Peak Shear Load Research Articles

Finite element study on the mechanism of the influence of pretension force and block strength on the shear resistance of the anchor cable with C-shaped tube

To prevent the early breakage of anchor cables under shear loads in support engineering, a combined structure of Anchor Cable with C-shaped Tube (ACC) has been proposed. The shear resistance enhancement mechanism of this structure and the mechanisms of various influencing factors have yet to be fully revealed. A refined nonlinear finite element model of ACC was original established using ABAQUS software, taking into account the actual structure of the steel strands and the interactions, such as contact and failure between the various components. Various anchor cable pretension forces and block strengths were set to investigate their effects on the shear mechanical response of ACC. The results successfully demonstrated a high correlation between peak shear load and pretension force. The results demonstrate that an increase in pretension force reduces the ACC’s peak shear load and break displacement. Additionally, the structure exhibited higher flexural stiffness, the block strength was mobilized earlier, and the block failed locally more quickly. Under high pretension forces, the system exhibited higher shear stiffness in the early stages of shearing due to the influence of the axial force component. With low pretension forces, the ACC exhibited a larger break displacement due to the minor tensile deformation at the shear plane position for the same shear displacement. At low pretension forces, the structure’s bending angle increased more rapidly during the middle and later stages of shearing, accompanied by a larger break displacement. Both of these factors led to a greater bending angle at the shear plane position at the point of failure. The results reveal the characteristic of the peak shear load initially increasing and then decreasing with the increase in test block strength, along with its underlying mechanism. As the block strength increased, the bending angle of the structure at the shear plane position increased more rapidly, resulting in higher shear stiffness. With high block strength, the combination of smaller break displacement and greater shear stiffness led to an initial increase followed by a decrease in peak shear load. A comprehensive RSSB (Relative Stiffness between Structure and Test Block) that considers both structural and test block stiffness was proposed. The deformation pattern of the structure was controlled by the RSSB. The higher the RSSB, the wider the plastic hinge extension range for the same shear displacement, the smaller the bending angle at the shear plane position, and the smaller the maximum curvature of the structure. The contact force of the C-shaped tube generally exhibited a “single peak” distribution. As the shear displacement increased, the peak position of the contact force moved away from the shear plane, and the maximum contact force increased rapidly and remained relatively stable. At the end of the shearing process, the contact force of the C-shaped tube exhibited a “double peak” distribution.

Cyclic frictional response of rough rock joints under shear disturbances: Laboratory experiment and numerical simulation

The cyclic frictional response of rock joints under shear disturbances is critical for understanding the stability and durability of rock engineering structures. Laboratory experiments and numerical simulations were conducted to examine the effects of varying cyclic shear displacement amplitudes, frequencies, and cycle numbers on the macroscopic and microscopic shear characteristics of rough rock joints. The experimental results reveal significant differences in shear strength between the first few cycle and subsequent cycles during the cyclic shear process. As the number of shear cycles increases, the asperities on the contact surface gradually sustain damage, leading to a reduction in normal displacement. During cyclic shear, the peak shear load exhibits a two-stage variation with the number of cycles: an initial sharp decline followed by a gradual increase as the cycles proceed. The peak shear strength shows no obvious pattern under different shear displacement amplitudes and frequencies in the early stages of cyclic shear. As cyclic shear progresses, the peak shear strength decreases with increasing shear displacement amplitude but increases with higher shear frequency. Numerical simulations indicate that significant plastic deformation and shear wear occur on the joint surface during the initial cycles. The growth of the wear area is primarily concentrated in regions of stress concentration. Additionally, the simulations reveal that the volume of shear wear increase nonlinearly with the number of cycles. This research provides new insights into the cyclic shear behavior of rough rock joints and offers valuable references for engineering applications.

