Static Pull-out Tests Research Articles

Bond-slip response of end-hook and half-hooked steel fibers in moderately strong SIFCON matrix

In this study, an attempt was made to study the bond-slip performance of end-hook and half-hooked steel fibers embedded in moderately strength SIFCON matrix, to find out the cause of excessive mechanical anchorage and to further optimize the bond-slip equation of steel fibers. Used end-hook steel fibers with embedded depths 10 and 15 mm, pullout offset angles 0°, 30°, 45°, and 60°; Half-hooked steel fiber with embedded depths 10 and 15 mm, end-hook bending angles 30°, 45°, 60°, and 90°; Novel end-hook and novel half-hooked steel fibers with end-hook length doubled, which were subjected to a static pullout test at a rate of 0.01 mm/s. Experiments showed that the half-hooked steel fiber took the best end-hook bending angle at 60°; The novel end-hook and half-hooked steel fiber had a good bonded performance. The single steel fiber anchorage performance evaluation index K was proposed. Through experimental phenomena, data analysis, and X-ray flaw detection, the existence of “local damage” was proved. Based on the traditional bond-slip formulation, a new bond-slip formulation for moderately strength SIFCON substrates is proposed by adding a plastic hinge in the “local damage” region. By comparing the old and new equation, it was found that the calculation error of the maximum pullout load of end-hook steel fibers was reduced by 3.77 times and that the calculation error of the maximum pullout load of half-hooked steel fibers was reduced by 2.8 times, and the calculation equation for the peak load of secondary reinforcement of half-hooked steel fiber was supplemented, which is of application value for further optimization of the shape of steel fibers.

Development of PSS-bolt with high load and large deformation capacities

As mining migrates to deep levels, engineering disasters such as excessive deformation, rockburst and massive roof collapse occur frequently. It is important to develop rockbolts that have high load and large deformation capacities, which translates into high energy-absorption capacity, for ground support. This paper presents a piston self-swelling bolt (abbreviated as PSS-bolt) that utilizes steel stretching and frictional sliding to maximize the bolt’s energy absorption capacity. The structure design and working mechanism of the PSS-bolt are introduced. The influence of rod strength, piston length and tube shape on the load–displacement curves of the PSS-bolt was investigated. Laboratory and field static pull-out tests were carried out to optimize the piston length of the PSS-bolt. The test results show that when the piston length is 1350 mm, the load varies between 180 and 210 kN, the displacement can reach 500 mm, and the energy absorption capacity is 95 kJ. In addition, the bolt can reach 71.4% and 100% of its ultimate strength 12 h and 24 h after installation, respectively. The PSS-bolt presented in this paper has high force and large deformation capacities, which can provide a large energy capacity for ground support in high stress and large deformation conditions.

Experimental validation of Orcaflex-based numerical models for the PEWEC device

To design a Wave Energy Converter mooring system that ensures maintainability, resistance, and low costs, without affecting productivity, it is necessary to foster reliable numerical models. In the present paper, the validation of Orcaflex© simulations against the experiment results of the Pendulum Wave Energy Converter (PEWEC) 1:25 scale model, conducted at the University of Naples Federico II, is presented. The experiments consist of free-decay and static pull-out tests to assess the inertial properties of the model and mooring system; tests in operative and extreme regular and irregular waves to fully characterize the mooring system and the device dynamics. The same wave records measured in the towing tank have been used in numerical simulations. PEWEC motion results from numerical simulations and experiments are given in terms of Response Amplitude Operators (RAOs) for regular waves, as statistical values in tabular form, and in Taylor's diagrams for irregular waves. The most probable fairleads tensions for the load dimensioning have been obtained from the Generalized Extreme Value (GEV) distribution of experimental and numerical data. The obtained differences show that the numerical model accurately predicts the experimental data and correctly estimates the dimensioning load of the mooring lines.

Analysis of Hard Point Mechanical Behaviour Due to Variations of Potting Agent Volume on a Composite Sandwich Panel

Composite sandwich panels are widely used in lightweight structures, especially in aerospace, automotive, and marine industries. They are chosen mainly because of the superiority of their specific stiffness as compared to solid panels. Stingray, a solar car designed by the UiTM Eco-photon team, applied this technology for its lightweight property. However, the honeycomb sandwich constructions were susceptible to localized load. Thus, load attachment points using metal inserts, also known as ‘hard points’, were introduced. In this study, the behaviour of hard points based on three volume variations of the potting agent was investigated. ESA recommended static pull-out tests to be conducted on the sandwich panels composed of Nomex honeycomb core, two laminates of carbon fibres/epoxy composite as the face-sheets to determine the failure load of the hard points. A finite element simulation using ANSYS was also performed to determine the displacement of the inserts in presence of normal-to-plane load. The results include load versus extension curves obtained by both methods. Potting agents were found to elevate the stiffness and the strength of the inserts by some degree. Therefore, the application of these hard points on the solar car was found to be effective.

