Bolt Tension Research Articles

ULTRASONIC MEASUREMENT OF HIGH STRENGTH BOLT AXIAL TENSION IN STEEL CONSTRUCTION

To guarantee the reliability and security of the steel construction, the clamp load of the joint bolt should be under strict control, sometimes even the tension of the bolt should be measured on-line. Referring to the sonic elasticity principles, an indirect method is proposed for bolt tension measurement, based on the relation between the axial tension of high strength bolt and the time difference for the echo to return from the opposite end before and after the bolt is tightened. This method also takes the material factors and the clamp length into account. The method achieves high accuracy measurement by removing the measuring error caused by the discreteness of the thickness of the couplant and change in temperature. Based on the method, a new way on forecasting and revising the material factors is brought forward. The accuracy in bolt tension measurement is proved to be better than five percent, and thus is acceptable in most of the industry use.

5244 偏心外力がボルト軸力に及ぼす影響 : VDI 2230指針の適用結果(S64-3 ねじ(3),S64 機械要素の設計・製造・応用技術)

In a strength design of a bolted joint, it is one of the important problems to estimate additional tension of a bolt accompanied with eccentric external loads. The VDI 2230 has been well known as a guideline for designing bolted joints and its new revised version was recently published. It is the purpose of this report to apply and examine an estimation method about influences of eccentric external loads to the bolt tension which is described in the new revised version. Comparisons are done between calculated values due to the above method and experimental ones. As a result, it is known that both values show similar inclinations and agree fairy well.

Theoretical Analysis of Preloaded Bolted Joints Subjected to Cyclic Loading

In this paper the performance of preloaded bolted joints is analysed. The prior torque tightening creates compression in the clamped members and tension in the bolt. So, when an external tensile load is applied to the joint a large amount of it is taken up by the members, thereby relaxing their compression, at the expense of only a slight increase in bolt tension. In this way preloading the joint has the effect of changing the bolt fatigue regime from a low mean load with high alternating load to a high mean load with a low alternating load. This is beneficial for its fatigue life.

A new approach to tightening bolts

The most common method for controlling the tightening of bolts is by specifying a value of torque. The inference of bolt tension from the torque has a number of potential inaccuracies, but the method offers the benefit of convenience and does not require any special equipment. This article discusses a system that can directly measure the applied load in the bolt during the tightening process.

Ultrasonic Control of Fastener Tightening Using Varying Wave Speed

A high precision ultrasonic technique and a test apparatus are developed for the real time control of the fastener elongation during the tightening process of bolted joints. This is accomplished by monitoring the propagation of longitudinal ultrasonic waves through the fastener material and the reflection of these waves at the end of the fastener. The round trip time of the longitudinal waves is continuously measured and monitored in real time. Using the wave speed in the fastener material, the change in the round trip time determines the fastener elongation, which creates fastener tension and joint clamp load. The wave speed through the bolt material is stress dependent; hence, it continuously changes as the fastener is being elongated during the tightening process. A varying wave speed algorithm is developed and utilized in order to compensate for wave speed variations. Because the torque-tension relationship in threaded fasteners is highly sensitive to friction variations, the scatter in such relationship is often unacceptable, especially in critical applications. By contrast, the automatic control of the fastener elongation during the tightening process would eliminate the dependence on the torque value as a predictor for the bolt tension. Hence, the new ultrasonic technique for the real-control of the fastener tension, by monitoring its elongation, would significantly enhance the reliability of bolted assemblies.

Effect of Thread Pitch and Initial Tension on the Self-Loosening of Threaded Fasteners

A mathematical model and an experimental procedure are presented to study the self-loosening phenomenon of threaded fasteners that are subjected to cyclic transverse loads. The study investigates the effect of thread pitch, initial bolt tension, and the amplitude of the external excitation on the loosening of a single-bolt joint. The rate of drop in the joint clamp load (fastener tension) per cycle, as well as the total number of cycles that would cause the complete loss of clamp load, are monitored. In the mathematical model, the differential equations of linear and angular motion of the bolt are formulated in terms of the system properties and the external cyclic transverse excitation. Numerical integration of the equation of angular motion provides the bolt rotation in the loosening direction, which causes the partial or full loss of the clamp load. An iterative MATLAB code is developed and used for the calculation of tension loss in the fastener tension due to the self-loosening. Analytical and experimental results are discussed.