Shear Behavior of Two-Dimensional Propped Rough Fractures

The deployment of proppant to fracture shear is a promising approach to stimulating hydraulic permeability in fractured reservoirs. However, the interactive effects of proppant and surface roughness have not been clearly revealed. To better understand this concern, direct shear tests (DSTs) are implemented on 2D rough fractures with a joint roughness coefficient (JRC) varying from 4 to 6 and 18 to 20 under propped conditions. The results show that peak shear strength is positively proportional to asperity amplitude. The highest peak shear strength is determined with a JRC of 14–16 due to it having the highest asperity of 6.34 mm. The peak shear load was decreased significantly by deploying the proppant. Shear damage only occurs in the localized zone where the upper–lower asperities contact. The shear dilatancy was attributed to both the “shear climbing” effects and the shear damage that caused the frictional slip. The proppants weaken the climbing effect but also prevent the shear damage that in turn promotes shear dilatancy.

A novel testing method for examining mode II fracture of rock and its application

Mode II fracture often occurs in rock, which often result in violent ruptures of rock and catastrophic failure of rock engineering. However, attempts to replicate mode II crack extension on a laboratory scale generally fail due to the existence of tensile stress at the notch tip. In this study, a novel testing method named the Z-shaped centre cracked direct shear (ZCCDS) test was developed to examine the mode II fracture of rock, and a series of tests were performed on sandstone with various dislocation ratios (α1) and crack ratios (α2). The equation for calculating the mode II fracture toughness (KIIC) of rock was determined using the finite element method. The validity and reliability of this test method were verified by digital image correlation analysis and comparison with KIIC values determined by the other methods. The testing results showed that the peak shear load changes slightly with increasing α1 and decreases with increasing α2. The mode I stress intensity factor (SIF) decreases while mode II SIF increases with increasing α1 or α2. When α1 = 0.25 and α2 = 0.3, relative sliding deformation at the notch tip was captured via displacement vector analysis, corresponding to a true KIIC of 4.16 MPa∙m0.5. In addition, the effect of α1 and α2 on the failure characteristics of ZCCDS sandstone specimens is slight, and the pure mode II crack of the sandstone satisfies “self-similar extension”. The fracture surface becomes smoother with increasing contribution of the mode II component due to the wide distribution of transgranular fractures. The findings of this study can facilitate better understanding of mode II fracture behaviour of rock.

Shear failure mechanism and parametric study for seawater sea-sand engineered cementitious composites beams reinforced by FRP bars: Finite element analysis

Seawater sea-sand engineered cementitious composites (SS-ECC) is recommended to be used in combination with fiber reinforced polymer/plastic (FRP) bars, which is beneficial to mitigate the lack of raw materials in offshore construction. In this study, finite element analysis was carried out to investigate the shear behaviors and failure mechanism of SS-ECC beams reinforced by FRP bars. The proposed finite element models were verified by the shear experimental results of SS-ECC beams with or without stirrups. It is observed that the shear behaviors of SS-ECC beams can be effectively reflected by the finite element models. Moreover, the shear failure mechanism of SS-ECC beams was carefully analyzed. SS-ECC in beams exhibits serious damage in the compression-shear zone, while FRP longitudinal bars and stirrups are not destroyed. Parametric study, including matrix material, shear span ratio and stirrup ratio, was conducted on. For stiffness and peak shear load, SS-ECC beams with stirrups are almost unchanged with the increment of stirrup ratio, which is due to SS-ECC’s failure rather than FRP stirrup rupture. In addition, the prediction method for shear capacity was further validated by the numerical results. The findings of this study lay a foundation for the engineering applications of SS-ECC beams.

Mechanical degradation and failure behavior of Al/steel electromagnetic assisted clinched joint in chloride salt environment

In this paper, mechanical degradation and failure behavior after salt spray test of Al/steel electromagnetic assisted clinched (EAC) joint were investigated. The Al/steel structure was firstly joined by EAC. These joints were exposed to the neutral salt spray environment, and then gravimetric method, cross-section observation and mechanical properties tests were carried out. The mechanical degradation laws and failure mode evolution were obtained. Results showed that the peak shear and pull-out load of joints decreased after the salt spray test. At the ageing time of 24 days, the peak shear and pull-out load of joints decreased by 22.6% and 41.5%, respectively. In addition, all shear failure modes were neck fractures. Pull-out failure modes ranged from neck fracture to mixed failure, and finally separation. This indicated that the pull-out performance of joints was greatly affected by salt spray ageing, compared with the shear performance of joints. Furthermore, the degradation of shear performance was mainly due to the gradual corrosion and dissolution of Al sheets under salt spray environment, while the degradation of the pull-out performance was mainly due to the damage of the interlocking structure. Therefore, it was necessary to develop appropriate corrosion protection measures for Al/steel joints.

