Steel Bolts Research Articles

Numerical and theoretical research on flexural behaviour of steel-precast UHPC composite beams

In order to promote the utilization of high strength materials and application of prefabricated structures, flexural behaviour of section steel-precast UHPC (Ultra-High performance concrete) slab composite beams prefabricated with bolt shear connectors are numerically simulated by the finite element (FE) software ABAQUS. The model is verified by three prefabricated steel-concrete composite beams tested. Numerical analysis results are in good accordance with experimental results. Furthermore, parametric studies are conducted to investigate the effects of strength of section steel and concrete of precast slab, thickness of section steel, width and height of precast concrete slab, diameters of steel bars and bolt shear connectors. The flexural behaviour of composite beams, in terms of bearing capacity, deflection, ductility and energy dissipation, are compared. The numerical results indicate that the improvement of strength of section steel results in a decrease of ductility, but a significant increase of the ultimate load and energy dissipation. Compared with composite beam made of section steel with thickness of 10 mm, the ultimate load of beams made of section steel with thickness of 14 and 18 mm improve by 29.0% and 58.8%, respectively, the ductility enhance by 2.8% and 8.3%, respectively, and the energy dissipation improve by 8.0% and 12.3%, respectively. With the increase of concrete strength, the ultimate load, deflection and energy dissipation gradually increase. The ductility of steel-UHPC composite beam is the highest, that of steel-HSC composite beam is the lowest. The effect of reinforcement ratio of concrete slab and diameter of shear bolts on the ultimate load of composite beam is limited. Simplified formulae for two different sectional types of proper-reinforced section steel-precast UHPC slab composite beams occurred bending failure are proposed, and the predicted results fit well with the simulated results. The results can be taken as a reference for the design and construction of section steel-precast UHPC slab composite beams.

Ultra-low cycle fatigue performance of grid structure with bolted spherical joints

This study aimed to investigate the effect of the specification of each grid structure component on the ultra-low cycle fatigue performance of the rod element of a grid structure with bolted spherical joints. Thus, an ultra-low cycle fatigue test of three identical composite steel tube and bolted sphere specimens was performed. The test was performed under three kinds of constant amplitude loading regimes for large axial cyclic plastic strain loads. Based on steel ductility damage and initial geometric defects, a finite element simulation of the test was then conducted using Abaqus/Explicit, which was calibrated according to the test results. In addition, parametric numerical simulations were performed to analyze the effects of different steel tube slenderness ratios, bolt diameters, and steel tube wall thicknesses on the seismic performances of the composite steel tube and bolted sphere specimens. The results indicated that the specimen dissipated energy mainly through material damage in the plastic hinge region in the middle of the steel tube. The steel tube slenderness ratio mainly affected the fatigue life and energy dissipation capacity of the specimen. Further, the ultimate tensile and compressive bearing capacity as well as deformation capacity of the specimen both increased with increasing steel tube wall thickness. Finally, the energy dissipation pattern of the specimen was most sensitive to the bolt diameter; thus, the energy dissipation capacity of the steel tube can be fully utilized only by selecting the bolt specification that matches the rod element.

Flexural Performance of Steel Beams Strengthened by Fastened Hybrid FRP Strips Utilizing Staggered Steel Bolts

Flexural strengthening of steel structures by fastening fiber-reinforced polymers (FRPs) has been proposed by a few researchers to overcome the brittle de-bonding failure associated with the bonded strengthening technique. This paper investigates the experimental flexural performance of steel beams strengthened by fastening hybrid FRPs (HFRPs). Staggered steel bolts are used to attach the HFRP strips to the steel tension flange. Fourteen steel beams were tested in a four-point loading setup to examine their behavior under various bolt spacing values, HFRP lengths and HFRP thicknesses. All strengthened beams experienced ductile failure with yield load enhancement ranging between 5.22 and 11.73% and improvement in the ultimate load from 8.5 to 18.76%. Reducing the spacing between the bolts from 150 to 45 mm enhanced the ultimate load and the level of composite action between the fastened components. Doubling the HFRP length resulted in a slight increase in the ultimate load and a remarkable reduction in the mid-span deflection. Meanwhile, doubling the thickness of the HFRP revealed an insignificant effect on the beam’s ultimate load and composite action. The recorded sectional strains were used to analyze the level of composite action between the fastened elements.

