Tension control BOLTS (TC BOLTS) are specialized fasteners mainly utilized in steel frame construction. They include a pre-assembled bolt, nut, and washer for simplified installation. In contrast to standard BOLTS, TC BOLTS have a domed head and a distinctive spline design that enables accurate tensioning during the installation process. This advancement has led to their growing popularity in the construction sector because of their effectiveness and dependability. In this article, examined this type of BOLTS, installation mechanism, their advantages over conventional high-strength structural BOLTS, challenges and considerations, durability comparison between traditional and TC BOLTS, design features, installation process, and also review the relevant standards associated with them.

One of the practical and useful methods that is used in Eurocode 3 to analyze the bending behavior of connections is the component method. Based on this method, the moment-rotation curves of joints are estimated bilinearly based on the two parameters of bending strength and initial stiffness. Therefore, one of the most important parameters to evaluate the moment-rotation curve using the component method is to find the exact initial stiffness of the connection (Sj,ini ). An issue that is not mentioned in the Eurocode 3 and causes the obtained results to be insufficiently accurate is the issue of pre-tensioning BOLTS. The main goal of this research is to add the effect of prestressing BOLTS to the component method. For this purpose, the stiffness of the spring elements modeling the column flange in bending, the end plate in bending, and the bolt in tension, which are necessary to predict the rotational stiffness of connections with the end plate with prestressed BOLTS, should be investigated. For this purpose, first, relationships are presented to consider the effect of prestressing BOLTS in the component method. Then, several end plate connections that have been investigated by the researchers are evaluated in two cases without considering the effect of pre-tensioning of the BOLTS and considering this effect in order to verify the correctness of the presented relationships. The results show that the presented method for considering the prestressing of BOLTS is a suitable and efficient method, which makes the accuracy of the developed component method more accurate than the conventional component method. So that the rotational stiffness difference of the laboratory model with the component method without considering the effect of pre-tensioning of the BOLTS was reduced to -13.81% and by considering the effect of pre-tensioning of the BOLTS to -2.41%.

Using steel shear walls is one way to increase the lateral load-carrying capacity of reinforced concrete moment-resisting frames and have been gaining the interest of researchers due to their excellent performance in earthquakes and ease of construction. In these shear walls, connection to the frame and force transfer between the wall and the frame are of particular interest. In this study, the connection type of these walls and transfer of forces between them and the frame via BOLTS were examined and controlled using the ABAQUS software. For this purpose, a two-story concrete frame equipped with steel shear walls was evaluated after verifying the numerical model. The frame was assessed under two connection conditions: the ideal state, in which the shear wall is fixed to the beam, and the realistic state, in which these shear walls are attached to the beam using connecting plates on the beams and BOLTS at the top and bottom of the beam. To design the BOLTS, first, the prestressing force needed to prevent sliding should be calculated, according to which the prestressing force and the BOLTS can be designed. Also, the simultaneous effect of tension and shear should be taken into account in the BOLTS design. .After designing the bolt diameter and prestressing force, the behaviors of the frame were compared in both cases. The numerical analysis revealed that the load-displacement behaviors in both cases were almost identical. Furthermore, the stress in the BOLTS in the second state was found to be lower than their strength, indicating that the bolt design method is safe and suitable for transferring forces between the shear wall and the reinforced concrete structural frame in floors. Also, by designing the bolt and its prestressing force according to the method of this paper, it is ensured that no slippage between the concrete and the connection plates occurs until the end of loading.

Using steel shear walls is one way to increase the lateral load-carrying capacity of reinforced concrete moment-resisting frames and have been gaining the interest of researchers due to their excellent performance in earthquakes and ease of construction. In these shear walls, connection to the frame and force transfer between the wall and the frame are of particular interest. In this study, the connection type of these walls and transfer of forces between them and the frame via BOLTS were examined and controlled using the ABAQUS software. For this purpose, a two-story concrete frame equipped with steel shear walls was evaluated after verifying the numerical model. The frame was assessed under two connection conditions: the ideal state, in which the shear wall is fixed to the beam, and the realistic state, in which these shear walls are attached to the beam using connecting plates on the beams and BOLTS at the top and bottom of the beam. To design the BOLTS, first, the prestressing force needed to prevent sliding should be calculated, according to which the prestressing force and the BOLTS can be designed. Also, the simultaneous effect of tension and shear should be taken into account in the BOLTS design. .After designing the bolt diameter and prestressing force, the behaviors of the frame were compared in both cases. The numerical analysis revealed that the load-displacement behaviors in both cases were almost identical. Furthermore, the stress in the BOLTS in the second state was found to be lower than their strength, indicating that the bolt design method is safe and suitable for transferring forces between the shear wall and the reinforced concrete structural frame in floors. Also, by designing the bolt and its prestressing force according to the method of this paper, it is ensured that no slippage between the concrete and the connection plates occurs until the end of loading.

Experimental investigations have been carried out on five specimens, out of which three were of single-draped tendon profile and two were of straight tendon profile.Rectangular RC beams of section size 150 mm X 275 mm with 4 m length were used for investigation. Crack was induced in RC beams to a limit in which strain in reinforcing steel was around 85 % of the yield strain by monotonically increased static two-point load at flexural zone. Strengthening by external prestressing was done while the member was subjected to superimposed dead load of a bridge girder, equivalent to 25 % of the calculated ultimate load of the specimen. Strengthened members were tested by monotonically increased two-point load. Role of the reinforcing steel were observed from electrical strain gauges, which were fixed throughout the length of the beams. It was observed that the ultimate load carrying capacity of strengthened members have increased 48 % and 17 % for single-draped tendon profile and straight tendon profile respectively.

In this study, the failure analysis of base plate BOLTS of radial forging machine is investigated. Premature failure had occurred from the BOLTS shank-head fillet and threads zones. Hardness, impact and tensile tests are carried out to investigate the mechanical properties and spectrophotometer is used to evaluate the BOLTS chemical composition. Optical Microscope (OM) and Scanning Electron Microscope (SEM) are used for the investigation of microstructure, defects, fracture surface and failure causes. The fracture surface morphology shows that the crack growth consisted of BOLTS shank-head fillet and threads zones including the initiation zone, fatigue crack growth zone along with the beach marks and ratchet steps and the rapid final fracture zone. Stress analysis shows that the amount of pre-tightening selected lower than the proposed value leads to the joint loosening and shortens the bolt’ s fatigue life. In addition, based on the paper results, the existing flowchart for component fabrication is analyzed and a flowchart based on research field is presented to enhance the quality of radial forging machine parts.