Prestressed Concrete Beams Research Articles

해상 프리캐스트 콘크리트 부유체 모듈 가접합을 위한 마이크로 실리카 혼입 수중용 에폭시 접합 성능 검토 : Part 2 - 구조 접합 성능 평가

ABSTRACT Recent studies to develop Very Large Floating Structure(VLFS) has shown that the construction procedure of the structure needs to acquire precast concrete module connection sy stem using prestressing. Howeve r, the loads occurring on water are complex combinations of various condition, so the safe and stable performance of the module joints and bonding materials are ke y to the success of the construction. Therefore, micro-silica mixed aqua-epoxy development was introduced in Part 1 using a bonding material developed in this study. The performance of the micro-silica mixed aqua-epoxy(MSAE) applied joint of concrete module specimens connected by prestressing tendon was evaluated to verify the usability and safety of the material. RC beam, spliced b eam connected by prestressing tendon and MSAE, and continuous prestressed concrete beam were tested for their initial cracking and maximum loads as well as cracking procedure and pattern. The results showed that the MSAE can control the stress concentration effect of the shear key and the crack propagation, and the maximum load capacity of MSAE joint specimens are only 5% less than that of continuous RC specimen. The details of the study are discussed in detail in the paper.

A comparative study of continuous beams prestressed with bonded FRP and steel tendons

This paper presents a numerical investigation of the performance of continuous prestressed concrete beams with bonded fiber reinforced polymer (FRP) and steel tendons. A finite element model has been developed and is validated against the available test data. A numerical test is carried out on two-span continuous bonded prestressed concrete beams. Three types of tendons are considered for a comparative study: aramid FRP (AFRP), carbon FRP (CFRP) and prestressing steel. Various levels of ωp (reinforcement index of prestressing tendons) are used. The results indicate that, with increasing ωp, the failure mode of FRP prestressed concrete beams would transit from tendon rupture to concrete crushing while the crushing failure always takes place in steel prestressed concrete beams. Moreover, FRP tendons mobilize significantly different behavior regarding the crack pattern, deformation characteristics and neutral axis depth compared to steel tendons. The moment redistribution at ultimate in AFRP prestressed concrete beams is comparable to that in steel prestressed concrete beams while, at a low ωp level, CFRP tendons register obviously lower redistribution than steel tendons.

Experimental study on moment redistribution of external prestressed concrete continuous beams

Experimental study on moment redistribution of external prestressed concrete continuous beams

Performance of non-prismatic simply supported prestressed concrete beams

Prestressing is the most commonly employed technique in bridges and long span beams in commercial buildings as prestressing results in slender section with higher load carrying capacities. This work is an attempt to study the performance of a minimum weight prestressed concrete beam adopting a non-prismatic section so that there will be a reduction in the volume of concrete which in turn reduces the self-weight of the structure. The effect of adopting a non-prismatic section on parameters like prestressing force, area of prestressing steel, bending stresses, shear stresses and percentage loss of prestress are established theoretically. The analysis of non-prismatic prestressed beams is based on the assumption of pure bending theory. Equations are derived for dead load bending moment, eccentricity, and depth at any required section. Based on these equations an algorithm is developed which does the stress checks for the given section for every 500 mm interval of the span. Limit state method is used for the design of beam and finite difference method is used for finding out the deflection of a non-prismatic beam. All the parameters of nonprismatic prestressed concrete beams are compared with that of the rectangular prestressed concrete members and observed that minimum weight design and economical design are not same. Minimum weight design results in the increase in required area of prestressing steel.

Aerodynamic characteristics of a trailing rail vehicles on viaduct based on still wind tunnel experiments

The aerodynamic behavior of rail vehicles subject to crosswind has become one of the hot topics to the Chinese railway community, due to the rapid expansion of the high-speed railway networks in the last decade. To investigate the aerodynamic interference between vehicle and viaduct, models of a typical simply supported 32m pre-stressed concrete box beam viaduct and CRH2 train with scale of 1:25 were tested in wind tunnel experiments. By using simultaneous pressure scanning technique, various tests combining different cases of vehicles on double tracks on the viaduct were carried out. Pressure measurements were performed on the trailing rail vehicle to avoid the three-dimensional effects of train nose. The influences of wind barrier height and porosity on the aerodynamic characteristics of the train were also addressed. The experimental results indicate that the wind pressure distribution on the trailing vehicle is almost uniform along its axial direction, while the aerodynamic influence of vehicles on different tracks (upstream and downstream tracks) is different. Moreover, the porosity and height of the wind barriers are found to require optimization for different configurations.

