Plate Bolt Research Articles

Effects of bolt–plate arrangements on steel plate strengthened reinforced concrete beams

A structure that can behave in a ductile fashion under extreme events is of paramount importance due to safety considerations. Because of such importance, ductility performance of bolted side-plated (BSP) concrete beams under different bolt–plate arrangements is investigated experimentally through four large-scale tests on BSP beams. It is observed that bolt–plate arrangements have a dominant effect on the ductility performance of beams in terms of both the post-elastic strength enhancement (defined as the ratio between the peak strength and the yield strength of the beam), and the displacement ductility (defined as the ratio between displacements at the ultimate and notional yield stages). In order to ensure ductile beam behaviour, the concept of maximum allowable plate–force demand is introduced, of which the strength of additional plates should be kept below the ‘balanced’ failure point, while sufficient shear strength of the bolt connections should be provided so that the strengthened beam will possess both sufficient strength enhancement and ductility.

Effects of plastic hinges on partial interaction behaviour of bolted side-plated beams

Slips of mechanical connectors in steel plate reinforced concrete (RC) structures can significantly affect the load-carrying capacity of the structures. The difference in deformation between the steel plate and the reinforced concrete counterpart is known as partial interaction. In this study, the flexural behaviour of bolted side-plated (BSP) reinforced concrete beams was investigated experimentally. Two new deformation-based parameters, namely the strain factor and curvature factor, were introduced to quantify the degree of partial interaction between the RC beam and the steel plates. The experimental results revealed that the degree of partial interaction between RC beams and steel plates could be reduced by as much as 50% when the BSP beam proceeded from a linear to a non-linear stage in which plastic hinges have formed in critical sections. Consequently, the load-carrying capacity was reduced by up to 30% of the theoretical additional strength provided by the bolt–plate system, which is more than double the allowance proposed previously in the literature. The under-estimation of the effect of partial interaction in composite structures can result in unsafe design.

A new energy-absorbing bolt for rock support in high stress rock masses

An energy-absorbing rock support device, called a D bolt, has been recently developed to counteract both burst-prone and squeezing rock conditions that occur during underground excavation. The bolt is a smooth steel bar with a number of anchors along its length. The anchors are firmly fixed within a borehole using either cement grout or resin, while the smooth sections of the bolt between the anchors may freely deform in response to rock dilation. Failure of one section does not affect the reinforcement performance of the other sections. The bolt is designed to fully use both the strength and the deformation capacity of the bolt material along the entire length. The bolt has large load-bearing and deformation capacities. Static pull tests and dynamic drop tests show that the bolt length elongates by 14–20% at a load level equal to the strength of the bolt material, thereby absorbing a large amount of energy. The impact average load of a 20 mm D bolt is 200–230 kN, with only a small portion of the load transferred to the bolt plate. The cumulative dynamic energy absorption of the bolt is measured to be 47 kJ/m. D bolts were tested in three deep mines. Filed measurements show that D bolts are loaded less than rebar bolts. This paper presents the layout and principle of the D bolt, and corresponding results from static, dynamic, and field tests.

Fitness for service evaluation of cracked divider plate bolt locking tabs for nuclear steam generators

This paper is to address the structural integrity issues related to continued service without repair or replacement for cracked locking tabs on divider plates of nuclear steam generators. Significantly high residual stress introduced by cold bending of locking tabs at installation was simulated by elastic–plastic finite element method and considered in the fitness for service evaluation. Significant work hardening resulted from the accumulation of large and inhomogeneous plastic deformation introduced by the in situ bending was quantified and considered. Failure and degradation mechanisms for crack stability and propagation were identified. Linear elastic fracture mechanics (LEFM) theory with crack tip plastic zone correction was adopted to establish critical crack sizes. Life of safe operation of the cracked locking tabs from inspected crack sizes to the critical crack sizes was then evaluated. Initial crack sizes at installation were also established through a highly contrived backward fitting evaluation procedure.

