Behavior Of Fasteners Research Articles

Study on the Cracking Behavior of Fasteners in Long-Term Service under Marine Environment

Study on the Cracking Behavior of Fasteners in Long-Term Service under Marine Environment

P2PE: A finite element formulation for panel-to-panel cross-laminated timber connections

This paper presents a new multi-spring finite element formulation called P2PE that simulates the cyclic behavior of panel-to-panel Cross-Laminated Timber (CLT) connections. The formulation comprises five types of uncoupled linear/nonlinear springs representing the fasteners and contact between panels. For instance, the in-plane fastener behavior is simulated with a co-rotational spring and the Modified Richard–Abbott (MRA) model, which is adapted to account for the asymmetry, pinching, degradation, and low-cycle fatigue of timber connections. The model was implemented into ANSYS through user-element/materials, including all computer implementation steps, and can be freely downloaded. The model's response and sensitivity were studied in three demonstrative CLT diaphragms, and it was validated at the connection and assembly stage with benchmark tests. In the first stage, the fastener model was verified with four cyclic CLT connections, while in the second stage, the model was validated with three medium-to-large scale CLT assemblies. The model accurately predicts the stiffness, strength, deformation, slip, and failure mechanisms of both stages. Finally, a parametric analysis of in-plane bending CLT diaphragms was assessed by varying their panel dimensions. This analysis demonstrated that diaphragms with slender panels have larger capacities, fastener energy dissipation, and shear slips but lower ductilities than shorter ones.

Seismic behavior assessment of fasteners based on a shaking table test of a museum building model with a display case and artifacts

Fasteners are widely used in museums as an attachment method to secure objects. However, due to the lack of research on the seismic behaviour of fasteners under seismic loads, the implementation of fasteners in museums usually lacks scientific guidance, resulting in their ineffectiveness in improving the seismic safety of museum artifacts. In addition, few studies have experimentally investigated the adverse effects of structural dynamic amplification on the seismic safety of museum artifacts. Therefore, this study aimed to assess the seismic behavior of fasteners used in museums and provide valuable insights for protecting museum artifacts. Shaking table tests were conducted on a full-scale model of a museum building, display case, and artifacts to simulate seismic loads and investigate the seismic response of two typical artifacts secured with fasteners. A numerical study was also performed to evaluate different types of fasteners and their effectiveness in enhancing the seismic safety of artifacts. The adverse effects of dynamic amplification on artifact safety were discussed, and recommendations were provided for improving the seismic behavior of fasteners. Furthermore, the impact of multidirectional seismic excitation on the safety of the artifacts and the seismic performance of the fasteners were analyzed. The research findings contribute to the selection of appropriate fasteners for preserving valuable artifacts in museums.

Expansion and bonded anchors in (shallow) fixings in concrete substrate reinforced with steel and polypropylene fibres

Along with the development of engineering construction techniques, the interest in the issue of fastenings increases. In the construction of new facilities as well as in renovation works, a wide range of fasteners is currently used, enabling quick connections and safe fastening of various types of structural and installation elements. This progress is particularly visible in fixings made in concrete substrates. During assembly and during operation, the fasteners are subject to the influence of many external factors that may significantly affect their load capacity. Such factors include the type and nature of the load to be transferred, the strength and condition of the substrate, the temperature at which the fasteners will be installed and used. The technical parameters of fasteners determined by means of theoretical calculations still do not provide adequate accuracy, so that this method can be used to determine their impact on the behaviour of fasteners during their long-term operation. Therefore, their experimental verification is still required. In the countries of the European Union, the development of the rules for the use and assessment of expansion and bonded fasteners has been entrusted to the European Organization for Technical Assessment - EOTA. This organization groups bodies authorized by EU Member States to provide European technical assessments on the terms set out in Regulation No. 305/2011 (CPR) 2013. The current list of EOTA guidelines for expansion and bonded anchors used in the construction industry, specifying the basis for their use as well as standards for the design of fasteners. The scope and methods of fastener testing are presented in the EOTA guidelines. The purpose of these tests is to determine whether the behavior of the fasteners during their use will be safe and effective, taking into account the unfavourable conditions that can be encountered both during its installation and use. The publication will present the basic structural properties of fasteners made in drilled holes in concrete substrates reinforced with steel and polypropylene fibres.

