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In pretensioned prestressed concrete elements, bond between reinforcement and concrete differs is fundamental for a safe design. The so-called Hoyer effect, produced by the lateral expansion of a material when subjected to load, increases the bond resistance, but it also increases the circumferential stresses and then, the risk of cracking due to the tendon expansion. The bond behaviour of FRP tendons has not been studied in depth. To study the bond performance of FRP tendons, and characterize the transfer and flexural development length, an experimental program was carried out. This program was based on a setup called ECADA developed for steel tendons by the Universidad Politécnica de Valencia. The test specimen represents the anchorage area of the tendon and the remaining part of the theoretical beam is substituted by an anchorage measurement access system that has the same rigidity of the replaced part. The test starts by prestressing from one side and after concreting, the prestressed force is released gradually, then the transfer length is measured. Afterwards, the tendon is pulled from the other side, and the total development length is determined iteratively by producing samples of different lengths. The results of the ECADA tests have indicated that the transfer lengths of the FRP tendons being studied lie within 100 and 300 mm. The authors acknowledge the support provided by Spanish Ministry of Science and Innovation (MCIN/AEI) and by the European Funds for Regional Development in the following projects RTI2018-097314-B-C21, and PID2021-123701OB-C21. The authors would like to acknowledge Sireg for their courtesy supplying the different FRP embedded reinforcement used in the experimental programs.

The increase in strength of Steel Fiber Reinforced Concrete (SFRC) depends mainly on factors such as the dosage, aspect ratio and number of hooked ends of the fibers. Previous studies proposed models to estimate the flexural and shear strength of SFRC beams, but the shear behavior of SFRC panels has not been extensively studied. The study includes diagonal tension tests on concrete panels to assess the shear performance of SFRC. The experimental program comprises 19 square concrete panels having 600 mm side and 75 mm thickness, including three nominal dosages of steel fibers (20, 40 and 60 kg/m3) and three different number of hooked ends (1, 1.5 and 2). The study proposes models to predict the shear strength and deformation capacity, stiffness degradation and toughness of SFRC panels with different number of hooked ends when subjected to diagonal tension. The models include four characteristic limit states of diagonal cracking, maximum residual strength, code-based acceptable degradation, and maximum deformation. The authors thank to Vicerrectoría de Investigaciones of UMNG for the financial support of the EXT-INV-3575 project. The authors also would like to thank Research Assistants Juan D. Vargas and Diego Silva at Universidad Militar Nueva Granada (UMNG) for data and figure processing. The authors also thank the companies Cemex-Colombia and Proalco-Bekaert-Colombia for supplying the concrete and steel fibers, respectively. All data that support the findings of this study are available from the corresponding author upon reasonable request. The views expressed in this paper are solely those of the authors and do not necessarily reflects the views of the sponsors.

The 19 September 2017 Puebla–Morelos earthquake provides a unique opportunity to (a) study the effectiveness of seismic rehabilitation methods implemented in Mexico City after 1985 and (b) collect large amounts of data on current building rehabilitation practices. This article presents and discusses seismic rehabilitation efforts conducted on concrete buildings after the 1985 and 2017 earthquakes. Building damage and vulnerabilities, code provisions for rehabilitation, and common repair and retrofit techniques used in these two periods of time are summarized. The performance of four buildings rehabilitated after 1985 is examined based on results from field investigations conducted after the 2017 event. These rehabilitations were effective in improving the performance of these buildings according to observed damages and estimated shaking intensities. To allow a more systematic assessment of seismic rehabilitations in future earthquakes, an inventory of rehabilitated buildings in Mexico City is currently under development. Preliminary data obtained from this inventory effort are presented and discussed.