Behavior of anchor cable bolts with c-shaped tube and cable bolts in shear test

The gradual development of coal mining in deep areas has brought new challenges to the surrounding rock support system. It is imperative to design surrounding rock support elements that exhibit strong tensile and shear resistance and are suitable for pretension load. In this paper, an anchor cable bolt with a c-shaped tube (ACC) is proposed, and in order to study the shear performance of the ACC, the mechanical properties of the ACC and ordinary cable bolts with various diameters and pretension loads are tested. In addition, a comparative analysis is performed to investigate the effect of diameter and pretension load on the shear strength of the ACC and cable bolts. The results show that compared with ordinary cable bolts, the ACC exhibits better shear resistance, where its ability to withstand transverse shear load and shear deformation increased by more than 26.8% and 7.0%, respectively. The diameter and pretension load of the bolt significantly affect its shear performance. The larger the diameter of the bolt, the greater the peak shear load. By increasing the pretension load, the shear load and shear displacement at the peak shear load decrease. The failure of the ACC and ordinary cable bolt is mainly due to a combination of shear and tensile failures. In addition, the action mechanism of the ACC is preliminarily explored, and it provides some references for clarifying the mechanical properties of the ACC.

Experimental study on the velocity-dependent frictional resistance of a rough rock fracture exposed to normal load vibrations

Changes in shear velocity can strengthen or weaken the frictional resistance of joints/faults in natural systems, but the mechanism remains unclear. We investigated the shear behavior of a rough basalt fracture in well-controlled, repeatable shear tests under constant and dynamic normal load conditions at different shear velocities. Normal load vibrations, simulating a dynamic normal load, were applied to the upper block of a fractured basalt sample. Simultaneously, a shear load was applied to the bottom block, providing a constant shear velocity. The peak shear strength increased with increasing shear velocity under constant normal load conditions. The peak shear strength decreased at a lower shear velocity under normal load vibrations. When the shear velocity exceeded the critical value, vc, the peak shear strength increased. The apparent coefficient of friction reduced under normal load vibrations. The reduction in the dynamic coefficient of friction increased with increasing shear velocity. We identified a phase shift between the peak normal load and peak shear load with peak shear load delay (D1) and a phase shift between peak normal load and the peak coefficient of friction with the peak coefficient of friction delay (D2). D1 and D2 were dependent on the quasi-static coefficient of friction and shear velocity, and both decreased with increasing shear velocity. D1 decreased with the increasing quasi-static coefficient of friction, while D2 was almost constant with changes in the quasi-static coefficient of friction. A new shear strength criterion was proposed for a rough joint under a constant shear velocity and normal load vibrations.

Enhancing the Performance of CFRP Shear-Strengthened RC Beams Using “Ductile” Anchoring Devices

Reinforced concrete (RC) beams that are shear-strengthened by externally bonded (EB) fiber reinforced polymer (FRP) often yield limited structural enhancement. This is due to the inherent weaknesses of EB-FRP strengthening, including the premature debonding of the FRP, its brittle rupture, and inadequate deformation capacity of the strengthening system. In this paper, two techniques of shear strengthening using U-wrapped carbon FRP (CFRP) and effective anchoring devices are proposed and tested with the aim of enhancing both the shear strength and the ductility of retrofitted RC beams. One of the techniques involves a hybrid-bonded (HB) CFRP system with adjustable normal pressure applied to the CFRP U-strips, and the other features the CFRP U-strips fastened by an H-type end anchor (EA). The main test variables of the former and latter shear-strengthening systems are normal pressures applied to the CFRP U-strips and the width of the deformation segment (or axial stiffness) of the H-type EA, respectively. The results indicate that both strengthening systems significantly enhanced the shear capacity and ductility of the strengthened RC beams. Compared with the control member, the increments in shear capacity were as high as 54.6% and 68.5% for beams retrofitted with the HB-FRP and the EA FRP systems, respectively, and their deflections at peak shear load increased by 43.9% and 84.1%, respectively. The shear failure modes were found to be related to the parameters used in both the HB-FRP and the EA FRP systems. The critical diagonal crack (CDC) inclination of all specimens was less than 45°, ranging from 38° to 44°. Both positive and negative shear interactions were observed between Vf and Vc plus Vs.

