Bolt Bearing Research Articles

Effects of bolt diameter and loading direction on bearing and withdrawal resistance of half-threaded bolts in glued laminated timber

Timber connections were prepared using glulam from tropical plantation species, focusing on key properties for dowel-type joints with half threaded bolts without nuts: Bolt bearing strength and bolt withdrawal capacity. Tests were performed according to ASTM standards. Three half-threaded bolt diameters (12 mm, 16 mm, and 20 mm) were tested in two loading directions, parallel and perpendicular to the grain, with 12 replicates for each configuration. Response Surface Methodology (RSM) using Design Expert Software was applied to optimize bolt diameter for both loading directions. Results showed that bolt bearing strength was higher in perpendicular loading, with the 12 mm bolt achieving 16.6 N/mm², compared to 6.01 N/mm² in parallel loading. Withdrawal capacities varied, with the 16 mm bolt showing the highest capacity in perpendicular loading at 54.2 kN. The study demonstrates that the 16 mm bolt exhibited the optimal diameter-to-embedment length ratio compared to 12 mm and 20 mm bolts, resulting in the highest withdrawal capacity. Consequently, the 16 mm bolt represented the best balance for achieving maximum withdrawal capacity. The optimization suggests using a 16 mm bolt for parallel loading to the grain and a 14 mm bolt for perpendicular loading.

A computational modeling approach for cold-formed steel bolted connections exhibiting bolt slip and bearing behavior

Cold-formed steel (CFS) is increasingly used for buildings and infrastructures, as it is lightweight and easy to install in the field when a bolted joint method is used to join elements. Unlike “rigid” welded joints, bolted joints allow for movement during load transfer, adding flexibility. Such flexibility is more prominent in thin-walled CFS bolted connections. The structural performance of a CFS structure with bolted joints is considerably governed by the mechanical behavior of the bolted joints. In many existing finite element (FE) simulations, an individual CFS bolted joint was modeled as a simplified linear or bilinear behavior, leading to less accurate results of both local and global behavior of the CFS structure. This study presents a novel FE-based method for modeling a bolted joint for CFS, which enables the simulation of nonlinear behavior of the bolted joint, characterized by the bolt slip and the progressive bearing. This approach utilizes the connector elements in series, defined with the friction and plasticity models, to model this bolt slip-bearing behavior. A well-known torque–friction force relationship is used to estimate the bolt friction slip load needed for the friction model definition. Rex equation is used to predict the bearing load–deformation response, which is inserted as the input into the plasticity model. The suitability and the capability of the approach is first validated using two of the CFS lap connections with a single bolted joint subjected to monotonic/cyclic loading. Then, the proposed approach is validated for the large-scale moment-resisting CFS connection beams with eight different configurations. It is expected that the application of the proposed approach can be extended to any type of thin-walled bolted connections exhibiting the bolt slip and bearing response.

Seismic behavior and reliability of variable friction damped self-centering prestressed concrete frames considering bolt bearing

This study comprehensively studied the bolt bearing behavior on the influence of friction based self-centering prestressed concrete (SCPC) frames. Based on the mechanism and test results of a SCPC connection with variable friction dampers (VFD), the theoretical analyses for the VFD-SCPC connection considering the whole procedure of friction bolts ranging from bearing to failure were carried out. The numerical model of the VFD-SCPC connection considering the bolt bearing behavior was proposed and the incremental dynamic analyses were carried out to obtain the seismic behavior of the VFD-SCPC frames when the friction bolts in the VFD ranged from bearing to failure. Taking the inter-story drift corresponding to the initiation of friction bolt bearing as variation, the fragility analyses for the SCPC frames with VFD and common constant friction dampers (CFD) were conducted to acquire the reliable design for the allowed bearing of friction bolts. The analyses results shown that to obtain the balance between the acceptable damage and expected reliability, the inter-story drift corresponding to the initiation of friction bolt bearing should be ranged from 2.0% to 2.5% for the VFD-SCPC frames and less than 2.0% for CFD-SCPC frames.

