Partially Prestressed Concrete Research Articles

Plasticity model for partially prestressed concrete

Recently, the partially prestressed concrete (PPC) has been widely used as an effective construction technique for structures to reduce yielding and damages. However, there is no proper analytical model for PPC frame elements (beam-column members) to perform the finite element analysis. Besides, an extensive review of the literature uncovered little available information about the possibility of identifying damage to PPC members during applied vibration loads such as earthquake excitation. Hence, this paper presents the development of a new 3D analytical model for PPC beam-column element subjected to static and dynamic loads. In addition, a theory of plasticity and yielding surfaces for PPC frame elements are formulated in order to detect damage and determine the location of plastic hinges in the structural components under dynamic load. The developed analytical and plasticity models were codified and implemented in a finite element program in order to perform inelastic static and dynamic analysis for PPC structures. Then, sample PPC beam and frame members were cast and tested experimentally for flexural and incremental loading, respectively, to verify the developed analytical and plasticity model for PPC. The results show a good agreement between the analytical model and numerical analysis and the experimental test results. In addition, a comparison of the seismic response of reinforced concrete (RC) and PPC structures indicated that the stiffness and energy dissipation capacity of the structure with PPC members improved noticeably and the total number of plastic hinge formations in the structural members decreased.

Shear crack pattern identification in concrete elements via distributed optical fibre grid

An experimental methodology to obtain the shear cracking pattern in concrete elements is presented. The method is based on the use of Distributed Optical Fibre Sensors (DOFS) connected to an Optical Backscattered Reflectometer (OBR). Using this OBR system and a 2D grid conformed by one or two DOFS, the crack patterns of three partially pre-stressed concrete (PPC) beams subjected experimentally to shear failure, were obtained for increasing level of load. The 2D distributed fibre optic sensoring mesh was formed by attaching the fibre to the shear span of each beam using an epoxy adhesive. The importance of a correct DOFS bonding procedure to the concrete surface to obtain accurate results is described, and the principal advantages of DOFS to complement the use of discrete sensors in concrete experimental shear tests are shown. The proposed technique is a powerful tool to be implemented in the structural health monitoring in shear of concrete structures, where the variable inclined cracks are difficult to monitor by other experimental techniques using discrete sensors.

Shear crack width assessment in concrete structures by 2D distributed optical fiber

This paper outlines the second part of an experimental study to show the capabilities of distributed optical fiber sensors (DOFS) in their application to the structural health monitoring (SHM) of the shear performance of concrete structures. SHM seeks to obtain the shear crack characteristics of concrete elements: detection, localization and quantification of shear damage. The two first were discussed in the first part of the experimental study. In the present paper, the quantification is dealt with by proposing a method to obtain the mean shear crack width in concrete beams. The method is based on the experimental data obtained by a DOFS bonded to the concrete surface. First, the basis of the methodology are presented and, later on, experimentally checked by testing of three partially pre-stressed concrete (PPC) beams subjected to a shear test with increasing level of load. The DOFS were deployed in the web of the beams to conform a 2D grid mesh to measure the strain profile along two orthogonal directions. The experimental data was obtained using an OBR (Optical Backscattered Reflectometer) system with high spatial resolution and sensitivity that allow a complete mapping of the cracking pattern and to obtain the required data for the calculation of the crack width. The results show the feasibility of the proposed method in calculating the shear crack width when compared to the results from traditional instrumentation.

Fatigue and post-fatigue monotonic behaviour of partially prestressed concrete beams

The objective of this work was to study the fatigue and post-fatigue monotonic behaviour of partially prestressed concrete (PPC) beams with a high degree of prestress. Eleven large PPC beams were tested under fatigue and monotonic loading. The effects of applied load level and severity of fatigue damage on the beams' fatigue and post-fatigue monotonic behaviour were studied and analysed. The results indicated that the fatigue behaviour of beams with a high degree of prestress was dependent on the applied load level. For an optimum and safe design, the applied load level should be less than 1·28 times the cracking load, the maximum crack width should be limited to 0·20 mm and the initial maximum stress range of non-prestressed reinforcing bars before repeated loading should be less than 170 MPa. The post-fatigue monotonic behaviour of beams was related to the severity of fatigue damage prior to the monotonic test. Low fatigue damage was found to have only a slight impact on the monotonic behaviour of the beams, whereas medium and high fatigue damage respectively reduced the ultimate strength by up to 15·2% and 18·0% and increased the deformability ductility index by up to 18·6% and 41·0%.