This paper presents a study on the in-plane shear response of partially-grouted reinforced masonry walls with bond-beam reinforcement. A database of 95 tests on partially-grouted walls made of concrete hollow blocks was compiled from experimental studies reported in the literature to characterize the capacity and damageability of walls subjected to in-plane lateral loading. The database has been used to evaluate the accuracy of existing design shear strength equations for partially-grouted walls. It is concluded that the shear strength expressions in the Masonry Standards Joint Committee (MSJC) code and Canadian standard are unconservative for partially-grouted walls. A modified equation based on the MSJC expression is proposed which better estimates the shear strength of this type of walls. Seismic fragility functions are also derived based on the experimental database to calculate the probability of experiencing moderate and severe damage in a partially-grouted wall for a given story-drift ratio deformation or normalized shear force demand. The resulting fragility functions show that the normalized shear demand is better correlated with the level of damage than the story-drift ratio. The first author Z. Zhang gratefully acknowledges the financial support provided by a Harbin Institute of Technology scholarship to conduct research as a visiting scholar at the University of Texas at Austin under the supervision of the second author J. Murcia-Delso. The co-authors C. Sandoval and G. Araya-Letelier are grateful for the funding provided by the Fondo de Fomento al Desarrollo Científico y Tecnológico (FONDEF) under Grant N° 17I10264 and the Fondo Nacional de Ciencia y Tecnología de Chile (FONDECYT Regular) through Grant No. 1181598.

Fragility functions are a key component of performance-based earthquake engineering methodologies. They relate the response of the building, quantified by means of engineering demand parameters (EDPs), with the probability of reaching or exceeding different levels of damage in structural or nonstructural components. This paper develops fragility functions for partially grouted reinforced masonry (PG-RM) shear walls with bed-joint reinforcement using data from 44 and 32 full-scale in-plane cyclic tests conducted on clay brick (CLB) walls and hollow concrete block (HCB) walls, respectively. Fragility functions for two levels of damage are derived for shear-dominated CLB and HCB walls using two different EDPs: the story drift ratio and a force-based normalized shear demand parameter. Fragility data based on story drift ratio has shown that HCB walls present a higher deformation capacity as compared to CLB walls. In addition, the dispersion observed in the fragility functions has indicated that the normalized shear demand parameter is better correlated to the level of damage than the story drift ratio parameter for both types of walls. Finally, a comparison with existing fragility functions developed in a previous study for HCB walls with bond-beams is presented.

This paper introduces a new approach for the seismic performance evaluation of planar RC walls. Compared to existing assessment guidelines, such as those in ASCE/SEI 41-17, where performance limits are described by plastic rotation or lateral drift, the proposed method uses local (strain) quantities, obtained from computational models. The analyses rely on a user-friendly implementation of the nonlinear truss model for RC structures, which eliminates the need to manually create a line-element representation of a wall and includes a material law for steel accounting for buckling and rupture of reinforcement. The capability of the models to capture common failure patterns for planar walls is validated for a set of six previously tested wall components which experienced a variety of damage modes (bar rupture, boundary element failure, diagonal compression and tension failures). The analytical models accurately predict the lateral strength, deformation capacity and failure modes observed in the tests. A set of acceptance criteria, based on the analytically obtained concrete and steel strains, is then established for the immediate occupancy, life safety and collapse prevention levels, consistent with different levels and types of damage. An initial calibration of the limit values associated with these criteria is proposed and verified using the analytical results for the six walls considered. The results of the proposed assessment methodology applied to the six walls are compared to those obtained using the nonlinear procedures in ASCE/SEI 41-17. The results indicate that ASCE/SEI 41-17 may not accurately describe the deformability of walls exhibiting mixed flexure-shear inelastic deformations. National Institute of Standards and Technology (NIST)National Institute of Standards & Technology (NIST) - USA [70NANB19H060] Published version The research presented in this paper is supported by the National Institute of Standards and Technology (NIST) under award No. 70NANB19H060. Any opinions and findings presented in this paper are those of the authors alone, and do not necessarily reflect the opinions of the sponsor.

This paper presents a detailed finite element modeling scheme to simulate the cyclic response of RC columns considering low-cycle fatigue and bond-slip of reinforcement. The modeling scheme includes a triaxial constitutive model recently proposed in the literature to simulate concrete failure under cyclic loading. For steel, a commonly used uniaxial model is enhanced to account for bar rupture using a new low-cycle fatigue criterion, which has been validated with data from fatigue tests on reinforcing bars. The bond-slip behavior of vertical reinforcing bars is modeled using a zero-thickness concrete-steel interface element. The interface element has a bond stress-slip constitutive law that predicts bond deterioration caused by generalized slip demands, tensile yielding of steel, and compression damage in concrete. The finite element models are validated with experimental data from cyclic tests on large-scale column and pile specimens which exhibited flexure-dominated responses. The models accurately simulate the lateral force–displacement response and failure of the specimens, and provide peak tensile strain demands along longitudinal bars which are similar to those measured experimentally. Sensitivity analyses are also conducted to study the effect of modeling assumptions related to low-cycle fatigue and bond-slip behavior.

