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The seismic resilience of structures and infrastructures is affected by damage accumulation phenomena, mainly related to the type of hysteresis. Specifically, pinching drives the cyclic response of several building materials, such as reinforced concrete and masonry. Structural systems affected by pinching phenomena are prone to exhibit a dramatic increment of their displacement response after multiple cycles (e.g. repeated earthquakes). The authors estimate a reinforced concrete pier's response using truncated incremental dynamic analysis by concatenating three earthquake scenarios. The authors adopted a Bouc–Wen class hysteresis model to simulate the reinforced concrete pier's cyclic response, matching its experimental cyclic response. The current analysis proved that ductility and resistance primarily drive the seismic response after a single earthquake. However, the performance after multiple earthquakes strongly depends on the pinching, degradation and drift accumulation, which are generally neglected in standard design practices. [ABSTRACT FROM AUTHOR]

This article attempts to define pinching of two structural joints, reinforced concrete (RC) and wood ones. In particular, the research outlines differences and analogies between pinching of an RC portal and a Light Timber Frame (LTF) wall. This is done by focusing on the concavity of pinching in their response under repeated cycles, which produces differences in the energy dissipation. The response of the two structural archetypes under pseudo-static and dynamic simulations is analysed using the Atan hysteresis model modification. The truncated incremental dynamic analysis (TIDA) of the two systems modelled as single-degree-of-freedom (SDOF) oscillators yielded the fragility curves, approximated by a lognormal cumulative distribution (CDF). The stability of RC under repeated cycles reveals its significant resilience compared to LTF structures. The examination of the fragility functions supports a discussion about the relation between the pinching concavity and the notion of structural resilience by introducing a robustness index ranging from 0 to 1. Ultimately, a parametric analysis of a fictitious structural system derived from the timber one by varying the concavity of the pinching path leads to the estimation of the robustness index as a function of the pinching concavity. [ABSTRACT FROM AUTHOR]

Infrastructures in coastal areas are often prone to several hazards, and thus the elaboration of effective risk management plans in such zones are possible if all relevant threats are considered and analyzed. In this context, the assessment of the corrosion hazard attributable to airborne chlorides is of utmost importance since the resulting deterioration phenomena can heavily jeopardize both reliability and resilience of the infrastructures. Therefore, this contribution aims at proposing the preliminary version of a possible framework for the elaboration of corrosion hazard maps at regional scale for coastal areas, with focus on reinforced concrete bridges. The proposed approach encompasses three main steps. First, the relevant stock of infrastructures vulnerable to chloride‐induced corrosion is identified and quantified. This requires the collection of relevant features, such as construction type, position, and age. Environmental conditions are examined next, including data about sea waves and salinity, wind, temperature, humidity, rainfall, and chloride deposition rate. Finally, the corrosion hazard is estimated in probabilistic sense. The proposed methodology is presented together with the preliminary results obtained from a relevant case study. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for rehabilitating plastic hinges with damaged/fractured weldable longitudinal rebars in severely damaged reinforced concrete (RC) bridge columns and possible improvements regarding connection protection and plastic hinge development. Damaged/fractured longitudinal rebars are replaced with new rebar segments, and the basis of this approach involves connecting intermediate machined parts to the original longitudinal rebars by welding with an off-the-shelf steel equal angle. The proposed rehabilitation design procedure is based on capacity design principles, with equations that define the new geometries and required ductility, and it is validated experimentally on three 1∶6 -scale RC circular column specimens. Compared with the original columns, the ductility capacity of the rehabilitated columns increased from 39% to 58%, and the energy dissipation (equivalent viscous damping ratio) increased from approximately 50% to 250%. The base shears of the rehabilitated columns were smaller than those of the original columns owing to the reduction in the rebar area; thus, shear failure was avoided, and the demand on the foundation was reduced. The rehabilitation procedure, by adopting a welding connection that is easily performed on site and concentrates the damage in the new rebar segments, promises to be a quick, simple, reliable, and effective means to improve the ductility and shear capacity of RC bridge columns without using mechanical couplers or changing the column dimensions. [ABSTRACT FROM AUTHOR]

