High Strength Friction Grip Bolts Research Articles

Data-Driven Prediction Model for High-Strength Bolts in Composite Beams

In recent years, the application of artificial intelligence-based methods to engineering problems has received consistent praise for their high predictive accuracy. This paper utilizes a BP neural network to predict the strength of steel–concrete composite beam shear connectors with high-strength friction-grip bolts (HSFGBs). These connectors are widely used in bridge and building construction due to their superior strength and stiffness compared to traditional beams. A validated finite element model was used to predict the strength of HSFGB shear connectors. A reliable database was created by analyzing 208 models with different characteristics for machine learning modeling. Previous studies have identified issues with result variation and overestimation or underestimation of shear connection strength. Among the machine learning methods evaluated, the backpropagation neural network model performed the best. It achieved a goodness of fit of over 93% in both the training and testing sets, with a low coefficient of variation of 6.50%. Concrete strength, bolt diameter, and bolt tensile strength were found to be important variables influencing the strength of shear connectors. Other variables showed a proportional or inverse relationship with compressive strength, except for concrete strength and bolt pretension. This study presents an accurate machine learning approach for predicting the strength of HSFGB shear connectors in steel–concrete composite beams. The study offers valuable insights into the effects of various variables on the performance of shear connection strength, providing support for structural design and analysis.

Study on the behavior of high-strength friction-grip bolts under combined shear and tensile forces

In order to investigate the shear behaviors of high-strength friction-grip bolts (HSFGBs) under combined shear and tensile forces in steel-SFRC composite beams, eight pull-out specimens with HSFGBs were fabricated and tested. Initial slip force, initial shear stiffness, post slipping stiffness, ultimate shear strength and ultimate slipping of HSFGBs were reasonably defined to quantitatively evaluate the shear behaviors of HSFGBs. Then, finite element models were carefully established and calibrated against test data using ABAQUS software. The influence of tensile force on the shear performance of HSFGBs was also discussed. Load transfer and failure mechanisms of HSFGBs and their influences on the shear behavior of HSFGBs under different tensile forces were analyzed. An improved interaction equation was derived for the calculation of HSFGB ultimate strength under combined shear and tensile forces. The obtained results indicated that both shear deformation and necking phenomenon of HSFGBs occurred under combined shear and tensile forces. Initial slip force, initial shear stiffness, post slipping stiffness and ultimate shear strength of HSFGBs were found to decrease with the increase of tensile force. HSFGB axial stress was first increased and then decreased with the increase of tensile force. In addition, HSFGB shear stress was only slightly changed under different tensile forces. Furthermore, improved interaction expression accurately predicted shear strength of HSFGBs under combined shear and tensile forces.

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.

Interfacial shear and flexural performances of steel–precast UHPC composite beams: Full-depth slabs with studs vs. demountable slabs with bolts

Two types of steel–precast ultra-high-performance concrete (UHPC) composite beams were investigated in this study, which can be vastly used in accelerated bridge construction (ABC). One of them contains full-depth slabs with stud shear connectors embedded in shear pockets, while the remaining one adopts demountable slabs with high-strength friction-grip bolts (HSFGBs). Four-point bending tests were conducted on six large-scale composite beams to investigate the interfacial shear and flexural performance of such innovative types of steel–precast UHPC composite structures. The failure modes, vertical deflection, horizontal interfacial slip and the stain distribution at mid-span cross-section were investigated. The experimental results indicated that the cracking patterns and failure modes of the composite beams were highly dependent on the slab concrete types and the degrees of shear connection. The composite beams adopting UHPC slabs achieved larger cracking resistance and higher ultimate strength than those containing normal-strength concrete slabs and favorable ductility. Similar trends were also presented by the composite beams with large degrees of shear connection. The composite beams with HSFGBs showed enhanced load capacities and larger vertical deflections and horizontal interface slips at peak load than those adopting stud shear connectors. Additionally, the composite beams that failed in shear connector fractures presented shear resistance–interface slip relationships comparable to their push-out counterparts. Finally, theoretical formulas based on rigid plastic analysis were proposed for predicting the flexural capacity of both types of composite beams.

