Bolt Yield Research Articles

Navigating the depths: Experimental study on the influence of ground fissures on metro shield tunnels considering different intersection angles

Ground fissures are a typical slowly changing geological hazard that poses great safety risks to metro shield tunnels crossing ground fissures. To thoroughly analyze the deformation and failure of shield tunnels under the action of ground fissures with different intersection angles, this study reviews the existing research and carries out model tests on metro shield tunnels crossing ground fissures considering different intersection angles. Based on the experimental results and numerical simulations under multiple conditions, the deformation and failure characteristics of shield tunnels are systematically analyzed for the first time, which confirms that the activity of ground fissures can lead to a series of problems, including segment dislocation, lining cracking, structural elliptical deformation, bolt yield, joint opening and closing, void areas at the tunnel bottom in the hanging wall and tunnel top in the footwall, as well as resulting waterproof failure and internal gauge changes. In addition, as the intersection angle between tunnel and ground fissure increases, the failure mode of the structure gradually transitions from torsional failure to shear failure, with a decrease in the number of segment rings under bias pressure and an increase in the number of segment rings under shear effect. Based on the deformation characteristics, failure positions, and the changes of structural state of shield tunnels, some reflections on countermeasures are discussed, which can provide guidance for the design and maintenance of metro projects in ground fissure sites.

Guided wave-based damage assessment on bolt in precast beam-to-column joints

This paper deals with theoretical, numerical, and experimental investigations of guided wave-based damage assessment on bolts in the precast joints under cyclic loads. The mechanical behavior of precast bolted joints is analyzed, and the relationship between the force and drift ratio of the energy-dissipating (ED) bolt is derived. The propagation characteristic of guided wave in ED bolt is revealed through finite element simulation. The influence of tensile damage and looseness damage on the received signals is further studied, and two indexes are developed for evaluating the health status of ED bolts. Cyclic loading tests were carried out on four precast bolted beam-column joints with different precast beams, and the guided wave signals of ED bolts under each level of loading were monitored by arranging lead zirconate titanate (PZT) sensors. The bolt yield drift ratios were obtained by skeleton curves and FBG strain detectors respectively. The relationships between the two damage indexes and the drift ratio are obtained, and the two developed damage index trends were very well reproduced by analytical expressions. The health state assessment of ED bolts and precast bolted structures is realized by the proposed damage limit method, whether in daily maintenance or after the earthquake.

Three-dimensional analysis of steel beam-column bolted connections

Abstract The design of steel beam-column end-plate bolted connections is becoming increasingly popular owing to its simplicity of production. This requires knowledge of the full nonlinear resisting moment–rotation (M–Φ) behavior of the joint. To investigate the impact of various geometrical factors on the overall behavior of the connection, this work provides a three-dimensional finite element model (FEM) utilizing ABAQUS software. The suggested model accounts for the pretension force on the bolts, material and geometrical deviations from linearity, and the proximity of surfaces that are adjacent. The numerical model’s ability to simulate and process both the total and specific behavior of varieties of end-plate steel riveted connections is confirmed by calibrating the finite element findings with experimentally disclosed outcomes, which are reviewed in this study. The ultimate behavior was then investigated through a parametric study using the verified FEM with variations in the bolt pretension load, yield strength of the sections, and yield stress of the bolt considering the M–Φ curve. The results of the parametric study showed that as the bolt pretension load and yield stress of the column, beam, and plate materials increased, so did the connection’s moment ability. The yield tension of the bolts, however, had only a minor effect on the connection’s moment capacity.

