Bolt Pattern Research Articles

Impact of bolt positioning on the stiffness of angular support brackets

Bolts and screws are usually preferred over other joining techniques when assembly and disassembly operations are required. However, they add extra weight to the system, so it is essential to reduce their size and weight by optimizing bolt parameters. Additionally, the stiffness of bolted members is very crucial; those with low stiffness may affect the correct functioning of the other connected components. This study focuses on the impact produced by bolt positions, specifically their center of gravity and spacing among them, on the stiffness of angular L-shaped brackets using Finite Element Analysis. Bending and torsional loads were applied to the free end of the member and deformations were recorded under these loads. The results revealed that a triangular bolt pattern is recommended for three bolts, whereas for four or more bolts, the pattern should be uniform to avoid stress concentrations. Moreover, the center of gravity and bolt spacing have a significant impact on stiffness. By optimizing bolt spacing and the center of gravity, a combination of six bolts can be replaced with four bolts of the same size while maintaining the same stiffness.

Fire behaviour of damaged wood–steel–wood beam connections retrofitted with self-tapping screws — experimental study

This experimental study aimed to investigate the structural fire behaviour of damaged glulam beam connections retrofitted using self-tapping screws (STS). Four full-size glulam beam-end bolted connections with wood–steel–wood connection configurations using four or six bolts arranged in two different bolt patterns were examined. All connections were retrofitted using STS after being deliberately damaged through physical testing until failure. In a subsequent stage, the retrofitted connections were experimentally tested under standard fire exposure while subjected to the maximum design load of the weakest, undamaged, unreinforced connection configuration. The influence of the application of STS in terms of preventing wood-splitting propagation and maintaining reasonable fire resistance for the retrofitted connections was experimentally investigated and proven in this study. Results show that the retrofitted glulam beam connections maintained a minimum of approximately 67% of the failure time of identical but undamaged, unreinforced connections under standard fire exposure.

Steel Arch and Rock Bolt Support in Terms of the Gateroad Stability Maintaining behind the Longwall Face

The longwall system is an extraction system commonly used in coal mining in many countries, including Poland. One of the methods for reducing extraction costs is the dual use of the gateroad. In the first instance, the gateroad serves as the tailgate, and during the exploitation of the second coal panel, it functions as the headgate. Such a situation requires maintenance of the roadway behind the longwall face, which is typically challenging, due to significant stress-related loads on the support and its substantial deformation. The support design for this kind of roadway should take into consideration the dual impact of exploitation pressure and the caved zone influence behind the longwall face. This article presents the results of in-situ research conducted on two roadways behind the longwall face. In both roadways, the effectiveness of specially designed steel arch frames and rock bolt patterns were examined to minimize roadway deformations and maintain their functionality. The research project was comprised of several stages. Initially, mining and laboratory studies were conducted to determine the geomechanical parameters of the rocks. Subsequently, excavation stability and functionality forecasts were performed based on the authors’ empirical indicators. Then, numerical analyses were carried out to design support schemes (steel arches and rock bolt) in both roadways. A fully automated monitoring system with programmed data loggers was designed to check the behaviour of a specific rock mass and the support elements. The load on the steel arch support was measured with the help of load cells, while the load on the rock bolt support was carried out with the help of measurement bolts. Behind the longwall face, the loads on the wooden cribs set from the goaf side were also monitored. Additionally, the measurement station was equipped with extensometers to monitor the movement of roof layers and stress meters to determine changes in rock mass stress. Laser scanning or traditional surveying methods were also used to verify the support schemes through roadway convergence measurements. The obtained results allowed us to draw conclusions regarding the optimization of support schemes and to give recommendations for the practical application of specific reinforcements in excavations maintained behind the longwall face.

