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.

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.

Life-Cycle Bearing Capacity for Pre-Stressed T-beams Based on Full-Scale Destructive Test

To investigate the evolution of load-bearing characteristics of pre-stressed beams throughout their service life and to provide a basis for accurately assessing the actual working state of damaged pre-stressed concrete T-beams,destructive tests were conducted on full-scale pre-stressed concrete beams.Based on the measurement and ana-lysis of beam deflection,strain,and crack development under various loading levels during the research tests,combined with the verification coefficient indicators specified in the codes,the verification coefficients of bridges at different stages of damage can be examined.The results indicate that the T-beams experience complete,incom-plete linear,and non-linear stages during the destructive test process.In the complete linear elastic stage,both the deflection and bottom strain verification coefficients comply with the specifications,indicating a good structural load-bearing capacity no longer adheres to the code’s requirements.In the non-linear stage,both coefficients exhi-bit a sharp increase,resulting in a further decrease in the structure’s load-bearing capacity.According to the pro-visions of the current code,the beam can be in the incomplete linear stage when both values fall within the code’s specified range.The strain verification coefficient sourced from the compression zone at the bottom of theflange is not recommended for assessing the bridge’s load-bearing capacity.

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.

Effectiveness of external prestressing in enhancing the non-ductile hanger failure mechanism in reinforced concrete inverted T-beams

Recently,inverted T-beams have been used in reinforced concrete(RC)bridges to support transverse precast stringers.Inverted T-beams,contrary to practice with conventional beams,are loaded on the flanges upper surface.This loading configuration causes hanger failure due to the generation of vertical tensile stresses near the bottom of the web.The key purpose of this study is to investigate the efficiency of vertical external prestressing stainless-steel bars in mitigating non-ductile hanger failure in reinforced concrete inverted T-beams.An experimental study on six inverted-T beams,including two un-strengthened specimens,was carried out.The study showed that the value of the prestressing level had a considerable impact on the performance of hanger mechanism in relation to crack pattern,ultimate loads,cracking behavior,load-deflection,strains,and ductility.The experimental results indicated that the suggested method for strengthening inverted T-beams had efficacy in reducing the seriousness of the non-ductile hanger failure and resulted in a strength increase of up to 53% when compared to that of the un-strengthened specimen.Additionally,two analytical models for estimating the hanger capacity and the average crack width of the strengthened RC inverted T-beams were proposed.The models that were proposed exhibited a high degree of agreement with the experimental results.

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.

Stiffness Degradation Characteristics Destructive Testing and Finite-Element Analysis of Prestressed Concrete T-Beam

The failure behavior of the precast prestressed concrete T girder was investigated by destructive test and finite-element analysis,and the mid-span deflection,girder stiffness and the variation of the cross section strain in the loading process were obtained,and the mechanical properties,mechanical behavior,elastic and plastic behavior and ultimate bearing capacity of T girder with large span were revealed.Furthermore,the relationship between the beam stiffness degradation,the neutral axis in cross-section,steel yielding and concrete cracking are investigated and analyzed.A method was proposed to predict the residual bearing capacity of a bridge based on the variation of the position of the cross section strain distribution and the section neutral axis,which provided a theoretical basis for predicting the stiffness detection and carrying capacity assessment of prestressed concrete beam.

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.

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.

预应力在我国大跨度结构中的应用研究综述

为了提高大跨度结构的正常使用性能,通常在混凝土结构中施加预应力.结果表明,预应力混凝土结构具有更好的使用性、耐久性和大跨度适用性,其中预应力混凝土空心板结构在不显著降低承载力和刚度的前提下明显减小结构自重,预应力型钢混凝土梁(板)结构采用较小的截面尺寸即可满足承载力和刚度的需求.开发城市地下空间是解决城市用地紧张的有效手段,我国地下大跨空间常用的结构形式主要包括密排框架(肋梁)结构、折板或拱形结构、变截面(加腋)板结构、预应力混凝土结构、型钢-混凝土组合结构和Y形柱结构6种形式,相比之下,跨度较大时宜采用预应力结构.

