External Prestressing Research Articles

Strengthening of RC dapped-end beams under torsional moment

Maintaining and strengthening existing structures is a very important issue in terms of extending the service lifespan of structures. Reinforced concrete (RC) beams with dapped ends are frequently found in bridge girders and precast concrete constructions. The reduction in depth near the supports of RC beams tends to produce a stress concentration and hence requires special analysis and detailing of the reinforcement, especially in the case of torsional stresses. This paper introduces an experimental investigation for the torsional behaviour of recessed RC beams. Along with a control specimen, three beams strengthened using different techniques (the application of fibre-reinforced polymer (FRP) sheets, FRP laminates and external prestressed steel) were constructed and tested under torsion. The results of the research showed that the external prestressing technique produced a higher ductility than the other techniques. On the other hand, the use of external prestressing and carbon fibre-reinforced polymer (CFRP) wrapping to strengthen RC dapped beams subjected to torsional moment increased cracking and failure loads compared with the use of externally bonded CFRP laminate. A three-dimensional truss model is presented to calculate the forces in the stirrups and the ultimate loads for the external prestressing technique. The model shows good agreement with the experimental results.

Research on CFRP External Pre Stress Reinforcing Vertical Crack of Box Girder Roof

the article is about longitudinal crack of concrete box girder roof, and it designed a reinforcement model. As the pre stressed material, CFRP could reach 30% of reinforcement efficiency under different loads in design model through external reinforcement upon calculation and analysis. And its crack width greatly reduces. In this way, the reinforcement purpose could be realized, and the mechanical properties of CFRP concrete could be fully played. The effect is obvious.

Strengthening the 100‐year‐old reinforced concrete dome of the Centennial Hall in Wrocław

AbstractThe Centennial Hall, a reinforced concrete structure with an auditorium for 10000 people, was opened in Wrocław, Poland (then Breslau, Germany), in 1913 after two years of construction. Its dome, covering the whole building, has a diameter of 65.0 m and in the year it was completed was the largest reinforced concrete dome in the world. This broke the previous record, held by the dome of the Pantheon in Rome (43.3 m), which had lasted for 1787 years. This paper describes the structure of the building, its condition after 100 years of use and the renovation works carried out in 2009–2011. An important part of the renovation was strengthening the lower (tension) ring of the ribbed dome by way of external prestressing. Details concerning the assessment of the technical condition of the hall, numerical calculations and the proposed system of strengthening are presented. In 2006 the monumental Centennial Hall was listed as a UNESCO World Heritage Site for its pioneering reinforced concrete structure, designed in the style of modernism.

Structural behaviour of a GFRP-concrete hybrid footbridge prototype: Experimental tests and numerical and analytical simulations

Glass fibre reinforced polymer (GFRP) pultruded profiles are being increasingly used in the construction industry since the last few decades. The high potential of GFRP profiles for structural applications stems from their high strength, low self-weight and corrosion resistance. In opposition, the high deformability, the susceptibility to instability phenomena and the lack of specific design codes have been hindering a wider use of these advanced composite materials. Several hybrid systems in which GFRP materials are combined with traditional materials, namely concrete, have been proposed in order to overcome the aforementioned limitations of the GFRP material. This paper presents experimental, analytical and numerical investigations about the flexural behaviour of a GFRP-concrete hybrid footbridge prototype comprising two I-shaped GFRP main girders and a thin steel fibre reinforced self-compacting concrete (SFRSCC) deck. With the aim of limiting the structure’s deformability, the footbridge features an external prestress system consisting of two ordinary steel rebars screwed tighten to the structure at the support sections. A small-scale footbridge prototype, 6.0m long and 2.0m wide, was built and tested in a 5.5m simply supported span. The experimental programme included (i) serviceability tests, with and without the application of the external prestress system, and (ii) failure tests. Results of flexural tests proved the feasibility and advantages of the structural concept proposed: the judicious combination of GFRP and SFRSCC enabled the development of a lightweight, high performance and relatively inexpensive structural system for footbridges; furthermore, the external prestress system was very effective in limiting deflections. The analytical and numerical models developed in this study were able to predict with good accuracy (i) the linear elastic behaviour of the structure up to failure, (ii) the effects of the external prestress, and (iii) the failure mode and strength, proving to be accurate tools for the design of GFRP-concrete structural solutions.