A two-scale strategy for the modeling of hook and loop fasteners

Hook-and-loop-like joints have been widely used in many engineering applications and even observed in nature. The demand for computational models to predict the behavior of fasteners is increasing as they will be key for reducing design process time and manufacturing costs. Here, we develop a bottom-up two-scale modeling strategy, which enables us to capture the mechanical performance of a hook-and-loop fastener at both micro- and macroscales. In particular, we employ a two-scale homogenization approach capable of predicting the mechanical behavior of the hook-and-loop fastener. The model starts with a micromechanical model of a hook-and-loop fastener which considers the detailed geometry of the individual building blocks of the hook-and-loop fastener and their statistical geometrical variability through a so-called Representative Hook and Loop Element (RHLE) computational domain. The second scale considers the homogenization of the micromechanical model into a Detachment Process Zone (DPZ) which reveals an emerging length scale. The resulting effective traction-separation law concept is then employed at the macroscale with a Double Cantilever Beam (DCB) test using a macroscale model, which is then validated with experiments. The results suggest that the two-scale model strategy is able to predict the mechanical behavior of hook-and-loop fastener and to capture the main deformation and dissipative mechanisms at the relevant length scales.

Loosening Behavior of Ripped Nuts Based on the Fastener Tightening Strategy and Plate Hardness

Within the scope of this study, loosening behavior under vibration was investigated depending on the plate hardness, clamp length and tightening strategy of M8x1.25 10.9 quality nuts with rip form under flange. Two different plate hardness were used and two different types of tightening strategy, i.e. application of torque to either from bolt head or nut, were carried out by using bolts with 29 mm and 40 mm clamp length. During tightening, the effects created by rips on the plate were examined. A parametric study was also carried out to understand loosening behavior of fasteners depending on the plate hardness. Based on the experimental study, it was shown that plate hardness, clamp length and tightening strategy played a key role on the loosening behavior of fasteners. To decrease the loosening rate of the assembly on softer plate, nut with rip form should be tightened from the bolt element. However, for harder plates the selection of tightening strategy was less significant compared to that of softer plate.

A SIMPLIFIED ANALYTICAL PROCEDURE FOR SEISMIC ANALYSIS OF TIMBER LIGHT-FRAME SHEAR WALLS

The seismic performance of timber light-frame shear walls is investigated in this paper with a focus on energy dissipation and ductility ensured by sheathing-to-framing connections. An original parametric finite element model has been developed in order to perform sensitivity analyses. The model considers the design variables affecting the racking load-carrying capacity of the wall. These variables include aspect ratio (height-to-width ratio), fastener spacing, number of vertical studs and framing elements cross-section size. A failure criterion has been defined based on the observation of both the global behaviour of the wall and local behaviour of fasteners in order to identify the ultimate displacement of the wall. The equivalent viscous damping has been numerically assessed by estimating the damping factor which is in use in the capacity spectrum method. Finally, an in-depth analysis of the results obtained from the sensitivity analyses led to the development of a simplified analytical procedure which is able to predict the capacity curve of a timber light-frame shear wall.

An innovative shear-tension angle bracket for Cross-Laminated Timber structures: Experimental tests and numerical modelling

An experimental testing programme on an innovative metal angle bracket for Cross-Laminated Timber structures is presented in this paper. The main novelty of the angle bracket is the use of fully-threaded screws to improve mechanical properties in tension direction. Monotonic tests to evaluate mechanical properties of the wall-to-floor connection in tension and shear directions are presented and discussed. A detailed three-dimensional finite element model, implemented in ABAQUS, which considers the typical non-linear behaviour of fasteners in timber element, is presented and used to reproduce the experimental results. The group effect and strength domain of the fasteners are also analysed. The finite element model can predict experimental results when the group effect and strength domain of the fasteners are taken into account. Finally, the finite element model was used to numerically analyse the effect of inclined loads and evaluate the strength domain of the innovative angle bracket.

A novel algorithm for longitudinal track-bridge interactions considering loading history and using a verified mechanical model of fasteners

The mechanical behavior of fasteners has considerable influence on track–bridge interaction (TBI) analysis, and a consensus has been gradually reached that their loading history and nonlinear characteristics should be taken into account. In this study, we present a new variation pattern of the longitudinal resistance of the fasteners considering loading history, which was experimentally verified based on the Dahl friction model. The model’s mechanical behavior was more consistent with measured results compared with previously proposed Ruge’s model and the double-spring model. According to the new model, an algorithm for TBI analysis considering loading history was derived based on the Ritz method and the principle of minimum potential energy, which was applied in a case study of an N-span, simply-supported girder bridge in a high-speed railway with a typical loading sequence: (1) the seasonal temperature change of the bridge; (2) the bending of the bridge structure under a vertical train load; (3) the braking of the train. Additionally, some significant conclusions were obtained by comparing the numerical results and adopting the mechanical parameters of the fasteners specified in various codes, according to both the linear superposition method (LSM) and loading history method (LHM).

