Bolt Force Research Articles

Numerical Study on Ultimate Deformation and Resistance Capacity of Bolted T-Stub Connection

Disproportionate or progressive collapse is a phenomenon in which entire structure or large part of it collapses because of the local failure of a structure. Resistance to such progressive collapse depends on continuity between elements and ductility of the connections. The ductility of commonly used bolted end plate connections may depend on the T-stub component of the connection. The aim of this paper is to study the behaviour of T-stub components of beam to column end plate bolted connections under large deformation demands associated with column loss scenario. For this purpose, a parametric study is carried out to evaluate the ultimate strength and deformation capacity considering two parameters i.e. distance between the bolts and endplate thickness. Based on the experimental data, numerical model has been validated and employed in a parametric numerical study aimed at improving the response under large deformation demands. The study indicate significant role of bolts in development of catenary forces since the ultimate tensile capacity of T-stub after undergoing large deformation in a ductile failure mode was controlled by the failure of the bolts. Parametric study reveals much higher bolt force in comparison with displacement controlled induced axial force in the T-stub indicating failure of the bolts at much lower applied axial force.

Study of reinforcement support mechanisms for wide-span horse-shoe-shaped openings in horizontally layered jointed rock using the distinct element method

Wide-span openings in horizontally layered jointed rock were analysed using the distinct element method (DEM) to provide additional insight into rock bolt support mechanisms and forces. The rock bolt forces in the DEM calculations exhibited distinct mechanisms, identified here as reinforced rock unit, beam building or suspension mechanisms. Each of these mechanisms was found to be associated with certain characteristics in the jointed rock structure. In jointed rock with thick horizontal beddings, the rock bolt forces at the roof tapered off with distance leading to a reinforced rock unit where each layer exhibited a self-support mechanism akin to a voussoir beam. In jointed rock with thinner horizontal beddings not capable of self-supporting, a beam building mechanism took place. When the rock bolts were extended into a rigid layer above the thinner layers, a suspension mechanism took place. Potential inaccuracies of thrust line predictions and the benefits of rock bolt tensioning were investigated, and their effects were found to be sensitive to the bedding thickness. A case history of the cavern roof of the underground car park for the Sydney Opera House was modelled. The calculated deflections of the cavern roof compared well with field measurements reported in the literature. The findings in this paper highlight the importance to ensure that the reinforcement support for wide-span underground excavations in horizontally layered jointed rock are tailored to the geological conditions being encountered.

The method of determining the efforts of the pre-tightening of bolts to a bearing of the crankshaft, automobile and tractor engines

The increase of power density of automotive and tractor engines leads to increased loads on parts of the crank mechanism. To ensure the specified reliability indicators, it is necessary to give an accurate analysis of the loads. There was studied currently used technique for calculating the pre-tightening force of rod bolts or mounting bolts of main bearing caps to ensure that the density of the junction of the threaded connections. It is shown that, first when the bolt is tightened, the liner shrinks by the amount of its protrusion and only then the joint is closed between the cover and the crank head of the connecting rod. This reduces the effort to ensure a given margin of safety of the joint density. The calculation of the force for deformation of the insert on the amount of its protrusion is carried out, which ensures the fit of the inserts when they are inserted into the bearing bore. It can be seen from the calculation that the force to deform the liner is not less than 30 ... 40 % of the value of the force of the tightening, which ensures the tightness of the joint between the components to be tightened. A procedure is proposed for determining the pre-tightening force of the connecting rod bolts or bolts for attaching the main bearings of the piston engine crankshaft, in case of providing the specified margin of joint density as a standard threaded joint. An example of calculating the torque settings connecting rod bolt for diesel engine D-245 when operating on the maximum idle speed.

