Magnitude Of Prestress Research Articles

Application of Multi-Channel Synchronized Dynamic Strain Gauges in Monitoring the Neutral Axis Position and Prestress Loss of Box Girder Bridges.

The aim of this paper was to explore the application of multi-channel synchronized dynamic strain gauges in monitoring the neutral axis (N.A.) position of prestressed concrete box girders. The N.A. position has recently been proposed as an indicator for monitoring the health of bridge structures. Laboratory experiments were conducted on a prestressed T-beam under different prestress level conditions to investigate the correlation between the prestress magnitude and the N.A. position. In the development of the multi-channel synchronized dynamic strain gauges, edge computing was employed to significantly reduce the amount of data transmitted from the sensor nodes on-site. In edge computing, only the dynamic strain response caused by the maximum vehicle load in each minute is transmitted. This approach greatly enhances the monitoring efficiency and enables the realization of on-site non-computer-based monitoring systems. The laboratory test results of the prestressed T-beam showed that the N.A. position tends to move slightly downward as the prestress force increases. In other words, when the prestress force decreases due to loss, the N.A. position exhibits a slight upward movement. This study selected a newly constructed prestressed box girder as the subject for on-site measurement of the N.A. position using multi-channel synchronized dynamic strain gauges shortly after the prestress was applied. The on-site monitoring data indeed revealed a gradual upward movement of the N.A. position. This phenomenon confirmed that soon after the completion of prestressed concrete bridges, there is a gradual loss of prestress due to the significant shrinkage and creep effects of the early-age concrete. The on-site monitoring result aligned with the findings from the laboratory experiments, where the N.A. position was observed to move upward as the prestress decreased.

Stress-dependent reflection and transmission of elastic waves under confining, uniaxial, and pure shear prestresses

Insights into the reflection and transmission (R/T) of waves at a prestressed interface are important in geophysical applications, such as evaluating the angle-dependent elastic properties for monitoring geopressure and tectonic stress using sonic logging data or seismic data. Although many studies deal with wave propagation in prestressed media, the angle-dependent R/T of waves at an interface subject to different prestress loading modes remains largely unaddressed. We address this issue by applying the theory of acoustoelasticity with third-order acoustoelastic constants to study the R/T coefficients at the interface between two prestressed media. Stress-induced elastic deformations are assumed to be locally homogeneous without boundary dislocations caused by stress concentration so that the static boundary conditions can be applied. We consider three typical prestress modes (confining, uniaxial, and pure shear), each of which takes into account the incidence of upgoing and downgoing P and S waves. The Knott equations under different types of prestresses are derived, followed by the estimation of angle-dependent R/T coefficients. The energy conservation at the interface and the acoustoelastic finite-difference simulation of predicted P and S modes verify the correctness of the angle-dependent R/T coefficients under confining prestress. Comparisons with the elastic case (prestress [Formula: see text]) indicate the important influence of prestresses on the energy distribution of reflected and transmitted waves, including stress-dependent critical angles, converted waves, and R/T energy ratios. Such acoustoelastic effects mainly occur around/after the critical angle. For small-angle incidence, prestresses mainly affect the gradient of R/T coefficients. The type and magnitude of prestress are closely related to the angle-dependent R/T coefficients and must be considered for amplitude-variation-with-offset analysis in prestressed media.

Identification of Dynamic Vibration Parameters of Partial Interaction Composite Beam Bridges Using Moving Vehicle

The vibration response of a partial composite beam bridge under the influence of moving vehicular loads was investigated. Due to the coupling effect between the vehicle and the bridge, the vibration information of the vehicle encompassed the vibration information of the bridge. Consequently, the dynamic response of the vehicle could be utilized to extract the dynamic information of the composite beam. A moving mass-spring-damping system and composite beam elements considering interfacial slips were used for the interaction vibration of a vehicle-composite bridge. A finite element program for the interaction vibration analysis of the vehicle-composite beam bridge was developed. The program was used to extract the vibration information of the composite beam bridge by analyzing the vehicle displacement, velocity, and acceleration in the interaction vibration of the beam and the vehicle. Taking the Hangzhou Jiubao Bridge as the engineering background, the influences of structural parameters such as shear stiffness of connections, prestress magnitude, as well as vehicle parameters, including vehicle stiffness, damping, and mass, on frequency identification were analyzed. Furthermore, the influences of road roughness, disturbance force generated by vehicle random vibrations, and interference signals generated by signal transmission on frequency identification of the bridge were investigated.

