External Tendons Research Articles

A Finite Element Analysis on Mechanical Property of Externally Strengthened Prestressed Box Beams

The mechanical property of external prestressed beams is affected by many parameters. Based on experimental study on externally strengthened prestressed box beams, a three-dimensional finite element analysis model was built in ANSYS. The calculation results was proved to be correct by being compared with experimental results. The effect of some parameters on deflection and stress in externally strengthened box beam was deeply analyzed in serviceability stage and ultimate status. The study shows that different original status of strengthened beam may affect the deflection and stress in different degree. The parameters change, such as effective prestress, concrete strength, the area and depth of external tendons and displacement coupling character for contact node, will result in a little difference in deflection and stress in serviceability stage, but obvious in ultimate status. For box beams in the model, changing the tendons lateral distance to the web results in litlle change in deflection and stress. No matter it is inside or outside the box at cross section.

Experimental Inspection of Damage and Performance Evaluation after Repair and Strengthening of Jiamusi Highway Prestressed Concrete Bridge in China

The main objectives of this study are to inspect an d identify any damage of jaimusi highway prestressed concrete bridge after repair and strengthening of damaged structura l members and to evaluate the performance of the bridge structural m embers by adopting static load test. Inspection program after repair and strengthening includes identifying and evaluating t he structural members of bridge such as T-shape cantilever struct ure, hanging beams, corbels, external tendons, anchor beams, sti cking steel plate, and piers. The results of inspection show that the overall state of the bridge structural member after repair and strengthe ning is good. The results of rebound test of concrete strength show t hat the average strength of concrete is 46.31Mpa. Whereas, the aver age value of concrete strength of anchor beam is 49.82Mpa. According to the results of static load test, the experimental value s are less than theoretical values of internal forces, deflection, and strain, indicating that the stiffness of the experimental structure, o verall deformation and integrity satisfy the designed standard and the working performance is good, and the undertaking capacity h as a certain surplus. There is not visible change in the length and width of cracks and there are not new cracks under experimental loa d. Keywords—Jiamusi Bridge, Damage inspection, deflection, strain.

Estimation of Cable Tension Using Measured Natural Frequencies

Estimating cable tension in cable-stayed bridges or in external tendons is essential for regular inspection and assessment of those structures. Vibration measurements provide a solution, however, may not be accurate in cases parameters such as amount of sag and flexural rigidity of cable are significant. In this study, the characteristic equation for vibration of the most general case of a cable, where both the sag and flexure in the cable are taken into account, is analytically derived. After that by considering proper simplifying assumptions of small flexural rigidity parameter, asymptotic forms of that equation are obtained. It renders a practically applicable procedure to estimate cable tension using measured natural frequencies. The developed procedure is verified by realistic data of a cable stayed bridge in Vietnam.

SHEAR CARRYING CAPACITY OF SEGMENTAL CONCRETE BEAMS WITH DRAPED EXTERNAL TENDONS

This study presents an investigation of the shear be havior of segmental concrete beams with draped external tendons. Deviator force and transfer mechanism of prestressing force from an anchorage that affect the shear failure mechanism have been examined base d on the results of experimental procedure and FEM with different location of deviator and inclined angle of draped tendons. The modified model proposed by authors has been extended for segmental concrete beam s with draped external tendons with considering the effect of deviator force and transfer mechanism of prestressing force from the anchorage. The results from the extended modified model for draped external tendons had a good agreement with experimental results.

Influence of External Tendons on Dynamic Characteristics of Box Girder with Corrugated Steel Webs

Based on Miyamoto’s method, the natural frequency of prestressed box girder with corrugated steel webs considering the impact of external tendons was obtained. And the result was modified based on the finite element model. It shows that: the external tendons will reduce the natural frequency of bridge with reduced range of about 3%. Beneficial references were provided to the layout of external tendons in order to avoid the resonance between the box girder with corrugated steel webs and the external tendons.

