Bolt Pretension Force Research Articles

A friction-strip hybrid damper with multi-phase energy dissipation mechanism: Cyclic test and numerical verification

By combining the frictional and plastic energy dissipation modules (FEDM and PEDM), a novel multi-phase friction-strip hybrid damper (MFSHD) is proposed in the current study. The theoretical analyses demonstrate that, when applied in a self-centering structure, the MFSHD is able to provide higher strength, secondary stiffness and energy dissipation and maintain the self-centering capacity compared with conventional friction dampers. A series of quasi-static tests was conducted on the MFSHD to evaluate the effects of different parameters on the hysteresis performance of the MFSHD. The results showed that increasing the strip number or the bolt pre-tension force could both improve the mechanical performance of the MFSHD. The MFSHD with sandglass-shaped strips had a better performance than that with I-shaped strips. In the MFSHD with lower slipping displacement, the PEDM was activated earlier and provided higher strength, stiffness and energy dissipation, whereas its low-cycle fatigue life was reduced. The numerical analyses based on the model validated by the test results showed that the self-centering braced frame substructure equipped with the MFSHD exhibited hysteresis behavior in consistency with the theoretical model. The superior performance of the MFSHD compared with conventional friction dampers was verified numerically.

Shear performance of high-strength bolted connections with stainless-clad steel plates in a corrosive environment

Stainless-clad (SC) steel plates offer desirable corrosion resistance at a relatively low cost, but their shear performance in high-strength bolted connections in a corrosive environment has not been fully explored. In this study, monotonic tensile tests were performed on specimens connected by normal and stainless high-strength bolts at different corrosion degrees. The results were used to determine the influence of corrosion on the slip coefficient, bolt pre-tension force, initial slip load, and ultimate bearing capacity, and a simplified method was developed for estimating the slip coefficient and initial slip load.

Numerical Behavior of Extended End-Plate Bolted Connection under Monotonic Loading

Extended end-plate connections, which act as joints providing resistance against moments between beams and columns, are commonly categorized as semi-rigid or partial-strength connections. The reason for their extensive application in steel frame constructions lies in their straightforward design, their ability to be reproduced easily, and the convenience they offer in the fabrication process. This research used the ABAQUS FE software to construct a three-dimensional finite element model (FEM) with the main objective of exploring how different geometric parameters impact the behavior of the extended end-plate bolted connection, which functions as a semi-rigid, partial-strength beam-to-column connection. Accurately determining the moment-rotation relationship and connection stiffness is of utmost importance for semi-rigid connections. The developed FEM models incorporate various factors such as geometric and material non-linearities, bolt pretension force, as well as contact and sliding between the connection elements. To establish the credibility of the numerical outcomes, the developed FEM model was meticulously calibrated and verified against experimental data obtained from previous studies available in the literature. Subsequently, using the validated finite element model, a parametric investigation was undertaken to evaluate the influence of distinct geometric parameters, namely the thickness of the end plate and column web stiffeners. This numerical model facilitates a comprehensive analysis of the extended end-plate bolted connection, encompassing critical aspects such as the moment-rotation curve and failure mode. The results demonstrated that the analyzed finite element model aligns well with experimental findings and that the use of column stiffeners is inevitable in the joint, as well as a moderated thickness of the end plate. Doi: 10.28991/HIJ-2023-04-02-04 Full Text: PDF

Numerical study of the behavior of friction-grip bolted shear connectors in composite beams with cold-formed steel sections

The concurrent use of concrete slab, and cold-formed steel section as a composite beam improves strength and stiffness, thus preventing local and lateral buckling of the beam. The composite action could be fulfilled by suitable shear connectors, though the codes do not prescribe any equation to determine the shear capacity, and design rule of these connectors. The friction-grip bolted shear connectors were introduced and their mechanical performance was studied via the experimental tests and finite element modeling. At first, ANSYS software was used for the 3D finite element modeling of these connections. The obtained results were verified by experimental results. It can be shown that the proposed model can estimate the behavior of friction-grip bolted shear connectors in composite beams with cold-formed steel section. Then, extensive parametric studies with 72 specimens were carried out and the effect of diameter and strength of the bolts, thickness and strength of cold-formed steel sections, clearance between the bolt and concrete hole and pretension force on the behavior of these connectors were evaluated. The effect of each parameter on the shear capacity of the connection was evaluated. Some equations were proposed for figuring out the shear capacity and load–slip curve of these connections based on the experimental and 3D finite element results.

