Bolt Slip Research Articles

Effect of faying surface treatments and bolt tightened levels on fretting fatigue performance of slip critical connections with high strength bolts

The experimental investigation focuses on the fretting fatigue performance of M24 high-strength bolt slip critical connections (SCC) under shear load, taking into account the influence factors of faying surface treatments and bolt tightened levels. A novel extensometer supporting device for measuring micro-displacement between connection plates is proposed. The μ-N curves are obtained. Three-dimensional surface morphology scanning and fracture morphology analysis are conducted on the specimens. The results showed that the SCC contact area can be divided into stick, partial slip, and gross slip, with distribution ranges determined for each zone. Meanwhile the fretting fatigue life decreases with the increase of μ and pre-tension. Finally, a prediction of fretting fatigue life is made based on a multiaxial fatigue critical plane model.

Component-based modelling of single-leg bolted steel angle connections at elevated temperatures

As a vital part of contemporary society, steel lattice transmission towers and communication towers play an important role in the power transmission grid and telecommunication, respectively. Being often located in rural areas, they are prone to bushfire attacks due to heatwaves and droughts, which are becoming increasingly commonplace. However, unlike the steel members found in a lattice tower, the behaviour and material properties of which at elevated temperatures have been comprehensively studied and codified in design standards, the semi-rigid behaviour of the bolted connection between such members at elevated temperatures has not been investigated thoroughly. Therefore, this paper aims to investigate both the axial and rotational behaviour of single-leg bolted steel angle connections at both ambient and elevated temperatures. A theoretical model using the component method is firstly proposed to model the axial load-slip behaviour incorporating the temperature increase, with the effects of the bolt shear, plate bearing, friction between clamped members, bolt slip, and member elongation being considered. Once the axial load-slip model is proposed, the component-based model for describing the moment-rotation behaviour of the bolted connection is derived based on the load-deformation relations of individual bolts in the bolt group. The reliability of the theoretical model is then validated by modelling the connection behaviour obtained from previous connection test results. A three-dimensional finite element model is also constructed using ABAQUS software to further validate the accuracy of the proposed theoretical model for predicting the axial and rotational behaviour of single-leg bolted angle connections at elevated temperatures. It is demonstrated that the proposed component-based theoretical model for the bolted angle connection accounting for axial and rotational semi-rigidity as well as temperature elevation is capable of effectively capturing the load-deformation relationship for the single-leg bolted angle steel connections, and would be applicable to the study of steel lattice towers under bushfire attack.

Experimental study on seismic performance of variable cross section replaceable link

This paper presents an innovative design for replaceable shear links, incorporating a variable cross-section that emphasizes concentrated plastic deformation in the energy-dissipating region. The design employs fully bolted connections involving non-energy-dissipating components, enabling both efficient elastic design and focused plastic behavior. To evaluate the seismic performance of this variable cross-section replaceable link, three section configurations were developed for cyclic loading tests: a low-yield-point (LYP160) specimen with an unchanged energy-dissipating region, a Q235 steel specimen with circular holes in the energy-dissipating region, and a Q235 steel specimen with elongated holes in the same region.Experimental results emphasize that plastic deformation is primarily localized in the energy-dissipating region, with failures characterized by buckling and tearing around the region's holes. Notably, the low-yield-point specimen exhibits an overstrength coefficient of up to 3.65, displaying a complete hysteresis curve, exceptional energy dissipation capacity, and a plastic rotation of 0.18 rad. Conversely, the elongated-hole specimen demonstrates notable overstrength exceeding 1.70, but its energy dissipation is compromised due to the weakened section. In contrast, specimens with circular holes exhibit an initial elastic stiffness similar to low-yield-point steel specimens, outperforming elongated-hole specimens by around 84% in stiffness. Additionally, a two-stage design method for bolted connections, accounting for bolt slip, is proposed. This approach enhances the overall understanding and utilization of these innovative replaceable shear links.

