Hole Clearance Research Articles

Theoretical and FEA study on shear performance of novel shear connectors

Shear connectors are essential components for force transfer in composite beams. Compared to conventional welded-bolt connectors, bolted shear connectors offer the advantage of easy removal. However, traditional bolted connectors for steel-concrete composite beams feature threads on the contact surface, reducing the shear cross-sectional area of the bolts. To address this limitation, this paper proposes a novel type of friction-clamping bolt connector, referred to as Connecting Lock Combination Bolts (CLCB11CLCB:Connecting Lock Combination Bolts；). The finite element software ABAQUS was used to develop an analytical model for the CLCB, and a comparative analysis was conducted with traditional connectors. The static performance of the new shear connectors was evaluated, and a shear load capacity formula applicable to CLCB connectors was derived. Additionally, linear and exponential functions were employed to fit the load-slip curve of the CLCB connectors. The results indicate that the shear load capacity of CLCB connectors exceeds that of conventional bolted connectors. Moreover, the bolt diameter and concrete strength are the primary factors influencing the ultimate shear load capacity and stiffness of CLCB connectors. The preload on the bolts enhances the shear stiffness, while parameters such as bolt hole clearance, the height of the lower nutted rod, and the clearance between the upper and lower bolt rods are crucial in ensuring the proper functioning of CLCB connectors. Furthermore, the shear capacity formula provides an accurate prediction of CLCB connector performance with an error margin of less than 6 %, and the load-slip curve model effectively illustrates the load-slip relationship under shear.

Analysis of relaxation characteristics of multi-bolted connections under the transverse cyclic load

A modeling method under lateral cyclic loading is proposed for the complex multi-bolt connection loosening problem. Firstly, the thread stress surface is divided into n small sectors, and the self-relaxation mechanical model of multi-bolt connection is established considering the interaction between bolts. Secondly, the self-relaxation model is solved by MATLAB software and compared with Nassar model to verify the correctness of the model. Finally, considering the influence of different bolt number, hole clearance and connection spacing, the relaxation characteristics of multi-bolt connection are studied. The results show that during the loosening process, the bolt head undergoes a bending-sliding-bending cycle process, and the bolt tension shows a wave downward trend. When multiple bolts are connected, the number of loosening cycles decreases linearly with the increase of hole clearance. With the equidistant increase of bolt connection spacing, the number of bolt loosening cycles shows a decreasing trend. Compared with the number of bolts, the change of bolt hole clearance and connection spacing is more likely to affect bolt loosening.

Push‐out tests of demountable shear connectors for sustainable composite structures

AbstractThe demountable shear connector is the most important component of sustainable composite structures, as it allows the elements to be reused. The ongoing research and development project – in the cooperation of the Budapest University of Technology and Economics and KÉSZ Group, bim.GROUP Ltd., Hungary – aims to design a new demountable steel‐concrete composite structural system. In the current research, bolted shear connectors with embedded bolts and threaded rods, which can fit the applied technology of the industrial partner, are being developed and studied. One of the main aspects of this connection is to consider the bolt hole clearance – to decrease initial slip and stiffness reduction – and also to provide the proper strength and ductility features. A push‐out experimental programme was designed and completed to study the behaviour of the developed shear connections. It is observed that the examined shear connectors have proper structural behaviour with adequate resistance and ductility, which is applicable according to the Eurocode 4 standard and fits the objectives of the current research project. This paper presents the developed structural details, the observations and the evaluation of the push‐out experimental results with the conclusions and statements.

Discussion on ultimate resistance formulas of high-strength bolts under tensile-shear coupling loading

Bolted connections are one of the key connection configurations in steel structures. The ductile fracture prediction is one of the challenges in the structural integrity evaluating of steel structures. To guarantee the safety of steel bridge in connections, an accurate assessment of the ultimate resistance of high-strength bolts under combined tensile-shear loads is necessary. However, the impacts of various parameters on high-strength bolts under combined tensile-shear loads are not sufficiently analysed in the existing references. Hence, in this paper, the validated mesoscale critical equivalent plastic strain (MCEPS) method is used to evaluate the ultimate resistance of high-strength bolts with different bolt grades, bolt diameters, bolt types, hole clearance, and preload force when the bolts are exposed to combined tensile-shear loading. The simulation results are compared to existing design specifications. Finally, the formula modifications in the existing design standards are proposed based on statistical analysis on numerical parametric results.