Friction Loss of Externally Prestressed Concrete Beams with Carbon Fiber-Reinforced Polymer Tendons

Friction loss is an important component of the calculation of prestressing loss for external prestress strengthening technology. Unfortunately, the test data of relevant curvature friction and wobble coefficients is scarce, especially for beams strengthened by external prestressing Carbon Fiber-Reinforced Polymer (CFRP) tendons. Through the experiment of 12 concrete beams strengthened by external prestressing CFRP tendons, this study attempts to discuss the friction loss algorithm and the reasonable value of friction coefficient. The test results demonstrated that traditional friction loss algorithm for prestressed steel tendons is also suit to external prestressing CFRP tendons, but the value of curvature and wobble coefficients should be determined by different types of CFRP tendons and saddle design. What is more, aiming at the domestic production of CFRP tendons and the adopted special saddle design in this paper, the curvature friction coefficient is 0.263 and the wobble coefficient is 0.0067 at the deviator. Results of the research provide a reference for external prestress strengthening design with CFRP tendons.

Monitoring of External Prestressing Tendons Construction Process of Jiamusi Highway Prestressed Concrete Bridge during Strengthening in China

Jiamusi highway prestressed concrete bridge is located in the Jiamusi City within Heilongjiang province in the east north of China. The strengthening and repairing of the bridge structure can be provided an effective and economic solution in appropriate situation. The objective of this study are to monitor the construction process of external prestressing tendons for strengthening of Jiamusi highway prestressed concrete bridge. Monitoring process includes measurement of external prestressing tendons natural frequency, monitoring of tensile forces values of external prestressing tendons, monitoring of development of anchor beams cracks, and monitoring of anchor beam deformation. The results of monitoring process show that the box girder No. 11 has the largest values of proportional coefficient (K) and the maximum value is 327.8. Box girder No. 8 has the largest values of frequency, the maximum value is 3.499. Five levels of tension are used in the application of tensile force in the tension process of external prestressing tendons. These levels are level 1=248.2kN, level 2=496.4kN, level 3=744.6kN, level 4=992.8kN, and level 5=1241kN. The measured tendons elongation values of left box girder No.8 are more than the theoretical values. For left and right box girder No. 9, side external tendons of left box No. 10, and left and right box girder No. 11, the measured values are less than theoretical values of elongation. After tension process, there are no new cracks in the top, web, and bottom of anchor beam and a small number of cracks developed slightly. These cracks are found around ducts of external tendons. The length of cracks rang from 0.03m to 0.5m and width rang from 0.05 mm and 0.25mm. The longitudinal deformation of the interface and top of anchor beam is very small, ranging from 0.001mm to0.115mm, which averaged 0.026mm. The overall state of anchor beams and box girders during strengthening is good.

Long Term Deformation Control of Long-Span Pre-Stressed Concrete Continuous Rigid Frame Bridge with Ballastless Track

Aiming to Ronggui Bridge (RGB) on Guangzhou-Zhuhai Intercity Rapid Rail Transit (GZIRRT), long term deformation control of long-span pre-stressed concrete continuous rigid frame bridge with ballastless track was studied. Comparing with the non-controlled deformation, extend track laying six months later after bridge construction, reserve 48 post-tensioned cables in middle spans and tension 12 external tendons after tracking laying were all effective in decreasing the long term deformation of RGB with individual application. Taking bridge construction and railway service in consideration, applying the foregoing three measures in combination, deformation of RGB 20 years later after track laying was effectively controlled within 12.8mm in the side spans and 21.9mm in the middle spans, which is less than the deformation limitation of bridges with ballastless track. The combined measure has been adopted in the actual construction of RGB.

Response of Concrete Beams Partially Prestressed with External Unbonded Carbon Fiber-Reinforced Polymer Tendons

To assess the behavior of concrete beams partially prestressed with external unbonded carbon fiber-reinforced polymer (CFRP) tendons, three specimens prestressed with CFRP tendons and one reference specimen prestressed with external steel tendons were tested to failure under third point loading. It was found that the load-deflection curve of all specimens exhibited three stages, namely, elastic, cracked-elastic and plastic. The transition from the elastic to the cracked-elastic stage was caused by the development of cracks at the bottom of the beam, while the transition from the cracked-elastic to the plastic stage was caused by yielding of the non-prestressed steel. For beams prestressed with external CFRP tendons and that with external steel tendons, the relationships between the stress increment in external tendons and the mid-span deflection of specimens were linear or approximately linear. Although CFRP materials are brittle in nature and behave linearly elastically until failure, proper combination of external CFRP prestress tendons with internal steel reinforcing bars can impart ductility to the beams.

