Vibration attenuation performance of wind turbine tower using a prestressed tuned mass damper under seismic excitation

With the rapid development of large megawatt wind turbines,the operation environment of wind turbine towers(WTTs)has become increasingly complex.In particular,seismic excitation can create a resonance response and cause excessive vibration of the WTT.To investigate the vibration attenuation performance of the WTT under seismic excitations,a novel passive vibration control device,called a prestressed tuned mass damper(PS-TMD),is presented in this study.First,a mathematical model is established based on structural dynamics under seismic excitation.Then,the mathematical analytical expression of the dynamic coefficient is deduced,and the parameter design method is obtained by system tuning optimization.Next,based on a theoretical analysis and parameter design,the numerical results showed that the PS-TMD was able to effectively mitigate the resonance under the harmonic basal acceleration.Finally,the time-history analysis method is used to verify the effectiveness of the traditional pendulum tuned mass damper(PTMD)and the novel PS-TMD device,and the results indicate that the vibration attenuation performance of the PS-TMD is better than the PTMD.In addition,the PS-TMD avoids the nonlinear effect due to the large oscillation angle,and has the potential to dissipate hysteretic energy under seismic excitation.

Discussion on Detection and Evaluation of Simply Supported Prestressed Concrete Small Box Girder Bridge After a Fire

The article takes a simply supported prestressed concrete small box girder bridge project as an example for inspection and evaluation after a fire incident.This includes appearance detection,concrete color hardness detection,concrete strength detection,concrete surface damage layer detection,reinforcement protective layer detection,and concrete carbonation detection.It is hoped that this analysis can be used as a reference for the detection and evaluation of future bridge projects with fire incidents to smoothen its subsequent repair and maintenance.

Study on damage-stress loss coupling model of rock and prestressed anchor cable in dry-wet environment

The loss of anchoring force is one of the problems to be solved urgently.The anchorage loss is a key factor causing the failure of anchoring engineering,so it is crucial to study the time-dependent variation of anchoring force.Alternating dry and wet(D-W)conditions have a significant effect on deformation of rock.The anchoring system is composed of anchoring components and rock mass,and thus rock deformation has a significant impact on the loss of anchoring force.Quantifying rock deformation under the effects of D-W cycles is a prerequisite to understanding the factors that influence loss of anchoring force in anchor bolts.In this study,we designed an anchoring device that enabled real-time monitoring of the variation in strain during D-W periods and rock testing.Nuclear magnetic resonance(NMR)measurements showed that under D-W conditions,the increment in porosity was smaller for prestressed rock than unstressed rock.The trends of prestress loss and strain variation are consistent,which can be divided into three characteristic intervals:rapid attenuation stage,slow attenuation stage and relatively stable stage.At the same stress level,the rate of stress loss and strain for the soaking specimen was the highest,while that of the dried specimen was the lowest.In the same D-W cycling conditions,the greater the prestress,the smaller the strain loss rate of the rock,especially under soaking conditions.The characteristics of pore structure and physical mechanical parameters indicated that prestress could effectively suppress damage caused by erosion related to D-W cycles.The study reveals the fluctuation behavior of rock strain and prestress loss under D-W conditions,providing a reference for effectively controlling anchoring loss and ideas for inventing new anchoring components.

Design on the Prestressed Concrete Frame Beam-column

A bidirectional ribbed concrete beam slab structure was widly adopted for the upper space of industrial buildings.To maintain ample space and minimize the presence of conventional columns,a bidirectional prestressed concrete beam is often employed.The intersection node of the prestressed concrete frame beam column was characterized by a high density of steel reinforcement,significant structural loads,and complex construction requirements.To ensure the quality,safety,and progress of prestressed frame beamcolumn intersection nodes during construction,this article proposed a new technology for constructing such nodes,which includes setting the tensioning and haunching ends of nodes at different positions,using ABAQUS finite element software to optimize the design of cross-sectional dimensions,conducting stress analysis simulations.