THE EFFECT OF RIVET GUN OPERATING PRESSURE AND HOLE CLEARANCE ON RIVET SHEAR STRENGTH IN SHEET METAL RIVETING PROCESS

Several parameters related to the riveting process and the quality or result of the rivets are squeeze force, rivet length, rivet diameter, and hole clearance. This riveting experiment uses a semi-automatic riveting tool to set riveting parameters. The parameter set is the operating pressure of the rivet gun with a semi-automatic riveting tool, while the drilling process on sheet metal makes the hole clearance. The results of riveting using an automatic rivet tool show that the operating pressure of the rivet gun and the hole clearance have a direct effect on the shear strength of the rivets; the higher the operating pressure of the rivet gun and the greater the hole clearance will increase the shear strength of the rivets. This rise in the rivet’s shear strength is because, during the riveting process, the rivets experience strain hardening when pounded using a rivet gun.

Filtering of high frequency motion due to the gap effect on bolted anchorage

In the context of the equipment qualification against induced vibration due to the impact on reinforced concrete structures, the question of the transmission of high frequency and high amplitude motion through bolted anchorages of the equipment is raised. To better comprehend this phenomenon, the 3rd phase of the “Improving Robustness assessment of structures Impacted by missileS” (IRIS 3) impact tests under the cover of the OECD/NEA has been carried out in the VTT laboratory in Finland. Two types of assemblage for equipment: bolted and welded, were specifically added to the mock-up in order to assess the influence of connection on induced vibration to equipment. Displacement and acceleration sensors compatible with high frequency and high amplitude motion are mounted to multiple locations, especially upstream and downstream of the anchorage locations. Analyses of measured data of these tests have shown significant differences between bolted and welded equipment while their experimentally identified modal characteristics (frequency and damping ratio) were the same. Indeed, the bolted equipment exhibits a reduced motion with respect to the one of welded equipment, especially regarding response spectra performed from time history acceleration measured on different equipment, so-called in-equipment response spectra. The filtering effect of bolted equipment occurs even without any damage around the bolted assemblage, which is used to be pointed out as the main reason for the filtering effect according to the literature. These analyses on IRIS 3 measurement raise the hypothesis that the main cause of the filtering effect is the annular space between the anchorage rod and the clearance hole, conventionally called by anchorage gaps. In effect, anchorage gaps enable the slip of different surfaces of bolted assemblage which transmit only low amplitude motion by the friction force. To check the validity of this hypothesis, a gap model is proposed to simulate the response of bolted equipment. A very good agreement of simulations with gap model and measurements confirms the important role of gaps on the filtering effect of bolted equipment in the context of induced vibration due to impact. In conclusion, the bolted anchorage should be regarded as a filter which allows to mitigate the transferred motion due to impact vibration from supporting structures to equipment. This conclusion of the gap effect on equipment in the impact field could have significant extension to seismic hazard, especially regarding to the reduction coefficient αgap=0.5 on the resistance of anchorage bolt in case of gaps. With new findings in this study, the gap could not be systematically considered as a harmful effect as proposed by the standard of concrete fasteners. Further studies on the gap effect should be carried out to identify the role of friction and impact phenomena on the gap effect.

Experimental Study of Novel Demountable Shear Connectors for Steel-concrete Composite Buildings

Sustainable composite structures in building construction are assembled using demountable structural elements that can be reused in the circular economy. The current research and development project, in cooperation with Budapest University of Technology and Economics and KÉSZ Group, bim.GROUP Ltd., Hungary, aims to design a novel demountable steel-concrete composite slab and frame system for buildings. The key component of this construction is the demountable shear connector. In the current research, novel bolted shear connectors with embedded bolts and threaded rods are developed and studied that can fit the applied technology of the industrial partner. One of the leading aspects of this connection is the consideration of bolt hole clearance, since it occurs initial slip and stiffness reduction of the composite beam. In the first phase of the research program, demountable and economical structural details were developed, which can reduce the stiffness reduction with the proper resistance and ductility features. To study the behavior of these shear connections, a push-out experimental program was designed and completed in March and April 2023. It is observed that novel shear connectors have a proper behavior with sufficient resistance and ductility, which is applicable according to the Eurocode 4 standard and fits the objectives of the research and development project. In the paper, the developed structural details and the push-out experimental program are presented with general results and statements besides a detailed evaluation of a specified specimen type.