Investigation on guided wave characteristics of prestressed bolts based on mechanics of incremental deformations theory

The magnitude of prestress can reflect the degree of anchor bolt failure, but currently there are relatively limited theoretical research methods for the wave characteristics of prestressed bolts. For this reason, this paper establishes a viscoelastic bolt model with prestress based on the Mechanics of Incremental Deformations theory and the Kelvin-Voight viscoelastic theory, and proposes a recursive Legendre polynomial series method (RLPSM) to solve the longitudinal guided wave propagation characteristics in free bolts with prestress. The dispersion and attenuation curves of longitudinal guided waves in free bolts with various prestresses are given, and the influences of prestress on dispersion curves are analyzed. Meanwhile, the ultrasonic guided wave detection system of free bolts with prestress is established for laboratory research, and compared with the theoretical results.

Hysteretic behavior and resilience analysis of a new self-centering buckling restrained braces

The self-centering buckling restrained braces (SC-BRBs) are capable of dissipating energy through BRBs elements during seismic events and restoring to their initial positions after the earthquake, thus reducing residual deformations in structures. The traditional design of the SC-BRBs has a complex structure with dual/three steel load transfer tubes and prestressed tendons anchored by steel end plates as a prestressing system. The complexity of these structures and the possibility of errors in machining dimensions and interactions between components can result in uncertainties of the mechanical behavior of the traditional SC-BRBs. As a consequence, a new design has been developed that uses the brace component as the inner load transfer tube for improved stability and load transfer capabilities in this paper. The structural features and mechanics of the new SC-BRB are first described. Then, to examine the performance of new SC-BRB, a quasi-static cyclic loading test was conducted on one scaled model specimen. The results showed that the new SC-BRB exhibited a consistent flag-shaped hysteretic response, with maximum residual strain of 0.15% within the target design drift of 2%. Nonlinear finite element analyses using ABAQUS were conducted to examine the influence of initial prestress magnitude and properties of prestressing tendon materials on the performance of the new SC-BRBs. The findings indicate that pretension is crucial for full self-centering capabilities of the new SC-BRB. When pretension exceeds the yield bearing capacity of the BRB core, it results in full self-centering and eliminates residual deformations. Additionally, the elastic elongation of the prestressing tendon material determines the deformation capacity of the new SC-BRB, while the elastic modulus of the material affects its post-yield stiffness.

Study on vibration characteristics of fine breccia soil subgrade reinforced with a new prestressed structure under train cyclic loading

Train cyclic loading generally results in significant dynamic responses of the breccia soil subgrade, resulting in a series of subgrade problems. A new prestressed reinforcement structure (PRS) is proposed to reinforce subgrade structures. However, characteristics of the prestressed subgrade under dynamic loading have not been investigated. This study investigates the vibration characteristics of a new prestressed subgrade structure under train cyclic loading. The acceleration responses of the subgrade surface under different train axle loads and prestress levels are measured and discussed by developing a 1:5 scale dynamic model test on a prestressed fine breccia soil subgrade structure. Subsequently, a three-dimensional dynamic finite element model of the prestressed subgrade is constructed for an in-depth analysis of the internal acceleration of the prestressed subgrade. The results showed that a periodic acceleration response of the subgrade should be observed, and its mean crest and mean trough are used to characterize the long-term vibration degree of the subgrade. The peak vertical acceleration of the subgrade is significantly affected by the prestress level, and the dynamic response of the subgrade around the lateral pressure plate (LPP) is reduced more obviously by the prestress than that of the subgrade’s inner region. The peak vertical acceleration at the subgrade shoulder presents linear increase and exponential attenuation with the rise in the train axle load and prestress level, respectively. In addition, an empirical model describing the relationships among the peak acceleration, train axle load, and prestress is proposed. The vertical dynamic displacement and dynamic stress decrease with the increase of the prestress. The average elastic deformation and peak dynamic stress of the subgrade under a prestress level of 100 kPa are found to be 95.8% and 87.22–90.07% of that with the absence of prestress, respectively. The vertical vibration of the prestressed subgrade structure can be reduced by taking measures such as adjusting the prestress magnitude and increasing the subgrade slope ratio, thereby achieving an effective prestress reinforcement effect.