Laminated Solid Timber Slab with Transverse Prestressing Using the Strategy of Interleaved Vertical Displacement of Lamellae

This article presents a study on the structural behavior of transversely prestressed laminated timber slabs,focusing on an innovative approach:vertically misaligned lamellae.This misalignment,achieved by sliding vertically the wooden lamellae rather than aligning them,enhances the slab’s cross-section moment of inertia,thereby improving load-bearing capacity and stiffness.Testing involved two groups of structural size specimens:one with vertically aligned lamellae(control group)and the other with misaligned lamellae(study group).Results showed the study group exhibited 42%superior stiffness and 10%less load capacity compared to the control.Failures typically occurred individually in the lamellae,particularly in those with defects or lower modulus of elasticity,concentrated in the middle third of the slabs’free span where tensile stresses peak.Despite a higher number of failed lamellae,the study group demonstrated promising performance.Analysis of prestressing bar indicated no damage at all in the thread,suggesting potential for reducing bar diameter.These findings offer crucial insights into applying these slabs in timber construction as well as to any kind of construction.

Experimental study on hysteretic behavior of prestressed truss concrete composite beams

This paper describes an experimental study of the hysteretic behavior of prestressed truss concrete composite beams （PTCCBs） under cyclic loading. Five beam models were designed and tested, in which the testing parameters include the global reinforcement index β0, the prestress level 2 and the ratio of stirrup ρsv in the potential plastic hinge zones. Based on the test results, the failure mode and hysteretic behavior of the tested models are obtained. In addition, the P-△ and sectional M-φ hysteretic models for the PTCCBs at the midspan are established. The P-△ hysteretic model shows good agreement with the test results.

Unified analogue method of effective prestress for post-prestressed tendon

In order to obtain the present effective prestress and its longitudinal distribution of prestressed tendon during the process of inspection and evaluation, a unified analogue method was put forward. Based on the theory for calculating instantaneous prestress loss of the tendons with complicated geometry, a universal numerical model was established. Therefore, the distribution of effective prestress could be simulated after recognizing the nominal coefficients of prestress loss with the obtained stress data of objective steel tendon. The numerical simulation results of a full-length tendon of a three-span continuous beam bridge show that the relative errors between the calculated value and the value in the code are within 5%, which meets the requirement for engineering application.

Temperature and Stress Analysis of An Experimental Model of Prestressed Lightweight Concrete Platform

This paper presents an experimental study of a prestressed lightweight concrete platform model with a tank and for five steel-columns. This platform can be used not only for extraction but also for storage of oil and is suitable for the Bohai Sea and other shallow seas of China. The platform is subjected to temperature. load, or both. The corresponding temperature distribution. strains, cracks. and vulnerable parts of the platform are analyzed respectively. By use of the finite element method and empirical formulas, the temperature field of the model is analyzed. The results agree with the experimental results, thereby verifying! the reliability of these two calculating methods. The paper provides an experimental basis for the des sign of the bearing capacity and normal service state of prestressed concrete platforms.

Dynamic finite element model updating of prestressed concrete continuous box-girder bridge

The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .

Theoretical analysis of natural frequency of externally prestressed concrete beam based on rigidity correction

A dynamic test on externally prestressed simply supported concrete beams separately with three typical types of tendon distributions was conducted. The results show that the natural frequencies of the beams increase with the increase in the prestressing force at the tensioning stage, and the natural frequencies decrease after the cracks occur in the beams. Following the calculation formula of natural frequency of externally prestressed beam, which was reported in a literature, the natural frequencies of the experimental beams are calculated, and big errors are found between the test results and the calculated ones of natural frequency values. As a result, this paper has tried to adopt two methods to correct the rigidity parameter of the concrete beam in the formula for natural frequency calculation, and to use the corrected formula to calculate the frequencies of the experimental beams. The calculation results indicate a good consistency with the experimental ones, which verifies the feasibility of the corrected formula.

Prestressed tensioning method and its application to testing anchor stress of anchor cables for side-slope stabilization

The anchor stress extent of a prestress anchor cable project has a direct relation with the project safety and performance. Prestressed tensioning method is a kind of nondestructive testing method, by which a reverse stretching load is applied on the external exposure section of anchor cable under construction or in service, and then the elongation variation of stress bars is measured to determine the anchor stress. We elaborated the theory and testing mechanism of prestressed tensioning method, and systematically studied key issues during the prestressed tensioning process of anchor cable by using physical model test, including the composition of tension stress-elongation curve, the variation of anchor stress, the compensation of locked anchor stress, and the judgment of anchor stress, and verified the theory feasibility of prestressed tensioning method. A case study on slope anchor cable of one highway project was conducted to further discuss on the test method, operation procedures and judgment of prestressed tensioning method on obtaining anchor stress, and then the test data of three situations were analyzed. The result provides a theoretical basis and technical base for the application of prestressed tensioning method to the evaluation of construction quality and operation conditions of anchor cable project.