Longitudinal shear performance of lightweight steel-UHPC composite connections based on large-diameter high strength friction-grip bolts

In order to improve the construction efficiency and reduce the self-weight of composite bridges, prefabricated thin UHPC (ultra-high performance concrete) decks can be connected to steel girders by high-strength, large-diameter friction grip through-bolts. This paper presents a pilot experimental study into the shear performances of such composite connections. Thirty push-out tests were carried out to observe the influences of bolt diameter, slab thickness, bolt strength, pretension force and random asymmetric clearance of the bolt within the slab and joist. The observed failure modes include bolt fracture, pronounced permanent flexure of the bolts due to extensive yield, and crushing/splitting of the UHPC. 36% and 25% increases in diameter (from 22 to 30 mm) and tensile resistance (from 795 to 995 MPa) in 55 mm thick slabs led to 43% and 11% improvement respectively in connection shear resistance. Moreover, a bolt pretension force increase from 150 to 200 kN and a slab decrease in thickness from 55 to 35 mm respectively changed the failure mode from bolt bending to bolt fracture and reduced the shear resistance by 15%. Random asymmetric clearances of the bolts between 0.17 and 5.43 mm led to 88%-100% reduction of connection stiffness at the first slip stage and decreased shear resistance by up to 11%. Regression analysis shows that connection shear strength, stiffness and ductility are mixed polynomial and exponential functions of the key connection variables.

Tightness problems at the flange connection in transient temperature and high pressure condition

The main goal of the article is to study, analyze and explain the most apparent cause of transient steam leakage from a high pressure turbine stage body. The analyses focus on transient heat transfer on the metal-metal flange connection of an external turbine casing and start-up tests. The coupled effect of thermal expansions and their impact on the residual bolt pretension force was analyzed in detail using FE models. Series of experiments were performed to confirm the results obtained by numerical calculation. The conclusion provided in this article can be used to improve the design of the flange connection working in variable temperature conditions.

Bending behavior of splice connection for corner-supported steel modular buildings

Splice connection consisting of slip-critical high strength bolt and side plate is a promising connection type for future modular construction. However, recognitions on basic performance for this connection are still limited. To fill this gap, this paper conducted a comprehensive research on basic bending behavior of a simple splice connection proposed by the authors for corner-supported steel modular building. The basic bending behavior of the proposed splice connection was analyzed in details by combined experiments and numerical simulations. It is found that the proposed splice connection can achieve a favorable ductile behavior in bending. Bilinear profile with two stages is clearly observed in the relationship between moment and connection rotation. These two stages have different stiffness but the applied load can keep increasing in the second stage with excessive deformation of the specimen. Such phenomenon reveals adequate reserve of bending resistance for the proposed splice connection under large deformation scenario. Based on method of farthest point, a transition point is defined and determined in the relationship between moment and connection rotation. This transition point represents an important change in the bending behavior, which is valuable for practical design. Numerical simulations are also introduced to supplement the tests. The analyses on stress states of components and variation in bolt pre-tension force properly explains anisotropy in resistance at the transition point for different loading directions. A parametric study is further conducted. Results indicate that the proposed splice connection possesses satisfactory tolerance for loss of bolt pre-tension force in the practical construction.

Finite Element Analysis of Proposed Self-Locking Joint for Modular Steel Structures

The intermodular connection between modules plays a vital role in the overall performance of modular structures. The separation between a column and connection is possible due to the absence of links (welding or bolting) since limited space is available between modules. This study proposed a self-locking joint to be used in a modular steel structure, connecting columns with a connection without need of extra space between modules. The behavior of the proposed connection subjected to monotonic load was evaluated using a finite element approach using ABAQUS software. The influencing factors contributed to the behavior of the self-locking connection and columns observed using a parametric study. The parametric study was conducted by varying beam thickness, bolt pretension force and friction coefficient µ. Results indicate that the proposed connection can be classified as a semirigid connection according to Eurocode 3 and special moment frame (SMF) as recommended by AISC.

