Loading Tests Research Articles

Validity and reliability of the T-Force and Chronojump systems to measure movement velocity on resistance machines with older adults

The current study aimed to analyze the validity and reliability of the T-Force and Chronojump systems to measure the movement velocity in the leg press (LP) and chest press (CP) exercises in older people. Eighteen older adults (6 men and 12 women, 79.9 ± 8.5 years) performed a set of procedures over three weeks: (i) the first week was to familiarize participants with the testing procedures, (ii) the second was to perform a progressive loading test until reaching one-repetition maximum (1RM) in the LP and CP, and (iii) in the third week, participants performed three repetitions against five loads (40, 50, 60, 70, and 80% of 1RM). The mean velocity of each repetition was recorded simultaneously through the T-Force and Chronojump devices. Linear regressions (coefficient of determination [r2] and standard error of the estimate [SEE]) analyzed the inter-device validity, and Bland-Altman plots illustrated the systematic differences between devices. A mixed-effects model estimated the mean velocity differences between devices. The relative reliability was analyzed by the intra-class correlation coefficient (ICC[1,k]), while the absolute reliability was by the standard error of measurement (SEM) and the coefficient of variation (CV). The results showed that the T-Force and Chronojump presented a high association level in measuring mean velocity in the LP and CP (r2 range: 0.96–0.99; SEE range: 0.01–0.02 m·s− 1) and low systematic bias (0.02–0.03 m·s− 1). The mean velocity values of T-Force were significantly higher than Chronojump only for 40% 1RM (p = 0.04). Excellent reliability inter-device (ICC range: 0.95–0.98; CV range: 1.7–3.2%) and intra-device (ICC range: 0.90–0.97; CV range: 3.4–6.5%) was observed. This study shows that the T-Force and Chronojump systems are valid and reliable for measuring movement velocity in the CP and LP machines when used by older adults.

Optimization of Load-transfer Functions for a Large-diameter Pile in Multi-layered Geological Conditions via a Stochastic Search Algorithm

The paper presents the combination of the load transfer method (computational model) and the genetic algorithm (optimization model) for the automated inverse analysis of instrumented pile load tests. The output of this process are the input parameters governing the shape of the load-transfer functions and thus the prediction accuracy when the load-transfer method is used as a design tool for deep foundations. The optimization problem is converted into an unconstrained task by applying the static penalty approach. Two types of measurements are considered in a newly proposed objective function: the load-displacement curve monitored in a pile head and the axial force profiles along a pile derived from strain gauges. Firstly, the local sensitivity analysis via the Design of Experiments is carried out to identify the parameters of the genetic algorithm which significantly influences the rate of convergence during the optimization process. Subsequently, a fully automated inverse analysis of the loading test of the large-diameter bored pile in multilayered geological conditions is presented. The simultaneous combination of two instrumentation sources leads to a stable unique solution with a sufficient match between the prediction and measurements despite a larger number of unknown – optimized variables.

A novel strategy to significantly improve wear resistance of amorphous alloys by immersion in NaOH solution

The application of amorphous alloys in tribology is constrained by their inherent brittleness. An alkaline treatment (AT) can address this limitation by hydrogen generated rejuvenation. Following AT in a 3 mol/L NaOH solution for 3 days, the hardness of as-cast Ti-based amorphous alloys decreased by about 10 %, while the relaxation enthalpy increased approximately 2.2 times. Concurrently, the average coefficient of friction (COF) decreased by more than 15 % under all test loads except at 10 N. Additionally, the wear rate significantly decreased by over 20 %, with a notable reduction of about 25 % under a 7 N load. The improvements in tribological properties are primarily attributed to increased plasticity and surface oxidative ability, resulting from the hydrogen absorption during chemical reactions. Thus, AT offers a practical and effective way to significantly enhance the tribological performance of amorphous alloys.