Flexural performance of steel tube roof slab and parameter optimization

This study introduces a steel tube slab (STS), a novel pipe-roof structure used in underground engineering, whose structural system affects the bending loading conditions during construction. However, previous study used the transverse force of the STS structure to evaluate the overall structure, which results in an unreasonable structural force and material waste. The purpose of this investigation is to analyze the longitudinal flexural performance of the STS structure through a combination of experimental and numerical investigation, and to optimize the key parameters. Firstly, by conducting three flexural experiments, the failure model, load versus displacement curves, deformation characteristics, load versus strain curves and flexural capacity are investigated. The results of laboratory tests show that there are three stages to the loading of the STS structure, including the elastic stage, the elastic-plastic stage, and the fully plastic stage, and the structure exhibits progressive ductile failure. Furthermore, the finite element software (ABAQUS) is used to establish a series of finite element models, which are verified through laboratory tests, and the parametric coupling analysis is conducted. The results show that the flange thickness, steel tube diameter and spacing between the steel tubes have significant effect on the longitudinal ultimate capacity of the STS structure, however, the bolt diameter and steel tube thickness has a limited impact. Finally, different combination parameters are analyzed using the Fuzzy mathematical theory. Subsequently, the optimum ratio of key parameters is proposed.

Enhanced progressive collapse resistance of bolted beam-to-column connections with ductile stainless steel components

With the use of ductile stainless steel bolts and hot-rolled sections/plates as critical connection components, the progressive collapse resistance of bolted beam-to-column connections may be effectively enhanced at relatively low costs. To verify the viability of this concept, a comprehensive numerical study is performed to investigate the collapse-resisting performances of flush end-plate (FEP) and web angle (WA) connections equipped with stainless steel components. Through a detailed parametric study with various connection configurations and structural layouts, it is proved that the use of stainless steel components can produce remarkable enhancement to the collapse resistance of the connections. The average increase in dynamic load capacity is 30% for FEP connections using stainless steel bolts instead of carbon steel bolts. This average ratio can be as large as 109% for WA connections with the use of stainless steel bolts and web angles. These results clearly demonstrate the great potential of using stainless steel components in steel connections for collapse-resisting purposes. Similar concepts may be naturally applied in many other scenarios where the ductility of a few critical components controls the robustness of the entire system.

Failure Analysis of Alloy Boron Steel Bolts in Steel Structure Assembly

Failure Analysis of Alloy Boron Steel Bolts in Steel Structure Assembly

Tests of demountable reinforced concrete slabs

This paper presents an experimental investigation of demountable reinforced concrete slabs using dry connections between reinforced concrete slab elements. The test specimens comprised six full-scale reinforced concrete slabs; one control slab monolithically cast, while the other five slabs were produced with mid-span demountable dry connections. The slab elements were cast separately and assembled using top and bottom steel plates joined to each side of the slab element by high tensile steel bolts with or without a shear key and embedded steel block. Theoretical analysis of the behaviour of the demountable slabs tested in comparison with the control specimen was also conducted.The test results showed that using a dry connection consisting of a shear key at the assembled section is the most effective technique in terms of moment resistance, deflection, and flexural stiffness. On the other hand, the dry connection with embedded steel blocks failed prematurely because of stress concentration at the block edges. The moment capacity and deflection predictions of demountable slabs have reasonably correlated with the experimental results but required additional calibrated data from experiments.