Design approach and its optimization for bolted steel plate strengthened RC beams considering the effect of connection bolt slip

The use of bolted steel plates (BSP) has been found to be an effective method for increasing the flexural capacity of reinforced concrete (RC) beams. However, slip in bolt connections is an inevitable occurrence that affects the mechanical behavior of the BSP beam. While prior studies have thoroughly examined the effects of bolt connection slip on the flexural capacity of BSP beams, assuming unlimited slip, experimental results revealed that bolt connection failure takes place when slip surpasses a specific threshold. The current design methodology does not accommodate this finding. To address this issue, a simplified design method for practical applications is proposed. Comprehensive parameter studies were conducted on the enhanced moment capacity ratio and maximum bolt slip, involving a total of 13,824 and 276,480 calculations, respectively. It is found that several parameters (e.g., the aspect ratio of RC beam, the tensile longitudinal reinforcement ratio, the height of steel plate) affect the two above-mentioned indexes. Equations were then developed to determine the enhanced moment capacity ratio and maximum slip. It is noteworthy that the recommended effective yield slip (0.55 mm) is obtained based on adhesive anchor, which should be checked when other types of anchors would be used. Relying on these equations, an optimized design approach for BSP beams is introduced that avoids complex iterative processes. The effectiveness of the optimized design methodology is substantiated through a practical example.

CALCULATION METHOD OF LATERAL STIFFNESS OF PVC CAVITY PARTITION WALL WITH DIFFERENT CONNECTION FORMS

To explore the difference in seismic performance of walls with different connections, this paper designs a pseudo-static test of three groups of steel frames infilled with walls and a group of empty steel frame as a control. The test phenomena and the datum are used to evaluate the performance of structures. The results show that: (I) the initial stiffness and the peak load of the cast-in-place wall are large. The main failure modes are cracking at the joint between the wall and the frame, crushing at the corner, and internal splitting as well as curving outwards under large displacement. (II) The wall with L-shaped connectors dissipates energy by bolt slip and the yield deformation of connectors, which has the lowest contribution to the frame in stiffness and strength. The main failure is the cracking of cement mortar at the joint. (III) The connection mode of U-shaped and L-shaped connectors is relatively safe and reliable, which could make the steel frame and wall panel work better together under the action of earthquake. It could be recommended to use according to the bearing capacity requirements; Walls connected by reinforcement are not recommended because of brittleness failure, poor ductility, ordinary bearing capacity and energy dissipation capacity. Based on the principle of equivalent tension and compression bar, a simplified formula for calculating the lateral stiffness of polyvinyl chloride (PVC) cavity wall panel embedded in fabricated steel frame is proposed, and the accuracy of the calculation results is verified.

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.

Numerical study on hysteretic characteristics of transmission tower K-joints

Introduction: The mechanical properties of joints have a significant impact on the dynamic response of transmission tower structures.Methods: Considering bolt slip, the numerical model of the transmission tower K-joint is established. The mechanical properties of K-joints are studied from three aspects: failure mode, load-displacement hysteretic curve, and stiffness degradation by numerical method. The effects of bolt preload, friction coefficient, and member strength on the hysteretic properties of the K-joint are analyzed.Results: The results show that due to the complexity of K-joints, bolt slip will lead to the reduction of ultimate bearing capacity and the change of failure position. In order to accurately obtain the mechanical properties of K-joints, the influence of bolt slip should be considered in the research process; The plumpness of load-displacement hysteretic curve is greatly affected by parameters; The stiffness of K-joints degenerates with the increase of loading times.Discussion: The results provide a reference for the mechanical analysis of the transmission tower.

Design theory of earthquake-resilient prefabricated column foot joint with lateral force-resisting energy-consuming device

Based on the design concepts of damage control and concentrated energy consumption of key energy-consuming components, this paper puts forward an earthquake-resilient prefabricated column foot joint. Expounds the structural composition, advantages and seismic design requirements of this new type column foot joint in detail. After comprehensively considering the mechanical mechanism of the column foot joint, the load-bearing capacity correction coefficient and the height ratio of lateral force-resisting shear member (LRSM) inflection point are introduced, and the design theory is established accordingly, including the dimension of LRSMs, the number of connecting bolts and the stiffness of connecting beams. The rationality and applicability of the proposed design theory are verified by 18 groups of 90 finite element models, and several test specimens. The research shows that the design theory proposed in this paper can accurately predict the yield load and initial stiffness of the new type column foot joint, and effectively control the bolt slip time and the connecting beam failure time. The new column foot joint designed according to this design theory has excellent bearing capacity and ductility. The plastic damage of this joint can be basically controlled on the lateral force-resisting energy-consuming device (LRECD), which has the premise of earthquake-resilient.

