bolt spacing rule of thumb

A natural pressure arch is formed in the rock at a certain distance behind the tunnel wall. Rule: When drilling a hole into concrete, brick or block base material- the hole must be drilled 1/2" deeper than the concrete anchor will penetrate. The working pressure for a B16.5 flange at ambient temperature is approximately 2.4 times the flange Class. Hardness is in excessive Rb90 need to be reviewed on an individual basis. A 10% reduction in friction can create a 25% increase in tension. The bolt length should be at least 1 m beyond the failure zone. Stemming . When vibration or sudden impact are part of the load conditions, the spacing should be increased. Proof strength is about 7-10% lower than yield strength. if the screw is ¼” diameter, the thread engagement needs to be a minimum of ¼”). This formula determines fastener spacing along a straight edge. Formula 1 below can be used to calculate fastener spacing for all our gaskets, with the special considerations shown for certain types of gaskets. Introduction Rules of thumb have a proud history in engineering. His current research interests are on understanding of rockburst and theories and practise of dynamic rock support. 40 to 50 hole diameters; 5. Bolts function like springs and need to be stretched to produce clamp force in the joint. It is not a substitute for actual planning and design. Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch. Structural Steel Rules of Thumb by Avery Morris Structural steel has been an integral part of the building industry since the development of the Bessemer process in the mid-1800s and its popularity as a construction material continues to be strong. Rockbolts should be long enough to reach the natural pressure arch when the failure zone is small. BLAST DESIGN RULES OF THUMB (Given: Hole depth, Rock type, and Distance to structure) HOLE DIAMETER (d) = hole depth (H) divided by 5 to 10. d(in) = H(ft) / 5 to H(ft) / 10 (Typically H/7) BURDEN (B) = 2 to 3 times the diameter. A rule of thumb is useful only in making … RIVET SPACING.—Rivet spacing (pitch) depends upon several factors, principally the thickness of the sheet, the diameter of the rivets, and the manner in which the sheet will be stressed. Changes, which appear to be small (adding wax to the bolt), can have significant effect. If the anchor is being placed at minimum embedment requirements, the … A minimum drive to fail ratio of 1/3 is typically required. The minimum recommended thread engagement of a bolt threaded into a nut member that is at least as strong as the bolt is one bolt diameter (i.e. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. © 2017 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. I have two, one on each side of keel. Because of these variables, and other not mentioned, it is not recommended that installation torque for clamp load critical joints be determined by torque tables based on an assumed nut factor K. The actual clamp load can easily be 50% more or less than the estimate on which these table are based. In fact, the bolt diameter is a little smaller and the nut diameter a little larger. Bench Height . This article introduces the principles of underground rockbolting design. I would like to know if there is a general rule of thumb for thru hull spacing. In fact, there was a time ... • Spacing of frames in industrial buildings (portal frames or trusses) without cranes: Span of frame (m) ... plus 1% for Grade 8.8 bolts and 0,5% for Grade 4.8 bolts. By continuing you agree to the use of cookies. He is the European Vice-President of the International Society for Rock Mechanics (ISRM) for the term of office 2015–2019. Corners require tighter spacing because of the increased stress placed on the cover at those points. Using a larger diameter bolt than needed will tend to have greater variation in initial clamp load and will lose a greater percentage of that clampload. A rule of thumb is to set the bolt spacing equal to 3–4 times the mean joint spacing in the case of a mean joint spacing in the range of 0.3–1 m, i.e. Fastening is a process and the best fastening process is the one with the least amount of variation in the fastener, assembly components and installation methods. Copyright © 2021 Elsevier B.V. or its licensors or contributors. between the bolts is 76.2 kips, and as is common in typical con-nections, it does not govern. You are here: Home / Uncategorized / ledger board bolt spacing. Another rule of thumb to consider for bolt spacing is that the yield strength of the material remaining between each bolt should be at least 30% (more is better, I never go below 50%) greater than the yield of the bolt. Sub-drill . 0.7 to 1.3 burden. The D-Bolt is as strong as a fully encapsulated rebar bolt but its deformation capacity is significantly higher than that of the rebar bolt. Most of the applied torque is NOT used  to general tension in the joint; it is generally consumed as follows: Friction plays a significant role in the torque/tension relationship. size greater than 140 mm (5½”) 1.2 to 1.5 burden; Hole size smaller than 140 mm (5½”) 1.5 to 1.8 burden; 3. Forming threads in materials ranging in hardness from Rb75 to Rb90 is not a problem. This would reduce the amount of clamp load generated for a given installation torque. InterNACHI's ledger fastener spacing formula provides inspectors with a rule-of-thumb: On-center spacing of ledger fasteners in inches = 100 ÷ joist length in feet. But neither the external threads of the bolt nor the internal threads of the nut are exactly .500 in diameter. For example, the working pressure for a Class 400 flange at 100 F is approximately 