Experimental study on influence of host rock strength on shear performance of Micro-NPR steel bolted rock joints

The development of deep underground engineering has brought new challenges to bolt materials. Micro-Negative Poisson's Ratio (NPR) steel is a new type of bolt material with high strength, high toughness, and super energy absorption. The effect of host rock strength on the shear performance of micro-NPR steel anchoring rock joints was studied by performing an indoor direct shear test . Ordinary Q235 steel bolted joints and unbolted joints were set as the test control groups. The shear force-shear displacement curves, surface failure characteristics, bolt deformation, fracture characteristics , shear strength, and shear energy absorption were all compared and analyzed. The study found that the bolted rock joints have significant ductile failure characteristics under shear load , which effectively improves the brittle failure characteristics of the unbolted rock joints. The ability of the rock to resist the crushing damage of the bolt is continuously enhanced with an increase in the host rock strength, while the damaged area of the grout and rock mass at the opening of the joint surface gradually decreases. The failure area of the Q235 steel bolted joint surface is significantly smaller than that of the micro-NPR steel. Additionally, the equivalent internal friction angle , equivalent cohesion, and peak shear strength of the micro-NPR steel are significantly higher than those of Q235 steel. The higher the strength of the host rock, the greater the bolt peak shear strength of the joint. The bolts undergo local shear deformation near the joint surface, and the bolt deforms into an ‘S’ shape after shearing. The improvement of the host rock strength limits the development of the bolt's plastic hinge to a position far from the joint surface. The shear fracture displacement and shear energy absorption of the bolt decrease with an increase of the host rock strength. The shear energy absorption capacity is at least 3.7 times higher than that of Q235 steel. When the host rock strength is low, the bolt yields in tension and bends at the plastic hinge, at which time tension-bending failure occurs. With an increase of the host rock strength, the bolt undergoes tension-shear failure. The high strength and high ductility of traditional steel are well balanced by the micro-NPR steel, with the tensile and shear resistance of the steel bolt being greatly improved, which allows for large deformation and super energy absorption in the bolt material, which allows for a wide range of applications at deep engineering sites.

Analytical and numerical analysis of angle steel joints for conductors in lattice transmission towers

This paper presents a theoretical and numerical study of angle steel joints for conductors in transmission tower structures in the medium and heavy icing area. The results show that the deformation of the angle steel joint in suspension towers is controlled by the vertical load, and the deformation of the angle steel joint in strain towers is controlled by the tension load. The bolt of the angle steel joint for conductors is tension-controlled. A theoretical method considering the bending stiffness ratio of the angle steel plate and the bolt is derived. The proposed theoretical method quantifies the bending stiffness difference in the angle steel plate and bolt group, and the effects of bolt layout and load cases are considered. The numerical results are in good agreement with theoretical results by validating the internal forces and neutral axis depth. The accuracy of the proposed theoretical method is higher than that of theoretical methods based on steel structure principles. The proposed theoretical method is of great significance to the development of transmission tower structure design.

Classification of progressive failure and mechanical behavior of dissimilar material hybrid joints at varying temperatures

This research illustrates the progressive failure mechanisms and variation in the mechanical behavior of dissimilar materials hybrid joints at elevated temperatures. For this purpose, a novel in-situ data fusion scheme was developed from experimental analysis which was validated through a coupled computational approach. The hybrid joint consisted of CFRP/Al worksheets joined through a steel bolt. The experimental analysis revealed distinct failure mechanisms in worksheets, i.e., yielding in Al sheet and a mixed failure mode in CFRP sheet while no signs of failure were observed in the steel bolt. Further, the progressive damage in the CFRP sheet was classified as a three-staged process which comprised elastic strain phase, crack initiation and progressive damage phase, and unstable fracture phase by correlating the temperature (Infrared Thermography) and strain variations (Digital Image Correlation). Further, degradation in mechanical behavior from room temperature was evaluated at three elevated temperatures, i.e., 50 °C, 75 °C, and 100 °C. A significant drop in mechanical properties (maximum strength and nominal stiffness) was noticed at high temperatures while a transition in failure mode was also evident (ply bending and pronounced fiber breakage) in comparison to the joints tested at room temperature. In computational analysis, Tsai–Wu, Maximum Stress, and Puck’s static failure criteria were coupled with the element deletion model to ascertain the critical ply and progressive damage in the joint. The experimental results were found in good agreement with the computational results in terms of critical ply and load-carrying behavior. In summary, this research helps to understand the progressive failure and variation in mechanical behavior about high temperatures in hybrid joints which can be extended to other dissimilar materials configurations as well.