Prestressed near-surface mounted fibre reinforced polymer reinforcement for concrete structures — a review

The specialized application of prestressing the near-surface mounted (NSM) fibre reinforced polymer (FRP) reinforcement for strengthening reinforced concrete (RC) structures combines the benefits of the FRP reinforcement with the advantages associated with external prestressing. By applying a prestress to the NSM FRP the material is used more efficiently since a greater portion of its tensile capacity is employed. This paper presents a comprehensive review on the performance of RC members strengthened using prestressed NSM FRP reinforcement. Several techniques and anchorage systems developed to prestress the NSM FRP are presented. The static flexural and fatigue performance of RC beams strengthened using prestressed NSM FRP in comparison to non-prestressed NSM is presented. Research on the long-term performance under freeze–thaw exposures and sustained loading is also presented.

부모멘트부의 효율성을 고려한 외부강선으로 보강된 콘크리트 거더 연속교의 거동

An effective method was proposed in this study which can improve the strengthening effect of continuous girder bridges by external tendons. The improvement of the proposed strengthening method in comparison with conventional methods was analyzed by applying equivalent load concept. In order to verify the strengthening effect, the enhancement of load-carrying capacity achieved by external prestressing was investigated through the test of continuous beams that were or were not strengthened by the external prestressing. The continuous beams were fabricated by making the deck slab continuous according to general construction practice of an actual concrete girder bridge. The test results showed that the deflections and strains of the strengthened beam were significantly reduced when comparing with those of the non-strengthened beam for the same level of external loads, and the stiffness of the member increased by strengthening. In particular, it was verified that the proposed method can effectively reduce the tensile stresses of the deck caused by negative moment at the intermediate supports of a continuous bridge.

Assessment of prestressed concrete bridge girders with low shear reinforcement by means of a non-linear filament frame model

The safety of existing bridges and the efficiency of strengthening measures can be accurately studied through non-linear numerical models, assisting decisions of dismantle, repair or change of use and avoiding unnecessary or inappropriate interventions. In this ambit, filament beam models due to their inherent simplicity and low computational demand are adequate for the engineering practice. Accordingly, in this paper, the structural assessment of a prestressed concrete bridge presenting low shear reinforcement, the Wassnerwald Viaduct in Switzerland, is presented. The bridge was dismantled due to, among other reasons, not complying with the safety standards related to shear. The girders of the bridge, which were submitted to full-scale in situ load tests, were numerically simulated by means of a non-linear filament beam model considering axial force (N)–shear (V)–bending (M) interaction. Hypothetical strengthening solutions for this bridge were also numerically studied: a shear strengthening through vertical prestressing and a bending strengthening through external longitudinal prestressing.

Research and Application of External Prestressing Curved Beam’s Tendons

With continuous development of the structural engineering, a perfect theoretical foundation and construction means is the key to its development. Combined with characteristics of the curved beam, it will be closely integrated together with external prestressing technology. The associated design and construction research can be carried out, in order to fully meet the need of the prestressing development. In this paper, the advantages of external prestressing curved beam was studied, and relevant contents are as follows: reasonable adjustment of external prestressing tendon’s diameter makes the structural force to become more uniform and prevents inappropriate use to tendon; reasonable external prestressing tendon and anchorage is the premise of good structure connection. The crucial problems should to be solved are the lower anchor position and stress concentration treatment. Considering the security need of prestressing curved beam’s tendon connection, attention should be paid not only to its materials and mechanical properties, but also to the convenience of construction. The external reinforcement work of prestressing curved beam is to ensure reasonable control parameters, as well as to ensure the optimal design of reinforced construction. As for the technical grasp on the theory and construction of external prestressing curved beam structure, it will make them have broader development space.

