Numerical Simulation Study on the Influence of Mine Earthquake on the Bolt Stress

Mine earthquake, as an underground disaster that occurs frequently, has a great impact on coal mine roadway and support. The stability analysis of the bolt support in roadway under different mine earthquake magnitudes is a key issue to be solved urgently in mining fields. This paper attempted to simulate the occurrence state of mine earthquake with explosive blasting process and verified it with actual coal mine microseismic monitoring data. ANSYS/LSDYNA software was used to analyze the impact of magnitude and location of mine earthquake hypocenter on the stability of bolt support and the dynamic stress characteristics of bolt. The results showed that with the increase in source energy of mine earthquake, the damage location of bolt mainly appears in the front of bolt and the loading position has no obvious change, but there is stress wave superposition effect, which deepens the damage of bolt. The bolts in the middle of the lane and the middle of the roof are greatly affected, so the support strength should be strengthened in these places. In addition, this paper compared the safety factor of bolt and the supporting effect of different schemes from three aspects such as roof subsidence, axial stress of bolt, and safety factor of bolt and then put forward a more economical and effective supporting scheme.

Research of the Surrounding Rock Deformation Control Technology in Roadway under Multiple Excavations and Mining

To effectively control the large surrounding rock deformation of the mining roadway under multiple excavations and mining in Wangcun coal mine, the field investigation, numerical simulation, field test, and monitoring were conducted, and the characteristics of stress and deformation evolution of the surrounding rock under the influence of multiple excavations and mining were analyzed; then the collaborative supporting technology of high prestressed bolt and short anchor cables was proposed in this study. The results show the following: (1) under the influence of multiple excavations and mining, the peak vertical stress of the typical air-return roadway reaches 23 MPa, and the deformation increases by about 2.8 times after the mining of adjacent panel. (2) The principle of the roadway support under the influence of multiple excavations and mining in Wangcun coal mine is determined; from the perspective of prestress, we can conclude that the active support of short anchor cables is better than that of long anchor cables. (3) Based on the results of the field monitoring, the bolt stress can be divided into four stages: the loss stage of prestress, the sudden-decrease stage of the roof periodic weighting, the decrease stage of advanced support, and the rapid-increase stage of strong disturbance. Due to the large anchorage range of anchor cables, there is no decrease stage of advanced support. After the application of prestress, the bolt stress of side bolts and top bolts decreases, and the reduction amplitude is up to 30 kN. (4) As the panel advances, the deformation of the surrounding roadway increases, and the growth rate is also increasing gradually. However, the final displacement of the roof, floor, and two sides is within 18 mm. The bolt and anchor cables are not broken, and the control effect is good. The research results have a certain reference value for similar roadway control.

Parametric Analysis on Seismic Performance of Hybrid Precast Concrete Beam-Column Joint

In this paper, a nonlinear finite element (FE) analysis of high-performance hybrid system (HPHS) beam-column connections is presented. The detailed experimental results of the ten half-scale hybrid connections with limited seismic detailing have been discussed in a different paper. However, due to the inherent complexity of HPHS beam-column joints and the unique features of the tested specimens, the experimental study was not comprehensive enough. The new connection (HPHS) detail suggested in this study is characterized by ductile connection, steel connectors, and engineered cementitious composite (ECC) which is a kind of high-performance fiber reinforced cement composite with multiple fine cracks (HPFRCCs). Therefore, in this paper, FE analysis results are compared with experimental results from the cycle tests of the two specimens (RC and PC) to assess model accuracy, and detailed model descriptions are presented, including the determination of stiffness and strength. The critical parameters influencing the joint’s behavior are the axial load on column, beam connection steel plate length, inner bolt stress contribution, and plastic hinge area.

Improving Flange Designs Based on ASME Section VIII Div. 1, Appendix 2

Although improved methods for flange design have been under development for many years, ASME Boiler and Pressure Vessel Code Section VIII, Division 1 Appendix 2 continues to be the basis for the design of most custom pressure vessel flanges. While the method does a reasonably good job of calculating flange stress and rotation from the design loadings, it does not closely constrain some of the design input variables, such as gasket width and geometry, allowing the designer to produce poorly-performing designs. Also, the gasket loading factors (m & y values) have long been recognized as needing improvement. These weaknesses occasionally result in flanges which are difficult to seal, even with very high assembly bolt stress. In response to these weaknesses in the Appendix 2 method, various attempts to improve the method may be employed, and are sometimes required by end-user specifications. This paper provides an assessment of the effectiveness of various improvement techniques by examining the actual effects on flange designs across a range of diameter and design pressure, and makes recommendations for the use of such techniques. The analysis methods in PCC-1 and WRC Bulletin 538 are used as the basis of the evaluation, with a focus on gasket stress as fundamental to sealing.

