Impact of corrosion deterioration on the seismic performance of steel frame structures

Steel structures designed before the introduction of modern seismic design codes may be characterised by high seismic vulnerability due to their reduced ductility capacity. Additionally, these structures may be affected by significant corrosion deterioration, as one of the major atmospheric degradation phenomena when built in corrosive environments. Corrosion deterioration leads to a thickness reduction of sections, reduced bearing capacity, stiffness degradation and loss of energy dissipation capacity. Thus, old-corroded steel structures located in seismically active regions could experience a reduction of their seismic performance, significantly increasing the failure probability under earthquake events. The present study investigates the effect of atmospheric corrosion deterioration on steel frames and uses a nonseismically designed three-storey moment-resisting frame for case-study purposes. Atmospheric corrosion models based on the recommendation of ISO 9224:2012 have been adopted considering a 50-years ageing time and modelled as uniform corrosion on steel members. A probabilistic seismic performance assessment of the pristine and ageing steel frames is performed through Incremental Dynamic Analyses (IDAs). IDAs are performed for a set of 43 ground motion records accounting for the influence of the earthquake input’s uncertainty (i.e., the record-to-record variability). The corrosion effects on the seismic performance are evaluated by monitoring both global and local engineering demand parameters (EDPs), allowing the development of seismic fragility functions at components- and system-level

Seismic Fragility Updating of Highway Bridges using Field Instrumentation Data

Seismic fragility assessment of deteriorating highway bridges using analytical methods often rely on empirical, semi-empirical or numerical models to predict the rate and nature of degradation. Consequently, the predicted structural vulnerabilities of bridge components or overall bridge system during seismic shaking are only as good as the adopted deterioration models. For the sake of simplicity and ease of computational modeling, these deterioration models are often far removed from observed manifestations of time-dependent aging. One such example is the nature of corrosion in reinforced concrete bridge components under chloride attacks. While this deterioration mechanism leads to the formation of pits along the length of the rebar, past literature often adopts the simplified uniform area loss model. This study proposes a probabilistic framework that assists in improved deterioration modeling of highway bridges by explicitly modeling pit formation and also provides the opportunity of updating the analytical models with field measurement data using Bayesian techniques. The framework and case-study results presented in this study are believed to render realistic seismic fragilities for highway bridges when located in moderate to high seismic zones.This research was funded by the Science and Engineering Research Board Grant No. ECR/2016/001622. Their support is gratefully acknowledged

Impact of asymmetrical corrosion of piers on seismic fragility of ageing irregular concrete bridges

This article investigates the seismic fragility of ageing irregular multi-span reinforced concrete (RC) bridges. Different irregularity sources are considered, including: (i) substructure stiffness irregularity arising from the unequal-height piers, (ii) substructure stiffness irregularity arising from the spatially variable (asymmetrical) corrosion damage of piers and (iii) irregular distribution of effective tributary masses on piers of varying heights. To this end, a three-dimensional nonlinear finite element model is developed for multi-span RC bridges and verified against a large-scale shake table test results of a two-span concrete bridge specimen available in the literature. Nonlinear pushover, incremental dynamic and seismic fragility analyses are performed on three groups of two-span RC bridges with different configurations. Moreover, a time-dependent dimensionless local damage index is employed to evaluate the failure sequence and collapse probability of selected bridge layouts. The analysis results of the three studied irregularity sources show the considerable significance of spatially variable corrosion of bridge piers and substructure irregularity on the failure sequence of piers and seismic fragility of multi-span RC bridges. Furthermore, analysis outcomes show that uneven corrosion of piers triggers an unbalanced distribution of seismic ductility demands and irregular seismic response of equal-height multi-span RC bridges

Impact of seismic retrofitting on progressive collapse resistance of RC frame structures