Stability Analysis of Bolts Reinforced Rock Jointed Slope by Considering the Transverse Effects

The fully grouted bolt is a convenient, effective, and economic technology for slope reinforcement. A new nonlinear Hoek-Brown strength reduction method based on the characteristics of a jointed rock mass is proposed. By analyzing the change in slope failure mode, effects of the bolt head, spacing, inclination, and arrangement on the stability of the slope are investigated. Results show that the shear strength of the bolted structure is contributed by the axial force and transverse shear force. The transverse shear force of bolts increases the slope stability and improves the bolt bearing capacity; the bolt head is important in determining the failure mode and factor of safety of a bolted slope, while the size and material parameters of the bolt head are not important when the size of the bolt head is sufficiently large. The vertical bolt spacing has a nonlinear effect on the slope safety factor, and the failure mode of the slope changes from deep sliding to partial deformation along the joint surfaces with increase in the bolt horizontal spacing. With increase in the bolt inclination angle, the safety factor first increases and then decreases, and the maximum safety factor occurs when the bolts are placed horizontal or perpendicular to the slip surface. The slope safety factor decreases with decrease in the bolt length. An optimal design of longer bolts at the bottom and shorter bolts at the top is recommended. A shear zone forms from the intersection of two joints to the slope surface in the upper part of the slope.

Experiment and design methodology of a double-layered flange connection in axial loads

This paper introduces a new type stiffened flange connection called inside and outside double-layered (IODL) flange connection for large circular hollow sections (CHS). This kind of connection not only make full use of the inner space of the circular tubes but also avoid safety problems by using smaller bolts and thinner flange plates. The purpose of the research presented in this paper is to thoroughly analyze the behavior of the connections by an experimental testing program and advanced finite element analysis (FEA) and propose corresponding design method for practical engineering. Experiments on four types of down-scaled specimens were performed. Results of advanced quasi-static FEA, using explicit dynamic solver and ductile damage material model for bolts, are compared to experimental results. Failure modes, bolt forces and distribution of stresses in the upper plates, stiffened plates and end plates are analyzed. Design models for high strength bolts, upper plates, stiffened plates and end plates are proposed. The connections designed according to these models will meet the demand of safety and economy.

An anchorage experimental study on supporting a roadway in steeply inclined geological formations

The support of rock bolt plays a significant role in maintaining the stability of a roadway in steeply inclined geological formations, yet choosing a reasonable support scheme of rock bolt in this situation is still not well understood. To reveal the force or stress distribution mechanism of anchor bolts and design an effective support scheme, an in situ anchorage experiment was conducted in a deep-buried roadway in steeply inclined rock strata. This results of this study demonstrate that in the steeply inclined rock formations, the intersection angle of a bolt length direction and the interface of rock layers have a great effect on the distribution and variation of axial force in bolts. The axial forces at the positions near the intersection of the interface and bolt increase a lot with time. In addition, the existence of no small or non-zero axial force at the end of anchor bolts indicates that much longer bolts should be used to prevent further deformation in steeply inclined rock.

Numerical modelling of staged stope extraction in a tabular steeply dipping deposit

ABSTRACTStope stability is a key factor for the success of a mining operation. To optimise ore productivity while maintaining stope stability, the mining block/stope must be extracted in stages. Ore dilution will occur if the stope is not properly excavated/blasted. This study examines stope stability during mining in three stages, where the height of each stage stope is 10 m. The paper also presents simulation analysis of a typical steeply dipping tabular orebody at 1200 m depth below the surface, which is common in many Canadian underground hard rock mines. Numerical modelling analysis was conducted using the finite element program, RS2D, where the non-linear elasto-plastic Mohr-Coulomb failure criterion was adopted. The rock reinforcement system (i.e. cable bolts) was modelled/installed in the stope footwall after each mining stage to strengthen access drifts and stabilise the rock mass around the stope that was disturbed by mining activity. Results are discussed in terms of depth of failure zones, total deformation and axial forces in cable bolts with respect to mining stage.

Seismic behaviour of connections between prefabricated RC flat slabs and square steel tube columns

Reinforced concrete (RC) flat slab column structure is a typical vertical support system and is often used in regions of moderate seismicity. Additionally, a steel structure is easy to assemble and exhibits good mechanical property, ductility and energy dissipation performance. Thus, this study presents a new type of connection between a prefabricated RC flat slab and square steel tube column. The connection effectively improves seismic performance and stress mechanism and leads to plastic deformation in the cantilever beams that can be replaced after an earthquake. The connection consists of a column base with four cantilever beams, a channel steel connection, and an RC flat slab. A gap connected by four square crossing I-steel cantilever beams is left between the column and channel steel connection, and this forms an opening around the column. An experiment was performed to study the seismic behaviour of the prefabricated slab column connection. The effects of the key parameters including the I-steel web thickness of the cantilever beam and axial compression ratio were investigated. The failure modes, hysteretic curves, and stress–strain curves with respect to relevant components were presented. A numerical simulation verified by the tests was performed to analyse the section stress and bolt forces for making up the test deficiency. The results indicated that the prefabricated slab column connection exhibits a superior seismic performance, thereby leading to earthquake-resilience. Finally, design considerations were presented to guide engineering practice for the proposed prefabricated slab column connection.