Frequency modulation analysis of solar array using genetic algorithm

In this paper, the optimal placement of prestress (OPP) is investigated for solar array frequency modulation using the genetic algorithm (GA). The purpose of OPP is to improve the solar array’s fundamental frequency and prevent coupling resonance between the solar array and the microwave imager. Prestress is applied to a solar panel by the tension actuators. For optimization producers, the finite element model is used to analyze the prestress configuration problem, which can be converted into the number of programming decision constraints. The automatic interactive updating calculation between MATLAB and finite element software is realized by programming. The GA is used to optimize the solution. Region detection is used, and the bad individuals can be eliminated directly to avoid fitness calculation and effectively improve the optimization efficiency. Simulations are conducted for a solar panel with four arrays. Single-, two-, and three-plate optimizations are investigated. Four optimization parameters include the abscissa value, ordinate value, the laying direction of the actuator in the global coordinate system, and the prestress magnitude. Results demonstrate that the fundamental frequency reaches the maximum at a horizontal layout of prestress after the frequency modulation. The optimal solution is obtained when the prestress is placed in No.2, No.3, and No.4 plates.

Investigating the relationship between radial pre-stress magnitude and ballistic projectile dwell in heavy confined ceramic targets

A series of bare silicon carbide ceramic armour disks were manufactured with high-strength steel containment to induce varying magnitudes of radial pre-stress. The induced radial stresses, ranging from 0 to 900 MPa, were measured via neutron diffraction and verified by comparison with numerical calculations. Four targets of each configuration, referred to as slip-fit, moderate pre-stress, and high pre-stress, were subject to ballistic testing with hemispherical-nose, tungsten heavy alloy long rod projectiles to determine the interface defeat transition velocity. In-situ diagnostics were unsuccessful in aiding the identification of interface defeat, necessitating a reliance on post-mortem assessment. A transition velocity of approx. 1000 m/s was identified for the unstressed target, increasing to approx. 1200 m/s for the pre-stressed configurations. No performance effect was discernible between the moderate (372 MPa) and high (899 MPa) pre-stress configurations, suggesting that an optimal performance may be achieved for lower pre-stress levels (i.e., <372 MPa). The test results were compared with four semi-analytical predictions of interface defeat performance and good agreement was found, albeit with significant range in the model predictions.

Wave propagation in mass embedded and pre-stressed hexagonal lattices

This paper investigates the elastic wave propagation, mode veering, and in-plane vibration of pre-stressed hexagonal lattice embedded in an elastic medium and composed of axially loaded Timoshenko beams with attached point masses. The frequency band structure of the lattice system is obtained by solving the corresponding eigenvalue problem based on the Bloch theorem and the finite element method. The parametric study is performed by investigating the effects of the pre-stress magnitude, stiffness of elastic medium, and attached point masses on the band structure of a lattice unit cell. For simulating the free vibration behavior of the proposed lattices with different topologies, the Hurty-Craig-Bampton method is introduced to reduce the number of degrees of freedom. Based on the reduced finite element model, the natural frequencies are determined for various boundary conditions. The additional interface reduction technique, called system-level reduction, has been observed to achieve accurate results compared to that of the full model. Numerical experiments demonstrated a significant influence of the additional masses, pre-stress, and stiffness of elastic medium on Bloch waves and eigenvalues of the proposed lattice systems. The effects of different parameters on the emergence of mode veering phenomenon and band gaps are investigated in detail.