Damage index correlation in massive granite-porous backfills under hydromechanical triaxial cyclic loading using acoustic emissions and X-ray computed tomography

The characterization accuracy of damage indices in massive and porous composite biomaterials under complex osmotic conditions has long been a challenge in engineering materials science. Establishing correlations between damage indices calculated using different methodologies is crucial to validate and improve defects characterizations. In this study, we investigated the damage index correlation of cylindrical massive granite-porous backfill structural composites under both dry and seepage conditions. A series of triaxial cyclic loading and unloading tests were conducted on specimens under hydromechanical conditions with varying osmotic pressures (0, 1, 3, 5, 7, and 9 MPa) and a confining pressure of 9 MPa involving acoustic emission monitoring and phase-based 3D nondestructive CT scanning. The results revealed the AE energy was lower under osmotic conditions compared to dry conditions. The AE Damage Index (DAE), defined by separating tensile and shear microcracking signals, significantly increased from 0.32 to 0.55 with rising osmotic pressure. 3D mesoscopic fracture visualization provided detailed insights into the fractures in granite and backfill interfaces. The number of small-angle cracks increased with osmotic pressure, and the crack inclination distribution range expanded from 63°- 85° to 49°–80°. The average crack angle showed a significant monotonic decrease with increasing osmotic pressure. An Energy Dissipation Damage Index (DED) was defined, and its correlation with the DAE under dry conditions was modeled using a reciprocal function DED=a/(DAE+bσ3)+c. This novel approach offers insights into the transition points between tensile and shear-dominated failure stages. Furthermore, an exponential function DV=aDAEb(b<0) was used to model the correlation between AE Damage Index and Visual Damage Index (DV) under osmotic conditions. The damage indices derived from different methods can be mathematically correlated, providing a comprehensive evaluation of material damage states. The study found the flow transition between different natural-human medias results in different damage mechanisms, which are all obey the correlation law. These damage mechanisms offered constructive recommendations for engineering applications based on varying ratios of osmotic pressure to confining pressure.

Impact performance of egg‐box core sandwich panels made from sisal fibers and castor‐oil‐based polymer

AbstractDeveloping sustainable composites for engineering applications is essential for minimizing environmental impacts and ensuring the long‐term viability of infrastructure and technological advancements. In this context, this work focuses on the manufacture and evaluation of the structural integrity of a sandwich structure composed of aluminum faces and egg‐box‐shaped, sisal fiber‐reinforced epoxy (SFE) or castor‐oil polyurethane (SFC‐O) composites. The sandwich panel is filled with a biobased foam and subjected to dynamic load (drop‐tower) test. For comparison, the base materials SFE and SFC‐O molded into the egg‐box‐shaped cores are also evaluated using Charpy impact tests to establish a potential correlation between their Charpy performance and the drop‐tower behavior of egg‐box sandwich structures. The findings reveal that SFC‐O laminates demonstrate superior Charpy impact resistance (~49%) compared to SFE laminates. Similarly, sandwich structures composed of egg‐box‐castor‐oil composite cores absorb approximately 42.5% more energy than those made with egg‐box‐epoxy cores. The impact behavior of the sandwich structures correlates directly with the impact resistance of the sisal fiber laminates. Overall, the results indicate that the castor‐oil polymer can effectively replace the epoxy polymer matrix phase, enhancing impact absorption and providing an environmentally correct and sustainable solution for fabricating sandwich panels.Highlights Castor‐oil polymer provides laminates with lower density relative to epoxy. Sisal‐castor‐oil‐based laminates possess higher impact resistance than those based on epoxy. Sisal‐castor‐oil‐based panels achieve higher absolute and specific drop‐tower impact properties. Panels subjected to drop‐tower impact tests reveal skin delamination, wrinkling and indentation. Debonding between the foam and egg‐box core is a typical failure mode for epoxy sandwich panels.

