Strength Bolts Research Articles

Failure analysis of fractured motor bolts in high-speed train due to cardan shaft misalignment

Motor of high-speed train is normally connected with suspending devices through bolts. This paper presents an investigation of six motor connecting bolts, based on GB/T 3077 standard and strength grade of 8.8, which fractured at the thread close to the contact surface of motor and suspending device before the designed service life. The investigation includes macro examination, chemical compositions analysis, tensile tests, hardness tests, metallographic examinations were used to analyze the cause of fracture. The results revealed that the strength and material of bolts met the standard, no metallurgical defect was found in examination, and the bolts fractured were due to alternating load. According to the spectrum of acceleration signal measured by the sensor mounted on the motor housing and subsequent inspection of the cardan shaft and rotor of motor, revealed the alternating load is caused by misaligned cardan shaft. Further dynamic analysis shows that the rotation of misaligned cardan shaft resulted in huge unbalance force. To confirm the findings, finite element analysis on the bolts subjected to pre-tensile load reveals that the materials at the bottom surface of the first thread suffered high alternating stress and reaches the fatigue limit. From the above findings, this paper proposes an innovative strategy to avoid similar accidents of high-speed train suspending devices.

Finite Element Analysis on Shear Behavior of High-Strength Bolted Connectors under Inverse Push-Off Loading

High-strength bolted shear connectors (HSBSCs), which can be demounted easily and efficiently during deconstruction, are recommended to replace the conventional steel studs in steel–concrete composite beams (SCCBs) to meet the requirements of sustainable development. The existing investigations on the behavior of HSBSCs mainly focus on the positive moment area of composite beams, in which the concrete slab is in compress condition. In this paper, a three-dimensional finite element model (FEM) was developed to investigate the performance of HSBSCs subjected to inverse push-off loading. Material nonlinearities and the interactions among all components were included in the FEM. The accuracy and reliability of the proposed FEM were initially validated against the available push-off test results. Load-carrying capacity and load–slip response of the HSBSCs under inverse push-off loading were further studied by the verified FEM. A parametric study was carried out to determine the influence of the concrete strength, the diameter and tensile strength of bolt and the clearance between the concrete slab and the bolt as well as the bolt pretension on the shear performance of HSBSCs. Based on the extensive parametric analyses, design recommendations for estimating the shear load at the first slip and load-bearing resistance of HSBSCs were proposed and verified.

Study on Safety Performance of Building Finish Layer under Thermomechanical Coupling Condition

The building finish layer is a comprehensive structural system including the building exterior insulation system and building exterior finish. Combining with buildings has the advantage of reducing wall heat loss and building deformation caused by large temperature differences. Since the building finish layer is prone to cracking, hollowing, and peeling, during the application process, its safety needs to be studied and certified. This study prepares 20 groups of specimens, 15 anchor bolts in each group. The anchor bolt pull‐out strength test is carried out. Anchoring damage evolution law and failure mode of anchor bolts are investigated. And the influence of anchoring methods on the pull‐out bearing capacity is analyzed. In addition, ABAQUS finite element data simulation is carried out. The stress state of finish in thermomechanical coupling condition and without the effect of temperature are compared and analyzed. The influence factors of anchor bolt pull‐out strength and the influence of temperature load on the long‐term performance of building finish layer are obtained. The durability of the building finish layer is analyzed. The results show that the anchoring strength of the anchor bolt is positively correlated with the anchoring depth. The anchoring strength is influenced significantly by anchoring construction sequence and temperature. The stress under the coupled effect of temperature and load is greater than that of the single effect of load, and the stress distribution changes significantly. Due to thermal expansion and contraction, the anchor bolt would loosen, which is more prone to damage the building finish layer in a low temperature environment. The weight relationship of each influencing factor of the building finish layer is proposed. A systematic evaluation index system is established. The results of this study provide a basis for subsequent related research work and engineering applications.

A study on the extreme value distribution of the minimum tensile strength of bolt

Taking M12.5 × 1.25 × 65-10.9 bolt as an example, this paper studies the extreme distribution of the minimum value of bolt tensile strength in order to evaluate the reliability and stability of bolt product quality and to verify the production process. Through data collection, parameter estimation, distribution test and extreme prediction, it is concluded that: 1) the distribution of the minimum value of bolt tensile strength conforms to Gumbel extreme distribution; 2) when the return period is 10000, the predicted minimum tensile strength is 1071.7 MPa ± 3.2 MPa, k = 2. It is higher than the minimum value of 1040 MPa required by ISO 898-1 standard.

