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Ali Sahrapeyma,Abdollah Hosseini,Mohammad S. Marefat 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.2
Fatigue deterioration profiles of critical elements in a railway truss bridge are determined using a probabilistic approach. A performance function including fatigue strength, R, and fatigue action, D, is used, where R is a material property with lognormal distribution. The random variable D depends on AASHTO category, stress spectrum and traffic features. By applying Monte-Carlo simulations on the performance function of each year, reliability index profile is calculated. The reliability profile decreases with life, and whenever reaches to a critical value, an MR&R action should be implemented. A numerical approach is presented to specify the effects of MR&R actions on the deterioration profile. These actions include re-welding, attaching CFRP and combination of them. The structural model is calibrated by results of a loading test. In addition, the uncertainties arisen from future traffic volume and the relevant S-N curve are considered by a statistical analysis. For a target reliability of 2.0, the retrofit time for deck and truss are estimated. Finally, the outputs of the research are used to recommend a plan for maintenance of Neka Bridge.
Cyclic load testing and numerical modeling of concrete columns with substandard seismic details
Mohammad K. Bahrani,Mohammad S. Marefat,Mohammad Khanmohammadi,Ali Goli 한국계산역학회 2005 Computers and Concrete, An International Journal Vol.2 No.5
Recent earthquakes have shown that many of existing buildings in Iran sustain heavy damage due to defective seismic details. To assess vulnerability of one common type of buildings, which consists of low rise framed concrete structures, three defective and three standard columns have been tested under reversed cyclic load. The substandard specimens suffered in average 37% loss of strength and 45% loss of energy dissipation capacity relative to standard specimens, and this was mainly due to less lateral and longitudinal reinforcement and insufficient sectional dimensions. A relationship has been developed to introduce variation of plastic length under increasing displacement amplitude. At ultimate state, the length of plastic hinge is almost equal to full depth of section. Using calibrated hysteresis models, the response of different specimens under two earthquakes has been analyzed. The analysis indicated that the ratio between displacement demand and capacity of standard specimens is about unity and that of deficient ones is about 1.7.
Ali Sahrapeyma,Mohammad S. Marefat,Abdollah Hosseini 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.4
The methodology presented in Part I is examined on Neka Bridge, a railway, truss bridge in northern Iran. The study includes:considerations of climate and air pollution, extraction of the stress-time histories from the FE model, prediction of future trafficvolumes in a probabilistic manner and assessment of the effects of MR&R actions on the deterioration profile. PDF of D isdetermined using Monte Carlo simulations, and the reliability profile is calculated from the performance function. The studyshows that for a target reliability of 2.0, the fatigue life of the bridge is reduced by either 29% or 31% if dose-response functionor qualitative-based y-t function is used, respectively.
Abdollah Hosseini,Ali Sahrapeyma,Mohammad S. Marefat 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.4
It is known that the effects of corrosion on fatigue originate from two major sources: stress concentration due to corrosiondiscontinuities (CNF factor) and stress amplification due to loosing net section (NAF factor). In order to account for theseeffects, a performance function is developed which takes CNF and NAF factors into account and considers both random andtime-dependent nature of the involved parameters. In order to consider real fatigue and environmental conditions, the availableCNF-y and y-t functions are extended employing α and ϕ factors, respectively. In addition, some recommendations have beenmade to establish corrosion pattern of different steel sections. The final output of the methodology is development of areliability-based procedure to establish time-dependent deterioration profile of a structural member, which assists in decisionmakingwith regard to maintenance activities. The proposed methodology has been applied to Neka Bridge, a railway bridgein northern Iran, which is presented in Part II.