Segment Thickness Design and Bearing Performance Analysis of Large Inner-Diameter Shield Tunnel under Lateral Unloading

In order to accommodate more transportation-supporting facilities, the expansion of structures’ inner diameter has become the development trend of metro shield tunnels. But for large inner-diameter shield tunnels, the segment thickness design and bearing performance characteristics of tunnels under lateral unloading are still unclear. The purpose of the research was to select the optimal segment thickness and clarify the bearing performance of large inner-diameter shield tunnels. Therefore, in this study, a 3D refined numerical model was established to analyze and determine the optimal segment thickness for a shield tunnel with an inner diameter of 5.9 m. Furthermore, a full-scale test was carried out to study the bearing performance of the shield tunnel under lateral unloading. The results showed that the maximum tunnel horizontal deformation difference between the calculation and the test did not exceed 5%, and the maximum difference in the overall structure deformation between the calculation and the test did not exceed 7%. Increasing the segment thickness can reduce the convergence deformation of the shield tunnel nonlinearly; the deformation reduction was no longer significant when the segment thickness increased to 400 mm with an inner diameter of 5.9 m. Under the lateral unloading condition, the internal force of the tunnel structure increased significantly at sections of 0°, 55°, 125°, and 190°. Compared with the normal design load stage, the maximum bending moment and axial force increased by 36% and 74.1%, respectively, in the final failure stage. There was no bolt yield during the entire unloading process, indicating that the excessive strength of the bolt could not fully play a role in the entire life cycle of the large inner-diameter tunnel structure. The failure mechanism of the shield tunnel can be described as follows: in the early stage of a load, a shield tunnel will appear with joints open and dislocated. As the load increases, cracks in different directions gradually appear near the tunnel joint. In the ultimate load stage, the shield tunnel loses load-bearing capacity, and large areas of falling blocks appear at the top and bottom of the tunnel.

Axial compression behaviour of circular concrete-filled double-skin steel tubular columns with bolted shear studs: Numerical investigation and design

The concrete-filled double-skin steel tubular (CFDST) columns have recently attracted significant attention for practical engineering constructions. The axial resistance behaviour of CFSDTs can be greatly enhanced by installing bolted shear studs as pin supports for the outer. This is a companion paper that expands on the authors' work [1]. The previous paper concentrated on full-scale experimental testing to ascertain the influence of bolted shear studs on the axial resistance of CFSDT columns, while this study focused on finite element (FE) analysis and a simplified design approach for such composite structural members. A three-dimensional FE model for predicting the axial behaviour of circular CFDST columns without and with shear studs was developed and validated using the test results of the specimens' typical failure mechanisms and load-displacement responses. The model was then employed to perform structural analysis by comparing the axial load-displacement curve, internal force distribution, longitudinal stress distribution over the sandwiched concrete, and confinement mechanism of a circular column with bolted shear studs with that of its counterpart without bolted shear studs. Parametric studies were carried out to examine the effects of bolt longitudinal spacing, diameter, length, and yield strength. It was found that the spacing of the bolts-to-width (bs/Do) ratio had significant effects on the axial resistance and ductile performance of columns. Also, a bolt spacing corresponding to bs/Do<0.44 was suggested to attain an acceptable ductile performance in practical application. Verification of the design model revealed that it led to satisfactory predictions of the ultimate strengths of circular CFDST columns without and with shear studs.

Genome-wide identification and characterization of the lettuce GASA family in response to abiotic stresses

BackgroundLettuce is one of the most extensively farmed vegetables in the world, and it prefers cool growing conditions. High temperatures promote premature bolt formation, reducing quality and yield. The gibberellic acid-stimulated Arabidopsis (GASA) family genes play critical roles in plant growth, development, and stress responses. However, the biological functions of GASA proteins in lettuce have yet to be thoroughly investigated.ResultsUsing genome-wide analysis, 20 GASAs were identified in lettuce including, three groups of LsGASA proteins based on the phylogenetic analysis. Except for one, all GASA proteins included a conserved GASA domain with 12 cysteine residues. Cis-element analysis showed that LsGASAs were closely associated with light, phytohormones, and stress resistance. Five segmental and three tandem duplication events were observed in the LsGASA family based on duplication analysis. GASA synteny analysis among lettuce, Arabidopsis, tobacco, and rice revealed that LsGASA5 is highly collinear with all species. Six of the 20 LsGASA showed increased expression patterns at specific time points in the shoot apical meristem when subjected to heat stress. According to gene expression analysis, the majority of GASA were highly expressed in flowers compared to other organs, and six GASA exhibited highly increased expression levels in response to NaCl, abscisic acid, and gibberellin treatment. Furthermore, LsGASA proteins are predominantly found in the plasma membrane and/or the cytosol.ConclusionsThis study provides a comprehensive characterization of LsGASA genes for their diversity and biological functions. Moreover, our results will be useful for further studies on the function of lettuce GASA in abiotic stress- and heat-induced bolting signaling.