A study on structural performance of deconstructable bolted shear connectors in composite beams

An experimental study according to EC4 on deconstructable steel-concrete composite bolted shear connectors is carried out to investigate the effect of various bolt size, concrete strength, bolt strength and clearance size between the precast concrete slab and bolt on the static behaviour of this type of composite connection. Shear load capacity for the first bearing, average major slip at the first bearing, maximum shear load capacity per bolt, slip corresponding to the maximum shear load capacity, maximum average slip between the precast concrete slab and steel beam and failure modes are assessed. A total of 12 composite specimens were tested according to EC4 with different parameters using deconstrcutable bolted shear connectors. In addition, two steel-concrete composite connection specimens using welded headed stud shear connectors were tested as control specimens to determine the influence of prefabricated concrete panels and deconstructable friction-grip bolted shear connectors on the performance of the steel-concrete composite connection. The experimental results show that deconstrcutable steel-concrete composite bolted shear connectors have completely different behaviour compared to welded headed stud shear connectors. Furthermore, a 3D finite element model of the steel-concrete composite connection having precast concrete slabs and deconstructable bolted shear connectors was performed. Numerical model was verified against experimental results, and was shown to accurately simulate their observed structural behaviour.

NON-DESTRUCTIVE APPROACH TO THE BOLT JOINTS QUALITY CONTROL

Bolted connections are often used to connect structural elements in steel, wood and reinforced concrete structures. In structural inspecting, there is often no marking on bolted joints. So, it is necessary to determine the bolt strength to assess the bolt joint bearing capacity. The bolt strength can be determined by destructive and non-destructive methods. The article presents the experimental research to determine the bolt strength using the scratch method and compares the results with the destructive method (bolt breaking).

Experimental Research on the Mechanical Performance of the Bolted Rock under Lateral Impact Load: Effect of Prestress, Body Material, and Anchorage Style

In order to reveal the impact mechanical properties and their key influencing factors of the bolted rock under the lateral impact load, through the lateral drop hammer impact test, the time-history curve of impact force, axial force of the bolt, and surface strain of the sample under different combination types of influencing factors is obtained, and the whole process of deformation and failure of the bolted rock is recorded. The test results show that the material of the bolt has a significant influence on the impact force and axial force of the bolt. There is a positive correlation between bolt strength and impact peak and impact attenuation slope and a negative correlation between bolt strength and impact action time. The effect of prestress on the impact resistance of the bolted rock was also evaluated by the test which suggested that prestress of the bolt can significantly reduce both impact time and bolt axial force of the bolted rock but has limited effect on the impact force. It was also found that the time-history curve of the impact force of anchoring rock mass had significant difference with full-length anchoring and nonanchoring. Compared with the nonanchoring bolt, the full-length anchored rock mass has a larger impact peak and shorter action time, which means that the impact resistance of the full-length bolted rock has a certain degree of weakening. Through scientific research, determining the reasonable bolt material, prestress value, and anchorage style can improve the impact resistance of the sample.

Analytical model for concrete cover separation of FRP strengthened RC beams with multiple steel bolts

AbstractIn this paper, analytical models for concrete cover separation (CCS) of FRP strengthened reinforced concrete (RC) beams with multiple steel bolts were developed based on concrete tooth model for strengthened RC beams without anchors. The derivation of the models involved three major steps: (a) determination of the crack spacing (width of the concrete teeth); (b) determination of the pull‐out strength of steel bolt considering the effect of shear crack; and (c) determination of the peak load of FRP strengthened beams when CCS occurs based on the concrete tooth model. Validation test on five RC beams was conducted to investigate the effect of anchorage systems on the premature debonding of FRP strengthened RC beams. Results showed that steel bolts with enough embedding length can effectively suppress the initiation and propagation of CCS, thus improve the performance of FRP strengthened RC beams. Moreover, a database of FRP strengthened RC beams with mechanical fasteners (MFs) and failed in CCS or FRP fracture (FR) was assembled from the literature. The analytical predictions agreed well with the experimental results.