Influence of key factors on deflection of bonded prestressed concrete simply supported slabs subjected to fire

In order to validate the accuracy of nonlinear fire simulation programs,comparison analysis is carried out between simulation and experiment induced from small-scale specimens,and then fire resistance of large-scale prestressed concrete slabs is further investigated through parameter expansion.The influences on fire resistance ratings controlled by deflection are explored and discussed,including effective span,concrete cover thickness,load level,prestress degree,effective prestress,composite reinforcement index and other factors.The calculated results indicate that fire resistance ratings of large-scale bonded prestressed concrete simply supported slabs are bigger than those of small-scale ones.Finally,the calculation formulas of fire resistance ratings controlled by deflection are established,which rationally consider the influence of effective span,concrete cover thickness,load level,composite reinforcement index and so on key factors.

Fatigue Damage Modeling for Partially Prestressed Concrete Beams under Repeated Loadings with Variable Amplitude

A full-range nonlinear analysis method for fatigue damage in prestressed concrete beams is presented. New damage accumulation models are proposed to describe the fatigue damage evolution in concrete and reinforcement respectively. Based on the stress analysis for cross section, the stress redistrbution in the fatigue damage process, due to the different damage mechanisms of concrete and reinforcement, is considered. The nonlinear damage analysis is achieved by means of piecewise linearity, and it is applicable on the condition of repeated loadings with variable amplitude. Fatigue damage modeling of a beam is implemented to illustrate that the proposed method can preferably fit the experimental results.

FLEXURAL CAPACITY OF RC BEAM STRENGTHENED WITH PRESTRESSED C/AFRP SHEETS

A method for strengthening concrete structures by prestressed intraply hybrid C/AFRP sheets(composed of aramid fiber and carbon fiber)is proposed,aiming at overcoming shortages of some current strengthening methods.The bending capacity of beams strengthened by prestressed intraply hybrid C/AFRP sheets is analysed.The result shows that the bending resistance,the extending performance and the economical efficiency of intraply hybrid fiber sheets are better than those of interlaminar hybrid fiber sheets and single-fiber sheets.Moreover,prestressed intraply hybrid C/AFRP sheets can improve the performance of the strengthened beam,effectively inhibit the expansion of the cracks,and reduce distortion and risk of early failure.

Model test of the stability degradation of a prestressed anchored rock slope system in a corrosive environment

The long-term stability of a prestressed anchored slope might be influenced by the durability of the anchorage structure.To understand long-term stability of anchored rock slopes,the research presented herein evaluated the performance evolution of a prestressed anchored bedding slope system in a corrosive environment by model test.The corrosion process in a prestressed anchor bar was monitored in terms of its open-circuit potential(OCP),corrosion current density(CCD),and electrochemical impedance spectroscopy(EIS).The stability of the prestressed anchored slope was evaluated by monitoring changes in anchorage force and displacements.The experimental results show that prestress and oxygen could reduce the corrosion resistance of the anchor bar,and anchor bars in a chloride-rich environment are very susceptible to corrosion.Prestressed tendons in a corrosive environment suffer a loss of anchorage force,the prestress decreases rapidly after locking,and the rate thereof decreases until stabilising;in the later stage,corrosion leads to the reduction of the cross-sectional area of the steel bar which may cause the reduction in anchorage force again.Anchorage force controls the deformation and stability of the anchored slope,the prestress loss caused by later corrosion may lead to an increased rate of displacement and stability degradation of the prestressed anchored rock slope.