Iron-based shape memory alloys (Fe-SMA) have shown a strong potential for strengthening applications in concrete structures. This paper presents an experimental study on the bond strength and bond-slip behavior of ribbed Fe-SMA bars embedded in concrete. A total of nineteen pullout tests were conducted to study the bond behavior of 16-mm Fe-SMA bars embedded in concrete specimens with different levels of passive confinement. Prior to specimen fabrication, the bars were pre-strained (at 4% or 8%) and then activated by resistive heating after concrete casting. The experimental study considered different activation temperatures (160 °C, 300 °C, and no activation) to evaluate their effects on bond performance. Five specimens with conventional steel bars were also tested to establish a direct comparison with conventional reinforcement. Unconfined pullout specimens failed by splitting of concrete in most of the cases, while confined specimens presented pullout failures and higher bond strengths. In general, the Fe-SMA bars presented similar bond performance as conventional steel bars. However, the bond strength of unconfined specimens was reduced with the activation temperature. For confined specimens, the activation temperature had a minor effect on the bond strength. Local bond stress-slip relations derived from tests have also been compared with two analytical bond-slip laws available in the literature. Finally, the transfer length of Fe-SMA bars in prestressing applications has been estimated based on the experimental data and a simple analytical model of the bond stress distribution along the embedment length of a bar.

Copyright © 2017 John Wiley & Sons, Ltd. The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior and to the strong interaction between concrete and steel, with several coupled failure modes. On the other hand, given the increasing awareness and concern on the worldwide seismic risk, new developments have arisen in earthquake engineering; nonetheless, some developments are mainly based on simple analytical tools that are widely used, given their moderate computational cost. This research aims to provide a solid basis for validation and calibration of such developments by using computationally efficient continuum mechanics-based tools. Within this context, this paper presents a model for 3D simulation of cyclic behavior of RC structures. The model integrates a bond-slip model developed by one of the authors and the damage variable evolution methodology for concrete damage plastic model developed by some authors. In the integrated model, a new technique is derived for efficient 3D analysis of bond-slip of 2 or more crossing reinforcing bars in beam-column joints, slabs, footings, pile caps, and other similar members. The analysis is performed by implementing the bond-slip model in a user element subroutine of Abaqus and the damage variable evolution methodology in the original concrete damage plastic model in the package. Two laboratory experiments consisting of a column and a frame subjected to cyclic displacements up to failure are simulated with the proposed formulation.

The 1985 Mexico City earthquake resulted in extensive damage and collapse of concrete construction. In the months and years following this earthquake, there was an unparalleled effort to repair and retrofit concrete buildings. On September 19, 2017, a new strong earthquake struck Mexico City. This event represented the first severe test for concrete buildings retrofitted after 1985, providing an unprecedented opportunity to study the actual performance of the retrofitting techniques applied in these buildings. This paper presents results of a field investigation and damage assessment of three retrofitted concrete buildings after the 2017 earthquake. The structures studied suffered different levels of damage during the 1985 earthquake, and they were subsequently repaired and retrofitted using a variety of techniques (e.g., jacketing of columns and beams, addition of steel bracing, RC infill walls). Except for the excessive tilting of one of the structures, the buildings presented minor damage after the 2017 event. The shaking intensities of 2017 can be considered similar to those of 1985 in the period range of interest for these buildings, while the structures presented in general better performance thanks to an increase of their capacity and/or a decrease of the seismic demands.

This paper presents an investigation on the bond–slip behavior and development of large-diameter bars embedded in well-confined concrete under seismic load conditions. Bond–slip tests and bar pull–push tests were conducted to characterize the bond strength, cyclic bond deterioration, and tension development of large-diameter bars up to No. 18 in size. A bond stress-versus-bar slip model was developed and implemented in a finite element analysis software. The model was validated with test data and used in a Monte Carlo simulation to evaluate the adequacy of the AASHTO requirements for tension bar development. Based on the results of this study, an improved development length formula was proposed. Furthermore, large-scale tests and finite element analyses were conducted to determine the minimum development length required for large-diameter bars connecting a bridge column to an enlarged pile shaft. Design recommendations were proposed based on the experimental and numerical results.

This paper presents a numerical investigation to examine the bond-slip behavior of column longitudinal reinforcing bars embedded in oversized pile shafts and to determine the minimum embedm...