Improving the T-stub component behavior tied to a rigid base

An improvement in the behavior of the T-stub component as the vital element in the bolted connections is significant. Therefore, the present research aims to enhance the T-stub behavior by refining the bolt pattern under static load. In order to observe the effect of the bolt pattern resulting in suitable T-stub behavior, both experimental and numerical studies were performed on the specimens including one-row and two-row bolts with rectangular and trapezoidal patterns. The major aim of the experimental study was to monitor the failure mode of the specimens besides their load–displacement curves. Then, after verifying experimental results with ABAQUS software, numerical study on not only the mechanical behavior of the specimens but also the bolt behavior were conducted. Based on the results, a novel failure mode in the subgroup of failure mode 1 was observed. Furthermore, the bolt type had direct effect on the kind of the bolt rupture in failure mode 2. The last but not least, modifying just the bolt pattern without varying the remaining parameters enhanced the T-stub and bolt behavior in each of the failure modes. Therefore, without increasing the weight and cost of the connection considerably, an appropriate behavior can be reached.

Effects of Bolt Number and Pattern on the Failure Time of Minimally Fire-Protected Glulam Beam Connections Reinforced with Self-tapping Screws

Effects of Bolt Number and Pattern on the Failure Time of Minimally Fire-Protected Glulam Beam Connections Reinforced with Self-tapping Screws

Research on Square and Circular Steel Tubular Columns with Deconstructable Splice Joint Under Cyclic and Axial Testing

Abstract: A steel tubular column is a vertical structural member used in construction to provide essential support. Splice joint is a method of joining two members end to end. When the material being joined cannot be obtained in the desired length, the splice joint is used. For high rise buildings the continuity of columns may break, hence splice connections are provided and columns are installed. Splice joints are deconstructable type joints as the failed parts can be repaired, reassembled or can be even removed when failure occurs. These papers focuses on developing models of square and circular cross sections of steel tubular columns with deconstructable splice joint using a finite element software ANSYS and study their structural behavior. This paper includes a parametric study on the effect of axial loading by varying splice length and thickness, bolt diameter and pattern of square and circular cross sections of steel tubular columns with deconstructable splice joints. Bending moment rotation curves were obtained from cyclic load testing for square and circular cross sections

Bolt: Scalable and Cost-Efficient Multistring Pattern Matching With Programmable Switches

Multi-string pattern matching is a crucial building block for many network security applications and thus of great importance. Since every byte of a packet has to be inspected by a large set of patterns, it often becomes a bottleneck of these applications and dominates the performance of an entire system. Many existing studies have been devoted to alleviating this performance bottleneck either by algorithm optimization or hardware acceleration. However, neither one provides the desired scalability and costs that keep pace with the drastic increase in network bandwidth and traffic today. To address these issues, in this paper, we present BOLT, a scalable and cost-efficient multi-string pattern matching system leveraging the capability of emerging programmable switches. BOLT combines the following techniques: (1) an efficient state encoding scheme to fit a large number of strings into the limited memory on a programmable switch; (2) a variable <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> -stride transition mechanism to increase the throughput significantly with the same level of memory cost; and <xref ref-type="disp-formula" rid="deqn2-deqn5" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(3)</xref> a compact <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pattern2rule</i> mapping method to accommodate multiple co-existing strings in one rule. We implement a prototype of BOLT and make its source code publicly available. Extensive evaluations demonstrate that BOLT can provide multi-hundred Gbps throughput and scales well with various pattern sets and workloads.

Experimental Investigation into the Capacity of Concentrically Loaded Steel Connections with Pretensioned High-Strength Bolts and Longitudinal Fillet Welds in Combination