Most of the existing buildings in seismic prone regions have been built before the publication of modern design provisions against earthquakes, resulting in the need for structural retrofitting. Furthermore, some of those buildings are also subjected to additional hazards that may be either triggered by earthquakes (e.g., landslides, soil liquefaction, tsunamis) or associated with other natural or anthropogenic events, such as floods, vehicle collision, blast, and fire. A multi-hazard performance assessment of building structures is thus of paramount importance to implement integrated retrofit strategies, which otherwise would not be economically sustainable if oriented to structural risk mitigation against a single hazard. While retrofit strategies to improve the seismic performance of reinforced concrete (RC) structures have been widely investigated, structural retrofitting against progressive collapse has received very little attention. Within this context, the present paper illustrates a numerical investigation on the influence of seismic retrofitting on structural robustness of a four-storey, five-bay, RC frame building designed only to gravity loads. Seismic performance and structural robustness were respectively evaluated in OpenSees through pushover and pushdown analyses of a fibre-based finite element model. Structural robustness was evaluated under two relevant column-removal scenarios, i.e., the sudden loss of a central and a corner column, whereas earthquake resistance was assessed according to the N2 method, evidencing the need for seismic retrofitting. A retrofit measure based on carbon fibre reinforced polymers was then considered to avoid premature brittle failures. Analysis results show that this retrofit strategy was able to increase both seismic safety and structural robustness. Subsequently, a parametric analysis was carried out in order to evaluate the impact of beam span length and shear strength of the retrofitting system

Uncertainty Quantification and Fragility Development of Deteriorating RC Bridge Piers

Corrosion can reduce structural capacity and increase the risk of bridge damage/failure under extreme events. The impact of corrosion on seismic fragility of bridges has been well studied. However, the methodology used in most existing studies requires detailed information on the structural design and condition of a bridge, which is a major hindrance in conducting seismic risk assessment for a large population of bridges. Furthermore, existing studies do not adequately address the time-dependency of uncertainties associated with fragility curve development. This study presents a methodology to generate time-dependent seismic fragility curves for deteriorating highway bridges based only on the limited information available from National Bridge Inventory (NBI) and the HAZUS technical manual. As a result, the methodology can be implemented for a large number of bridges and potentially be integrated in existing bridge management practice. Despite the limited information required, a full probabilistic analysis was conducted in this study to develop these fragility curves, accounting for various uncertainties in material properties, geometric imperfection, corrosion development, and model error of seismic capacity/demand models. The methodology was implemented as an example for highway bridge class 5, as defined by the HAZUS technical manual. Results showed that during the 100-year service life, corrosion can potentially cause 30% decrease in median seismic capacity and 20% increase in capacity-side uncertainty. However, the effect of corrosion hinges on the corrosion models and model parameters

Consideration of time-evolving capacity distributions and improved degradation models for seismic fragility assessment of aging highway bridges

This paper presents a methodology to develop seismic fragility curves for deteriorating highway bridges by uniquely accounting for realistic pitting corrosion deterioration and time-dependent capacity distributions for reinforced concrete columns under chloride attacks. The proposed framework offers distinct improvements over state-of-the-art procedures for fragility assessment of degrading bridges which typically assume simplified uniform corrosion deterioration model and pristine limit state capacities. Depending on the time in service life and deterioration mechanism, this study finds that capacity limit states for deteriorating bridge columns follow either lognormal distribution or generalized extreme value distributions (particularly for pitting corrosion). Impact of column degradation mechanism on seismic response and fragility of bridge components and system is assessed using nonlinear time history analysis of three-dimensional finite element bridge models reflecting the uncertainties across structural modeling parameters, deterioration parameters and ground motion. Comparisons are drawn between the proposed methodology and traditional approaches to develop aging bridge fragility curves. Results indicate considerable underestimations of system level fragility across different damage states using the traditional approach compared to the proposed realistic pitting model for chloride induced corrosion. Time-dependent predictive functions are provided to interpolate logistic regression coefficients for continuous seismic reliability evaluation along the service life with reasonable accuracy. (C) 2016 Elsevier Ltd. All rights reserved

Vulnerability assessment of sign-support structures during transportation and in service

