Axial Deformation Research Articles

Experimental study on joint behaviour of immersed tunnel subjected to differential settlement

Differential settlement can cause concentrated deformation in the joints of immersed tunnel during its service stage. In this study, a model for simulating immersion joint was proposed, and tests on immersed tunnels under varying differential settlement were conducted. The mechanical behaviours of joints, including vertical displacement, shear displacement, rotation angle, and joint opening, were systematically analysed. Upon the successful simulation of joint against other works, further experiments were performed to underscore the influence of axial constraint and location of differential settlement. Results indicate that axial constraints can enhance the load transfer capacity and improve the uniformity of joint shear forces and rotation angles, accommodating a larger allowable range of differential settlement for immersed tunnel. The parameter of accommodating deformation ratio was defined to characterise the ratio between maximum axial deformation of joint to compression amount of Gina gasket, which could evaluate the effects of axial constraints on joint opening. Setting the accommodating deformation ratio to 1 can increased the allowable differential settlement by 36%. The location of differential settlement affected the load distribution greatly, with respect to shear and bending behaviour of joints. Settlement at the mid-span of a tunnel element rather than a joint was generally safer for immersed tunnel.

A Comprehensive Weightbearing Computed Tomography Study on Patients With Hallux Valgus: Exploring Multiplanar Deformity Interrelationships.

Hallux valgus (HV) is a complex, multiplanar deformity. In this study, we examined the interrelationships between various components of this deformity using weightbearing computed tomography (WBCT). We hypothesized that the severity of traditional axial plane deformities would correlate with malpositioning of the metatarsosesamoid complex, first-ray coronal rotational deformity, and malalignment of the hindfoot and midfoot. The findings may offer valuable insights for guiding the correction of HV deformities. Patients with an HV angle greater than 15 degrees who underwent WBCT were included. Traditional 2-dimensional parameters were semiautomatically assessed. Manual measurements included hindfoot and midfoot WBCT parameters, for example, foot and ankle offset, talar posterior and middle facet morphology, and forefoot arch angle. First-ray parameters, including first metatarsal rotation, sesamoid rotation angle, hallucal pronation angle, and sesamoid position, were measured using established methods. Patients were categorized by hindfoot moment arm values to evaluate hindfoot-forefoot relationships. Sixty-eight feet (53 patients) were included. Manual measurements exhibited excellent interobserver reliability, with ICCs of 0.845 to 0.987 and a kappa coefficient of 0.899 for the sesamoid position. The mean HV angle was 27.4 ± 7.8 degrees, whereas the mean IM angle was 15.8 ± 3.5 degrees. Significant correlations were observed between the HV and intermetatarsal (IM) angles, with all metatarsosesamoid complex parameters and first-ray coronal plane rotational parameters distal to the metatarsal head. The axial and sagittal talar-first metatarsal angles correlated with the HV angle but not with the IM angle. Significant differences in the HV angle, sagittal first tarsal-metatarsal joint angle, and first metatarsal head rotation were observed between the hindfoot moment arm groups, as confirmed by post hoc analysis. The findings support our hypothesis, identifying significant correlations between metatarsosesamoid complex malposition, distal first-ray coronal pronation, and traditional axial plane deformities in HV. Some hindfoot-midfoot alignments correlated with the HV angle but not with the IM angle.

The aortic-vertebral distance is more associated with axial plane deformities than coronal and sagittal deformities in idiopathic scoliosis patients of Lenke types I and II.