Damage evolution and acoustic emission characteristics of sandstone under different true triaxial cyclic loading and unloading modes

In the process of deep coal mining, the cyclic mining disturbance behavior produces significant cyclic loading and unloading effects, to ensure safe production in the mining area, it is necessary to study the damage characteristics and acoustic emission characteristics of the rock body under different cyclic loading and unloading effects. This study developed a TAWZ-5000/3000 rock true triaxial (disturbance) test system and used it to carry out true triaxial cyclic loading and unloading tests in different modes, with acoustic emission (AE) monitoring of the deformation and damage processes. The test results proved that a large number of cycles weakens the rock’s ability to control deformation, and this weakening ability is also related to the types of cyclic loading and unloading modes. The hysteresis loop characteristics and mechanical parameters show obvious path dependence. Based on the damage equivalence method, it is found that the absolute damage parameter increases with the increase of the number of cycles in the same mode, and the accumulation rate of the cumulative damage parameter is faster; the cumulative damage parameter in the equal amplitude cyclic loading and unloading (EAC) mode is always higher than that in the other two modes. The normalized AE ring count rate in the rock samples under cyclic loading and unloading has a significant relationship with the damage percentage, and the crack extension scale function (b-value) shows the “steady increase – strong fluctuation − significant decline” trend. By analyzing the AE characteristic parameters, namely rise time/amplitude (RA) and ringing count/duration (AF), it is found that the sandstones in EAC, graded cyclic loading and unloading (GC), and stepped cyclic loading and unloading (SC) modes are mainly damaged by tension-shear and shear, respectively. By analyzing the values of the acoustic emission parameters RA-AF, it is found that the sandstone is mainly damaged by tensile shear, tensile tension, and shear under EAC, GC, and SC modes, respectively, corresponding to the rock samples’ damage patterns. The study results have important guiding significance for preventing and controlling disasters in deep mines.

ACTH stimulation and oral salt loading tests detect biochemical outcome early after primary aldosteronism surgery.

In primary aldosteronism (PA), the biochemical outcomes of the Primary Aldosteronism Surgical Outcome study are used to assess aldosterone hypersecretion 6-12 months after surgery. However, few studies have investigated whether the outcomes can be predicted in the early postoperative period. In this retrospective study, we evaluated whether the adrenocorticotropin stimulation test (AST) and oral salt loading test (OST) performed immediately after surgery could predict biochemical outcomes 1 year after surgery. We assessed 268 patients with PA who underwent adrenalectomy at our hospital between 2008 and 2020, underwent AST and OST within 15 days of surgery, and were assessed for biochemical outcomes 1 year after surgery. Patients were divided into two groups: biochemical complete success (B-com; n = 219) and incomplete success (B-inc; n = 49). Patients were divided into clinical complete and partial success and absent success groups. The relationships between various AST and OST values and outcomes were analyzed. The B-inc group had significantly higher plasma aldosterone concentration (PAC) and PAC/serum cortisol ratio (PAC/Cort) at baseline and after ACTH loading in AST and 24-hour urine aldosterone in OST than the B-com group. PAC/Cort at 30 min after ACTH loading (area under the curve (AUC) = 0.76) and 24-hour urine aldosterone (AUC = 0.77) were relatively superior predictors of the outcome. Parameters after ACTH loading were better predictors of biochemical and clinical outcomes than baseline. AST and OST immediately after surgery can predict biochemical and clinical outcomes 1 year after surgery in patients with PA.

Base joint hysteresis model for reinforced concrete assembly columns with post-pouring area