Shear performance of single-keyed dry joints between reactive power concrete and high strength concrete in push-off tests

Shear key joints are commonly used in constructions of precast concrete segmental bridges. Most researches focused on shear performance of the dry joints with the identical-strength concrete, leaving a research gap on that of composite joints between different concrete segments. This research aims to investigate shear behavior of shear key joint between reactive powder concrete and high strength concrete. Totally 12 specimens of single-keyed dry joint were tested, with the parameters of concrete compressive strength, steel fibers, and confining stress. The experimental results indicated that shear failure was observed, but crushing phenomenon occasionally occurred in composite joints in testing, which was confirmed by stress distribution from numerical simulation. In terms of shear capacity of composite joint, peak shear loads of reactive powder concrete specimens without steel fibers were enhanced by 10%–12% as increasing of concrete compressive strength, while those with steel fibers achieved 22%–25% enhancement. Nevertheless, a slight reduction of normalized shear strength was obtained because of its lower volume fraction of coarse aggregate. In numerical simulation, as increasing the concrete compressive strength of convex part, peak shear load was enhanced, but the increment rate of peak shear load decreased. Shear design formulae underestimated shear capacity of reactive powder concrete specimens with steel fibers, but the models proposed by Buyukozturk and Rombach gave accurate predictions on those without steel fibers.

Direct shear tests of glass fiber reinforced polymer connectors for use in precast concrete sandwich panels

The precast concrete sandwich panel (PCSP) is a popular structural type used for prefabricated construction. In this study, three kinds of glass fiber reinforced polymer (GFRP) connector, including a flat plate, a corrugated plate, and a hexagonal tube connector, were investigated for potential use in PCSPs. In-plane direct shear tests were conducted to evaluate the performance of the connectors based on a typical push-out configuration (i.e., three concrete wythes linked with connectors and two rigid foam layers in between). Twenty-five specimens were tested, and the parameters investigated consisted of GFRP laminate thickness, projected length, and shear force direction. The shear force vs. relative slip relationships and failure modes of all types of connector were compared and are discussed in detail in this paper. Meanwhile, finite element (FE) analysis was conducted to reproduce the test results. All three types of GFRP connector exhibited a progressive failure manner in spite of the linear brittle nature of the FRP materials; the corrugated plate connector achieved higher deformability than the flat plate connector, particularly when the GFRP laminate thickness was small; and the hexagonal tube connector exhibited similar behavior along two orthogonal directions, making them well suited for use as two-way connectors. The developed FE model was able to well predict the peak shear load and stiffness of all types of connector based on comparisons with the test results.

A Practical Methodology to Evaluate and Predict Edge Cracking for Advanced High-Strength Steel

With the increased application of advanced high strength steel (AHSS), the development of a reliable methodology for evaluating and predicting edge cracking is in high demand. In this study, different shear edge conditions of three different AHSS materials, TRIP 780, DP 980, and DP 1180, were evaluated. The edge cracking is evaluated in four steps: shear test, sheared edge characterization, HSDT, and prediction of edge cracking using FEA. The shear edges were prepared with five different shear clearances between 5 and 25% of the material thickness to obtain variable shear quality. In the HSDT, the strain and thinning distribution is captured using a digital image correlation system as the edge cracking limit and failure criteria in FEA. The preferred shear clearance is characterized by the largest stroke in HSDT and highest thinning value of the onset of edge cracking. FEA showed good correlations with the experiment comparing strain and load-displacement curves. The optimized shear clearance for TRIP 780 is 15% material thickness which for DP 980 and DP 1180 is 20%. By comparing test results from shear test, HSDT and FEA simulation, the peak shear load and burr height from simple experiment observation were found to be important indicators of edge condition, which can be monitored in production.