Experimental study of slip‐resistant connections under cyclic load

AbstractThe slip‐resistant shear connections with preload bolts have traditionally use in the steel structures exposed to cyclic / fatigue loading or in the cases when the bolt slipping or connection deformations should be restricted. Hence, the shear load is transferred through the friction surfaces rather than the contact between bolt surface and hole. The main influencing parameters determine the connection slip resistance are the friction between the contact surfaces and the level of preload in the bolts. This paper presents an experimental study of preloaded bolted connections under cyclic load. Experiment was performed on double lap shear connections using high strength bolts and lock bolts, both M20 of grade 10.9. The steel plates used in experiment are grade S355JRG2. Sandblasting was performed using quartz sand as the abrasive after which the zinc‐silicate coating was applied on plate surfaces. To address the required pretension force in the bolts, the strain gauge method was employed. All strain gauges were calibrated. Six specimens were exposed to cyclic loading after monitoring initial and short‐term losses of pretension forces in the bolts. The main objective of the presented study is to investigate the influence of the cyclic load on the losses of pretension force in high strength bolts and lock bolts. The results of comparative experimental analysis are presented and discussed.

Numerical analysis of ring flange connection with defined surface area

AbstractRing flange connections with preloaded high strength bolts are most commonly used to connect two segments of steel tubular towers. Behaviour and durability of ring flange connections is influenced by various factors, including stiffness of ring flanges, fabrication and execution imperfections, welding technology and welding details of the ring flange/segment connection, type of bolts, pretension technique and control of accomplished pretension force in bolts. This paper focuses on ring flange connections with defined contacts compared to the “full ring flange connection”. No imperfections are considered. Behaviour of the ring flange connections is investigated by advanced finite element analysis (FEA). The realistic geometry of bolted connection, ductile damage material model and element removal are used in the advanced FE model with explicit numerical solver. In addition, the influence of two types of high strength bolts, fully‐threaded and partial‐threaded bolts, on the mechanical behaviour of connections is considered. The failure modes and tensile stiffness are compared using different analytical models. Finally, recommendations for calculation of the tensile resistance of the connection and the bolt force with defined surface area are provided.

Shear Behavior of Lapped Connections Bolted by thread-fixed one-side bolts at elevated temperatures

The Thread-fixed One-side Bolt (TOB) is the bolt that can be installed from outside of a steel tube column, which is anchored by the threads on the bolt hole wall instead of the nuts. A series of tests were carried out to investigate the shear behavior of the lapped connection bolted by TOBs using both the steady state fire tests and the transient state fire tests. The two observed failure modes of TOB connected lapped connections were the bolt hole bearing failure (failure mode 1) and the bolt shank fracture (failure mode 2). The high temperature might cause the change of failure mode from failure mode 1 to failure mode 2. Lapped connections using Standard High Strength Bolt (SHSB) were also tested. The comparison results showed that the ultimate shear resistance of lapped connections using TOBs at different temperatures was about 90% of that using SHSBs with the same configuration at steady state fire test. Applicability of the design equations provided by Eurocode 3 was validated by the steady state fire test results. A Finite Element Model (FEM) was built and validated by the test results and the FEM was used to further study more derailed parameter studies including the influence of bolt strength, the bolt pretension force and the high temperature to the shear behavior of TOB connected lap connections.

Analytical Performance and Design of CECFST Column Assembled to PEC Beam Joint

Concrete-encased concrete-filled steel tube (CECFST) columns and partially encased composite (PEC) beams are both steel-concrete composite members which have outstanding advantages and have been applicated in some engineering constructions. This paper makes an attempt to employ blind bolting technique to assemble CECFST columns to PEC beams. For the purpose of exploring the mechanical performance of this type of assembled joints, firstly, a nonlinear finite element (FE) model was established and validated, where complicated contact interaction was taken into consideration. Plenty of parametric analysis were adopted to find out the effect of ten parameters on strength and initial stiffness of the assembled joint. Numerical analysis showed that mechanic behavior is notably affected by axial load ratio, width and thickness of end-plate, bolt pretension force, bolt diameter, and steel ratio of CECFST column. Full-range analysis was then carried out to observe stress and strain developments and failure modes. Load transfer mechanism in CECFST column was also studied. Design methods to estimate the flexural capacity and initial stiffness of the connections were proposed in accordance with the component models. In comparison, it could be concluded that the calculation results fit well with the analytical results, which confirms that the design formulas could provide a favorable basis in practical design.