Engineering Application of External Prestressing Curved Beam

Using the finite element software ANSYS to analyze dynamic characteristics of external prestressing structure, reasonable control parameter, as well as external prestressing reinforcement joints of security, the main research contents and results are as follows: Dynamic performance analysis is about variation law and internal feature. With the increase of external prestressing, on the contrary, the natural vibration frequency will reduce. However, external prestressing effects on the structural dynamic performance improvement that is not obvious in general. Based on sensitivity analysis, control parameter of external prestressing reinforcement curved beam must be analyzed and the reasonable value range of sensitive control parameter can be found. For the control parameter of external prestressing process, its reasonable control parameter’s range should be about 6% in the theoretical calculation. While simulating of anchoring system, local force on anchoring system must be analyzed finely and accurately. A comprehensive understanding should be mastered on variation law, which is about the internal forcing and stress response of special area. The setting of anchoring device shall be arranged at 1/3 place of original prestressing position. To ensure the safety, it should guarantee the mechanical continuity of anchor joints.

Bending-Shear Interaction Domains for Externally Prestressed Concrete Girders

In prestressed concrete structures, the evaluation of the safety level is generally carried out by separating the bending moment strength and the shear force capacity. Actually interaction between bending moment (M) and shear force (V) can have significant consequences on evaluations in service life, especially when the ultimate limit state (ULS) is considered. In this paper, the M-V interaction is addressed for prestressed concrete girders, in the cases of both bonded and unbonded prestressing tendons. It can be demonstrated, by drawing the interaction domains (M-V), that a significant reduction of the safety level has to be considered when shear force is evaluated together with bending moment on the ULS of the cross-section, especially for external prestressing in concrete T-shaped or box sections of bridge girders. Interaction domains allow designers to evaluate and optimize reinforcement ratios, geometric properties of the beam, and effects of shear on the ultimate state. An analytical model, based on the stress field theory, is developed and proposed in this paper. A numerical example is developed and interaction domains are given for an example of a box section with variation in reinforcement ratio and tendon slope. A validation of the presented model is given, by comparing experimental data in the literature with results found using the proposed analytical approach.

Study of the Effect on Efficiency of External Prestressing and Economy to Box-Girder Bridge with Different Styles of Webs

Prestressed box-girder bridges have been applied in modern bridges widely as the perfect structural performance, the design method and calculation theory of prestressed box-girder bridges have been relatively perfect. The self-weight of box-girder bridges is reduced during the process of development from concrete structure to composite structure. The prestressed efficiency and the economy are also improved, simultaneously. But up to now, the quantitative research of the effect on efficiency of external prestressing to box-girder bridge with different styles of webs is lack. This paper illustrates the effect on efficiency of external prestressing and economy to box-girder bridge with different styles of webs. The results show that the box-girder bridge with corrugated steel webs has the highest prestressed efficiency and the lowest life cycle cost and the best economy.

Towards a model of dry shear keyed joints: modelling of panel tests

This paper presents a study on the behaviour of the joints of segmental concrete bridges with external prestressing, focusing on the structural response of dry non-epoxied joints with shear keys. A Finite Element joint model to study such structures is validated modelling eight concrete panel tests. The most important feature of this model is that it has been validated with experimental tests on concrete panels which were specifically designed to fail in shear. Interface elements are used to reproduce the non linear behaviour of the joint and parameters deduced from the tests are used to define the constitutive law of these elements. This joint model is of great importance because it will permit the development of a structural model that faithfully reproduces the behaviour of these structures under combined flexure and shear and the study of its global behaviour after the opening of the joints. Interesting conclusions about the behaviour of the dry joints, about the contribution of the different mechanisms transferring shear (friction and cohesion) and about the shear stress distribution in the joint have been reached.