Experimental study of externally prestressed segmental beam under torsion

Externally prestressed segmental (EPS) concrete beams are widely used in the construction of bridge structures today. The EPS concept has become an attractive tool for rehabilitation and strengthening of existing bridges which have insufficient strength and/or excessive deflection and cracking. EPS bridges are affected by combined stresses (bending, shear, normal, and torsion) at the joint interface between the segments. This paper presents an experimental investigation of the structural behaviour of EPS bridge beams under combined stresses, i.e. bending, shear and torsional stresses. An experimental study of two different external tendon layouts, two types of joint between segments and different levels of torsional force applied at different load eccentricities was conducted. It was concluded that torsion reduced the vertical load and vertical deflection at the onset point of nonlinearity as well as at a failure load. Furthermore, the opening between segments was the reason behind the nonlinear behaviour of EPS beams. Torsion did not only alter the value of the failure load, tendon strain and deflection of the beams but it also altered the failure mechanism. Furthermore, due to the shear key, there was a difference between the onset points of nonlinearity load for the different tendon layouts and joint types.

Numerical analysis of second-order effects of externally prestressed concrete beams

A numerical procedure for the geometrical and material nonlinear analysis of concrete beams prestressed with external tendons is described, where the effects of external prestressing are treated as the equivalent loads applied on the concrete beams. The geometrical nonlinearity is considered not only the eccentricity variations of external tendons (second-order effects) but also the large displacement effects of the structure. The numerical method can predict the nonlinear response of externally prestressed concrete beams throughout the entire loading history with considerable accuracy. An evaluation of second-order effects of externally prestressed concrete beams is carried out using the proposed analysis. The analysis shows that the second-order effects have significant influence on the response characteristics of externally prestressed concrete beams. They lead to inferior ultimate load and strength capacities and a lower ultimate stress increase in tendons. Based on the current analysis, it is recommended that, for simply-supported externally prestressed beams with straight horizontal tendons, one deviator at midspan instead of two deviators at one-third span be furnished to minimize these effects.

Study on the Fretting Fatigue Properties of PC Strands at External Tendon Deviators

Study on the Fretting Fatigue Properties of PC Strands at External Tendon Deviators

Inelastic behaviour of PSC beams with unbonded external tendons

In this paper, an analytical method that can describe the structural behaviour of prestressed concrete (PSC) bridges with unbonded external tendons is developed. Since the unbonded external tendon is directly connected to the deviators while maintaining a straight configuration, it has a different deformation field from that of concrete and accompanies a secondary effect caused by the change of the primary eccentricity between the concrete and external tendon. The friction slip at the deviators is also taken into consideration on the basis of the force equilibrium between the friction force and the driving force. Moreover, all the material non-linearities and time-dependent deformations such as creep and shrinkage of concrete and relaxation of the tendon are included because the centroidal axis of a section changes according to cracking and time-dependent effects in the constituent materials. Through correlation studies between experimental data and analytical results, it is verified that the proposed numerical model can effectively predict the structural behaviour of PSC bridges with comparative precision.

Space Frame Latice Model for Stress Analysis of Bridge

This article presents a space frame lattice model for the analysis of stress of entire cross-section of bridge. The authors focused on analyzing the relatively weaker position of stress in box-girder section, using as an example the Xintan Bridge over the Qijiang River in Chongqing, China. The Xintan Bridge has a continuous prestressed concrete rigid frame with 75+130+75 m span. They calculated and analyzed the shear stress and principle tensile stress of the box girder cross-section in this bridge, using an innovative layout method of mixed internal and external prestressed tendons. They conclude that the space frame lattice model is accurate for calculating the stress state of a bridge. This model can simulate the process of long-term cracking as well as deflection of large-span pre-stressed concrete girder bridges.