2.4 x 400 = 960 psi. Li received his BSc degree in 1981 and MSc degree in 1984, both in geological engineering, in Central South Institute of Mining and Metallurgy (at present Central South University), and his PhD in mining rock mechanics at Lulea University of Technology (LUT), Sweden, in 1993. energy-absorbing, in high in situ rock conditions. Using the ratio Pmax/Pmin = 3, bolt spacing is reduced by less than 7% for Pmax to Pmin ratio of 6. When there is adequate length of engagement, start with a hole size that provide 65% thread engagement. Peer review under responsibility of Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. A frequently used rule of thumb is that the foundation should be about five times the weight of the pump/motor assembly and approximately 6″ longer and wider than the baseplate. How far apart should they be? Spacing . It is important to note, however, that the depth of a member is influenced not only by the span but by such variables as spacing, loads, support conditions, deflections, and clearance require- The RPM’s of the installation tool usually affects the torque/ tension relationship, though to varying degree depending on the mating materials and finishes. B(ft) = 2 X d(in) to 3 X d(in) (Typically 2.5 X d) SPACING (S) = 1 to 2 times the burden. Dr. Li has practical expertise in ground support in difficult rock conditions (for instance, rock squeezing and rockburst), stability analysis of underground caverns and in situ measurements and interpretation. For example, all else being equal, a flange head screw would generate less a clamp load than a hex cap screw because the under head friction acts on a larger diameter. A simple rule-of-thumb that was pointed-out to me years ago concerns the Class rating of flanges. Either the nut or bolt can be rotated as long as the bearing surface is designed for that purpose (some form of washer face). Dr. Charlie C. Li is professor of rock mechanics for civil and mining engineering at the Norwegian University of Science and Technology (NTNU) in Norway. Engagement in weaker nut members must be greater in proportion to the relative shear strength of the bolt and nut member. For example, a bolt and nut may be described as being ½” diameter. He is a member of the Norwegian Academy of Technological Sciences (NTVA). Nominal diameter is a more of a label than a size. The number of bolts required and thus their spacing will be determined by their tensile strength. ing rules of thumb to be useful in estimating the approximate depth of a structural member as well as reviewing the reasonableness of a design. The D-Bolt is particularly powerful in combating stress-induced rockburst and squeezing. Length of engagement is typically the same as guidelines in “Joint design.”  Do not include lead threads in “full thread engagement.”. In the case of a vast failure zone, tightly spaced short rockbolts are installed to establish an artificial pressure arch within the failure zone and long cables are anchored on the natural pressure arch. Lower grade bolts are softer and more ductile while higher grade bolts have higher strength and higher hardness. greater than the nominal bolt diameter, rather than using a bolt hole diameter ⅛ in. InterNACHI's ledger fastener spacing formula provides inspectors with this rule of thumb: On-center spacing of ledger fasteners in inches = 100 ÷ joist length in feet. 1. on page Inspecting a Deck, Illustrated - InterNACHI is this “rule of thumb”. The rule of thumb does not determine the minimum number of bolts (although you could acquire that number using multiplication). The traditional principle of selecting strong rockbolts is valid only in conditions of low in situ stresses in the rock mass. Thread-cutting fasteners typically provide lower driving torque than thread forming fasteners. As a rule of thumb, the expansion anchor industry has established a minimum standard of ten (10) anchor diameters for spacing between anchors and five (5) anchor diameters from an unsupported edge. The ledger bolt is not installed perpendicular to the ledger board. Actual correction factors for other values of P max and P min are shown in table A. Pmax / Pmin Correction He carried out thorough studies of rock behaviour under compression in laboratory. Rivet spacing should never be less than three times the rivet diameter. Various test methods can be employed to ensure more accurate results. Based on the models, Li identified the shortcomings of the conventional rockbolts and pointed out that rockbolts, as well as other support elements, must be not only strong and but also deformable, i.e. In addition to the factor of safety, the maximum allowable displacement in the tunnel and the ultimate displacement capacity of rockbolts must be also taken into account in the design. The bolt hole diameter (assuming standard holes) used in the calculation of bolt hole spacing can be taken as 1⁄16 in. Therefore, the strength of the connection is: (2 bolts)(52.2 kips/bolt) + (2 bolts)(29.4 kips/bolt) = 163 kips The predicted strength, 163 kips, is higher than the 147 kips I would like to add another intake to serve a live well pump on my boat. Finally, rockbolts should be compatible with other support elements in the same support system in terms of displacement and energy absorption capacities. plates do not govern. The bolt has been used worldwide in many deep mines and also in hydropower projects, for instance in Sweden, Canada, USA, Chile, Australia and South Africa, to combat instability problems of rockburst. 