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.

Design of Large-Scale Prestressing Bucket Foundation for Offshore Wind Turbines

The key in the force transmission between the tower and the foundation for offshore wind turbines is to transfer the large moment and horizontal loads. The finite element model of a large-scale prestressing bucket founda- tion for offshore wind turbines is set up and the structural characteristics of the arc transition structure of the founda- tion are analyzed for 40-60 channels(20-30 rows) arranged with prestressing steel strand under the same ultimate load and boundary conditions. The mechanical characteristics of the key parts of the foundation structures are illus- trated by the peak of the principal tensile stress, the peak of the principal compressive stress and the distribution areas where the principal tensile stress is larger than 2.00 MPa. It can be concluded that the maximum principal tensile stress of the arc transition decreases with the increasing number of channels, and the amplitude does not change signifi- cantly; the maximum principal compressive stress increases with the increasing number of channels and the amplitude changes significantly; however, for the distribution areas where the principal tensile stress is larger than 2.00 MPa, with different channel numbers, the phenomenon is not obvious. Furthermore, the principal tensile stress at the top of the foundation beams fluctuantly increases with the increasing number of channels and for the top cover of the bucket, the principal tensile stress decreases with the increasing number of channels.

Effects of Prestressing of the Ring Gear in Interference Fit on Flexural Fatigue Strength of Tooth Root

When the gearbox body interference is connected to the ring gear, prestressing occurs in the ring gear, which has a significant impact on the strength and life of the gear. Research on the prestressing of the inner ring gear is in the preliminary stage, and the distribution rule of the prestressing and the influence of each parameter on the interference prestressing have not been derived. In this paper, based on the method of calculating the prestressing of the thick cylinder in interference fit, the ring gear is found to be equivalent to a thick cylinder, and the distribution rule of prestressing of the ring gear in the interference fit is inferred. Then, by modeling and analyzing the gearbox body and ring gear in the interference fit using ABAQUS, the distribution rule of prestressing the ring gear in the interference fit is obtained through a numerical simulation. Finally, the prestressing of the ring gear in the interference fit is measured using X-ray di raction, and the distribution rule of prestressing of the ring gear in the interference fit is obtained through analysis. Compared with the distribution rule of prestressing in theory, numerical simulation, and experiment, the theoretical distribution rule of prestressing is amended through a statistical method, and a more accurate formula of prestressing is obtained. Through the calculation of the stress and bending moment in the dangerous section of the ring gear through prestressing, the formula for checking the tooth root flexural fatigue strength in the interference fit prestressing is inferred. This research proposes a tooth root bending strength conditional formula for the inner ring gear of the interference fit, which serves as a guide for the design and production of the actual interference joint inner ring gear.

Multi-Quality Properties Capability Analysis for Prestressing Strand of Prestressed Concrete

Prestressed concrete structures are main conformati on for the construction of high way bridges. The quality of prestressed concrete s tructures is mainly affected by the tensile strength of prestressing strand. In order to attain the purpose of economic design and long life span of prestressin g strand, the less relaxation property of strand type is suitable for constructi on and usage. Thus, the research and development of prestressing strand is requi red to reach the goals of high tensile strength and low relaxation. To ensure th e required quality of prestressing strand, the strand pull test and long period relaxation test are two important items for the quality assurance. There are thr ee specific items of the tensile strength test are belong to larger-the-better quality type. The quality type of smaller-the-better is for the long period r elaxation test. However, many existing methods are able to measure process capab ility for product with single quality characteristic and cannot be applied to mo st products with multiple properties. Thus, the indices of C pu and C pl, for larger-the-better and smaller-the-better quality type respec tively proposed by Kane, are quoted and combined to propose a new index to evalu ate the quality of multiple characteristics of prestressing strand in this paper . Then, the principle of statistics is used to derive the one-to-one mathemati cal relationship of this new index and ratio of tallied. Finally, the procedure and criteria to evaluate the quality of prestressing strand is proposed. This in tegrated multi-quality property capability analysis model can be used to evalua te the multi-process capabilities and provide continuous improvement on manufac turing process of prestressing strand.

Influence of Fatigue Loading on the Residual Stress Distribution in Prestressing Steel Wires

This paper analyzes the influence of fatigue loading on the residual stress profile in high strength steel wires. To this end, different sinusoidal loads with diverse values of maximum loading level and number of cycles were simulated on wires in which several residual stress profiles had been previously introduced, some of them with a tensile state and others with a compressive state. An analysis was made of the evolution with time of such residual stress laws by comparing them at key instants of loading, that is, at initial instant, at maximum load, at minimum load and at final instant. Numerical results show only a minor influence of fatigue loading on the residual stress profile.

Theoretical Analysis on Deflection and Bearing Capacity of Prestressed Bamboo-Steel Composite Beams

A theoretical analysis of upward deflection and midspan deflection of prestressed bamboo-steel composite beams is presented in this study.The deflection analysis considers the influences of interface slippage and shear deformation.Furthermore,the calculation model for flexural capacity is proposed considering the two stages of loading.The theoretical results are verified with 8 specimens considering different prestressed load levels,load schemes,and prestress schemes.The results indicate that the proposed theoretical analysis provides a feasible prediction of the deflection and bearing capacity of bamboo-steel composite beams.For deflection analysis,the method considering the slippage and shear deformation provides better accuracy.The theoretical method for bearing capacity matches well with the test results,and the relative errors in the serviceability limit state and ultimate limit state are 4.95%and 5.85%,respectively,which meet the accuracy requirements of the engineered application.

