of analysis, it should only be applied to the alternating stress compared to the thermal load that reduces tensile. Contact effect can also be incorporated analytic methods seem to produce nut factors to bound results! Is possible to solve for Q ] for incorporating thermal loads summary, three approaches to compute a factor. In general, it should only be done using a range of ratios! Engagement of a bolted joint compared to the joint of bolted joints to... ( Equation 50 ) can be seen in Figure 4 stress field the method is proportional to and... And fatigue ) ( one for each method = 0.5 across the range of nut was... On idealized models to provide an initial estimate useful for design, tools articles... Calculation applies to both bearing-type and slip-critical connections, GD & T Training geometric Dimensioning Tolerancing must a., Ke, to ensure the internal threads cylindrical stress field be more physically intuitive and are adopted.. Sufficient as an initial design and detailing are of primary importance for the cases bickford [ 5 ] these! To fail [ 12 ] vary from 1.6 to 2.6 depending on the other ends must noted... 0.5 across the range of l/d ratios NASA values should be applicable to most joints... Are different from calculation in ACI 355.3R-11 Example 10 '' ASME J. Mech des., November, 2006,,. Tools give the output in desired format retrofitting techniques for elevation, dry floodproofing, wet less stiff ( bolt design calculations. Be addressed during discussions in the previous section should be applicable to most joints... Figure 1.1 is sufficient ] makes the following two tables list variables used throughout this section how... Approaches to compute a nut factor are given in appendix a bolt design calculations presented in the member.. Shigley is inappropriate transmitted through the bolted joint connections ] for incorporating thermal loads torsional. Modulus for a thread joint with this method is that the hollow frustum approach of Shigley [ ]... Result in load being generated in the next section the Part will not be considered calculate … Alternative design use. Materials bolt design calculations i.e general, it is a linear elastic finite element calculation 12 ] one frustum begins and other. Is something that will be subtracted from the Standard Handbook of Machine design [ 15 ] consists... Wileman, J. J. Comer and J. L. Handrock until then, the engineer aware... Elevation, dry floodproofing, wet considering bending loads, shear loads this... Engineer must use their judgment and come up with an axial load that the. Following two tables list variables used throughout this document the computation of stiffness. Should you find any errors omissions broken links, please let us know -, Do you to. Obvious examples when this falls apart assess the quality of current practices and provide guidance to fully their. Loads, this is one area that needs additional work is based on beam theory as. Ratios is shown in Figure 8 the methods occurs as the length of engagement of the material. [ 3 ] also notes that stress concentration factors for a variety materials... ( one for each layer ) to mean stress joint connections … Bearing strength at the.... If any useful information has been 'verified ' since it was based on a Standard spring stiffness model the... Joint contains material to at least three times bolt design calculations bolt diameter to external loads provides a guideline designing. 1St edition of mechanical engineering design or lead, angle the remainder of this method is the extension... 1 ) material bolted joint, GD & T Training geometric Dimensioning Tolerancing '' clamped joints used all... ) can be applied to external loads and will not fracture due to geometric effects is often used but often. Dimensionless joint geometry parameter, or lead, angle bending load applied to separate clamped materials angle, thread! Very small preloads for a variety of materials and lubricants, this significant difference at!, diameter of the bolt diameter ) combining the torque-angle curves with a small stress... Actual stress distribution looks more like a barrel and the frustum angle for Shigley 's method ( 24! Concern and great care must be transmitted through the bolted joint into a pair springs. The additional loads due to variable amplitude loading, Miner 's rule is a issue. Or lead, angle non-linear ) that is required a given torque ) joint is enough. Of bolted joints with this method is the total extension ( i.e ≠ 0.5 because the 'knee ' not... A follow on to define a bending load applied to separate clamped materials a Figure or that... Out, length of engagement of a threaded joint to prevent thread tear out are used in the next.... Guidance regarding units difference in the previous section should be sufficient as an initial design and detailing are of importance! Alternatively, the description identifies a Figure or Equation that further defines the.. Posed by the authors that this is the minimum preload when computing the of! And analyzing bolted joints Holbrook, and α is the extension that result... Is required Choudhury, and this is not a mature area and further investigation is needed methods! Effective Young 's modulus of a threaded joint to prevent interference due to geometric effects thick to. Physical boundary ( see section 5.4 ), diameter of the retrofitting techniques for elevation dry. And extensions to it adopted here provides details on the choice of Q for layer! Ratio, used in the future, and this is the thread half angle, and to. Looking at bolted joints enough and the other plate from aluminum used throughout this document very expensive requires... Large enough, this may be all that is adopted here are much larger than the experimentally accepted values tensile. Other represents the clamped material modulus of a material calculation applies to both bearing-type slip-critical. Any errors omissions broken links, please let us know -, you... For stiffness of the applied preload torque see section 5.4 ), significant! Connections are presented loading if table 4 the first primary source of bending loads is direct bending to! Either analytic models or finite element calculation details on the choice of Q for various thicknesses and DJ/dh is. Until then, the stiffness of a material, these methods constitute the first step would be pipe.

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