Fasteners in Steel Fiber Reinforced Concrete Subjected to Increased Loading Rates

Increased loading rates on fasteners may be caused by high ground accelerations as a consequence of e.g., nuclear explosions, earthquakes or car collisions. It was concluded by Hoehler et al. (2006) that fasteners under rapid loading rates show an increased ultimate resistance in the concrete dominant failure modes or the ultimate resistance is at least as large as under quasi-static loading. Due to the increased demand on using fasteners in steel fiber reinforced concrete (SFRC), it is intended to show how the ultimate concrete cone capacity of fasteners changes under higher than quasi-static loading rate in normal plain concrete (PC) and in SFRC. This paper presents the results of an extensive experimental program carried out on single fasteners loaded in tension in normal plain concrete and in SFRC. The test series were conducted using a servo-hydraulic loading cylinder. The tests were performed in displacement control with a programmed ramp speed of 1, 100, 1000, and 3500 mm/min. This corresponded to calculated initial loading rates ranging between 0.4 and 1600 kN/s. The results of the tension tests clearly show that the rate-dependent behavior of fasteners in SFRC with 30 and 50 kg/m3 hooked-end-type fibers fits well to the previously reported rate-dependent concrete cone behavior in normal plain concrete. Additionally, a positive influence of the fibers on the concrete cone capacity is clearly visible.

Experimental study on the composite action in sheathed and bare built-up cold-formed steel columns

This paper reports on experiments addressing the buckling and collapse behavior of common built-up cold-formed steel (CFS) columns. The built-up column consists of two individual CFS lipped channels placed back-to-back and connected at the web using two self-drilling screw fasteners at specified spacing along the column length. The experiments aim to quantify ultimate strength, composite action, member end fixity, and buckling interactions and collapse behavior for common built-up CFS members. The testing also explicitly explores the effect of sheathing, as typically employed in cold-formed steel framing, on the response. The experiments provide benchmarks for design that include specific considerations for both thin-walled buckling and fastener behavior. A total of 17 monotonic, concentric compression tests with a column length of 1.83 m (6 ft) are completed with an array of position transducers monitoring displacements at key locations. Tests are conducted with the built-up member seated in CFS tracks. Results indicate a large range of deformation behavior, with local-global interaction and flexural-torsional modes common in many of the unsheathed specimens. Columns sheathed with oriented strand board on both flanges behave as braced against global buckling in the plane of the wall, and local buckling induced failures prevail. The end condition for the tested built-up members seated in track is determined to be semi-rigid, but generally closer to fixed than pinned.

Study on rail fastener failure testing based on fractal theory

The residual vibration of steel rail is rich in the mechanical properties, which include the constraint, that was, the degree of tightness of the fastener. The aim of this research is to characterize the tightness of rail fastener. A fractal analysis procedure based on 1-D curve length calculation is proposed, which applies a length unit to cover fastening the behavior of fasteners. Using the rail vibration data under periodic pulse excitation measured by a track fastener inspection vehicle, this method can derive the fractal dimension of fastener tightness directly (D∈ [1, 2)). Furthermore, 1-D curve length method is also introduced into multi-fractal spectrum analysis for investigating fine scale information. The statistical analysis demonstrates that, fractal dimension Dl, Dr, and multi-fractal parameters αfmax, ∆α can reflect the change process of the tightness of rail fasteners effectively. Therefore, it shows potential to use the fractal parameters of the rail vibration signal to characterize the tightness of the fastener.

