Anchorage Slip Research Articles

Bond-slip at anchorage under unidirectional and bidirectional seismic excitation: Search for an efficient mathematical model

Reinforcement anchorage slip can significantly contribute to the seismic response of bridge columns, especially to residual deformation. For a reliable numerical model of slip action, the present study evaluates three advanced models, each founded on distinct principles: (a) a macroscopic model (M−I), (b) a microscopic model (M−II), and (c) a mixed model that employed micro-model material properties derived from a macro-model (M−III). The performance of each model under unidirectional shaking has been first validated. The M−I cannot account for bidirectional loading, and as such, the performance of the M−II and M−III has, for the first time, been rigorously examined against the two-component shake table test results. Beginning with the simplified pulses, the responses of representative bridge columns are computed to unidirectional and bidirectional shaking for several near-fault motions. The M−I, M−II, and M−III are fairly similar in mimicking the slip action for unidirectional loading. Also, the M−II and M−III can closely represent the responses to bidirectional shaking. A simple extension of the M−I is proposed to capture the effects of bidirectional loading. The performance of the M−I (extended), M−II, and M−III are shown similar from the viewpoint of representing (i) the seismic fragilities, (ii) the uncertainties of the influential parameters, and (iii) the consequences of a sequence of motions. The detailed scrutiny of a range of models helps select the most appropriate scheme in a specific design context. On the other hand, the less-rigourous model, viz., M−I with the proposed extension, can be used within the limitations of commercial software and can prove useful in routine design for bidirectional seismic action.

Analytical study for prediction of stress distribution on orthodontic archwire considering short-term stress loss

This article proposes a method to predict the stress distributions on orthodontic archwires by considering the short-term stress losses. First, finite element (FE) analysis and numerical analysis using stress-loss formulations were performed. The FE models of the upper teeth and archwire were generated, and the initial stresses along the archwire were predicted from the FE model. The initial stresses on the wire were released in a relatively short amount of time due to shortening of the teeth, and slip and friction between the wire and brackets. Therefore, the formulations for the short-term stress losses were adopted from prestressed concrete design techniques and used to calculate the wire stress releases. To validate, loading tests and image processing were conducted, and the stresses were calculated from the deformations and curvatures of the loaded wire images. FE analyses without considering the stress losses predicted the stress distributions are unrealistically large; hence, including losses from elastic shortening, anchorage slip, and friction area could reduce the initial stresses by 16–34%. Comparing the average wire stress from FE analysis with image processing, a difference of only 0.82% was noted, which validates the method for predicting stress distribution using FE analysis and the method for stress loss calculations.

Shear behaviour of reinforced straw-bale plaster sheathed cold-formed steel-framed shear walls

The introduction of cold-formed thin-walled steel (CFS) framed systems into straw-bale construction is a new development construction. A CFS stud frame without blocking or strap-brace provides little in-plane shear stiffness, however it can provide lateral support for the thin and low-reinforcement sheathing through self-tapping screw anchorage, allowing the sheathing to subject to shear failure rather than buckling failure. Straw-bales with different thicknesses can satisfy different requirements for heat transfer and sound insulation. Since straw-bales are reliably bonded to the sheathing, the straw-bales can provide lateral support for the thin sheathing and can also effectively slow down the decline of the shear strength after the sheathing cracks. Moreover, the anchorage slip and the shear deformation of the sheathing material are the major factors affecting shear stiffness. The theory presented in this paper predicts the shear deformation response of the reinforced straw-bale plaster sheathed CFS framed shear wall specimen. The behaviour of the self-tapping screw anchorage was defined using power curve to predict the wall deformation due to anchorage slip. The deformation caused by shear in the sheathing material was estimated using refined softened truss model, which was based on the mechanical equilibrium condition, strain compatibility condition, and the constitutive relationship of softened cement mortar and mesh wire embedded in cement mortar. Comparing the theoretical results with the experimental data, the two were in good agreement. The shear strength of different configurations of reinforced straw-bale walls described in the literature were estimated, which proved the applicability of the theory. • Introduction of cold-formed thin-walled steel (CFS) framed system into straw-bale construction. • Estimation of the two major factors affecting the wall shear stiffness. • Validation of the predicted results according to experimental data. • Prediction for the shear strength of reinforced plaster straw-bale walls with different configurations.

