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. 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 if the screw is ¼” diameter, the thread engagement needs to be a minimum of ¼”). 25 to 35 hole diameters; 2. 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. Don’t assume that a bigger bolt is always better and more reliable. This article introduces the principles of underground rockbolting design. Changes, which appear to be small (adding wax to the bolt), can have significant effect. A deck with substantially fewer ledger fasteners than that recommended by InterNACHI's formula may be unsafe. 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. 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. 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. For example, a bolt and nut may be described as being ½” diameter. The number of bolts required and thus their spacing will be determined by their tensile strength. energy-absorbing, in high in situ rock conditions. This formula determines fastener spacing along a straight edge. 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. 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. He is a member of the Norwegian Academy of Technological Sciences (NTVA). Sub-drill . Preferred failure mode is screw or bolt Fracture rather than thread strip. Preferred failure mode is screw or bolt Fracture rather than thread strip. Proof strength is about 7-10% lower than yield strength. plates do not govern. 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. 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). How far apart should they be? 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. 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. 0.7 to 1.3 burden. For example, the working pressure for a Class 400 flange at 100 F is approximately 2.4 x 400 = 960 psi. A simple rule-of-thumb that was pointed-out to me years ago concerns the Class rating of flanges. A minimum drive to fail ratio of 1/3 is typically required. The bolt length should be at least 1 m beyond the failure zone. 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. 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. We use cookies to help provide and enhance our service and tailor content and ads. Formula 1 below can be used to calculate fastener spacing for all our gaskets, with the special considerations shown for certain types of gaskets. 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. Actual correction factors for other values of P max and P min are shown in table A. Pmax / Pmin Correction He invented a new type of energy-absorbing rockbolt, called D-Bolt in 2006. Different types of rockbolting used in engineering practise are also presented. I would like to add another intake to serve a live well pump on my boat. Stemming . In fact, the bolt diameter is a little smaller and the nut diameter a little larger. He worked then in the Kristineberg mine of Boliden Mineral Ltd., Sweden, as a mining engineer for 4 years. Rockbolts should be long enough to reach the natural pressure arch when the failure zone is small. The traditional principle of selecting strong rockbolts is valid only in conditions of low in situ stresses in the rock mass. 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- between the bolts is 76.2 kips, and as is common in typical con-nections, it does 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. 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. He carried out thorough studies of rock behaviour under compression in laboratory. The working pressure for a B16.5 flange at ambient temperature is approximately 2.4 times the flange Class. 1. By inspection, the limits states for the 3∕8-in. Production and hosting by Elsevier B.V. Journal of Rock Mechanics and Geotechnical Engineering, https://doi.org/10.1016/j.jrmge.2017.04.002. A deck with substantially fewer ledger fasteners than that recommended by InterNACHI's formula may be unsafe. Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch. 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. Rules of Thumb is intended to provide general guidelines for estimations of property, building space, and other needs prerequisite to actual planning. The RPM’s of the installation tool usually affects the torque/ tension relationship, though to varying degree depending on the mating materials and finishes. Rivet spacing should never be less than three times the rivet diameter. 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. Peer review under responsibility of Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. The ledger bolt is not installed perpendicular to the ledger board. larger as is required in the calculation of net area for steel tension elements (see Chapter 6). Rules of Thumb for Fastening and Joint Design. When tapping holes in the ends of shafts the two cross sections should be (at least) approximately equal Example an M6 has a core of approx 5 diameter then the minimum OD would be (5^2 + 6^2)^0.5 or 7.8mm diameter - at this point the bolt and shaft have the same tensile strength - if … greater than the nominal bolt diameter, rather than using a bolt hole diameter ⅛ in. 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. But neither the external threads of the bolt nor the internal threads of the nut are exactly .500 in diameter. 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. 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 The rule of thumb produces a spacing between ledger fasteners that, if exceeded, may be unsafe. 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.