In response to the problem of uncontrollable grouting quality of traditional grouting sleeves in the connection between prefabricated components, a column base joint with post pouring area connected by grouting sleeves (PCGS) is proposed. Both the sleeve and post pouring area could cause differences in hysteresis characteristics between prefabricated and cast-in-place components. In order to investigate the hysteresis model of PCGS column base joint, the cyclic load tests and finite element parametric analysis of PCGS column base joint were conducted. The theoretical calculation method for load and displacement of PCGS column base joint at yield, peak, and ultimate characteristic points was established based on equivalent rectangular stress and plastic hinge length in joint area. The average ratios of theoretical calculations to test results for load and displacement at the above three characteristic points are 0.997, 0.983, and 0.983, and 1.020, 1.041, and 0.970, respectively, indicating that the theoretical calculation method can accurately predict the strength and deformation of PCGS column base joint. The dimensionless skeleton curve model with double broken lines in the elastic and strengthening stages, and exponential function in descending stage has been established based on the test and simulated results. The degradation behavior of unloading stiffness and bearing capacity was quantitatively described using the regression fitting method, and the hysteresis rule was defined. The established hysteresis model can effectively reflect the strength and stiffness degradation under cyclic loading, which can provide guidance for the elastic-plastic seismic response analysis of PCGS column base joint.

Macro-micro deformation mechanism of tantalum‑tungsten alloy flyer under explosive loading

This study investigates the macro-micro deformation mechanism of tantalum and tantalum‑tungsten alloys under extreme rate loading. Flyers with varying tungsten contents (0 wt%, 2.5 wt%, 5 wt%, 7.5 wt%, 10 wt%) and different texture were subjected to explosive loading tests. Molding and penetration capabilities of the flyers were comprehensively assessed by the mild-steel witness plate, recovered penetrator and plug. Tantalum‑tungsten alloys with 10 wt% tungsten were crushed, forming discrete holes on witness plate, while those flyers with 0 wt%, 2.5 wt%, 5 wt%, and 7.5 wt% tungsten content formed complete circular perforations on the witness plate. Recovered penetrators and plugs indicated partial fracture of pure tantalum. The increased tungsten content in the alloy enhances the penetration stability and recovery integrity of the penetrator, while simultaneously reducing dynamic plastic deformation. Microstructural analysis via Electron Back Scatter Diffraction (EBSD) revealed a robust {111}//Z axial texture at impact side of the penetrator, which weakened with increasing tungsten content; While un-impacted side showed a {110}//Z axial texture. And uniform equiaxial crystalline structures outperformed long strip grain structures subjected. Therefore, the alloys' molding abilities and penetration stabilities ranked as Ta2.5 W > Ta5W > Ta&Ta7.5 W > Ta10W. These findings provide a foundation for the application of tantalum and tantalum‑tungsten alloys under explosive loading.

BI-DIRECTIONAL STATIC LOAD TESTING

A full-scale static load testing program can optimise many of the requirements in terms of costs and remove uncertainties. The bi-directional load testing method, by eliminating the reaction structures of the traditional top-down testing methodology, opens up unseen possibilities of the testing program in the most efficient, safe, and cost-effective manner for all types of foundations, particularly for larger test loads. The benefits of using bi-directional load tests and how effective they are will be described in the paper. The revolutionary bi-directional static load testing method has also a significant side effect of reducing CO2 emissions for such tests by up to 80%.

Natural Seawater Impact on Crack Propagation and Fatigue Behavior of Welded Nickel Aluminum Bronze

ABSTRACTNickel aluminum bronze (NAB) is a complex alloy used extensively in the marine environment. Fatigue strength of NAB is reduced by welding and prior seawater corrosion. This study investigated the combined effect of corrosion and plasma welding on the fatigue behavior of NAB. Natural seawater corroded samples were used in tension‐tension cyclic loading tests to observe fatigue crack initiation, propagation, and failure. Fatigue cracks initiated from corrosion pits at the weld toe. Stress corrosion and fatigue cracks propagated along the path of β′ and κIII phases. A short crack growth model (SCGM) predicted fatigue strength using experimentally obtained material properties and corrosion pit dimensions. Model predictions were used to develop S‐N curves and were within 30% of experimental results. The SCGM produced accurate and reliable fatigue life results that could be applied by industry to aid in revalidation decision making and inspection scheduling.