Experimental study on axially compressed square RC stub columns strengthened with prestressed CFRP strips

Five square reinforced concrete (RC) stub columns were fabricated and experimental tested under an axial compression load in order to study the effectiveness of strengthening by using prestressed carbon fiber reinforced polymer (CFRP) strips. The specimens tested included one un-strengthened and four strengthened. Three specimens were strengthened by using prestressed strips, and the other one strengthened by using non-prestressed was used to compare. The prestress of the strip was achieved by tensed using a special device before it was pasted to the column. The experimental data such as the failure modes, load-displacement curves and strain distribution of CFRP strips were obtained. The effects of prestress magnitude of CFRP strips on the ultimate bearing capacity and deformation capacity of the specimens were analyzed. The results show that the prestress of CFRP strips can effectively increase the ultimate capacity and delay the crack occurrence of the specimens. And ultimate strain, plastic deformation of the specimens were also improved with increase of prestress magnitude of strip.

Effect of mechanical fastener induced pre-stress on power efficiency of soft PZT energy harvesters

Experiments to determine the effects of mechanical fastener induced pre-stress on a piezoelectric energy harvester (PEH) were conducted. Using a mechanical pre-stress fixture and an electro-dynamic MTS material tester, experiments conducted on soft-PZT showed that are optimized PEH by modulating the magnitude of pre-stress induced on the soft-PZT. Experiments also showed that by adjusting the number of mechanical fasteners used to induce the pre-stress, the energy harvesting capabilities of a PEH may be further optimized.

Quantitative Definition of Seismic Performance Levels for Precast Bridge Piers with Continuous Reinforcement

For construction sites within cities, which require fast construction because of restrictions in road occupation time, or for other occasions where construction period is an important factor because of similar reasons, application of a modular construction method using precast members is efficient in terms of shortening the construction period. The substructures of bridges are normally constructed using cast‐in‐place, which has been a major cause of delays in construction. Application of a modular construction method could decrease the occupation time in the sites. A prime example is the Accelerated Bridge Construction (ABC) by the Texas Department of Transportation (TDOT) and Federal Highway Administration (FHWA). Precast members are the key components of ABC. The main purpose of this paper is to provide clear seismic performance standards for precast bridge piers. Current seismic design codes require force‐based design checks and provide qualitative evaluation of the overall structure. They do not provide specific qualitative criteria for individual structures with particular types. Previous research has been focused on reinforced‐concrete bridge piers, while lacking on research towards prefabricated bridge piers with continuous reinforcements. In order to quantitatively evaluate the seismic performance level of prefabricated bridge piers, the seismic performance was quantitatively suggested in accordance with the classification of four which are operational, immediate occupancy, life safety, and collapse prevention. These criteria are cracking of cover concrete, crushing of cover concrete, yielding of axial steels, and fracture of axial steels. Based on the given seismic performance evaluation criteria, evaluation and verification were conducted on four prefabricated bridge piers with continuous reinforcement that have undergone quasistatic cyclic experiments. The moment‐curvature analysis model was constructed for the parametric study and verified through experimental results. Based on the developed M‐Phi model, prefabricated bridge piers with continuous reinforcement, which were designed force‐based using response correction factor, were evaluated. In addition, parametric study was also conducted focusing on concrete strength, magnitude of prestress, and transverse reinforcement. Depending on the level of individual performance produced by ranges of these variables within possible runs on actual piers, the impact of 3 variables was analyzed. Furthermore, in response to changes in each variable, the impact on the relevant seismic performance level was verified through response spectrum analysis.

Increased Cell Traction-Induced Prestress in Dynamically Cultured Microtissues.