Although idiopathic scoliosis is a common three-dimensional deformity, there is a lack of studies evaluating the associations between the aortic-vertebral distance (AVD) and spinal deformities in all planes. The study therefore aimed to evaluate how the coronal and sagittal curvature, vertebral rotation and aortic-vertebral angle (AVA) affect the AVD in idiopathic scoliosis. The AVD, AVA, vertebral rotation and curve angles were measured on preoperative magnetic resonance imaging and radiographs in 46 patients who underwent posterior spinal fusion with pedicle screw instrumentation for idiopathic scoliosis Lenke types 1 and 2. Associations between variables were examined using correlation and multivariable regression analyses. A significant weak to strong correlation was found between the AVD and AVA, and the AVD and vertebral rotation (r = 0.315 to 0.712) within the thoracic curve. The sagittal kyphosis and coronal Cobb angles showed weak correlations with the AVD (r = -0.311 to 0.338). The regression model for the apical vertebral level, which included the four variables, explained 40% (R²=0.40) of the variation in AVD. AVA and vertebral rotation were significantly associated with AVD (p < 0.01 for each), together accounting for 34% (R²=0.34) of the variation. The shortest distance from the aortic wall to the vertebral body wall is primarily influenced by vertebral rotation and the AVA within the thoracic curve. Thus, these factors need to be taken into consideration when planning pedicle screw placement especially in freehand techniques.

The formation mechanism of geological disasters on loess fill slopes revealed by the deformation characteristics of remolded loess under different stress paths

In recent years, geological disasters on loess fill slopes have occurred from time to time, which has attracted widespread attention. In order to deeply understand its deformation and failure laws and promote the disaster prevention and mitigation work, this paper takes remolded loess as the research object, systematically explores the effects of three different stress paths (conventional triaxial compression test (CTC), triaxial compression test with constant average principal stress (TC), and triaxial compression test with reduced confining pressure (RTC)) on its mechanical properties, and observes and analyzes its microstructural characteristics by scanning electron microscopy (SEM). The results show that the soil is strain hardening under the CTC path, while it is strain weak hardening under the TC and RTC paths. In the order of CTC, TC, and RTC paths, the shear strength and volume shrinkage of the soil are reduced in turn, and its deformation has both shear reduction and shear expansion plastic deformation. In the order of CTC, TC, and RTC paths, the degree of particle crushing decreases in turn and the pore content increases in turn. It is inferred that in the initial deformation of loess under loading, the soil is compressed and compacted, and its strength is improved to a certain extent. As the loading continues to increase, the deformation rate increases steadily, and the soil deformation develops gradually, which is mainly axial compression deformation, while the lateral bulging deformation is small until it is destroyed. For the deformation behavior in the form of lateral unloading, the soil is maintained in a relatively stable state at the beginning, and the deformation is very small. When the lateral constraint is reduced to a critical state, the structure is completely unstable, and the deformation develops rapidly in a short time until it is destroyed. This study is of great significance for reducing the occurrence of geological disasters on fill slopes in loess areas.

Anchor test and long-term monitoring of grouted anchors instrumented with Fiber Bragg Grating sensing technology

Geotechnical monitoring of anchors provides fundamental data for analysis and evaluation to ensure safe environment. The use of optic fiber sensing technology, especially Fiber Bragg Gratings, brings many advantages of optic fiber sensors, such as high measurement accuracy, real-time continualmonitoring of deformation, on-line access to data and resistance against electromagnetic interferences. This article deals with anchor tests instrumented with FBG deformation gauges of the root and the tendon of the pre-stressed strand anchor in a test field in the Central Bohemian Region. First, the anchor with three optic cables with FBG sensors for measurement of axial deformation was subjected to six loading stages of the anchor test. Most of the sensors measured values of axial deformation less than 200 με and the root mobilisation was observed. Then, the measurement continued by 26-day long-term monitoring and a trend of a small increase of deformations occurred.

Determining the deformation of an absolutely elastic axis of curved rods under bending