Simulation and experimental study on contact pressure distribution of contact interface in single and double bolted connection structures

Bolted joints play an important role in aerospace, machinery manufacturing, weapons and other fields, and the contact pressure distribution at the connection interface seriously affects the service performance of the bolts. Contact pressure analysis is an essential basis and reference for structural design, calibration, inspection, and safety monitoring of bolted connection structures. Considering the preload force and frictional contact between the joint components, a block mapping hexahedron mesh generation and finite element modeling method for bolted connections is presented, and the finite element models of single and double bolted structures are constructed. Then, an experimental test platform for measuring contact pressure distribution is constructed. Comparison of finite element analysis results with experimental results for the contact pressure distribution in the single and double-bolted joints; the root mean squared error of contact pressure distribution is less than 5%, which verifies the effectiveness of the finite element models. After that, the models are used to study the contact pressure distribution in single-bolted joints and contact pressure coupling effect of double-bolted joints, and the normal stress distribution features within members and contact pressure distribution contour are revealed for single and double-bolted joint. Finally, the finite element models are adopted to investigate the effects of the clamping length, preload, material properties, hole clearance, and bolt size on contact pressure distribution in single-bolted joints. The coupling effect of contact pressure distribution in double-bolted joints under different preloads and geometric parameters are also examined.

Capsizing due to friction-induced twist in the failure of stopper knots

We investigate the failure mechanism of stopper knots, with a particular focus on the figure-8 knot as a representative example. Stopper knots are widely used in climbing, sailing, racket stringing, and sewing to maintain tension in ropes, strings, or threads while preventing them from passing through an orifice. Combining high-precision model experiments and Finite Element Analyses, we systematically explore the influence of frictional interactions and their role in the build-up of mechanical twist. Our findings reveal that the failure of stopper knots via capsizing, which involves configurational alterations of the filament, is primarily due to friction-induced twisting when loading the knot against a restraining plate containing a clearance hole. Our study offers a comprehensive understanding of the mechanical behavior of stopper knots under diverse loading conditions, thereby providing crucial insights for their reliable application across various domains.

Investigation on interference and damage behaviours of electromagnetic riveted double-sided countersunk 30CrMnSiA/CFRP joints

Carbon fibre reinforced polymer (CFRP) structures benefit from electromagnetic riveting (EMR). However, incorrect riveting parameters could result in damages in CFRP structures during the EMR process. Excessive interference size may introduce initial damages to the joints. As a result, in this paper, the damage behaviours and the interference characteristics of the 30CrMnSiA/CFRP double-sided countersunk electromagnetic riveted joints are investigated. The riveting damage experiment was conducted, with the regular pressing riveting (RPR) process as a comparison. Moreover, a progressive damage FE model considering multiple typical damage modes of CFRP was developed for EMR damage prediction. The results show that when the rivet-hole diameter increases by 5% (4.08mm to 4.28mm), the average interference size of the joint under EMR and RPR processes decreases by 41% and 53%, respectively. Double-sided countersunk riveted joint interference size along the rivet axial distribution is not uniform, the CFRP sheet side of the interference size is relatively small. The EMR achieves a tighter, more uniform interference fit, while causing more severe riveting damages to the CFRP structure. Initial riveting damage exhibits a variety of modes, with delamination damage showing most significant sensitivity to rivet hole clearance.

Impact of standard and unexpected bolt-hole-washer tolerances on the performance of pinned and torqued joints in CFRP composites

This study aimed to investigate the impact of some practical assembly errors on the performance of composite joints with M6 bolts in quasi-isotropic CFRP laminates with stacking sequence of [±45/0/90]2S, which are increasingly used in aerospace and automotive industries. The detailed experimental explanations of the behaviors of the bolted joints in CFRP composites with standard and unexpected joining parameters, exhibited a vital impact on the bearing and ultimate joint strength, stiffness, energy absorption, and failure mechanisms. The joining parameters include tightening torque (0-16Nm), bolt-hole clearance (0–240 μm), and washer-to-bolt hole clearance (0–500 μm) with different offset arrangements. The bolt axial force is monitored during the testing of double-lap bolted composite joints. The maximum performance of the bolted joints was observed at tightening torque of 12Nm, bolt-hole clearance up to 60 μm, washer-to-bolt hole neat-fit or with negative clearance arrangement. The first peak, 2 % offset, and ultimate strengths are increased, respectively, by 55.9 %, 56.4 % and 52.4 % compared to those of the pinned joints. The 2 % offset strength and stiffness of bolted joints with negative washer-to-bolt hole clearance arrangements is improved by 26.8 % and 57 % respectively compared to those having positive arrangements. Energy absorption increase almost linearly with bearing load with correlation coefficient of 0.982.