A practical numerical model for thin-walled steel connections and built-up members

The interaction between the cold-formed steel members and fasteners in a structural assembly often involves complex stress states, material plasticity, significant in-plane deformations and curling, rendering computational modelling of the resulting structural system challenging. In addition, the presence of initial geometric imperfections and the susceptibility of cold-formed steel members to local instabilities adds a further degree of complexity to the numerical modelling. The behaviour of bolted connections between cold-formed steel members has traditionally been assessed based on physical tests, though these can be time consuming and expensive. In this paper, a practical numerical approach to the simulation of bolted cold-formed steel connections, capturing all the key behavioural features including bolt preload, slippage and bearing, is introduced. Starting from a typical shell finite element (FE) model of a cold-formed steel plate, a small number of solid elements is introduced around the bolt holes, to allow accurate replication of the bolt-ply interaction, with contact pairs defined between the bolts and the surrounding material. An explicit dynamic solver is then employed to solve the geometrically and materially nonlinear problem, both with and without bolt slippage. Validation of the FE model is conducted using benchmark tests reported in the literature. It is shown that the proposed numerical method can accurately capture the structural behaviour of bolted cold-formed steel connections and cold-formed steel built-up sections, while being computationally efficient and numerically stable; the proposed approach is therefore recommended for the numerical modelling of cold-formed steel systems assembled using fasteners.

Behavior of different bolted connection configurations in frames composed of cold-formed sections

Rigid bolted cold-formed steel connections have been very popular for their better distribution of straining actions and for better full-filling serviceability requirements. However, the behavior of every single element in the connection as well as the interaction between them is not clear due to its complex behavior. A nonlinear finite element parametric study was conducted on the apex knee connection of a portal frame constructed with cold-formed back-to-back double-lipped C sections for both the rafter and the column. These back-to-back lipped C sections, connected by gusset plates are used as beam and column members. Only the webs of lipped C sections are connected to the connection gusset plates with bolts. The section flanges are not connected to the columns for ease of construction. The study focused on investigating the effect of different parameters on the ultimate capacity and the failure mode of the eave connection. Studied parameters include different bolt configurations, bolt diameters, gusset plate thickness, the bolt pre-tensioning force, and the edge distance. The effect of bolt bearing on the C-section web was considered in the calculation of the capacity of the connection. Five modes of failure were identified namely; lateral out-of-plane buckling of the gusset plate, local buckling of the connected section, bolt bearing of C-section web and the gusset plate, tearing of C-section web. It was observed that bearing failure is the dominant mode of failure. However, in some cases, the lateral-out-of-plane buckling of the gusset plate takes place and causes the premature failure of the connections at low values of applied loads. The local failure of the connected sections occurs at the ultimate loading phase. Several observations were found and some useful recommendations for optimum connection configuration are suggested. A simple interaction design procedure for special configuration to calculate the resistance of the joint connection under moment, shear, and normal forces based on the bolt bearing failure for different bolt pitches is proposed.

An improved and robust finite element model for simulation of thin-walled steel bolted connections

Thin-walled cold-formed steel (CFS) structures are widely used in low-storey buildings and are seeing increased applications in multi-storey buildings as well as long-span structures. The bolted connection is one of the most common types of fasteners employed in CFS structures. The bolt slippage and load-bearing mechanism in CFS connections have a significant influence on the structural behaviour of cold-formed steel construction assemblies, which are typically numerically simulated using spring/connector elements. However, the determination of input parameters for the spring/connector elements generally requires load-deformation characteristics obtained from physical tests of lap joints, which are costly and time-consuming. Moreover, the use of spring/connector elements fails to explicitly capture the bolt bearing behaviour, resulting in inaccuracy in the simulation of CFS connections. In this paper, an accurate, efficient and robust numerical method that can fully replicate the behaviour of CFS connections considering both the effects of bolt slippage and bearing has been introduced. In the proposed numerical methodology, the cold-formed plates are modelled using the conventional shell elements, while a number of solid elements are introduced around the bolt holes, enabling the bolt-plate interaction to be explicitly accounted for, with contact pairs defined between the bolts and their surrounding solid element surfaces. The proposed numerical method could find a convergence solution using dynamic implicit solver in the general-purpose finite element (FE) software ABAQUS. Good agreement between the FE models using the proposed method and the available test results of CFS bolted connections were achieved, which sheds light on the promising application of the proposed method for simulating CFS assembled using bolted connections.