Behavior of splice connection during transfer of vertical load in full-scale corner-supported modular building

Splice connection, comprised of splice plates and slip-critical high strength bolts, is an efficient and convenient connecting technique for modular buildings. Previous investigations on this splice connection were mainly conducted based on tests of substructures, which may not reveal the real connection behavior in the whole modular building. To fill this research gap, this paper presents a comprehensive research on a full-scale corner-supported modular building assembled with splice connections. Behavior of the splice connection during the transfer of vertical load in the full-scale modular building is analyzed in details with combined experimental and numerical techniques. Test results showed that no unfavorable phenomenon was caused by the proposed splice connection before the global buckling of the module column. Based on the validated numerical model, a three-stage behavior during the entire loading process is found for the splice connection. The involvement of splice connection in the transfer of vertical load is negligible in the first stage while the splice connection provides sufficient constraint for the second-order moment at the bottom of module column in the second stage. The localized deformation and obvious formation of gap are found in the third stage. However, the analysis on the full-range bolt pre-tension force of the bolt group indicates that the origin of such negative phenomenon is located after the global buckling, which will not affect design on the vertical-load transfer performance of the module column. The sensitivity of connection behavior to the values of initial imperfections are also investigated by the parametric study. It is found that the proposed splice connection has a satisfactory tolerance for extreme initial imperfections. A transitional initial imperfection is further proposed, which may be used as an important reference for the practical control on the initial imperfection.

Studies on T-shaped one-side bolted connection to hollow section column under bending

A novel T-shaped One-side Bolted endplate Connection (TOBC) for steel beam to Hollow Square Steel Tube (HSST) was proposed and the behavior of TOBC under static bending moment was investigated through Finite Element Model (FEM). The FEM was verified by test results on Standard High-strength Bolted Connection (SHBC) in terms of the failure mode, the bending moment-rotation curve and the yield bending moment. Parametric analysis of TOBC was carried out. Studied parameters included both the general parameters of an endplate connection, such as the endplate width, the endplate thickness, the endplate strength, the bolt diameter, the bolt pretension force, the axial compression ratio of the column and the beam length, and the unique parameters of the TOBC, such as the direction of slotted bolt hole, the gap between infill block and bolt hole, the angular deviation of the T-head and the two-bolt hole of T-shaped One-side Bolt (TOB). A total of six failure modes were found namely: the beam yielding failure, the bolt failure, the endplate yielding failure, the column wall yielding failure, the column wall yielding accompanied with endplate yielding failure and the column wall yielding accompanied with bolt failure. The TOBC with slotted bolt hole in vertical direction had better performance than that in horizontal direction in terms of the initial stiffness, the yield bending moment and the ultimate bending moment. The gap between infill block and bolt hole had no effect on the bending performance of TOBC in moment connection. The angular deviation of the T-head had little influence on the bending performance of TOBC, if it was less than 30 degrees. The initial stiffness and yield bending moment of TOBC could be greatly increased by using two-bolt holes in the connection tension region.

Mechanical properties of bolted connections for aluminum alloy structures at elevated temperatures

This study investigates the tensile properties of bolted connections for aluminum alloy plates from room temperature to 400 °C through elevated-temperature tensile tests of 30 single- and 24 multiple-bolted connections. Accordingly, the failure modes and tensile bearing capacity are defined at different temperatures. Then, ABAQUS is used to establish the finite element models of bolted connections for aluminum alloy plates at elevated temperatures, and the tests verified the rationality of finite element models. Considering the parameters such as thickness and width of plates, diameter and end distance of bolt holes, pretension force, and arrangements of bolts, the study performs a parametric analysis of connections and further examines the contribution of these parameters on tensile properties of bolted connection for aluminum alloy plates at elevated temperatures. This study employs a statistical regression method to derive the theoretical formula. Finally, it proposes a set of elevated-temperature reduction factors of ultimate bearing capacity suitable for aluminum alloy joints, which can serve as a guide in the analysis and design of fire resistance for aluminum alloy structures.

Control Effects of Pretensioned Partially Encapsulated Resin Bolting with Mesh Systems on Extremely Soft Coal Gateways: a Large-Scale Experimental Study