The Shear Behavior of Precast Concrete Sandwich Panels with W-shaped SGFRP Shear Connectors

This paper presents a horizontal direct shear push-out test program to evaluate the shear behavior of Precast Concrete Sandwich Panel (PCSP) systems with W-shaped Steel Glass Fiber-reinforced Polymer (SGFRP) shear connectors. The experimental program is composed of twelve PCSPs reinforced with W-shaped SGFRP connectors and six PCSPs for comparison that were panels using pure W-shaped GFRP connectors, GFRP pin connectors and stainless-steel truss connectors. The peak shear load, the relationships of shear force-average relative slip, the shear performance of each connector, and the effects of different height, angle and diameter of the SGFRP connector were investigated in this paper. The test results indicate that all specimens with the W-shaped SGFRP shear connectors in this study exhibited an elastic-brittle response caused by pull-out of certain connectors before the ultimate strength was utilized fully and the ductility of the SGFRP material did not play out. Nevertheless, the shear capacity of panels with SGFRP connectors was approximately 2 times that with pure W-shaped GFRP connectors in the case of all parameters being the same, approximately 2 times that with stainless-steel truss connectors for which diameter was reduced by a half, and approximately 2.5 times that with GFRP pin connectors. A reasonable design of connector diameter, spacing and measure of strengthened anchorage is required to ensure the ductile failure of panels.

An Experimental Study on the Shear Performance of Fully Encapsulated Cable Bolts in Single Shear Test

A set of single shear tests on fully encapsulated cable bolts was carried out using a newly developed and integrated Megabolt single shear apparatus. The instrument is designed to determine the pure shear strength of cable bolts where there is no contact between the host body faces during the shearing process. Eight different types of cable bolt were encapsulated in 40 MPa concrete cylinders, using Stratabinder HS grout. Prior to encapsulation, cable bolts were pretensioned at the desired value using a manual pretensioner. Effects of surface profile, pretension value and debonding on shear strength of cable bolts were investigated. It was found that the shear strength of spiral/indented cable bolts was lower than that of plain cable bolts. Increasing the pretension load decreased the peak shear load of cable bolts. In general, no debonding was observed for spiral/indented cable bolts during shear testing; however, all tested plain cable bolts were debonded.

Shear strength properties of cable bolts using a new double shear instrument, experimental study, and numerical simulation

A newly developed double shear apparatus without contact between concrete blocks was developed to conduct a series of double shear tests. This new double shear apparatus is capable of determining the pure shear strength of pre-tensioned fully grouted cable bolt without friction between sheared concrete blocks. Five different types of cable bolt, with various pretension loads, were tested to investigate the influence of surface profile type and pretension load on the shear strength of cable bolt. Concrete blocks of 40MPa strength and the Stratabinder HS grout were used for consistency across the entire tests. The results showed that the plain cable bolts had higher peak shear load compared with the indented and spiral strand cable bolts. The shear displacement and peak shear load decreased by increasing the pretension load. A numerical analysis was carried out, based on the Fast Lagrangian Analysis of Continua (FLAC 2D) and the result was compared with the experimental data. It was observed that FLAC 2D is capable of simulating the performance of cable bolt satisfactorily.

A New Equation for the Shear Strength of Cable Bolts Incorporating the Energy Balance Theory

The application of cable bolts as a secondary support system is an increasing trend in underground coal mines worldwide. The performances of cable bolts have been evaluated under both axial and shear loading conditions. Two methods of testing cables for shear, single and double shear, have been recognised. This paper examines the shear behaviour of a variety of cable bolts under different pre-tension loads by double shear testing. Plain, spiral and the combination of both cable types were used in this study. The initial axial load and the type of cable bolts are the main factors affecting their shear strength. By increasing the axial pre-tension load, the peak shear load occurs at lower shear displacement. The failure angle due to cable bending across the joint at different pre-tension loads varied between 41° and 49°. This demonstrates that the ratio of axial and perpendicular displacements is almost constant and on average the failure occurs at about 45°. A novel analytical model is proposed to evaluate the shear behaviour of pre-tensioned fully grouted cable bolts subjected to double shearing. Energy and Fourier Series methods were incorporated in the model to simulate the shear behaviour of cable bolts. The comparison of the experimental results with the proposed model shows a good agreement.