The rehabilitation of reinforced concrete (RC) bridge columns subjected to chloride‐induced corrosion is addressed in the present paper. The proposed strategy is based on the replacement of the original external layer made of normal‐strength concrete (NSC) with ultra‐high performance fiber reinforced concrete (UHPFRC), and it additionally involves the substitution of the existing corroded longitudinal reinforcement with new machined steel rebars. This repair technique aims at restoring strength, stiffness, and ductility of the original column in a short time without altering its cross‐section dimensions. Because of the high compactness of the UHPFRC, it also serves at improving its durability. The main contribution of the present work is a numerical investigation carried out in order to identify how the design decisions about the repair strategy influence the behavior of the restored column. The parametric investigation reveals that the length of the zone in which NSC is replaced by UHPFRC as well as the machined index (i.e., ratio between turned and original rebar cross‐section area) must be properly selected to make the intervention effective. Numerical results also highlight that the main design issue to deal with is the relocation of the plastic hinge from the repaired zone towards the weak unrepaired part of the column. Practical design recommendations are finally formulated. [ABSTRACT FROM AUTHOR]

An efficient yet accurate procedure was developed for the seismic assessment of reinforced concrete (RC) bridges subject to chloride-induced corrosion. The procedure involves using incremental modal pushover analysis to assess corroded bridges as an alternative and less computationally demanding approach to non-linear dynamic analysis. A multi-physics finite-element analysis is performed to evaluate the effects of chloride-induced corrosion on bridge columns. In doing so, chloride ingress in concrete is numerically simulated as a diffusion process by considering the effects of temperature, humidity, corrosion-induced cover cracking and concrete aging. The estimated chloride concentration is then employed to evaluate the corrosion current density, from which the effects of corrosion on reinforcement, cracked cover concrete, confinement and plastic hinge length can be determined for subsequent non-linear static analysis. A case study of a typical bridge structure is presented. The proposed procedure can be used to assess the seismic performance of irregular RC bridges exposed to severe corrosive environments. [ABSTRACT FROM AUTHOR]

This study presents the results of a refined numerical investigation meant at understanding the time‐dependent cyclic behavior of reinforced concrete (RC) bridge columns under chlorides‐induced corrosion. The chloride ingress in the cross‐section of the bridge column is simulated, taking into account the effects of temperature, humidity, aging, and corrosion‐induced cover cracking. Once the partial differential equations governing such multiphysics problem are solved through the finite‐element method, the loss of reinforcement steel bars cross‐section is calculated based on the estimated corrosion current density. The nonlinear cyclic response of the RC bridge column under corrosion is, thus, determined by discretizing its cross‐sections into several unidirectional fibers. In particular, the nonlinear modeling of the corroded longitudinal rebars exploits a novel proposal for the estimation of the ultimate strain in tension and also accounts for buckling under compression. A parametric numerical study is finally conducted for a real case study to unfold the role of corrosion pattern and buckling mode of the longitudinal rebars on the time variation of capacity and ductility of RC bridge columns. [ABSTRACT FROM AUTHOR]

A generalized cyclic steel model characterized by isotropic and kinematic hardening, inelastic buckling in compression and corrosion of rebars in reinforced concrete (RC) structures is presented. The model has been implemented in a fiber code, to perform seismic analyses of RC sections. The model is particularly accurate with respect to experimental cyclic behavior of rebars with buckling in compression when the strain does not exceed 1.5%. Twelve configurations of RC cross sections were selected as case studies for three geometries and different steel arrangements, assumed representative of RC columns or bridge piers (in a suitable scale). Each section was subjected to two groups of cyclic curvature histories representative of severe seismic loads, not far from collapse. Different axial loads and corrosion percentages (no corrosion, moderate, or high) have been selected to perform cyclic parametric analyses. One of the cases was taken from an experimental test on columns, deriving also steel characteristics used in all numerical cases. The results of the comparison among RC sections have been discussed. Numerical results show that the maximum compressive strain for steel rebars is always smaller than 1.5%, therefore the proposed steel model is accurate and represents a valid tool for structural assessment. Corrosion reduces RC section capacity, affecting various rebar mechanical characteristics, in particular buckling behavior. [ABSTRACT FROM AUTHOR]