The Buoyancy of the Tunnel Segmental Lining in the Surrounding Filling Material and its Effects on the Concrete Stress State

Segmental lining is subject to significant upward buoyancy forces when a grouting material (slurry), initially fluid, is adopted to fill the gap between its external profile and the wall of a tunnel excavated with a TBM machine. The analysis of the effects of these forces is important in order to correctly dimension the segmental lining and avoid damage to the lining and subsequent costly maintenance and restoration actions. Given the complexity of the behavior of a segmental lining consisting of segmental rings and circular joints that alternate in the longitudinal direction of the tunnel, a specific numerical model has been implemented, adopting the Finite Element Method (FEM). This model is able to obtain the development of the vertical displacements of the segmental lining starting from the TBM tail, together with the bending moments and the shear forces induced inside it. The developed model is able to assess the risks of breaking and damaging the concrete and steel bolts that are used to connect the segmental rings at the circular joints; therefore, it represents a useful design tool for being able to correctly dimension the segmental lining also in relation to the risks produced by the appearance of considerable buoyancy forces around it, due to the presence of the initially fluid filling material. The proposed numerical model was applied to a real case (Ningbo metro tunnel) and allowed to obtain satisfactory results from the comparison of the calculated displacements with in situ measurements. Some sensitivity analyzes developed on the studied case have made it possible to detect which are the influencing parameters that have the greatest impact on the behavior of segmental lining in the presence of the studied buoyancy forces.

Hydrogen-induced delayed fracture behaviour of V+Nb-microalloyed high-strength bolt steel with internal and environmental hydrogen

Hydrogen-induced delayed fracture (HIDF) behaviour of a V+Nb microalloyed 1300-GPa-grade high-strength bolt steel was explored by slow strain rate tensile (SSRT) tests under pre-hydrogen-charging (internal hydrogen) and dynamic hydrogen-charging (environmental hydrogen) conditions. The tested steel exhibited much lower HIDF resistance in the condition of environmental hydrogen than that of internal hydrogen, which is primarily due to the difference in hydrogen diffusion and accumulation characteristics and the hydrogen trapping effect of MC carbides. Therefore, for applications of high-strength bolt steels based primarily on the designing strategy of hydrogen trapping, it is extremely important to prevent environmental hydrogen entry in service.

In-service failure of mechanically galvanised low alloy steel bolts of three 25,000 m3 bolted water tanks

Several single-lap bolted joints fastening the steel plates of three 25,000 m3 water tanks showed premature failure. Most fractured bolts were in the lower sector of the tanks.The tempered martensitic steel bolts were mechanically galvanised, and the poor quality of the galvanisation allowed the corroding agents (Cl− and SO4−2) to percolate through the Zn and Sn coating particles, finally reaching the steel surface of the bolts. Additionally, multiple 6 μm-deep intergranular pre-cracks were observed at the threads’ roots of the new bolts. During service, these pre-cracks accumulated the corrosive agents, creating numerous 10 μm-deep corrosion pits, nucleating the bolts’ environmentally assisted cracks. Microfractographic examination of the bolts featured stable growth of brittle cracks (intergranular and quasi-cleavage cracking) followed by mixed-mode cracking and a small region of ductile overload fracture. This failure sequence confirms that the fracture mechanism of the low alloy steel bolts is due to environmentally assisted cracking. Finite elements analysis investigated the effect of the bolt diameter, bolted joint design and pre-load force on the tensile stress distribution. Improvements in the bolts’ quality control and bolted joint design were discussed to prevent new failures.

