•Cyclic loading tests were conducted for the ACE and ECE technologies corroded RC columns.•Appearance, corrosion crack, corrosion characteristics of corroded columns using ACE and ECE were ...compared.•The corrosion products due to ACE and ECE were analyzed using X-ray diffraction.•Specimen’s failure mode, hysteresis curve, backbone curve, and seismic performance indexes were compared.
Corrosion of reinforcement bars can cause reinforced concrete (RC) columns more vulnerable under seismic loads. In this study, the seismic behavior of corroded RC columns was experimentally studied with a focus on the comparison between two different accelerated corrosion techniques by using artificial climate environment (ACE) and electrochemical chloride extraction (ECE). To do this, six RC square columns were designed and fabricated as the test specimens. The test specimens were categorized into two groups with a low level and a high level of axial compression ratio (i.e., 0.1 and 0.45), respectively, and each group includes three test specimens, i.e., an uncorroded column and two corroded columns under ACE and ECE techniques. An X-ray diffraction approach was used to examine the major ingredients of corrosion products attached on the corroded reinforcement bars under ACE and ECE techniques. The column specimens were subjected to repeated cyclic loadings, and the failure modes, hysteresis and backbone curves, stiffness degradation, ductility level and energy dissipation of the specimens corroded under different techniques were compared. The results show that, under a consistent target corrosion level, the ECE corrosion technique can cause more significant damage to the corroded RC columns than the ACE corrosion technique, leading to a change of failure mode and worse hysteretic performance.
•A total of 29 corrosion damage models were collected to represent the corrosion induced deterioration mechanisms.•The variability in the available corrosion damage models was examined.•Seismic ...collapse fragility relationships were developed for the corroded RC frame structures with different corrosion damage models.•The effect of the variability in the corrosion damage models on the seismic collapse fragility of corroded RC frames was investigated.
Corrosion of embedded reinforcement is an important form of degradation of reinforced concrete (RC) structures. The corrosion damage can degrade the mechanical behaviors of the corroded reinforcement, the surrounding concrete, and the interaction between them. These deterioration mechanisms can be simulated by different corrosion damage models. Different corrosion damage models could result in difference in the structural collapse capacity under earthquake excitations. However, the variability in these corrosion damage models and its effect on seismic collapse fragility of corroded RC structures are not well examined in the past studies. This study conducts an investigation of the variability in the available corrosion damage models. To do this, a total of 29 empirical models are collected to represent the corrosion-induced deterioration mechanisms. The results show that different corrosion damage models lead to significant variability. The changing range of the prediction by different corrosion damage models for the bond strength is even beyond three times wider than the minimum prediction value. As a further step, two typical RC frame structures are designed as the study cases. Then a suite of 19 corroded frame cases are modeled with their material parameters deteriorated according to the collected corrosion damage models. Their seismic collapse fragility curves are then generated and compared. It is found that, at a high corrosion rate of 0.2, the variability in the corrosion damage models can cause a significant difference in the collapse probability as high as 8.4% and 6.54% for the case frames designed with a low and high earthquake hazard levels, respectively. However, this effect due to the variability in the corrosion damage models is limited to the collapse probability when the structure is slightly or moderately corroded. Among the considered deterioration mechanism due to corrosion damage, the maximum difference of collapse probability are caused by the variability in the corrosion damage models for the yield strength and ultimate deformation of the corroded reinforcement, which are as high as 6.18% and 5.32%, respectively. While for the other deterioration mechanisms, the variability in their corresponding damage models leads to a limited effect on the collapse probability of structures.
•A phenomenological hysteretic model for corroded RC columns was developed.•The parameters of the phenomenological hysteretic model were calibrated based on test data.•Empirical prediction equations ...were generated for the parameters of the developed hysteretic model.