Numerical Investigation on the Hysteretic Performance of Self-Centering Precast Steel–Concrete Hybrid Frame

To improve the construction performance and seismic resilience of precast reinforced-concrete frame structures, an innovative self-centering precast steel–concrete hybrid frame has been proposed and subjected to cyclic loading tests. In this paper, a comprehensive numerical analysis was conducted to further investigate the frame’s hysteretic behavior. Initially, a numerical model was developed using the finite element software OpenSees. Numerical analyses of two frame specimens were conducted, demonstrating good agreement between the numerical and experimental hysteretic characteristics, thus validating the model’s accuracy. Subsequently, based on the numerical simulations, a quantitative comparison of hysteretic performance between a novel frame and a traditional reinforced-concrete frame of the same scale was performed. While the proposed frame exhibited slightly lower initial stiffness and energy dissipation capacity than the traditional frame, it outperformed in terms of load-carrying capacity and self-centering ability. Finally, parametric analyses were carried out to assess the influence of various design parameters on the hysteretic performance, including friction force in the web frictions devices, initial post-tensioned force of the prefabricated steel–concrete hybrid beams, the steel arm length, and the column longitudinal reinforcement ratio. The results showed that increases in these four parameters improved the load-carrying capacity and initial stiffness of the proposed frame. Additionally, an increase in the friction force, steel arm length, or column longitudinal reinforcement ratio enhanced the frame’s energy dissipation capacity, while an increase in the initial post-tensioned force or a decrease in the friction force enhanced the frame’s self-centering capacity.

Experimental and numerical analysis of instrumented caissons in tropical soil

This paper presents an experimental and numerical study on the behavior of three (3) instrumented caissons in a tropical laterite soil in the Planalto Central, DF, Brazil. The concrete caissons have a shaft diameter of 0.6 m, a bell diameter of 1.2 m and 1.3 m and lengths of 8.9 to 14.4 m. Static load tests were conducted out to investigate the behavior of the caissons. The results of load vs displacement and their interactions with the tropical soil were measured and evaluated using the methodology of Camapum de Carvalho et al. (2008, 2010) and numerical modeling with back-calculation of static load tests in the Plaxis 3D software. The paper presents the analysis of the load transfer lines and the comparison with the proposed methods. The results pointed to a constant load transfer along the shaft, with a significant contribution from the skin friction, developed for a fraction of the displacement necessary for its mobilization. The accuracy of using the Camapum de Carvalho et al. methodology stands out (2008, 2010), identifying the region dominated by skin friction, tip and plasticization of the foundation, confirming the authors’ predictions for a tropical soil in the Distrito Federal/DF, Brazil. The numerical method using the Plaxis 3D software, proves that for the limit test load there was a significant contribution from skin friction, which must be consider in the analysis of the behaviour of caissons.

A NOVEL WAY TO CLASSIFY THE SLAKE DURABILITY INDEX OF ROCKS

Slaking, the disintegration of rocks upon exposure to moisture and air, poses significant challenges in engineering applications, such as in slope stability and embankment design. This study improves the slake durability index test by introducing several enhancements to better reflect the field conditions of rocks. A new test methodology is developed which includes a revised slake durability classification table, a novel Discard Method for calculating weight retention in the test drum, and an updated classification chart. The improved methodology considers parameters such as porosity and strength, evaluated through index, Schmidt hammer rebound and point load tests. The new classification table categorizes rocks into durability classes according to the field observations and laboratory test results. The Discard Method improves accuracy by eliminating broken pieces from the durability calculation, addressing the limitations in the suggested method. A Configured Discard Method equation further defines the durability estimation by combining porosity, strength and slake durability data. Field investigations and laboratory tests conducted with various rock types demonstrate that the new classification system provides more accurate and practical assessments of rock durability. This study highlights the importance of effective porosity and strength impact which enhance the reliability of slake durability evaluations, offering a revised classification framework that simplifies field assessments while maintaining the accuracy. Future research should focus on developing these methods and expanding their applicability to diverse geological contexts by including more material to test.