Static Pullout Tests on Retrofitted Anchorage System in Concrete Using Supplementary Reinforcement

This paper presents experimental results of retrofitted anchorage system of structural concrete by using Post-Installation of Supplementary Anchorage (PISA) as a implicit strengthening measure and to improve the nonlinear performance of conventional anchorage system in hardened concrete. A total sixty specimens of M25 grade concrete (150x150x300mm) with two different size of rebar anchorage of 12mm, 16mm and five different configuration of conventional anchorage system was retrofitted by PISA technique is verified under direct tension pullout quasi static loads. The configuration of anchorage comprised by straight bar (A1), 90degree bend (A2), 180degree hook (A3), single head bar (A4) and double head bar (A5). The test parameters considered are bond strength, ductility, stiffness and bar-slip and test variables are configuration of anchorage, size of rebar and presence of supplementary steel. The obtained results validated by ANSYS modeling. This study concludes that a considerable improvement of nonlinear parameters such as ultimate load (3-8%), stiffness (4%-17%), ductility (16%-52%) and concrete contribution (6%-23%) by using PISA technique.

Deformation and Mechanical Properties of a Constant-Friction-Force Energy-Absorbing Bolt

The conventional bolts used in surrounding rock tunnels with large deformation often fail. As a solution to this problem, we developed an extensible bolt with energy-absorbing and constant-friction-force (EACF) characteristics. The EACF bolt mainly comprises a damping device, a hollow threaded bolt, a tightening nut, and a face plate. To reveal its working mechanism, the bolt was tested in terms of its friction, displacement, and energy absorption through a modified tensile test device in a laboratory. The static pull-out test results showed that the axial force-displacement curve of the bolt can be mainly divided into three stages: a conical extrusion stage, an elongation stage, and an elastic failure stage. The EACF bolts exhibited stable energy absorption behaviors when subjected to static loading. The maximum constant friction force could be adjusted by increasing the size and diameter of the straight section of the damping block, and the maximum elongation could be adjusted by increasing the length of the damping cylinder. When the properties of the bolt materials are kept constant, increasing the diameter of the damping block can help achieve a high constant resistance. The proposed EACF bolt has reliable deformation and energy-absorption properties, which ensure its stability when employed in tunnels under the combined action of support and surrounding rocks.

A cable supporting test under impact loading based on 5G-IoT

Reliable supporting effect is of utmost important for the deep mining roadway to prevent the hazards during deep mining activities. Traditional supporting equipment are not satisfying in the absence of the energy-absorbing capacity, whereas the Constant-Resistance-Large-Deformation (CRLD) cable, which can endure a large deformation of 2 m and provide a constant resistance in the meantime, would be a reasonable choice. To verify the CRLD performance of the new cable and highlight its energy-absorbing capacity under impact loading, this paper designed an in situ blasting test in a discarded deep roadway, which is divided into four sections and reinforced by the traditional and CRLD cables, respectively. Firstly, a numerical study of the blasting testis is carried out, the CRLD cable element is proposed, based on the existing one of the FLAC3D software, and a static pullout test is simulated to verify the new element, the adapted impact loading is estimated and the dynamic calculation is performed. Furthermore, under the blasting, which releases the energy of the 1st seismic magnitude, the monitored axial forces of the cables are transmitted in real time using 5G-IoT, and the supporting effects of the two types of cables are compared. According to the numerical and experimental results, the CRLD cable is proven reliable to support the deep roadway, at least shocked by the released energy corresponding to the 1st seismic magnitude.

Biomechanical Properties and Resistance to Uprooting of Laboratory‐Scale Wood Logs

AbstractWood dynamics affects riparian ecosystem functioning and river morphology. The spatial and temporal dynamics of wood pieces in river corridors, in particular of deposited rejuvenated wood logs, depend on their biomechanical properties and resistance to uprooting. The ability of stranded wood logs to withstand drag forces depends on how efficiently their roots have sprouted and on the interarrival time, magnitude, and duration of the moderate floods to which they are subjected. We performed static pullout tests on small‐scale wood logs (Salix species) of four different sizes, growth stages, and sediment moisture content. Statistics of root biomass growth rate and related spatial distribution along the trunk reveal important insights for upscaling dynamics. Similarly, force‐displacement curves indicate the maximum resistance and related energy for uprooting. Autocorrelation analysis of the sequence of force drops in the force‐displacement signal reveals the statistical nature of the mechanism of load redistribution among roots. These results are then used to advance a physically based mathematical model of the resistance of wood log roots to flow‐induced drag forces. Given that the magnitude, duration, and return period of hydrologic events are typically correlated, our model implies the existence of windows of opportunity for wood logs to either survive or remobilize.