Numerical simulation of the behavior of steel T-stubs connected by Fe-based shape memory alloy bolts

The article focuses on the numerical simulation of the thermomechanical behavior of steel T-stubs connected by iron-based shape memory alloys bolts. The three-dimensional macroscopic model used in this work was previously developed by the authors considering different thermomechanical properties between austenite and martensite, and coupling between phase transformation and plasticity. The model is implemented in a UMAT code using an implicit time-discrete integration scheme that follows a “multisurface plasticity”-like approach. The numerical results show that the shape memory effect can be used to preload the bolt if the initial length of its shank is less than the total thickness of the flanges. For an initial shank length of 21.38 mm and a total flange thickness of 21.4 mm, the shape memory effect produced average contact forces of 101 N between the bolt head and the flange, and 37 N between the two flanges. The resulting average contact pressures were 210 and 25 MPa, respectively. The average bolt force after preload was approximately 22.6 kN. Subsequent application of 2 mm normal displacements at the top and bottom faces of the upper and lower webs induced local plastic deformation around the flange holes and phase transformation in the bolt. The reversibility of martensitic transformation and the confinement of the plastic deformation in a limited zone around the holes allowed nearly complete shape recovery by heating. The obtained results highlight the advantage of using low-cost iron-based shape memory alloys as alternatives to steel bolts for connecting T-stubs.

Analysis of Deformation Law of Tunnel Surrounding Rock based on Visualization of Rock Mass Structure

In order to accurately obtain the characteristic parameters of the rock mass structural plane of the tunnel and provide effective basis for numerical calculation, based on tunnel of Guiguang railway, this paper measured the structural characteristics of typical tunnel side wall and excavating face by using Sirovision non-contact measurement technology of 3d photogrammetry and accomplished digital geological logging, information statistics of structural plane attitude, rock stability analysis. By using the discrete element software UDEC, the whole process of tunnel excavation, primary support and secondary lining are simulated. The study show that the surrounding rock deformation, internal force of primary support, axial force of anchor bolt will improve with the increase of fragmentation degrees of surrounding rock. The primary support is the determinant of constraint of surrounding rock deformation and bearing the load after tunnel excavation. Secondary support only as a permanent support structure, as a safety margin, the internal force is small compared with the primary support, but taking into account the decreasing of physical and mechanical parameters of the surrounding rock excavation, rheology of soil and reducing of mechanical properties of primary support material. The secondary lining should be calculated and designed as force structure.

Analysis of the metal-to-metal contact flange joint subject to external bending moment

Metal-to-metal contact flange joints are widely used in nuclear and petrochemical industry for severe conditions, because of the relative stability of the sealing gasket stress under complex service condition. In the present work, finite element models were used for analyzing the stress distribution of metal-to-metal contact pipe flange connection under different internal pressures, temperatures, and external bending moments to evaluate the sealing and strength performance. A metal-to-metal contact pipe flange connection device was also experimented. It was found that the results of the axial bolt force and flange hub stress obtained from the experiments were in fairly good agreement with the finite element simulations. The leakage test of metal-to-metal contact type gasket was conducted to highlight its leakage characteristics under different temperatures. The methods to determine the maximum allowable bending moment of a metal-to-metal contact flange joint according the strength criterion and the sealing criterion were analyzed. The results showed that the maximum allowance bending moment was determined by the strength criterion rather than by the sealing criterion with different thermal loadings when the initial bolt-up stress was high enough to achieve metal-to-metal contact contact.

An experimental and numerical investigation of clamping force variation in simple bolted and hybrid (bolted-bonded) double lap joints due to applied longitudinal loads

Abstract In this research, the variation of clamping force in double lap simple bolted and hybrid (bolted-bonded) joints subjected to longitudinal loads were studied via experimental and FE methods. In order to obtain the initial values of the clamping force as a result of bolt tightening torque in double lap simple bolted and hybrid joints, an experimental method was designed. In another part of the experimental section, the variation of bolt pretension values in both kinds of specimens, under the application of static longitudinal loads were measured. Furthermore, FE simulation was used to analysis the bolt clamping process and obtain the variation of clamping force of bolt in both kinds of the joints, due to longitudinal applied loads. The results of this investigation revealed that in the hybrid joints the clamping force is reduced during tensile longitudinal load application. While in the simple bolted joints the decrease of clamping force in lower longitudinal loads is followed by the latter increase due to further increment of longitudinal load. This can be related to the method that the joint transmits the applied loads.