This paper presents an experimental investigation to determine the embedment length required for longitudinal reinforcement in a bridge column extending into an oversized pile shaft, and the amount of transverse reinforcement required for the pile shaft to prevent premature bar anchorage failure due to concrete splitting induced by bar slip. Four full-scale column–oversized pile assemblies were tested under quasi-static cyclic lateral loading. The test specimens had different embedment lengths for the column reinforcement, different amounts of transverse reinforcement in the piles, different sizes of longitudinal bars, ranging from No. 8 to No. 18 (25 to 57 mm) bars, and different column-to-pile diameter ratios. All column–pile assemblies behaved in a ductile manner with plastic deformation occurring near the base of the columns despite some cone-shaped fractures and tensile splitting cracks occurring in the top portion of the piles. The test results show that the embedment length for the column r...

This paper presents a new interface model to simulate the cyclic bond-slip behavior of steel reinforcing bars embedded in concrete. A multi-surface plasticity formulation is used to model two major inelastic deformation mechanisms occurring in bond slip. One is the crushing and shearing of the concrete between the bar ribs, and the other is the sliding between the concrete and bar surfaces. These two mechanisms are represented by different yield surfaces and nonassociated flow rules. The flow rules account for the shear dilatation of the interface induced by the wedging action of the bar ribs and crushed concrete particles. The interface model has been implemented in a finite element analysis program and has been validated with experimental data. The model is easy to calibrate and is able to reproduce the bond-slip behavior of bars under a wide range of confinement situations, including bar pullout and concrete splitting failures.

The influence of stress-reduction methods on the strength of adhesively bonded joints composed of brittle adherends was studied. Experimental and numerical investigations were carried out on two types of adherends: (a) fibre reinforced polymers and (b) timber, considering three different stress-reduction methods: (i) adhesive roundings, (ii) chamfering and (iii) adhesive grading. The experiments showed that the increase in strength using these stress-reduction methods is negligible. Numerical analyses showed that although the stress peaks are reduced, these act over a larger volume. A probabilistic strength prediction method is applied, which explains most of the experimental results. The presented work allows for a better insight into the relation between stress reduction and strength increase of adhesively bonded joints, which are greatly affected by the brittleness of the adherends.

This paper presents the three-dimensional finite element analysis of squat RC walls using a continuum constitutive model for concrete developed at ANATECH. The concrete model is based on the smeared-cracking concept and an elastic-plastic formulation that permits the simulation of cracking and other particular response characteristics of concrete. The laws governing the normal and tangential stresses on a crack are suitable for the simulation of shear failures and crack closing and reopening under load reversals. Finite element models have been developed to reproduce experiments on squat walls found in the literature. These tests were conducted on walls with rectangular and non-rectangular sections subjected to cyclic lateral loading. The finite element models provide a good representation of the nonlinear response and shear failure of these walls. Results of a blind simulation of a five-story shear wall building tested on a shake-table, in which a diagonal shear failure was well predicted, are also presented.

This paper presents a study on the tension development length of large-diameter reinforcing bars embedded in well-confined concrete. Pull-push tests were conducted on No. 14 and 18 (43 and 57 mm) bars to evaluate whether the development length requirements in the AASHTO LRFD (American Association of State Highway and Transportation Officials Load and Resistance Factor Design) Specifications are adequate for large-diameter bars subjected to severe cyclic loading. The data have been used to validate finite element models, which have been subsequently employed in a parametric study to establish a formula to determine the tensile capacity of a bar as a function of the embedment length, and the concrete and steel strengths. Monte Carlo simulations conducted with this formula have shown that the AASHTO requirements are adequate to develop the yield strength of a bar in tension, but they do not have the desired reliability to develop its ultimate tensile strength when uncertainties are considered. Hence, an improved development length requirement is proposed.

A new interface model to simulate the bond-slip behavior of reinforcing bars is presented. The model adopts a semiempirical law to predict the bond stress-versus-slip relations of bars, accounting for the bond deterioration caused by cyclic slip reversals, the tensile yielding of the bars, and the splitting of concrete. The wedging action of the ribs is represented by assuming that the normal stress of the interface is proportional to the bond stress. The model has been implemented in a finite-element analysis program and has been validated with laboratory experiments that include monotonic and cyclic bond-slip and anchorage tests of bars with different embedment lengths and a test on an RC column subjected to cyclic lateral loading. The model is easy to calibrate and computationally efficient, and it accurately predicts the bond-slip behavior of bars embedded in well-confined concrete. It also simulates bond failure attributable to the splitting of concrete in an approximate manner.