Anchorage System to Prestress FRP Laminates for Flexural Strengthening of Steel-Concrete Composite Girders

Using externally bonded (EB) fiber-reinforced polymer (FRP) laminates for strengthening steel-concrete composite girders has recently received more attention from researchers. By prestressing the EB FRP laminates, the material is used more efficiently because a greater portion of its tensile capacity is employed and it contributes to the load-bearing capacity under both service and ultimate conditions. This is an ideal technique because it combines the advantage of using noncorrosive and lightweight advanced composite materials in the form of bonded FRP laminates with the high efficiency offered by external prestressing. An innovative mechanical anchorage system was developed to prestress the FRP laminates directly by jacking and reacting against the steel girder itself. The efficiency of the system was investigated using two types of FRP laminates for flexural strengthening of large-scale steel-concrete composite girders. The used FRP composite materials included carbon-fiber-reinforced polymer (CFRP) plate and steel-fiber-reinforced polymer (SFRP) sheets. The developed anchorage/prestressing system was easy to use/apply and proved to be a feasible and practical system for prestressing both CFRP plate and SFRP sheet. The prestressing levels in the FRP laminates were sufficiently maintained. The prestressing losses were insignificant.

Experimental Study of Deformation Characteristic and Application on External Prestressed Wooden Beam

People have widely uesd long- history wooden buildings in the ancient and mordern architecture.But the modulus of elasticity of the wood is smaller as well as the fact that the stiffness of wood is lower. In order to solve the problem of deficiency of the stiffness of large-span wooden beam from the practical engineering, this paper presents the method of external prestressed wooden beam, and the calculation method of deflection of wooden beam through model test of 1:2 scale. In addition to it, the paper also analyzes the factors which affect stiffness of wooden beam. The result shows that stiffness of this kind of wooden beam is greatly improved compared with the common wooden beam in the same cross section. Steel has a predominant tensile characteristics, it is an effective method to reduce undue deflection of large-span wooden beam by external prestress method. This construction techniques has greatly applicational value in the reinforcement and strengthening ancient buildings and modern design and construction of large-span timber structure buildings and bridges.

Reinforcement Experiment of a Hollow Slab Bridge by External Prestressing

Simply supported hollow slab bridge is widely used in highway network of China. Under overload vehicles, the concrete hinges of such bride are easily damaged, which usually causes single slab bearing and tremendously reduces the bridge’s load capacity. It is necessary to take some reinforcement measures to enhance the carrying capacity of such impaired bridge for traffic safety. In this paper, a field reinforcement experiment of an actual hollow slab bridge, which has experienced a destructive test with its transverse connections seriously damaged, was performed by applying external transverse and longitudinal prestress to it. The strengthening scheme adopted in this experiment was detailed. By means of static truck load test, the variation of deflections of the bridge before and after strengthening was obtained. The test results showed that the proposed strengthening method can effectively enhance the damaged hollow slab bridge’s transverse stiffness and improve its bearing capacity.

Retrofitting of reinforced concrete beams in shear using external prestressing technique

Retrofitting of existing concrete structures has become an important issue nowadays in the construction industry. There are many causes for repair and/or strengthening, but normally change of use, increased demands on the structure, errors in the design or/and construction phase or accidents are responsible. Many methods to repair and/or strengthen concrete structures exist, such as concrete overlays, shotcrete, external prestressing using cables and so on. This research presents laboratory tests of nine reinforced concrete beams with 2 m span strengthened in shear with external prestressing technique. In addition to a non-strengthened reference beam, the present work studied in three groups to examine beams strengthening using different configuration of prestressing details in shear domain, the effect of repairing beams cracked in shear with different damage levels, and the strengthening of beams using carbon fibre reinforced polymer plates in flexure and prestressing in shear. The tests results showed that prestressing is a very effective strengthening method to increase the shear load-carrying capacity of existing concrete beams. The external post-tensioning method can reduce the effect of the existing crack and increase the member capacity up to 95% of the original capacity. The beam strengthened with external carbon fibre reinforced polymer laminate in flexure and using external post-tensioning technique in shear failed owing to peeling of the carbon fibre reinforced polymer laminate. In addition, a numerical model was presented and verified with the experimental result and showed good agreement.