Clamp Load Loss due to Elastic Interaction and Gasket Creep Relaxation in Bolted Joints

An experimental study is presented in order to determine the clamp load loss due to elastic interaction and gasket creep relaxation in bolted joints. Studied parameters include the gasket material and thickness, bolt spacing, tightening sequence, fastener grip length, and level of the fastener preload. The joint is composed of two steel flanges and a gasket made of styrene butadiene rubber or flexible graphite. The flanges are fastened together using M12x1.75 Class 10.9 fasteners. Force washers are used to monitor bolt tensions in real time. Four different gasket thicknesses of styrene butadiene rubber (1/16, 1/8, 3/16, and 1/4 in.) and two thicknesses of flexible graphite (1/16 and 1/8 in.) are considered. For the same bolt circle of the flange, the bolt spacing is varied by using a different number of bolts; spacing that corresponds to using three, five, or seven bolts is considered in this study. The effect of the tightening strategy is studied by using sequential, star, or simultaneous tightening patterns. Bolt tightening is accomplished by using either an electric digital torque wrench with various control options or by using a production-size multiple spindle fastening system that is capable of simultaneous tightening of all fasteners. Experimental data is presented and analyzed, in order to study the effect of the various parameters on the clamp load loss due to the combined effect of elastic interaction and gasket creep relaxation at room temperature.

Parametric analysis of steel bolted end plate connections using finite element modeling

This paper presents and discusses results of parametric analyses on the behavior of bolted extended end plate connections using Finite Element (FE) modeling tools. The analyses were calibrated to experimental results that are also briefly reviewed in this paper. The analytical models took into account material nonlinearities, geometrical discontinuities and large displacements. Comparisons between numerical and experimental data for moment-rotation curves, displacements of the end plate, and forces on bolts showed satisfactory agreement. Phenomenological T-stub failure models were also used for calculations of the flexural strength for the end plate. These models clearly support the numerical results and show how the interaction between the end plate and the bolts changes the connections’ behavior. The results presented herein show that failures associated with either formation of yield lines in the plate (Mode 1) or bolt tension failure (Mode 3) are well-defined, while failures due to combinations of these mechanisms (Mode 2) represent levels of interaction between the end plate and bolts that are difficult to predict accurately. These results also indicate that the T-stub analogy has limitations in representing the yield lines at the end plate, leading to limitations both in accounting for prying action and in predicting values for strength and stiffness of the connection.

壁式プレキャスト鉄筋コンクリート系低層住宅の構造性能に及ぼす直交壁の効果

An experimental study on real scaled one-bay-one-story frames with transverse walls in precast reinforced concrete housing of low-rise wall-building system was carried out to examine the effect of the transverse walls on the structural performance of the housing. An outline of the testing is described and the shear resistant mechanisms of the transverse walls are examined based on the test results in this paper. The conclusions obtained are; (1) The transverse wall effect is effectively developed in the frame. (2) Strength induced by the transverse wall effect can be estimated as the minimum value among the followings: a) direct shear of the floor rib at the top of wall panel, b) punching shear of the floor rib at the top of the transverse walls, and c) tension of joint bolts at the top of the transverse walls. (3) Relationship between the horizontal displacement of the frame and the transverse wall effect can be evaluated by bi-linear skeleton curves.

2725 管フランジ締結体の締付け手順とボルト軸力特性(S58-2 ねじ(2),S58 機械要素の設計・製造・応用技術)

2725 管フランジ締結体の締付け手順とボルト軸力特性(S58-2 ねじ(2),S58 機械要素の設計・製造・応用技術)

Intelligent fastening with A‐BOLTTM technology and sensor networks

Threaded fasteners appear to be the best low cost option for applying a desired clamp load to assemble a joint, which can be disassembled, if necessary, at a low cost. A large number of joint failures are due to inadequate tension on the joint. Most conventional tightening methods only provide a vague indication of the bolt tension. In this paper we will discuss the development of the A‐BOLT™ system, which can measure the tension in the mechanical bolt to ±1 per cent accuracy of the proof load. The key element of the system is a specially designed mechanical bolt with a top‐mounted sensor to measure the bolt elongation. We will also describe the development of different generations of the A‐BOLT™ system and its industrial applications. Finally we will present an overview of research on the cluster based networking of wireless sensors to minimize energy consumption in a network of sensors.

