Large Bolt Research Articles

Behavior of steel liner tray walls under external blast: Experimental testing and numerical simulations

Explosions produced in urban or industrial areas due to accidental or intentional detonation of explosives are low-probability but high-impact events. If standoff distance from buildings or other constructions is small, explosions can cause structural failures and serious injuries or deaths of occupants. Although heavy/stiff enclosure systems were long considered appropriate to protect buildings against explosive threats, lighter and flexible steel-based systems, which are increasingly used for modern buildings, may also provide satisfactory performance. The study presents the results of full-scale blast tests on liner tray walls attached to a steel frame building. Walls were tested against increasing blast charges until failure. Due to very high peak pressures and very short durations, the loading regime could be classified as impulsive. The ultimate strength is given by the failure of the end fasteners, after large bolt hole elongations coupled with the pull-through of the end fasteners. If the insulation and outer cladding are lost, the liner trays are directly exposed to blast and the seaming fasteners at overlapping sheets are prematurely lost. As a result, the wall panels work mostly independently, as one-way elements. On the contrary, if the outer cladding protects the seaming fasteners, the overlapping provides additional capacity due to membrane effect (two-way behavior). Numerical models were calibrated using test data and were further used to obtain more information about liner tray behavior under blast.

Comparative assessment of failure in single shear lap joints fabricated using various joining techniques

The current research endeavour reports the performance of single shear lap joints of flax/PP composite laminates. The joints were fabricated using mechanical joining, fusion bonding (ultrasonic and hot plate joining), and hybrid joining techniques (mechanical/ultrasonic joining and mechanical/hot plate joining). In case of the mechanical and hybrid joining, the effect of the bolt size, and number of bolts (single and double) on the tensile failure load was investigated. Pertaining to mechanical joining, the large bolt size and double bolts recorded higher tensile failure load compared to smaller bolt size and single bolt, respectively. Whereas with double bolts, no increase in the tensile failure load was observed for the hybrid joints, due to reduction in bonded area. The hybrid joints (mechanical/ultrasonic) recorded the maximum tensile failure load compared to all other type of joints. The load-extension behaviour and failure of joints was also examined. Expect mechanical joints, all other joints exhibited structural type of failure. In contrast, the mechanical joints resulted in a net-tension failure mode with failure line passing through the hole. However, the thermal decomposition and crystalline behaviour (XRD spectra) of developed joints did not vary significantly. The morphology of failed joints was examined using scanning electron microscope.

Experimental Study of the Role of Gap Size on Bolt Failure in Clevis and Lug Joints

Abstract A common standard for conservatively evaluating the required bolt strength in a clevis–lug joint is to assume that the bolt must survive under an interaction equation that combines loading caused by bending, shear, and axial preload–induced stresses. In practice, this leads to unnecessarily large bolts because the true failure mode is typically closer to simple shear with some bending stresses. In this experimental study, a clevis and lug joint with a variable gap between the clevis arms was used to determine the force necessary to break high strength bolts with various gaps between the clevis and the lug, ranging from pure shear (no gap) to a gap 2.8 times the diameter of the bolt. The testing results clearly show that failure occurs at forces that are often significantly higher than would be predicted by classic, closed-form analysis of the combined loading. In particular, the bolt failed at the force predicted by simple double shear failure theory for gap sizes up to half of the bolt diameter, and for larger gaps, the failure force was consistently higher than would be predicted by classic interaction equations. Thus, although assuming failure that is due to combined bending, shear, and axial stresses is safely conservative, the necessary bolt size is actually significantly smaller than this method predicts.

Hole-edge crack monitoring in attachment lug with large bolt hole based on guided wave and circular piezoelectric sensor array

The crack damage monitoring of aircraft structures is very significant for ensuring aircraft safety, reducing maintenance costs and extending service life. Due to the extreme service environment, the attachment lug is prone to initiate crack damage at the hole edge, which leads to crack propagation and fracture failure. Structural health monitoring technology based on piezoelectric guided wave has been widely studied, promoting the development of crack monitoring. However, at present, research on hole-edge crack damage monitoring of attachment lugs still needs to be further carried out. It is difficult to monitor small cracks at the initial stage of crack propagation, and the accuracy of crack monitoring needs to be improved. By focusing on the accuracy of the crack monitoring in the attachment lug, a crack damage monitoring method based on the circular piezoelectric sensor array is proposed in this paper. Combined with damage alarming and localization imaging, this method comprehensively evaluates the hole-edge crack damage monitoring situation and improves the monitoring effect. The method is verified by an experiment in attachment lug, and this verification includes small crack monitoring and crack propagation monitoring. The experimental results demonstrate that this method can achieve correct damage alarming results, and the maximum localization error of crack damage is only 3.02 mm, which provides a research idea for the accurate monitoring of crack damage at the hole edge.