The object of this study is the deformation of an elastic axis with a large deflection of a cantilever clamped absolutely elastic rod under the action of an applied concentrated force. The rod in the free state can have a rectilinear or curved elastic axis. This fact implies a difference in the analytical description of the bending process. However, there is a factor by which some similarity can be found between the bending of rectilinear and curved rods. This factor is the curvature of the elastic axis of the rod in a free state. According to this feature, they can be divided into rods of constant and variable curvature of the elastic axis. The former include rectilinear rods and those that in the free state have the shape of an arc of a circle, and the latter – rods with a variable curvature of the elastic axis. There is a difference between the bending of these groups of rods: in the first case, the deformation of the elastic axis of the rod during its bending will be the same regardless of which end will be cantilever pinched. A distinctive feature of the current research is that the bending of rods with variable curvature of the elastic axis was carried out by alternate pinching of their opposite ends. Moreover, the rods of constant and variable curvature were of the same length s=0.314 m, the same cross-section of 0.005×0.02 m. That has made it possible to visually show the difference between the shape of the elastic axis of the bent rod under the action of the same force when the pinch end is changed. When attached to the rods of the working bodies of agricultural machines, pulsating dynamic loads are smoothed out due to their elasticity. It is important for practice to be able to calculate the value of their deviation, which should be within the given limits. The results are explained by the fact that in the analytical description of the shape of the elastic axis of a curved rod, a technique was proposed in which the length of the axis can start counting both from one end and from the opposite end

Effect of Slenderness Ratio on the Behavior of RC Bearing Walls under Fire Exposure

Reinforced concrete (RC) bearing walls are commonly used in building structures to resist axial and lateral loads. Therefore, their ability to withstand loads when exposed to fire is important. The behavior of RC walls under fire exposure is affected by various factors, such as slenderness ratio, concrete strength and composition, and axial load. This paper investigates the effect of slenderness ratio on the structural performance of RC walls subjected to fire. A series of numerical simulations were conducted on RC walls with different slenderness ratios. The simulations are performed on a three-dimensional (3D) finite element (FE) model, after validating its thermal and structural behavior using previously published experimental data. The walls were exposed to standard fire curves (ISO834) on one side. The thermal and structural response of the walls were assessed in terms of axial deformations, out-of-plane deformations, and fire resistance. The results showed that slenderness ratio had a significant influence on the fire behavior of RC walls. The walls with higher slenderness ratios exhibited higher temperature gradients and larger deflections compared to the walls with lower slenderness ratios. Moreover, the fire resistance of the walls was significantly reduced when the slenderness ratio was increased.

Anterior Vertebral Body Tethering (AVBT) in the Treatment of Adolescent Idiopathic Scoliosis: A Retrospective Study.

Background/Objectives: Anterior Vertebral Body Tethering (AVBT) is a relatively novel minimally invasive surgical technique for the treatment of adolescent idiopathic scoliosis (AIS) that enables deformity correction of the spine diminishing vertebral motion reduction caused by the standard posterior spinal fusion approach. This paper reports the introduction of a new technical variant of AVBT, with the aim of evaluating its effectiveness on the correction of both axial and coronal spinal deformity. Methods: A single-centre single-surgeon retrospective cohort study was conducted. AVBTs were performed between 2020 and 2024. Radiographical values, surgical details, and complications of 67 patients affected by AIS were compared before surgery, immediately after surgery, and at the most recent follow-up. Results: Postoperative results have revealed a statistically significant coronal curve correction of 29.85% in the main thoracic (MT) curves (from mean preoperative width of 54.81 ± 11.86° to 38.45 ± 10.19°) and of 26.93% in the thoracolumbar (TL/L) curves (from 35.15 ± 11.83° to 25.69 ± 10.50°) in line with that obtained by the standard technique. Coronal correction at the most recent follow-up was maintained. Postoperative axial rotation reduction was found to be statistically significant in the main thoracic (MT) curves (from mean Nash-Moe value of 1.84 ± 0.71 to 1.36 ± 0.73), with a further decrease at the most recent follow-up compared with preoperative values. Improvement in other radiographical measures did not reach statistical significance and the complication rate was comparable to the standard technique. Conclusions: The extent of coronal correction in patients treated with the proposed modified AVBT technique is satisfactory and in line with results from studies testing the standard AVBT technique. The findings of this study seem to suggest that this technical variant of AVBT is effective in the correction of both axial and coronal deformity, with a surgical complication rate comparable to the standard technique.