Pathology, appraisal, repair and management of old prestressed concrete beam and slab bridges

The beam and slab bridges named in France VIPP are viaducts with multiple single spans made of prestressed concrete beams that are precast on site and post-tensioned, and then assembled transversely by prestress. A great number of those bridges were built in France at the beginning of the development of the prestressing technique. Some of them present strong losses of prestress related to the corrosion or the rupture of tendons. After a presentation of the pathology and its various causes, the paper presents the difficulties of the appraisal and the methodology that has been developed to assess their residual load-carrying capacity. The appraisal method is based on several levels of investigations and re-calculations. Then the paper addresses the problem encountered with the management of such structures by emphasising the interest of the risk analysis for helping owners to optimise the management of such bridges, with respect to safety. Finally, different solutions of repair that have been used with success to maintain or to strengthen the capacity of these structures are reviewed.

Seismic Performance Study on Side-Strengthened Concrete Beam Using Finite Element Analysis Method

Side-strengthened reinforced concrete or precast prestressed concrete beam for inadequate seismic performance is proposed in this paper. The factors are simulated by ABAQUS software for the impact of seismic performance, which are difference of material strength grade, initial load and the order of prestressing and pretightening. The strengthening technology can improve the seismic performance of side-strengthened beam. The meterials with different strength grades which used for beams give full play to their role. The initial load has little effect on the seismic performance. The way of prestressing after pretightening plays a favorable effect for the seismic performance. The simulation results can accurately reflect the impact of these factors on the side-strengthened beam.

프리스트레스트 콘크리트 보 부재의 잔류변형 산정에 대한 연구

Ulsan College, School of Environment & Building Design, Ulsan 682-715, KoreaABSTRACT To perform performance-based seismic design of buildings, it is necessary clear goal for usage and stability after an earthquake. To clear this goal, it requires a review of the constituent material of the building and, in particular, a member u sed as an indicator of the residual strain is useful. There are more usage of prestressed concrete because of prestressing steel witch has characteristics of the origin-oriented. In this study, the goal is estimating of residual strain on the prestressed concrete be am member. The expression for angle of deformed prestressed concrete beam member was obtained from using of curvature on the critical sect ion and the equivalent plastic hinge length based on ‘equivalent plastic hinge length method’. Considering the balance of strength and deformation conditions, suitable analysis values were derived from ‘split Element Method’. Through various parametric studies, various factors affecting the residual strain were decided. Based on the results of this study, it is expected many researches will be proceed in the future.Keywords : performance-based seismic design, stability, prestressed concrete, residual deformation, equivalent plastic hinge length

Theoretical model for the mechanical behavior of prestressed beams under torsion

AbstractIn this article, a global theoretical model previously developed and validated by the authors for reinforced concrete beams under torsion is reviewed and corrected in order to predict the global behavior of beams under torsion with uniform longitudinal prestress. These corrections are based on the introduction of prestress factors and on the modification of the equilibrium equations in order to incorporate the contribution of the prestressing reinforcement. The theoretical results obtained with the new model are compared with some available results of prestressed concrete (PC) beams under torsion found in the literature. The results obtained in this study validate the proposed computing procedure to predict the overall behavior of PC beams under torsion.

MIDAS-Based Finite Element Analysis of the Short Line Method of the Precast Segmental Bridge Construction

This paper studies the precast and cantilever erection process of pre-stressed concrete continuous beam bridge alignment control in short line method, basis on the construction of a light rail. Various stages of bridge construction performed on simulation analysis and calculated by the finite element software MIDAS, concluded the ultimate internal force and deformation values, and the maximum deformation are within the scope of design elevation deviation 20 mm allowed, as to achieve the target of bridge assembly.

Factors governing the fire response of bonded prestressed concrete continuous beams

Results from fire resistance experiments on nine bonded prestressed concrete (PC) continuous beams are presented in this paper. The test variables included concrete cover thickness, load level, degree of prestressing and effective prestress. Data from the experiments are utilized to study the effect of critical parameters on thermal and structural response of bonded PC continuous beams under fire conditions. Test results show that concrete cover thickness, load level, degree of prestressing and fire induced secondary moments have significant influence on the fire resistance of bonded PC beams. Specifically fire induced secondary moments increase the total moments at intermediate supports by as much as 1.6 times of that due to imposed external loading under ambient conditions. It is also shown that the fire resistance of PC continuous beams is significantly higher than similar PC simply supported beams. These critical factors are to be considered for evaluating the fire resistance of PC continuous beams under fire conditions.