Optimal three-dimensional strut-and-tie models for anchorage diaphragms in externally prestressed bridges

As a typical D-region in externally prestressed bridges, an anchorage diaphragm is usually severed as the end anchorage of external tendons. In this paper, an optimal three-dimensional strut-and-tie model for the anchorage diaphragm is proposed, and direct equations to facilitate the design are also developed. Both the topology optimization technique and the principle of minimum strain energy are incorporated to find out the optimal configuration of the strut-and-tie model, which makes the model rational based. A design procedure for dimensioning and detailing the model is then given according to ACI 318-08 provisions. The proposed model is further evaluated using three test results, and the comparisons show that the model predictions are consistent and conservative. Moreover, a design example is presented to demonstrate the effectiveness and convenience of the proposed method.

Stresses in External and Internal Unbonded Tendons: Unified Methodology and Design Equations

A unified methodology is proposed to compute the tendon stresses in externally prestressed beams in elastic and ultimate states, and practical design equations are developed to predict the ultimate tendon stresses. Previous test results have shown that there is an almost linear relationship between the tendon stress increment and the beam midspan deflection in both elastic and inelastic ranges. The key point is to seek this relationship and then the prediction of the tendon stress increment is transferred to the problem of calculating the beam midspan deflection. The second-order effect of external tendons is included in this deformation compatibility based analysis. Moreover, reasonable simplifications are made to establish practical design equations for the prediction of the ultimate tendon stress. The proposed equations are shown to be able to account for most of the important variables and result in good agreement with test data. It is shown that the ultimate stress increment is mainly dependent on the tendon eccentricity and the neutral axis depth, and the second-order effect can be reasonably taken into account using the stress and depth reduction factors.

Evaluation on structural behaviors of prestressed composite beams using external prestressing member

In this study, experimental, numerical, and analytical approaches were carried out to evaluate the behavior and prestressing effect of prestressed composite beam by external tendon and cover plate. Behavior of prestressed composite beam, load-carrying capacity, effects of prestressing, and ultimate strength were estimated. The contribution of the section increase of the prestressing method using tendon was less than the prestressing method using cover plate. In accordance with numerical and analytical approaches, the ultimate strength of the prestressed composite beam is shown to be the same value because strength is determined according to the plastic resistance moment and the plastic neutral axis; however, both plastic resistance moment and neutral axis are not affected by prestressing force but affected by sectional stiffness of the prestressing member. Based on these approaches, we concluded that the prestressing method using tendon can be useful in applications without an increase in self-weight, and the prestressing method using high-strength cover plate can be applied to reduce the deflection of the composite beam. The prestressing method using high-strength cover plate can also be used to induce prestress of the composite beam in the case of a large deflection due to a smaller sectional stiffness of the composite beam.

MODIFIED MODEL FOR SHEAR CARRYING CAPACITY OF SEGMENTAL CONCRETE BEAMS WITH EXTERNAL TENDONS

The study presents an investigation of the shear behavior of segmental concrete beams with external tendons considering the effect of joint opening. Joint position and prestressing force that affect the joint opening have been examined based on the results of experimental procedure and FEM. The simplified truss model with the small number of degree of freedom has been modified for segmental concrete beams with external tendons. The formulations to predict the variable angle and the thickness of struts are suggested with considering the effect of joint opening. A satisfactory prediction for the shear carrying capacity and the failure mechanism of segmental concrete beams with external tendons has been obtained.

Inspection of Voids in External Tendons of Posttensioned Bridges

Segmental posttensioned bridges are major structures that carry significant traffic. Recent investigations of these bridges identified voids in their ducts. The exposed strands at these void locations can undergo corrosion. The corrosion of strands may lead to the failure of tendons. As such, an effective inspection process for identifying these voids is needed. From a literature review, several nondestructive testing methods are compared for applicability to void inspection in external tendons. The impact echo, ultrasonic pulse velocity, and sounding inspection methods are then selected and assessed for further preliminary testing. The sounding inspection method is further assessed for its effectiveness in identifying voids in a full-scale, external tendon system. The results indicate that sounding inspection slightly underestimates the size of the voids. However, the inspected size and locations of voids have a close correlation with actual voids in ducts. Thus, sounding inspection can be an effective tool for identifying voids because of its easy application in the field.

Vibration serviceability for the PC stress ribbon pedestrian bridge with external tendons and supports

Vibration serviceability for the PC stress ribbon pedestrian bridge with external tendons and supports