25 to 35 hole diameters; 2. He invented a new type of energy-absorbing rockbolt, called D-Bolt in 2006. In stock and ready to ship. • A325 bolts require a washer under the element (head or nut) being turned to tighten the bolt (shown under the nut, above right) • A490 bolts require a washer under both the head and nut (AISC& NISD2000) Washers 7 • Grip is the distance frombehind the bolt … 4.3 Installation of High-Strength Bolts, 52 4.4 Relaxation, 61 4.5 Reuse of High-Strength Bolts, 62 4.6 Galvanized Bolts and Nuts, 63 4.7 Use of Washers, 65 4.8 Corrosion and Embrittlement, 66 4.9 Effect of Nut Strength, 69 4.10 Basis for Design Recommendations, 70 4.10.1 Bolts Subjected to Tension, 70 4.10.2 Bolts Subjected to Shear, 71 “On-center spacing of ledger fasteners in inches = 100 ÷ joist length in feet.” This implies to me that for a deck that is 15’ x 15’ the formula would read 100/15=6.67 so for a 15’ ledger you’d need 15x12/6.67=27 ledger fasteners. The anchor bolts are usually of the sleeve type— or the “J” type —shown in Fig. Don’t assume that a bigger bolt is always better and more reliable. When there is a choice, it generally suggested that the nut is turned as it eliminates the possibility of the bolt rubbing against the edge of the hole during tightening. The most common range of target clamp load for hard joints is 70% to 80% of the fastener’s proof strength (a tensile load which produces no permanent elongation). Choose from our selection of thumb bolts, including knurled-head thumb screws, spade-head thumb screws, and more. While the coefficient of friction between the threads and under the head have the greatest influence of the torque-tension relationship, it is less widely understood that fastener geometry plays a significant role. After a thorough study of the performances of rockbolts, he proposed analytical models for the rockbolts currently used in rock engineering practise, which have been acknowledged in the circle of rock mechanics. Below is 7 rules of thumb for open bit blast pattern. Different types of rockbolting used in engineering practise are also presented. Burden. A deck with substantially fewer ledger fasteners than that recommended by InterNACHI's formula may be unsafe. Preferred failure mode is screw or bolt Fracture rather than thread strip. Preferred failure mode is screw or bolt Fracture rather than thread strip. He has been the professor of rock mechanics at NTNU since 2004, in charge of the teaching and research program in the subject of rock mechanics as well as the rock mechanics laboratory. Bolts function like springs and need to be stretched to produce clamp force in the joint. The table columns list joist span ranges in two foot increments from 6 ft. to 18 ft.; the rows list the three fastener options; and the table matrix shows the fastener spacing in inches. larger as is required in the calculation of net area for steel tension elements (see Chapter 6). I don't want to be too close to the other ones already in pace. We use cookies to help provide and enhance our service and tailor content and ads. He made numerous field observations of rock failure and responses of rock support elements in mines and other types of underground excavations. Bolts 8–14 Bearing Stress of Wood under Bolts 8–14 Loads at an Angle to the Grain 8–15 Steel Side Plates 8–15 Bolt Quality 8–15 Effect of Member Thickness 8–16 Two Member, Multiple Member Joints 8–16 Spacing, Edge, and End Distance 8–16 Effect of Bolt Holes 8–16 Pre-1991 Allowable Loads 8–17 Post-1991 Yield Model 8–17 A deck with substantially fewer ledger fasteners than that recommended by InterNACHI's formula may be unsafe. The items discussed include underground loading conditions, natural pressure zone around an underground opening, design methodologies, selection of rockbolt types, determination of bolt length and spacing, factor of safety, and compatibility between support elements. In this case, the rockbolts are usually less than 3 m long in mine drifts, but can be up to 7 m in large-scale rock caverns. Rules of Thumb is intended to provide general guidelines for estimations of property, building space, and other needs prerequisite to actual planning. Production and hosting by Elsevier B.V. Journal of Rock Mechanics and Geotechnical Engineering, https://doi.org/10.1016/j.jrmge.2017.04.002. Bolted joints are often tightened to 75% to 80% of bolt proof load. Design criteria should be primarily focused on joint strength requirements and maximizing the drive to fail ratio. Rules of Thumb for Fastening and Joint Design. By inspection, the limits states for the 3∕8-in. (4) s = (3 − 4) e where e represents the mean joint spacing. The rule of thumb produces a spacing between ledger fasteners that, if exceeded, may be unsafe. Energy-absorbing rockbolts are preferred in the case of high in situ stresses. But it is easier to specify the 4. Rules of thumb for steel structures 1. After that, he was employed as a research associate and then associate professor at LUT until 2000. Explanation: The extra depth of the hole will ensure that the anchor does not bottom out and will allow space for any dust that may be created in the drilling process. Prof. Li's research interests are in rock failure, stability analysis of underground spaces, ground support and application of rock mechanic principles for underground space design. For most gaskets, Pmax is normally greater than twice Pmin. The minimum recommended thread engagement of a bolt threaded into a nut member that is at least as strong as the bolt is one bolt diameter (i.e. The only rule I would state is that the thread should not break through. He worked then in the Kristineberg mine of Boliden Mineral Ltd., Sweden, as a mining engineer for 4 years.

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