A phenomenological hysteretic model is developed for corroded RC columns in this study. To this end, the test data of 77 corroded rectangular RC columns and 26 uncorroded ones under repeated cyclic loads are collected to establish a database. A polygonal hysteretic model that can well incorporate the degradation of stiffness and strength is adopted to describe the hysteretic behavior of corroded columns. The hysteretic model parameters related to monotonic backbone (i.e., yield moment My, yield rotation θy, pre-capping rotation θp, post-capping rotation θpc, the ratio of capping moment to yield moment k) and cyclic deterioration (i.e., cyclic deterioration parameter λ) are identified for each of the test specimens in the database after a careful calculation with the experimental data. The backbone parameters identified for the corroded columns are compared to those for the uncorroded columns to quantify the corrosion-induced deterioration coefficients (CIDCs). Multivariate-linear-type empirical relationships are then developed to relate each of the CIDCs to the corrosion rate and critical structural design variables using stepwise regression analysis. A multilinear empirical relationship is also proposed for the cyclic deterioration parameter. The developed hysteretic model together with the predictive equations for the model parameters are proved of high accuracy through simulating the intra-database tests considering varying corrosion levels. They are further applied to the corroded columns beyond the database, those without data on uncorroded counterparts provided in particular, also indicating a desirable accuracy.
•Database contains of FRP retrofitted corroded columns was established.•Rotation angles of FRP retrofitted corroded columns at yielding and ultimate states are determined.•The prediction models for ...yield and ultimate rotation angles of FRP retrofitted corroded columns were developed.•Nonlinear modeling parameter a consistent with ASCE 41 for FRP-retrofitted corroded columns was determined.
FRP retrofitting is an effective way to promote the degraded seismic capacity of reinforced concrete (RC) columns with corroded reinforcing bars. It is important to evaluate whether the performance of a corroded RC column meets the requirement of safety after FRP retrofitting. However, there is little available guidance for evaluating the deformation capacity of FRP retrofitted corroded columns. In this study, the test data of 63 FRP retrofitted corroded columns and 17 FRP retrofitted uncorroded columns under repeated cyclic loads are collected to establish a database. For each specimen, the rotation angles at yielding and ultimate states are determined from the backbone curve. The empirical prediction models are then developed for the yield and ultimate rotation angles of FRP retrofitted corroded columns, which include two parts: 1) the predicted rotation angle for the FRP retrofitted uncorroded RC column, and 2) a Corrosion Influence Factor (CIF) defined as the ratio between the rotation angles of the FRP retrofitted corroded columns to that of the FRP retrofitted uncorroded ones. The former part is represented using the available empirical prediction models, whereas the latter part is represented using the multi-linear relationships through stepwise regression with a backward elimination procedure. Through comparing with the experimental data, the developed empirical prediction models for the yield and ultimate rotation angles of FRP retrofitted corroded columns provide sufficient accuracy. Finally, the parameter “a” is determined in corresponding to different target probability of exceedance, which is required by the ASCE 41-compliant force versus displacement relation for FRP retrofitted corroded RC columns.
This study experimentally examined the seismic performance of corroded reinforced concrete (RC) columns designed with low and high axial forces. To do this, ten RC columns were designed and ...fabricated as the test specimens. They were categorized into two groups corresponding to low and high axial load ratios (ALRs), i.e., 0.1 and 0.45, respectively. Each column group consisted of an uncorroded column and four corroded columns with growing corrosion rates of 2%, 5%, 10%, and 20%. The seismic performance of each of column specimens was tested under quasi-static cyclic loadings from failure modes, hysteresis and backbone curves, ductility, stiffness, and energy dissipation. The results show that the axial load level significantly affects the seismic performance of corroded RC columns. The severely corroded RC column designed with a high ALR fails in a brittle mode, showing the detrimental and coupling effect of reinforcement corrosion and axial loads. Finally, six shear strength models that were commonly used to predict the shear strength of uncorroded columns were applied for corroded columns with accounting for the deterioration of concrete and reinforcement materials. The prediction results show that the model proposed by FEMA 273 has the highest accuracy among the considered models in predicting the shear strength of corroded columns. This study reveals the effect of axil loads on the nonlinear behavior of corroded columns under cyclic loadings. The results can benefit the engineers’ understanding of seismic performance of corroded columns.