This paper presents a smooth hysteresis model for reinforced concrete (RC) structural elements based on the differential equation of the Bouc–Wen model. Stiffness degradation and strength degradation are defined by introducing a damage index that includes both dissipated energy and maximum displacement. The pinching effect acts directly on the stiffness of the system and is controlled by an activation energy. The degrading functions are connected to the actual processes with which the damage occurs, thereby giving each parameter a physical meaning. The simple formulation of the model allows a straightforward identification of the best-fitting parameters and an easy interpretation of the results. Applications to the cyclic behaviour of RC structural elements demonstrate that the model is well capable of describing complex hysteretic behaviours involving degradation and pinching effects. [ABSTRACT FROM AUTHOR]

This paper discusses the seismic behavior of reinforced concrete (RC) bridge structures, focusing on the shear–flexure interaction phenomena. The assessment of reinforced concrete bridges under seismic action needs the ability to model the effective non-linear response in order to identify the relevant failure modes of the structure. Existing RC bridges have been conceived according to old engineering practices and codes, lacking the implementation of capacity design principles, and therefore can exhibit premature shear failures with a reduction of available strength and ductility. In particular, recent studies have shown that the shear strength can decrease with the increase of flexural damage after the development of plastic hinges and, in some cases, this can cause unexpected shear failures in the plastic branch with a consequent reduction of ductility. The aim of the research is to implement those phenomena in a finite-element analysis. The proposed model consists of a flexure fiber element coupled with a shear and a rotational slip spring. The model has been implemented in the OpenSEES framework and calibrated against experimental data, showing a good ability to capture the overall response. [ABSTRACT FROM AUTHOR]

In the last few years, nonregular reinforced concrete (R/C) slabs have become more popular in buildings and bridges due to architectural or functional requirements. In these cases, an optimum design method to obtain the ultimate load capacity and the minimum reinforcement amount should be used. For simple R/C slabs, the yield-line method is extensively used in engineering practice. In addition to strength, the "true" failure mechanism is also obtained by identifying the parameters that define it and minimizing the collapse load. Unfortunately, when the mechanism is too complicated to be described or defined by several parameters (e.g., in slabs with complicated geometry), the method becomes more difficult because the system of nonlinear equations becomes harder to solve through traditional methods. In this case, an efficient and robust algorithm becomes necessary. In this paper, a structural analysis of R/C slabs is performed by using the yield-line method in association with a zero-th order optimization algorithm (the sequential simplex method) to avoid calculating gradients as well as any derivatives. The constraints that often limit these parameters are taken into account through the exterior penalty function method, leading to a successful solution of the problem. Considering that the direction of each yield-line is sought by minimizing the ultimate load and finding the parameters defining the collapse mechanism, another parameter concerned with the direction of an orthotropic reinforcement grid is introduced. In this way, the number of unknown parameters increases, but aside from obtaining the ultimate load and the parameters defining the collapse mechanism, the solution also finds both best and worst reinforcement orientations. [ABSTRACT FROM AUTHOR]

Integral abutment bridges (IABs) are becoming rather common due to the durability problems of bearings and expansion joints. Monolithic connections between the deck and sub-structure allow, on one side, to increase the structure redundancy and reduce the maintenance costs. However, from the other side, soil-structure effects are also introduced due to the interactions between the abutment and the backfill and between the pile and soil induced by thermal variations, long-term effects (creep and shrinkage) and dynamic loads, such as earthquakes. Several authors have investigated the soil- structure interaction for IABs both theoretically and experimentally, but there is still a lack of common line guidelines and codes. After a literature review of the main studies regarding the seismic response of IABs, this paper introduces some recent contributions given by investigators in this field. In particular, the following topics are discussed: (a) an experimental study on an innovative deck to pier/abutment joint; (b) the possibility of using prestressed concrete or ultra-high performance piles in IABs; (c) a pile isolation technique based on a pre-hole filled with damping materials; and (d) a research project supported by European Union inside the Horizon 2020 SERA project on the seismic behaviour of novel integral abutment bridges. The paper clearly demonstrates the potential applications of the proposed technologies for IABs built in seismic zones. [ABSTRACT FROM AUTHOR]