Numerical Analysis of Anchor Bolt Pull-out Test by Cohesive Zone Model Combined with Finite Element Method

In this paper, to characterize the pull-out process of anchor in concrete, we combined the cohesive zone model and the finite element method. The embedding cohesive elements simulate the contact effect of the bolt interface. The results show that the numerical predictions are in good agreement with the experimental results. With the change of pull-out load, the shear stress of anchorage interface changes correspondingly until it is destroyed, which is consistent with the laboratory test. The strengths of the anchorage material and the concrete have a positive correlation with the bond strength of anchor bolt. The radial and lateral stresses acting along the bolt are similar. Therefore, in bolt anchorage, the bond strength increases as the radial (lateral) stresses increase.

Glass-fibre-reinforced polymer: the low carbon dioxide option for permanent rock bolts

Traditionally steel has been used for rock bolts in tunnelling. Faced with the challenge of reducing mankind's environmental impact, it is necessary to look at using better alternatives. Glass-fibre-reinforced polymer (GFRP) has been used for many years in tunnelling applications, primarily for temporary applications. GFRP has many advantages such as its excellent durability characteristics, its light weight, which reduces manual handling impacts on workers in the tunnel, and its lower environmental impact. One obstacle to the more widespread adoption of GFRP for permanent applications has been a concern over its performance in shear. It is well understood that during shearing the rock bolts actually deform under bending and the tensile strength of the bolt governs the behaviour. This paper will describe a new design method to account for the benefit of the bolts in resisting shearing on discontinuity planes. This method can be used in numerical models to demonstrate that GFRP bolts function as well as steel bolts in terms of resisting both tensile and shear loading from the rock mass. This opens the path for the wider use of GFRP rock bolts, which offer superior durability and a lower environmental impact.

Numerical Investigation of Effect of Rock Bolt Angle on Shear Behavior of Rock Bridges

In this work, the effect of rock bolt angle on the shear behavior of Rock Bridges is investigated using the particle flow code in two dimensions (PFC2D) for three different Rock Bridge lengths. Firstly, the calibration of PF2D is performed to reproduce the gypsum sample. Then the numerical models with the dimensions of 100 mm * 100 mm are prepared. The Rock Bridge is created in the middle of the model by removal of the narrow bands of discs from it. The uniaxial compressive strength of the Rock Bridge is 7.4 MPa. The Rock Bridge lengths are 30 mm, 50 mm, and 70 mm. The rock bolt is calibrated by a parallel bond. The tensile strength of the simulated rock bolt is 360 MPa.One rock bolt is implemented in the Rock Bridge. The rock bolt angles related to the horizontal axis are the changes from 0 to 75 degrees. Totally, 18 models are prepared. The shear test condition is added to the models. The normal stress is fixed at 2 MPa, and the shear load is added to the model till failure occurs. The results obtained show that in a fixed rock bolt angle, the tensile crack initiates from the joint tip and propagates parallel to the shear loading axis till coalescence to rock bolt. In a constant Rock Bridge length, the shear strength decreases with increase in the rock bolt angle. The highest shear strength occurs when the rock bolt angle is 0°.

Strength and Deformation Properties of Low-Alloy Steel Bolts with Electroless Ni-P Coating: An Investigation of Two Thermal Routes

Low-alloy steel bolts are used in applications where high strength is needed, although they presented low corrosion resistance, limiting their application in harsh environments. Ni-P coatings could be an alternative to protect low-alloy steel bolts against corrosion. However, Ni-P coatings must be submitted to an interdiffusion post-heat treatment, which provokes severe microstructural changes in the steel substrate, lowering its strength. This research aims to investigate two new thermal routes to obtain Ni-P coatings on low-alloy steel bolts, aiming to preserve the steel substrate's resistance and deformation properties, addressing the ASTM A320/L7 requirements. The first route proposed consists of obtaining the Ni-P coating on an austempered steel substrate, instead of a quenched/tempered one. This approach resulted in less microstructural changes during the post-heat treatment, although poor impact properties were achieved. The second thermal route consists of Ni-P coating on a quenched substrate, followed by a single-step post-heat treatment aiming to temper the substrate and promote the coatings' interdiffusion at the same time. The single-step post-heat treatment performed at 600 °C for 4 h resulted in appropriated mechanical properties while assuring the creation of a proper coating/steel interdiffusion layer, showing the feasibility to use Ni-P coatings in low-alloy steel to be used in harsh environments.