Static and Cyclic Tension Behavior of Post-Installed Rebar after Exposure to High Temperature

In order to investigate the static and cyclic tension behavior of post-installed rebar along with cement-based adhesive that is adopted after exposure to high temperature, a three-phase experimental program has been carried out and two typical embedment depths, 10d and 15d are designed. The surfaces of specimens are firstly heated up to 800°C, and then the residual strength at different temperatures of cement-based adhesive has been studied by consequent static pull-out tests. Experimental results show that the tensile strength has a significant reduction at elevated temperatures compared with that of room temperature. The cement-based adhesive has almost lost its full bond strength when the temperature exceeds 350°C. Finally, the bond performance of cement-based adhesive under cyclic loading has been further tested and analyzed. It is found that both 10d and 15d specimens have failed abruptly with rebar pull-out. The employment of long embedment depth has been verified to be an effective method to improve the bond performance of cement-based adhesive under static and cyclic loading. Static numerical investigation indicates that the bond stress distribution is not uniform along the embedment length of post-installed rebar at different temperatures of cement-based adhesive. The temperature-dependent tensile strength prediction has also been obtained based on the experimental data.

A novel energy-absorbing rock bolt with high constant working resistance and long elongation: Principle and static pull-out test

With mining at deep levels worldwide, surrounding rocks of roadways are prone to suffer from high stress fields, large deformation, and burst-potential. Therefore, it is critical to develop high performance energy-absorbing rock bolts to carry high load, accommodate large rock deformation, and energy absorbing. In this paper, a novel energy-absorbing rock bolt with high constant working resistance and long elongation is theoretically and experimentally investigated. The new bolt is composed of three main parts: a rebar, a sleeve tube with a partial slope in the inner surface, and a circle of steel balls. The working resistance is generated by plastic flow of the sleeve tube by contact force between the steel balls and the sleeve tube. A mechanical model is established based on Contact Mechanics to better understand the factors affecting the working resistance and to guide the static pull-out tests. Two batches of the new rock bolt with constant working resistances ranging from 60 kN to 145 kN were developed by changing the number and radius of the steel balls in static pull-out experiments. The load-displacement curves of the new rock bolt indicate the performance of the new rock bolt is characterized by high stiffness, high constant working resistance and adjustable supporting length. The constant working resistance corresponds positively to the gouging depth and the radial expansion of the sleeve tube, based on theoretical analysis verified by test results. A numerical simulation of deep soft roadway is applied to investigate the performance of new energy absorbing rock bolt.

Pullout Tests on Post-installed Bonded Anchors in Ultra-high Performance Fiber Reinforced Concrete

ABSTRACT An experimental study was completed on the behavior on post-installed bonded anchors in ultra-high performance fiber reinforced concrete with a compressive strength higher than 150 MPa. The aim was to analyze the failure mechanisms in static pullout tests. The diameter of the tested anchors was 12 mm and the studied parameters were the embedment depth, the edge distance and the state of cracking of the concrete block. In case of tests without edge effect in uncracked concrete, a combined pullout and concrete cone failure occurred for an embedment depth lower than 60 mm. The recorded mean bond stress was 32.5 MPa for uncracked concrete and 16.3 MPa for cracked concrete with a crack width of approximately 1 mm. A splitting failure was observed for shallow embedment and for edge distances lower than 60 mm. For this tested special anchor system, the increase in tensile strength provided by the metallic fibers enhances the tensile behavior of anchors in comparison to normal strength concrete. It is necessary to adapt the design codes developed for normal strength concrete in order to have more accurate and reliable prediction methods.

Pullout simulation of post installed chemically bonded anchors in UHPFRC

An experimental and numerical study was completed in order to examine the mechanical behaviour of post-installed bonded anchors in ultra-high performance fibre reinforced concrete with a compressive strength higher than 130 MPa. The aim was to analyse the failure mechanisms in static pullout tests and to suggest a simple numerical model, which can be employed in a design stage, to reproduce the global behaviour of the anchor. The experimental observations show that a combined pullout and concrete cone failure occurred for an embedment depth of 40 mm and a steel rod failure for an embedment depth of 100 mm. The numerical model was set up using Abaqus software, by adopting the concrete damage plastic model and a surface-based cohesive behaviour for the interface concrete-anchor. The obtained failure modes and ultimate loads are in good agreement with experimental results. A minimum embedment depth of 50 mm was assessed to prevent a pullout failure of the anchor.