A new strategy that repairs severely damaged reinforced concrete (RC) columns after an earthquake is proposed as a simpler and quicker solution with respect to the strategies currently available in the literature. The external concrete parts are removed from the column surface along the whole plastic hinge region to uncover the steel reinforcement. The transverse steel is cut away, and each longitudinal rebar is locally substituted by steel rebar segments connected by welding connections to the original undamaged rebar pieces outside the intervention zone. The new rebar segments have a reduced diameter achieved by turning to ensure plastic deformation only in the plastic hinge, protecting the original rebar and the welding connections. The connection is specifically designed to be effective and simple, and is directly realized on column reinforcement. Finally, the removed concrete is restored by a jacket built with high-performance concrete with steel or polymer fibers. The use of concrete with high volume fraction of polymer fibers to repair the column is investigated for the first time in this paper. This concrete was characterized by compression and flexural tests in the laboratory and its mechanical characteristics were compared with those of the concrete with steel fibers, which are being increasingly used in construction. The repair strategy was applied to two RC columns (1:6 scaled bridge piers), tested by asymmetric cyclic tests. The results show that the column strength, stiffness, and ductility were restored, and the energy dissipation capacity improved. The experimental evidence was investigated by fiber models in OpenSees. [ABSTRACT FROM AUTHOR]

Several methods of analysis used for the design of base-isolated buildings are proposed in many structural specifications. According to different structural codes, limited conditions of equivalent linearization of the friction pendulum system (FPS) and application scopes of simplified linear static analysis (LSA) are introduced. LSA of a reinforced concrete frame building isolated by FPS is performed and compared with fast nonlinear time-history analysis (FNA) to evaluate the suitability of the simplified method. Based on a specific spectrum used in the new Italian code, seven spectrum-compatible earthquake ground motions are selected and scaled as seismic input. To perform both linear and nonlinear analyses systematically, a program is specially developed by MATLAB in combination with a commercial software. Base displacement, story shear force, and energy dissipation are selected as response indicators. The results reveal that, as a substitute for the exact nonlinear analysis method in the preliminary design of base-isolated buildings, the LSA method yields conservative estimates in base displacement and total input energy. However, because of the uniform acceleration profile assumed over the structural height, the story shear forces are significantly underestimated by LSA. [ABSTRACT FROM AUTHOR]

The compressive behavior of steel tube reinforced concrete (STRC) columns under eccentric loads was investigated experimentally and numerically in this paper. Primary parameters included the eccentricity ratio, the concrete-filled steel tube (CFST) area ratio, and the longitudinal rebar ratio. This paper analyzed the impacts of these parameters as well as the failure modes, the full-range compression process, and the strain development. Similar to the reinforced concrete (RC) column, the full-range compression process of STRC column under eccentric loads can be divided into three stages, i.e., elastic stage, elastic-plastic stage (cracking stage), and plastic stage (descent stage). The experimental findings showed that, on the near-load side of the STRC column, the outer concrete crushed, and the longitudinal rebars buckled in compression. Conversely, on the far-load side, the concrete exhibited cracking in tension, and the longitudinal rebars exhibited tension. Finite element (FE) analysis results demonstrated that, similar to a RC column, three distinct failure mechanisms can be identified for STRC columns under eccentric loads, i.e., compression-controlled, balanced, and tension-controlled failures. During the compression process, analyses were conducted on the contact stress between the steel tube and concrete, as well as on the load distribution between the inner CFST and the outer RC. The ultimate load of the STRC column decreased with an increase in the eccentricity ratio, while it increased with larger longitudinal rebar ratio and CFST area ratio. Based on the experimental and FE analysis results, a simplified calculation method was developed to determine the eccentricity reduction coefficient for STRC columns. • The eccentric test result of steel tube reinforced concrete (STRC) column with low CFST area ratio was presented. • The effect of eccentricity ratio, CFST area ratio and rebar ratio on the compressive behavior of STRC column were analyzed. • The failure mechanisms, load distribution and contact stress was analyzed by refined finite element analysis. • The simplified calculation method of eccentricity reduction coefficient was proposed for the ultimate load of STRC column. [ABSTRACT FROM AUTHOR]

