![]() These bolts are relatively insensitive to over tightening during preloading although site control is still important. The longer thread length is necessary to ensure that the induced strain is not localised. This system uses thick nuts and long thread lengths in the bolt assembly to obtain ductility predominantly by plastic elongation of the bolt. There are several different types available but the most common in the UK is the System HR (to BS EN 14399-3 ). This type of bolt is tightened to a defined pre-load to clamp the connecting plates together to ensure that the load transfer occurs through the development of friction between faying surfaces. These were previously referred to as High Strength Friction Grip bolts (HSFG). High strength structural assemblies for preloading These were previously referred to as “black bolts”. These bolts rely on the shear resistance of the bolt and the bearing resistance of the connected plates to establish the load path. These bolts are used for connections in Categories A and D where no preloading is to be applied. The reference standards for these bolts are EN 14399-1 (other parts of the standard cover various types of bolt) and BS EN ISO 4014 and BS EN ISO 4016. Fasteners may also be rivets or pins.Īll bolts, nuts and washers should comply with the reference standards listed in clause 1.2.4 of BS EN, within these standards are two main types of bolts, those that are used as ordinary bolts and those that are used as high strength bolts for pre-loading. The Eurocode refers to “fastener” and “fastener assembly” as a general term for bolt plus nut and (if relevant) washer. Corresponding characteristic values of yield strength and ultimate tensile strength are given in Table 3.1 of BS EN. ![]() Hence, a bolt designated as property class 8.8 will have a nominal tensile strength of 800N/mm 2 and a nominal yield strength of 640N/mm 2. Multiplying these numbers together gives 1/10 th of the nominal yield stress in N/mm 2. The second number is 10 times the ratio between lower yield stress (or stress at 0.2% non-proportional elongation) and nominal tensile strength. The first number is 1/100 th of the nominal tensile strength in N/mm 2. Bolted connections Bolt property classīolts are classed by BS EN ISO 898-1 according to their strength properties by two numbers. A properly detailed bolted splice connection is not normally obtrusive – more guidance on this issue is contained in Guidance Note 1.09. Occasionally clients may demand connections to be welded to achieve a uniform appearance though this would be unusual for highway or railway bridges. Site welding is nearly always technically feasible however, the additional expense required to set up welding and testing facilities on site coupled with the increased erection time usually make bolted connections more efficient except for very large projects. The modern fabrication facilities available in the UK mean that the majority of shop made connections are most economically achieved through welding. The chief criteria for whether to use a bolted or a welded connection is whether the connection is to be made in a factory or on site. This article generally follows traditional terminology. ![]() Traditionally, in bridges, reference has been made mainly to “connections” and “splices”, with much less use of the term “joints”. It should be noted that a joint may contain several individual connections the most obvious example of this is a beam splice with web and flange connections. For design purposes it is the assembly of all basic components required to represent the behaviour during transfer of the relevant internal forces and moments between connected members". For design purposes it is the assembly of the basic components required to represent the behaviour during the transfer of the relevant internal forces and moments at the connections".Ī joint is defined as "the zone where two or more members are interconnected. The definition of the term “connection” in BS EN is "the location at which two or more elements meet. Įurocode 3 makes a distinction between “connection” and “joint”. The key parts of Eurocode 3 for designing connections in bridges are:Īll references in this article refer to these documents, as implemented by their respective National Annexes. 3.4 Typical girder bolted splice connection. ![]()
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