Effects of deflection angle on the mechanical properties of constant-resistance, energy-absorbing, and anti-scouring bolts

In practice, constant-resistance, energy-absorbing, and anti-scouring bolts inevitably deflect at an angle from the coal wall and other bearing surfaces, eventually giving way and losing their energy-absorbing function. The aim of this study was to determine the applicable range of deflection angles for constant-resistance, energy-absorbing, and anti-scouring bolts and to provide a reference design for bolt construction. The principle of application of bolts under various deflection angles was proposed, and the numerical simulation of use of constant-resistance, energy-absorbing, and anti-scouring bolts was carried out using ABAQUS finite element software. The effects of deflection angle, impact energy, and impact velocity on the deformation performance, load-bearing performance, and energy absorption performance of the bolts were investigated. The deformation process of the bolt based on deflection angle was found to change from axial stretching to “stretching and bending”. As the deflection angle increased, the load bearing capacity of the anti-punching device increased, and the bolt’s breaking force increased after decreasing, and then decreased again while absorption energy decreased non-linearly. The bolt yield distance decreased while the displacement of bolts remained essentially the same and the deflection distance of the anti-punching device decreased. The stroke efficiency of bolts decreased and, based on the design principles of constant-resistance, energy-absorbing, and anti-scouring bolts, it was determined that the bolt was still applicable within a deflection angle of 0–17°. The impact energy had a minor effect on the bolt indicators of yield force, breaking force, and energy absorption, and the bolt’s impact resistance time decreased non-linearly with increasing impact energy. Impact velocity had less effect on bolt yield force and breaking force. Both yielding time and anti-punching load capacity of the bolt decreased with increased impact velocity. As the impact velocity increased, yield distance, anti-punching deflection distance, and stroke efficiency all increased. The absorption energy increased linearly with increasing impact velocity. The results of this study provide a reference for similar anchor angle studies and a guide for the design of field construction.

Effect of rolling angle on segment cracking and damage of shield tunnel - field investigation and modelling

Based on a curved shield tunnel, this study classified the grades of segment cracking and damage during the construction and counted the segment cracking and damage. Combined with the data of tunnelling parameters, the significance of segment cracking and damage factors was analysed by the ordered multi-classification logistic regression method. Furthermore, the refined finite element numerical model was established to study the damage mechanism of the segment under the rolling angle. The results indicate that the analysis results of numerical simulation correspond to the field phenomena, which confirms that the rolling angle is a critical factor affecting the segment disease. The total stiffness of the segment attenuates significantly after torsion. When the torque is 43580.17 kN·m, the maximum longitudinal bolt stress connecting the segment out of the shield shell and the segment in the shield shell reaches 619.6 MPa, close to 640 MPa of the bolt yield stress.

Seismic behavior and design of repairable precast RC beam–concrete-filled square steel tube column joints with energy-dissipating bolts

The dry jointed precast frame structure has the potential in less reliance on wet concrete, low cost and repairability after earthquake. The seismic behavior of the novel precast dry connections with different beam end arrangements was studied in this work. For the precast specimens, the concrete-filled square steel tube (CFSST) column and RC beam were prefabricated, and field assembly was carried out by energy-dissipating (ED) bolts and unbonded prestressed tendons. Design equations were formulated according to the strong-column–weak-beam concept and the capacity design philosophy. The viability of the repair method of the precast internal beam–column connections after earthquake was explored. The joints were repaired by replacing the ED bolts and loaded again. The seismic indicators, such as ductility and energy dissipation capacity, were determined and compared. The results showed that the excellent structural characteristics and practical design method could ensure low damage to the joints except for the ED bolt yield. The new-type precast beam–column joints exhibited good hysteretic performance with high ductility factors greater than 5. After repair, the failure mode of the joints was controlled by the plastic hinge on the beam. The repaired joints had good strength stability, and the ultimate bearing capacity was the same as before repair. The ductility of the repaired joints was 13.29%–32.14% higher than before. The energy dissipation capacity could reach more than 1.2 times that of the cast-in-place concrete joints, which proved the feasibility of the repair method.