Defect Analysis to Improve Quality in Traditional Shipbuilding Processes

As one of the livelihoods of the Indonesian people, the sea has many benefits, such as fish, marine plant cultivation, and others. Most Indonesian live in the coastal area and work as fishermen. Its existence and role are very important in coastal development, especially fisheries. This study aims to investigate logic tree analysis to solve defects in traditional shipbuilding. It is envisaged that such implementation shall improve the quality of ships produced. Traditional ships are currently experiencing a significant demand proportionally to the increase in the number of fishermen utilizing traditional ships. However, shipbuilders experienced many obstacles during the manufacturing process. Therefore, the quality of the ships produced was different from the ship owners' standards or demands. For solving this problem, initial identification processes should be conducted to determine any potential defects that may affect the quality of the ships. Defects that pose a high risk to the quality of the ship were resolved using a logic tree analysis to obtain recommendations for improvements. The result shows that four risks of damage have been identified that affect the quality of the traditional ships produced: the selection of the quality of raw materials, imperfect wooden joints, easily corroded steel bolts, and poor installation of additional equipment.

Modelling of demountable steel-concrete composite connections: Validation of finite element model and parametric study

A three-dimensional finite element modelling and parametric analysis of a composite connection having prefabricated concrete slabs and preload bolted shear connectors are presented in this study. The load-slip relationship for this type of shear connection subjected to monotonically loading with the effect of different parameters including bolted shear connector size, bolt grade, hole size in precast concrete slab and steel beam top flange, concrete strength, and bolt preloading force is studied by means of ABAQUS software. A finite element model of the composite connection considering the non-linearities of the geometry, interfaces between the components, and materials is developed and verified against the results of the experimental study. An extensive parametric study is conducted, and the influences of different parameters on the structural behaviour of demountable steel-concrete composite shear connection are discussed in detail. In addition, a comparison of the estimated values obtained from design equations proposed by current standards, including EC4 and AISC for headed stud shear connectors, and the design recommendations provided in other studies for bolted shear connectors are conducted. According to the calculation result, the accuracy of different design methods is evaluated. Finally, a regression analysis of the data produced by the FE analysis has been employed to propose a new design equation to determine the ultimate strengths for the post-installed preload bolt shear connectors. It is concluded that the ultimate shear load capacity values predicted by EC4 and AISC provisions for composite connections having prefabricated concrete slabs and preload bolted shear connectors found to be relatively less accurate but conservative.

Tension and interaction resistance of austenitic and duplex stainless steel bolts

The current design rules in EN 1993-1-4 for non-preloaded stainless steel bolted connections under pure shear and tension are essentially based on the regulations for carbon steel bolted connections. Furthermore, the load bearing behaviour under combined tension and shear (category A + D bolted connections) was adopted from EN 1993-1-8 as well. Recent research activities within the German IGF research project “Load-bearing capacity of bolted connections loaded in shear and tension made of stainless steel M12 to M36” (P 1386/IGF-No. 20651 N) showed that stainless steel bolting assemblies behave different. Herein, systematic experimental investigations and an extensive literature review into the shear, tension and interaction resistance of stainless steel bolts were conducted. Furthermore, reliability analyses according to EN 1990, Annex D were accomplished to prove the partial safety factor of γM2 = 1.25 for connections made of stainless steel bolting assemblies. The results regarding the shear resistance have already been presented in a former paper in this journal. In these investigations, it could be shown that an increase of the tension resistance Ft,Rd with k2 = 1.0 is in principle possible following the normative regulations of EN ISO 3506-1 regarding the minimum ultimate tensile strength as well as North American ANSI/AISC 360 and Australian Standard AS 4100. Furthermore, a new interaction approach for both unthreaded and threaded part of the bolt lying in the shear plane could be proposed which has statistically been verified for all property classes with γM* < γΜ2 = 1.25. The new regulations have already been implemented in the current revision of EN 1993-1-4. The background for the new regulations is presented in this contribution.