Numerical analysis of the influence of curling on the strength of connections with one bolt

AbstractCurling failure typically appears in bolted connections with thin plates, where the force is transferred by bolt bearing. The curling phenomena is related to the high compressive stresses caused by bolt bearing, which cause the plates to buckle, reducing the bearing strength of connections. Since the reduction of the bearing strength due to curling is not considered in design codes, the curling phenomenon has been studied numerically to understand the mechanical behaviour and to develop simple design rules that take into account reduction in bearing strength. The reduction factor for reducing the bearing resistance by curling was developed taking into account the Eurocode approach, i.e. by calculating the elastic critical force associated to curling and the relative slenderness. Therefore, the elastic critical force in relation to curling was obtained by parametric buckling analysis in finite element software Abaqus. These results were used to develop a simple analytical model for the calculation of the elastic critical curling force. The reduction factor was obtained from the relationship between the results of parametric GMNIA and relative slenderness. The strength of single bolt connections was determined by geometrical and material nonlinear analysis with imperfections (GMNIA) considering various parameters, namely ratio of the bolt diameter to plate thickness, end distance e1, edge distance e2, material grade (S235, S690), shape and amplitude of imperfections and boundary conditions. The accuracy of the reduction factor for bearing strength is checked on the basis of experimental data given in literature.

Research of combined grey model based on entropy weight for predicting anchor bolt bearing capacity

A combined prediction model based on entropy weight was proposed to overcome the shortcomings of single grey model for predicting anchor bolt bearing capacity. Firstly, the grey GM (1,1) model and grey Verhulst model are used to predict the bearing capacity of anchor bolt according to the P-S curve obtained from pull test. Secondly, the entropy weight method is utilized to obtain the weight indexes of the two mode. Then two models are combined by the weight index to achieve final bearing capacity prediction. The experimental results show that the combined prediction model based on entropy weight can improve the accuracy of the grey prediction model as the load increasing.

On the progressive fatigue failure of mechanical composite joints: Numerical simulation and experimental validation

In this study, a novel holistic progressive damage model for mechanical fiber-reinforced polymer (FRP) joints under static and fatigue loading is presented. The model is implemented as a user-defined subroutine in the finite element software ABAQUS/Implicit. First, the theoretical basis of both the static and the fatigue damage model are explained in detail. Here, special emphasis is put on the introduction of the FRP fatigue damage model (FDM), which is based on a physically-motivated hypothesis enabling the consistent coupling of static and fatigue damage properties. Furthermore, detailed insights concerning the experimental calibration of the FDM are presented for the first-time. Subsequently, the presented damage model is validated using first-hand experimental results for standard bolt bearing, as well as T-bolt bearing, test setups. The experimental bearing setups are tested and analyzed until ultimate failure, applying static and fatigue loading. It is shown that the model prognoses are in close accordance with experimental measurements and observations in terms of static joint strength, cyclic stiffness degradation and cycles to failure. The rich information provided by the damage model concerning the progressive damage evolution under static and fatigue loading conditions allows for its application within virtual test rigs for mechanical FRP joints. In that context, this work demonstrates the promising abilities and features of the energy hypothesis applied for the FDM for use-cases of significant relevance in the composite industry for the first time in literature.

Cyclic behavior of high-strength steel framed-tube structures with bolted replaceable shear links