Mechanical Response and Failure Analysis of Stainless-Steel Beams Exposed to Elevated Temperatures

This research investigates the structural behaviour of stainless-steel beams (SSBs) when subjected to extreme temperatures, specifically in the context of fire-induced deformations. High temperatures, typical of fire occurrences, exert large thermal loads on SSBs, leading in material property changes that make the metal more brittle, stiffer, and brittle. The objective of this study is to investigate extensively the behaviour of SSBs under the combined impact of heat transfer and applied loads, with a focus on substantial deflections. To completely assess the performance of SSBs, we undertake parametric investigations and systematic research efforts. The initial phase comprises a thorough review of relevant data about the behaviour of SSBs at increased temperatures. Afterwards, a parametric study of the web section is conducted to determine the performance of the SSBs under exposure to fire and applied stresses. In order to ease the numerical research, the finite element (FE) program ABAQUS CAE is used to simulate stainless steel I-section beams of varying diameters subjected to realistic fire conditions according to the ISO 834 standard fire curve. The average discrepancy between numerical forecasts and experimental data for six separate models about the final temperature readings is 2.74 percent. Prior to actual collapse, the axial displacement of the SSBs decreases by around 7.5%, showing significant temperature influences on their strength. In addition, the axial deformation of the SSBs exhibits greater displacements in the web portion than in the flange section following fire exposure and loading. This discovery highlights the need to take into account the unique thermal expansion and stiffness characteristics of the web and flange components during fire occurrences. Utilising the finite element approach in ABAQUS reveals the resistance of SSBs to increased temperatures. The findings highlight the potential advantages of using stronger SSBs to maximise the structural response under fire conditions. This study gives useful insights into the thermal behaviour of SSBs and has important implications for building fire-resistant structures, boosting the fire safety of constructions, and enhancing their resistance against fire risks.

A Novel Methodology for Detecting and Quantifying Transformer Winding Deformation Using Frequency Response Analysis

A transformer has windings and its structural integrity depends on several factors such as system short circuits,mechanical shocks during transporting,reduction of pressure of winding clamping etc.A transformer can experience severe electromagnetic forces on its winding structure during short circuits. These electromagnetic stresses can lead to winding deformation in both the radial and axial directions.Obviously it will lead to transformer failure. Historicallythe winding deformation and movement in transformer winding is detected by the measurement of leakage inductance. However immediate radial deformation results in a significant change in the leakage inductance. But axial deformation has less change in leakage inductance. Thus leakage inductance measurement method has less sensitivity.Another method was introduce in 1978 based on the frequency response analysis(FRA). In FRA testing method a signal is injected in to one terminal at the same time the response at the other terminal is measured. The commonly used methods for signal injection are swept frequency method(SFRA) and Impulse method(IFRA). This topic proposes a methodology for locating and quan tifying winding deformation in transformers.It is based on the fitting of a Gray Box transformer model to FRA measurements. Here the FRA measurements were recorded both before and after the fault. The refined variations in the key parameters of the model can be then used to quantify winding deformation with in power transformers. Key words: Frequency response analysis, Swept frequency response analysis (SFRA), Impulse response analysis (IFRA), Gray box transformer model. Winding deformation. Keywords: Frequency response analysis, Swept frequency response analysis (SFRA), Impulse response analysis (IFRA), Gray box transformer model. Winding deforma tion,Buckling

Mechanical Behavior of Metastable β Ti–10V–2Fe–3Al Alloy with and without Presence of α Phase

A combination of digital image correlation during uniaxial tensile testing with electron microscopy characterization of microstructure is used to study the details of mechanical behavior of the Ti–10V–2Fe–3Al (wt%) alloy with α phase amount variation from 0 to 20%. Although the triggering stress for deformation‐induced α″ martensite formation has increased and the extent of transformation reduced with an increase in α phase fraction, the deformation mechanism has not changed. The α″ martensite transformation starts from the initiation of single variants of martensite at grain boundaries and/or α/β interfaces in favorably oriented toward deformation axis β grains. It follows by self‐accommodation of strain by α″ martensite via formation of grids and V‐shaped arrangements of {111}α″ type I twins at higher tensile strains.