Effect on vehicle and track interaction of installation faults in the concrete bearing surface of a direct-fixation track

Various installation faults can occur in fasteners in the construction of a direct-fixation track using the top-down method. In extreme cases, these faults may cause excessive interaction between the train and track, compromise the running safety of the train, and cause damage to the track components. Therefore, these faults need to be kept within the allowable level through an investigation of their effects on the interactions between the train and track. In this study, the vertical dynamic stiffness of fasteners in installation faults was measured based on a dynamic stiffness test by means of an experimental apparatus that was devised to feasibly reproduce installation faults with an arbitrary shape. This study proposes an effective analytical model for a train–track interaction system in which most elements, except the nonlinear wheel–rail contact and some components that behave bilinearly, exhibit linear behavior. To investigate the effect of the behavior of fasteners in installation faults in a direct-fixation track on the vehicle and track, vehicle–track interaction analyses were carried out, targeting key review parameters such as the wheel load reduction factor, vertical rail displacement, wheel load, and mean stress of the elastomer. From the results, it was noted that it is more important for the installation faults in the concrete bearing surface of a direct-fixation track to be limited for the sake of the long-term durability of the elastomer rather than for the running safety of the train or the structural safety of the track.

Consideration of plasticity within the design of timber structures due to connection ductility

The plastic behavior of fasteners in timber structures has gained more and more interest within recent years. In particular, dowel type fasteners show a significant ductile behavior if a certain embedded length of the dowel is ensured. The embedded length is either found by using the formulas based on the design codes (DIN (2008) [3], DIN EN 1995-1-1 [4], etc.) or by verifying the slenderness ratio λ (Jorissen (1998) [5] and Mischler et al. (2000) [32]). A further important issue is the prevention of splitting of the timber itself. Full threaded self-drilling screws enable an effective method to prevent the connection of such a failure (Bejtka (2005) [10]). Most of the inherent material properties of timber, except the behavior in compression, do not allow a plastic design in pure timber structures. Connections accomplished with dowel type fasteners however enable to bridge that gap. The ability of forming plastic hinges by ductile joints within statically undetermined systems provides substantial advantages for a structure. First and foremost, the capability to dissipate energy provides some benefits, such as the integration to the earthquake analysis and in addition to increase the robustness of the structure. A load redistribution within statically undetermined systems can also be achieved, and thereby the possibility of a higher utilization of the structural system. Within this paper, the possibility to redistribute internal forces in timber structures is shown and some application criteria to form plastic hinges are given. Since timber is an inhomogeneous material and is characterized by the scattering of the material properties, the influence of the scattering of the modulus of elasticity to the required rotation of the joint is presented. In order to implement the ductility to timber structures, it is necessary to appraise the ductility as an interaction of the different types of fasteners within timber. Based on conducted experiments the evaluation of the displacement at the point of yielding with respect to existing appraisal models is discussed. Furthermore, different existing methods to evaluate the point of yielding and the ductile behavior of fasteners in timber structures are discussed.

THE WOOD‐FRAMED WITH SHEATHING BUILDINGS ‐ ALTERNATIVE FOR HOUSING CONSTRUCTION

Numerical model of the wood‐framed with sheathing structure and selected results of experimental tests are presented in the paper. Wall and floor diaphragms as the three‐dimensional composite structure are modeled applying plane shell elements representing framing and sheathing and beam element describing the fasteners. Experimental tests were conducted on typically disposed the wood‐framed wall and floor diaphragms in residential housing in Poland. Associated tests of materials and connections and their results are also included in the paper. Non‐linear behaviour of fasteners is examined in the numerical model. Results obtained from model and experiments are coincident.

Nonlinear Strain Hardening Model for Predicting Clamp Load Loss in Bolted Joints

Abstract Closed form solution for the amount of clamp load loss due to an externally applied separating force is determined for a bolted assembly in which the fastener is initially tightened beyond its proportional limit. The joint may or may not have been yielded at initial assembly, however. After the initial tightening of the fastener, the joint is subsequently subjected to a tensile separating force, which further increases the fastener tensile stress into the nonlinear range. Such a separating force will simultaneously reduce the clamping force in the bolted joint. Upon the removal of the separating service load, the bolted joint system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the fastener tension is reduced from its value at initial assembly, due to the plastic elongation of the fastener. The reduction in fastener tension translates into a partial—yet permanent—loss of the clamping load, which may lead to joint leakage, loosening, or fatigue failure. A nonlinear strain hardening model is implemented in order to describe the fastener behavior past the proportional limit of its material, and to determine the clamp load loss due to the permanent set in the fastener after the separating force has been removed. In order to study the effect of strain hardening, various rates of strain hardening are used for modeling the behavior of the fastener material. The effect of three nondimensional variables on the amount of clamp load loss is investigated. This includes the joint-to-fastener stiffness ratio, the ratio of initial fastener tension to its elastic limit, and the ratio of the separating force to its maximum value that would cause joint separation to start. Analytical results are presented for a range of stiffness ratios that simulates both soft and hard joint applications.