Large-Scale Triaxial Test on Mechanical Behavior of Coral Sand Gravel Layered Samples

Layered structures comprising coral sand and gravel have been observed in hydraulic filled foundations in the coral reefs in the South China Sea, leading to anisotropy in their physical and mechanical properties. However, the effect of a layered structure on the strength and deformation of the coral soil foundation remains unclear. In this study, a series of large-scale triaxial compression tests and step-loading tests were carried out on four types of samples, i.e., clean coral sand, clean coral gravel, sand-over-gravel layered sample, and gravel-over-sand layered sample, to investigate the impact of confining pressure and the layered structure on the strength and failure modes of these soils. The results indicate that the stress–strain relationships of all samples predominantly exhibit strain hardening under drained conditions. Under identical confining pressures, the peak strength of clean coral sand is the lowest, while that of coral gravel is the highest. The peak strengths of the two layered samples fall between these extremes, with the gravel-over-sand layered sample exhibiting higher strength. All four samples have similar peak friction angles, slightly exceeding 40°. The difference in peak strength among the four types of samples is attributed to the variations in cohesion, with the cohesion of clean coral gravel being up to four times that of clean sand, and the cohesion of layered samples falling between these two. Both clean sand and clean gravel samples exhibit a bulging phenomenon in the middle, while the layered samples primarily exhibit bulging near the coral gravel layer. In the step-loading tests, the bearing capacity of the layered samples falls between those of clean coral sand and coral gravel, with the gravel-over-sand layered samples demonstrating higher strength. Moreover, the p-s curve of the gravel-over-sand layered samples obtained from the large-scale triaxial apparatus under a confining pressure of 400 kPa resembles that from the plate load tests on the same samples.

Cyclic axial loading tests on mortar-filled rectangular tube with various connection details

Although a mortar-filled rectangular hollow structural section (RHS) under monotonic loading has achieved large tensile capacity using various connection details and buckling capacity of RHS members, the structural capacity of the mortar-filled RHS tubes has not been investigated under cyclic loading. In this study, the seismic performances of newly developed mortar-filled RHS tubes with various connection details were evaluated under cyclic axial loading. The major test parameters included the end connection type, the thicknesses of the RHS tube, cap plate, and cleat plate, as well as the length of the RHS tube. The test results showed that the RHS tube in all specimens failed by tensile fracture before axial compression failure. The seismic performance of the embedded shear plate end connection with penetrating rebar was superior to that of a conventional welded T-end connection. The test results were compared with the current design code to evaluate the seismic capacity of the RHS tube according to the connection details. Design considerations for the connections of the mortar-filled rectangular tubes were also provided.

Research into multi-directional high stability techniques in the same plane for satellite static testing

In order to ensure the structural strength reliability of spacecraft base plate during launch and operation, it is necessary to perform the structural strength test of load synchronous loading on the base plate in the same plane to evaluate its structural bearing capacity under certain axial and shear loads. In order to meet the test requirements and simulate the real stress condition of the base plate, a reliable implementation scheme is proposed in this paper. Multi-directional uniform loading of a satellite base plate is completed by using the same plane multi-directional high stability test technology. The mechanical test of a satellite using this technology shows that the test strain is consistent with the theoretical simulation deformation. This technology effectively solves the problem of uniform loading in the same plane of the satellite base plate in mechanical testing.

Validity and Concordance of a Linear Position Transducer (Vitruve) for Measuring Movement Velocity during Resistance Training.