Although the use of steel framed-tube structures (SFTSs) under intense earthquakes loads helps to prevent fatalities, the plastic hinges at the ends of spandrel beams cannot properly developed due to low clear span-to-depth ratios, resulting in poor ductility and recoverability. To address this problem, high-strength steel framed-tube structures with replaceable shear links (HSS-FTS-RSLs) were proposed, which combine the advantages of replaceable shear links and high-strength steel (HSS). This paper presents an experimental research program including three 2/3-scale single-story single-span sub-structure specimens with three types of spandrel beam-to-link connections: bolted end-plate connection, bolted web connection, and bolted splice-plate connection. The global seismic response and replaceability of the specimens were evaluated. Nonlinear finite element models of the specimens were established and validated with the experimental results. Test results demonstrated that the three specimens developed the expected ductile failure of the shear links while the spandrel beams and columns were damage-free, showing excellent energy dissipation and deformation abilities. The usage of HSS effectively maintained the structural components in essentially linear elastic range. The specimen with bolted end-plate connection exhibited a stable hysteretic response and high resistance. This connection type possesses reliable force transmission, convenient construction, no-slippage property, and the shortest replacement time. The connection rotation as a result of bolt slipping and bolt bearing significantly contributed to the total shear link rotation for the specimens with bolted web connection and bolted splice-plate connection. This led to the increased deformation ability and ductility as well as the pinching of hysteretic loops. Post-earthquake recoverability can be achieved as expected. The acceptable residual story drifts θre that allow for easy replacement of the shear links were 0.41%, 0.31%, and 0.42% corresponding to the specimen with bolted end-plate connection, bolted web connection and bolted splice-plate connection, respectively. The detailed finite element models of the test specimens accurately predicted the experimental behavior.

Behaviour of H-section purlin connections in resisting progressive collapse of roofs

When a truss roof is subjected to sudden local damage, purlins are capable of bridging the damaged truss unit, thereby increasing the robustness of the integrated roof system. To investigate the bridging capacity purlins can provide, experiments were carried out on bolted fin plate connections that join thin-walled H-section purlins to the main truss, investigating their behaviour under a main truss-removal scenario. Eight specimens with varied connection details were tested. Results of all experiments are provided in detail, including the full-range vertical resistance versus displacement curves, the collapse-resisting mechanisms, and the failure modes, being either bolt shear failure or combined bolt bearing and net-section tensile failure. Experimental results showed that better bridging capacity can be achieved by adopting relatively larger diameter bolts, reducing the bolt group height, applying higher preloading force when installing bolts, and increasing the end distance for the bolt holes. Meanwhile, a theoretical model is proposed to predict the vertical resistance versus displacement response of the purlin-to-connection assembly. This model is capable of capturing the slip of bolts, and the gradual yielding and failure of the connection components, and thus gives predictions that are in reasonably good agreement with the experimental results.

Thermal creep behavior of shear tabs in fire using modified burgers model

A mechanical model is developed to predict the time-independent (fast) and time-dependent (due to thermal creep) force-rotation characteristics of shear tab connections subjected to fire. The time-independent behavior of the connection is modeled using a group of springs that can predict the rotational stiffness and the strength of the connection when subjected to fire temperatures. A modified Burgers model is incorporated in the mechanical model to include the thermal creep effect. The modified Burgers model is composed of linear springs and viscous dashpots that can predict the time-dependent behavior of the shear tab connection before and after beam-column contact, and bolt bearing. The proposed model shows excellent agreement when compared with experimental results and finite element (FE) simulations. Furthermore, isochronous curves are developed to study explicitly the effect of different parameters, on the strength and rotational capacity of shear tab connections. The proposed model can be considered an important step toward the inclusion of thermal creep in fire design of shear tab connections.

Experimental and numerical study of the axial stiffness of bolted joints in steel lattice transmission tower legs

Steel lattice transmission towers are constructed through the bolted assembly of various sizes of angle steel members and joint slip is inevitable; ignorance of this slip, which is the prevailing practice in transmission tower design engineering, can lead to an overestimation of the axial stiffness of bolted joints. This study investigates the impact of joint slip effects under tensile loading through a series of 30 tensile tests of 10 typical bolted joint configurations (3 specimens for each tested configuration) used in classic 500 kV lattice steel transmission line towers in China. Finite element analyses were also conducted as a complement and validation of concepts. Particular focus was placed on the load-deformation/slip curves of the tensile tests. The experimental results show that the joint slip was realized through a complicated process consisting of elastic deformation caused by the frictional load transfer and the asynchronous joint slip. Meanwhile, when subjected to an incremental axial tension, the axial stiffness of the bolted joints was highly nonlinear with regard to the elastic deformation. A simplified multi-linear strain-stress model was created using the experimental data to represent this nonlinearity in finite element analysis. The results from finite element analysis of the 30 tensile tests using this multi-linear strain-stress model show that the model can well predict the failure load level and positions of rupture of the angle members. The actual average axial stiffness of the tested bolted joints during the elastic deformation process of load transfer by bolt bearing is approximately 30% of the theoretical value. Finally, a general nodal element is proposed to describe the joint slippage effects and introduce this important factor in the structural analysis of lattice transmission towers in view of safer and more reliable design.