This paper presents the results of an experimental study aiming to investigate the behavior of steel connections that combine pretensioned high-strength bolts and longitudinal fillet welds on a common faying surface. A total of 75 double-shear tension splices were tested under direct tension loading to quantify the effect of various connection variables on the load-deformation behavior of the connection. These variables include the (1) bolt pattern (2×2 and 2×3), (2) bolt size (3/4 in. and 1 in.), (3) bolt grade (ASTM F3125 Grade A325, A490, and F1852), (4) bolt pretensioning method (turn-of-nut and tension control bolts), (5) faying surface class (Class A and B), and (6) weld/bolt strength ratio. The variation in the connection characteristics covered a wide range of weld/bolt strength ratios from 0.50 to 2.00. The bolts were installed in oversized holes, and the specimens were assembled in a negative bearing condition to allow for a maximum slip distance. The load-deformation behavior of the combination connections was recorded and compared to that of the bolted- and welded-only control specimens. In all tests, the addition of welds increased the capacity of the connection. The investigation shows that the capacity of the combination connection with pretensioned high-strength bolts and longitudinal fillet welds can be computed by adding the capacities of the individual connecting elements while considering the strain compatibility.

Numerical and theoretical analysis of staggered cruciform stubs

The stiffened top-and-seat angle (STSA) connection has seen sensitive use due to its considerable stiffness, resistance, and replaceability. However, the requirement for ductility prevents further resistance enhancement. This issue could be solved by a new improved configuration (termed staggered large STSA), but it is urgent to evaluate the mechanical property and parameter influence. This paper employs the component method to conduct a numerical and theoretical investigation of the critical tensile component-cruciform stub, taking into account the influences of stub thickness, bolt pattern, and bolt diameter. With the theory of plates and shells, a model for predicting initial stiffness is proposed to provide a detailed design procedure. In addition, the paper simplifies and verifies the method for plastic resistance based on the theory of virtual work. These methods are followed by a suitable curve model to depict the tensile behavior of staggered cruciform stubs. The average prediction error is less than 10%.

Tensile behavior of cruciform stubs with staggered bolt patterns

Welding stiffeners to angles improves the initial rotational stiffness and resistance of top-and-seat angle connections, but the unintended side effect is lower ductility. To balance ductility and resistance, a novel large angle connection has just been designed. As a result, there is an urgent need to test the behavior and perform theoretical research. Six cruciform stubs were designed and tested with monotonic load to reveal the plastic development of such connections. The comparison with parallel bolt patterns proved that the staggered bolt pattern could improve the ductility factor from 6.06 to 14.17 without lowering resistance. Furthermore, finite element models were used to investigate the development of bolt force. Finally, a modified method for predicting plastic resistance and a model to calculate initial stiffness are accurately presented.

Experimental study on bond strength failure of GFRP lap joints

Bonding has many advantages such as high adhesive strength, peel resistance, good toughness, shrinkage and corrosion-resistance, compared with bolting, welding and other connection patterns, which is the basic connection of the composite materials. The mechanical properties of the bond depend on the type and geometric parameters of the bond. In this paper, experiments were conducted to study the bond strength failure of GFRP single and double lap joints and explore related influencing factors. The variable factors of test specimens include bond type, length and thickness. The quasi-static tensile test was carried out at room temperature to analyze multiple influencing factors of lap joints and characteristic of GFRP bond failure strength. The results showed that the failure of the bond usually occurred at the interface of bond, and bond types, length and thickness have significant effects on the failure of bond. Failure strength increased firstly and then decreased with the increase of adhesive thickness. With the increase of bonding length, the failure mode of the double-lap joint become complex failure mode, which is accompanied by GFRP delamination near the surface of fiber of the bonding.

Drop-In Motors: What You Need to Consider Beyond the Bolt Pattern

The push to improve efficiency and lower costs has impacted electric motors. It is not uncommon to see a reduction in mass for modern medium-voltage machines, and the actual footprint of newer machines is smaller in most cases, too. Many drop-in motors (mechanically interchangeable) perform very well. There are design constraints that may be overlooked when ordering a functional drop-in replacement machine. Depending on the power, size, and speed of a motor, failure to meet the minimum base stiffness requirements can cause severe vibration issues. The combination of a transition base with a machine of a different mass can cause resonance problems, which can cost more than the motor to resolve. Changing from a stiff to a flexible rotor can result in unexpected vibration without an easy solution. The issues described in this article could be experienced by any end user, regardless of the original equipment manufacturer.