Experimental investigations on pre-tensioned hybrid joints for structural steel applications

ABSTRACT The choice of a suitable joining method is of major importance for the performance and durability of structural connections in any type of construction and in other branches of industry, such as the manufacturing of sliding vehicles. In addition to mechanical joints using high-strength bolts as well as welding, adhesive bonding is more and more being considered as a serious alternative. Hybrid joints are the focus of the research, especially to increase load-bearing capacity and reduce deformation. This project specifically aims at the combination of elementary bonded joints and High Strength Friction Grip Bolts to form the so-called pre-loaded hybrid joint. The pre-loaded hybrid joint optimally combines the specific advantages of both elementary joining methods and thus creates an efficient structural joint. This research takes up the findings of a previous project and focuses on the characterisation of the pre-loaded hybrid joint with regard to its application in the field. For this purpose, a comprehensive experimental test programme is carried out, which served for the validation of a numerical model generated for the computational load prediction in a companion paper.

Rotational fatigue analysis on Shanghai 65-m fully-steerable antenna structure during its normal operation

Structural fatigue property of Shanghai 65-m fully-steerable antenna structure is analysed. According to the active fully-steerable working pattern, the typical fatigue stress piece is put forward based on simple sampling and decomposed by real-time rain flow counting algorithms. Subsequently, the fatigue lives of pitch mechanism bearings were computed by miner linear accumulative damage criterion. What’s more, in a complete cycle of dynamic observation, the shear force and axial force of high strength friction grip bolts for all of the supporting nodes are extracted and counted aiming at each pitching angle. As a result, fatigue analysis is carried out on the supporting nodes of the back-frame structure connected with the pitching mechanism. Last but not the least, finite element refinement model is conducted for the contact part between antenna wheels and the rail. Based on contact fatigue curve spectrum, the contact fatigue existing between the antenna structure roller and the track is analysed. The results show that the fatigue life of the whole antenna structure can meet the safety requirements in the design reference period which is intended to be 30 years. This systematic fatigue analysis procedure, method and results can provide valuable references for design, construction and maintenance of such similar fully-steerable antenna structures in future.

Investigations on prying forces in flexible connections of steel beams

PurposeThe use of flexible connections throughout the steel structures provides a high level of stiffness compared to that of fully welded connections. Flexible connections allow for rotation to an extent, which make them perform better during earthquake than welded connections. In hanger connections, the applied load produces tension in the bolts and bolts are designed for tensile forces. When the deformation of the flange plate is equal to that of the bolts, a plastic hinge is formed in the flange plate at the weld line and the bolts are pulled to failure. If the attached plate is allowed to deform, additional tensile forces called prying forces are developed in the bolts. The paper aims to discuss these issues.Design/methodology/approachThis paper includes the results of investigation on prying force in T-stub connection fabricated with normal grade bolts and high strength friction grip (HSFG) bolts. Finite element analysis has been carried out by creating models and analyzing the effect of external tensile force and bolt force. For different grades of bolt (4.6, 8.8, 10.9, 12.9), the prying force is calculated.FindingsIt is found that prying force is increasing with the change in grade of bolt used from normal to HSFG. The results obtained from analysis using IS 800:2007 codal provision are also included. It is observed that HSFG bolts do not allow for any slip between the elements connected and hence rigidity is increased.Originality/valueThe prying force mainly depends on geometrical parameter of the connection. In this research work, the variation of prying force was studied based on the variation in dimensions of T-stub angle section and bolt grade (4.6, 8.8, 10.9, 12.9). The method of obtaining prying force from bolt load and applied load is a unique approach. The results of FE analysis is validated with the analytical calculation as per IS 800:2007 code provisions, which shows the originality of the research.

Environmental benefits arising from demountable steel-concrete composite floor systems in buildings

This paper presents an assessment and quantification of the environmental impacts arising from different steel-concrete composite floor systems. In particular, a demountable composite floor system using pretensioned high-strength friction grip bolts as shear connectors is compared with three conventional composite floor systems that use welded shear studs as shear connectors. The first type promotes the end-of-life scenario of disassembly and reuse of structural elements, while the conventional systems are related to the current practices of waste management for building materials, i.e. demolition and recycling. To analyse these different structural systems and relative scenarios, a comparative Life Cycle Assessment investigating two entire life cycles of the materials is developed. Based on the evaluation of several impact categories, the building with demountable composite floor system is identified as the most environmentally friendly solution among all the considered structural solutions, and the saving of emissions and resources is quantified for each impact category.

