Study on the Effects of Mass and Stiffness Variations on Fundamental Periods of Structures

Fundamental period is an important parameter in seismic design and performance assessment of buildings.Hence,comprehensive and detailed investigations of effectiveness as well as affectability of this parameter can result in the design of high-performing earthquake-resistant structures.On this basis,this research intends to evaluate the effects of variations of mass and stiffness on the fundamental periods of two three-and nine-story structures representing low-and high-rise buildings,respectively.To this end,a MATLAB code was developed and validated to determine the fundamental periods of structures with various mass and stiffness characteristics.Numerous case studies were performed to investigate the effects of mass and stiffness variations along the stories of the considered structural models.The objective of this research endeavor is to provide a better understanding of affectability of fundamental period under different design considerations.

Bayesian Optimized LightGBM model for predicting the fundamental vibrational period of masonry infilled RC frames

The precise prediction of the fundamental vibrational period for reinforced concrete(RC)buildings with infilled walls is essential for structural design,especially earthquake-resistant design.Machine learning models from previous studies,while boasting commendable accuracy in predicting the fundamental period,exhibit vulnerabilities due to lengthy training times and inherent dependence on pre-trained models,especially when engaging with continually evolving data sets.This predicament emphasizes the necessity for a model that adeptly balances predictive accuracy with robust adaptability and swift data training.The latter should include consistent re-training ability as demanded by realtime,continuously updated data sets.This research implements an optimized Light Gradient Boosting Machine(LightGBM)model,highlighting its augmented predictive capabilities,realized through the astute use of Bayesian Optimization for hyperparameter tuning on the FP4026 research data set,and illuminating its adaptability and efficiency in predictive modeling.The results show that the R^(2) score of LightGBM model is 0.9995 and RMSE is 0.0178,while training speed is 23.2 times faster than that offered by XGBoost and 45.5 times faster than for Gradient Boosting.Furthermore,this study introduces a practical application through a streamlit-powered,web-based dashboard,enabling engineers to effortlessly utilize and augment the model,contributing data and ensuring precise fundamental period predictions,effectively bridging scholarly research and practical applications.

Surface Soil Effects Studies Based on HN Ratios of Microtremors at Kingston Metropolitan Area, Jamaica

The authors performed single mobile microtremor measurements at 218 sites at KMA （Kingston Metropolitan Area） with the objective of estimating the amplification effects due to the earthquake ground motion on the surface geology. The Fourier transform was applied to the most stationary parts of the triaxial wave motion recordings for each individual site and applied the traditional Nakamura technique, namely, the horizontal to vertical spectral ratio （H/V） to retrieve the predominant shear wave period of vibration of the soil profiles above the bedrock. The results yield predominant long periods of about 3.0-4.0 s in the port area and the waterfront, 1.0-2.0 s in the central part of Kingston, 0.3-1.0 s in Portmore and very stiff soil conditions in the surrounding area of the city. The results coincide fairly well with previous geological studies in the region, geotechnical data in boreholes, gravimetric measurements and strong motion recordings, suggesting a high degree of amplification of ground motion in the whole period range of engineering interest. Additionally, the authors obtained the liquefaction vulnerability factor Kg proposed by Nakamura based on the H/V ratio of microtremors. The results suggest that the port area, the waterfront and the Port Royal are highly susceptible to liquefaction. Finally, the authors obtained fundamental periods of vibration based on microtremor measurements on the roof and the basement of four important buildings in the KMA and indicated future lines of research employing ambient noise measurements on structures.

Analytical and numerical studies for seiches in a closed basin with various geometric shapes of longitudinal section

Seiches are long-period standing waves with a unique period called a natural resonant period,during which the phenomenon of resonance occurs.The occurrence of resonance in coastal areas can cause destruction to surrounding natural and man-made structures.By determining the resonant period of a given basin,we can pinpoint the conditions that allow waves to achieve resonance.In this study,a mathematical model is developed from the shallow water equations to examine seiches and resonances in various types of closed basin.The developed model is solved analytically using the separation of variables method to determine the seiches’fundamental resonant periods.Comparisons between the analytical solutions and experimental measurements for resonant periods are also provided.It is shown that the analytical resonant period confirms the experimental data for closed basin of various geometric profiles.Using a finite volume method on a staggered grid,the model is solved numerically to simulate the wave profile when resonance phenomenon occurs.Through those numerical simulations,we also obtain the fundamental resonant period for each basin which agrees with the derived analytical period.