Component-based model of semi-rigid connections for nonlinear analysis of composite structures

In order to achieve better mechanical performance and construction efficiency, the outrigger bracket with a “through type” interior diaphragm (OBTID) connection is proposed for application in semi-rigidly connected composite structures. The mechanical behaviour of OBTID connections in two frame tests under lateral cyclic loads is investigated to reveal the failure mechanism. Based on the test observations, a component-based model is proposed to analyse the nonlinear behaviour of semi-rigid connections by decomposing the connection components and putting forward the constitutive law of each component. Furthermore, the proposed model is implemented in a general commercial finite element package and a program for nonlinear analysis of semi-rigidly connected composite structures is developed by combining the component-based model with the previous fiber beam-column model. Then, a comparison between the numerical results and experimental results in both connection level and frame level indicates that the proposed component-based model can predict the complex nonlinear behaviour of semi-rigid connections with good accuracy. Additionally, the contribution of bolt slip to connection rotation is analysed to clarify the pinching effect, and the semi-rigidity of OBTID connections are compared with provisions of Eurocode 3 and that of other similar semi-rigid connections.

Failure Analysis of Transmission Tower in Full-Scale Tests

With the rapid development of Ultra-High Voltage (UHV) transmission lines, it is necessary to study the performance of UHV transmission towers. First, we performed full-scale tests on a transmission tower under seven loading patterns. Then, the test results were compared with the calculation results of the Chinese tower design software Transmission Tower Analysis Program (TTA), and the failure location of the tower and the stress characteristics of the key parts were studied. Finally, we discuss the influence of bolt slippage and a new joint on the tower performance, and propose some design proposals for the current Chinese code, based on the test results. The results show that a bolt slip will significantly increase the displacement of the transmission tower, but the residual displacement can correct it. The new joint design has good mechanical performance. The bracing member at the bottom of the tower leg is located at the connection of the tower leg and the foundation, and there is a significant sudden change in stiffness, which we recommend designing according to 4% of the axial force of the main members.

EVALUATION OF BOLT AXIAL TENSION FORCE AND SLIP STRENGTH FOR HIGH-STRENGTH BOLTED CONNECTIONS AFTER HEATING AND COOLING PROCESSES

EVALUATION OF BOLT AXIAL TENSION FORCE AND SLIP STRENGTH FOR HIGH-STRENGTH BOLTED CONNECTIONS AFTER HEATING AND COOLING PROCESSES

Research on the hysteretic performance of flower-gusset composite joints for single-layer aluminium alloy lattice shell structures

Joints are the most critical component of reticulated shell structures, and their hysteretic performance is crucial to the mechanical properties of the whole reticulated shell structure under seismic action. Therefore, the hysteretic behaviour of aluminium alloy flower-gusset composite joint for an out-of-plane bending moment was studied by experiments and numerical analysis. The results show that the hysteretic curves of flower-gusset composite joints and gusset joints contain four stages: an elastic stage, a bolt slip stage, a hole wall pressure-stiffness degradation stage and a failure stage. The hysteretic performance of the new flower-gusset composite joint is obviously better than that of the traditional plate joint. With the increase in the thickness of the cover plate, the bending stiffness of the flower-gusset composite joint increases significantly, while the rotational deformation decreases. Then, a restoring force model of the flower-gusset composite joint is proposed through theoretical analysis based on experiments and numerical analysis.

Conventional I-shape brace member bolted connections under seismic loading: Laboratory study

In many regions of the world, a conventional low-ductility concentrically braced frame (CBF) is commonly chosen as the seismic force resisting system. The energy dissipation is not restricted to yielding and buckling of the braces, as would be required for ductile braced frames; rather, energy dissipation is assumed to occur through localised yielding and friction in connections, as well as limited member yielding. The objective of this study was to characterize by means of laboratory testing the inelastic response of full-scale conventional I-shape braces and their bolted connections under reversed-cyclic seismic loading. Six brace specimens comprising two commonly used bolted connection types, flange plate and flange angle, were designed following the Type CC provisions prescribed by CSA S16. The brace specimens achieved storey drift ratios of 1%–2%, due to inelastic deformations in both the braces and the connections, even though capacity based design provisions were not incorporated in their design. Energy dissipation resulted from overall and local brace buckling, gusset plate buckling, tension yielding of flange plates, angles and gusset plates, block shear failure of brace webs and angles, bolt fracture and fracture of the gusset plates, along with bolt slip. However, the observed performance of these braces and connections in this laboratory based study is not necessarily guaranteed to be replicated for all conventional CBF designs due to the conservative nature and variability in accuracy of the existing CSA S16 design equations that were relied upon to design and detail the test specimens.