Finite Element Analysis and Tests on Bolted End-Plate Connections in Steel Portal Frames

Bolted end-plate connections are being widely used in steel portal frames. In this paper, some tests on beam-to-column and beam-to-beam end-plate connections are reported and the corresponding finite element analysis (FEA) is carried out to analyze their loading resistance and rotational stiffness characteristics. The design method about extended end-plate connections in current design code is discussed, and the necessary improvements are proposed. Especially, some precautions about the classification criterion of the joint stiffness in steel structures are recommended. From the results of comparison, one new model of the bolt tension force distribution and the corresponding design method are presented. It has been verified by the tests that this method can calculate the actual stresses of the bolts and the end-plates more accurately and mobilize their loading capacities more efficiently with sufficient safety and reliability.

Lubrication Analysis of a Connecting-Rod Bearing in a High-Speed Engine. Part II: Lubrication Performance Evaluation for Non-Circular Bearings

In this article a numerical investigation of a connecting rod bearing operating at 6,500 rpm is performed. This is a companion to an earlier article that took into account the effects of the inertial force and the variable bolt tension force, which are considered to be the principal factors that affect the connecting rod bearing lubrication characteristics of an engine running at high speed. It was found that a thinner minimum oil film and a larger peak hydrodynamic pressure are predicted in a deformed connecting rod bearing than in a rigid connecting rod bearing. Multi-peaked hydrodynamic pressure was found to appear as well because of two or more converging-diverging film regions.

Extrusion analysis of a bolt-reinforced tunnel face with finite ground-bolt bond strength

In this paper a new analytical model is proposed to analyse the displacement behaviour of a tunnel face reinforced by bolts, using the homogenization approach for periodic media. Based on previous works, this new model was developed to take into account a finite bond strength of the grout–soil interface, which is more realistic than the perfect bonding assumption. The interface behaviour is simulated by an elastic – perfectly plastic constitutive law. The interface sliding occurs when the shear stress reaches the bond strength. This new feature allows for a more correct estimate of the bolt tension and the quantitative contribution of the bolt to reducing displacement of the ground surface. Despite using less restrictive hypotheses, the solution process remains sufficiently simple, thus preserving the analytical character of the solution. This new analytical model has been validated by three-dimensional (3D) numerical calculations using the finite difference code FLAC3D and by comparing its predictions with in situ data from the Tartaiguille Tunnel construction project, which forms part of the Mediterranean TGV (high speed railway) network. The developed approach results in simple and efficient design tools, which are very useful at the preliminary design stage of a project.Key words: tunnels, soil–structure interaction, reinforcement, numerical modelling and analysis, deformation, plasticity.

Monitoring the stability of hydro-caverns with rock mechanics instrumentation - a case study

The Ghatghar pumped storage hydro-electric project is under construction in the Thane district of Maharastra state in India for the generation of 250MW of electricity. The scheme consists of two underground caverns, a machine hall, a transformer hall and intersections. The interconnections between the caverns and connections to the surface, as well as to the reservoir, are made through a network of tunnels. The rock mass is predominantly of basaltic formation. The joints are mostly tight and undulating with generally rough to very rough contact surfaces. The rock mass characterization was conducted using Bieniawski’s RMR (1979) and Barton’s Q. The associated values vary from 66 to 81 and from 5.9 to 25, respectively—which indicate very good rock mass conditions. The support requirements for these structures were estimated from empirical approaches and numerical modeling. The support system consists of 6m long fully grouted rock bolts at 2m grid spacing with 50mm thick SFRS for the two caverns and 7m long rock bolts around the intersections of all openings. An extensive instrumentation scheme was implemented in these structures as a means to evaluate the efficacy of the support system and to have detailed knowledge of the rock mass behavior during and after construction. The instrumentation consisted of: tape extensometers for measuring convergence; multi-point and single point borehole extensometers for radial displacements; load cells for rock load and strain meters for rock strains. These instruments were embedded during the process of cavern excavation. The rock mass deformations around the cavern openings, as indicated by the MPBXs (Fig. 1), the convergence measured by the tape extensometer, and the rock bolt tension measured by the load cells were too low to be significant and collectively indicate that the roof and the walls of both the caverns and of the bus ducts and passageways are stable, indicating that the support system is adequate. It was, however, suggested that the vulnerable wedges should be identified on account of the jointing; these would need to be stitched to the rock mass and the wedge stability be monitored by site specific arrangements. This paper presents in detail the instrumentation scheme implemented at this project plus the analysis of the monitored data, highlights the stability status of the caverns, and recommends the future strategy for monitoring.

