Curved bridges live load bending moment distribution using straight and curved girders

abstract: The present study focuses on comparative parametric analysis of curved precast concrete bridges using straight and curved I-girders. The live load bending moment distribution for girders was studied using the bridge curvature and its relationship with the results obtained for a straight bridge. FEM 3D models were developed with restrictions on the transverse live load positions and with two different load models types: HL-93 (AASHTO) and TB-450 (NBR 7188, 2013). The parametric analysis results were calculated using the Modification Factor (MF) and the Bending Moment Distribution Factor (BMDF), calculated from the structural analysis of each model at the midspan. Globally, an increase was found in the total bending moment for the curved bridge models in relation to the straight bridge. In the examples herein studied, the larger the bending radius, the larger the maximal bending moment in the bridge center. For the external girders, the MF increases with the increase of the L/R. For the internal ones, the MF decreases with the increase of the L/R. In addition, the occurrence of “Load Shift” was different from the rigid body behavior, for there was demonstrated a different bending moment variation between external girder (G1) in relation to its adjacent (G2). Therefore, the structural behavior of straight (SG) and curved girders (CG) was analyzed, revealing that, in the SG, a significant gap occurred in the BMDF between G1 and G2 girders for all curvatures. For L/R = 0.6, it caused a difference of 17.8% in the BMDF between the G1 and G2 girders, while on the curved girders, a difference of only 6.6% was found.

Study on the Seismic Performance of Prefabricated Single-Segment Steel Jacket Bridge Piers

To study the seismic performance of prefabricated single-segment steel jacket piers connected by grouting sleeves, two scaled symmetrical pier models with different anchorage lengths of the longitudinal reinforcement in the grouting sleeves and a comparative symmetrical cast-in-place (CIP) model were designed. OpenSees finite element models were established and shaking table tests were carried out on the three scaled pier models. The seismic response of each pier was compared and analyzed. Results showed the stiffness of the two prefabricated piers was greater than that of the CIP pier, and other seismic responses were less than those of the CIP piers, The dynamic responses of the two prefabricated bridge models were similar and changing the anchorage length of the reinforcement in the grouting sleeve had little effect on the seismic performance of the prefabricated pier. The simulation results were in good agreement with the experimental results. In the parameter analysis, the counterweight of the pier top had the greatest influence on the seismic performance of the prefabricated pier. The anchorage length of the longitudinal reinforcement in the grouting sleeve could be 6–14 times the diameter of the longitudinal reinforcement. Moreover, the seismic performance was found to be optimal when the thickness of the steel jacket was 5–7 mm.

Chromosome breaks in breast cancers occur near herpes tumor virus sequences

This work finds viral DNA associates with most chromosome breaks in breast cancer and provides a mechanism for why this is so. Nearly 2000 breast cancers were compared to known Epstein Barr virus (EBV) variant cancers using publicly available data. Breast cancer breakpoints on all chromosomes cluster around the same positions as in nasopharyngeal cancers (NPCs), cancers 100 per cent associated with EBV variants. Breakpoints also gather at the same differentially methylated regions. Breast cancer further has an EBV methylation signature shared with other cancers that inactivates complement. Another known EBV cancer (Burkitt lymphoma) has distinctive MYC gene breakpoints surrounded by EBV like DNA. EBV like DNA consistently surrounds breast cancer breakpoints, which are often near known EBV binding sites. EBV explains why a break in a chromosome does not simply reconnect in breakage fusion bridge models, but instead destabilizes the entire genome. This work does not prove EBV variants cause breast cancer, but establishes links to high risk chromosome breaks and other changes.

Seismic Vulnerability Assessment of Skewed Reinforced Concrete Bridges

Skewed bridges are commonly used in highway interchanges where the straight (unskewed) bridges are not suitable. There have been several observations of heavy damage of bridges that have geometric irregularities, especially significant skewness. Such damage severely disrupts transportation systems, leading to substantial economic consequences. Skewed bridges are often inevitable due to the complexity and lack of orthogonality of transportation networks; hence better quantification of the effects of skewness on the bridge performance is a more viable approach than avoiding skewed bridges. This research focuses on the seismic vulnerability analysis of skewed reinforced concrete (RC) bridges. From the straight to highly skewed, various bridge models are created based on design example No. 4 prepared by the US Federal Highway Administration (FHWA). A set of earthquake ground motion records is carefully selected to impose consistent seismic demands on bridges. The fragility relationships for all bridge configurations are derived from the non-linear dynamic response history analysis. A new structural reliability method is utilized to handle the computational challenge in deriving fragility curves, which incorporates the structural analysis and reliability analysis to calculate the failure probability efficiently and accurately with the first-order reliability method (FORM). An attempt is made to parameterize the problem based on the skew angle. It is shown that the skew angle has a direct effect on the seismic vulnerability of RC bridges. The results reported will be helpful for new designs of skew RC bridges.

