Identification of Track Stability Model Parameters Based on Numerical Experiments

In the article, an identification method of railway track stability model parameters based on energy equilibrium is presented by the authors. A study of two parameters directly influencing the continuous welded track (CWR) stability is described by the authors, i.e., the rail-sleeper structure stiffness Bz is considered one beam, and the ballast lateral resistance r0. These parameters were estimated with the use of a numerical model for various railway track types. The adopted concept is based on the assumption that it is possible to determine substitute values for both parameters. Therefore, using one value of both of these parameters, we label them substitute parameters. The assumed numerical model forced lateral displacements of a track section, and, based on the obtained track section displacement results, energy equilibrium was determined. The equilibrium takes into account the work of external load and the bending work of rail-sleeper structure with the substitute stiffness Bz and the ballast deformation work, also with the substitute value of lateral resistance r0 with lateral displacement. The aim is to identify these substitute values to be used for analysing track stability with the semi-analytical model. These analyses are part of the studies related to the development of a method of assessing various methods of increasing track stability.

Monitoring and Evaluation of the Lateral Stability of CWR Track

Continuous welded rail (CWR) track has great advantages of low-cost maintenance, environmental influence, and ride comfort. However, the CWR track is subjected to the longitudinal stresses in rails due to temperature influence as well the inhomogeneous stress accumulation due to train loadings. The stresses cause the accelerated track lateral irregularity accumulation that without timely maintenance can cause track buckling. The present paper present a method of the CWR track lateral stability estimation during its lifecycle using the track geometry monitoring information from the track measurement cars. The methods proposes a systematic approach of track stability evaluation based on multiple criteria of track stability evaluation. It takes into account the lateral resistance of the track, actual temperatures, and the lateral geometry condition of the track. The presented case study of a half-year track geometry monitoring and the track stability evaluation in a track curve shows the practical possibility of the recent detection of the track sections with low lateral stability and buckling prevention.

Improving the robustness of steel frame structures under localised fire conditions

PurposeThe robustness of building structures in a fire has recently drawn wide attention. This study presents the progressive collapse analysis of steel frame building structures under localised fire. The main objective of this study is to propose methods to enhance the structural collapse resistance of such structures in fire.Design/methodology/approachA modelling method was developed and validated against both experimental and analytical studies. Then, a series of robustness analyses were performed to investigate the interaction among the members and the pattern of load distribution within the structures. These analyses show that lateral resistance and load redistribution have a vital role in the robustness of the building. Thus, two approaches have been adopted to enhance the robustness of the focused steel frame during a fire.FindingsIt is found that increased size of floor beams and vertical bracing systems are effective measures in preventing whole structure collapse. The larger beam section is able to prevent catenary action so that the load in the failed columns can safely transfer to the adjacent columns without buckling. On the other hand, the bracing system improves the lateral resistance that can accommodate the lateral force when catenary action occurs in the beam.Originality/valuePrevious studies have focused on the collapse mechanism of steel frame structures. However, the parameters affecting the structural robustness in a fire have not yet been explored. To address this gap, this study adopted numerical modelling to undertake parametric studies to identify effective methods to improve the robustness of such structures under fire conditions.

Recycling of damaged RC frames: Replacing crumbled concrete and installing steel haunches below/above the beam at connections

Experimental and numerical studies are presented evaluating the efficacy of a recycling technique applied to a 1:3 reduced scale damaged RC frame. The crumbled concrete at the beam-column connections was replaced with new high-strength concrete. Epoxy mortar was applied at the interface to secure bonding between the old and new concrete. Additionally, the connections were provisioned with steel haunches, applied below and above the beams. The retrofitted frame was tested under quasi-static cyclic loads. The lateral resistance-displacement hysteretic response of the tested frame was obtained to quantify hysteretic damping, derive the lateral resistance-displacement capacity curve, and develop performance levels. The technique improved the response of the frame; exhibiting an increase in the lateral stiffness, resistance and post-yield stiffness of the frame in comparison to the undamaged original frame. This good behaviour is attributed to the steel haunches installed at connections. A representative numerical model was calibrated in the finite element program SeismoStruct. A set of spectrum compatible ground motions were input to the numerical model for response history analysis. The story drift demands were computed for both the design basis and maximum considered earthquakes. Moreover, the technique was extended to a five-story frame, which was evaluated through nonlinear static pushover and response history analyses. Overstrength factor WR = 4.0 is proposed to facilitate analysis and preliminary design of steel haunches and anchors for retrofitting the low-/mid-rise RC frames.

Seismic Resistance of Timber Frames with Mud and Stone Infill Walls in a Chinese Traditional Village Dwelling

Traditional Chinese wood residences consist of timber frames with masonry infill walls or other types of infill, representing valuable heritage. A field investigation of traditional village dwellings in northern China consisting of timber frames with mud and stone infill walls was conducted. Their construction characteristics are reported, and static cyclic tests were performed on two full-size wood-stone hybrid walls with different configurations (exterior transverse wall and internal transverse wall) and no openings (doors or windows). Their failure mechanics and seismic capacity, i.e., the strength, stiffness, ductility, and energy dissipation, were investigated. The results are compared with a previous experimental study of two full-size timber frames with the same traditional structure but no infill to determine the effect of the mud and stone infill on the lateral resistance. The experimental results indicate that the stone infill has a critical influence on the lateral performance of traditional village buildings, resulting in a high lateral stiffness, high strength (>20 kN), and a high ductility ratio (>10). An increase in the vertical load leads to an increase in the lateral resistance of the timber frame with infill walls, larger for the internal transverse wall than the external gable wall. The incompatibility of the deformation between the timber frame and stone infill is the main failure reason, resulting in falling stones and collapse with undamaged timber frames. Suggestions are provided for the protection and repair of traditional wood residences in northern China.