Full-scale test on seismic performance of circumferential joint of shield-driven tunnel

A shield-driven tunnel is deformed along the longitudinal direction when subjected to seismic loadings; the circumferential joint is the key position of the shield-driven tunnel when such longitudinal deformation occurs. In this study, the variations of the internal forces (including both axial forces and bending moments) in the longitudinal direction of the tunnel are analyzed through a numerical method based on the longitudinal equivalent continuous model (LECM). The results show that the internal forces of the tunnel are mainly an axial force caused by longitudinal excitation, and a vertical bending moment caused by transverse excitation. Based on the stress distribution of the circumferential joint, a full-scale test is conducted, and the test results are compared with those obtained by a refined numerical model with 16 segmental rings. It is shown that the variation of the opening and bolt strain of the circumferential joint follows that of the internal force. When the tunnel is subjected to longitudinal tensile forces or bending moments, the distribution rules for the bolt stress at the position of the largest opening are essentially the same. Moreover, the distribution characteristics of the concrete strain on the segment surface at the position of the largest opening are essentially the same. The maximum tensile strain appears on the outer surface of the sleeve side segment. However, the maximum compressive strain appears on the inner surface of the hand hole side segment. The maximum principal stress and damaged plasticity of the segment generally appear near the sleeve and hand hole, and have a limited influence on the segment surface. Finally, a failure test shows that the segment becomes damaged before the bolt yield, with more severe damage occurring in the sleeve side segment.

Experimental study on tensile behavior of blind bolt

AbstractAs blind bolt can be installed only on one side, it has the advantage that ordinary high strength bolt doesn't have in the application of closed section connection. In this paper, the existing non‐standardized sleeve high strength blind bolt (NSHSBB) is improved, and standardized sleeve high strength blind bolt (SSHSBB) and small diameter blind bolt are put forward, and the tensile tests of two kinds of bolts of 8.8 and 10.9 grades with diameters of 12mm, 16mm and 20mm are carried out. It is clear that the tensile process of blind bolt can be divided into three stages by analyzing it, and the tensile stiffness and boundary loads of three stages are obtained, that is: steel plate separation load, bolt yield load and tensile bearing capacity of blind bolt. By adjusting the installation torque, the separation loads of steel plate under different torques of each blind bolt are obtained, and the relationship between the pre‐tension and the separation load of steel plate and the two stages stiffness is clarified by deducing formulas. According to the above results, the recommended installation torque and pre‐tension of blind bolt are given. The bearing capacity of blind bolt is equal to that of high strength bolt of the same grade, and its stiffness is lower than that of high strength bolt, which has little influence on the rotational stiffness of the joint is very small yet, based on the analysis.

Safety assessment of cable bolts subjected to tensile loads

Cable bolts are one of the most common tension anchorage systems for reinforcing the stability of rock/soil masses; however, the quantitative assessment of cable bolt safety via numerical simulations has not been deeply explored until now. In this technical study, a bolt tri-linear tensile model and a bolt–grout (B–G) interface tri-linear shear model were integrated into a cable bolt tri-linear model to reflect the large tensile deformation-broken failure of the bolt and the B–G interface slip-softening failure after cable bolt yielding. A dimensionless index was developed by defining the maximum of the failure approach index (FAI) for bolt tensile failure and the FAI for B–G interface shear failure based of this cable bolt model to quantitatively assess the cable bolt safety. The comparison between the laboratory and numerical test results and engineering case analyses showed that the cable bolt FAI combined with the cable bolt tri-linear model, which could quantify the cable bolt safety and determine the cable bolt failure position and sequence as an improved substitute for cable bolt yield state indicators in numerical simulations. The present study is expected to offer a more accurate numerical simulation technique than existing simulation techniques in the quantitative assessment of cable bolt safety, finally contributing to the quantitative evaluation-based support design.

