Fatigue life prediction of bridges considering the effect of Multiaxial stresses

This paper presents a new low cycle fatigue model to predict life of steel bridges. It consists of Coffin-Manson strain-life curve with a new strain based damage index. The damage variable is based on a modified von Mises equivalent strain to account for effects of loading non-proportionality and strain path orientation in low cycle multiaxial stress state. The proposed model was verified by comparing with experimental test results of two materials. Then, it was applied an existing riveted wrought iron railway bridge to estimate fatigue life due to usual traffic and earthquake loadings. The obtained results verify the importance and effectiveness of the proposed model over commonly used Miner’s rule model in fatigue life estimation of steel bridges

Development of Autonomous Multi Agent System for Multi-Hazard Risk Assessment

Developing autonomous multi agent systems are to be considered anadvancement of multi agent systems can be applied in both the physical and the logicalworld. Constructions of multi hazard risk assessment using spatial data for disastermanagement have a problem of effective communication because of implicitknowledge. Risk assessment is the determination of quantitative or qualitative value ofrisk related to a concrete situation and a recognized hazard. Multi hazard riskassessment requires commonsense knowledge related with the hazard. This complicatesthe effective communication of data to the user in real-time machine processing insupport of disaster management. The aim of the approach is to identify the influences ofdeveloping autonomous multi agent systems for risk assesmnet in disaster management.The objectives should a) contribute to a better understanding of the transformationprocesses in commonsense knowledge related with a hazard and b) provide effectivecommunication of data to the user in real-time machine processing in support of disastermanagement.In this paper we present a metodology to modeling commonsenseknowledge in Multi hazard risk assessment using Autonomous multi agent system. Thisgives three-phase knowledge modeling approach for modeling commonsenseknowledge in, which enables holistic approach for disaster management. At the initialstage autonomous agents are initialized to convert commonsense knowledge based onmulti hazards into a questionnaire. Removing dependencies among the questions aremodeled using principal component analysis. Classification of the knowledge isprocessed through fuzzy logic agent, which is constructed on the basis of principalcomponents. Further explanations for classified knowledge are derived by agent basedon expert system technology. We have implemented the system using FLEX expertsystem shell, SPSS, XML and VB. This paper describes one such approach usingclassification of human constituents in Ayurvedic medicine. Evaluation of the systemhas shown 77% accuracy.Key words: Autonomous multi agent systems, Multi hazards, risk assessment,commonsense knowledge, Fuzzy logi

Combined high and low cycle fatigue model for prediction of Steel bridge lives

A new fatigue model is presented to predict life of steel bridges for combined high and low cycle fatigue. It consists of a modified strain-life curve and a new strain based damage index. The damage variable is based on a modified von Mises equivalent strain to account for effects of loading non-proportionality and strain path orientation in multiaxial stress state. The proposed model was verified with experimental test results of two materials, available in the literature. Then, the proposed model was applied to a wrought iron railway bridge to estimate the fatigue life due to usual traffic and earthquake loadings. The obtained results confirm the importance and effectiveness of the proposed model over commonly used Miner’s rule based life prediction of steel bridges

Maintenance strategy for bridges using reliability concept and analytical hierarchy process

Civil infrastructure in most of countries is getting old and therefore, there is a tremendous need to assess their safety levels. Among civil infrastructure, bridges are one of the main components and there is a need to study more on their safety and durability to minimize the maintenance cost and to avoid sudden failures. This paper presents bridge maintenance strategy which consists of two parts: (1) reliability based condition assessment procedure and; (2) analytical hierarchy process (AHP) based resources prioritization. In reliability based assessment, safety margins are initially proposed depending on the types of bridges. It is assumed that load and strength are random variables. Elementary reliability indices and thereby elementary failure probabilities are estimated for each safety margins. Then, system failure probability of the bridge is calculated for the time of consideration. Finally, this system failure probability is used to get system reliability index of the bridge and it is used as an index to express the condition of the bridge for the considered time. Secondly, AHP is implemented to identify the order of resources prioritization among set of bridges. The selected criteria are safety, cost of maintenance actions and relative importance of the bridge. Relative importance varies depending on historical importance, age and route of bridge location. The proposed methodology is applied to a collection of five bridges in Sri Lanka to estimate their safety levels and resources prioritization in bridge maintenance

Heterobimetallic Catalysis: E-Selective Semi-Hydrogenation via Spectroscopic and Theoretical Studies

