Determination of bond model for 7-wire strands in pretensioned concrete beam (original) (raw)
Related papers
Finite Element Bond Models for Seven-Wire Prestressing Strands in Concrete Crossties
2015 Joint Rail Conference, 2015
Seven-wire strands are commonly used in pretensioned concrete ties, but its bonding mechanism with concrete needs further examination to provide a better understanding of some concrete tie failure modes. As a key component in the finite element (FE) analysis of concrete crossties, macro-scale or phenomenological FE bond models are developed for sevenwire strands in this paper. The strand-concrete interfaces are homogenized with a thin layer of cohesive elements applied between the strand and concrete elements. Further, the cohesive elements are assigned traction-displacement constitutive or bond relations that are defined in terms of normal and shear stresses versus interfacial dilation and slip. The bond relations are developed within an elasto-plastic framework that characterizes the adhesive, frictional and/or dilatational bonding mechanisms in the interface. The yield functions and plastic flow rules specific for the seven-wire strands are presented. The bond parameters are calibrated from untensioned pullout tests and pretensioned prism tests conducted on concrete specimens. The bond models are then verified with (1) the surface strain data measured on actual concrete crossties made at a tie manufacturing plant, and (2) the force-displacement relation obtained in a center negative moment test conducted also on concrete crossties.
2015
This work presents an interactive graphics computational tool for the verification of prestressed concrete beams with post-tensioned bonded tendons to the serviceability limit state (SLS) stress check according to the Brazilian code NBR 6118. The software Autodesk Robot Structural Analysis Professional® is adopted as a structural modeling platform. With data supplied by the user through a graphics user interface, the program calculates the prestressing’s equivalent load considering all relevant prestress losses that occur throughout the structure's life-cycle. In order to adopt an incremental method for the calculation of the differed losses, modifications had to be done to the equations given in the NBR 6118. Examples and results are also presented, validating the adopted methodology. At the end of the software's calculation, the user receives two outputs: the prestress’ equivalent loads in the Robot model and a spreadsheet. The equivalent loads may be used in other calcula...
Structures Congress 2014, 2014
Pretensioned concrete ties are increasingly employed in railroad high speed and heavy haul applications. The bond between prestressing wires or strands and concrete plays an important role in determining the transfer length of pretensioned concrete members, but little research was done to characterize the transfer length in terms of steel reinforcement and concrete factors for railroad concrete ties. Federal Railroad Administration is sponsoring a comprehensive test program at Kansas State University (KSU) aimed at quantitatively correlating prestressing steel and concrete variables with the transfer length of pretensioned concrete crossties, and Volpe Center has been applying the data obtained in the KSU test program to develop bond models that can be used in transfer length prediction and failure analysis of concrete ties. This paper describes finite element (FE) model development related to the smooth prestressing wire whose dominant bonding mechanisms with concrete are chemical adhesion and friction. The commercial FE software Abaqus is employed, and the steel-concrete interface is discretized with cohesive elements. A user bond model is developed within the elastoplastic framework and implemented for axisymmetric and 3D cohesive elements. The bond model defines constitutive relations in terms of normal and shear stresses vs. interfacial dilation and slips. The bond behavior is initially linear elastic, followed by adhesion and friction that are governed by a yield function and a plastic flow rule specific for the smooth wireconcrete interface. The main bond material parameters are normal and shear elastic stiffness, initial adhesive strength, plastic slip at which adhesion first breaks completely, and coefficient of friction. Except for the coefficient of friction, which is determined with reference to the open literature, the bond parameters are calibrated from untensioned pullout tests and pretensioned prism tests conducted at KSU. The calibrated bond parameters exhibit a dependence on the nominal compressive strength of concrete at the time of pretension release. Because considerable concrete creeping has been observed in the periods between pretension release and concrete strain measurement in the test program, an additional concrete material parameter, basic creep compliance, can be calculated and applied to adjust the concrete surface strain data. The user bond model is then validated with transfer length data measured on actual concrete crossties made with a smooth prestressing wire in a tie manufacturing plant.
Bond and anchorage of pre-tensioning tendons
2017
Pre-tensioning is a type of prestressed concrete and is commonly used in precast construction. In pre-tensioning, the bond anchorage between the prestressing tendons and the concrete is of great significance. The bond mechanisms of the anchorage are complex and depend on various influencing factors. To consider the mechanisms in the design process, a sophisticated design model is required. The current codes contain design models for pre-tensioniong anchorage; however, they have some deficiencies. For this reason, theoretical and experimental investigations on different aspects of pre-tensioning anchorage were conducted. Finally, the results were used to derive an enhanced design model for pre-tensioning anchorage. The first part of this work summarizes the state of the art on pre-tensioning anchorage. The bond mechanisms of pre-tensioning anchorage and the relevant design models are presented. In addition, an overview of testing setups for the investigation of pre-tensioning anchora...