Reliability analysis of prestressed anchors in rock slopes of open-pit mines

Prestressed anchor cables are widely used for slope reinforcement,but the loss of prestress makes it difficult to guarantee the reinforcement effect.Anchor cable prestress degradation was considered as a stochastic process,and the probability density function of this process was established using gamma theory and impact theory respectively.Combined with the failure threshold,the probability density was integrated to find the time-dependent reliability of the anchor cable.Based on the monitoring data of the prestress degradation of the anchor cable,parameters in the probability density function were solved by the maximum likelihood method,and the time-varying reliability and service life of the anchor cable were obtained analytically.The applicability of two degradation theories,gamma stochastic process and impact theory,was compared.The results showed that the probability density curves of both degradation models were normally distributed and the error of reliability results did not exceed 0.06.The life prediction results of the gamma stochastic process were closer to the actual life of 400 h than the 500 h of the impact theory,and the probability curves of the anchor cable life also indicated that the impact theory overestimated the service life probability of the anchor cable.Taking the anchor cable reinforcement within the slope of the Dagushan open-pit mine as an example,and the results verify the feasibility of using gamma theory to predict the degradation of anchor cables and provides theoretical support for prevention of the degradation of anchor cables in the slope of an open-pit mine under the action of external forces.

Experimental Behavior of Partially Prestressed High Strength Concrete Beams

In the last few decades, prestressed concrete has been rapidly used in bridge engineering due to the enormous development in the construction techniques and the increasing need for long span bridges. High strength concrete has been also more widely spread than the past. It currently becomes more desirable as it has better mechanical properties and durability performance. Major defect of fully prestressed concrete is its low ductility;it may produce less alarming signs than ordinary reinforced concrete via smaller deflection and limited cracking. Therefore, partially prestressing is considered an intermediate design between the two extremes. So, combining high strength concrete with partial prestressing will result in a considerable development in the use of prestressed concrete structures regarding the economical and durability view points. This study presents the results of seven partially prestressed high strength concrete beams in flexure. The tested beams are used to investigate the influence of concrete compressive strength, prestressing steel ratio and flange width on the behavior of partially prestressed beams. The experimentally observed behaviors of all beams were presented in terms of the cracking load, ultimate load, deflection, cracking behavior and failure modes.

Structural Behavior of Continuous Prestressed Steel Fiber Reinforced High Strength Concrete Beam

The flexural behaviors of continuous fully and partially prestressed steel fiber reinforced high strength concrete beams are studied by experiment and nonlinear finite element analysis. Three levels of partial prestress ratio （PPR） are considered, and three pairs of two-span continuous beams with box sections varying in size are designed. The major parameters involved in the study include the PPR and the fiber location. It is concluded that the prestressed high strength concrete beam exhibits satisfactory ductility; the influences of steel fiber on the crack behaviors for partially prestressed beams are not as obvious as those for fully prestressed ones; steel fibers can improve the structural stiffness after cracking for fully prestressed high strength concrete beams; the moment redistribution from mid-span to intermediate support in the first stage should be mainly considered in practical design.

Aseismic safety analysis of a prestressed concrete containment vessel for CPR1000 nuclear power plant

Abstract： The containment vessel of a nuclear power plant is the last barrier to prevent nuclear reactor radiation. Aseismic safety analysis is the key to appropriate containment vessel design. A prestressed concrete containment vessel （PCCV） model with a semi-infinite elastic foundation and practical arrangement of tendons has been established to analyze the aseismic ability of the CPR1000 PCCV structure under seismic loads and internal pressure. A method to model the prestressing tendon and its interaction with concrete was proposed and the axial force of the prestressing tendons showed that the simulation was reasonable and accurate. The numerical results show that for the concrete structure, the location of the cylinder wall bottom around the equipment hatch and near the ring beam are critical locations with large principal stress. The concrete cracks occurred at the bottom of the PCCV cylinder wall under the peak earthquake motion of 0.50 g, however the PCCV was still basically in an elastic state. Furthermore, the concrete cracks occurred around the equipment hatch under the design internal pressure of 0.4MPa, but the steel liner was still in the elastic stage and its leak-proof function soundness was verified. The results provide the basis for analysis and design of containment vessels.

Experimental and analytical studies on the vibration serviceability of long-span prestressed concrete floor

An extensive experimental and theoretical research study was undertaken to study the vibration serviceability of a long-span prestressed concrete floor system to be used in the lounge of a major airport.Specifically,jumping impact tests were carried out to obtain the floor’s modal parameters,followed by an analysis of the distribution of peak accelerations.Running tests were also performed to capture the acceleration responses.The prestressed concrete floor was found to have a low fundamental natural frequency（≈8.86 Hz）corresponding to the average modal damping ratio of≈2.17%.A coefficients plate with simply-supported edges.The calculated analytical results（natural frequencies and root-mean-square acceleration）agree well with the experimental ones.The analytical approach is thus validated.