Simple rebar anchorage slip macromodel considering corrosion

Reinforcement slip in the footing of a reinforced concrete (RC) column can significantly influence the lateral displacement of the column, a critical structural response under lateral loads such as seismic loading. Many past researchers studied and developed models to capture the anchorage slip of rebar; however, there is still a need for a model that can reflect the actual bond-slip relationship (especially in the presence of corrosion) and yet is simple-to-use for structural analysis. In this study, a simple bar stress-slip macromodel is developed to predict reinforcement anchorage slip given a rebar stress. The proposed rebar anchorage slip model is derived by implementing a macromodel solution based on a simple bond stress distribution function that captures the bond stress distribution numerically obtained from a real bond-slip relationship. Available experimental bond stress-slip data collected from literature are used to optimize the model parameter in the proposed bond stress distribution function, which reflects the impact of the structural parameters on the rebar slippage such as concrete strength and corrosion level. The proposed rebar slip model is then incorporated into a fiber beam-column model for numerical analysis, and is further validated by comparing flexural behavior of several RC columns (with and without corrosion) based on the numerical model with the experimental data. The results demonstrate the importance of incorporating rebar slippage and corrosion effect on bond. Using this fiber beam-column model, seismic performance of an example RC bridge column is evaluated, and one can conclude the rebar slip plays a critical role in the seismic evaluation. As the proposed rebar slip macromodel provides simple formulation and it is explicitly expressed with a model parameter that can be updated easily to incorporate new information, it is practical for structural analysis applications.

Cyclic behavior of bridge columns with partially unbonded seven-wire steel strands to increase post-yield stiffness

A new method of increasing post-yield stiffness of bridge columns to reduce the residual displacement after large earthquakes is proposed. In the proposed method, partially unbonded unstressed seven-wire steel strands are used as elastic element to increase the post-yield stiffness of the column. Three large-scale column specimens were tested using lateral cyclic loading to investigate the seismic performance of the proposed column. Test results showed that the use of the unstressed partially unbonded steel strands effectively increased the post-yield stiffness ratio of a conventional bridge column from −0.3% to 6.4%, which exceeded the 5% post-yield stiffness ratio that has been shown in the literature to reduce the residual displacement significantly. Test results also showed that the post-yield stiffness could not be maintained when the strands started to bulge in compression. The ultimate drift was slightly reduced from 5.76% to 4.77%. The use of fully bonded strands further increased the post-yield stiffness ratio to 8.8%. However, the ultimate drift ratio was greatly reduced to 2.84%. To predict the behavior of the proposed column under lateral load, a pushover model was developed. The strain of the partially unbonded strand was calculated based on deformation compatibly with the longitudinal deformed steel bar. The effect of anchorage slip was considered. Comparison with the test results showed that the proposed model captured well the envelope response of the proposed column.

Analysis of Short-Term Prestress Losses in Post-tensioned Structures Using Smart Strands

The proper estimation of prestressing force (PF) distribution is critical to ensure the safety and serviceability of prestressed concrete (PSC) structures. Although the PF distribution can be theoretically calculated based on certain predictive equations, the resulting accuracy of the theoretical PF needs to be further validated by comparison with reliable test data. Therefore, a Smart Strand with fiber optic sensors embedded in a core wire was developed and applied to a full-scale specimen and two long-span PSC girder bridges in this study. The variation in PF distribution during tensioning and anchoring was measured using the Smart Strand and was analyzed by comparison with the theoretical distribution calculated using the predictive equations for short-term prestress losses. In particular, the provisions for anchorage seating loss and elastic shortening loss were reviewed and possible improvements were proposed. A new method to estimate the amount of anchorage slip based on real PF distributions revealed that the general assumption of 3–6-mm slip falls within a reasonable range. Finally, the sensitivity of the PF distribution to a few of the variables included in the equation of the elastic shortening loss was examined. The study results confirmed that the developed Smart Strand can be used to improve the design parameters or equations in PSC structures by overcoming the drawbacks of conventional sensing technologies.