Experimental study on the mechanical properties of longitudinal joints of shield tunnels under large deformation conditions

Known to be the weakest part of the shield tunnel lining rings, the longitudinal joints render the lining rings prone to large deformation and related diverse defects under nonuniform pressure loading, thereby seriously compromising the safety, serviceability and durability of the tunnel structure. In light of the paucity of studies regarding the performance of joints under large deformation, this paper presents a series of experiments examining the damage mechanism of longitudinal joints under large deformation and investigating the effects of the bolt strength, initial joint configuration, and loading level on the mechanical properties of longitudinal joints. Moreover, a finite element model was developed for the joint, capable of simulating large deformation and bolt yielding. Results show that the specimen’s failure is characterized by concrete cracking and spalling at the compression side of the joint, and/or the thread stripping or fracture failure of the bolts. Besides, an increase in bolt strength can increase the bending capacity of the joint. The discontinuous joint configuration determines the compression height of the joint section cannot be continuously changed, which results in an abrupt change in structural stiffness and a four-stage change in bolt strain. Changes in the loading level not only affect the joint’s bending capacity to some extent, but also alter how cracks develop near the joint. Furthermore, the relationship between the joint opening angle and the segmental rotation angle proves the rigid body deformation characteristics of the segment before the bolts yielded. With the segmental rotation angle increased, the maximum joint opening width and mid-span deflection increased linearly, but the compression height decreased meantime. In addition, the relationship between the bolt strain and the segmental rotation angle exhibited a two-stage linearity after the bolt began to be stressed.

Experimental testing of liner tray walls subjected to near field blast

AbstractExplosions produced in urban or industrial areas due to accidental or intentional detonation of high energy explosives (e.g., improvised explosive devices IED) are low‐probability but high‐impact events. If standoff distance from buildings or other constructions is small, explosions can cause structural failures and serious injuries or deaths of people. Preventing buildings from collapse is essential to minimizing casualties among occupants. However, experience has shown that even if the collapse is prevented, high number of injuries can result from fragments and flying debris generated by the non‐structural components or building envelopes. This risk could be minimized through appropriate design and selection of construction materials for most exposed elements (i.e., building envelopes). Although heavy/stiff systems were long considered appropriate to protect buildings against explosive threats, lighter and flexible systems are increasingly used for modern buildings. By allowing damage (but not fragmentation), the envelope system can provide predictable response, with minimal injuries in case of an explosion.The study presents the results of full‐scale blast tests on liner tray walls attached to a steel frame building. Walls are tested against increasing blast charges until complete failure. The ultimate strength is given by the failure of the end fasteners, after large bolt hole elongations coupled with the pull‐through of the end fasteners.

Structural behavior of large anchor bolts used for sign-support structures

Anchor bolts are commonly used to tie sign-support structures to their concrete base through a double-nut moment connection. Over the past decade, loose anchor rod nuts have proven to need frequent attention, incurring significant cost, while endangering the safety of sign-support structures. In particular, connections tightened with the current pre-tensioning specifications are found to have been loosened within only a year (if not sooner) after installation. Considering this long-standing issue, the objective of this study is to investigate the structural behavior of large anchor bolts used at the base of sign-support structures and evaluate the parameters that influence the rod tightening and loosening process most. For this purpose, a set of Skidmore-Wilhelm bolt tension calibrator tests were performed on different sizes of bolt that had been lubricated with various methods. The tests were to evaluate the effects of the lubrication method on the tightening process. In addition, a sign-post structure removed from the field was tested in the laboratory to study the bolt behavior when it was subjected to the lateral load. Finite-element models were then developed and calibrated using the data collected form the laboratory test. A parametric study was conducted on the calibrated model to understand the effects of key contributing factors, such as level of tightening preload, variation of preload level, washer size, and grip length, on the tightening and loosening process. The investigations determined that the current tightening process can generate a stress concentration in the rod in the range of 30 ksi, which was 55% of the rod's yield strength. The clamping force was also noted to experience a significant reduction during the first few cycles of loading (i.e., up to 20 cycles), beyond which further reduction was minimal. The outcome of this study directly helps choose a preload level that ensures adequate tightening, while avoiding permanent damage to the rod. This is critical for preventing or alleviating the issue of nut loosening.

