Dynamic Characteristics of a Double-Pylon Cable-Stayed Bridge with Steel Truss Girder and Single-Cable Plane

The dynamic characteristics are closely linked to the seismic stability and wind-resistant of the bridge. But different bridge types have different dynamic characteristics. In order to study the dynamic characteristics of a double-pylon cable-stayed bridge with a single-cable plane and steel truss girder whose main span is the longest in the world, the dynamic load test was done, and the finite element and the subspace iteration methods were used to analyze the vibration mode of the bridge. The influence of different structural parameters on the dynamic characteristics of the bridge was analyzed. The changed structural parameters are cable layout, stiffness of steel truss girder, stiffness of stayed cables, stiffness of pylons, the concentration of dead load, number and location of auxiliary piers, and structural system. The results show that the bending and torsion resistance of the double-pylon cable-stayed bridge with a single-cable plane and steel truss girder is weak. The torsional stiffness of the cable-stayed bridge with a double-cable plane is stronger than that of the cable-stayed bridge with a single-cable plane. The seismic stability and wind-resistant of the bridge can be improved by using light dead load, improving the stiffness of pylon and girder, and adding auxiliary piers scientifically. However, the change of cable stiffness has a complex influence on the dynamic characteristics of the bridge. The conclusion can offer references for the construction, maintenance, and design of the same type of bridges.

Seismic stability of vibration-insulated turbine foundations depending on the frequency composition of seismic impact

The seismic resistance of vibration-insulated turbine foundations is a complex and multifaceted problem that includes many aspects. The turbine foundation is a special building structure that unites parts of the turbine and generator unit into a single machine and it is used for static and dynamic loads accommodation. The number of designed and constructed power plants in high seismic level areas is large and steadily growing. In addition, engineers and designers deal with the issue of the frequency composition of the seismic impact influence on the seismic resistance of vibration-insulated turbine foundations. Dynamic calculations were performed in Nastran software using time history analysis and the finite element method. The main criteria for the seismic resistance of a vibration-insulated turbine foundation are the values of the maximum seismic accelerations in the axial direction at the level of the turbine installation and the values of vibration-insulated foundation maximum seismic displacements (deformations of vibration isolators). The results of the calculation experiments proved a significant effect of seismic action frequency composition on the behavior of the vibration-insulated turbine foundations. Calculations of foundations, taking into account earthquakes of the same intensity, but with different values of the prevailing frequencies of the impact, lead to the differing by several times values of the maximum seismic accelerations at the turbine level and seismic displacements.

PROPOSALS OF SOLUTIONS OF THE PROJECT DEVELOPMENTS OF ENERGY-EFFICIENT GEO-HOUSES IN UKRAINE

One of the new approaches in civil engineering is geodetic domed houses. These are quite economical buildings that most fully reflect the idea of energy saving and the concept of environmentally friendly housing. The symmetry of the sphere allows the most efficient placement of solar panels and solar collectors. The structures of the house are assembled quickly and do not require heavy construction equipment. By reducing the volume of the heating room, we save on heat resources, so the heating of the domed house in the winter requires 20 – 30% less energy in comparison to the rectangular buildings. The purpose of the article is to offer solutions for the development of projects of energy-efficient geo-houses in Ukraine. To search for the most rational design and technological solutions; to analyze the characteristics, advantages and disadvantages of energy efficient geo-house buildings in order to build them in Ukraine. The geodesic dome is made of polyurethane foam, reinforced concrete, wood, fiberglass concrete. Frame structures of the geo-house are made of metal or timber, the "skeleton" is lined with plywood or special OSB-boards. This method provides lightness and strength of the building. The dome must have the optimal size of the ribs, not more than 2.5 m in length, which allows you to erect a frame without the use of technology, with a force of 2 ÷ 3 people. Two installation methods of the frame are considered: connector and non-connector. The proposed solutions for the development of energy-efficient geo-houses' projects in Ukraine will allow in the near future to solve the problems of ecology, energy saving, natural resources saving in the country. Energy-efficient geo-house is the best option for any region of Ukraine, thanks to the undeniable advantages: rigidity and stability of the frame, geometric symmetry of shapes and strength, energy efficiency, high seismic stability, erection speed and originality.

A Method for Quantitative Evaluation of Seismic Stability of Loess Slope Based on the Shaking Table Model Test

The large-scale shaking table model test, which can directly reproduce the process of slope instability and failure, is an important technical means for the prediction and evaluation of slope seismic stability. However, up to now, the systematic slope stability evaluation method based on the shaking table slope model test has not been established, which limits the application of the expensive shaking table model test in slope seismic design. Therefore, the slope stability evaluation method based on the model test needs to be developed and innovated. In this research, through three loess slope model tests with different rainfall, according to the change law of the peak value of transfer function spectrum, combined with the macrodestructive characteristics of the slope model, an accurate calculation method of the critical instability acceleration of the slope is proposed. Based on the behavior similarity theory, for the shaking table model test of slope whose soil cohesion cannot meet the similarity ratio, the reduction method of applying the critical instability acceleration obtained from the model test to prototype slope is proposed. Based on first-order natural frequency and damping ratio extracted from the TF spectrum curve, a calculation method for the stability factor Fs of loess slope based on the shaking table model test is proposed, and the stability factors of loess slope under the action of different seismic ground motion would be quantitatively calculated. The above methods provide another effective way for qualitative prediction and evaluation of seismic stability of loess slope.

Efficient Seismic Stability Analysis of Embankment Slopes Subjected to Water Level Changes Using Gradient Boosting Algorithms

Embankments are widespread throughout the world and their safety under seismic conditions is a primary concern in the geotechnical engineering community since the failure events may lead to disastrous consequences. This study proposes an efficient seismic slope stability analysis approach by introducing advanced gradient boosting algorithms, namely Categorical Boosting (CatBoost), Light Gradient Boosting Machine (LightGBM), and Extreme Gradient Boosting (XGBoost). A database consisting of 600 datasets is prepared for model calibration and evaluation, where the factor of safety (FS) is regarded as the output and four influential factors are selected as the inputs. For each dataset, the FS corresponding to the four inputs is evaluated using the commercial geotechnical software of Slide2. As an illustration, the proposed approach is applied to the seismic stability analysis of a hypothetical embankment example subjected to water level changes. For comparison, the predictive performance of CatBoost, LightGBM, and XGBoost is investigated. Moreover, the Shapley additive explanations (SHAP) method is used in this study to explore the relative importance of the four features. Results show that all the three gradient boosting algorithms (i.e., CatBoost, LightGBM, and XGBoost) perform well in the prediction of FS for both the training dataset and testing dataset. Among the four influencing factors, the friction angle φ is the most important feature variable, followed by horizontal seismic coefficient Kh, cohesion c, and saturated permeability ks.