Analysis of the causes of accidents of the VIPO 32-01 hydraulic lift

With the development of technologies, the number of accidents related to construction machines in one way or another increases. The article deals with the analysis of the causes of accidents of the VIPO 32-01 auto-hydraulic lift. According to the results of engineering and technical expertise, the cause of the accident was a break in the connection of the two upper traction chains with anchor bolts fixed to the main section of the boom. During this break, there was a spontaneous movement of the third and fourth sections of the telescopic boom of the auto-hydraulic lift. The main reason for the lack of strength of anchor bolts of the upper traction chains according to the results of the research was the use of steel grades with insufficient strength characteristics in their manufacture. Material did not have sufficient load-bearing capacity in the cross sections of the eyes of anchor bolts intended for fastening chains, for the perception of the calculated forces in the traction chains.

Numerical study on the behaviour of vertical bolted joints for precast concrete wall-based low-rise buildings

This paper presents a numerical study on the cyclic behavior of the vertical bolted joints in low-rise precast concrete buildings. A finite element analysis model was developed for predicting the cyclic behavior of the joints which was proved with the experimental results. A step-by-step procedure was developed to carry out the finite element analysis for the contact analysis in the bolted connections. The developed approach was then applied for a parametric study to investigate the effects of main structural design factors on the joints, including the number of bolts per joint, the compressive strength of concrete, the yield strength and diameter of bolts, the thickness of blocks, the yield strength and thickness of gusset plates, the clearance of bolt as well as the arrangement of bolts in joints. Results show that the number of and the properties of steel bolts both have a significant influence on the connection performances of and the failure modes of the joints. Based on the analysis results, a smiplified model was proposed for predicting the shear capacity of the bolted joints which was expected to improve the design of proposed low-rise precast concrete buildings.

Variasi Spasi Baut terhadap Kuat Geser Sambungan Baut pada Pelat Baja

Errors in planning the spaces/distances between the bolts can weaken or create defects in the connection. Therefore, a research on the effect of bolt space on shear strength of bolt joints on steel plates is needed to find out the influence of the distance between bolts to the strength of double bolt joints on steel plate joints, whereas the long-term goal of this study is to determine the effect of the distance between bolts to the strength of the bolt connection in a plate connection system having more than two bolts. In the planning, the connection used bolt connecting devices that meet SNI 1729:2015 requirements. A tensile testing machine was used and the direct test method was conducted for shear strength of bolts in the plate joint system using two bolts. The bolt sample was installed in the plate connection system then the connection system was given a tensile load until it broke in the bolt sample. The peak load of the experimental results indicated the shear strength of the double bolt connection on the plate fluctuates. Average peak load for the sample of group I (20 mm bolt space), group II (40 mm bolt space), group III (60 mm bolt space), group IV (80 mm bolt space) and group V (100 mm bolt space) are 21.962 kN, 23.512 kN, 22.925 kN, 23.725 kN and 22.975 kN, respectively. The experimental results from each sample group showed the average peak load strength was greater than the theoretical shear strength value of 17.4974 kN.

A Review of Bolt Tightening Force Measurement and Loosening Detection.

Pre-stressed bolted joints are widely used in civil structures and industries. The tightening force of a bolt is crucial to the reliability of the joint connection. Loosening or over-tightening of a bolt may lead to connectors slipping or bolt strength failure, which are both harmful to the main structure. In most practical cases it is extremely difficult, even impossible, to install the bolts to ensure there is a precise tension force during the construction phase. Furthermore, it is inevitable that the bolts will loosen due to long-term usage under high stress. The identification of bolt tension is therefore of great significance for monitoring the health of existing structures. This paper reviews state-of-the-art research on bolt tightening force measurement and loosening detection, including fundamental theories, algorithms, experimental set-ups, and practical applications. In general, methods based on the acoustoelastic principle are capable of calculating the value of bolt axial stress if both the time of incident wave and reflected wave can be clearly recognized. The relevant commercial instrument has been developed and its algorithm will be briefly introduced. Methods based on contact dynamic phenomena such as wave energy attenuation, high-order harmonics, sidebands, and impedance, are able to correlate interface stiffness and the clamping force of bolted joints with respective dynamic indicators. Therefore, they are able to detect or quantify bolt tightness. The related technologies will be reviewed in detail. Potential challenges and research trends will also be discussed.