The capacities of unstiffened T-stubs with thin plates and large bolts

A comprehensive experimental study on unstiffened T-stubs was conducted in order to examine the effects of parameters influencing the capacities of the T-stubs. Pursuant to this goal, 35 unstiffened T-stubs were tested under monotonic loading up to failure, where significantly large deformations were observed. Flanges of T-stubs were selected from the thin plates of 6, 8 and 10 mm whereas bolts were selected as the large bolt of 27 mm. In this way, the capacity of T-stubs was governed by the bending capacity of flanges. Thickness of flange, width of flange, distance from a T-stub stem to bolt row, edge distance, bolt diameter and thickness of weld are selected as the parameters. The results showed that unstiffened T-stubs with thin plates and large bolts can exhibit significantly high ductility and capacity. Moreover, the results revealed that the design recommendations given by AISC 358-16 and EN1993-1-8 predict the capacities of T-stubs conservatively. The average ratios of the actual to predicted plastic capacity by AISC 358-16 and EC3:1-8 are 1.96 and 1.66 (1.34 for Method 2), respectively. These ratios modify to 8.36 and 7.14 (5.88 for Method 2) for the ultimate capacity. The source of the underestimation is attributed to the distance between the plastic hinges. A new yield line pattern is proposed to predict the plastic resistance more accurately. Moreover, an expression is developed to estimate the ultimate resistance. The averages of actual to predicted ratios of the proposed modifications are 1.05 and 1.03 for the plastic and ultimate capacities, respectively.

Fatigue life prediction of nuclear reactor main bolt based on temperature effect and size effect

The temperature effect and size effect on the fatigue life of nuclear reactor main bolt material were studied, and the high temperature fatigue limit of actual bolt thread was evaluated based on the temperature effect and exponential model of size effect. The results showed that the fatigue life of bolt material decreased with the increase of temperature, which exhibited obvious temperature effect. On the other hand, the size effect mainly depended on the loading stress levels because of different effects of stress level on fatigue crack initiation. When the stress level was higher than 340 MPa, fatigue crack initiation was less dependent on defects and the size effect was small, which the fatigue life of large size component could be approximately evaluated by smaller size specimen; by comparison, when the stress level was lower than 300 MPa, fatigue crack initiation was strongly dependent on defects and the size effect became obvious, and at that time the fatigue limit of different size specimen was consistent with exponential model. The fatigue limit of large size bolt under actual service temperature could be obtained by the product of size effect and temperature effect. By combining the theory of critical distance (TCD) with a series of small size fatigue test, the fatigue life of large size components could be efficiently evaluated under the premise of greatly reducing small size fatigue tests.

Improvements in the fatigue design of support structures for offshore wind turbines

AbstractExtended keynote paper of Eurosteel 2021This article provides an overview of the various support structures for offshore wind turbines and addresses the challenges that arise for the different design variants. First of all, the existing types of support structures are explained and their benefits and shortcomings discussed. Following that, the focus is on material fatigue and its analysis, which is of great importance due to the cyclic loading on the structures. A central topic of this article is the experimental evaluation of fatigue strength using large‐scale test setups and state‐of‐the‐art measurement methods. Critical and complex design details such as welds for extremely thick plates, tubular joints, grouted connections, large HV bolts and ring flanges are investigated to improve methods of analysis. Further, the new series of German standards (DIN 18088) for support structures for wind energy turbines and platforms is addressed. Finally, these topics are summarized and the importance of offshore wind energy for the transition to cleaner energy is emphasized.

