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This paper introduces an innovative bolt-free preloaded inter-module connection for steel-framed modular buildings, referred to as the 'AJ' connection. It provides the vertical connection between columns by engaging a preload induced by long steel rod bolts (SRB) and specially designed couplers. The preload is applied using a torque or impact wrench. Consequently, the connection simplifies the on-site assembly and disassembly processes of the modular building, thereby enhancing both construction speed and reusability of modules. In this study, the structural performance of the AJ connection was investigated experimentally and numerically. First, the coupler was tested under a uniaxial tensile load to check its strength. Then, preloading tests on assemblies of a coupler and a 3m long SRB were conducted to determine the torque-preload relationship. Subsequently, full-scale beam-to-column joints featuring the AJ connection were tested under monotonic loading to investigate its lateral-force resisting mechanism. Lastly, the seismic performance of the AJ connection was investigated using FE joint models calibrated against a combination of test results and geometric and material nonlinear analyses with imperfections (GMNIA). A comparative analysis with a welded connection was also conducted to evaluate the seismic performance of the AJ connection. The findings indicated that the AJ connection demonstrates seismic performance comparable to the welded connection, exhibiting Strong column-Weak beam behaviour for seismic moment-resisting frames. Additionally, it satisfies the ductility requirements for structures of ductility class DCM as specified by EN 1998–1. • Developed a novel preloaded inter-module connection for steel modular buildings. • The connection enhances construction speed and module reusability. • Assessed experimentally the connection, including preloading and joint tests. • Assessed numerically seismic performance of the connection using FE models. • The connection satisfies the ductility class medium as specified by EN 1998–1. [ABSTRACT FROM AUTHOR]

Bolted joints are widely used in industrial applications and joint failure can cause a disastrous accident if loosening happens. Bolt loosening detection can be made by regular manual inspection or by using sensors based on different physical principles, such as acoustoelastic effect, piezoelectric active sensing, and electromechanical impedance. Compared with the above methods, vibration based bolt looseness monitoring using accelerometers is appealing for its economy and convenience for measurement. In this paper, cargo bolts looseness monitoring under random excitation is studied based on vibration transmissibility, which overcomes the drawback of commonly used vibration methods in finding local bolt looseness. Vibration transmissibility analysis only uses two vibration transducers to monitor bolt group looseness, where the vibration signal below the cargo bolts is used as the "input" and the other one above the cargo bolts is used as the "output." There are 12 bolts in the cargo bolts studied in this paper, providing an essential clamping force to fix cargo during transportation. Six kinds of bolt group looseness with an increasing degree are simulated in the experiment. The experimental analysis shows that variation of the spectral moment can be used to monitor the global variation of the torque wrench exerted on the cargo bolts. The early stage of the bolt group looseness is that some one or two bolts begin to loose; however, the spectrum moment factor is insensitive to the local bolt looseness in the bolt group. To address this issue, the eigensystem realization algorithm (ERA) based on random input and output is utilized to find the subtle eigenvalue variation of the system matrix, which is neglected by the frequency transmissibility function. The experimental results show the effectiveness of the proposed method for detecting local bolt looseness. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to determine preload in a bolted joint at installation or point of use. This approach uses both tightening torque and removal torque measurements. This work reveals preload is proportional to tightening torque minus removal torque and that taking this torque difference subtracts out friction. Tests with bolts, nuts, lock nuts, inserts and locking inserts are provided to assess this approach, and the results show good agreement with measured preload. The tests reveal the uncertainty in preload determined from this torque difference is less than the uncertainty in preload from tightening torque alone. A useful application of this work is to obtain a desired preload with nothing more than fastener thread pitch and a torque wrench to measure tightening torque and removal torque. This application is illustrated with data. The significance of this application is that preload is determined without any previously acquired torque–tension data as needed with tightening torque alone to achieve preload. In addition, this paper presents analysis and test data for quantifying self-loosening and primary locking in threaded fasteners from tightening and removal torque measurements. [ABSTRACT FROM AUTHOR]

• The repeatability experiment was carried out to investigate the pre-tightening force loss after the removal of torque wrench and the loss in service. • The pre-tightening force may increase after the initial loss stage for the first tightening. • When the lubricant is used, the service loss has a significant positive correlation with its pre-tightening force. • The use of lubricant at the threads is easier to lead the service loss of pre-tightening force. The clamping force of the bolted joint is a key factor in maintaining its service performance. However, when the torque wrench is removed after tightening, there will always be a certain degree of loss in the pre-tightening force. Herein, the stress state of the bolt and the nut during tightening and service was analyzed. The repeatability experiment of the threaded fasteners during repeated tightening was carried out to investigate the pre-tightening force loss after the removal of torque wrench (initial loss) and the pre-tightening force loss in a period of service (service loss). Different forms of lubrication was considered, namely without lubrication, thread lubrication and nut surface lubrication. The influence of the pre-tightening force, repeated tightening and lubrication on the initial loss and the service loss was analyzed according to the experimental results. It showed that the pre-tightening force and its loss have a large dispersion. At the first tightening, the pre-tightening force may increase after the initial loss stage. When the lubricant is used, the service loss has a significant positive correlation with its pre-tightening force. The use of lubricant at the threads is easier to lead the service loss of pre-tightening force. [ABSTRACT FROM AUTHOR]

Bamboo structures have various types of connections, such as bolting and lashing. One crucial issue in bamboo structures is that the connection with bolts and nails has a lower load-carrying capacity associated with the bamboo failure resulting from the bolt or nail invading them. This paper focuses on the connection for raw bamboo members with steel hoops (BHC), of which the two semi-circular steel hoops are fastened to the raw bamboo with high-strength bolts. The sliding friction is controlled by the interfacial pressure, which can be increased by tightening the bolts. A push-out experiment on thirty-six specimens was conducted considering the following two parameters: the different surface conditions of raw bamboo (with or without the epidermis) and the different interfacial pressure. The test results mainly showed the two failure modes of specimens under certain conditions: continuous longitudinal slip after the vertical load reached the peak; and the steel hoop stuck in the bamboo skin after a period of slip. It is found that the sliding friction was controlled by the interfacial pressure, and the difference in the anti-sliding capacity between the epidermal bamboo specimen and the non-epidermal bamboo specimen was magnified with the increase of interfacial pressure. The contact stress on the surface of bamboo is approximately uniformly distributed based on the finite element analyses. The interfacial pressure can be predicted by the torque value of the digital electronic torque wrench and the equations established by mechanical analysis, respectively. Moreover, the design formulae of bearing capacity for BHC under three guaranteed rates (50%, 95%, and 99.9%) were developed based on probability theory, while the fourth design formula was derived by regression analysis. The reliability indices of the four design formulae were up to 0.07, 1.44, 3.09, and 0.97, respectively, and the resistance partial coefficients were suggested accordingly. [ABSTRACT FROM AUTHOR]

The article presents an experiment which examines the visualization of contact areas in bolted joints using ultrasonic waves (UW). The study includes tests on bolted joints characterized by different values of applied torque, and the ultrasonic results were compared using fuji prescale pressure-sensitive film. It is also mentioned that ultrasonic waves is a useful tool to supply information about the contact status of bolted joints. Several illustrations and diagrams about the bolted joints and the experimental results are also presented to support the study.