The plastic-damage factor of concrete structures is important for structural load-capacity assessment, while it has not been determined properly. In this article, two methods perspectively based on the strain equivalent principle and Sidiroff energy equivalent principle are proposed to determine the plastic-damage factor of the concrete uniaxial constitutive relation in a specification. Both of them were applied to a finite element analysis model of a simply-supported beam for nonlinear load-capacity analysis. The load-capacity experiment of the beam was carried out in unison. From the comparison of the result obtained by the energy equivalent principle method coincides better with the experimental result, which suggests that the energy equivalent principle method is reasonable and applicable. Therefore, the factor could be recommended for further consideration in specification and finite element analysis calculations.
Because lack of long-term effective technical means to test prestressing loss for continuous rigid frame bridges, an automation monitoring system based on the principle of megneto-elastic effect method had been built for testing prestressing loss and applied in the Niu Lan river bridge to fulfil long-term, online and automatic monitoring. Application shows that prestressed loss measured values consistent with the theoretical analysis values, and with good agreement. The tension error is smaller. It can be better controlled and meet the specification requirements, which shows that the magnetic bomb effect method is stable and reliable and it can effectively guide the construction. It is verified that the magneto-elastic detection method for continuous rigid frame bridge is the feasibility and rationality of automatic monitoring system.
Present approaches for assessing bridge redundancy are mainly based on nonlinear finite element (FE) analysis. Unfortunately, the real behavior of bridges in the nonlinear range is difficult to evaluate and a sound basis for the nonlinear FE analysis is not available. In addition, a nonlinear FE analysis is not feasible for practitioners to use. To tackle this problem, a new simplified approach based on linear FE analysis and field load testing is introduced in this paper to address the particular structural feature and topology of adjacent precast concrete box-beam bridges for the assessment of structural redundancy. The approach was first experimentally analyzed on a model bridge and then validated by a case study. The approach agrees well with the existing recognized method while reducing the computation complexity and improving the reliability. The analysis reveals that the level of redundancy of the bridge in the case study does not meet the recommended standard, indicating that the system factor recommended by the current bridge evaluation code for this bridge is inappropriate if considering the field condition. Further research on the redundancy level of this type of bridges is consequently recommended.
Analyses of catastrophic collapse of some adjacent precast concrete box beam bridges reveal the fact that the hinge joints between the adjacent beams were not sufficiently designed. e joint failure caused by deterioration is the result of system reliability deficiency of this type of bridges. To understand the system performance of the bridges, the redundancy and robustness of a bridge model with a scale of 1 ∶ 2, based on the prototype design drawings for 10-meter adjacent box beam bridges in China, were assessed through a system safety evaluation procedure. e result confirmed the assumption that the redundancy and robustness of certain adjacent precast concrete beam bridges did not meet the pertinent requirements proposed in National Cooperative Highway Research Program (NCHRP) reports 406, 458, and 776 as a result of hinge joint failure. To address the current design deficiencies, a system factor is recommended in this paper to calculate the nominal resistance that reflects the level of redundancy of this type of bridges. In addition, a new framework is proposed to address the particular structural feature and topology of adjacent precast concrete beam bridges for the assessment of structural redundancy and robustness, which can reduce the computation complexity compared to existing approaches. e full-range load test performed in this research verified the previous research results on bridge system safety that were mainly based on theoretical analysis and simulations.
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