The stepwise reaction development of a unique cooperative H2 activation reaction by heterobimetallic (NHC)M’-MCp(CO)2 complexes (NHC = N-heterocyclic carbene, M’ = Cu or Ag, M = Fe or Ru) to yield a catalytic E-selective semi-hydrogenation transformation of alkynes is presented. Late-late heterobimetallic complexes featuring polar metal-metal bonds, introduced by the Mankad group, are utilized and improved in this study. To design catalysts methodically, it is important to gain insight into the structure and function of these heterobimetallic complexes. Therefore, an experimental and a theoretical analysis is pursued first. Initially, the electronic structure and the function of heterobimetallic complexes are investigated using XANES, IR and Mössbauer spectroscopy. Bimetallic oxidative addition is studied extensively and the individual roles of the metals and ligands are elucidated. Reactivity is investigated further using theoretical calculations. A DFT analysis of a bimetallic oxidative addition and a bimetallic N2O activation reveal transition states and thermodynamic parameters comparable to experimental values. The key components of the catalysts are identified, and a series of novel complexes are synthesized by the Mankad group. A theoretical analysis of these complexes is presented and structural trends are deduced. The actual implementation of the heterobimetallic strategy into reaction development is carried out next. The initial catalyst screening is performed by thermodynamic energy calculations using DFT. A robust heterobimetallic catalyst that utilizes H2 under atmospheric pressure for E-selective semi-hydrogenation of alkynes, a rare selectivity mode in high yields, is developed. The mechanistic features of this reaction are also explored. Experimentally, the proposed mechanism is examined using model complexes. Theoretically, the transition state of the bimetallic H2 activation step, bond orders and fragment charges along the reaction coordinate, and key orbital interactions, are calculated. A kinetic study motivated by calculations from a collaborating group is also presented. Finally, the future directions inspired by this work are discussed. Preliminary work on the development of bifunctional catalytic reactions by trapping the intermediates of the initial hydrogenation reaction to introduce new substrates, is presented, revealing a gateway for many future developments

<i>E</i>‑Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis

A unique cooperative H₂ activation reaction by heterobimetallic (NHC)­M′-MCp­(CO)₂ complexes (NHC = <i>N</i>-heterocyclic carbene, M′ = Cu or Ag, M = Fe or Ru) has been leveraged to develop a catalytic alkyne semi-hydrogenation transformation. The optimal Ag–Ru catalyst gives high selectivity for converting alkynes to <i>E</i>-alkenes, a rare selectivity mode for reduction reactions with H₂. The transformation is tolerant of many reducible functional groups. Computational analysis of H₂ activation thermodynamics guided rational catalyst development. Bimetallic alkyne hydrogenation and alkene isomerization mechanisms are proposed

Heterobimetallic H₂ Addition and Alkene/Alkane Elimination Reactions Related to the Mechanism of <i>E</i>‑Selective Alkyne Semihydrogenation

Mechanistic aspects of an <i>E</i>-selective alkyne semihydrogenation catalyst are studied through computational modeling and experimental model reactions. We previously communicated the semihydrogenation of diarylalkynes to produce <i>trans</i>-alkenes using the heterobimetallic catalyst (IMes)­AgRuCp­(CO)₂. In this report, we disclose further details on the catalyst decomposition products under catalytic conditions, the mechanism of bimetallic H₂ activation, and the factors affecting selectivity for <i>E</i>-alkene generation. Under hydrogenation conditions, the catalyst decomposition product HRuCp­(CO)­(IMes) was isolated and characterized. Resubmitting this species to the catalytic conditions did not provide useful hydrogenation catalysis, confirming the presence of a bimetallic mechanism under optimal catalytic conditions. The detailed nature of heterobimetallic H₂ activation was probed by calculating internuclear bond orders, atom/fragment charges, and NBO occupancies as functions of reaction coordinate for a model reaction between (IMe)­CuRp and H₂. The collected results indicate a late transition state involving deprotonation of a Cu­(H₂) σ-complex by the proximal Rp fragment. Late stages of the reaction profile feature H···H dihydrogen bonding between (IMe)­CuH and HRuCp­(CO)₂, indicative of heterolytic H₂ activation. NBO analysis indicates that the key orbital interactions involved in H₂ activation are (a) donation from the filled H₂ σ-orbital into a Cu 4p acceptor orbital and (b) back-donation from a filled Cu–Ru bonding orbital of predominantly Ru 4d character into the empty H₂ σ*-orbital. Experimental support for the previously proposed cascade alkyne → <i>Z</i>-alkene → <i>E</i>-alkene process was provided by stoichiometric reactions between HRuCp­(CO)₂ and isolable (IPr)­CuR models of catalytic (IMes)­AgR intermediates (R = alkenyl, alkyl). The collected experimental results indicate that selectivity for <i>E</i>-alkene generation is dictated by the relative rates of monometallic β-hydride elimination and bimetallic alkane elimination, which are impacted by several structural features of the catalyst. The mechanistic detail provided by these studies will inform the development of second-generation hydrogenation catalysts

<i>E</i>‑Selective Semi-Hydrogenation of Alkynes by Heterobimetallic Catalysis

A unique cooperative H₂ activation reaction by heterobimetallic (NHC)­M′-MCp­(CO)₂ complexes (NHC = <i>N</i>-heterocyclic carbene, M′ = Cu or Ag, M = Fe or Ru) has been leveraged to develop a catalytic alkyne semi-hydrogenation transformation. The optimal Ag–Ru catalyst gives high selectivity for converting alkynes to <i>E</i>-alkenes, a rare selectivity mode for reduction reactions with H₂. The transformation is tolerant of many reducible functional groups. Computational analysis of H₂ activation thermodynamics guided rational catalyst development. Bimetallic alkyne hydrogenation and alkene isomerization mechanisms are proposed