This paper studied the axial compression behavior of the steel tube reinforced concrete (STRC) column, which consisted of inner CFST and outer RC components. Ten specimens, including seven STRC columns, two RC columns, and one CFST column were tested. The test parameters included the CFST area ratio (inner CFST to the whole section), longitudinal rebar ratio and stirrup space. The test results showed that the compressive behavior of STRC column with a CFST area ratio of 0.04 was close to that of the RC column, and the compressive behavior of the STRC column with a CFST area ratio of 0.13 was between that of the RC column and CFST column. The finite element (FE) models were developed and verified by test results to investigate the effects of longitudinal rebar ratio and stirrup space on the axial compression behavior of STRC column with various CFST area ratios. The load distribution between inner CFST and outer RC components was analyzed. The FE results showed that the effects of the longitudinal rebar ratio on the ultimate load of STRC column were related to the CFST area ratio. The accuracy and applicability of the five methods suggested by codes for predicting the ultimate load of STRC column were discussed based on the test and FE results. • The compression test of steel tube reinforced concrete (STRC) column with low CFST area ratio was firstly carried out. • The influences of both CFST area ratio and longitudinal rebar ratio on ultimate strength of STRC column were discussed. • The refined finite element model of STRC column for parameter analysis is established. • The five methods of codes for ultimate strength of STRC column was calculated and discussed. [ABSTRACT FROM AUTHOR]

Rehabilitating corroded or seismically damaged reinforced concrete (RC) bridge columns often involves replacing the longitudinal steel rebar. Welded joints offer a practical and efficient in-situ solution for connecting new rebar segments to existing undamaged rebar, even with irregularities in the steel reinforcement. However, traditional approaches to rebar joint welding have paid little attention to the overstrength of the welding seam, which can result in a brittle response. Properly designing such joints should aim for a ductile rebar failure. However, in-situ rehabilitation solutions often require reducing the seam length to save time and material costs and, not secondarily, avoiding the plastic hinge formation in the rehabilitated column. Therefore, providing the seam with adequate overstrength is crucial to achieving a ductile failure of the welded joint. This study presents an experimental investigation into the most effective methods for connecting existing and new rebar segments through welding, addressing on-site welding challenges such as limited operational space and weld orientation. Over 100 tensile tests have been conducted at Fuzhou University's laboratory in China to understand the response of nine welded joints. Among indirect butt joints, the study identifies two performance groups based on the ductile failure rate as the welding seams reduce. The symmetry of the joint and the presence of additional direct butt welding also in asymmetric joints can significantly improve the joint performance, determining a ductile failure with minimal welding lengths. In a second step, following a probabilistic approach, the study assesses the overstrength of indirect butt joints as a function of seam length for the two identified performance groups. Empirical failure probabilities of the rebar and the seam are estimated to fit probability density functions representative of the tensile strength of the rebar and the seam. Based on a target reliability class, the overstrength factors are estimated. • Tensile tests on 152 rebar welded joints. • Two groups: brittle (prevalent weld failure) and ductile (prevalent rebar failure). • Optimal configuration is R4V*: indirect butt joint with V coupler and additional butt weld. • R4V* has the minimum welding length with optimal ductility. • Probabilistic estimation of overstrength factors to prevent weld failure. [ABSTRACT FROM AUTHOR]