Stainless steel bolts subjected to combined tension and shear: Behaviour and design

Stainless steel (SS) bolts have become increasingly popular in steel construction industry primarily due to their excellent corrosion resistance and compatibility with other SS structural members. However, to date there is still very limited knowledge on the mechanical behaviour of these types of bolts as structural connections. As a result, practical design guidelines for SS bolts are direct extrapolation of those of carbon steel bolts. Moreover, these guidelines were initially proposed for most commonly used SS bolt grades, i.e. austenitic bolts with property class up to 80 (800 MPa ultimate strength), while their applicability to higher strength and duplex SS bolts are still not clear. To close the gap, this study presents detailed experimental and numerical investigations on the behaviour of austenitic and duplex SS bolts under combined tension and shear, with an emphasis on high strength grades (with ultimate strength higher than 800 MPa). Three phases of experiments were conducted including machined coupon tests, pure tensile tests, as well as combined loading tests. The failure mode, strength and ductility of SS bolts under different combinations of tension and shear were evaluated based on test results. In addition, finite element models were applied to simulate the behaviour of SS bolts up to final failure. Detailed numerical analysis was thereafter carried out to extend the experimental database and study the effects of a few key parameters which were not included in the experiments. Based on the available test and analytical data, the applicability of existing design methods was assessed in predicting the strength of SS bolts (including both common and high strength grades) under combined loading. Improved design formulae were proposed accordingly.

Design and optimization of noise barrier based on mechanical analysis of ANSYS

In order to ensure the structural strength of the noise barrier and optimize its design, in this paper, the Finite Element Analysis software ANSYS is used to model the noise barrier, and the mechanical properties are analyzed. The effects of different numbers of reinforcing ribs on the deformation and stress of the noise barrier under natural wind are studied. From the perspective of wind load, load bearing and bolt strength, the number of reinforcing ribs of the noise barrier is optimized. The results show that the structural strength of our self-developed noise barrier can meet the requirements. This design method provides guarantee for the future engineering design and application.

Reinforcing effects of 3D printed bolts on joint-separated standard soft rock specimens

Many studies have used numerical models, analytical models and laboratory models to investigate the factors influencing the shear strength of bolted rock joints. This study presents the preparation of a reinforced standard cylindrical specimen containing a joint; the jointed specimen was reinforced with a 3D printed (3DP) rock bolt and planting-bar anchorage glue. The surface profile of the 3DP rock bolt was identical to that of an actual rock bolt, and the strength of the 3DP bolt was satisfactory. Afterwards, the digital image correlation (DIC) method was applied to capture the changes in the strain/displacement fields on the surfaces of the specimens during testing. In addition, two pressure sensors (PSs) were attached to the external threaded sections of each 3DP bolt; these PSs recorded the changes in the load at the bolt ends positioned in the upper section above the joint plane and in the lower section below the joint plane. The influences of the joint plane and joint angle on the cracking process, DIC changing pattern, and stress-strain evolution were comprehensively discussed. The research approaches proposed in this study provide new methods with which to investigate the reinforcement effect of bolts on jointed rock masses, the results of this study can be used as a reference in engineering areas where jointed rock masses must be reinforced by rock bolts.

Dimensional Tolerances and Length Determination of High-Strength Bolts

Structural engineers and detailers are often removed from the process of manufacturing bolts, and thus the tolerances and variances that go along with common manufacturing processes. While this does not represent a problem in most cases, being familiar with the manufacturing processes and tolerances associated with high-strength bolts can help prevent some problems from occurring before the design process even begins, particularly when shorter bolt lengths are needed. This lack of familiarity, in some circumstances, might lead to mistaken assumptions regarding the location of the shear plane relative to the threads of the bolt, which may lead to incorrect designs. While an engineer might presume that bolt strength would not control in such short grips, this paper will discuss the cases in which this can become an issue. This paper summarizes the major variances between nominal and actual dimensions, evaluates some of the consequences that those variances can have on design, presents solutions to those issues, and culminates with a proposed design procedure for proper length determination of high-strength bolts with several illustrative examples.