A point-by-point impact vibration method for damage detection in beam-type structures

This paper develops the point-by-point impact vibration method, a damage diagnosis method for beam structures. The theoretical development and experimental verification were carried out on aluminum beams with single and double cracks in the vertical direction and on pre-stressed concrete beams with local breaks. The processing signals were the time histories of the acceleration responses of the beams and the impact force. The point-by-point impact vibration method is combined with the Dynamic Reciprocal Theorem, the Frequency Domain Decomposition method, and the Damage Index idea, all of which cover the modal curvature change (MCC) and the change of strain energy, as well as other measures. One of the advantages of this method is the ability to use fewer sensors to obtain higher order eigenmodes, which can be applied in the damage index. Experimental results indicate that higher order vibration modes exhibit great potential for damage identification.

Size Effect in Flexure of Prestressed Concrete Beams Failing by Compression Softening

The typical cause of flexural failure of prestressed beams is compression crushing of concrete, which is a progressive softening damage. Therefore, according to the amply validated theory of deterministic (or energetic) size effect in quasi-brittle materials, a size effect must be expected. A commercial finite-element code, ATENA, with embedded constitutive equations for softening damage and a localization limiter in the form of the crack band model, is calibrated by the existing data on the load-deflection curves and failure modes of prestressed beams of one size. Then this code is applied to beams scaled up and down by factors of 4 and 1/2. It is found that the size effect indeed takes place. Within the size range of beam depths of approximately 152–1,220 mm, the size effect represents a nominal strength reduction of about 30% to 35%. In the interest of design economy and efficiency, a size effect correction factor could be introduced easily into the current code design equation. However, this is not really necessary for safety since the safety margin required by the code is exceeded for the normal practical size range if the hidden safety margins are taken into account. The mildness of the size effect in the normal size range is explained by the fact that the compression softening zone occupies a large portion of the beam and that, at peak load, the normal stress profiles across the softening zone exhibit only a minor stress reduction below the strength limit. Fitting the type 2 size effect law to the data can provide a simple extrapolation to much deeper beams, for which a stronger size effect is expected. But the extrapolation has some degree of uncertainty because of higher scatter of the test data used for calibrations.

Ductility of externally prestressed continuous concrete beams

Ductility is a desirable structural property that allows stress redistribution and provides warning of impending failure. Factors affect the ductility of beams prestressed with external FRP tendons are different than those affect the ductility of ordinary bonded prestressed concrete beams due to lack of bond and linear stress-strain relationship of FRP tendons. This paper investigated the effect of several variables on the ductility of continuous concrete beams, externally strengthened using Parafil ropes. The test variables included external prestressing force value, depth of external prestressing tendons, loading pattern, tendon profile and location of deviators. Test results show that the ductility of the externally prestressed concrete beams significantly reduced due to prestressing. Also, the eccentricity of the prestressing force and the tendon profile had the main influence on ductility of the externally prestressed beams, while the variation in prestressing force value, loading pattern and location of deviators had a less effect.

Creep in Prestressed Concrete Beams Under Time-Varying Sustained Loading

In the design of prestressed concrete fl exural members it is necessary to allow for the longterm effects of creep and shrinkage, particularly in regard to defl ections and prestress loss. Various analytic methods can be used to evaluate these long-term effects, but the calculations for creep become extended and complex if, as is usually the case, the sustained load on the member varies over time. In this study a simplifi ed, approximate method is proposed for dealing with creep under a varying load history. The time-varying moment history in the cross-section of a member is replaced by a constant, sustained, “equivalent” moment, Meq, which has the same long-term effect as the time-varying moment. This equivalent moment can be used together with any appropriate constant-moment creep analysis, but is here combined with previously-derived, closed-form expressions for loss of prestress and creep curvature. The result is a simple procedure for dealing with creep in prestressed members under time-varying sustained loads.