Optimizing Reduction Guide Stability in Osteotomy Using Patient-Specific Instrumentation: A Basic Guideline.

The use of patient-specific instruments (PSIs) for osteotomies is becoming more popular in orthopaedic surgery for correcting mechanical axis and posttraumatic deformities. However, the PSI reduction guides have great potential for intraoperative deformation, which adversely affects the accuracy of the procedure. To conduct a finite element analysis (FEA) to analyze different design parameters to improve the intraoperative stability of the reduction guides. Descriptive laboratory study. A reduction guide with a rectangular cross section and four 4-mm K-wire slots was simplified, and the following parameters were modified: width, height, profile design, K-wire thickness, and positions. Bending and torsional moments were applied to the guide construct and guide deformation and equivalent stress were determined using FEA. Increasing the profile height by 25% resulted in a 44% reduction in guide deformation for bending (37% for torsion). A 25% increase in profile width led to an 18% deformation reduction for bending (22% for torsion). Transverse K-wire slots resulted in 51% less deformation in torsion compared with longitudinally oriented slots. Placing the central K-wire slots 25% closer to the osteotomy reduced guide deformation by 20% for bending and 11% for torsion. The most effective methods to increase reduction guide stability are to increase the guide height and reduce the central K-wire distance to the osteotomy. When performing opening or closing wedge osteotomies, which mainly involve bending of the guide, a high-profile guide and longitudinally oriented K-wire slots should be used. When torque is expected as in rotational osteotomies, the K-wire holes in guides should be oriented transversely to reduce intraoperative deformation.

Assessing the Impact of Various Industrial Wastes on the Volumetric and Mechanical Properties of Warm Mix Asphalt (WMA)

In recent decades, sustainable practices in pavement construction have been studied to promote circular economy principles and protect the environment. This research seeks to determine the potential benefits of using three different industrial waste materials in formulating warm mix asphalt (WMA). WMA mixes were prepared using ground granulated blast furnace slag (GGBFS) from steel production and biomass fly ash (FA) from the paper industry as virgin filler replacement, and an industrial waste rich in lignin biopolymer (LB) from the hardboard industry as a partial substitute for binder. The study analyzed their volumetric and mechanical properties, including moisture damage resistance, resilient modulus, fatigue resistance, permanent deformation, and abrasion resistance, which were compared with those of a control WMA mix (without any waste). The findings provide insights into an important gap in the literature on the use of GGBFS and LB in WMA. GGBFS-2 mix (75% GGBFS) exhibited the best fatigue performance but the highest axial deformation and rut depth. LB-1 mix (5% LB) performed slightly worse than the optimum control WMA in all tests.

Influence of lining thickness and impedance on the explosion driving of prefabricated fragments

Abstract Prefabricated fragments may deform or crack during explosion driving process, which is adverse to kinetic energy damage. Setting up lining between explosive charges and prefabricated fragments is considered to be an effective way to prevent the excessive load on fragments. This paper studied the influence of lining thickness and impedance on explosion driving of prefabricated fragments based on LS-DYNA finite element simulation. Steel lining of different thickness between 0∼14mm have been studied, as well as steel liner with Kevlar fiber. Fragments accelerated drive process were analysed from the perspective of energy conversion. The results show that the initial speed of the fragment is mainly affected by the quality of the lining and the fracture radius. The axial deformation of the fragment is positively correlated with the initial impact pressure. Steel-fiber composite lining can reduce the shock wave pressure transmitted though, which significantly reducing the initial pressure on the fragments. Low-impedance Kevlar fiber on the outside of the 4340 steel lining can reduce the initial impact pressure of the fragment by about 75%.