Simulation Analysis of Riveted Joint Specimen with Parameter of Working Pressure and Hole Clearance Using Semi-Automatic Riveting Tool

Simulation Analysis of Riveted Joint Specimen with Parameter of Working Pressure and Hole Clearance Using Semi-Automatic Riveting Tool

Fatigue performance of preloaded bolted connection with oversized holes

AbstractMoving towards a more sustainable and circular infrastructure has increased the demand for demountable connectors in hybrid structures combining steel, concrete, and nowadays FRP composite components. Large, prefabricated components need to be transported to the construction site and assembled by means of bolted connections for easy reuse of the components. Slip‐resistant connections are required for such hybrid structures in bridges, which are usually provided by injection or preloaded bolts. The former satisfies the need for large tolerances during execution. However, the behavior of such injection bolts depends on the environmental conditions and the resin complicates the installation and demountability. The current practice of preloaded bolts uses standard hole clearances that do not provide sufficient tolerance for the assembly of large structural components made of different materials and many connectors. This paper focuses on the fatigue performance of preloaded bolted connections with excessively oversized holes that could provide sufficient tolerance for execution. Double lap bolted joints for two different bolt‐hole diameters, regular and 60 mm oversized, are tested under cyclic loading and the increase in slip displacement during the load cycles is compared. The static performance is numerically obtained in terms of residual stiffness, slip and ultimate resistance. It was found the stiffness variation between normal holes and significantly oversized holes is insignificant.

Demountable shear connectors – constructional details and push‐out tests

AbstractThe sustainable composite structures are built by demountable elements in order to reuse them which can fit to the circular economy. The current research and development project – in the cooperation of Budapest University of Technology and Economics and KÉSZ Group, bim.GROUP Ltd, Hungary – is aiming to design a new kind of demountable steel‐concrete composite structural system. The key component of this construction is the demountable shear connector. In the current research, bolted shear connectors with embedded bolts and threaded rods are developed and studied which can fit to the applied technology of the industrial partner. One of the main aspects of this connection is to consider the bolt hole clearance since it occurs initial slip and stiffness reduction of the composite beam. In the first phase of the research program, the aim is to develop demountable and economical structural details which can reduce the stiffness reduction with proper strength and ductility features. To study the behaviour of these shear connections, a push‐out experimental program is developed and tested in March 2023. In the paper, the developed structural details and the push‐out experimental program with the first results are presented.

Numerical parametric evaluation of ultimate resistance of high-strength bolts

High strength bolts are widely used in the engineering field due to their good compressive properties. Accurate assessment of the ultimate capacity performance of high strength bolts under combined loading is essential to ensure the safety of steel structures in the connection zone. Existing studies are not sufficiently clear on the economic and condition-specific limits on the effects of various factors on high-strength bolts under complex stress conditions. In response to these problems, the aim of this paper is to analyse the effects of different factors on the load-bearing performance of high-strength bolts on the basis of numerical simulations. The mesoscale critical plastic strain (MCEPS) method was used on the model fracture and the accuracy of the model evaluation was verified. The effects of grade, type, diameter and bolt hole clearance on the ductile fracture behaviour of high-strength bolts were investigated. It was found that fully threaded bolts and through-hole clearances can mainly affect the load-bearing properties of high-strength bolts and increase the bolt's fracture-deformation capacity. The load-bearing performance of high-strength bolts under the influence of different factors was also compared with the Eurocode design (EC3) predictions.

Nonlinear spring modelling approach for concrete edge breakout failure of shear loaded anchorages of arbitrary configurations