Residual strain analysis of non-prestressed reinforcement in PPC beams under fatigue loading

This paper presents the results of an experimental and analytical study on the residual strain behavior of non-prestressed reinforcement in partially prestressed concrete (PPC) beams under fatigue loading. For the strain measurements, fiber Bragg grating sensors were used. Two beams were initially tested under monotonic loading in order to determine their ultimate load-bearing capacity. Six were tested under fatigue loading conditions. The experimental results show that fatigue failure mode of PPC beams is fracture of the non-prestressed reinforcement. Moreover, residual strain in the non-prestressed reinforcement gradually increases during the fatigue life and the corresponding residual strain evolution can be divided into three stages. Finally, an analytical model for estimating the residual strain of non-prestressed reinforcement in beams is developed. Comparisons of the predicted curves with the experimental data indicate a good agreement. The results of investigation in this paper furnish the experimental basis for the fatigue design and analysis of PPC beams.

Steel Stress Redistribution and Fatigue Life Estimation of Partially Prestressed Concrete Beams under Fatigue Loading

The objective of this paper is to investigate the steel stress/strain variation and redistribution in partially prestressed concrete (PPC) post-tensioned T-beams with bonded tendons under various ranges of fatigue loading by using an embedded Fiber Bragg Grating (FBG) sensor. A total number of six beams were tested to failure under fatigue loading, and two control beams were tested for determing the monotonic bearing capacity. Test results indicated that the initial fatigue failure of all beams was caused by fatigue fracture of the non-prestressed reinforcement rather than failure of the prestressing strands. Based on the strain recorded, the development trends of non-prestressed steel strain and the ratio of strain range between prestressed and non-prestressed reinforcement during fatigue loading were described. Moreover, an analytical model for fatigue life prediction of partially prestressed concrete beams by using the sectional analysis and local strain-life method was developed. Good agreement between analytical and experimental results for fatigue life of PPC beams is observed.

Investigating the use of high performance concrete in partially prestressed beams and optimization of partially prestressed ratio

The main objective of this study is to investigate the behaviour of partially prestressed concrete (PPC) beams subjected to pure flexure. The test beams were produced using both high performance concrete (HPC) and traditional concrete (TC). Test beams were compared with each other for strength, strain and cracking cases. The comparison was done by theoretical and experimental methods. Test measurements included failure loads, deflections, strains in concrete and steels, failure moments and service moments, experimental safety coefficients, number of cracks, crack widths, curvatures. Thus, optimum partially prestress ratio was determined for HPC and TC. Advantages of using HPC in partially prestressed beams were brought out. According to the results of the study, optimum partially prestress ratio for PPC beams produced using traditional concrete is ~ 60%; while it is ~ 70% when HPC is used. The test results are shown that the usage of HPC in PPC beams is more convenient than the TC under some boundaries and conditions.

Investigating the use of high performance concrete in partially prestressed beams and optimization of partially prestressed ratio

The main objective of this study is to investigate the behaviour of partially prestressed concrete (PPC) beams subjected to pure flexure. The test beams were produced using both high performance concrete (HPC) and traditional concrete (TC). Test beams were compared with each other for strength, strain and cracking cases. The comparison was done by theoretical and experimental methods. Test measurements included failure loads, deflections, strains in concrete and steels, failure moments and service moments, experimental safety coefficients, number of cracks, crack widths, curvatures. Thus, optimum partially prestress ratio was determined for HPC and TC. Advantages of using HPC in partially prestressed beams were brought out. According to the results of the study, optimum partially prestress ratio for PPC beams produced using traditional concrete is ~ 60%; while it is ~ 70% when HPC is used. The test results are shown that the usage of HPC in PPC beams is more convenient than the TC under some boundaries and conditions.

Experimental Study on Anti-Impact Properties of Prestressed Concrete Beams

The dynamic displacement ductility and ultimate load-carrying capability of three partially prestressed concrete (PPC) and unbonded beams, has been experimentally investigated by applying impact load to their middle with falling hammers. The typical measurement wave curves are described. Influences of a falling hammer’s gravitational potential energy on the dynamic properties of the PPC beam are analyzed. Based on the analog simulation theory, the impact-load carrying capability of the actual unbonded PPC beam with span 12 m is gained. Results indicate that the unbonded PPC beams have favorable performance of anti-impact properties fragile destruction will not happen, and the unbonded PPC beams can be used in wide-span underground structures.