Evaluation of the efficiency of UHP-SHCC beams in flexure under external prestressing (comparative study)

Externally prestressed beams are structural concrete members in which prestressing tendons are placed outside the concrete section. Design provisions of many international codes for external prestressed beams are limited to ordinary concrete (OC). However, the main advantage of using an ultra high performance strain hardening cementitious composite (UHP-SHCC) is to increase the flexural load-carrying capacity for concrete members. The aim of this research was, therefore, to find the coupling effect of external prestressing and the use of UHP-SHCC. To achieve this objective, three prototype beams were tested to evaluate the effect of prestressing on the behaviour of UHP-SHCC beams. The experimental results were also compared with those of an OC beam. Basic section analysis was carried out on uncracked, cracked elastic and ultimate strength conditions. The analytical model was verified and validated against experimental tests. An extensive parametric study using a basic analysis was carried out for prestressed UHP-SHCC beams under quasi-static monotonic loading. Comparative studies were conducted to achieve the efficiency of UHP-SHCC beams under external prestressing as compared with ordinary and high-strength concrete (HSC) beams with and without reinforcement. The test results indicate the efficiency of using UHP-SHCC material with external prestressing to improve the failure loads and ductility of beams relative to ordinary and HSC beams.

Structural behaviour of segmental concrete continuous bridges with unbonded prestressing and dry joints

This work presents a finite-element method (FEM) analysis of the behaviour of continuous segmental concrete bridges with external prestressing and dry joints, focusing on the response under combined shear and flexure, at the service limit state (SLS) and at the ultimate limit state (ULS). A previously validated FEM model has been applied to simulate the structural behaviour of continuous bridges until failure. A geometrically non-linear analysis has been performed, where the particular behaviour of the dry joints, the concrete plasticity and the slipping of the prestressing tendons at the deviators have been considered. Results of the analysis have been compared with the available data of the modelling of simply supported bridges, and the different behaviour introduced by the support redundancy has been pointed out. Analysis proves that the SLS can govern the design of the prestressing force, whereas in simply supported bridges, it is the ULS that always governs the design. Concrete and steel remain essentially linear under ultimate loads, which implies that there is an extra safety factor against failure. Before failure, when support and mid-span joints are opened, moment redistribution has occurred and an arch springing from the bearings is formed within the concrete, which equilibrates the external loads.

A Survey on Project Application of External Prestressing Technology

This article mainly introduce the major effect factor of external prestressing technology, for instance: The reasonable external prestressing’s transmission system chiefly includes two aspects of prestressing size and prestressing function position; The tendon steering system is to solve the centralized solution of local stress and the grasp stress of weak link ; The external prestressing anchor system must guarantee multiplicity and construction security; In construction monitoring process，it must grasp the monitor parameter of the prestressing and the deflection and so on; The anti-vibration localization of the external prestressing is to enhance the structure durability etc., which have provided the advantageous technical guidance for the actual projects.

The Ultimate Shear Bearing Capacity of RC Beam Strengthened with SWR External Prestressing under Dead Load Level when Strengthening

The shear resistant with SWR (steel wire rope) external prestressing is a kind of new type of reinforcement technique. The advantages of the method are ideal reinforcement effect, durability, and convenient construction. So the method has been paid attention by more and more scientists and technical workers. Through the experiment of 1 basic beam and 3 strengthened beams which are in different dead load levels, the influence of damage degree of original beams and the dead load level of strengthened beams are analyzed. The reduction coefficient values of shear capacity under different dead load level are researched. The research is shown that: with the dead load level increasing, the improve degree of shear capacity of strengthened concrete beams is smaller. The mathematical model is established, which is about dead load level and reduction coefficient of shear capacity of strengthened concrete beams. The result is to take 0.75 as the reduction coefficient of shear capacity. The value is reasonable in calculating the shear bearing capacity of strengthened beams under dead load.