Evaluate the Clamping Force of Torque-Shear High Strength Bolts

A torque shear type high strength bolt is clamped as the pin-tail is broken by a specially designed electric wrench. However, it is uncertain that the tension is properly induced to the shank of a bolt when the pin-tail is removed from the bolt. In order to solve a problem involved in the uncertainty, this study was conducted to develop a method to identify the clamping force of high strength bolts quantitatively. The new method to identify the induced tension suggested in this study is to analyze electric energy applied to high strength bolts until the pin-tails are broken by diverse type of electric torque wrenches. Clamping force was measured and accumulated current data was obtained through various tests. Regression analysis of tension as a function of accumulated currents was conducted with various values of bolt diameter and wrench rpm. The error between the values measured by a tension meter and those estimated by a trial product of a measuring device developed in this study was 4% regardless of different parameter values. The device including algorithms to compute load based on electricity was found reliable enough to be applied to construction sites. The trial product embedded with the algorithms for different bolt diameters and electric wrench types was upgraded through three stages. The method to determine the clamping force of a high strength bolt is deemed reasonable because total energy applied to the clamping force of the bolt is the same as the electric energy accumulated by an electric torque wrench.

Impact of nonlinearity on bolt forces in multi-bolted joints: A case of the assembly stage

This article concerns modeling, computation and analysis of multi-bolted joints in the assembly stage. The physical joint model is introduced as the assembly of the following three basic subsystems: a set of fasteners (bolts), a flexible joined flange and a contact layer between it and a rigid support. The finite element method (FEM) is used for modeling. Bolts are replaced by the bolt models of the spider type. The joined flange is modeled with spatial finite elements. As a model of the contact layer, the Winkler contact layer model is adopted. The truth of the theorem has been tested, according to which nonlinear characteristics of the contact layer may have an insignificant impact on computational final values of bolt preloads in the case of sequential tightening of the joint. The results of the calculations for the selected multi-bolted joint are given and compared with the experimental results. Conclusions of paramount importance to the engineering practice are comprised.

Discontinuum analyses of openings constructed with side drift and limited rock cover

The design of rock support for a typical horseshoe shaped tunnel with considerations of it being excavated into a twin arch tunnel was studied using the distinct element method (DEM). Two different competent rock covers, i.e. 4 m and 7.5 m above the tunnel crown, were analysed. The results are relevant to the granitic geological unit in Singapore which has a weathering profile with rockhead found at some locations to be only 20–35 m below ground level and undulating, leaving limited rock cover for some sections along tunnels of similar depth. The verification of the adequacy of competent rock cover is important to ensure that the choice of ground support is suitable, particularly when the tunnel is excavated using the drill-and-blast method. In the opening geometry analysed in this study, a side drift is excavated adjacent to the first tunnel to create a twin arch opening. This creates a pillar between the openings during the intermediate construction stage. The influence of excavating the side drift on the support of the first opening was studied. We found that the bolt forces in the pillar approximately doubled during the excavation of the side drift, which may have been due to the rock joint inclinations and adopted strength parameters. This paper shows how DEM analyses may be used to complement conventional empirical rock mass classifications to design rock supports. Limitations of the pressure relaxation approach to model 3D effects in 2D are acknowledged.

Numerical simulation of the uplift behavior of shield tunnel during construction stage

In this study, a new 3D numerical model that considers the circumferential joint, longitudinal bolt, grout pressure, jacking force and the constraint of shield on the linings is developed to derive deeper insights into the lining uplift behavior during shield tunneling. The numerical analysis is conducted using ANSYS, which is verified by a case history in soft soils. Revealed by both the measurements and calculation results, it is found that the lining uplift due to shield tunneling in soft soils can be divided into three stages: dislocation, stretch and steady deformation stages, respectively. In the dislocation stage, the lining deformation attributes principally to the dislocation deformation between neighboring linings. In the stretch stage, the lining deformation is mainly caused by the stretch deformation of circumferential joints. The major uplift is caused during dislocation stage. Thereafter, the impacts of shield-driving parameters including gradient of grout pressure, jacking force and pre-tightening force of longitudinal bolts on the uplift behavior are investigated by a series of parametric studies. The jacking force during segment preparation and assembly shows the most significant impact on the uplift of the tunnel, while the pre-tightening force of longitudinal bolts shows negligible impact. Finally, the control criterion for lining uplift related to the allowable dislocation and opening angle of circumferential joints is proposed.