This study aimed to analyze the intra-device agreement of a new linear position transducer (Vitruve, VT) and the inter-device agreement with a previously validated linear velocity transducer (T-Force System, TF) in different range of velocities. A group of 50 healthy, physically active men performed a progressive loading test during a bench press (BP) and full-squat (SQ) exercise with a simultaneous recording of two VT and one TF devices. The mean propulsive velocity (MPV) and peak of velocity (PV) were recorded for subsequent analysis. A set of statistics was used to determine the degree of agreement (Intraclass correlation coefficient [ICC], Lin's concordance correlation coefficient [CCC], mean square deviation [MSD], and variance of the difference between measurements [VMD]) and the error magnitude (standard error of measurement [SEM], smallest detectable change [SDC], and maximum errors [ME]) between devices. The established velocity ranges were as follows: >1.20 m·s-1; 1.20-0.95 m·s-1; 0.95-0.70 m·s-1; 0.70-0.45 m·s-1; ≤0.45 m·s-1 for BP; and >1.50 m·s-1; 1.50-1.25 m·s-1; 1.25-1.00 m·s-1; 1.00-0.75 m·s-1; and ≤0.75 m·s-1 for SQ. For the MPV, the VT system showed high intra- and inter-device agreement and moderate error magnitude with pooled data in both exercises. However, the level of agreement decreased (ICC: 0.790-0.996; CCC: 0.663-0.992) and the error increased (ME: 2.8-13.4% 1RM; SEM: 0.035-0.01 m·s-1) as the velocity range increased. For the PV, the magnitude of error was very high in both exercises. In conclusion, our results suggest that the VT system should only be used at MPVs below 0.45 m·s-1 for BP and 0.75 m·s-1 for SQ in order to obtain an accurate and reliable measurement, preferably using the MPV variable instead of the PV. Therefore, it appears that the VT system may not be appropriate for objectively monitoring resistance training and assessing strength performance along the entire spectrum of load-velocity curve.

Study on construction technology and bearing mechanism of pressure cast-in-situ pile with spray-expanded frustum

The pressure cast-in-situ pile with spray-expanded frustum (PCPSF) is a new type of pile developed by the last author, which is composed of pile body, ribbed plate and expanded body with double-frustum. This paper presents the equipment used to produce the PCPSF and the spray-expansion extrusion vibration and pressure method used for construction of the PCPSF. The PCPSF model of cement soil transition layer around pile is built with finite element software. The accuracy of the numerical calculations is verified through a comparison with the results of static load tests conducted on PCPSF. Furthermore, the impact of the expanding ratio, expanded body location, and ribbed plate length on the response of the PCPSF is investigated. The results show that: (1) the ultimate bearing capacity (UBC) of PCPSF single pile is proportional to the diameter expanding ratio and the length of the ribbed plate; (2) the improvement of the bearing capacity of single cubic concrete of PCPSF decreases with the increase of expanding ratio; (3) the bearing capacity of expanded body can be activated ahead of time as it advances up in position, and there is a trend toward a steady increase in the combined bearing capacity of the expanded body and pile end; (4) as the expanded body moves up, the vertical stress of the soil below pile tip decreases, the rate of decay of additional stress is accelerated; (5) under the identical circumstances, the PCPSF's bearing capacity is 1.5 times greater than the traditional cast-in-place pile's, and the presence of cement soil transition layer contributes 15 % of the lateral resistance of the PCPSF.

Experiment and restoring force model study of precast shear walls with new rabbet-unbonded horizontal connection

The 'rabbet-unbonded horizontal connection' (RUHC) is a new connection form of precast shear wall. This study conducted a low-cycle repeated loading test on three RUHC walls to investigate the hysteretic performance of the walls with the 'axial compression ratio' and 'unbonded level' as the main variables and the results showed that the above two parameters remarkably affected the seismic performance of RUHC walls. Based on the analysis of test skeleton and hysteresis curve characteristic, the influence of parameters such as axial compression ratio and unbonded level on the load and displacement during the loading process was analyzed. The theoretical values of yield, peak and limit points were calculated, and the skeleton curve model was proposed. Moreover, the unloading stiffness formula was proposed by the non-linear relation of dimensionless parameters and Matlab software fitting, and the hysteresis rule model was established. Finally, a three-fold-linear restoring force model of RUHC walls composed of the theoretical skeleton curve and hysteresis rule was established and verified. This model provides an effective prediction for the hysteresis characteristics and a theoretical basis for conducting elastic-plastic analysis of RUHC structures.