Prestress is a phenomenon present in many cardiovascular tissues and has profound implications on their in vivo functionality. For instance, the in vivo mechanical properties are altered by the presence of prestress, and prestress also influences tissue growth and remodeling processes. The development of tissue prestress typically originates from complex growth and remodeling phenomena which yet remain to be elucidated. One particularly interesting mechanism in which prestress develops is by active traction forces generated by cells embedded in the tissue by means of their actin stress fibers. In order to understand how these traction forces influence tissue prestress, many have used microfabricated, high-throughput, micrometer scale setups to culture microtissues which actively generate prestress to specially designed cantilevers. By measuring the displacement of these cantilevers, the prestress response to all kinds of perturbations can be monitored. In the present study, such a microfabricated tissue gauge platform was combined with the commercially available Flexcell system to facilitate dynamic cyclic stretching of microtissues. First, the setup was validated to quantify the dynamic microtissue stretch applied during the experiments. Next, the microtissues were subjected to a dynamic loading regime for 24 h. After this interval, the prestress increased to levels over twice as high compared to static controls. The prestress in these tissues was completely abated when a ROCK-inhibitor was added, showing that the development of this prestress can be completely attributed to the cell-generated traction forces. Finally, after switching the microtissues back to static loading conditions, or when removing the ROCK-inhibitor, prestress magnitudes were restored to original values. These findings show that intrinsic cell-generated prestress is a highly controlled parameter, where the actin stress fibers serve as a mechanostat to regulate this prestress. Since almost all cardiovascular tissues are exposed to a dynamic loading regime, these findings have important implications for the mechanical testing of these tissues, or when designing cardiovascular tissue engineering therapies.

Evaluation of the Active Support and Yielding Bearing Properties of Artificial Pillars Supporting a Stope Roof Using 3DEC Numerical Simulation

Before achieving yielding support with artificial pillars, it is significant to evaluate their active support and passive bearing performances on the stope roof. This paper focuses on three aspects of research using 3DEC numerical simulation, which are support patterns of artificial pillars, magnitude of support stresses, and the magnitude of prestresses of the load‐increasing yielding support pattern. Simulation results show that the superior sequence of supporting effect is load‐increasing yielding support, load‐shedding yielding support, and constant and nonyielding support under the same initial support stress. When the magnitude of support stress or the magnitude of prestress is larger with load‐increasing yielding support, the supporting effect is superior and the load‐increasing yielding support with a lower magnitude of support stress is superior to some other support patterns with higher magnitude of support stresses. The active support can improve the support effect compared with no prestress, and under the same final support stress, the support effect is superior when the roof stress releases more in the early supporting stage regardless of the prestress.

Computational simulations of wave propagation in microcrack-damaged media under prestress

Direct computational simulations of unidirectional wave propagation through uniaxially prestressed, microcrack-damaged media are conducted to study the interaction between the prestress and stress wave parameters. Tensile and compressive waves, tensile and compressive prestresses and various orientational distributions of microcrack damage are analyzed. The relationships among the input wave amplitude, wavelength and prestress magnitude and the output wave speed and wave attenuation are studied. The results show that wave speed and attenuation depend on the prestress and the wavelength in a complex way. In the cases of compressive waves traveling through tensile prestress and tensile waves passing through compressive prestress, the wave response depends on the ratio of the amplitude of the applied stress pulse to the magnitude of the prestress (defined as R). Specifically, the simulations show that the compressive wave speed through tensile prestressed media increases gradually with an increase in R, while the tensile wave speed in media under compressive prestress, decreases with increase in R, but the change is abrupt at a particular R value. In the cases of sufficiently small R, the wave speeds match the results of Su et al. (Eng Fract Mech 74:1436–1455, 2007) where the cracks are always open or always closed. However, above a certain wavelength (a cut-off wavelength), the wave speed is no longer a function of wavelength and, furthermore, this cut-off wavelength varies with R.

An approach to the dynamics and control of a planar tensegrity structure with application in locomotion systems

The use of mechanically compliant tensegrity structures in vibration-driven mobile robots is an attractive research topic, due to the principal possibility to adjust their dynamic properties reversibly during locomotion. In this paper vibration driven planar locomotion of mobile robots, based on a simple tensegrity structure, consisting of two rigid disconnected compressed members connected to a continuous net of four prestressed tensional members with pronounced elasticity, is discussed. The dynamic behaviour of the considered system is nonlinear, due to large vibration amplitudes and friction between robot and environment, and is mainly influenced by the magnitude of prestress. Therefore, the movement performance of the robot can be essentially influenced by the actuation parameters, e.g. by modifying the frequency or the magnitude of actuation the locomotion direction of the system varies. To study the system behaviour, the nonlinear equations of motion are derived and transient dynamic analyses are performed, including the consideration of chaotic system behaviour near to the primary and secondary eigenfrequencies. The dependency of the movement behaviour on the actuation parameters and on the prestress are discussed focused on single-actuated systems with minimal control effort.