Dynamic modeling method of the bolted joint with uneven distribution of joint surface pressure

The dynamic characteristics of the bolted joints have a significant influence on the dynamic characteristics of the machine tool. Therefore, establishing a reasonable bolted joint dynamics model is helpful to improve the accuracy of machine tool dynamics model. Because the pressure distribution on the joint surface is uneven under the concentrated force of bolts, a dynamic modeling method based on the uneven pressure distribution of the joint surface is presented in this paper to improve the dynamic modeling accuracy of the machine tool. The analytic formulas between the normal, tangential stiffness per unit area and the surface pressure on the joint surface can be deduced based on the Hertz contact theory, and the pressure distribution on the joint surface can be obtained by the finite element software. Futhermore, the normal and tangential stiffness distribution on the joint surface can be obtained by the analytic formula and the pressure distribution on the joint surface, and assigning it into the finite element model of the joint. Qualitatively compared the theoretical mode shapes and the experimental mode shapes, as well as quantitatively compared the theoretical modal frequencies and the experimental modal frequencies. The comparison results show that the relative error between the first four-order theoretical modal frequencies and the first four-order experimental modal frequencies is 0.2% to 4.2%. Besides, the first four-order theoretical mode shapes and the first four-order experimental mode shapes are similar and one-to-one correspondence. Therefore, the validity of the theoretical model is verified. The dynamic modeling method proposed in this paper can provide a theoretical basis for the accurate dynamic modeling of the bolted joint in machine tools.

Finite Element Analysis of Eccentrically Braced Frames with Removable Link

Steel eccentrically braced frames (EBFs) are expected to sustain damage during an ultimate limit state design level earthquake through repeated cyclic plastic deformation of the active link. Traditionally the active link has been integral with the collector beam, but following the 2010/2011 Canterbury earthquakes, the benefit of having a readily replaceable active link became apparent. The development of this was undertaken by New Zealand Heavy Engineer Research Association (HERA) and Steel Construction New Zealand (SCNZ), with input from the University of Auckland. This paper describes the finite element analyses performed to determine the behaviour of the system including the bolted endplate connections through the range of inelastic cyclic loading expected. The numerical simulations answer a number of questions, like at which loading cycle the von Mises stress is above 300MPa in collector beam adjacent to the removable link; history of all bolt forces; component forces (shear) in slab and removable link; rotation of the link versus cycles; equivalent plastic strain contour for the last cycle and others. This paper also describes how the interaction with the concrete slab was modelled in the elastic and inelastic range.

Application of Fiber Bragg Grating Sensing Technology for Bolt Force Status Monitoring in Roadways

Bolts support have become a major active support method in coal mine roadways to control roadway roof failure and improve surrounding rock structure stability. The traditional bolt force status monitoring (BFSM) method has poor anti-interference performance, is easily affected by harsh downhole environments, and cannot support remote real-time monitoring. This paper presents a fiber Bragg grating (FBG) bolt force sensor that monitors the force of roadway bolts. This sensor uses a cantilever and a diaphragm as elastic elements and two FBGs bonded on the top and bottom surfaces of the cantilever as sensing elements. The experimental results indicate that the measuring sensitivity is improved by using the center wavelength difference between the two FBGs. The sensitivity is 38.79 pm/kN within the range from 0 to 150 kN, and the correlation coefficient reaches 99.98%. The engineering applications show that the FBG sensing technology can automatically acquire, and monitoring results are of great significance in roadway anchorage engineering safety and bolt support quality evaluation. Furthermore, such a sensor is also widely used in quasi-distributed measurement and long-term online monitoring of bolt force status in such fields as geotechnical engineering, tunnel engineering, and slope engineering.

Degradation of Axial Bolt Force caused by Creep Behavior

Degradation of Axial Bolt Force caused by Creep Behavior