•Ten corroded columns with axial load ratios of 0.1 and 0.45 were tested under quasi-static cyclic loading.•Seismic performance of column specimens with different axial load ratios were compared.•The severely corroded RC column designed with a high axial load ratio fails in a brittle mode.•Six models were used to predict shear strength prediction corroded columns.
Fragility functions for structural members play an important role in the FEMA P-58 methodology for the seismic performance assessment of structures. In this study, fragility functions were developed ...for aged reinforced columns with corroded reinforcing bars. To this end, an experimental database containing 120 specimens subjected to repeated cyclic loads was compiled from 20 previous studies. The experimental specimens were categorized into three groups: no corrosion damage (NCD), low corrosion damage (LCD), and high corrosion damage (HCD). These damage states were identified by experimental hysteretic responses in terms of the drift angle, which are linked to common methods of repair, including structural repair, structural enhancement, and component replacement. The obtained drift angles were used to fit the log-normal fragility functions of the NCD, LCD, and HCD columns. The effect of reinforcement corrosion was examined by comparing the fragility functions of uncorroded and corroded columns. According to the principles suggested by FEMA P-58, the developed fragility functions were mostly judged to have a high level of quality. The fragility medians of the corroded columns showed a clear decreasing trend along with an increasing degree of corrosion damage. However, the corrosion of the reinforcing bars had a limited effect on the fragility dispersion. The maximum differences in the exceedance probability were calculated by comparing the fragility curves for the LCD and NCD columns, which were greater than 20 % for all concerned damage states. For the HCD columns, the corrosion of the reinforcing bars led to the maximum difference in the exceedance probability, even beyond 50 %, compared to the results for the NCD columns. The above results reveal the significant effect of the corrosion of the reinforcing bars. The specific fragility functions developed for the corroded reinforced concrete columns will facilitate the seismic loss and resilience assessment of aging reinforced concrete building structures.
•The fragility functions of corroded RC columns were developed.•The methods of repair were suggested for three main damage states.•The quality levels of the developed fragility functions were evaluated.•The effect of reinforcement corrosion on the fragility functions was examined.
Recognition of cyber threats from open threat intelligence can give advantages to incident response in very early stage. Previous related studies mostly focus on finding general hot terms instead of ...specific continuously changing targets; as a result, usage of these methods may be limited when given specific theme as default. To our best knowledge so far, the proposed Sec-Buzzer is the first web-based service not only finding the various emerging topics of cyber threats and its corresponding annotations (i.e., nearly zero-day attacks) but also providing the possible remedy solutions. Unlike previous works, Sec-Buzzer leverages different kinds of open source, Twitter and domain-specific blogs, and benefits a lot from the community-oriented filtering strategy as well as novel topic-association graph. Therefore, a set of highly contributing Twitter users will be grouped and scored as an expert community, and information from that will be explored then efficiently exploited. Demonstrations show that, by combining several measurements to quantify significances of experts and terms, Sec-Buzzer indeed uncovers unseen valuable domain experts to be information providers, as well as identifies emerging (or suddenly appearing) topics which are highly related to real security events happened recently.
Display omitted
Despite great advances in contemporary medicine, brain death still remains enigmatic and its cellular and molecular mechanisms unsettled. This review summarizes recent findings that ...substantiate the notion that PTEN/FLJ10540/PI3K/Akt cascade, the classical tumorigenic signaling pathway, is actively engaged in experimental brain stem death. These results were based on a clinically relevant animal model that employs the pesticide mevinphos as the experimental insult in Sprague-Dawley rats to mimic brain stem death in patients died of organophosphate poisoning. The neural substrate investigated is the rostral ventrolateral medulla (RVLM), a brain stem site classically known to maintain arterial pressure (AP) and is established to be the origin of a “life-and-death” signal detected from AP, which reflects brain stem cardiovascular dysregulation that precedes death. Activation of PI3K/Akt signaling pathway in the RVLM upregulates the nuclear factor-κB/nitric oxide synthase II/peroxynitrite cascade, resulting in impairment of brain stem cardiovascular regulation that leads to the loss of the “life-and-death” signal in experimental brain stem death. This process is reinforced by FLJ10540, a PI3K-association protein; and is counteracted by PTEN, a negative regulator of PI3K/Akt signaling. The concept that a classical signaling pathway in tumorigenesis is also an active player in cardiovascular dysregulation in brain stem death provides new ramifications for translational medicine. It promulgates the concept that rather than focusing on a particular disease condition, a new vista for future therapeutic strategy against both fatal eventualities should target at this common cellular cascade.