Numerical analysis on the ultimate bearing resistance of single-bolt connection with high strength steels

This paper presents a numerical investigation on the bearing behavior of single-bolt connections with high strength steels in double shear. To simulate the phenomenon of accumulation damage shown in the post-peak behavior of bolt bearing and investigate the failure mechanism of tearout and splitting, the framework of ductile metal damage was used in the numerical model. The model was verified against the test results of bolted connections between high strength steel members. With the validated numerical model, a saddle-shaped distribution of the equivalent plastic strain was observed around the bolt hole, which explains the initiation and propagation of the fracture. A pure shear stress band, which is coincidence with the shear fracture in the experiments, was observed in the numerical analysis. In addition, the reduction of ultimate bearing resistance in splitting failure is explained by the increasing of lateral tensile stress at the tip of plate end with the decrease of edge distance. An extensive parametric study of 513 specimens was carried out to evaluate the effect of edge distance and end distance on ultimate bearing resistance. The boundary between tearout and splitting failure was established based on the distribution patterns of lateral tensile stress around the plate end. Finally, a new formula for predicting the ultimate bearing resistance with consideration of splitting failure was proposed.

Stability Analysis of Bolts Reinforced Rock Jointed Slope by Considering the Transverse Effects

The fully grouted bolt is a convenient, effective, and economic technology for slope reinforcement. A new nonlinear Hoek-Brown strength reduction method based on the characteristics of a jointed rock mass is proposed. By analyzing the change in slope failure mode, effects of the bolt head, spacing, inclination, and arrangement on the stability of the slope are investigated. Results show that the shear strength of the bolted structure is contributed by the axial force and transverse shear force. The transverse shear force of bolts increases the slope stability and improves the bolt bearing capacity; the bolt head is important in determining the failure mode and factor of safety of a bolted slope, while the size and material parameters of the bolt head are not important when the size of the bolt head is sufficiently large. The vertical bolt spacing has a nonlinear effect on the slope safety factor, and the failure mode of the slope changes from deep sliding to partial deformation along the joint surfaces with increase in the bolt horizontal spacing. With increase in the bolt inclination angle, the safety factor first increases and then decreases, and the maximum safety factor occurs when the bolts are placed horizontal or perpendicular to the slip surface. The slope safety factor decreases with decrease in the bolt length. An optimal design of longer bolts at the bottom and shorter bolts at the top is recommended. A shear zone forms from the intersection of two joints to the slope surface in the upper part of the slope.

Bearing strength at bolt holes in connections with large end distance and bolt pitch

The paper presents test results of one and two bolt connections with very large end distances that failed in bolt bearing, where very high bearing forces were recorded. The purpose of the tests was to investigate the behaviour of the plate in bearing that was not limited by shear, splitting, bolt or net cross-section failure, but with tearing of the material in front of the bolt. The tests showed that the bearing capacity increased insignificantly as the width of the plate increased. Numerical simulations show that bearing resistance is in cases of large end distances significantly influenced by friction forces. They develop because the bolt head and nut, together with the lap plates, constrain the increase of the plate thickness related to plastic deformation. The paper deals with the formation of the stress-strain field as well as the influence of the inner bolt determined by the numerical simulations. The resistances obtained from the tests agree very well with the bearing strength model presented recently by Može and Beg (2014). The coefficient of the bearing strength model that considers the influence of the inner bolt is calibrated on the basis of the presented test results as well as on high strength steel connections with several bolts. The presented bearing strength model was adopted in the final draft of the second generation of EN 1993-1-8.