Journal of Materials and Engineering Structures « JMES », 2020
The objective of this paper is to investigate the bond properties of prestressing strands embedded in Ultra-High-Performance Concrete (UHPC).The UHPC was made in laboratory using local materials in Vietnam.Its mixture contains: silica aggregates, portland cement PC40, fly ash, silica fume, polycarboxylate superplasticizer and the micro steel fibers.The experimental process is realized on a pull-out test. The volume fraction of micro steel fibers in UHPC was 2%. The prestressing strand with diameters of 15.2mm was considered. The interface shear strength between strand and UHPC is identified based on the results of force and displacement obtained during the pull-out test. The Cohesive Zone Model (CZM) is implemented in finite element model to study this interface behavior. This model described by a piecewise linear elastic law. The CZM's parameters are identified based on experimental results of pull-out test.The numerical studies are used the CZM in ANSYS software. Two numerical tests are realized and compared with experimental results: pull-out test and other test to verify the deflection of I girder due to prestressing force.
Analysing the Route of PCI Girder-Type Prestressed Concrete Tendons
International Journal of Science and Research (IJSR)
This paper will analyse the middle span of the 31m-in-length bridge. The calculation stages undertaken here were to design the form and dimensions using PCI Girder-Type Prestressed Concrete, to determine the prestress force, eccentricity as well as the number of tendons and routes of each cable; and to calculate the resulting stress of the beam cross-section and the resulting loss of prestress forces. There were 4 tendons of prestressed cables for the PCI Girder design, each of which consisted of 19 high quality wires, i.e. uncoated 7 Wire Super Strands ASTM A-416 grade 270 with the cross-section equal to 12.7 mm in width and the ultimate tensile stress by1,860 Mpa, with a total of 76 strands. The tendon tensioning system implemented was the post-tensioning one where the prestress force was given when the concrete has already achieved the required age. The Bridge of Meureudu City experienced a total prestressed loss by 26.32%. The tendon route was parabolic with the greatest moments by 7,556.75 kNm derived from a combination of its own weight, additional dead loads, lane loads, the brake force and wind loads.
The purpose of this research is to establish mathematical models that predicts the bond strength of a reinforcement wire in prestressed concrete members, given the known geometrical features of the wire. A total of nineteen geometrical features of the reinforcement wire were measured and extracted by a precision non-contact profilometer. With these mathematical models, prestressing reinforcement wires can now be analyzed for their bond strength without destructive testing. These mathematical models, based upon a large collection of empirical data via prestressing reinforcement wires from various wire manufacturers in US and Europe, have the potential to serve as quality assessment tools in reinforcement wire and prestressed concrete member production. Most of these models are very simple and easy to implement in practice, which could provide insight into which reinforcement wires provide the greatest bond strength and which combinations of geometrical features of the reinforcement wire are responsible for providing the bond strength.
Engineering Structures
An innovative strategy for the analysis and design of the anchorage zones of pre-tensioned, concrete girders is presented. In this approach, the bond behaviour of the prestress strands is first characterised in a small-sized beam model. A new relation between the slip and radial strain of the prestress strand is introduced and used together with the radial stress-strain relation resulting from a thick-walled cylinder model to establish the bond-slip behaviour at the steel-concrete interface. This bond behaviour is implemented in a numerical model and validated via a comparison of the computed transfer length with the results of two experimental campaigns. Next, the bond-slip relation of the small-scale model is applied in full-scale models of pre-tensioned, concrete girders to derive the stress distribution in the anchorage zones. The non-linear material behaviour of concrete is taken into account and a comparison of the numerical results with full-scale experimental data is made. An acceptable agreement is achieved between the experimental results and the numerical calculations regarding the bond behaviour and transfer lengths as well as the crack patterns and the stress values in the reinforcement bars. This efficient modelling approach allows for a full analysis of the anchorage zone based solely on the geometrical and material properties known at the design stage.
Effects of Debonded Strands on the Production and Performance of Prestressed Concrete Beams
2011
Strand debonding is a common approach used to reduce cracking at the ends of pre-tensioned concrete beams. While the method has been successful to some extent, end cracking of pre-tensioned beam ends continues to be a problem. Experimental and numerical approaches were conducted in this study in order to achieve a further understanding of strand debonding. Twenty-four small-scale prestressed concrete beam units were tested and used for the calibration of nonlinear finite element models simulating concrete-strand bond behavior, while three models of AASHTO box girders were established to investigate an incident of end cracking encountered in the manufacturing of a bridge girder. The numerical simulations were in good agreement with the experiment data and damage evidence on prestressed girders production indicating that the lack of bonding will maximize the dilation of strand after release in the debonded region and that such dilation may cause concrete damage in the debonded region ...