Analysis and Design of Fly Over

Bridges remain the key components in any road network for infrastructure development. For use of prestress girder type bridges become popular for the reason that of its stability, economy, serviceability, aesthetic appearance and structural competence. The grillage analysis method for analysing bridge structures has been in use. In this work, an attempt is made to provide advise on grillage idealisation of the structure, as well as background information. The mesh layout is explained in detail. Analysis of proposal of prestressed concrete bridges are carried out using relevant IRC codes and IS codes. The bridge deck is analysed by grillage analysis. The present work was accepted out to exterior girder of span 28.2 m, width 12.5 m and with thickness of slab as 0.225m. The members are designed for maximum shear forces & bending moment. Losses of stress due to friction, anchorage slip, elastic shortening concrete & relaxation of stress in steel are also considered. The analysis has analysed by STAAD PRO software

Strain penetration effect on cyclic response of corroded RC columns

The anchorage slip of longitudinal reinforcement in the foundation (also called strain penetration effect) may affect the cyclic behavior of RC columns by inducing fixed-end rotations. This strain penetration effect could become more significant under reinforcement corrosion, which frequently occurs in RC structures exposed to the attack of aggressive agents such as chlorides. It is hence important to take corrosion effects into account in the modeling of strain penetration phenomena. This paper presents a modification of an existing stress versus slip hysteretic model for reinforcing steels to incorporate corrosion effects. Results of both pull-out tests of deformed steel bars and quasi-static tests of corroded RC columns are adopted for validation. Moreover, a parametric investigation is carried out to demonstrate the impact of structural parameters and corrosion levels on the cyclic response of corroded RC columns considering the strain penetration effect. The results highlight that the modified hysteretic model can efficiently simulate the anchorage slip. In addition, it is found that the strain penetration effect tends to be more significant for the RC columns with higher corrosion level, smaller aspect ratio, larger longitudinal reinforcement ratio, or lower axial load ratio.

Modeling the lateral behavior of freeze-thaw damaged reinforced concrete columns including reinforcement slip and shear effects

This paper focuses on modeling the lateral load-deformation response of reinforced concrete columns subjected to freeze-thaw cycles (FTCs). Freeze-thaw effects are accounted for by means of a non-uniform reduction in concrete strength and bond deterioration between the steel and concrete. The new column response model that is proposed includes deformations due to flexure, reinforcement slip, and shear effects, and the influence of freeze-thaw effects on each of these aspects. The slip displacement is formulated and solved using governing equations among four bond fields. The moment-rotation relationship is then developed and introduced into the zero-length spring element to compromise the rotations caused by reinforcement anchorage slip and by curvatures over the column height. A shear spring element is used in series to represent the shear backbone curve and to capture the onset of shear failure. The proposed model is validated using experimental data on freeze-thaw damaged columns with a wide range of typical design parameters. Overall, the proposed column model accurately simulates the cyclic behavior of both flexure and flexure-shear columns that experience freeze-thaw cycles.

Behaviour of BFRP tendon systems under cyclic loading and its influence on the dual-tube SC-BRB hysteretic performance

Basalt fibre-reinforced polymer (BFRP) is an excellent pretensioned tendon material due to its high elongation, and it has been used in the self-centering buckling-restrained brace (SC-BRB). During previous experiments on SC-BRBs, although the BFRP tendon did not cause anchorage slip failure, pretension loss occurred. To determine the cause of the pretension loss, in this paper, cyclic tensile tests were conducted on multiple sets of BFRP tendon systems. Based on the experimental results, the pretension loss of the SC-BRB was due to the deformation of the colloid in the anchor under cyclic loading, and the regression formula of the colloidal deformation of the anchor was established. According to the results of a quasi-static experiment on a SC-BRB, the BFRP tendon can provide a reliable self-centering restoring force for the brace, and the accuracy of estimating the pretension loss based on the regression formula is demonstrated. Finally, a rheological model that can accurately describe the hysteresis performance of the SC-BRB and consider the pretension loss is established. Based on this model, the influence of the pretension loss on the brace performance is studied.

Extended Tension Chord Model for Boundary Elements of RC Walls Accounting for Anchorage Slip and Lap Splices Presence

This paper presents a mechanical model for the simulation of reinforced concrete (RC) wall boundary elements with lap splices, which builds on the tension chord model. The model is composed of an assembly of components, each one accounting for a different source of deformation. Namely: (i) an anchorage-slip element accounting for the strain penetration of the longitudinal reinforcement into the foundation; (ii) a basic tension chord element evaluating the response outside the lap splice zone; and (iii) a lap splice element describing the behaviour within the lap splice region. For an imposed global displacement, the model provides the steel and concrete stress and strain distributions, the crack distribution and opening, as well as the global resisting axial force. For spliced members, the ultimate displacement is computed through a semi-empirical relationship providing the average lap splice strain at failure. Validation is carried out against a series of uniaxial cyclic tests on RC wall boundary elements featuring both continuous and spliced reinforcement; different lap splice lengths and confining reinforcement are considered. Overall, a good match is obtained between numerical and experimental results in terms of crack width, rebar strain distribution along the splices and ultimate displacement.