Experimental and numerical study of LY315 steel moment connection with bolted cover plates

To study the seismic performance of LY315 steel moment connection with bolted cover plates, the tests of three full-scale connection specimens subjected to cyclic loads were conducted. The slip resistance coefficient among high-strength bolts and LY315 steel plates was experimentally obtained. The failure modes, load-carrying capacities, hysteretic responses, deterioration performance, ductility, and energy dissipation capacities of the connections were investigated. The impact of the splicing position on the cyclic behavior of the connections was explored. Besides, the corresponding nonlinear numerical modeling approach was proposed, which was validated against the test results. Finally, the influence of the configuration details on seismic responses and damage control was discussed. The analysis results showed that the slip resistance coefficient with surface treatment of wire brush to remove floating rust was 0.29 for LY315 steel. The connections with bolted cover plates exhibited large load-carrying capacity, satisfactory energy dissipation capacity and ductility (the ultimate rotations of three specimens exceeded 0.04 rad, and the ductility coefficients were more than 5.0). When the cover plates were relatively stocky, as the decrease of the splicing position, the load-carrying capacities slightly decreased, while the deformed capacity and the cumulative dissipated energy of the specimens were slightly enhanced, which was probably caused by the local deformation of the cover plates and the slippage of bolts. The change of the splicing position had a minor effect on the stiffness degradation. The strategy of thickening the shear domain significantly enhanced the load-carrying capacities of the connections, and effectively lowered the shear deformation of these regions and the energy proportion of the column, however, the primary members of frame still dissipated most of the system energy. The strategies of shortening the splicing position or thinning the cover plates were effective options to mitigate the plasticity in the primary members and limit the damage within the replaceable cover plates.

Reduction of Stress Concentration at Stop-Hole by Bolting a Crack

A stop-hole, which is drilling at the crack tip, is one of the famous tentative repairs of fatigue cracks in steel structures. When the crack becomes longer, the stress concentration of the stop-hole also increases. Therefore, during the tentative repair of long fatigue cracks, the chances for re-initiation of the fatigue cracks from the stop holes are high. The bolting stop-hole method is a useful technique against fatigue cracks. In this technique, bolting is applied only for the stop-holes at the crack tips. Therefore, as the crack length increases, the effect of the bolting stop-hole method decreases. In this paper, the authors propose a stress concentration reduction technique for a stop-hole by bolting the fatigue crack between stop-holes. The effect of the proposed technique was verified by tensile and bending tests of specimens as well as finite element analysis. From the tensile and bending tests, it was clarified that the stress concentration of the stop-hole was drastically reduced by bolting a crack under the condition before the slippage of bolts. Additionally, multi-bolting cracks have the advantage of improving the slippage load of the bolts in a crack. Furthermore, finite element analysis verified the reduction in stress concentration of the stop-hole by bolting a crack, and the effectiveness of bolting cracks and stop-holes was also shown.

Mechanical Behavior and Failure Mode of Steel-Concrete Connection Joints in a Hybrid Truss Bridge: Experimental Investigation.

The core part of a hybrid truss bridge is the connection joint which combines the concrete chord and steel truss-web members. To study the mechanical behavior and failure mode of steel–concrete connection joints in a hybrid truss bridge, static model tests were carried out on two connection joints with the scale of 1:3 under the horizontal load which was provided by a loading jack mounted on the vertical reaction wall. The specimen design, experimental setup and testing procedure were introduced. In the experiment, the displacement, strain level, concrete crack and experimental phenomena were factually recorded. Compared with the previous study results, the experimental results in this study demonstrated that the connection joints had the excellent bearing capacity and deformability. The minimum ultimate load and displacement of the two connection joints were 5200 kN and 59.01 mm, respectively. Moreover, the connection joints exhibited multiple failure modes, including the fracture of gusset plates, the slippage of high-strength bolts, the local buckling of compressive splice plates, the fracture of tensile splice plates and concrete cracking. Additionally, the strain distribution of the steel–concrete connection joints followed certain rules. It is expected that the findings from this paper may provide a reference for the design and construction of steel–concrete connection joints in hybrid truss bridges.