Experimental studies on slip friction device using symmetric friction connections

The use of friction-based energy dissipater is rapidly growing in seismic active zones to avoid interruptions and costs resulted from local or global damage to buildings due to severe earthquakes. Well designed and detailed friction devices using symmetric friction connections (SFCs) are often considered as an efficient way to dissipate energy for not only their stable hysteretic behaviour and low strength degradation but also the comparable assembling cost to that of conventional construction. The sliding commences when the designed sliding shear force is achieved, which relates to the contact surface’s Coefficient of Friction (CoF) and the total amount of clamping force. This paper reports 15 quasi-static testing of a slip friction device utilizing SFC clamped by two grade 10.9 M20 black finished high strength structural steel bolts in a single row. Shims using brass, aluminium, high strength steel, semi-metallic brake pads and copper-iron alloy were tested. Results show that all five shim materials tested can provide a stable hysteretic behaviour under a cumulated sliding distance of more than 4000 mm. The effect of installed bolt tension, loading rates and bolt-bearing mode are also discussed. Given the stable hysteretic response and the low strength degradation observed, the proposed slip friction device can be considered as a low damage energy dissipater.

Force and Slip Displacement of Fibre Cemboard Panels Subjected To Four-Point Bending Test

For many years, fibre cemboard has been widely used in the construction industry. This material has many advantages, including a long-life span, ease of installation and low maintenance, which can reduce the cost of maintenance. However, due to its limitation of being unable to support heavy loads, it is only suitable for the lightweight floor system. Therefore, the fibre cemboard panel is introduced. Basically, the fibre cemboard panel consists of several layers of fibre cemboard that stack together using a special bond mechanism. This study aims to investigate the flexural capacity and slip displacement of fibre cemboard panels with different bond mechanisms (polyurethane glue, steel bolts and polyurethane glue + steel bolts) and spacings (50 mm, 75 mm, 100 mm, 150 mm, and 200 mm). The specimens were fabricated with a size of 305 mm width, 1220 mm span and 2@16 thickness. The four-point bending test was carried out using Universal Testing Machine (UTM) that yield the force-slip displacement curves.The results of experimental testing indicate that the bond mechanism has an apparent impact on the flexural capacity and slip displacement. The fibre cemboard panels bonded by steel bolts have the best performance. Meanwhile, the spacing was found to control the slip displacement the most than the flexural capacity. Close distance of spacing may increase the stiffness that appreciably contributes to better performance. The optimum spacing for the polyurethane glue is 50 mm, while the specimens bonded by steel bolts and polyurethane glue + steel bolts should have 75 mm and100 mm spacings. The polyurethane glue can hold the stress concentration before the detachment. When polyurethane glue fails, the steel bolts resume the function to resist the slip displacement until the rapture.

The Influence of Heat Treatment on Corrosion Resistance and Microhardness of Hot-Dip Zinc Coating Deposited on Steel Bolts.

The analyzed topic refers to the corrosion resistance and changes in microhardness of the heat-treated (HT) hot-dip zinc coating deposited on bolts. The research aimed to evaluate the influence of the HT on the increase of the coating hardness and changes in anticorrosion properties. Hot-dip zinc coating was deposited in industrial conditions (acc. EN ISO 10684) on chosen bolts (M12x60). The achieved results were assessed based on corrosion resistance tests in neutral salt spray (salt chamber) and microhardness measurements. Tests were conducted in accordance with the adopted fractional plan, generated in the DOE module of the Statistica software. Using the conjugate gradient method optimal parameters of HT were determined. The conducted tests proved that the controlled heat treatment may increase the hardness of the hot-dip zinc coating without a significant deterioration in its basic protective function (corrosion resistance). The observed changes in the hardness and corrosion resistance of the zinc coating are a consequence of changes in its structure.

Strength and Failure Behaviors of a Jointed Rock Mass Anchored by Steel Bolts: A Numerical Modeling Study

Strength and Failure Behaviors of a Jointed Rock Mass Anchored by Steel Bolts: A Numerical Modeling Study