Experimental study on anti-impact properties of a partially prestressed concrete beam

The dynamic displacement ductility and ultimate load-carrying capability of three partially-prestressed concrete (PPC) beams which were unbonded, were experimentally obtained by applying impact load to their middle with dropping hammers, and the typical measurement wave curves were given. Influences of a dropping hammers gravitational potential energy on the dynamic properties of the PPC beam were analyzed. Based on the analog simulation theory, the impact-load-carrying capability of the real unbonded PPC beam with span 12 m was gained. Results show that the unbonded PPC beams anti-impact properties are good, the fragile destruction will not happen, and the unbonded PPC beams can be used in wide-span underground structures.

Residual Displacements of Concrete Bridge Piers Subjected to Near Field Earthquakes

This research sought a solution to reduce residual displacements of reinforced concrete (RC) bridge piers after earthquake excitations. Because prestressed concrete (PC) members normally show recovery from elastic stiffness during unloading, this work proposes the possibility of using PC to minimize the residual displacements. However, prestressed members will have reduced ductility. Therefore, a new technique that employs partially prestressed concrete (PPC) for the bridge piers is examined in order to take advantage of the positive features of both RC and PC. An extensive experimental program, using reversed cyclic loading and pseudo-dynamic tests, was conducted. The experimental variables included the relative ratio of prestressing tendons to non-prestressing reinforcement and flexural to shear capacities. Based on test results, the inelastic response behavior of PPC bridge piers was substantially clarified. The advantages and disadvantages of their use were clearly identified. The study revealed that employing prestressing tendons in RC bridge piers could result in subsequent reductions of residual displacements, restrain associated cracking, and enhanced concrete shear strength after earthquake excitations.

プレストレスト鉄筋コンクリート曲げ部材におけるひび割れ幅と仮想引張応力度との関係

The estimation of crack width is one of the most important tasks in designing partially prestressed concrete (PPC) members. However, this task, which includes calculation of crack spacing, average steel stress etc., is very tedious using current existing procedures. In this paper, relationship between crack width and hypothetical tensile stress was derived in order to simplify control of crack width in reinforced conctrete and PPC members. The hypothetical tensile stress is calculated on the assumption that the entire section is still effective even after cracking has occurred. The instantaneous and long-term crack widths are calculated by using the PPC Recommendation of Architectural Institute of Japan. Factors which had been taken into account in developing procedure of this method are: concrete strength, ratio of reinforcement, depth of beam, concrete cover depth, prestress, shrinkage and creep.

Minimum cost design of multispan partially prestressed concrete T-beams using DCOC

A previous study on the minimum cost design of multispan partially prestressed concrete (PPC) beams using DCOC is extended to multispan T-beams. The cost of construction which includes the costs of concrete, prestressing steel, nonprestressing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the Australian Code AS 3600. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, eccentricity of prestressing steel and non-prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. The self-weight of the structure is included in the equilibrium equation of the real system, as is the secondary effect resulting from the prestressing force. An iterative procedure for updating the design variables is outlined. Two numerical examples of multispan PPC beams with T crosssection are solved to show the applicability and efficiency of the DCOC-based technique.

Flexural Ductility of Structural Concrete Sections

This paper investigates in detail the flexural ductility of structural concrete section, i.e., reinforced concrete (RC), prestressed concrete (PC), and partially prestressed concrete (PPC) sections. Flexural ductility is defined sas the ratio of the section ultimate and yield curvatures. Realistic, rather than conventional, standard estimates are attempted on the basis of actual material behavior states, and unified analysis of structural concrete sections. The effects of section shape, degree of prestressing, material laws, compression reinforcement, and other parameters are considered. Finally, some ACI Code revisions are proposed.

コンクリート梁部材断面の曲げ終局限界点に関する研究 : (その2)終局限界点特性値の算定式の誘導

In the previous paper (Part 1), ultimate limit index points of partially prestressed concrete (PPC) beams are proposed, which relate to ultimate failure of concrete in flexural compression zones, fracture of tensile reinforcement and buckling of compressive reinforcement. Usefulness of the points are shown in evaluating the deformation capacity taking into account for falling behavior of moment-curvature relations of concrete flexural members. This paper describes on derivation of equations to calculate extreme fiber strains, flexural resistance moments and curvatures at the proposed ultimate limit index points of sections of concrete flexural members from prestressed concrete section to reinforced concrete one. The transition of ultimate failure modes and equations to calculate those limit index points of PPC flexural sections with the change of amount of reinforcement index is investigated, and wideness of applicable range and simpleness of the derived equations to calculate the points of ordinary PPC flexural sections are shown.