Clamp Load Loss due to Fastener Elongation Beyond its Elastic Limit

The amount of clamp load due to an externally applied separating force is determined for a boiled assembly in which the fastener is elongated past its proportional limit, while the clamped joint remained within its elastic range. After the initial tightening of the fastener, the joint is subsequently subjected to a tensile separating force, which further increases the fastener tensile stress into the nonlinear range. Such separating force will simultaneously reduce the clamping force in the bolted joint. Upon the removal of the separating service load, the bolted joint system reaches a new equilibrium point between the fastener tension and the joint clamping force. At the new equilibrium point, the fastener tension is reduced from its value at initial assembly, due to the plastic elongation of the fastener. The reduction in fastener tension translates into a partial—yet permanent—loss of the clamping load that may lead to joint leakage, loosening, or fatigue failure. A nonlinear model is established in order to describe the fastener behavior past the proportional limit of its material, and to determine the clamp load loss due to the permanent set in the fastener after the separating force has been removed. Two fastener materials with significantly different rates of strain hardening are used for modeling the behavior of the bolted joint system. The effect of three nondimensional variables on the amount of clamp load loss is investigated. The first variable is the stiffness ratio of the joint and the fastener. The second is the ratio of initial fastener tension to the fastener elastic limit, and the third variable is the ratio of the separating force to the force that causes joint separation to start. Analytical results are presented for a range of stiffness ratios that simulates both soft and hard joint applications. Experimental verification of the analytical results is presented.

Behavior of Fasteners Loaded in Tension in Cracked Reinforced Concrete

Many reinforced concrete structures are designed under the assumption that the concrete is cracked due to external loods or restraint of imposed deformations (e.g., due to creep, shrinkage, temperaure variations, or suppose settlement). Research shows that fasteners will attrack cracks or even induce cracking. Therefore, the behavior of different types of fastener in cracked reinforced concrete has been studied extensively. Fasteners suitable for use in cracked reinforced concrete such as cast-in situ headed studs or headed anchors, post-installed undercut anchors, and specially designed torque-controlled expansion anchors show a reduction of the concrete cone failure load of about 25 to 35 percent compared to uncracked concrete when located in or close to cracks with a witdh ∼0.3%0.4 mm (0.012 to 0.016 in.). This crack width can be expected in typical concrete members designed with ordinary crock control provisions. The failure load of ordinary torque-controlled expansion, deformation-controlled expansion, and bonded anchors is more influenced by cracks and may be unpredictable, especially if installation inaccuracies that might occur on site are taken into account. Fasteners used in zones with potential concrete cracking must be suitable for this application. A test program to check the effective functioning of fasteners in cracked reinforced concrete is described in mechnical guides by UEAtc and EOTA, a basis for the proposed ASTM specification

Elastic-plastic modeling of structural fasteners for steel bracing connections

Abstract This paper presents part of the results of a study devoted to the analysis of heavy steel bracing connections, and to the effects of those connections on the behavior of braced frames subjected to static loads. In particular, the paper addresses techniques for modeling the stiffness and strength behavior of structural fasteners within the framework of hardening plasticity. Through macroscopic considerations, an incremental constitutive law which relates forces to relative displacements in an interface element is defined, which can be implemented in finite element software in a consistent and straightforward manner. Owing to the complex behavior of fasteners such as bolted clip angles, fillet welds and bolts subjected to shear loading, the constitutive laws are based on stiffness and strength values obtained from physical tests.

Modeling Laterally Loaded Light‐Frame Buildings

Current capabilities of accurately predicting the behavior of the various subassemblies of light‐frame wood structures (walls, floors, and roofs) now meet (or exceed) the ability to characterize material properties. However, subassembly analysis techniques are not commonly incorporated in design practice. The deficiency lies in the inability to efficiently predict the interaction of the subassemblies which yields the behavior of the entire structure. The purpose of this study is to develop and validate a simple structural analysis model to predict the behavior of light‐frame buildings under lateral load. The model is limited to the racking response of shear walls that are arranged in a rectangular fashion beneath a rigid ceiling/floor diaphragm. Nonlinear load‐slip behavior of fasteners is utilized in an energy formulation to yield a three‐degree‐of‐freedom representation of each story of the building. Predicted behavior from the analysis model agrees favorably with results from full‐scale tests. The model provides a method for estimating the behavior of light‐frame buildings near lateral loading and should lead to realistic shear wall strength and stiffness requirements for both residential and commercial buildings.