Experimental and Numerical Investigation of Impingement Cooling in a Combustor Liner Heat Shield

A combined experimental and numerical investigation of the heat transfer characteristics inside an impingement cooled combustor liner heat shield has been conducted. Due to the complexity and irregularity of heat shield configurations, standard correlations for regular impingement fields are insufficient and detailed investigations of local heat transfer enhancement are required. The experiments were carried out in a perspex model of the heat shield using a transient liquid crystal method. Scaling of the model allowed to achieve jet Reynolds numbers of up to Rej=34,000 without compressibility effects. The local air temperature was measured at several positions within the model to account for an exact evaluation of the heat transfer coefficient. Analysis focused on the local heat transfer distribution along the heat shield target plate, side rims, and central bolt recess. The results were compared with values predicted by a standard correlation for a regular impingement array. The comparison exhibited large differences. While local values were up to three times larger than the reference value, the average heat transfer coefficient was approximately 25% lower. This emphasized that standard correlations are not suitable for the design of complex impingement cooling pattern. For thermal optimization the detailed knowledge of the local variation of the heat transfer coefficient is essential. From the present configuration, some concepts for possible optimization were derived. Complementary numerical simulations were carried out using the commercial computational fluid dynamics (CFD) code ANSYS CFX. The motivation was to evaluate whether CFD can be used as an engineering design tool in the optimization of the heat shield configuration. For this, a validation of the numerical results was required, which for the present configuration was achieved by determining the degree of accuracy to which the measured heat transfer rates could be computed. The predictions showed good agreement with the experimental results, both for the local Nusselt number distributions as well as for averaged values. Some overprediction occurred in the stagnation regions, however, the impact on overall heat transfer coefficients was low and average deviations between numerics and experiments were in the order of only 5–20%. The numerical investigation showed that contemporary CFD codes can be used as suitable means in the thermal design process.

Bolt–plate contact assemblies with prestress and external loads: Solved with super element technique

In dynamically loaded bolted assemblies fatigue is the designing factor. The primary quantity that controls the fatigue is the part of the external load that is transferred to the bolt, as described by the ratio between transferred load to external load. In an idealized setting this ratio can be expressed by a stiffness ratio between the plate members and the bolt. The ratio of transferred load is, however, highly dependent on the size and position of the external loading.

Reduction in clamping force due to applied longitudinal load to aerospace structural bolted plates

The main purpose of the present work is to experimentally and numerically study why and how the magnitude of the bolt clamping force reduces in the aerospace structural bolted plates when they are subjected to a longitudinal tensile load. In the experimental method, a holed plate of aluminium alloy 7075-T6 was clamped using a single bolt fastener, and then tested under an increasing static longitudinal tensile load. The bolt clamping magnitude was determined by using the measured axial compressive strains of a steel bush placed between the nut and plate. Two clamped specimens with different initial clamping forces were studied. In each specimen the actual clamping forces were determined during the longitudinal loading on the plate. In the numerical method, a three-dimensional (3D) finite element model was generated in order to simulate and quantify the bolt clamping force in the plate model loaded in tension. Both experimental and numerical results showed that the clamping force reduces considerably in the aluminium bolted plates under the longitudinal tensile loading. This is because of the transverse contraction of the plate material that causes the clamped material to release from the initial compression, and as a result, the clamping force to relax.

Mechanical Behavior of High-Tension Bolted Joints with Varying Bolt Size and Plate Thickness

The use of steel plates has been greatly increased in bridge construction, particularly for long-span bridges, and connections between the plates are made usually using high-tension bolts. However, the specifications on the use of large-sized high-tension bolts are not adequately stated in the currently available construction manuals. In order to provide further information on the use of the large-sized high-tension bolts, this study experimentally investigated the relaxation and slip behavior of M30 bolts with varying bolt size and plate thickness. In addition, numerical evaluation using FEM was performed to investigate the compressive stress occurred on the inside of bolt hole. The analyzed results were compared with the stress distribution measured from strain gages attached on the bolts and bolt holes. From the study presented herein, it was found that the relaxation was increased as the size of bolt increased, and that the M30 high-tension bolts developed slip coefficient greater than 0.4. The thickness of plate did not significantly affect the compressive stress distribution around the bolt holes.