A study on the bond strength and cyclic bond deterioration of large diameter reinforcing bars embedded in well-confined concrete is presented. The study included monotonic pullout tests and cyclic pull-pull tests conducted on No. 11, No. 14, and No. 18 (36, 43, and 57 mm) reinforcing bars. The bond stress-slip relations obtained from the tests are presented, and the effects of the compressive strength of concrete, bar size, pull direction (for a vertically cast bar), and slip history on the bond strength are examined. Moreover, a phenomenological bond stress-slip law for monotonic and cyclic loading is proposed for bars embedded in well-confined concrete. This law has been validated with experimental results obtained in this study and in previous research.

This paper presents results of an ongoing study on the seismic performance of a retrofitted concrete building located in the soft soil area of Mexico City. The original structure consisted of reinforced concrete frames in two directions. The building was repaired and retrofitted after having been damaged during a moderate earthquake in 1979. The retrofit strategy consisted mainly of installing external steel braces in one direction of the building, and reinforced concrete infill walls in the other direction. The retrofitted structure showed minor damage after the 1985 and 2017 earthquakes. The goal of this investigation is to assess the structural response of the building and the effectiveness of the retrofit strategy by combining post-earthquake damage inspections, analytical modeling and ambient vibration testing. This paper focuses on the development and calibration of a three-dimensional analytical model of the building, and on the analysis of the vibration properties of the retrofitted structure. The analytical model has been calibrated using data from ambient vibration tests conducted after the 2017 event. The study of the vibration properties of the building has shown the strong influence of soil-structure interaction in the response of this building.

This paper presents an analytical method to predict the bar slip and pullout capacity of straight bars embedded in well-confined concrete, such as column bars extended into a footing or cap beam. Closed-form solutions of the slip at the loaded end of the anchorage length and the pullout strength of the anchorage are derived based on a set of a priori bond stress distributions for elastic and plastic loading situations. The model assumes a linear distribution of bond stresses along the elastic portion of the anchorage length, and a constant bond resistance within the region where the bar has yielded in tension. For relatively short embedment lengths, the slip at the unloaded end is also considered. The accuracy of the model in predicting the loaded-end slip, the strains along the embedment length, and the bar pullout capacity has been verified with experimental data. The model provides an accurate representation of the global response of straight anchorages up to the ultimate tensile strength or the pullout failure of the bar. It also results in a sufficiently accurate representation of the strain distributions obtained experimentally in pullout tests on bars with different embedment lengths.

This paper presents three-dimensional finite element models for the accurate response simulation of RC columns subjected to severe cyclic loading. The models integrate advanced constitutive models for concrete, steel reinforcement, and bond-slip behaviour of bars. Concrete is modelled with a triaxial constitutive capable of simulating material degradation due to cracking and crushing, crack opening and closing behaviour, and the increase of strength and ductility under multiaxial compression conditions. The cyclic response of steel reinforcement is modelled with a Menegotto-Pinto law modified to account for the low-cycle fatigue of bars using an energy criterion. The bond-slip behaviour of longitudinal bars is modelled using a concrete-steel interface element previously proposed by one of the authors of this paper. The interface element has a bond stress-slip constitutive law that predicts bond deterioration caused by bar slip, cyclic loading and tensile yielding of steel. The finite element models predict well the damage mechanisms and force-displacement responses of cantilever columns tested under fully-reversed lateral cyclic loading.

This paper presents a unified analytical method to predict the slip and tensile strength capacity of both straight anchorages and lap splices. Closed-form solutions of the slip at the loaded end of an anchorage or lap splice are derived based on a set of simplified bond stress distributions applicable for different geometrical and loading conditions. The model assumes a linear bond stress distribution along the elastic portion of the anchorage/splice, and a constant bond resistance within the region where the bar has yielded in tension. Closed-form solutions of the ultimate strength capacity of the anchorage/splice are also obtained by combining the proposed model with a simple bond failure criteria and the local bond strength specified in the 2010 Model Code. The proposed formulation is shown to predict with overall good accuracy the slip response of bar anchorage tests reported in the literature, including pullout failures, and the lap-splice strength of 457 test specimens from the ACI 408 database.