Pretensioned partially encapsulated resin bolting with mesh systems (PPERBMSs) are commonly employed in underground mines, particularly for soft coal gateways requiring immediate support. However, the behavior of bolts and reinforced coals has not been explained, and supporting schemes are determined by engineering analogy and experience. Herein, two large-scale physical models of extremely soft coal gateway sidewalls, reinforced with traditional and improved PPERBMSs, were constructed to probe the performance of pretensioned bolts and the deformation evolution of reinforced coal during roadway driving and panel extraction. Results reveal the bolting effect distribution characteristics of traditional PPERBMS. The mechanism and mode of bolts-mesh-surrounding coal system (BMSCS) instability were analyzed. The control effects of the two supporting schemes were compared, and stability-controlling principles for extremely soft coal roadways were proposed. High bolt pretension force and mesh stiffness are found to be important for improving the bearing capability of BMSCS, especially for reducing the extent of squeezing deformation and severe failure zones in shallow coals. The control method of “high-pretension-force bolts + fine mesh steel–plastic or rhombic screen + high-stiffness welded wire mesh + long bolt/cable for compensating reinforcement at key parts” is proposed to promote the formation of a supporting force interaction zone within surface and shallow coals, reduce the weakly reinforced region causing BMSCS structural instability, and improve the stability and bearing capability of the interaction zone in the bolt anchorage section. These findings are helpful for understanding the bolting effect of PPERBMSs and could provide guidelines for bolting design in soft coal roadways.

Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Slip factor of high strength steel with inorganic zinc-rich coating

Abstract The loading resistance of slip critical steel connection is determined by the slip factor between faying surfaces and pretension force in bolts. The shot-blasting treatment is a commonly used and simple type of surface treatments. In order to avoid the risk of rusting of shot-blasted surfaces which threatens the structure safety, shot-blasted surfaces are generally coated with aluminum or zinc-based product. In this study, the slip factors of high strength steels (Q550, Q690 and Q890) with inorganic zinc-rich coating are investigated. Two values of coating thickness (60 μ m and 80 μ m ) are selected and the influence of thickness of coating on slip factor is studied. Based on classical friction mechanism theory, compared with slip factor of shot-blasted surface, the decreasing of slip factor of surface with inorganic zinc-rich coating is analyzed. Moreover, the coating thickness effect on slip factor is also investigated. Because the difference between the measured slip displacement at 5 min (short-term tests) and 3 h (long-term tests) exceed 2 μ m , corresponding creep tests are carried out to evaluate long-term effects. Based on tests results, the recommended values of slip factor of high strength steel surface with inorganic zinc-rich coating is 0.30.

Performance evaluation of a rocking steel column base equipped with asymmetrical resistance friction damper

A novel asymmetrical resistance friction damper (ARFD) was proposed in this study to be applied on a rocking column base. The damper comprises multiple steel plates and was fastened using high-strength bolts. The sliding surfaces can be switched into one another and can cause strength to be higher in the loading direction than in the unloading direction. By combining the asymmetrical resistance with the restoring resistance that is generated due to an axial load on the column, the rocking column base can develop a self-centering behavior and achieve high connection strength. Cyclic tests on the ARFD proved that the damper performs a stable asymmetrical hysteretic loop. The desired hysteretic behavior was achieved by tuning the bolt pretension force and the diameter of the round bolt hole. In this study, full-scale, flexural tests were conducted to evaluate the performance of the column base and to verify the analytical model. The results indicated that the column base exhibits a stable self-centering behavior up to a drift angle of 4%. The decompression moment and maximum strength reached 42% and 88% of the full plastic moment of the section, respectively, under a column axial force ratio of approximately 0.2. The strengths and self-centering capacity can be obtained by determining the bolt pretension force. The analytical model results revealed good agreement with the experimental results.

Mechanical performance of an improved semi-rigid joint system under bending and axial forces for aluminum single-layer reticulated shells

In this study, the traditional Temcor joint (TR-Temcor) is modified using a central hollow hexagonal prism and some front bolts. The Finite Element Analysis (FEA) model is established and verified by experiments. Then, a parametric analysis is carried out for the improved Temcor joint (IM-Temcor). To obtain the optimal parameters for the modified joint, the key factors, namely: number and location of the front bolts, bolt-hole deviation, pretension force in bolts, thickness of front plate and heat-affected zone caused by the welding work, are considered in the FEA models. The modified joint, with the optimized factors, is analyzed for different static load conditions, considering axial pressure, axial tension, pure bending, bending with axial force, and eccentric axial forces. The overall mechanical behavior of the joint, including the M-Φ curves, initial stiffness, ultimate strength and deformation capacity, as well as the failure modes are identified. The results from the improved joint are compared with corresponding values from of the traditional Temcor joints. The results show that the central hollow hexagonal prism and front bolts significantly improves the stiffness and ultimate strength of the joint, especially when the joint is subjected to pure bending, bending with shear force, axial force, bending with certain axial force and eccentric force.