Transient, Two-Dimensional Heat Conduction Model for Rewetting a Hot Vertical Plate Surface by a Falling Liquid Film.(Dept.M)

A transient, two-dimensional heat conduction model for rewetting a hot plate surface by a falling liquid film is developed. It is assumed that the plate thermal properties are Independent on temperature, and the heat transfer coefficient is a constant value in the wet region and zero in the dry region. The mathematical model equations are transformed to a dimensionless form solved numerically . The results indicate that the heat conduction problem in the rewetting process is substantially two-dimensional one, not only for thick plates, I.e., a large Bolt number, but also for a low initial wall temperature. An explicit simple formula for predicting the rewetting velocity is obtained by correlating the numerical results, Comparisons with other studies are made.

Study on Monitoring Technology of Surrounding Rock in Deep Layered Roadway Based on Constant Resistance and Large Deformation Bolt

The stability monitoring of surrounding rock in layered roadway is an important method to ensure the safety of deep mining coal mine. In view of the actual situation of roadway stability monitoring, based on similarity theory, the deep roadway model is built and small-sized ordinary bolts and constant resistance and large deformation (CRLD) monitoring bolts are developed to detect the mechanical real-time information of surrounding rock in the model, the accurate measurement information of the displacement field and the force value of the bolts are obtained. According to the time series characteristics of the deformation field and the force curves of the monitoring bolts, the criterion of stability and instability pattern of surrounding rock in deep layered roadway are studied. The results show that the force monitoring method based on CRLD bolt is superior to displacement monitoring, the force monitoring curve of CRLD bolt can be divided into stable mode and instability mode, the characteristic of stable mode curve is rising slowly and the instability model with rapid rising and falling stages. The stability monitoring system of roadway with CRLD bolt is developed and applied in deep rock roadway, it has been proved by field practice that the early warning of surrounding rock instability of deep layered roadway is feasible.

Anchoring effect and energy-absorbing support mechanism of large deformation bolt

To research the anchoring effect of large deformation bolt, tensile and drawing models are established. Then, the evolution laws of drawing force, bolt axial force and interfacial shear stress are analyzed. Additionally, the influence of structure element position on the anchoring effect of large deformation bolt is discussed. At last, the energy-absorbing support mechanism is discussed. Results show that during the drawing process of normal bolt, drawing force, bolt axial force and interfacial shear stress all gradually increase as increasing the drawing displacement, but when the large deformation bolt enters the structural deformation stage, these three values will keep stable; when the structure element of large deformation bolt approaches the drawing end, the fluctuation range of drawing force decreases, the distributions of bolt axial force and interfacial shear stress of anchorage section are steady and the increasing rate of interfacial shear stress decreases, which are advantageous for keeping the stress stability of the anchorage body. During the working process of large deformation bolt, the strain of bolt body is small, the working resistance is stable and the distributions of bolt axial force and interfacial shear stress are steady. When a rock burst event occurs, the bolt and bonding interface cannot easily break, which weakens the dynamic disaster degree.

Shear performance of high-strength bolt connector considering different pad and bolt hole

Better than traditional stud connectors, the high-strength bolts enable rapid assembly of steel–concrete composite beams and replacement of decks. However, the researches on the shear performance of high-strength bolt connectors in prefabricated steel–concrete composite beams are relatively limited. Existing studies have not considered the effect of bolt holes in concrete slabs on structural performance. In this paper, the shear performance of high-strength bolt connector of prefabricated steel–concrete composite beams was investigated. The shear bearing capacity, shear stiffness and failure mode were obtained by push-out test. The impact of different bolt hole diameters and pad sizes were considered. Bolt hole diameter of 24 mm, 28 mm and 32 mm, pad size of 50 mm × 50 mm, 80 mm × 80 mm, 200 mm × 100 mm were used in the push-out tests. The results showed that all the specimens were damaged due to crushing of concrete along with shear deformation of bolts. Increasing the pad size can effectively reduce the cracking of concrete slab and improve the slip load and post-slip shear stiffness of specimens. The slip load and peak load of specimens are mainly dependent on the diameter of bolt hole. Specimens with small bolt hole achieve significantly higher pre-slip and post-slip shear stiffness compared to specimens with large bolt hole diameter.

Mechanical comparison of two small interlocking nails in torsion using a feline bone surrogate.