Analysis of the results of acoustic emission diagnostics of a structure during helicopter fatigue tests

The study is devoted to a perspective diagnostic method, which makes it possible to deal with diagnostic tasks – the acoustic non-destructive inspection method based on acoustic emission (AE) signal parameter analysis. The practical use of this method is related to the interpretation of diagnostic measurement data. The parameters of acoustic emission (AE) signals were measured during bench tests of the tail boom structure and fin, as well as the joint areas of the fin, tail boom, and fuselage of the helicopter (joint area No.1 and No.19, frames of the tail boom and fuselage respectively).The analysis of fatigue damage kinetics was carried out in several stages for groups of bolts and for characteristic structure loading intervals. Bolt fracture was predicted at least 26 to 44 flight hours before the actual collapse. Using the AE parameters, the micro crack origin intervals identified when the bolt bearing capacity after the occurrence of the damage reached 96%.

Discussion on the installation checking method of precast composite floor slab with lattice girders

Based on the installation checking requirements of China’s current standards and the international norms for prefabricated structural precast components, it proposed an installation checking method for precast composite floor slab with lattice girders. By taking an equivalent composite beam consisted of a single lattice girder and the precast concrete slab as the checking object, compression instability stress of upper chords and yield stress of slab distribution reinforcement at the maximum positive moment, tensile yield stress of upper chords, slab normal section normal compression stress and shear instability stress of diagonal bars at the maximum negative moment were checked. And the bending stress and deflection of support beams, strength and compression stability bearing capacity of the vertical support, shear bearing capacity of the bolt and compression bearing capacity of steel tube wall at the bolt were checked at the same time. Every different checking object was given a specific load value and load combination. Application of installation checking method was given and testified by example.

13.10: Angles connected by one leg in tension

ABSTRACTThe paper deals with bolted connections of angles connected by one leg subjected to tension force. These connections are characterized by the eccentricity of the tension force and are dealt with in the EN 1993‐1‐8 standard that provides the design resistance for block tearing, for bolt bearing and for reduced effective net cross‐section that is based on β factors. A closer look on the design resistance of the reduced effective net cross‐section shows that the calculation of β may lead to inconsistencies. An addition of a bolt may lead to decrease of the net cross‐section resistance. Moreover, the formulas for the calculation of the reduced net cross‐section resistances are only a different presentation of the formulas for the block tearing resistance. Analysis of 631 test results from literature shows that the calculation of the block tearing resistance is sufficient and that equations 3.12 and 3.13 of EN 1993‐1‐8 are redundant. The study will also show that a constant distribution of stress on the tension face may be assumed in the formula for the block tearing resistance of the angles connected by one leg in tension (eq. 3.9, EN 1993‐1‐8), similarly to the provisions in American standard AISC 360–05. A modified bolt bearing strength function is also presented and statistically analysed on 631 test results. It is simpler and less conservative than the one in EN 1993‐1‐8.

01.10: Different approaches towards numerical modelling of bolt bearing

ABSTRACTBolt bearing is characterized by large plastic deformations that occur mainly near the contact between bolts and plates and may possibly lead to fracture. Numerical modelling of such behaviour is not trivial. The paper focuses on the procedures for numerical analysis that allow numerical modelling of bolt bearing up to fracture. The commercially available software Abaqus software was used for this purpose, taking the advantages of built‐in material models and numerical procedures without introducing the user subroutines. The problem of bolt bearing is assessed using static stress analysis, explicit analysis and coupled Eulerian‐Lagrange analysis. The fracture model considered is based on stress modified fracture model and relies on the accumulating damage and on the reducing stiffness of finite elements to the point, where they offer no resistance and can be either removed from the model or are left with negligible stiffness. The required parameters (stress triaxiality, equivalent plastic strain to failure and displacement to failure) were determined from the experimental data.A few different bolted connections with different types of failure are analysed with full failure model and the results are compared with experiments. The advantage of Eulerian meshing is considered, where excessive plastic deformations lead to contact problems. Coupled Eulerian‐Lagrange analysis with model parts expected to have large deformations were modelled with Eulerian approach and the rest with more conventional Lagrange approach. Diverse material models, element options, time step and their impact on numerical simulation were compared and optimized for speed and accuracy.