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Extended Hollo‐Bolts (EHBs) are blind bolts that have an extended bolt shank ending in an anchor nut. When used with concrete‐filled tubes, the extension and the anchor in the concrete serve to enhance significantly the performance of both connection components: bolts in tension and tube face in bending. The enhancements are a result of confining the concrete, preventing local buckling of the steel tube and allowing the blind bolt to achieve a tensile strength equal to that of standard bolt+nut fasteners. Overall, the use of the EHB results in a moment‐resisting bolted connection to hollow sections which can achieve rigid behaviour under certain configurations. This paper summarizes research work done to date on such connections at the University of Nottingham. This includes experimental, numerical and analytical modelling. The aim of the work is to provide a fundamental understanding of the behaviour of anchored blind bolt connections to concrete‐filled columns, leading to the specification of appropriate design rules that allow the use of such bolted moment‐resisting connections in practice. The work has proposed analytical models for: connection stiffness, column face‐bending strength considering both single and group behaviour of bolt rows, anchored bolts in tension and anchored bolts under combined tension and shear. [ABSTRACT FROM AUTHOR]

Wind turbine towers and their flange connections are highly fatigue loaded structures. Previous investigations have shown that initial parallel gaps between L‐flange connections, which are resulting from their respective flatness of the contact surfaces, can increase fatigue loads of the connecting fasteners significantly. Flange flatness and/or gap sizes in between flanges must comply with limitations given in relevant standards and therefore must be measured after the manufacturing process and/or during installation. More than 1900 flatness measurements of several offshore wind projects were collected and used to determine initial gaps between flanges analytically. A statistical evaluation allows to determine the distribution of expected gap sizes. The increase of gap height with increasing gap length can be described with linear correlations. Furthermore, the distributions of gap heights are approximated with log‐normal distributions. Parameters for generic log‐normal distributions are derived considering all performed mating simulations. Following the described methodology, gaps can be determined from any large number of flatness measurements. It is proposed to consider the results for flange design. [ABSTRACT FROM AUTHOR]

Increasing loads on the connections of tubular towers that support wind turbines are making the traditional bolted L‐flange more challenging to design, while the large mass of components and tools make installation challenging from a safety perspective. The C1 Wedge Connection is a symmetrical connection between tubular sections. The connection consists of a cylindrical lower flange and a fork‐shaped upper flange that slides over the lower flange. Both flanges have radial elongated holes distributed along the perimeter allowing the C1 fasteners to pull the two flanges together. The fastener assembly of the C1 Wedge Connection uses a small, horizontally placed bolt to pull two wedges together. The wedges transform and magnify the horizontal bolt force into a larger preload between the flanges by pulling them together. The orientation of the bolt in the fastener prevents significant load fluctuations under external loading. As a result, unlike a bolted L‐flange, the C1 Wedge Connection is less susceptible to preload loss, thereby eliminating the need for regular maintenance and inspection. The scalability of the C1 Wedge Connection makes it suitable for larger loads. These larger loads are expected with increasing size of wind turbines and when connections are used in more demanding locations such as hurricane and seismic conditions or where connections are subjected to high dynamic loads caused by extreme wave conditions or on floating foundations. [ABSTRACT FROM AUTHOR]

Many mechanical joints in steel structures use conventional bolts. Nevertheless, this proven joining technology has some significant disadvantages. These basically include the high levels of scatter during application of the assembly preload using the torque‐controlled tightening process, the risk of loosening during cyclic loads due to transverse displacement of the components and the low fatigue resistance under axial loading. Lockbolt technology was invented as long ago as the 1930s and mainly used for the aviation and space industry because of its evident advantages. This joining technology has been constantly further developed in response to the most diverse demands from sectors such as aviation, commercial vehicles, rail vehicles, agricultural machinery, defence technology and steel structures. The application of lockbolt technology, which is primarily used in mechanical engineering, was in most cases based on individual studies, since no consistent rules and guidelines were available for the design and execution of lockbolt connections in steel structures. Within the scope of several public research projects funded by the AiF (German Federation of Industrial Research Associations) and conducted by the iGF (Industrial Collective Research) organization as well as through approval investigations, the Fraunhofer Institute for Large Structures in Production Engineering (IGP) has successively developed the necessary design rules according to the EN 1993 standard (Eurocode 3) for use in structural connections. These design rules will be presented within the context of this article in order to make the benefits of this joining technology available to other users. In addition, insights into the use of technical approvals will be presented together with some current applications. [ABSTRACT FROM AUTHOR]