To compare the torsional behavior of two small angle-stable interlocking nails (I-Loc and Targon) with that of locking compression plates (LCP). To evaluate the effect of implant removal on the torsional strength of feline bone surrogates. Experimental. Fracture gap constructs and intact explanted bone surrogates. Fracture gap constructs were stabilized with one of six implants (I-Loc 3 and 4, Targon 2.5 and 3.0, LCP 2.0 and 2.4) and then cyclically tested in torsion (n = 4/group). To simulate implant removal, intact surrogates with implant-specific pilot holes were then twisted to failure (n = 4/group). Torsional compliance (TC; °/Nm), angular deformation (AD; °), and failure torque (FT ; Nm) were statistically compared (P < .05). The I-Loc 4 had the smallest TC and AD of all constructs (P < .05). The largest TC (P < .05) was seen with the LCP 2.0. The Targon 2.5 had the largest AD (P < .05) secondary to locking interface slippage. Targon surrogates FT were the lowest of all groups (P < .05). Conversely, there was no difference between the FT of the I-Loc, LCP, and intact surrogates (P > .05). We showed that I-Loc nails provided greater torsional stability than size-matched Targon nails and LCPs. Conversely, Targon 2.5 locking interface slippage may jeopardize that construct's stability. Furthermore, the significantly reduced bone surrogate torsional strength provided evidence that the large Targon bolt holes increased the risk of postexplantation iatrogenic fracture. Our results provide evidence to conclude that the small I-Loc nails may be valid alternatives to other osteosynthesis options for feline fracture repair.

Strength design of concrete-infilled double steel corrugated-plate walls under uniform compressions

Concrete-infilled double steel corrugated-plate walls (CDSCWs) are composed of two steel corrugated-plates (SCPs) which are connected through bolts, and concrete filled the spacing formed between the two SCPs. Two vertical boundary elements are installed additionally at both sides of CDSCWs. On the one hand, the corrugated configuration of SCPs has great improvement on the load-bearing efficiency of CDSCWs; on the other hand, much higher bearing capacities and better seismic performance for CDSCWs are provided owing to the interactions among SCPs, bolts and infilled-concrete. This paper investigates the load-bearing mechanism and strength design formulae of CDSCWs under compressions. Since SCPs are prone to local buckling failure between two rows of bolts under the conditions of large vertical bolt spacing and small thickness of SCPs, this paper mainly focuses on the load-bearing mechanism of SCPs in CDSCWs under uniform compressions. The unilateral constraint on SCPs provided from infilled-concrete and the restraining effect on the flexural deformation of SCPs owing to bolts are considered. At first, series of finite element (FE) eigenvalue buckling analyses are conducted to study the elastic buckling behavior of SCPs subjected to uniform compressions. On the basis of Euler's formula, the formulae for predicting the elastic buckling stresses and corresponding normalized slenderness ratios λs of SCPs are achieved respectively. The instability performance of SCPs under uniform compressions is then investigated through FE nonlinear analyses, and accordingly the stability coefficient φs is attained. The corresponding φs−λs curve is therefore established in order to calculate the ultimate bearing capacities of SCPs. In addition, the cooperative performance of material strengths between SCPs and concrete is analyzed numerically when CDSCWs reach their compressive ultimate strength. With this consideration, the design method for predicting the cross-sectional strength of CDSCWs under compressions is proposed. Moreover, a CDSCW specimen with I-section is tested under a compressive load. Its cross-sectional strength is investigated experimentally. The results of the experiment coincide with those of numerical simulation, this verifying the safety and validity of the design method for cross-sectional strength design of CDSCWs.

A review of fatigue performance of bolted connections in offshore wind turbines

Flanged bolted connections are used in offshore wind turbines to connect the monopile to the transition piece, and the transition piece to the tower. Forces and moments generated by the effects of winds, waves and currents subject these connections to variable amplitude cyclic loads. In the harsh marine offshore environment areas such as bolt threads are vulnerable to fatigue cracking and failure. Their structural integrity and life are influenced by coatings, lubricants, bolt size, design and tension, manufacturing tolerances and flange contact.This paper presents a review of the main challenges for fatigue life assessment of M72 bolted connections used in offshore wind turbines to connect the monopile to the transition piece, and the factors affecting the fatigue performance. Existing standards and guidelines along with different fatigue assessment methods presented in the literature are discussed in terms of their suitability for fatigue life assessment of M72 bolted connections for offshore wind turbines. One of the key challenges in fatigue life assessment of large scale bolts (e.g. M72) is the lack of experimental data points from which fatigue design curves can be derived. Recommendations are made for how to improve the current best practice for fatigue assessment of large scale bolted connections in the offshore wind industry and potential areas for further investigation are proposed for future research.