대형 부유식 파력-해상풍력 복합발전 구조물의 극한환경 운동 성능에 대한 실험적 연구

The present study experimentally considers dynamic performance of large floating wave-offshore hybrid power generation platform in extreme conditions. In order to evaluate the motion performance of the large floating hybrid power generation platform, 1/50 scaled model was manufactured. A mooring line was also manufactured, and free-decay and static pull-out tests were carried out to check the mooring model. A mooring line table was introduced to satisfy the water depth, and environmental conditions were checked. Motion responses in regular waves were measured and complicated environmental conditions including wave, wind, and current were applied to see the dynamic performance in extreme/survival conditions. Maximum motion and acceleration were judged following the design criteria, and maximum offset and mooring tension were also checked based on the rule. The characteristics of hybrid power generation platform are discussed based on these data.

Design of Truncated Mooring Line Model in KRISO's Deepwater Ocean Engineering Basin

The present work was an attempt to investigate the applicability of truncated mooring systems to KRISO's deep ocean engineering basin (DOEB) with ratios of 1:100, 1:60, and 1:50. The depth of the DOEB is 15 m. Therefore, the corresponding truncated depths for this study were equal to 1500 m, 900 m, and 750 m. The investigation focused on both the static and dynamic characteristics of the mooring system. It was shown, in a static pull-out test, that the restoring force of a FPSO vessel could be modified to a good level of agreement for all three truncation cases. However, when the radius of the mooring site was reduced according to the truncation factor, the surge motion response during a free-decay test showed a significant difference from the full-depth model. However, the reduction of this discrepancy was achieved by increasing the radius up to its maximum possible value while considering the size of the DOEB. Especially, in terms of the time period, the difference was reduced from 24.0 to 5.3 s for a truncation ratio of 1:100, 54.1 to 8.6 s for a truncation ratio of 1:60, and 31.7 to 3.9 s for a truncation ratio of 1:50. As a result, the study verified the applicability of the truncated mooring system to the DOEB, and therefore it could represent the full-depth mooring system relatively well in terms of the static and dynamic conditions.

Fatigue Bond Characteristics and Degradation of Near-Surface Mounted CFRP Rods and Strips in Concrete

AbstractThis study investigates the bond characteristics and degradation under fatigue loading of near-surface mounted (NSM) carbon-fiber-reinforced polymer (CFRP) rods and strips embedded in concrete. Thirty-six concrete block specimens (350×300×150 mm) were tested under single shear. Sinusoidal waveform fatigue loading with a range of 10–50% of the corresponding static bond strength was applied with the number of cycles varying from 0 to 10,000, which was then followed by static pullout test to determine the local bond-slip relationship between the NSM reinforcement and concrete. Two separate sets of specimens were also subjected to the same fatigue loading up to failure to obtain the corresponding fatigue life. It was found that specimens strengthened with NSM rods mostly failed due to the breakage of concrete and epoxy, while those with NSM strips all failed due to slippage of NSM reinforcements at a lower pullout strength after the fatigue cycles. For both types of reinforcement, as the number of fa...

FPSO 안정성 평가를 위한 절단계류선 모델링 수치 연구

In this paper, a numerical analysis for an internal turret moored vessel located at a 400-m water depth is conducted. The target vessel has an internal turret that is located at the 0.2 Lpp position from the fore-side, with 3 × 4 complex mooring lines installed around the turret circumference. To investigate the motion response of the vessel and the structural reliability of the lines, model tests were conducted. The KRISO ocean basin has a water depth of 3.2 m, which represents 192m using a scaling of 1:60. In order to precisely represent the real-scale condition, equivalent mooring lines needed to be designed. Truncated mooring lines were designed to supplement the restriction of the flume's water depth and increase the reliability of the model testing. These truncated mooring lines were composed of two different chains in order to match the pre-tension, simultaneously restoring the curve and variation in the effecti ve line tension. The static similarities were compared using a static pull-out test and free decaying test, and the dynamic similarities were matched via a regular wave test and combined environments test. Consequently, the designed truncated mooring system could represent the prototype mooring system relatively well in the aspects of kinematics and dynamics.

