Author: Han, Xiaozhou
Title: Development and behaviour of swift-constructed demountable blind bolt for structural hollow section connection
Advisors: Chan, Tak-ming (CEE)
Degree: Ph.D.
Year: 2024
Subject: Bolts and nuts
Columns, Iron and steel
Structural engineering
Hong Kong Polytechnic University -- Dissertations
Department: Department of Civil and Environmental Engineering
Pages: xxiii, 214 pages : color illustrations
Language: English
Abstract: The use of hollow section members in construction has lots of advantages. Nevertheless, owing to no access to the inside of the hollow section column to tighten the nut, it is challenging to adopt normal bolt when connecting the beams to the hollow section columns. As such, in the past decades, blind bolts were developed for structural hollow section connections, and various types of blind bolt products have been commercially available. Nevertheless, several existing blind bolts cannot be easily demounted without the need of machine cutting after installation. Moreover, even if a part of existing blind bolts can achieve the demountable function of structures by leaving specific components inside the tube during removal process, their installation and removal speed probably require further enhancement, or their mechanical performances may need to improve further for wider application. Therefore, it is worthy to develop a demountable blind bolt that has better mechanical performance, as well as can be installed and demounted easily and fast.
In this thesis, a new type of blind bolt that possesses satisfactory mechanical performance with easy and fast installation/demounting capabilities is proposed, named Swift-Constructed Demountable Blind Bolt (SCDBB). The investigation process of SCDBB in this thesis can be divided into three stages, comprising the development stage, the investigation of bolt behaviour stage, and the study of typical structural behaviour stage.
During the development stage of SCDBB, the components, intended working mechanism, and fabrication process are introduced. Geometric constraints of critical components are then derived based on the desired behaviour. To study the behaviour of SCDBBs under tensile loading and their behaviour during the installation process, 9 experimental tests were conducted. Two failure modes, namely, bolt shank fracture and buckling of the expansion nut blades, were revealed when subjected to maximum tensile loading. In addition, experimental comparison with existing blind bolt reveals that the improvement of mechanical performance of current products can be achieved by SCDBB. Subsequently, finite element (FE) models were developed and validated by comparing the numerical results with the experimental data. To further explore the impact of key design parameters on the behaviour of SCDBB under tensile loading and performance during installation, parametric studies consisting of 106 FE models were conducted for SCDBBs of three sizes with variations in four key design parameters. The findings indicate that the failure modes under maximum tensile loading and maximum installation force are sensitive to the length, thickness, and gap of the elastic expansion nut. The optimised ranges for each design parameter were identified to prevent undesirable blade buckling.
At the stage of bolt behaviour investigation, a comprehensive experimental study of the bolt behaviour of SCDBB at the component level was conducted, ranging from the investigations of material properties, preloading performance, and characteristics of installation process, to the evaluations of the tensile, shear, and slip-resistance behaviour of SCDBB. Through 186 tests, the tensile strength, hardness, preloading value, nut factor range, and installation force range of SCDBB were determined accordingly. In addition, it has been established that the SCDBB can consistently surpass the design values specified in relevant standards of normal high-strength bolts in terms of tension resistance, shear resistance, and slip resistance. This applies whether the SCDBB is classified as a bearing type or a slip-critical type. Based on the results, this chapter not only provides the recommendations for material testing of regular bolts, but also suggests that the current design equations for normal high-strength bolts can be safely applied to SCDBB. Moreover, this chapter also suggests prioritizing the SCDBB as a bearing-type bolt in design for economic viability.
With regard to the last stage, the study of its typical structural behaviour applied the SCDBB to the T-stub to hollow section column connection. A series of experimental and theoretical investigations for swift-constructed demountable blind (SCDB) bolted connections were carried out at this stage. In general, two types of major tests were conducted, comprising the bolt comparison test and the SCDB bolted connection test. Corresponding research purposes can be consequently revealed as two aspects, on the one hand, to compare the structural performance of SCDBB with other existing bolt products in connections under bolt failure mode; on the other hand, to study the structural behaviour of SCDB bolted connection with varies geometric parameters under different failure modes. Experimental programme, observations during experimental works, test results with relevant discussions, as well as the theoretical approaches, were explained and depicted successively. Test results reveal that compared with other blind bolts studied in this stage, SCDBB that combines high tensile resistance and stiffness can be regarded as a blind bolt product with more comprehensive and excellent performance. In addition, under the failure mode of column wall yielding with EEN buckling, owing to the uncertainty of the ultimate resistance of connection, design value of the tensile resistance of SCDBB connection should adopt the yield strength instead of the ultimate resistance of connection, for conservativeness and safety. While under the failure mode of bolt shank fracture, the design value of the tensile resistance of SCDBB connection can simply employ the sum of the relevant design values of bolt shanks. Based on the test results, corresponding modified analytical models and formulae with high prediction accuracy are suggested for the SCDB bolted connection.
Rights: All rights reserved
Access: open access

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