Yellow line to make bolt load checking easier

Maintenance engineers will soon be able to check bolt tension at a glance on high integrity applications. This is a short news story only. Visit www.worldpumps.com for the latest pump industry news.

Experimental Response of Precast Infill Panel Connections and Panels Made with DFRCC

This paper describes the results of an experimental investigation of an infill system that utilizes precast ductile fiber reinforced cementitious composite (DFRCC) panels in lieu of traditional materials. The system is intended for use as a retrofit strategy in steel framed hospital structures. Bolted connections are utilized both between individual panels and to the frames, allowing the system to be moved or altered in the event of changes in facility use. Results from laboratory tests of panel connections and panels are presented. The connection tests studied the effect of bolt orientation with respect to applied load, the effect of the DFRCC surface condition within the connection, and time-dependent bolt tension loss. The connection tests demonstrated the viability and the capacity of the proposed connections. DFRCC panels were tested to evaluate the cyclic load-displacement response and energy dissipation in the panels with various panel geometries, panel reinforcements and DFRCC materials. The panel tests also demonstrated the viability of the connection system used. Selected panel test results are presented here, indicating the variation in stiffness and energy dissipation possible with different panel reinforcement.

高力ボルト摩擦すべり接合に関する研究 : その1 アルミニウム合金板を摺動材に利用した接合要素実験

In this paper, dynamic loading tests were conducted using the bolted frictional slippage connection specimens that sandwiched aluminum alloy sliding plates in order to investigate frictional slipping behavior such as the variation of slip coefficient while slipping and the influence of the initial bolt tension to the kinetic slip coefficient. As the result, specimens using high strength aluminum alloy sliding plates showed stable enough frictional slipping behavior rather than other two aluminum alloy sliding plates and the initial bolt tension had little influence on the slipping coefficient. In addition, in order to predict the slip coefficient of the specimen, a nonlinear regression equation was applied and its regression coefficients were obtained using nonlinear least squares fitting. This equitation predicted varying slip coefficient of specimens using high strength aluminum alloy approximately.

Experimental Study of Breakaway Highway Sign Connections

Highway signs require breakaway base connections. These connections will slip under impact, therefore preventing injuries to the occupants of an impacting vehicle. The breakaway connection works as long as the tension of the bolts is maintained between an allowable range. A method to ensure that the bolts are tensioned to the proper value is presented. It is based on the use of Belleville spring washers. Laboratory and field tests were performed to verify the adequacy of the new method. Seven signs were selected along Florida highways. At each sign, the variations of tension in bolts installed with flat washers and with spring washers were monitored over a period of 1 year. The measurements showed that, at the time of installation, the new method was significantly more effective in ensuring the proper tension in the bolts. Similarly, over the long term, the bolts installed with spring washers maintained the tension in the bolt more effectively and without any loosening. The effectiveness of the breakaway connection with spring washers was also demonstrated during an actual car accident.

Application of high strength plate bolts in friction grip joints

High Tension Bolts (HTB) are known to exert a significant influence on the strength characteristics of connections and have a significant influence on the ductility and behaviour of the joint. Normally HTB failure occurs in the shape resultant high stress concentration neck and thread areas resulting in relatively low ductility characteristics. Creep and relaxation occur after HTB tightening causing shaft tension loss and further stress redistribution in the connected components. Past research has shown that waisting the HTB shaft diameter reduces stress concentrations, shaft tension loss and increases ductility. With the further modification of making the HTB head plate shape counter sunk, a plate HTB with an aesthetically pleasing flat surface less susceptible to rain corrosion results. In this research, tensile, relaxation and friction grip joint slip experiments were done on waisted shank, counter sunk plate head HTB to ascertain the ductility improvement, the resulting decrease in shaft tension loss and its magnitude, as well as their applicability in friction grip steel connections. Apart from significant shaft tension loss reduction, no detrimental effects are induced in the slip coefficient results when these HTBs are applied in friction grip joints. Within these experimental parameters, the closest to ideal HTB shape is proposed. (Journal of Civil Engineering, JKUAT: 2002 7: 67-80)