Identification of Elastic Modulus and Effective Pre-Stress Based on Inversion Theory

Due to vehicle load, shrinkage, creep, temperature and other factors, the strength and stiffness degenerate increasingly for the pre-stressed concrete continuous beam bridge in service. The problem, such as cracking, excessive deflection in the mid-span caused by the deterioration of the elastic modulus and pre-stress, has a direct impact on the usability, durability and security. To solve the problem mentioned above, according to the monitored deflection of the bridge in service at different time, the elastic modulus and the effective pre-stress are evaluated by establishing the inversion analysis model based on the inversion theory.

Effect of insufficient grouting and strand corrosion on flexural behavior of PC beams

An experimental study is proposed in this paper to investigate the effect of insufficient grouting and strand corrosion on flexural behavior of prestressed concrete (PC) beams. First, experimental design is discussed with different insufficient grouting conditions and the strand corrosion in ungrouted duct. Thirteen PC beams were designed and divided into two groups: five beams with different insufficient grouting conditions; eight beams subjected to accelerated corrosion to different strand corrosion levels. Next, experimental study was performed and the characteristic of strand corrosion in the PC beams with insufficient grouting is discussed using experimental observation. The influences of insufficient grouting including void and ungrouted length and position on flexural behavior are addressed. Following this, the flexural behavior deterioration induced by the combined effect of strand corrosion and insufficient grouting is analyzed. The experimental results show that the cracking behavior of beams is sensitive to the bond between strand and insufficient grout. The effect of no grouting on beam’s flexural behavior depends on its length and position. The strand corrosion in ungrouted duct can significantly decrease the ultimate strength of beam. The different levels of strand corrosion in ungrouted duct have different effects on the cracking behavior, the load–deflection curve, and the failure mode of beams.

Performance of 45-year-old corroded prestressed concrete beams

The design of prestressed concrete bridge beams usually assumes that the full capacity of the tendons can be achieved under ultimate load, based on the assumption of sufficient deformation capacity of the prestressing wires. Whether this is achieved also in older bridges is of increasing interest in remaining-life assessments since, especially in aggressive marine environments, corrosion of steel is known to cause loss of wire ductility. Results are reported herein of load tests to destruction for three full-sized and deteriorated prestressed concrete bridge beams recovered from a 45-year-old bridge exposed to an aggressive marine environment. The two beams with the greatest superficial deterioration showed progressive and premature failure of the prestressing wires. The beam with little superficial deterioration also showed progressive failure and failed to reach the ultimate load capacity based on current design theory and actual material properties. Possible reasons for the observed behaviour and the practical implications are discussed.

Comparative study of the flexural behavior of lightweight and normal weight prestressed concrete beams

The objective of this research was to evaluate the feasibility of producing structural lightweight concrete prestressed girders with load-bearing capacities similar to conventional concrete girders. The methodology consisted of comparing the results of the production and monitoring of scaled prestressed concrete beams at a precasting plant and the subsequent flexural testing. The beams were produced using two types of lightweight concrete and a conventional reference concrete with similar compressive strengths to allow for a comparison of the structural performance of the beams. The goal was to estimate an upper bound for the development length of fully developed prestressing strands with a diameter of 15.2mm (0.6″). The load-bearing capacity and ductility of the beams were determined by flexural tests. All lightweight and conventional concrete beams exceeded their nominal flexural strengths, which were calculated without accounting for the splitting cracks that all manufactured lightweight concrete beams developed after the prestress release on their lower side. Based on these tests, upper bounds were determined for the development length of the prestressed strands with a diameter of 15.2mm for the three types of concrete tested. Subsequently, the ductility factors of the beams tested under flexure were determined. Despite all of the tested beams were able to develop the full strength of the prestressed strands and showed a remarkably ductile behavior, it was concluded that the use of these lightweight concretes is not recommended in the fabrication of prestressed concrete bridge girders because of the potential reduction in their durability and bearing capacity due to stress corrosion, which is a result of the splitting cracks detected in all of the produced prestressed lightweight concrete beams.

Modal Parameters Identification of Bridge Structure Based on Excitation of Wind Load

Applying the combination of the natural excitation technique and the Eigen system realization algorithm, a finite element numerical simulation was performed for the dynamic behavior identification of a pre-stressed concrete continuous beam bridge under simulating wind load excitation. The results were validated comparatively using the combined algorithm of random decrement technique and Ibrahim time domain technique as well as the finite element modal analysis. The simulation results show that the wind load as the most common environmental excitation can be used effectively to identify the modal parameters of the concrete bridge.