Double Shear Testing of Cable Bolts with No Concrete Face Contacts

A new series of double shear tests were carried out using a newly modified double shear apparatus which prevented contacts between concrete block surfaces during shearing. 13 double shear tests were carried out using 21mm diameter 19 (9 × 9 × 1) seal construction wire strand cable (also called Superstrand cable), Plain SUMO, Indented SUMO, Spiral MW9 and Plain MW10 cable bolts. These cables were tested subjected to different pretension loads. Concrete blocks with Uniaxial Compressive Strength (UCS) of 40MPa and Stratabinder grout were used for all the tests to maintain test consistency. The results show that the peak shear load and the corresponding shear displacement decrease by increasing the pretension load of the tested cable. The Ultimate tensile strength, lay length, number of wires and cable bolt surface profile type (plain and spiral/indented) are important factors in total shear strength of the cable bolt.

Performance Prediction for Ultrasonically Welded Dissimilar Materials Joints

Ultrasonic metal welding has been used to join multiple layers of battery tabs with the bus bar in lithium-ion battery assembly operations. This paper describes joint performance models for ultrasonic metal welds of multiple layers of dissimilar battery tab materials, i.e., aluminum and copper. Finite element (FE) models are developed to predict the mechanical performance of the ultrasonically welded joints. The models predict peak shear load, energy absorption capability, and failure modes, which are necessary for modeling product performance and defining process requirements for the welds. The models can be adjusted to represent different quality of welds created in conditions of underweld (UW), normal-weld (NW), or overweld (OW) using physical attributes observed through microscopic analysis. The models are validated through lap shear tests, which demonstrate excellent agreement for the maximum force in the NW condition and good agreement for the UW and OW conditions. The models provide in-depth understanding of the relationship among welding process parameters, physical weld attributes, and the weld performance. The models also provide significant insight for further development of ultrasonic welding process for battery tabs and help optimize welding process for more than four-layered joints.

Estimation of shear load sharing in moderately degenerated human lumbar spine

Shear load sharing between intervertebral discs and apophyseal joints was investigated experimentally in human lumbar motion segments with moderately degenerated intervertebral discs. ‘Motion-Segments’ (21–42 years, n=6) and ‘Disc-Segments’ (22–42 years, n=6) were subjected to shear in 0° flexion, using a modified materials testing machine, while immersed in a Ringer bath at 37°C. Initially, two cycles of anterior and posterior shear loading up to 200N (50N/s) were applied, to evaluate stiffnesses in both directions. Specimens were then exposed to 15mm of anterior displacement at a rate of 0.5mm/s. A physiological compressive load of 500N was applied throughout. The initial 5mm of the load–displacement curves were approximated with 6th order polynomials for evaluation of the mean behaviour in each group. ‘Disc-Segments’ were 66% (p=0.002) and 43% (p=0.026) less stiff than ‘Motion-Segments’ for anterior and posterior shear directions, respectively. ‘Disc-Segments’ exhibited 44% lower peak shear load (p=0.015) than ‘Motion-Segments’. All specimens in the ‘Disc-Segments’ group showed damage either at the interface between the endplates and the disc. The intervertebral disc contributes 38% to initial anterior shear load-bearing, increasing to 66% at 5mm displacement. Some over-estimation of disc load-bearing might have been caused by the comparison of segments from different levels. The apophyseal joints make a substantial contribution (65–55%) to anterior shear load-bearing over the initial 2mm of shear displacement but this decreases with increasing shear displacement.

Numerical Analysis of Joint Rock Shear Properties Considering Joint Geometrical Characters

The purpose of this paper is to study the shear behavior of rock specimens containing joints with various distribution forms. Two sets of specimens are simulated by the rock failure process analysis code (RFPA2D). The friction-sliding failure pattern occurs with the lower undulation angle specimen, and the failure pattern turns to be tensile-shear failure mode gradually with the increase of undulation angle. The specimen possesses the highest peak shear load when the undulation angle is about 30º. And joint rock shear character also deteriorates with the increase of weak interlayer thickness. In the intermittent joint model, the unified connection ratio specimen’s peak shear load increases with rock bridge amount, and the multi-joint mode is beneficial to keep rock mass shear stiffness. This study comes to meaningful results to the expansion of joint rock strength evolution law with various joint distribution forms.