Study on the secondary stresses of joint effects in transmission tubular towers

Transmission tubular towers are widely used in urban and large span transmission network, analyzed as ideal frame-truss systems without explicitly considering slippage effects in bolted joints. In this paper, a special beam element considering bolt slip effect is established based on the secondary development module UPFs provided by ANSYS software. A series of semi-rigid model of transmission tubular tower with different parameter features are simulated by directly calling the special beam elements instead of using spring elements and ordinary beam elements. Distribution form and influence factor of secondary stresses of main members in transmission tubular tower leg considering the bolt slippage effect is analyzed. The results indicate that secondary stresses are mainly related to three factors: the layout scheme of auxiliary members, the main member slenderness ratio, the angle between main members and diagonal members. By contrast, it is found that secondary stresses of two lattices are mainly larger than that of a lattice. Under two lattices the angle between the main member and the diagonal member is the major influence factor, while, a lattice, the secondary stresses are mainly depended on the main member slender ratio. Design suggestions are given based on the analysis results.

Development of cold-formed steel moment-resisting connections with bolting friction-slip mechanism for seismic applications

This paper presents an investigation into a friction-slip mechanism in bolted joints in cold-formed steel (CFS) moment-resisting connections suitable for seismic areas. The aim is to achieve higher ductility and energy dissipation capacity through an appropriately designed bolted connection, enabling activation of bolt slip, acting as a fuse mechanism, postponing the initiation of non-ductile local buckling in the CFS beams. By means of validated finite element analysis (FEA), both monotonic and cyclic performance of CFS connections comprising two types of square (SB) and circular (CB) bolt group arrangements, with four types of beam sections, are studied comparatively without and with slip at various levels. It is shown that the connections with slip provide higher energy dissipation capacity by up to 75% compared with that of the connections without slip. A design approach to predict an appropriate level for the connection slip moments to be initiated before the beam buckling moment is introduced using the direct strength method (DSM). On comparing the bolt forces obtained for the SB and CB groups, the CB connections produce a more uniform bolt-group force distribution which is closer to the idealised method; while the SB connection encounter a significant delay of up to 30% in activation of bolt group slip which could lead to unfavourable beam local buckling. Furthermore, to avoid an unfavourable hardening effect due to the bolts bearing action, slotted holes are used with a recommended length obtained for the cyclic movements of the bolts in the range of the designed connections. The instantaneous centre of rotation results show that the connections with slip have less deviation from the idealised centre of rotation than the connections without slip.

Pull-out performance of a novel anchor blind bolt (TubeBolt) for beam to concrete-filled tubular (CFT) column bolted connections

The utilisation of beam to concrete-filled tubular (CFT) column bolted construction remains limited due to the severe slippage of bolts, column surface deformation and low moment-resisting capacity. This study proposes a novel blind bolt, known as the TubeBolt, for beam to CFT column connections. Ten pull-out test specimens were evaluated under tensile monotonic loading. Bolt type, bolt diameter, end anchor member, hollow tube wall thickness and bolt hole diameter were varied for the test. The failure modes, anchorage performance, load-carrying capacity, strength, slippage and elongation of the bolts were analysed. The behaviour of the TubeBolt specimens was compared with that of the Extended Hollo-bolt specimens under the same condition. Experimental results indicated that the novel TubeBolt in concrete-filled tubes exhibited excellent anchorage performance, higher strength and less slip and elongation until the failure state was reached.

Joint stress based deflection limits for transmission line towers

Experimental investigations have revealed significant mismatches between analytical estimates and experimentally measured deflections of transmission towers. These are attributed to bolt slip and joint flexibility. This study focuses on effects of joint flexibility on tower deflections and proposes criterions for permissible deflection limits based on the stresses in joints. The objective has been framed given that guidelines are not available in the codes of practices for transmission towers with regard to the permissible limits of deflection. The analysis procedure is geometric and material nonlinear with consideration of joint flexibility in the form of extension or contraction of the cover plates. The deflections due to bolt slip are included in the study by scaling up the deflections obtained from analysis by a factor. Using the results of the analysis, deflection limits for the towers are proposed by limiting the stresses in the joints. The obtained limits are then applied to a new full scale tower to demonstrate the application of the current study.