Influence of Structural Interface Opening of Bolted Joints Under Eccentric Load

It is important to evaluate the safety of bolted joint under a load eccentric to a bolt axis. We examined tapped thread joints, with which a clamped plate is tightened with bolts to a base body, by applying eccentric loads to the bolts. The structural interface opening between the clamped plate and base body occurs due to the eccentric load based on the principle of leverage. During the growth of the interface opening, nonlinearity noticeably appears on the tensional and bending components of bolt stress, and these stress components become larger than expected in an early phase before a fatal bolt pull-out occurs. However, an evaluation method taking into account nonlinearity has not been investigated. We propose a normalized-bolt-stress evaluation method for tapped thread joints that takes into account the effect of the nonlinearity of bolt stress during interface opening. We conducted numerical calculations, experiments, and finite element analyses to quantitatively validate the stress under the following conditions: (i) tapped thread joints with the clamped plate thinner than the bolt diameter and (ii) load eccentric to the bolt axis. We confirmed that the bolt preload and lever ratio should be fixed at an initial phase, in which has no interface openings for the appropriate normalization. By using the normalized-bolt-stress evaluation method, strength evaluation becomes easily applicable to layout changes of bolted joints as a similarity rule.

Relaxation of the Bolted Flange Connection

This study researches the total relaxation of a bolted flange connection, taking into account, the relaxation of various bolt grades in conjunction with different semi-metallic gaskets. The test temperatures are: 300 °F (149 °C), 500 °F (260 °C), 650 °F (343 °C) and 800 °F (427 °C), where each temperature setting will cycle three times to obtain the relaxation value for each cycle. The three types of bolt materials for evaluation include ASTM A193 B7, ASTM A193 B16 and ASTM B8M CL2 along with gaskets styles of spiral wound gasket with inner ring, spiral wound gasket with NO inner ring and the kammprofile gasket (grooved metal gasket with covering layers), all in accordance to ASME B16.20 – 2017. The above variations and conditions will be tested at two different initial bolt stresses of 35,000 psi (241 MPa) and 65,000 psi (448 MPa) with a constant internal pressure of 150 psi (10.3 Bar). The results will show relaxation values for the different bolt and gasket types versus the various temperature cycling conditions indicated above. Focusing on: does a certain gasket style offer lower relaxation properties through less creep and/or higher recovery? Does a certain bolt grade offer better stress retention? Is there variation in initial bolt stress for the different style of gasket? How does the initial bolt stress affect the relaxation properties of the bolted connection?

Finite-Element Analysis of the Load Factor and Design for Bolted Circular Flange Joints Consisting of Dissimilar Clamped Parts Under Tensile Loadings

The load factor for bolted circular flange joints where two dissimilar material (steel-aluminum) of circular flanges are clamped by a lot of bolts and nuts under external tensile loadings is examined newly using Finite Element analysis. Furthermore, the effects of the bolt pitch circle diameter D and number of tightened bolts N on the load factor and a load when the interfaces start to separate are examined. The value of the load factor for steel-aluminum circular flange joint is a little bit larger than that for steel-steel circular flange joints and it increases as the value of D decreases. In addition, it decreases as the value of N increases. A maximum bending stress is also found newly about 5% larger than the bolt stress due to the load factor. The experiments to measure the load factor, the maximum bending bolt stress and a load when the interfaces start to separate were carried out. The FEM results are fairly coincided with the experimental results. Finally, based on the obtained load factor, a design method for bolted joints with dissimilar circular flanges is demonstrated for determining the nominal bolt diameter and the bolt strength grade and the effect of bolt number N is examined. It is found that the contact stress at the bearing surfaces of aluminum circular flange is critical and it is shown that washers are needed in some cases.

Further Work on Analyzing Accuracy and Overall Performance of Torque Tools for Assembling Bolted Flanged Joints

Over the past two years, the accuracy and repeatability of equipment used to assemble bolted flanged joints have been studied, and progress has been reported in past papers. One of the findings has been that pneumatic torque wrenches demonstrated a broader plus/minus range on bolt stress from the targeted value (e.g., lack of accuracy) than manual or hydraulic torque wrenches. What was notable, however, was that the repeatability of the bolt stress that was achieved did remain consistent with the other types of torque wrenches. Since the repeatability has been shown to be consistent, attention has turned to investigating and determining the reason for the perceived lack of accuracy. One aspect that might account for this is the calibration of the pneumatic torque wrenches. This paper outlines and documents the research that has recently taken place to identify the parameters that are key elements in improving the accuracy of pneumatic torque wrenches that might form the basis of development of a standard for calibration of powered torqueing equipment.