Flexural performance of innovative sustainable composite steel-concrete beams

Composite beams comprising of concrete slabs and steel beams joined by conventional headed stud shear connectors are commonly used in modern steel-framed building construction. However, because the headed stud shear connectors are welded onto the top flange of the steel beam and cast into the in situ concrete slab, deconstruction of the composite beam and the reuse of its components at the end of structural life in defence to demolition is virtually impossible, which is at odds with the increasing demands placed on improving the sustainability of building infrastructure. As an alternative, an innovative sustainable composite beam and slab system is proposed, in which precast geopolymer concrete panels are attached to the steel beams using high-strength friction-grip bolts instead of cast in situ floors with pre-welded headed stud connectors. The advantages of a low-carbon design, both by the use of geopolymer concrete elements and system deconstructability, can be achieved in this proposed system. In this paper, a three-dimensional finite element model is developed to investigate the structural behaviour of the proposed sustainable composite beam and slab system. Material non-linearities and the interaction of the structural components are included in the model. The accuracy and reliability of the finite element formulation developed are validated by comparisons with experimental results. Extensive parametric studies are conducted to elucidate the effects of the change in the concrete panel configuration, the number and diameter of the bolts, the type and strength of the concrete and the grade of the steel beam on the behaviour of the system. The use of modified rigid plastic analysis is assessed, and a modification is suggested to predict the flexural strengths of the composite beams and slab system.

Experimental study of flush end plate beam-to-column composite joints with precast slabs and deconstructable bolted shear connectors

Composite steel-concrete floor systems represent a ubiquitous structural steel framing system for commercial and industrial buildings in the developed world, which exploit the strengths of reinforced concrete and structural steel both symbiotically and in a complementary fashion. However, as attention is being focused increasingly towards minimising emissions and maximising recycling, these composite systems are problematic for many reasons. This paper describes the results of tests on three full-scale sustainable flush end plate semi-rigid beam-to-column joints and three push-out tests with deconstructable tensioned bolted shear connectors, needed to establish the strength of the shear connection in order to design the joints. For this system, precast concrete slabs having a reduced content of ordinary Portland cement are attached compositely to the steel beam using post-tensioned high-strength friction-grip bolts that are unbolted readily at the life-cycle end of the building. This innovative connection system is proposed to circumvent the high-carbon attributes associated with the demolition of conventional steel-concrete composite framing systems. The push-out tests show that the behaviour of specimens with post-installed bolts in clearance holes is significantly different to that of members with stud shear connectors in slabs cast in situ, and the bolted connectors provide reliable and adequate shear connection to composite beams and joints with precast concrete slabs. The test results show that these composite joints have credible rotation and moment capacities within the recommendations of EC3 and EC4, and that fracture of the joint occurs after substantial rotational deformations had been achieved.

Experimental study of composite beams having a precast geopolymer concrete slab and deconstructable bolted shear connectors

Traditional steel–concrete composite beams are known to exhibit excellent structural characteristics, in terms of their stiffness and strength, when compared with bare steel or reinforced concrete beams. However, within current paradigms of lowering carbon emissions and enhancing the possibly of material recycling, such traditional composite beams cannot be deconstructed easily and their elements are not recyclable because they rely on welded headed stud connectors that are encased within cast in situ concrete to achieve the necessary shear connection. This paper presents the detailed results of quasi-static tests conducted on full-scale composite beams as part of a novel deconstructable and sustainable structural system. For this system, precast concrete slabs are attached to a steel beam using tensioned high-strength friction-grip bolts in clearance holes as the elements to provide the shear connection. The precast slabs are made using geopolymer concrete in lieu of concrete made from ordinary Portland cement, whose manufacture is a major contributor to anthropogenic CO2 emissions worldwide, thereby enhancing the low-carbon attributes of the structural system. The test results demonstrate the very significant ductility of the beams, with substantial interface slips being developed and sustained at loads close to the ultimate strength limit state. The tension induced in the bolts provides sufficient frictional resistance between the precast slabs and steel beams to ensure that the composite system has full shear interaction throughout the range of service loading. It is also confirmed that composite beams with bolted shear connectors can be deconstructed easily at the end of their service life, with the slabs, steel beams and bolts being reusable in other structural applications.

