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.

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.

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.

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.

Tension-compression asymmetry and corresponding deformation mechanism in ZA21 magnesium bars with bimodal structure

We investigated the asymmetric tension-compression(T-C)behavior of ZA21 bars with bimodal and uniform structures through axial tension and compression tests.The results show that the yield strengths of bars having bimodal structure are 206.42 and 140.28 MPa under tension and compression,respectively,which are higher than those of bars having uniform structure with tensile and compressive yield strength of 183.71 and 102.86 MPa,respectively.Prismatic slip and extension twinning under tension and basal slip and extension twinning under compression dominate the yield behavior and induce the T-C asymmetry.However,due to the basal slip activated in fine grains under tension and the inhibition of extension twinning by fine grains under compression,the bimodal structure possesses a lower T-C asymmetry(0.68)compared to the uniform structure(0.56).Multiple extension twins occur during deformation,and the selection of twin variants depends on the Schmid factor of the six variants activated by parent grains.Furthermore,the strengthening effect of the bimodal structure depends on the grain size and the ratio of coarse and fine grains.

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.

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.

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.

Strengthening reinforced concrete beams using prestressed glass fiber-reinforced polymer-Part I: Experimental study

This work is aimed at studying the strengthening of reinforced concrete (R. C.) beams using prestressed glass fi- ber-reinforced polymer (PGFRP). Carbon fiber-reinforced polymer (CFRP) has recently become popular for use as repair or rehabilitation material for deteriorated R. C. structures, but because CFRP material is very stiff, the difference in CFRP sheet and concrete material properties is not favorable for transferring the prestress from CFRP sheets to R. C. members. Glass fi- ber-reinforced polymer (GFRP) sheets with Modulus of Elasticity quite close to that of concrete was chosen in this study. The load-carrying capacities (ultimate loads) and the deflections of strengthened R. C. beams using GFRP and PGFRP sheets were tested and compared. T- and ⊥-shaped beams were used as the under-strengthened and over-strengthened beams. The GFRP sheets were prestressed to one-half their tensile capacities before being bonded to the T- and ⊥-shaped R. C. beams. The prestressed tension in the PGFRP sheets caused cambers in the R. C. beams without cracks on the tensile faces. The PGFRP sheets also enhanced the load-carrying capacity. The test results indicated that T-shaped beams with GFRP sheets increased in load-carrying capacity by 55% while the same beams with PGFRP sheets could increase load-carrying capacity by 100%. The ⊥-shaped beams with GFRP sheets could increase load-carrying capacity by 97% while the same beams with PGFRP sheets could increase the loading-carrying capacity by 117%. Under the same external loads, beams with GFRP sheets underwent larger deflections than beams with PGFRP sheets. While GFRP sheets strengthen R. C. beams, PGFRP sheets decrease the beams’ ductility, especially for the over-strengthened beams (⊥-shaped beams).