Fatigue fracture behaviors and damage evolution of coal samples treated with drying–wetting cycles investigated by acoustic emission and nuclear magnetic resonance

Constructing pumped-storage power stations using underground reservoirs in mines offers a promising method for large-scale energy storage. Watertight coal pillars have the potential to destabilize under the mine-shock cyclic dynamic loading and the drying–wetting cycles (DWCs). Understanding the fatigue damage mechanism and failure precursors in watertight coal pillars under cyclic dynamic loading disturbances in overburdened rock strata has become challenging. This study investigated the fatigue fracture behavior and precursor information of coal samples under acoustic emission (AE) monitoring over 1–7 DWC times. We analyzed the effects of DWC and fatigue cycles on the dynamic parameters and AE response, investigated crack spatial extension behaviors and the tensile-shear cracking evolution law, and analyzed the fatigue damage evolution law and failure precursor with energy and b-value. The results demonstrated that fatigue loading produced a strengthening effect on the DWC coal samples, and DWC promoted plastic softening damage to the specimens and increased the percentage of the elastic phase. The average dynamic fatigue strength and life of the specimens decreased exponentially under 7 DWC times. The average dynamic axial stiffness decreased by 15.67 %, the axial deformation increased by 6.1 × 10−4 in a single cycle, and the dynamic elasticity modulus of the fatigue damage instant decreased by 8.86 %. The greater the number of DWC, the smaller the b-value and the larger the fluctuation amplitude at fatigue failure of the specimen. A large short-term increase or decrease in the b-value can be regarded as a precursor to fatigue failure. This study provides a reference for the stability monitoring and forewarning of underground pumped-storage facilities.

Axially loaded rectangular FRP-concrete-steel hybrid multi-tube concrete stub columns: Performance, confinement mechanism, and design-oriented model

This paper presents an experimental investigation of rectangular glass fiber-reinforced polymer (FRP)-concrete-steel hybrid multi-tube concrete columns (MTCCs) subjected to monotonic axial compression to explore their mechanical behavior and confinement mechanism. Sixteen rectangular MTCCs and eight concrete-filled FRP tube columns (CFFTs) were tested. Four experimental variables, namely aspect ratio, FRP thickness, steel volume ratio, and steel tube configuration, were taken into consideration. The experimental results demonstrated that rectangular MTCCs’ load-bearing capacity and deformability diminished with increasing aspect ratio, as it reduced the effective confinement area of FRP tube to concrete. Additionally, the confined concrete’s compressive strength and axial deformability of rectangular MTCC (with a 6.4% steel volume ratio) enhanced by 21.5% and 32.9%, respectively, compared to the corresponding CFFT. This demonstrated the effectiveness of additional steel confinement. Furthermore, the confinement mechanism of rectangular MTCCs was clarified based on the full-range compressive behavior and dilation property of confined concrete. It included unconfined stage, transition stage, and hardening stage. Finally, a stiffness-based design-oriented model for rectangular MTCCs was established with favorable accuracy.

Mode decomposition to identify oscillation patterns of flexible aeroshell

Flexible aeroshells, featuring deformable membrane surfaces supported by pressurized gas, offer a novel re-entry system for high-altitude deceleration during re-entry. The flexibility of structural components introduces unique challenges in predicting aerodynamic behavior, as deformations can significantly alter the flow field, affecting pressure distribution and potentially causing aerodynamic instabilities. Therefore, coupled analysis is crucial to ensure the performance reliability of inflatable aeroshells. This study investigates the unsteady aerodynamic behavior, considering structural deformation in a two-way partitioned coupled manner in transonic flow. The dominant deformation patterns are identified using dynamic mode decomposition and the greedy compressive sensing algorithm. The findings reveal that the primary deformation pattern combines axial deformation and swing oscillation. The dominant oscillation frequencies remain different from the eigenfrequencies, indicating that the aerodynamic force is the primary driving force of such oscillations. The time evolution of these dominant modes indicates purely oscillatory behavior rather than increasing or decreasing trends. These insights are critical for the design and reliability assessment of inflatable aeroshells in varying aerodynamic environments.