Sustainable Design of Deconstructable Steel-Concrete Composite Structures

As attention is being focused increasingly towards minimising carbon emissions and enhancing the possibly of material recycling in the construction industry, traditional composite systems are recognised as being problematic on several counts. Composite action between the conventional concrete slab and steel beam is provided typically by stud shear connectors welded to the top flange of the steel beam, and the demolition of such members requires a considerable amount of time and energy, as well as being environmentally intrusive and creating much waste. In addition, existing composite systems mostly utilise conventional concrete made from ordinary Portland cement whose production is attributed to a large portion of carbon emissions worldwide. As an alternative, it is proposed that precast concrete slabs be attached to a steel frame with semi-rigid bolted connections using high-strength friction grip bolts as the elements to provide the shear connection. Moreover, the use of geopolymer concrete in the casting of the slabs eliminates the use of ordinary Portland cement entirely. The paper reports tests undertaken on full-scale beams and on full-scale joints in this sustainable and deconstructable system. This study shows that both the joints and beams demonstrate very significant ductility, with large rotations, deformations and interface slips being developed and sustained during the testing.

Finite element modelling of steel–concrete composite beams with high-strength friction-grip bolt shear connectors

High-strength friction-grip bolts (HSFGBs), that can be easily unbolted during deconstruction and structural modification, are proposed as shear connectors between the steel beam and concrete slab of composite beams in lieu of conventional headed shear studs for which deconstruction is problematic. These beams are potential sustainable and recyclable element for modern construction, but research contributions on composite beams with HSFGB shear connectors are very limited. This paper develops a three-dimensional finite element model to investigate the structural behaviour of steel–concrete composite beams with HSFGB shear connectors. Material non-linearities and the interaction of structural components are included in the model. Quasi-static finite element analysis using the dynamic explicit procedure is adopted for the analysis. The accuracy and reliability of the proposed finite element model are validated by comparing their results with available experimental results. An example is contrived to elucidate the typical mechanical performance of the composite beam, which the finite element study shows is different to that normally encountered in composite beams with headed stud connectors. Parametric studies are presented to quantify the effects of the change in the bolt spacing, diameter of hole, bolt pretension and the longitudinal reinforcement on the behaviour of the beam, so that usable design rules may be crafted.

Study on an Innovative Flange Bolted-Welded Connection

This paper proposes a new type of spliced joint, named flange bolted-welded hybrid joint, which is designed to splice I-shape beam to facilitate the construction of industrialized buildings. The flange, welded with the bottom beam flange as well as the web close to bottom flange, are jointed by high strength bolts. Stiffening plate is welded at top of the flange while downhand welding and high strength friction grip bolts are used for the top beam flange and the beam web, respectively. The connection reduces the construction period and costs. In this paper, monotonic and reversed cyclic loading tests were conducted on three full-scale specimens of this innovative joint to investigate its load-bearing capacity, energy-dissipating capacity and failure modes. The results indicate that the joint has high load-bearing capacity and great ductility. The failure mode is due to the slippage of flange bolts as well as the gap development between the two flange plates. The experimental studies enabled improvement of the design of the connection to be used in moment-resisting steel frame structures.

High strength friction grip bolts—optimal parameters for the combined method of tightening

Abstract The economic need to realize high preloads in slip resistant connections has promoted the tightening of fasteners above the yield stress. The tensile and torsional stresses at this tightening level and the eventual consecutive deteriorations of the screws and the nuts are more or less unknown. An experimental research program undertaken in Belgium has given more precise information on the behaviour of the fasteners during tightening until the ultimate state (maximal preload) as well indications of how to improve this behaviour by using nuts of a higher hardness and better lubricants. The tests have shown that when tightening with the combined method, as specified in Eurocode 3, and when using higher grade nuts and better lubricants, no excessive deformations occur.

Interactive design and detailing of structural steelwork connections using a computer : Moore, M. G. and Brotton, D. M.Struct. Eng. Vol 52 (1974) No 4 pp 133–142

A technique for the automatic and interactive design of connections in structural steelwork using a computer with visual display facilities is described. The program can deal with inclined, oblique and eccentric beams with welded end plates and high-strength friction-grip bolts. A design example is given to illustrate the facilities provided. The discussion includes an economic assessment which indicates that the cost of using the technique is low.

Effect of Shapes on the Delayed Fracture Strength of High Strength Friction Grip Bolts

As one of trial improvement of delayed fracture strength of high strength friction grip bolt, the mitigation of stress concentration of each part of bolt was carried out and there obtained the following results.(1) By cutting off incomplete thread up to effective diameter, the delayed fracture life can be extended.(2) The fine thread with bigger area of core section is more excellent than the coarse thread, but the effect is small in large diameter.(3) The delayed fracture strength is better if the thread root radius is larger.(4) Larger radius of head-to-shank fillet is desirable.(5) The usage of self-aligning nut is effective for the mitigation of the bending stress which grows in tightening and the said usage extends the delayed fracture life.