Load‐bearing control of slender bridges

An active control of the load‐bearing capacity of slender bridges is treated in the present paper. Interactive conditions in ultimate response are considered. A numerical treatment of the occurring/appearing non‐linear problems is made using the updated Lagrangian formulation of motion. Each step of the iteration approaches the solution of linear problem and the feasibility of the parallel processing FETM‐technique with adaptive mesh refinement and substructuring for the analysis of ultimate behaviour of bridges is established. Application to an actual bridge is submitted in order to demonstrate the efficiency of the procedures suggested. Copyright © 2004 John Wiley & Sons, Ltd.     

Methodology for development of live load models for refined analysis of short and medium-span highway bridges

Abstract

The accuracy of bridge system safety evaluations and reliability assessments obtained through refined structural and finite element analyses depends not only on the accuracy of the structural model itself but also on the proper modelling of the maximum traffic loads. While current code-specified live load models were calibrated to properly reflect the safety levels of bridge structures analysed using the simplified methods adopted in bridge design and evaluation manuals, these load models may not lead to accurate results when implemented during refined structural analysis procedures. This paper describes a method to calibrate appropriate live load models that can be used for advanced analyses of bridges. The calibration procedure is demonstrated using actual traffic data collected at a representative weigh-in-motion station in New York State. The proposed calibration methodology is applicable for developing live load models for different bridge service periods, bridge types and design/assessment codes or standards. Live load models obtained using the proposed calibration procedure are readily implementable for deterministic refined analyses of highway bridges to produce similar results to those of complex traffic load simulations. Examples are presented that describe how results of such calibrated live load models would be used in engineering practice.     

Uncertainty in risk of highway bridges assessed for integrated seismic and flood hazards

Probabilistic risk assessment for bridges under natural hazards is of great interest to engineers for the development of risk mitigation strategies and implementation plans. The present study evaluates risk of an existing highway bridge in California, USA, under the integrated impact of regional seismic and flood hazards. A sensitivity study combining tornado diagram and first-order second moment reliability analyses is conducted to screen significant uncertain parameters to which bridge response is mostly sensitive. A rigorous uncertainty analysis, employing random sampling and Monte Carlo simulation techniques, is performed to obtain variations in fragility and risk curves of the bridge. Observed variations in risk curves at various risk levels are quantified through 90% confidence intervals and coefficients of variation (COV) of risk. It is observed that uncertainty in the estimated risk increases due to the presence of flood hazard at the bridge site, although mean risk does not vary with flood hazard level. Research outcome signifies that the variation in risk due to parameter uncertainty and varied flood hazard level should not be ignored to ensure bridge safety under the stated multi-hazard condition.     

Ribosomal Synthesis of Natural‐Product‐Like Bicyclic Peptides in Escherichia coli

Methods to access natural‐product‐like macrocyclic peptides can disclose new opportunities for the exploration of this important structural class for chemical biology and drug discovery applications. Here, the scope and mechanism of a novel strategy for directing the biosynthesis of thioether‐bridged bicyclic peptides in bacterial cells was investigated. This method entails split intein‐catalyzed head‐to‐tail cyclization of a ribosomally produced precursor peptide, combined with inter‐side‐chain crosslinking through a genetically encoded cysteine‐reactive amino acid. This strategy could be successfully applied to achieve formation of structurally diverse bicyclic peptides with high efficiency and selectivity in Escherichia coli. Insights into the sequence of reactions underlying the peptide bicyclization process were gained from time‐course experiments. Finally, the potential utility of this methodology toward the discovery of macrocyclic peptides with enhanced functional properties was demonstrated through the isolation of a bicyclic peptide with sub‐micromolar affinity for streptavidin.     

泉州湾跨海大桥引桥宽幅箱梁节段预制安装关键技术

以泉州湾跨海大桥引桥为工程背景,探讨了宽幅箱梁横向变形对预制和安装精度的影响,同时对墩顶块临时锚固措施展开研究。研究结果表明,预应力钢绞线临时锚固效果优于精轧螺纹钢锚固。最后对线形调整措施展开研究,加垫环氧树脂垫片调整线形时,胶结层厚度对调整效果影响很大。     

斜塔斜拉城市景观桥梁施工监控应变测试误差分析及修正方法研究

在桥梁施工监控过程中,常会埋设较多振弦式应变传感器来监测桥梁结构控制截面的应力。但由于受传感器安装误差、温度变化以及混凝土收缩、徐变等因素影响,造成测试的结果与实际应力水平往往差别较大。通过对影响测试结果因素的分离、剔除与修正,得到结构弹性应变,并给出简易计算公式。结合工程实例,验证了计算方法的可行性和可靠性。