Bolt Material Types and Grades 1- Bolts made of carbon steel and alloy steel: 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 10.9 Nuts made of carbon steel and alloy

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1 Bolt Material Types and Grades 1- Bolts made of carbon steel and alloy steel: 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 10.9 Nuts made of carbon steel and alloy steel: 4, 5, 6, 8, 10, Bolts made of stainless steel: steel grade A1, A2, A3, A4, A5 Material Class 50, 70, 80 (tensile strength of 500, 700 and 800 MPa) Nuts made of stainless steel: 50, 70, Washers (if appropriate) according to hardness class HV 100 or HV 200

2 Standardised connections In a typical braced multi-storey frame, the connections may account for less than 5% of the frame weight, and 30% or more of the total cost. Efficient connections will therefore have the lowest detailing, fabrication and erection labour content; they will not necessarily be the lightest. Use of standard connections, where the fittings, bolts, welds and geometry are fully defined, offers the following benefits: A reduction in the number of connection types which: - leads to a better understanding of their cost and performance by all sides of the industry. - encourages the development of design aids and computer software. The use of standard components for fittings which: - improves availability - leads to a reduction in material costs - reduces buying, storage, and handling time. The use of one property class and diameter of fully threaded bolt in a limited range of lengths which: - saves time changing drills or punches in the workshop - leads to faster erection and fewer errors on site - leads to economy of bulk purchase. The use of small, single pass fillet welds which: - avoids the need for any edge preparation - reduces the amount of testing required. In practice, steel structures can be complex and there will be times when the standard connections presented here are not suitable. However, even in these cases, it will still be possible to adopt some of the general principles of standardisation, such as limiting the range of fittings, sections and bolt sizes.

3 A summary of the recommended components adopted for this publication is shown in Table 2.1. Classification of Connections 1- Based on connecting elements - Bolted Connections - Welded Connections 2- Based on type of imposed action - Simple connections - Eccentric connections 3- Based on load transfer - Shear connections - Tension connections - Shear tension connections - Shear torsion connections 4- Based on initial load in the bolts - Non-loaded bolts (Bearing type connections) - Pre-loaded bolts (slip resistance connection)

4 Categories of bolted connections 1- Shear connections Bolted connections loaded in shear should be designed as one of the following: Category A: Bearing type In this category, bolts from class 4.6 up to and including class 10.9 should be used. No preloading and special provisions for contact surfaces are required. The design ultimate shear load should not exceed the design shear resistance nor the design bearing resistance. Category B: Slip-resistant at serviceability limit state In this category, preloaded bolts should be used. Slip should not occur at the serviceability limit state. The design serviceability shear load should not exceed the design slip resistance. The design ultimate shear load should not exceed the design shear resistance nor the design bearing resistance. Category C: Slip-resistant at ultimate limit state In this category, preloaded bolts should be used. Slip should not occur at the ultimate limit state. The design ultimate shear load should not exceed the design slip resistance nor the design bearing resistance. In addition for a connection in tension, the design plastic resistance of the net cross-section at bolt holes Nnet,Rd should be checked, at the ultimate limit state. 2- Tension connections Bolted connection loaded in tension should be designed as one of the following: Category D: non-preloaded In this category, bolts from class 4.6 up to and including class 10.9 should be used. No preloading is required. This category should not be used where the connections are frequently subjected to variations of tensile loading. However, they may be used in connections designed to resist normal wind loads. Category E: preloaded In this category, preloaded 8.8 and 10.9 bolts with controlled tightening can be used.

5 The design checks for these connections are summarized in Table 3.2.

6 Positioning of holes for bolts and rivets Minimum and maximum spacing and end and edge distances for bolts and rivets are given in Table 3.3. Figure 3.1: Symbols for end and edge distances and spacing of fasteners Bolt Holes Bolt holes are made larger than the bolt diameter to facilitate erection and to allow for inaccuracies. The clearance = 2 mm for bolts 24 mm diameter = 3 mm for bolts > 24 mm diameter. Bolt holes reduce the gross cross-sectional area of a plate to the net cross-sectional area. The net value is used for calculations where the structural element, or parts of an element, are in tension. The gross cross-section of a member is used in compression because at yield the bolt hole deforms and the shank of the bolt resists part of the load in bearing.

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8 Shear Bolted Joint A shear joint can fail in the following four mode of failures: Failure Mode Prevention measure 1 Shear on the bolt shank provide sufficient bolts of suitable diameter 2 Bearing on the member or bolt. 3 Tension in the member design tension members for the effective area 4 Block shear at the end of the member Provide sufficient end distance

9 The basic provisions for bolted shear joints are the following: 1. Effective area resisting shear A When the shear plane occurs in the threaded portion of the bolt, A = As where As is the nominal tensile stress area of the bolt. When the shear plane occurs in the non-threaded portion, the effective resisting area is A = bolt shank area based on the nominal diameter For a more conservative design, the tensile stress area As may be used throughout. 2. Shear resistance per shear plane f v,rd = α vf ub A γ M2 where f ub is the ultimate tensile strength for bolts given in Table 3.1 in BS EN When the shear plane passes through the threaded portion of the bolt (A is the tensile stress area of the bolt As): 1- For Classes 4.6, 5.6 and 8.8, αv = For Classes 4.8, 5.8, 6.8 and 10.9, αv = 0.5 where the shear plane passes through the unthreaded portion of the bolt (A is the gross cross section of the bolt): αv = 0.6. Also, - when the shear plane passed through the threaded portion of the bolt, A is the tensile stress area of the bolt. - when the shear plane passed through the unthreaded portion of the bolt, A is the gross cross-sectional area of the bolt.

10 3. Bearing resistance on the member or bolt f b,rd = k 1α b f u dt γ M2 d is the bolt diameter t is the thickness γm2 = 1.25 fu is the ultimate tensile strength Where α b is the smallest of ( α d, f ub fu or 1. 0 ; ) A- in the direction of load transfer, α b = min (α d, f ub f u, 1.0) For end bolts, α d = e 1 3d 0 For inner bolts, α d = P 1 3d B- Perpendicular to the direction of load transfer, For edge bolts, k1 = min of (2.8 e 2 d or 2.5) For inner bolts, k1 = min of (1.4 p 2 d or 2.5) 4. Block Shear Resistance on the member or bolt Block shear failure should also be checked to prevent shear failure through a group of bolt holes at a free edge. The combined block shear capacity for both the shear and the tension edges or faces in a shear joint is given by:

11 For symmetric bolt group subject to concentric loading For eccentric loading V eff,1,rd = f ua nt γ M (f ya nv γ M0 ) V eff,2,rd = 0.5f ua nt γ M (f ya nv γ M0 ) Where, A nt is the net area subject to tension and A nv is the net area subject to shear