Effects of Various Environmental Exposures and Sustained Load Levels on the Service Life of Postinstalled Adhesive Anchors

AbstractThis paper presents an experimental study on the long-term creep behaviour of adhesive anchors under sustained tensile loads in combination with different environmental exposures. A total of 72 pull-out test specimens with post-installed anchors were used. The test variables included the type of adhesive anchor, loading conditions (static, sustained), and the environmental exposures (room temperature, moisture, and freeze-thaw). Two sustained load levels of 32 kN and 48 kN (40% and 60% of the anchor’s yield strength) were considered. Sustained load tests lasted for a period of at least 90 days. The static pullout tests showed that specimens with epoxy adhesive exhibited stronger bond strength, forcing the anchor to fail by rupture prior to bond failure. Under sustained load tests, the total displacements over the service life were extrapolated and compared to displacement limits at 50 years (room temperature) and 10 years (moisture and freeze/thaw) in accordance with ICC-ES AC308. Specimens with s...

Comparative Experimental Study of Hook and Pedicle Fixation Systems Used at Surgical Treatment of Spine Deformities

Using human cadaver spines we compared the stiffness of pedicle screws and laminar hooks under cyclic and static pull-out loads. Transpedicular and hook fixation (sub- and supralaminar) of cadaveric thoracic spine segments was performed. Axial pull-out strength was measured using w+b (walter + bai ag) servoelectric testing machine (LFV-10-T50, Switzerland). Static pull-out tests were performed on 7 spine blocks with transpedicular and 7 blocks with hook fixation. The same blocks were tested under cyclic loads. At cyclic pull-out loading 800 N strength with 5 Hz frequency was applied. It was shown that at increasing static load hook implants could bear 1417 N at average. At higher loads the vertebral arch was destroyed. Transpedicular implants could bear 2286 N at average and at higher loads the screw migrated from the arch root. Cyclic tests showed that hooks could bear 2935 cycles at average and at prolonged loading the arch was destroyed. The hooks could bear the full; program of cyclic loads without destruction (18 000 cycles).

A comparison of parallel and diverging screw angles in the stability of locked plate constructs

We investigated the static and cyclical strength of parallel and angulated locking plate screws using rigid polyurethane foam (0.32 g/cm(3)) and bovine cancellous bone blocks. Custom-made stainless steel plates with two conically threaded screw holes with different angulations (parallel, 10° and 20° divergent) and 5 mm self-tapping locking screws underwent pull-out and cyclical pull and bending tests. The bovine cancellous blocks were only subjected to static pull-out testing. We also performed finite element analysis for the static pull-out test of the parallel and 20° configurations. In both the foam model and the bovine cancellous bone we found the significantly highest pull-out force for the parallel constructs. In the finite element analysis there was a 47% more damage in the 20° divergent constructs than in the parallel configuration. Under cyclical loading, the mean number of cycles to failure was significantly higher for the parallel group, followed by the 10° and 20° divergent configurations. In our laboratory setting we clearly showed the biomechanical disadvantage of a diverging locking screw angle under static and cyclical loading.

A Biomechanical Comparison of Patellar Tendon Repair Materials in a Bovine Model

We evaluated the biomechanical properties of FiberWire (Arthrex, Inc, Naples, Florida), a new suture material, for both repair and augmentation as compared to standard Ethibond suture (Ethicon, Inc, Somerville, New Jersey), hypothesizing that primary repair and cerclage augmentation with the new suture material would have similar biomechanical properties as a standard repair with wire augmentation. Forty-five fresh bovine knees were placed in 3 groups of equal size: (1) #5 Ethibond tendon repair plus 18-gauge wire augmentation; (2) #5 FiberWire repair plus #5 FiberWire augmentation; and (3) #5 Ethibond repair plus #5 FiberWire augmentation. A straight static pullout test was performed, randomly alternating between the different groups. Gap formation was measured at the center of the repair by a metric ruler, with the examiner blinded to the developing force-tension readout. For each millimeter of gap formation (1-10 mm), the force on the repair was recorded, as well as the force at the ultimate failure of the repair, designated by breakage of any repair material. Analysis showed no significant difference between the standard Ethibond/wire repair and the FiberWire/FiberWire repair. The Ethibond/FiberWire repair was shown to be significantly weaker than the other 2 groups. Ultimate failure data indicated that the Ethibond/wire repair was significantly stronger than both other groups. No significant differences were found between the FiberWire/FiberWire repair and the Ethibond/FiberWire repair. Newer, stronger suture material for both primary repair and augmentation may provide equivalent biomechanical strength at clinically significant levels.