Distorted Magnetic Flux Ropes within Interplanetary Coronal Mass Ejections

Magnetic flux ropes (MFRs) at the center of interplanetary coronal mass ejections (ICMEs) are often characterized as simplistic cylindrical or toroidal tubes with field lines that twist around the cylinder or torus axis. Recent multipoint observations suggest that the overall geometry of these large-scale structures may be significantly more complex. As such, contemporary modeling approaches are likely insufficient to properly understand the global structure of any ICME. In an attempt to rectify this issue, we have developed a novel flux rope modeling approach that allows for the description of arbitrary distortions of the flux rope cross section or deformation of the magnetic axis. The resulting distorted MFR model is a fully analytic model that can be used to describe a complex geometry and is numerically efficient enough to be used for event reconstructions. To demonstrate the usefulness of our approach, we focus on a specific implementation of our model and apply it to an ICME event that was observed in situ on 2023 April 23 at the L1 point by the Wind spacecraft and also by the STEREO-A spacecraft, which was 10.°2 further east and 0.°9 south in heliographic coordinates. We demonstrate that our model can accurately reconstruct each observation individually and also gives a fair reconstruction of both events simultaneously using a multipoint reconstruction algorithm, which results in a geometry that is inconsistent with a cylindrical or toroidal approximation.

Study on seismic performance of a novel connection for exterior wall panels

In order to avoid the damage of the external wall panel and connecting joints caused by the incompatibility between the steel structure and the external wall panel under earthquake loads, as well as to control the interaction between the structure and wall panel to ensure favorable impacts on the main structure, a new connection for external wall panel is proposed. This connection combines the features of the sliding connection and the energy dissipating connection. To investigate the deformation behavior, failure modes, and energy dissipation capacity of the connection, a total of ten specimens with different parameters were designed for cyclic loading. The results indicate that the new connection dissipates energy through bending plastic deformation and pull-bending plastic deformation of the side plate, demonstrating excellent deformation and energy dissipation capacity with noticeable post-yield strengthening effect. Additionally, the effects of different geometric parameters on the initial stiffness, yield load, bearing capacity and hysteretic properties of the connections are also analyzed. Finally, based on the theoretical model of the space rigid frame, the calculation formula of the characteristic parameters at elastic stage of the joint is proposed by the assumptions of ignoring torsion, axial and shear deformation, which is validated by the test results and finite element simulation.

Seismic Response Analysis of Hydraulic Tunnels Under the Combined Effects of Fault Dislocation and Non-Uniform Seismic Excitation

Hydraulic tunnels are prone to pass through faults and high-intensity earthquake areas, which will cause serious damage under fault dislocation and earthquake action. Fault dislocation and seismic excitation are often considered separately in previous studies. For tectonic earthquakes with higher frequency in seismic phenomena, fault dislocation and ground motion are often associated, and fault dislocation is usually the cause of earthquake occurrence, so it is limiting to consider the two separately. Moreover, strong earthquake records show that there will be significant differences in the mainland vibration within 50 m. The uniform ground motion inputs in previous studies are not suitable for long hydraulic tunnels. This paper begins with the simulation of non-uniform stochastic seismic excitations that consider spatial correlation. Based on stochastic vibration theory, multiple multi-point acceleration time-history curves that can reflect traveling wave effects, coherence effects, attenuation effects, and non-stationary characteristics are synthesized. Furthermore, a fault velocity function is introduced to account for the velocity effect of fault dislocation. Finally, numerical analyses of the response patterns of the tunnel lining under four different conditions are conducted based on an actual engineering project. The results indicate the following: (a) the maximum lining response values occur under the combined effects of fault dislocation and non-uniform seismic excitation, indicating its importance in the seismic resistance of the tunnel. (b) Compared to uniform seismic excitation, the peak displacement of the tunnel under non-uniform seismic excitation increases by up to 6.42%, and the peak maximum principal stress increases by up to 28%. Additionally, longer tunnels exhibit a noticeable delay effect in axial deformation during an earthquake. (c) Under non-uniform seismic excitation, the larger the fault dislocation magnitude, the greater the peak displacement and peak maximum principal stress at the monitoring points of the lining. The simulation results show that the extreme response values primarily occur at the crown and haunches of the tunnel, which require special attention. The research can provide valuable references for the seismic design of cross-fault tunnels.