Some Evaluations on the Technical State of Metal Products and Determination of their Safe Operation Period on the Basis of Criterial Control

Over a long period of operation, under the influence of corrosion and stresses from the acting forces, metal structures lose their strength. There is a need for their periodic non-destructive testing. The development of new methods is relevant in the field of control of building metal structures, such as bridge structures, structures of building cranes and other mechanical engineering products. The applied methods should be reliable and should not require huge material and labor costs. In this work, informational relationships between acoustic characteristics and parameters of metal microstructure are established. The proposed method can be useful for specialists and experts in the field of monitoring the technical condition of metal products requiring non-destructive testing. The safety of the operated objects depends on the accuracy of the applied criteria, as well as the degree of resource saving due to the full use of the product resource.

Simultaneous Identification of Bridge Structural Damage and Moving Loads Using the Explicit Form of Newmark-β Method: Numerical and Experimental Studies

Bridge infrastructures are always subjected to degradation because of aging, their environment, and excess loading. Now it has become a worldwide concern that a large proportion of bridge infrastructures require significant maintenance. This compels the engineering community to develop a robust method for condition assessment of the bridge structures. Here, the simultaneous identification of moving loads and structural damage based on the explicit form of the Newmark-β method is proposed. Although there is an extensive attempt to identify moving loads with known structural parameters, or vice versa, their simultaneous identification considering the road roughness has not been studied enough. Furthermore, most of the existing time domain methods are developed for structures under non-moving loads and are commonly formulated by state-space method, thus suffering from the errors of discretization and sampling ratio. This research is believed to be among the few studies on condition assessment of bridge structures under moving vehicles considering factors such as sensor placement, sampling frequency, damage type, measurement noise, vehicle speed, and road surface roughness with numerical and experimental verifications. Results indicate that the method is able to detect damage with at least three sensors, and is not sensitive to sensors location, vehicle speed and road roughness level. Current limitations of the study as well as prospective research developments are discussed in the conclusion.

AERODYNAMIC STABILITY OF BRIDGES WITH VARIOUS LEVELS OF STRUCTURAL DAMPING

Introduction: Structural damping is one of the most important parameters affecting the aerodynamic stability of bridge structures. Purpose of the study: We aimed to assess the effect that structural damping of a bridge structure has on its stability in a wind current. Methods: In the course of the study, we performed experimental studies of the aerodynamic stability in typical girder bridge structures (with two and four main girders) with different levels of structural damping, facilitated by a unique experimental unit: Large Research Gradient Wind Tunnel, courtesy of the National Research Moscow State University of Civil Engineering (NRU MGSU). Results: The results of the experimental studies show that, despite the general trend towards the decrease in the amplitude of bridge span structure oscillations as the structural damping level increases, the dependence between these parameters is nonlinear. When providing R&D support in the design of real-life structures, in case it is necessary to increase the aerodynamic stability of the superstructure by increasing the level of structural damping (changing the type of joints in structural elements, using mechanical damping devices), it is recommended to conduct experimental studies in wind tunnels to assess the effectiveness of a given solution.

Justification of the development and application of express assessment programs for road bridges when heavy vehicles pass through them

The theoretical prerequisites for justifying the development of two rapid assessment programs for road bridges to quickly determine the possibility of passing heavy vehicles on road bridge structures of a split and non-split system, made of wood, metal, steel-reinforced concrete, reinforced concrete with stressed and non-stressed reinforcement, according to the measured angle of rotation of their support sections, taking into account their actual operational condition, are presented. The programs implemented an experimental and analytical method for assessing the technical condition of road bridges for reliability. The features, conditions of application, positive and negative aspects of each version of the program are revealed. The creation of two variants of programs is due to, on the one hand, the need to ensure the safety of the driver of the vehicle and the bridge structure, and on the other hand, the need to guarantee the possibility of safe passage of heavy vehicles, both under the conditions of the load-bearing capacity of superstructures and the load-bearing capacity of road bridge supports, taking into account their actual operational condition. Both developed calculation programs were implemented by using a personal computer and certificates of state registration of computer programs were obtained. The developed programs will be used as part of the modernized IR-AM measuring complex.

Shear live load analysis of NEXT beam bridges for accelerated bridge construction

Using precast concrete elements in bridge structures has emerged as an economic and durable solution to enhance the sustainability of bridges. The northeast extreme tee (NEXT) beams were recently developed for accelerated bridge construction by the Precast/Prestressed Concrete Institute (PCI). To date, several studies on the live load distribution factor (LLDF) for moment in NEXT F beam bridges have been reported. However, the LLDFs for shear in NEXT F beam bridges are still unclear. In this paper, the lateral distributions of live load shear in NEXT F beam bridges were examined through a comprehensive parametric study. The parameters covered in this study included bridge section, span length, beam section, number of beams, and number of lanes loaded. A validated finite element (FE) modeling technique was employed to analyze the shear behavior of NEXT F beam bridges under the AASHTO HL-93 loading and to determine the LLDFs for shear in NEXT beam bridges. A method for computing the FE-LLDF for shear was proposed for NEXT beam bridges. Results from this study showed that the FE-LLDFs have a similar trend as the AASHTO LFRD-LLDFs. However, it was observed that some LRFD-LLDFs are lower than the FE-LLDFs by up to 14.1%, which implied using the LRFD-LLDFs for shear could result in an unsafe shear design for NEXT beam bridges. It is recommended that a factor of 1.2 be applied to the LRFD-LLDF for shear in NEXT F beam bridges for structural safety and design simplicity.

Evaluation of the efficiency of aerodynamic dampers based on preliminary numerical modeling

The article is devoted to the issues of ensuring the stability of large-span bridge structures by means of their aerodynamic damping. Aerodynamic damping allows you to change the nature of the wind flow around structures or their individual elements, which can significantly reduce the loads that cause the occurrence of various aeroelastic phenomena. Aerodynamic damping devices (fairings, deflectors) are based on the phenomenon of changes in the circulation of the wind flow around the structure, the purpose of their use, as a rule, is to disrupt regular vortex formation. The main problem when using these devices is the lack of recommendations for their selection and the need for costly experimental studies to assess their effectiveness for each specific bridge. One of the ways to reduce the time and cost of research is preliminary numerical modeling in specialized software systems. Within the framework of this study, the most common types of aerodynamic dampers have been analyzed, and typical designs of large-span beam bridges have been selected. For the selected structures, a preliminary numerical simulation was carried out in a two-dimensional formulation. Based on the results obtained, the most effective designs of deflectors and fairings were determined.