Numerical Simulation of Granite on Pre-Stressed Machining by Discrete Element Method (DEM)

The bonded particle model (BPM) of granite for pre-stressed machining is build by using the discrete element method (DEM). This model can not only descript the intergranular fracture behavior but also the transgranular fracture behavior of the granite. The processes of crack propagation under different pre-stressed machining conditions are studied by means of DEM simulation. Damages and cracks of surface/subsurface are also observed. The simulation results show that, while the magnitude of pre-stress is controlled in a certatin range, the number of radial cracks reduce as the increasing of pre-stress magnitude, contray to the transverse cracks. It could be seen that maching damage is decreased and surface quality is improved by applying the pre-stressed machining method, and the discrete element method is an effective way to simulate the machining process of granite.

Research on the Reinforcement Mechanism of Stretched Rock Bolt and Analyzing of the Impact Parameters

The rock bolt has been widely used as an effective reinforcement in civil and mining engineering for a long time. However, the anchored mechanism of it is not well understood. This paper obtained the expression of the shear stress and axial force of stretched fully grouted rock bolt base on previous working, and detailed analysis the influence parameters of stress distribution. It is considered the anchored effect is influenced by some factors. Augmenting diameter of rock bolt, increasing the pre-stress magnitude and improving the strength of grout may all improve the anchored effect of rock bolt. As the rock character and the grout property are similar, the rock bolt anchored effect is optimal. There is a stress concentrated phenomena at the front of rock bolt. It is shown that the distribution of shear stress and axial force are not even distribution and exponentially attenuated along a fully grouted bolt.

AN EXAMINATION OF ABRASIVE WATERJET PEENING WITH ELASTIC PRE-STRESS AND THE EFFECTS OF BOUNDARY CONDITIONS

Abrasive Waterjet Peening (AWJP) has emerged as a potentially viable method of surface treatment for components requiring compressive residual stress and a rough surface texture. In the present investigation the residual stress distributions resulting from AWJP of Ti6Al4V with load and displacement control flexure pre-stress were compared. An experimental evaluation was conducted to quantify the variations in the residual stress characteristics (magnitude and depth) as a function of boundary conditions over a pre-stress ranging from 0 to 75% of the material's yield strength. In addition, a finite element model for indentation-based surface treatments was developed to investigate the mechanisms contributing to the observed trends in experimental results. Overall, AWJP of the Ti6Al4V resulted in a surface residual stress ranging from approximately 800 to 1600 MPa. Load control pre-stress resulted in a larger surface residual stress (up to 50% greater) than that achieved under displacement control treatments. Although the maximum surface residual stress was obtained at the largest applied pre-stress, the difference between load and displacement control treatments decreased with pre-stress magnitude. Boundary conditions had limited influence on the depth of residual stress achieved, but were important to the depth of plasticized zone beneath the treated surface.

Nonlinear pre-stress for cloaking from antiplane elastic waves

A theory is presented showing that cloaking of objects from antiplane elastic waves can be achieved by employing nonlinear elastic pre-stress in a neo-Hookean elastomeric material. This approach would appear to eliminate the requirement of metamaterials with inhomogeneous anisotropic shear moduli and density. Waves in the pre-stressed medium are bent around the cloaked (cavity) region by inducing inhomogeneous stress fields via pre-stress. The equation governing antiplane waves in the pre-stressed medium is equivalent to the antiplane equation in an unstressed medium with inhomogeneous and anisotropic shear modulus and isotropic scalar mass density. Note however that these properties are induced naturally by the pre-stress. As the magnitude of pre-stress can be altered at will, this enables objects of varying size and shape to be cloaked by placing them inside the fluid-filled deformed cavity region.