Experimental and numerical investigations of the plastic response and fracturing of an aluminium-plated structure with transition circular arcs subjected to impact loading

A new aluminium-plated structure with transition circular arcs used for railway vehicles is presented. Two impact experiments were performed using a test trolley to examine the plastic response and fracturing of the aluminium-plated structure. The results show that the deformation mode of the aluminium-plated structure switches from global plastic bending deformation to local fracturing at the transition circular arc region, which is consistent with the design. Numerical results are presented in terms of deformation modes, force responses and levels of absorbed energy, demonstrating good agreement with the experimental results. From the results of the numerical simulation, fracturing processes and variations in element stress triaxiality are presented. It is found that the stress state of elements affecting the initiation of cracking is of a tension state, while the stress state of elements affecting the end of cracking is of a shear state. A validated finite element analysis of an aluminium-plated structure with right-angled, circular arcs and chamfering transition sections is presented. Plastic and fracture energy levels of the aluminium-plated structure with three transition sections are measured as 2.56, 27.62, and 30.13 kJ and 0.98, 2.41, and 2.16 kJ, respectively, as the second fracturing point. Finally, the finite element analysis illustrates the impact energy effects involving different combinations of trolley mass and velocity, and experimental boundary conditions for varying bolt yield stress and pre-stress levels are defined in the finite element model to investigate the effects of bolted joints on the dynamic responses of an aluminium-plated structure with transition circular arcs.

Full-scale tests on bending behavior of segmental joints for large underwater shield tunnels

This paper presents an experimental and numerical study on the bending behaviour of segmental joints for large underwater shield tunnels. A series of full-scale tests of segmental joint for underwater shield tunnel are carried out to investigate the bending performance under compression-bending loads. And comparative numerical simulations are conducted to compare with the test results and analyze the occurrence and development process of joint failure. The results indicate that the joint opens linearly and deforms nonlinearly after the visible concrete cracking occurred, the shape of joint interface is a curved surface during joint opening. The time when the bolt becomes stressed depended on axial force, and the bolt stress increased linearly with the growth of bending moment. Joint bending stiffness can be divided into three stages according to turning point of 'visible concrete cracking' and 'bolt yield', large axial force has a great influence on keeping it. The joint waterproof material could hardly promote the bending stiffness and capacity of segmental joint for its small rigidity. The failure process of segmental joint was different between under positive and negative bending moment, the compressive capacity of concrete in compression zone near the intrados played a vital role in the process of improving the bending capacity of segmental joint. The numerical results of joint opening and bending stiffness were in good agreement with tests during small deformation stage, while after visible cracking the results differ relatively. It is reasonable to simulate joint bending performance before visible concrete cracking, and estimated joint failure mode and its approximate range by using the proposed numerical model.

A Simplified Method for the Design of Steel Beam-to-column Connections

The moment resistance of beam-to-column connections is frequently utilised in steel structures. Eurocode 3 suggests the component method to analyse such connections, and it implements the equivalent T-stub method to determine the resistance of the end plate of the beam. The latter method requires tedious and concentrated work. A simplified method is suggested to reduce the number of calculations and enable the designer to focus on construction aspects in the pre-design phase, or in education.The resistance of the T-stub covers three possible failure modes: the yield of the plate, the failure of the of the bolt and simultaneous yield. The yield of the plate and simultaneous yield depend on numerous parameters, and they are verified by multiple equations. The failure of the bolts are more easily checked.In the present paper, requirements for geometric ratios are defined for the widely used steel sections to assure failure of the bolts at a lower level of the load than the yield of the plate. These parameters facilitate the simple calculation of the resistance of the bolts instead of the tedious work needed for the end plate resistance.The paper presents a proper explanation for the design rules and the effect of the geometric parameters on the resistance of the end plate. Geometric parameters are suggested for the widely used hot rolled and typical welded beam sections. All the parameters fulfil the requirements of the equivalent T-stub method of Eurocode 3.