Bearing strength at bolt holes in connections with large end distance and bolt pitch

The paper presents test results of one and two bolt connections with very large end distances that failed in bolt bearing, where very high bearing forces were recorded. The purpose of the tests was to investigate the behaviour of the plate in bearing that was not limited by shear, splitting, bolt or net cross-section failure, but with tearing of the material in front of the bolt. The tests showed that the bearing capacity increased insignificantly as the width of the plate increased. Numerical simulations show that bearing resistance is in cases of large end distances significantly influenced by friction forces. They develop because the bolt head and nut, together with the lap plates, constrain the increase of the plate thickness related to plastic deformation. The paper deals with the formation of the stress-strain field as well as the influence of the inner bolt determined by the numerical simulations. The resistances obtained from the tests agree very well with the bearing strength model presented recently by Može and Beg (2014). The coefficient of the bearing strength model that considers the influence of the inner bolt is calibrated on the basis of the presented test results as well as on high strength steel connections with several bolts. The presented bearing strength model was adopted in the final draft of the second generation of EN 1993-1-8.

Control Measures on Surrounding Rock of Extra Large Soft Rock Chamber for Belt Unloading in Shajihai Coal Mine

In order to solve problem on the surrounding rock control for extra-large chamber in Mesozoic soft rock in western mining area, taking the belt unloading chamber engineering in Shajihai coal mine as research object, the methods of field investigation, laboratory test, numerical calculation and field test were used, and control strategies and failure mechanism of chamber were studied. The results shows that the main reasons for deformation and failure of surrounding rock are extra-large section, insufficient self-bearing capacity, high expansive and loose pressure, defects with support design and construction. The mechanics mechanism of surrounding rock deformation is determined as composite type, i.e., I_AII_BCDIII_E type through mechanics theory of soft rock engineering. Based on the supporting philosophy of constant resistance with yielding, combination of softness and hardness, and cooperative control, the compound mechanics mechanism is reasonably transformed into some single types, then the control measures with "constant resistance with large deformation bolt (cable) &amp; U shaped steel frame off wall &amp; bottom anchor pipe with grouting &amp; pouring concrete" are put forward. The engineering practice shows that the measures can effectively control the deformation of the super large soft rock chamber for belt unloading, which ensured stability of the project, and the application effect is good.

Innovative constant resistance large deformation bolt for rock support in high stressed rock mass

Bolt supporting is a major technology used in highly stressed surrounding rock support. Although significant developments of new patterns of bolts have been documented, the stiffness problem which causes the bolt to cannot adapt to the large deformation of surrounding rock was still unsolved. Hence, a novel bolt with constant working resistance and steady large deformation was developed to bear creep deformation and impact load. The constant resistance large deformation bolt (CRLD bolt) was composed of constant resistance element, bolt rod, baffle plate, and tightening nut, which would efficiently control the engineering disasters such as collapse and rock blast. The results of static tensile tests indicated that the CRLD bolt could provide constant resistance ranging from 120 to 130 kN, and the maximal elongation length was 1100 mm without bolt breaking at tensile rate of 10, 20, and 100 mm/s, respectively. Tensile rate has no obvious relationship with constant resistance force. Dynamical impact tests showed that bolt resistance property and its absorption capacity of impact energy were stable, and the dynamic constant resistance changed from 90 to 120 kN, with the impacting height for drop hammers of 10 and 1000 mm. It has also been proved that this kind of bolt has good performance in practical application such as in Qing Shui coal mine. The in situ monitoring results indicate that the CRLD bolt is able to retain rock mass stability and prevent the surrounding rocks from being destructed due to its large-scale deformation. Overall, CRLD bolt is suitable for large deformation, constant resistance, and energy absorption.