Test and numerical simulation of failure mechanism of barrel and wedge anchorage in coal mines

This paper aims at analyzing the slip mechanism of barrel and wedge anchorage in dynamic soft roadway. We conducted static load tests of the strand-anchorage assembly on YJJ5000A static loading test system, and the results show that YJM18-1 anchorages fully meet the requirements of specification, so common factors such as anchorage quality could not explain the reasons for anchorage slip. In this paper, the slip mechanism of barrel and wedge anchorage is analyzed from two aspects: anchorage corrosion and stress disturbance. On the one hand, the roadway deformation increases rapidly under the influence of stress disturbance, the axial force of anchor cable increases sharply to control roadway deformation, on the other hand, anchorage corrosion causes the friction angle between wedge and barrel increase and the friction force between wedge and strand decreases, so under the combined effect of stress disturbance and anchorage corrosion, the slip of anchorages is easy to occur. Based on this, new anti-slip anchorage which combine extrusion anchor with screw anchor together were adopted. The field test shows that the roadway basically stabilized after repairing one month, the roof to floor deformation was reduced from 280 mm to 125 mm compared with the original support scheme, and none of the anchorages slip. These findings can make a significant contribution to prevention of roof accident in coal mining industry.

Reinforcement slip model considering corrosion effects

A new bar slip model is developed to account for the contribution of reinforcement anchorage slip to the total displacement of corroded reinforced concrete (RC) members. An analytical procedure is proposed to model the distribution of the reduced bond stress along the corroded steel bar to predict the reinforcement slip in the anchorage area. The reinforcement slip is formulated using an existing model and by new governing equations defined for different bond regions. The possibility of having an insufficient embedment length is also considered, and a corresponding failure criterion is defined. The bar model is validated by comparing the available data from single bar pullout experiments and an existing bar force-slip model. The proposed column model is implemented using a fiber element model to capture both the monotonic and cyclic behavior of corroded columns. Pseudo-static test data from corroded column specimens are used to validate the proposed column model. Overall, the proposed model captures the slip of a single corroded bar reasonably well to accurately simulate the total lateral displacement of columns with corrosion damage.

Load Carrying and Hydrostatic Performances of Innovative Encapsulated Anchorage System for Unbonded Single Strand

A new anchorage system is proposed having a circular bearing plate and curvature between the bearing plate and the anchor head to improve stress concentration. A lid with a screw instead of the grouting method is also proposed to prevent moisture penetration. The details of the anchorage device have been chosen to reduce stress concentration based on the finite element analysis. Static load test, load transfer test, and hydrostatic test of fabricated devices were carried out according to ETAG 013 to evaluate the proposed design. As results, the anchorage slip and stabilization satisfied the recommendations of ETAG 013. The maximum load in the load transfer test was at least 1.1 times the ultimate tendon strength. The results of the hydrostatic test showed that the developed anchorage device is watertight to protect against corrosion. As a result of bursting force test, it was confirmed that the proposed anchorage device has more advantages than the conventional rectangular anchorage devices in terms of stress distribution.

Finite element modelling approach for precast reinforced concrete beam-to-column connections under cyclic loading

In this paper, a finite element modelling approach is developed for the analysis of the cyclic behavior of precast beam-to-column connections. In particular, the modelling takes into account the compression-softening of concrete, the bond-slip effect in the critical regions and the representation of the post-cast concrete interface. A newly developed softened damage-plasticity model, which can reproduce the typical cyclic behavior of reinforced concrete, is adopted for concrete. Meanwhile, to reflect the significant bond-slip effect between concrete and reinforcement bars, the M-P stress-strain model is modified to account for the slippage by assuming the bar strain is the sum of the bar deformation and the slip, while the anchorage slip is theoretically derived and validated through benchmarking the pull-out tests. Additionally, a concrete layer between the precast concrete and the cast-in-situ concrete is incorporated to reflect the features of the interface. The proposed numerical modelling approach is validated through simulation of both interior and exterior precast beam-to-column connection tests. The validated models are subsequently employed to investigate the influences of key factors such as the compression-softening and the bond-slip effect on the analysis of the cyclic behavior of the precast beam-to-column connections. Results demonstrate that the proposed model is capable of reproducing the typical behavior of precast beam-to-column connections and can serve as an effective tool for the seismic performance analysis and investigation of design parameters of precast connections.