Dynamic Message Signs (DMSs) are increasingly used in highways as an effective means to communicate time-sensitive information with motorists. To ensure their long-term performance, it is critical to ensure that the truss structures that hold them can resist not only extreme loading events, but also fatigue induced by service loads. For this purpose, a comprehensive study has been conducted on the fatigue performance of this important category of structures. The current study evaluates the fatigue performance of DMS-support structures during transportation under road-induced excitations as well as throughout their service life under loads induced by environmental stressors. In the first section, fatigue analysis of these structures during transportation under road-induced excitations is conducted. To investigate this, a comprehensive field test and numerical study are conducted. For short-term monitoring, one span of a sign-support structure is instrumented. Additionally, detailed finite element simulations are conducted to obtain an in-depth understanding of the potential modes of damage under the road-induced excitations. The outcome of this study is expected to determine the extent of fatigue of DMS-support structures during transportation. In the second part, vulnerability assessment of these structures is investigated under thermal loads. For that purpose, two DMS-support structures located in Iowa are selected for long-term monitoring. Moreover, detailed finite element simulations are conducted to obtain an in-depth understanding of the expected extent of damage. Based on the results obtained from this study, the DMS-support structures are found to demonstrate a great performance under thermal loads, which strongly supports the recent transition from aluminum to steel truss structures. Finally, fatigue performance of DMS-support structures under the combined effects of diurnal temperature changes and natural wind excitations is investigated. Field monitoring has been paired with detailed FE simulations to understand the fatigue performance of DMS-support structures under multiple stressors. The current study is concluded with the investigation of wind directionality effects. The outcome of this study is expected to not only contribute to the long-term performance and safety of DMS-support structures, but also pave the way to implement similar multi-stressor perspectives for other transportation infrastructures in service

Korozyon etkisi altındaki betonarme çerçevelerin doğrusal olmayan davranışının sabit tek modlu itme yöntemi ile incelenmesi

xxv, 111 sayfa: şekil29 cm. 1 CDÖZETÜlkemizde yetersiz beton örtüsü, elverişsiz malzeme, çevresel etkiler gibinedenlerden dolayı donatı korozyonuna uğramış betonarme yapı elemanlarına sıkça rastlanmaktadır. Korozyonun neden olabileceği hasarların kontrol altına alınması, yapı emniyeti, güvenilirlik ve ekonomiklik açısından gereklidir. Bu çalışmada, korozyon mekanizmasının Türkiye Bina Deprem Yönetmeliği’ne (TBDY2018) göre tasarlanan bir çerçeve yapı üzerindeki etkileri sabit tek modlu itme analizi ile araştırılmıştır. Betonarme çerçeve modeli için yapılan analizler sonucunda beton örtüsü ile orantılı olarak üniform korozyon başlama zamanının arttığı belirlenmiştir. Üniform korozyon sonrası kalan donatı alanları beton örtüsü arttıkça artmakta olup donatı mekanik özelliklerinin değişimi beton örtüsü ile paralel olarak artmaktadır.İtme analizleri neticesinde taban kesme kuvvetleri - tepe yer değiştirmesi grafikleri depremin yatay yer değiştirme istemlerine göre elde edilmiştir. Özellikle deprem bölgelerinde yer alan betonarme binalarda korozyonun yapısal davranış üzerindeki olumsuz etkileri, TBDY2018 yönetmeliği esaslarına göre gösterilmiştir. Betonarme binaların depremin yer değiştirme istemine göre gerekli taban kesme kuvvetlerinin korozyon nedeniyle zamana bağlı değişimleri beton örtüsü ve korozyon tipi dikkate alınarak incelenmiştir.ABSTRACTReinforced concrete structural elements which are corroded due to reasons such as insufficient concrete cover, unfavorable material and environmental effects are frequently encountered in our country. Control of damages caused by corrosion is essential in terms of structural safety, reliability and economy. In this study, effect of corrosion mechanism is investigated on a frame structure that is designed according to Turkish Earthquake Code (TBDY2018) using pushover analysis. Analysis resultsof the reinforced concrete frame show that uniform corrosion initiation time increases proportionally with the concrete cover. The remaining sectional areas of rebars after uniform corrosion increase as concrete cover increases and alteration of the material properties of rebars after uniform corrosion increases in parallel with the concrete cover. Due to the results of pushover analysis, base shear – top horizontal displacement graphics are obtained according to seismic demands. Detrimental effects of corrosion on structural behavior, especially in reinforced concrete buildings that are located in earthquake zones, have been studied according to TBDY2018 regulations. Time-dependent changes of the base shear forces of thereinforced concrete buildings according to the seismic displacement demands due to the corrosion are investigated by considering the concrete cover and corrosion type