Assessment of Provisions for Load Rating Gusset Plates in Steel Truss Bridges

Many states have load rated their truss bridge gusset plates following the guidelines published in 2009 by the Federal Highway Administration in response to the catastrophic failure of the I-35W Bridge. As the Manual of Bridge Evaluation released new load rating provisions after 2014, the urgency in adopting and applying these mandated provisions became a pending burden for state agencies requiring extensive work to update the ratings of gusset plates. Moreover, this paper argues that the current states’ load rating practices do not involve the rating for the welded gusset plate owing to the lack of established provisions. In addition, the gusset plate with no plans also poses particular challenges for the state agencies. To provide state agencies with better insights on the load rating approach of gusset plates, this paper presents a study that carefully reviewed the states’ current practices and load rating provisions. The results of the study indicate the necessity of adopting the new provisions, as the former load rating methodology exhibited inaccurate results in some cases. Additionally, this paper reviews extensive work done for welded connections and proposes a load rating guidance for welded gusset plates. To deliver better interpretations, a case study is provided for the welded gusset plates. This paper also reviews the evaluation method for deteriorations and staggered bolt patterns with relevant case studies. Lastly, the paper provides guidance on estimating the unknown bolt strength as well as weld metal strength for the gusset plate.

Rockburst simulation using dynamic tests on the support system

Ground support for dynamic conditions must be able to withstand the associated loads and deformations and the support scheme must work as a system. In order to prove the suitability of such support systems with high-tensile steel mesh and bolts and to analyze the bearing behavior of them, a large-scale test setup was commissioned in Walenstadt, Switzerland. On this test rig it is possible to apply large energies on variable ground support systems with variable bolt patterns and meshes with a total support area of 3.6 × 3.6m in a full-scale way. The test site is instrumented by load cells, high-speed video analysis and accelerometers. In this paper the analysis of the load cells, the accelerometers and the high-speed video cameras is given, and results of system tests are discussed.

Numerical investigations on large size stiffened angle connections with different bolt patterns

The top-and-seat angles are commonly used in the design of beam-to-column joints, however, designing the bolt pattern is a challenge when the large stiffened angle (often connected by four or more bolts) is adopted. The purpose of this study was to propose useful design rules for such joints. The failure modes applicable to large stiffened top-and-seat angle joints are classified and formulas for calculating a so-called cruciform stub's resistance in each mode are developed. They were verified with finite element modeling after the verification of modeling method. A staggered bolt pattern is found to best exploit the combined strength of multiple bolts and avoid the premature failure of a single bolt. A method for designing the best staggered bolt pattern is developed through the analysis of key geometrical parameters using 158 simplified cruciform stubs. Failure modes and methods for calculating the tension resistance of such stubs are proposed. They provide useful suggestions for the selection and design of angle thickness and bolt type.

Modified Rock Bolt Support for Mining Method with Controlled Roof Bending

The article presents methods of making the rock bolt support more yieldable, especially for a stratified roof. Alongside the increasing depth of exploitation of raw material deposits, rock bolt support units are more often designed taking into account more intensive deformations and displacements of underground excavations. In the article, a room and pillar method with mined roof bending and roof reinforcement with bolt patterns of 1 m × 1 m, 1.5 m × 1.5 m and 2 m × 2 m is presented. Moreover, the laboratory tests included 1.8 m long bolts, which were embedded segmentally on the lengths of 100 mm, 150 mm and 200 mm were tested. Based on the load–displacement characteristics, the deformation energy for flat and profiled dome bearing plates was calculated. Making the segmentally embedded resin rock bolt support yieldable enabled it to perform additional work. Furthermore, it was found that rock bolt support with a dome bearing plate took over 2.5 times more energy compared to a rock bolt support equipped with a flat bearing plate.

