Methodology For Calculation Of Bridge Safety Factor In Lithuania

The paper reviews the United States and Slovenian safety factor calculation methodologies and proposes a method for more accurate estimation of residual strength of bridges designed and built in Lithuania. For more detailed analysis, the main parameters and defects directly affecting the strength of the bridges were analysed in detail, and the flows of heavy vehicles, which have significantly increased for previously designed bridges, were assessed. This article proposes to calculate the dynamic factor of bridges, not according to the empirical formulas used in the United States and Slovenian safety factor calculation methodologies, but after performing the bridge dynamic test, because the results of Lithuanian bridge dynamic tests show that the parameter strongly depends on smoothness and damage of carriageway wearing surface. In order to evaluate the suitability of the Lithuanian bridge safety factor calculation methodology proposed in this article, a real bridge was selected, and its safety factors calculated according to the above mentioned and proposed methodology and the results obtained were compared.

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.

Numerical investigation on redundancy of bridges with AASHTO I-girders

Bridge safety is one of the most critical concerns among civil engineering fields due to its high importance. The redundancy of bridges was heavily investigated in the literature; however, they were focused on twin girder redundancy cases. Additionally, literatures were scarce in studies that focused on the improvement that should be made to achieve redundancy systems in different AASHTO I-girder types. Thus, this study focused on assessing the additional required number of tendons for different AASHTO I-girder types and spacing between them to achieve the redundancy of I-girder bridges. The additional unbonded tendons are suggested to be added externally or internally. The parameters varied in this study are compressive strength of ultrahigh-performance concrete (UHPC), spacing between girders (i.e. number of girders) and type of girders. Leap Bridge Concrete software was used to simulate the required structural modes. After performing extensive numerical analyses following AASHTO LRFD guidelines, the results have shown that in case of the removal of external I-girder, the tendons in the nearest girder need to be nearly increased by 1.85 to 2.3 times compared to the original design, depending on spacing, compressive strength, and the number of girders. On the other hand, in the case of interior girder removal, the number of tendons in the nearest two girders need to be increased by 1.24 to 1.32 times the original design. The effect of compressive strength variation of the used UHPC was negligible compared to spacing and type of girder. It is worth mentioning that all simulations in this study were verified using CSI Bridge software.