Axle Configuration and Weight Sensing for Moving Vehicles on Bridges Based on the Clustering and Gradient Method

Traffic information, including vehicle weight and axle spacing, is vital for bridge safety. The bridge weigh-in-motion (BWIM) system remotely estimates the axle weights of moving vehicles using the response measured from instrumented bridges. It has been proved more accurate and durable than the traditional pavement-based method. However, the main drawback of conventional BWIM algorithms is that they can only identify the axle weight and the information of axle configuration (the number of axles and axle spacing) is required to be determined using an extra device in advance of the weight identification procedure. Namely, dedicated sensors (pressure-sensitive sensors placed on the deck surface or under the soffit of a bridge) in addition to weighing sensors must be adopted for identifying the axle configuration, which significantly decreases the utility, feasibility, and economic efficiency of BWIM technology. In this study, a new iterative procedure simultaneously identifying axle spacing as well as axle weights and gross weights of vehicles is proposed. The novel method is based on k-means clustering and the gradient descent method. In this method, both the axle weight and the axle location are obtained by using the same global response of bridges; thus the axle detectors are no longer required, which makes it economical and easier to be implemented. Furthermore, the proposed optimization method has good computational efficiency and thus is practical for real-time application. Comprehensive numerical simulations and laboratory experiments based on scaled vehicle and bridge models were conducted to verify the proposed method. The identification results show that the proposed method has good accuracy and high computational efficiency in axle spacing and axle weight identification.

Experimental study on blast damage of RC T-beam bridge

Purpose The purpose of this paper is to investigate the explosive performance and explosion damage mechanism of T-beam bridge structure. Design/methodology/approach On the basis of the existing specification, two T-beam bridge models were designed and fabricated. Test specimens of different explosive dosage and different blast height were carried out. The mechanical process, failure mode, blast damage model, damage identification mechanism and blast evolution law and quantitative evaluation were taken into account. Findings The results revealed that the web plate fracture failure is the key to the unstable failure of the whole T-beam bridge. The explosion failure phenomenon and blast damage evaluation criterion of RC T-beam bridge was divided into five stages: the original cracks stage of concrete material (D = 0 ∼ 0.1), the fractures initiation stage of concrete material (D = 0.1 ∼ 0.3), the stable expansion stage of cracks in concrete material (D = 0.3 ∼ 0.55), the unstable expansion stage of cracks in concrete material (D = 0.55 ∼ 0.8), the explosion fracture of steel bars and the overall instability and damage of the bridge (D = 0.8 ∼ 1.0), which can also be described as basically intact, slight damage, moderate damage, severe damage and collapsed. Social implications The research result will provide basis for the antiknock evaluation and damage repair technical specifications of the RC T-beam bridge. Originality/value The research results of damage evaluation serve as a basis for damage repair and reinforcement of bridge structures after explosion.

Relationship between the Dynamic Parameters of a Structure’s Vibration Process and the Loading Model Moving on a Bridge

A sufficiently strict conduction of supervision during bridge operation is a crucial matter for many countries, including the underdeveloped country of Viet Nam. In recent times, the budgets in developed countries used for funding the implementation of quality-assessment procedures are quite high compared to the lower budgets in underdeveloped countries. The plan proposed in this work addresses the current lack of information available in the process of structure-quality evaluation. The vibration signals will be acquired from the random circulation status to determine the structure’s behavior so as to utilize the signal information during the bridge span’s operation. The study’s main goal is to find various parameters that can be used to evaluate the actual bridge performance. These parameters must meet certain criteria, such as high sensitivity, low measurement cost, and efficiency in the measurement process, but must not affect the itinerary of vehicles moving on the bridge. The actual structural vibration signals used in this work currently serve as a best trend model for evaluating the operation of the bridge span structure. This study will focus on determining the relationship among deflection, acceleration, and vehicle load so as to evaluate the structure’s working process. This study has also fabricated an experimental model to evaluate and test the sensitivity of the parameters utilized in this study in order to verify the results obtained. The results obtained in this research will be applied for the quality-control process in several bridge models with span structures built with the composite steel concrete cross section of the beam. Many developing countries, including Viet Nam, will receive benefit in the future from the useful advantages presented in this study.

Experimental and theoretical studies of composite multiple-box girder bridges

Due to their high torsional and wrapping stiffness as well as economic and aesthetic reasons, multi spine composite concrete-deck steel-box girder bridges became a very popular choice in highway bridges. Currently, North American Codes of Practice have recommended some analytical methods for the design of curved multiple-box girder bridges, providing a geometrically defined criterion to establish when horizontally curved may be treated as a straight bridge. To meet the practical requirements arising during the design process, a simple design method is needed for straight and curved composite box girder bridges in the form of load distribution factors. This study consisted of an experimental and a theoretical investigation. The experimental investigation included testing up-to-collapse three bridge models. While the theoretical investigation used a finite element software to examine the behavior of 225 different bridges to extract stress distribution factors for maximum bending stresses that occur at the mid span.

Experimental and theoretical studies of composite multiple-box girder bridges

Due to their high torsional and wrapping stiffness as well as economic and aesthetic reasons, multi spine composite concrete-deck steel-box girder bridges became a very popular choice in highway bridges. Currently, North American Codes of Practice have recommended some analytical methods for the design of curved multiple-box girder bridges, providing a geometrically defined criterion to establish when horizontally curved may be treated as a straight bridge. To meet the practical requirements arising during the design process, a simple design method is needed for straight and curved composite box girder bridges in the form of load distribution factors. This study consisted of an experimental and a theoretical investigation. The experimental investigation included testing up-to-collapse three bridge models. While the theoretical investigation used a finite element software to examine the behavior of 225 different bridges to extract stress distribution factors for maximum bending stresses that occur at the mid span.