The direct displacement-based design (DDBD) is based on the equivalence between the nonlinear hysteretic response of a structure and a simple linear oscillator with equivalent viscous damping (EVD). Typically the EVD is calibrated for different types of structures as a function of the ductility. However, those simple relationships exhibit a huge dispersion and uncertainty since the specific properties of the structural system are not considered. This work proposes an original approach for estimating the EVD of infilled reinforced concrete (RC) frames. We focus on a ductility demand corresponding to an ultimate limit state and we investigate the effect of the properties of infilled RC frames on the EVD. A data-driven hysteresis model proposed by the authors in a previous research is implemented in OpenSees to represent the nonlinear response of infill panels. The optimal EVD at the ultimate limit state is computed using an extensive series of time-history analyses (THAs) on a dataset of 14 infilled RC frames. Afterwards, an empirical correlation law for the estimate of the optimal EVD is calibrated as a function of the geometrical and mechanical properties of infilled RC frames. This formula is meant to be a practical tool for a preliminary design of infilled RC frames. A comparison with the EVD estimated by quasi-static tests and the EVD of bare frames is made. The methods and results presented in this work may be the basis for more robust predictions of the EVD of infilled RC structures. • Equivalent viscous damping (EVD) of infilled RC frames from time-history analyses. • Empirical formula for EVD as a function of geometrical and mechanical properties. • Comparison of optimal EVD for infilled and bare frames. • Comparison of optimal EVD from time-history analyses and quasi-static cyclic tests. • Hysteresis model for infilled RC frames implemented in OpenSees. [ABSTRACT FROM AUTHOR]

The piles represent the most vulnerable structural components in Integral Abutment Bridge (IAB). They must adsorb the thermal deformation and the seismic loading transferred from the superstructure to the substructure. The use of pre-holes filled with high-damping material represents a possible solution for enhancing the dissipative performance of reinforced concrete (RC) piles in IABs. This paper presents the experimental tests of four RC pile specimens backfilled with different damping material to assess their effect on the soil-structure hysteretic response. The authors developed a physical hysteresis model of the soil-pile interaction to assess the optimum length of the damping pre-hole. Firstly, the model is calibrated to the experimental tests. Then the authors extrapolated the hysteresis models to full-scale specimens to estimate their optimum design in practical applications. • Experimental tests of piles with pre-hole filled with high-damping material. • The use of rubber particles or foam reduces pinching effects due to soil and reinforced concrete. • The experimental backbone is independent of the damping features of the soil. • Development of a physical hysteresis model of the soil-pile interaction based on a Winkler plane beam. • The optimum length of the pre-hole ranges between 0.1% and 0.15% the pile length. [ABSTRACT FROM AUTHOR]

Concrete filled steel tubular (CFST) structures have become a viable alternative to reinforced concrete or steel structures due to several advantages. One of the most important is the confinement effect of the concrete core provided by the steel tube. However, this beneficial composite action will be probably weakened by debonding, so reliable formulations to predict the reduced ultimate resistance are needed. In this paper, a review of existing specifications and experimental tests carried out on compressed circular CFST columns with and without debonding, is given. Accordingly, more circular CFST long specimens with debonding should be necessary to understand the combined influence of slenderness ratio, load eccentricity ratio and confinement factor on the reduction coefficient (K D) of ultimate load capacities (N u). The combined influence of arc-length ratio and thickness of circumferential debonding gap on K D should be further studied by experimental tests. Moreover, the existing formulae for K D and N u show a low accuracy in predicting the test results and should be improved. To this aim, an evolutionary polynomial regression (EPR) MOGA-based methodology was performed to obtain more accurate formulations for N u and K D of circular CFST columns with debonding. The formulae extracted from the Pareto front of non-dominated solutions, demonstrate good accuracy, higher than the ones in literature. The proposed models are consistent with the physical interpretation of the studied phenomenon according to which N u and K D decrease as debonding parameters increase and can be used to calculate the real resistance of CFST structures. • Experimental tests on compressed circular CFST columns with debonding are summarized. • The accuracies of existing models to predict the reduction coefficient K D of N u are low. • Formulaeto predict the ultimate load capacities N u with debonding are missing. • New formulaefor K D and N u are proposed by EPR. • The proposed models have good accuracies and physical meaning. [ABSTRACT FROM AUTHOR]