A case study on the efficacy of different roof bolting schemes in Lhoist North America’s Crab Orchard Mine

Roof bolting has long been used in underground mines across the world to provide ground support. Modern roof bolts are cheap and easy to install with the use of specialized machines as a part of the production cycle. Lhoist North America’s Crab Orchard Mine is an underground room and pillar limestone mine that uses mechanically anchored roof bolts for ground support. The mine currently employs two different roof bolting patterns: a standard 1.5 × 1.5 m pattern, and another 0.8 × 0.8 m pattern for use in areas with particularly hazardous roof conditions. The purpose of this study is to evaluate the relative effectiveness of each bolting pattern. A series of numerical models were created using RocScience’s RS2. The models were based on a symmetrical section of the mine at its deepest point, and were modeled using generalized Hoek-Brown failure criterion along with a discrete fracture network. A series of sensitivity analyses were performed on the models by varying parameters such as joint friction angle, crack persistence, joint randomization, and tensile strength of the limestone. Based on the results of the original models and sensitivity analyses, it appeared that the standard bolting pattern provided sufficient roof support capacity under almost all the expected conditions at the mine, since safety factors below the design value of 1.5 were only found for individual bolts in a few of the worst test cases considered. These results can help improve the mine’s productivity and reduce operating costs without compromising safety.

Use of virtual reality in underground roof fall hazard assessment and risk mitigation

Virtual reality (VR) simulations are some of the alternative practice environments for safety education. Trainees gain experience under the most realistic conditions without being exposed to any real hazard. Virtual reality also serves as a tool to expedite the decision-making process where quick decisions and actions are necessities for a safe operation. One example of such a situation in underground mines is the failure risks in a tunnel face after blasting. Ground support systems must be installed based on the stand-up time to ensure the safe access of personnel and equipment to the working area. Generally, a competent person inspects the area to identify risks and determines the required support systems. However, training of a competent person requires large amount of time and effort. This study presents virtual reality simulations developed for improving the assessment of the roof fall hazards and taking necessary measures for mitigating the risk related to roof fall. The virtual reality simulation involves decision-making tasks for a particular scenario in which participants can experience creating a safe working environment in a timely manner. First, they are asked to identify the potential hazard in a tunnel after blasting, namely, rock fall, wedge failure or groundwater inflow. If the hazard identification is successful, participants are requested to install rock bolts as a safety measure by selecting the bolt pattern (e.g. bolt length and spacing). Finally, participants evaluate the roof fall hazard by viewing displacements around the opening, before and after the support measures. This study illustrates the benefits of VR in safety training as well as enhancing the decision-making process to enhance safety.

Discrete element analysis of the influence of bolt pattern and spacing on the force‐displacement response of bolted steel mesh

SummarySteel wire mesh held by a pattern of bolts can be used to stabilize a rock slope. Knowledge of the force‐displacement response of steel mesh is essential in the design of this support system. Laboratory tests have been used to test mesh that is held to rigid steel frames. These testing conditions differ from how steel mesh is held in the field by bolts. The existing laboratory test data may underestimate the deformation and overestimate the load‐bearing capacity of the steel mesh. This paper focuses on the response of the high tensile strength steel mesh held by commonly used bolt patterns. Discrete element models were used to study the force‐displacement response of the steel mesh pinned by bolts. The influences of different bolt patterns and varying ratios of bolt spacing on the effectiveness of steel wire mesh were analyzed. Relationships between the resistance force of steel mesh and bolt density at various mesh deformations were developed. These relationships can help engineers choose the bolt spacing and provide an estimate of the resistance force that a steel mesh can mobilize at a desired deformation limit for a given bolt pattern.

Anchor Bolt Patterns for Mechanically Fastened FRP Plates

AbstractThis paper examines the results of material testing of hybrid carbon and glass fiber-reinforced polymer (FRP) plates for use in prestressed mechanically fastened applications. The small-sca...