Quantifying the performance of resin anchored rock bolts in the Australian underground hard rock mining industry

1. IntroductionThe purpose of rock support and reinforcement is toensure excavations remain safe and open for their intendedlife span. The effectiveness of a reinforcement strategy isimportant for two main reasons: these being safety topersonnel and equipment, and achievement of the mosteconomical access to extract ore. For a particular rockmass, a stabilization scheme capable of matching theexpected behaviour is selected based on an assessment ofthe likely failure modes predicted from the interaction ofan excavation (geometry and purposes), the network ofgeological discontinuities, weathering and the loadingconditions from stress and blast damage [1–4].In most underground mines, the primary form ofexcavation stabilization is provided by a pattern of rockbolts installed within the rock mass. This is complementedwith the use of passive support, such as that provided bymesh or shotcrete, in order to provide surface restraint atthe exposed excavation boundaries.The reinforcement controls the overall excavationstability through keying, arching or composite beamreinforcing actions [5], while the mesh and/or shotcretesupports the small loose pieces of rock that may detachbetween the rock bolt plates [6,7].In general, a stabilization scheme cannot be selectedwithout consideration of the ground support drillingequipment available at a particular mine site. A modern,optimal strategy would consist of mechanized installationof reinforcement and support in a single pass in order toincrease productivity and reduce exposure of personnel andequipment during installation.2. Mechanized resin anchored bolt installationOver the last decade or so, jumbo-installed, 45mmdiameter galvanized and black steel friction bolt stabilizershave become the preferred form of reinforcement inunderground hard rock mining in Australia [8,9]. Thishas been mainly driven by a desire to achieve fastdevelopment rates and low costs in order to allow theextraction of low-grade orebodies. In more recent years, asthe mining operations are getting deeper and the rockmasses are becoming highly stressed, other reinforcementschemes such as fully encapsulated resin anchored bars arebeing considered as an alternative to friction bolts for long-term reinforcement [10–13].The typical bolts being used in the underground hardrock mines have been modified from the bolts used in thecoal mining industry. The modifications have beennecessary due to the need to drill larger hole diameterswith the type of equipment used in the hard rockmetaliferous mines. The modification is mainly in the formof paddles or the use of a spring welded on to the endsection of the bolts. Fig. 1 shows the anchor sections for a24mm Posimix bolt with spring arrangement and a 27mmSecura bolt showing a paddle arrangement. The Posimixwire is 3mm in diameter and has a length of 500mm. Thepaddle width is 29.2mm and they have been sheared intothe end of the bolt for the purpose of mixing resin.Nevertheless, the introduction of mechanized resinanchored bolting using jumbos has been difficult toimplement economically due to the high cost of resintransport and storage: this requires the use of refrigerated

Three-dimensional investigation of thick single-lap bolted joints

Stresses in single-lap bolted joints of thick plates are complex and difficult to analyze. Previous studies involving stresses through the thickness of bolted joints have been limited to finite element method (FEM) simulations and have been implemented only for the joining of relatively thin plates. In this paper we report on several experimental and numerical analyses that were conducted to evaluate the stress distribution inside thick bolted plates along the bearing plane normal to the plate surface. Experimental analysis was conducted via embedded-polariscope photoelasticity and embedded resistance strain gages. The FEM analysis was performed with the ABAQUS commercial code using material properties and other data obtained experimentally as input. Experimental and numerical results agreed reasonably well, and are believed to depict the behavior of the joint under load well enough to assist in development of improved joint design.

Application of high strength plate bolts in friction grip joints

High Tension Bolts (HTB) are known to exert a significant influence on the strength characteristics of connections and have a significant influence on the ductility and behaviour of the joint. Normally HTB failure occurs in the shape resultant high stress concentration neck and thread areas resulting in relatively low ductility characteristics. Creep and relaxation occur after HTB tightening causing shaft tension loss and further stress redistribution in the connected components. Past research has shown that waisting the HTB shaft diameter reduces stress concentrations, shaft tension loss and increases ductility. With the further modification of making the HTB head plate shape counter sunk, a plate HTB with an aesthetically pleasing flat surface less susceptible to rain corrosion results. In this research, tensile, relaxation and friction grip joint slip experiments were done on waisted shank, counter sunk plate head HTB to ascertain the ductility improvement, the resulting decrease in shaft tension loss and its magnitude, as well as their applicability in friction grip steel connections. Apart from significant shaft tension loss reduction, no detrimental effects are induced in the slip coefficient results when these HTBs are applied in friction grip joints. Within these experimental parameters, the closest to ideal HTB shape is proposed. (Journal of Civil Engineering, JKUAT: 2002 7: 67-80)