The failure of anchorages placed close to the concrete edge and loaded in shear perpendicular towards the edge is often governed by the concrete edge breakout failure. Several assumptions are made in the current design methods to calculate the anchorage resistance, which simplify the calculations but may also lead to over-conservative or even unconservative design solutions. This paper presents a novel nonlinear spring modelling approach for the realistic evaluation of shear loaded anchor groups in case of concrete edge failure. The model follows a displacement-based approach and is developed on the basis of evaluation of a comprehensive experimental study carried out on shear loaded anchor groups. The basic philosophy follows the principles of the nonlinear spring model for the concrete cone failure mode of tension loaded anchorages, published earlier by the authors. In the nonlinear spring modelling approach for shear, it is assumed that the shear forces acting on a group are transferred from the base plate directly to the anchors. Nonlinear springs are used for modelling the anchor behavior to account for the distribution of forces among the anchors of the group. The nonlinear springs are provided to resist the forces acting in the loading direction and opposite to the loading direction, which might occur case of eccentric loading. While defining the properties of the nonlinear anchor springs, due consideration is given to the neighboring anchors through a tributary volume approach, to the vicinity of further edges and to the hole clearance. The friction between base plate and concrete is conservatively neglected. The postulates of the method are justified through a detailed evaluation of test results. The accuracy of the model is validated against a vast number of experimental results on anchor groups of arbitrary configurations.

Modelling and verification of sesame seed particles using the discrete element method

The size of sesame seed particles has been measured and analysed to build a sesame seed particle model using the discrete element method (DEM). Despite the strength of simulations using the DEM method, one of the challenges that still require to be overcome is approximating the form of the actual particles, especially for irregular shapes, to obtain more realistic simulations. Thus, the sesame seed particle was simplified to be quite close to the actual seed forms by drawing an irregular 3D sesame particle model using Fusion 360 software with the average dimensions of five hundred randomly selected sesame seeds. Consequently, a modelling approach for sesame seed particles based on a multi-sphere (MS) method was suggested. In this paper, the simulated results of the sesame particle model were close to those obtained experimentally, with 28 filling spheres. The results for both piling tests and oscillating seed meter calibration have shown that the 28- sphere model is appropriate for modelling the sesame seed particle. Thus, the validity and feasibility of the modelling approach for sesame seed particles we proposed have been verified. Finally, the simulation analysis provided a good prediction for the outflow process of sesame seeds from the oscillating seed meter. The optimum values for the main parameters of the oscillating seed metering device for sowing sesame seeds are 9 mm for seed exit hole clearance, 20° for oscillation angle, and 0.022 sec for opening time, providing a sesame seed rate of 2.7 kg/ha. As a result, it provides a reference for the design and optimisation of oscillating seed meter for sowing sesame seeds.

Tests and Numerical Study of Single-Lap Thermoplastic Composite Joints Bolted by Countersunk.

Tensile tests were carried out to investigate the effect of stacking sequences on the bearing strength of single-lap thermoplastic composite countersunk bolted joints. A 3D elastoplastic model was built based on a plastic theory for numerical analysis. The damage initiation was judged based on LaRC05 criteria, and the damage propagation was described by using a nonlinear, gradual unloading method based on crack band theory. The accuracy of the present model was validated by comparing the numerical results to those from the tests. The test results showed that the effects of stacking sequences on the ultimate bearing strength and the 2% offset bearing strength are limited. Moreover, the numerical results depicted that the ultimate bearing strength and the 2% offset bearing strength reduce when the bolt-tightening torque or the bolt–hole clearance is increased.

A Review of Fibre Reinforced Polymer Structures

This paper reviews Fibre Reinforced Polymer (FRP) composites in Civil Engineering applications. Three FRP types are used in Structural Engineering: FRP profiles for new construction, FRP rebars and FRP strengthening systems. Basic materials (fibres and resins), manufacturing processes and material properties are discussed. The focus of the paper is on all-FRP new-build structures and their joints. All-FRP structures use pultruded FRP profiles. Their connections and joints use bolting, bonding or a combination of both. For plate-to-pate connections, effects of geometry, fibre direction, type and rate of loading, bolt torque and bolt hole clearance, and washers on failure modes and strength are reviewed. FRP beam-columns joints are also reviewed. The joints are divided into five categories: web cleated, web and flange cleated, high strength, plate bolted and box profile joints. The effect of both static and cyclic loading on joints is studied. The joints’ failure modes are also discussed.

A dual material removal mechanism for clearing of obstructed holes via electrical discharge machining

Cooling hole blockages in gas turbine blades can occur during operation, detrimentally reducing performance and resulting in premature removal from service. Here, electrical discharge machining (EDM) is used to unblock fine holes, which have been obstructed with a mixture of both conductive and non-conductive contaminants representative of post-service condition. This work demonstrates EDM is a viable process to unblock fine holes containing material which is partially non-conductive. The mechanism results from a combination of conventional EDM discharges and mechanical spalling, resulting in a dual removal process. This method allows accurate and repeatable hole clearance in a conventional EDM hole-drilling setup.