Evaluation of nonlinear behavior and resisting capacity of reinforced concrete columns subjected to blast loads

Abstract A numerical method to estimate the dynamic response of reinforced concrete (RC) columns subjected to axial and blast loads is introduced in this paper. Upon adopting Timoshenko's beam theory, both the flexural and direct shear behaviors are incorporated into the numerical formulation. The moment-curvature relationship of a reinforced concrete (RC) section is based on the construction of the bending stiffness and, in advance, a dynamic increase factor (DIF), usually defined in the stress-strain relations of concrete and steel, is newly designed to be defined in the moment-curvature relation. In addition to the description of the dynamic characteristics in the RC section, additional modification of the moment-curvature relation is also performed to exactly simulate the large plastic deformation concentrated at the mid-span or beam-column joint due to the bond-slip or anchorage slip after yielding of the main reinforcement. Finally, the validity of the proposed method is verified by comparing the analytical results with the experimental data, and then the pressure-impulse (P–I) diagrams are constructed and compared to review the change in the resisting capacity of a RC column according to the variation of the axial force and slenderness ratio.

An efficient fiber beam-column element considering flexure–shear interaction and anchorage bond-slip effect for cyclic analysis of RC structures

In this paper, a fiber beam-column element considering flexure–shear interaction and bond-slip effect is developed for cyclic analysis of reinforced concrete (RC) structures. The element is based on conventional displacement-based Timoshenko beam theory, where the transverse shear deformation is included, and adopts the fiber model to describe the section force–deformation behavior. In the fiber model, shear deformation is assumed to be uniformly distributed along the section and is only resisted by concrete, thus the multi-dimensional concrete damage model is used for concrete fibers and therefore flexure–shear interaction is reflected naturally at the material level. Meanwhile, to account for the significant bond-slip effect at critical regions, the anchorage slip of bars at these regions is analytically derived. Then it is used to modify the uniaxial stress–strain model for steel fibers by assuming that the total strain can be treated as the sum of the bar deformation and anchorage slip, therefore the bond-slip effect is implicitly but simply represented. To validate the proposed element, a series of RC member and structure tests under cyclic loading are simulated. The results indicate that the proposed element can predict cyclic responses of RC structures, and can be used as a reliable tool for analysis of RC structures.

Rebar Anchorage Slip Macromodel Considering Bond Stress Distribution: Monotonic Loading and Model Application

AbstractThis study presents a modified macromodel for calculating the anchorage slip of rebar under monotonic loading and its application to the fiber beam–column element model. The proposed macrom...

SOME ADVANCES IN CONVENTIONAL FIBER BEAM-COLUMN MODEL

The fiber beam-column model, which is an important milestone in the development of simulation technique for structural systems, has been widely used in recent years with its simplicity, efficiency and generality. However, the poor simulation results in many key issues of the structural system using the model cannot be avoided due to the limitation of the basic assumptions of the model. This paper thoroughly reviews the research group's 7-years' efforts and progress in improving the conventional fiber beam-column model to solve several critical problems in structural simulation. Firstly the conventional fiber beam-column model is developed on the platform of general finite element software MSC.Marc and further expanded to the simulation of steel-concrete composite frames. Then four new fiber beam-column models are proposed to give satisfactory prediction results to four key issues in structural simulation including the slab spatial composite effects in composite frames, the nonlinear shear and sliding effects of coupling beams, the rebar anchorage slip in the footings and the whole-process cracking behavior of RC beam and columns, respectively. These models are proved to completely keep the advantages of conventional fiber beam-column models and accurately consider the above complicated effects, according to the verifications by numerous test data and elaborate finite element analysis. Based on the proposed models, a nonlinear analysis program COMPONA-MARC is developed for commonly used structural systems such as RC, steel and steel-composite structures, which provides a powerful platform and tool for elaborate nonlinear structural simulations.

Estimation of Tendon Force Distribution in Prestressed Concrete Girders Using Smart Strand

The recently developed smart strand offers the possibility of measuring the prestress force of the tendon from jacking and all along its service life. In the present study, a method estimating the force distribution in all the tendons of a prestressed concrete (PSC) girder installed with one smart strand is proposed. The force distribution in the prestressed tendons is formulated by the friction and the anchorage slip, and is obtained through an optimization process with respect to the compatibility conditions and equilibrium of the forces in the section of the PSC girder. The validation of the proposed method through a numerical example and experiment shows that it can be used to estimate the force developed in the tendon.