DJ-1 (also known as PARK7) is a redox-active protein that protects against oxidative stress. This study evaluated the hypothesis that DJ-1 sustains brainstem cardiovascular regulation via maintaining ...mitochondrial function in the rostral ventrolateral medulla (RVLM), a brainstem site known to maintain blood pressure and sympathetic vasomotor tone, during cardiovascular depression elicited by the organophosphate insecticide mevinphos. In Sprague–Dawley rats, intravenous administration of mevinphos (640 μg kg−1) resulted in progressive hypotension, accompanied by an increase (Phase I) followed by a decrease (Phase II) of an experimental index for spontaneous baroreflex-mediated sympathetic vasomotor tone, alongside elevation in mitochondrial superoxide levels in the RVLM. There was concurrent activation of DJ-1 induced by oxidative stress in the RVLM, which was causally and temporally related to translocation of DJ-1 to mitochondria, reduction in mitochondrial membrane potential, increase in cytosolic apoptosis-inducing factor level, and apoptotic cell death in this brainstem site. Loss-of-function by immunoneutralization of DJ-1 in the RVLM significantly exacerbated those biochemical and cellular events, enhanced the progressive hypotension, diminished the increased and augmented the decreased spontaneous baroreflex-mediated sympathetic vasomotor tone respectively during Phases I and II, and heightened lethality during mevinphos intoxication. We conclude that DJ-1 in the RVLM sustains brainstem cardiovascular regulation induced by mevinphos via maintaining mitochondrial function.
•Oxidative stress underlies cardiovascular dysregulation in mevinphos intoxication.•Oxidative stress also causes activation of DJ-1.•DJ-1 translocates to mitochondria and maintains mitochondrial membrane potential.•DJ-1 sustains cardiovascular regulation via maintaining mitochondrial function.
Previous studies have shown that freeze-thaw cycle (FTC) action in severe cold environments is a durability issue that seriously threatens the seismic performance of concrete members. However, ...research on the seismic resistance of reinforced concrete (RC) beams under FTC action is still scarce. This paper presents an experimental study of six undamaged and frost-damaged RC beams subjected to a low-cycle reciprocating load. The paper aims to investigate the influences of FTC number and concrete strength on the seismic resistance of damaged beams. The paper reports on frost damage at different levels, cyclic damage process, hysteresis response, strength, ductility, shear deformation, and energy dissipation. The test results demonstrate that as the FTCs rose, the width and number of frost-heave cracks on the surface of the beam gradually increased. Moreover, frost action had a significant negative effect on strength, deformation, and energy dissipation, especially when the beams were highly frost-damaged. Further, the shear deformation and shear component to whole deformation gradually increased. Based on the experimental results, a time-dependent evaluation model is proposed to estimate the residual capacity of key elements of RC frame structures in severe cold climates, taking into account the effects of FTCs, concrete strength, and uneven distribution of freeze-thaw damage.
•Artificial climate rapid freeze-thaw technique to simulate the cold environment.•An investigation in the seismic performance of frost-damaged RC beams.•A weakening effect that the FTC action has on the seismic behavior of RC beam.•An equivalent conversion model of FTCs proposed between standard test schemes.•A time-dependent model proposed to evaluate the residual capacity of RC members.