考虑锚杆预应力作用下隧道围岩力学分析及参数设计

隧道工程中锚杆设计多依靠经验法和类比法,为研究预应力锚杆支护体系下围岩的力学效应,建立预应力锚杆与围岩力学耦合模型,考虑围岩开挖损伤效应,通过弹塑性力学理论推导出隧道开挖后围岩应力分布及径向位移解析表达式,采用有限差分软件FLAC3D进行算例验证并分析预应力锚杆参数对围岩状态的影响。研究结果表明:理论解析和数值模拟中最大切向应力和围岩塑性区半径分别为4.77 MPa、15 m和4.49 MPa、15.86 m,理论解析与数值模拟所计算隧道围岩应力分布、位移基本一致,在Ⅳ、Ⅴ级围岩地层中验证了理论解析解的合理性;随着预紧力增大,处于塑性区的围岩径向位移及塑性区半径逐渐减小,弹性区基本不受影响;当锚杆自由段长度位于塑性区时,随着锚杆长度增加,围岩塑性区径向位移及塑性区半径逐渐减小。在实际工程中应尽量增大锚杆预紧力,锚杆长度增加对围岩位移以及塑性区的发展控制效果有限,应控制锚杆自由段长度在塑性区内。

预应力UHPC槽形节段与整体式混凝土板组合梁受剪性能

将预制的UHPC槽形节段通过干缝连接和预应力张拉形成槽形梁,再与整体现浇的混凝土板组合成的组合梁,称为预应力UHPC槽形节段与整体式混凝土板组合梁(PUCS-MCS组合梁)。它是一种能充分发挥不同材料的性能、施工方便且整体性能好的新型桥梁结构。为探究其抗剪性能,开展了9根模型梁的试验。分析了接缝数、接缝处剪力键数、剪跨比、UHPC钢纤维体积率、配箍率和纵筋率等参数对试件变形、破坏模式、抗剪承载力的影响;基于试验研究结果,提出了PUCS-MCS组合梁抗剪承载力计算方法。结果表明:PUCS-MCS组合梁均为剪压破坏,所有梁在开裂前的荷载-挠度曲线差异不大,在开裂后刚度不断下降;PUCS-MCS组合梁的抗剪承载力随接缝处剪力键数、UHPC钢纤维掺量、配箍率和纵筋率的增大而增大,随干接缝数量增加和剪跨比的增大而减小,其中影响最显著的是干接缝和剪力键,影响最小的是钢纤维掺量和配箍率,因此PUCS-MCS组合梁可不配箍筋,并可采用较低钢纤维掺量的UHPC。

新型预应力混凝土钢管桁架叠合梁抗剪性能有限元分析

为解决施工现场中现有装配式混凝土叠合梁、梁柱结点钢筋相互影响的问题,设计一种新型预应力混凝土钢管桁架叠合梁。为进一步研究该叠合梁的抗剪性能,共设计6个叠合梁、3个整浇梁进行ABAQUS有限元模拟,分析其破坏特征机理、荷载–跨中挠度曲线等,研究试件剪跨比、底板厚度参数对抗剪性能的影响,以及新型预应力混凝土钢管桁架叠合梁与整浇梁的抗剪性能对比。数值模拟分析结果显示,新型叠合梁与整浇梁均为剪切破坏,在底板厚度相同的情况下,随着剪跨比的增大,叠合梁的极限承载力略微降低。此外,预制高度增加会导致叠合梁的极限承载力减小。叠合梁表现出与整浇梁相似的受剪性能,随着剪跨比增加,叠合梁相对于整浇梁表现出更好的抗剪性能。综合而言,新型预应力混凝土钢管桁架叠合梁具有良好的抗剪性能。

基于缩尺模型的高铁桥梁预应力损失试验研究

【目的】为更好的评估在役预应力混凝土桥梁结构预应力损失状况。【方法】选用国内高铁中应用最广的32 m预应力混凝土箱梁作为研究对象,按照1:16的缩尺比例将箱梁转化为T形截面制作了26根C50混凝土试验模型梁。通过对试验梁预应力钢绞线应变、伸长量的瞬时和长期监测得到预应力损失的实际值,并将此实际值与目前国内外常用预应力损失规范计算所得值进行对比分析。【结果】预应力损失主要发生在前期即瞬时损失,约占总损失的70%;84.6%的试验梁锚固损失占瞬时损失总和的70%以上,最高达80.57%;试验梁的长期损失在锚固后的前10 d内变化较快,后期逐渐趋于稳定;将5种规范的计算结果与试验实测值进行对比,对于长期损失,数据显示实测数据与《铁路桥涵设计规范》(TB 10002—2017)计算结果最为吻合。【结论】研究结果可为实际工程中预应力梁的预应力损失计算提供参考。