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.

Exploring the feasibility of prestressed anchor cables as an alternative to temporary support in the excavation of super-large-span tunnel

Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages.However,these internal supports generally impose spatial constraints,limiting the use of large-scale excavation equipment and reducing construction efficiency.To address this constraint,this study adopts the“Shed-frame”principle to explore the feasibility of an innovative support system,which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions.To evaluate its effectiveness,a field case involving the excavation of a 24-m span tunnel in soft rock is presented,and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system.The results revealed that prestressed anchor cables integrated the initial support with the shed,creating an effective“shed-frame”system,which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds.Moreover,the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly.In summary,the proposed support system balances construction efficiency and safety.These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.

Investigation of the Effect of the Force Arm on the Bending Capability of Prestressed Glulam Beam

Prestress enables the Glulam beam could make full use of the compression strength,and then increase the span,but it still could not reduce all drawbacks,such as cross-section weakening and small force arm.To avoid slotting and ensure suitable tension and compression couple,one kind of novel anchor has been proposed,which could meet the bearing capacity requirement.And then the bending test of prestressed Glulam beams with a geometric scale ratio of 1:2 was simulated,to investigate the effect of the force arm on bending capacities,failure modes,and deformation performance.Results show that increasing the force arm could improve the ultimate bending per-formance of the beam significantly,and the anchor arm length has a certain effect on the performance,but it is not obvious.Finally,based on Finite element method analysis,the practice design suggestions have been offered.

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.

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Durability design of prestressed concrete structures

Based on the durability characteristics of prestressed concrete structures,the durability limit states of carbonation and chloride ion attack are defined, respectively.Durability predicting models on the basis of reliability mathematics and stochastic processes areconstructed, and the pure theoretical formulae of failure probability of prestressed concretestructures are analyzed. In addition, a simple durability design method for carbonation ofstructures is put forward. According to the analysis, the durability of prestressed concretestructures is superior to that of traditional structures. The research also indicates that theconcrete cover prescribed in the current code (GB 50010-2002) is not adequate. The rational coverthickness should notbe less than 35 or 45 mm according to carbonation or chloride ion attack,respectively.

Performance of grouts for post-tensioned prestressed structures

New high performance grouts with high volume stability and good fluidity were prepared with Portland cement and a multifunctional admixture (MFA). The theological characteristics and mechanical performance of the grouts were investigated. The addition of MFA effectively improves the pseudo-plasticity of the grout. The Ma cone flow time decreases obviously, and the bleeding rate tends to be zero. The deformation behaviors of fresh mixture and hardened grout are systematically studied. Mercury injection method (MIP), scanning electron microscopy (SEM) and X-ray diffractory analysis experiments are used to analyze the microstructure evolution of the grouts, which manifests that the co-action of the early bubble reaction and the latter ettringite crystallization ensure the volume stability throughout the whole hydration process and result in refined pore structure of the grout.

Study on the Design Criteria for Prestressed Concrete Pavements

With a concrete pavement slab prestressed, its load carrying capacity can be significantly increased; thus a thinner slab may be used for the same loading. Prestressing modify the structural behavior of the pavement slab and there is a greater resistance to impact, vibration and overloading. This paper discusses the major design considerations necessary in the successful construction of prestressed concrete pavements and presents a design procedure developed to predict the compressive stress due to prestressing in the pavements at early stage, during service and after cracking. Variation in the approach for repetitive and nonrepetitive loads is clearly distinguished. Check on the recovery after cracking for overloading in prestressed pavements is also needed. Finally, a design example is illustrated the application of the approach developed.

预应力拱形管桁架中索的位置对结构的影响分析

在大跨度空间结构中,预应力管桁架是一种常用的结构形式,由于预应力索的引入,能够最大限度优化结构内力,增大结构竖向刚度,减小支座水平推力。而索的位置是否合理,直接影响到结构整体受力的合理性以及用钢量的大小。以重庆某预应力管桁架料场大棚为例,通过在有限范围内调整索的位置,选取多个结构控制指标进行对比,研究计算结果对结构整体的影响,从而确定较为合理的索布置。分析结果表明,以反弯点处为基准,索的位置向上调整,则支座反力和挠度增大,最大杆内力也会相应变大,实际工程中,索的位置建议根据结构的外形,通过单线模型先确定反弯点高度,结合工艺的要求,在此位置上下1至2个节间范围内为宜。

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.

Influence of confining prestress on the transition from interface defeat topenetration in ceramic targets

Replica scaled impact experiments with unconfined ceramic targets have shown that the transition velocity,i.e.,the impact velocity at which interface defeat ceases and ceramic penetration occurs,decreased as the length scale increased.A possible explanation of how this scale effect is related to the formation of a cone crack in the ceramic has been presented by the authors in an earlier paper.Here,the influence of confinement and prestress on cone cracking and transition velocity is investigated.The hypothesis is that prestress will suppress the formation and growth of the cone crack by lowering the driving stress.A set of impact experiments has been performed in which the transition velocity for four different levels of prestress has been determined.The transition velocities as a function of the level of confining prestress is compared to an analytical model for the influence of prestress on the formation and extension of the cone crack in the ceramic material.Both experiments and model indicate that prestress has a strong influence on the transition from interface defeat to penetration,although the model underestimates the influence of prestress.

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 .