Influence of Semi-Circular Cracks on Threaded Connection Fatigue by Means of Kitagawa-Takahashi Diagram and El Haddad Equation

Evaluation of semi-circular surface crack influence on threaded connection fatigue behavior, made of 42CrMo4 heat treatable steel, was carried out. Crack diameters were defined as 0.02, 0.05, 0.1, and 0.15 mm. Influence of semi-circular surface cracks was investigated by means of Kitagawa–Takahashi diagram and El Haddad equation. Assessments were done for survival probability of 99% on detailed FE model with normal metric thread profile and preload force at 70% of force at bolt yield point. The most critical location on threaded connections usually are thread roots which contain a very high notch effect. In order to accurately consider multiaxial stress field in thread root, multiaxial fatigue stress criterion based on a critical plane theory for fatigue assessment, was used. Mean stress influence was taken into account by means of Haigh diagram. Variable amplitude loading history of low-high (Lo-Hi) sequence spectrum was analyzed with the numerical algorithm of Rainflow cycle counting in the time domain. Fatigue damage was calculated according to the modified Palmgren-Miner linear damage accumulation hypothesis.

Structure Analysis for Tunnel Longitudinal Deformation Based on Segment Dislocation Mode

According to tunnel structure around joints, tunnel longitudinal deformation is analyzed and a three-dimensional finite element model is built based on segment dislocation mode. Tunnel structure stress analysis is conducted from two aspects of segment in the shear and bolt in the tension. The analysis results show: (1) Segment shear model. When segment dislocation reaches 0.03mm, the principal stressσ1 exceeds 3.0Mpa which is over concrete's tensile strength. Therefore, when convex tenon and concave tenon generate shear, there must be horizontal slipping and bolt is tensioned. (2) Bolt tension model. When joint opening value reaches 2mm, bolt stress exceeds 640Mpa, which is bolt's yield strength. When joint opening value reaches 6mm, which is the waterproof control standard for tunnel, bolt stress reaches 688.7Mpa, which is less than bolt's failure strength. The subway tunnel's structure safety should be controlled from the perspective of waterproof.

Fatigue Strength of Bolted Joints

This paper summarizes the results of 400 fatigue tests of high‐strength bolted joints that were reported in eight domestic and six foreign studies. The following variables were investigated: type of bolt and washer, bolt pattern, bolts‐to‐member strength ratio, initial bolt tension, yield strength, skew, joint length, and partial connection of member elements. The analysis of the data showed that within the limits on maximum stress imposed by the American Association of State Highway and Transportation Officials (AASHTO) specifications on edge distance, bolt spacing, etc., both friction‐type and bearing‐type joints can be designed to Category B on the basis of the gross area stress range. The fatigue of long bolted joints with more than four bolt rows in a line of stress must be lowered from Category B to C. The stress range in members that transfer load through some, but not all, cross‐sectional elements must be calculated using a reduced effective gross area.

Bearing Strength of Bolted Timber Joints

Design values for bolted timber joints are empirically based on research conducted over 50 years ago. The analytical and experimental results of this study confirm that the previous recommendations are still valid. The analytical method used in this study, the European yield theory, explains much of the observed behavior of bolted timber joints and can be used for material properties not included in the original research. It also incorporates the effect of bolt yield stress, which is not considered in current design.

高力ボルト引張接合に関する研究 : その一 ボルト初張力の影響

The influence of initial bolt tension upon the mechanical characteristics of bolted connections are investigated by using simple specimens, of which bolts have different initial tension, and idealized model. The main results are as follows. 1) The separation load is in proportion to initial bolt tenssion without regard to the magnitude of initial bolt tension. 2) The ultimate strength of the bolted connection is constant regardless of the magnitude of initial bolt tension. 3) In order to keep the behavior of bolted connection in reversible condition, the limit of repeated loads is restricted under the elastic proof load of bolts. when the connection is subjected to the load, which gets beyond the elastic proof load of the bolts, the reduction of residual bolt tension, separation load and the rigidity of the connection take flace after unloadindg. The degree of those reduction changes according to the total deformation of the connection after separation. So the degree of those reduction is small, when bolts have large initial tension. Judging from the general test results, the magnitude of initial bolt tension has great influence upon the mechanical characteristics of bolted connection. So initial bolt tension is recommended to be large, but there is no advantage, when the bolt are stressed in plastic range. Finally the recommended initial bolt tension is as large as the bolt yield load.