Conformal Symmetries of the Energy–Momentum Tensor of Spherically Symmetric Static Spacetimes

Conformal matter collineations of the energy–momentum tensor of a general spherically symmetric static spacetime are studied. The general form of these collineations is found when the energy–momentum tensor is non-degenerate, and the maximum number of independent conformal matter collineations is 15. In the degenerate case of the energy–momentum tensor, it is found that these collineations have infinite degrees of freedom. In some subcases of degenerate energy– momentum, the Ricci tensor is non-degenerate, that is, there exist non-degenerate Ricci inheritance collineations

Assessment of aerodynamic response of the Nissibi cable-stayed bridge using three-dimensional computational fluid dynamics

Aerodynamic behavior has the greatest impact on long-span bridges and is the most important factor in the design of cable stayed bridges, which should not be overlooked. CFD (Computational Fluid Dynamics) is the most widely used technique, among bridge engineers, to predict wind speed, direction and vortex-shedding form before conducting wind tunnel tests. In this study, a bi-directional CFD analysis with the wind flow parallel and perpendicular to Nissibi Bridge's, which has a main span of 400 m and claimed the spot of Turkey’s 3rd largest bridge, deck cross-section has been performed by approximate modelling of the bridge and the surrounding structures. The study is done by using CFD++ software/computer program. The results showed that the effect of wind acting on x direction of impact with 30 m/s has caused turbulence and vortex on conjugation area of the tower and it is observed that the upside down Y shape of the tower breaks down the balance of wind flow. However, bridge deck is not exposed to serious amount of vortex influence due to the wind on y direction. In addition, the analysis revealed that maximum pressure distribution occurred on vertical surface of the tower and it increases in direct proportion to the height of the tower

Post-Earthquake Assessment and Numerical Modeling of Freestanding Heritage Structures

Historic and heritage structures are particularly vulnerable to earthquakes, where damage or collapse can not only lead to loss of a structure but also the loss of irreplaceable heritage. Many heritage structures can be classified as freestanding (detached) structures, including unreinforced masonry walls, classical multi-drum columns, and statue-pedestal systems. However, the seismic response of freestanding structures (sliding, rocking, rock-slide, overturning) is poorly predicted by existing methods due to geometric non-linearities as well as sensitivity to interface conditions and modeling parameters. Previous studies have focused on analytical modeling of simplified systems and/or experimentation under controlled laboratory conditions. In contrast, this paper presents the post-earthquake assessment of multiple statue-pedestal systems following the 2014 South Napa earthquake. The objective is to examine the seismic response of these complex freestanding structural systems, under real-world conditions, to elucidate key characteristics of the response and evaluate the influence of both physical and modeling parameters. In this study, the responses of the selected statues from the Napa area are numerically simulated under original ground motion records. The complex geometries of the statues are represented using meshes generated from lidar-based point clouds obtained during post-earthquake reconnaissance. The responses of the statues are simulated using the Distinct Element Method (DEM) where the statue and pedestal have been modeled as rigid blocks with deformation concentrated at the joints (i.e. interface of statue and pedestal or pedestal and ground). The study analyzes the results of the numerical simulations in comparison to the observed physical response during the earthquake event. Results emphasize the significant impact of ground motion parameters (e.g. directionality), the presence of soil, and modeling parameters such as contact stiffness