An Evaluation of Ground Vibrations Induced by Heavy Free-Falling Structural Elements

Ground vibrations generated during a large structural demolition event can be potentially damaging to nearby structures or sensitive equipment. In this paper, an approach for the prediction of the ground vibration induced by a large free-falling heavy weight is proposed based on both measured and collected data. A series of field ground vibration measurements were performed relative to the dynamic motions induced by free-falling heavy structural elements during demolition of a generating plant in the upper Midwest, USA. Using this information and the collected data, correlations between the measured PPV and normalized distance from the impact source with various ground impact energy were developed. Subsequently, an empirical PPV estimation method is suggested. This methodology will be useful in estimating dynamic effects induced by very large demolition events; especially where existing structures are located in close proximity to the impact site

Evaluation of Frequency Dependent Equivalent Linear analysis

One dimensional equivalent linear site response analysis is widely used in practice due to the simplicity and ease of use. In the method, the dynamic soil properties are assumed to be independent of the loading frequency. To better simulate the nonlinear behavior, equivalent analysis methods that models the loading frequency dependence of the shear modulus and damping were developed. The backbone of the methods is the frequency-dependent shear strain curves. Various forms of the frequency-dependent shear strain curves were developed. However, the effect of the frequency - shear strain curves are not well known and documented. In this study, a series of frequency – strain curves were used to evaluate the accuracy of the frequency dependent equivalent linear analysis. Results show that the effect of the curves is significant and that the frequency dependent analysis does not always provide an improved estimate and can highly overestimate the amplification of the high frequency components of the ground motion. The degree of overestimation is dependent on the characteristics of the input ground motion and the soil profile. It is therefore concluded that the frequency dependent equivalent linear analysis should be used with caution and that standard equivalent linear analysis can be a more reliable option

Uniform Hazard Response Spectra of Korea Considering Uncertainties in Ground Properties

The seismic site coefficients derived deterministically are often used with ground motion parameters determined by probabilistic seismic hazard analysis in construction of the design response spectrum. There is, therefore, an inherent incompatibility between two approaches. New methods have been developed to resolve this incompatibility by developing probabilistic seismic site coefficients. In such approaches, the uncertainties in the properties of the ground were not systematically accounted for due to lack of measurements of the ground. In this study, an integrated probabilistic seismic hazard analysis which can quantify the nonlinear seismic site effects and account for the uncertainties in soil properties is developed and used to generate the uniform hazard response spectra in Korea. The procedure used an extensive database of measured shear wave velocity profiles and dynamic curves, which included more than 114 shear wave velocity profiles and more than 15 dynamic curves. The calculated uniform hazard response spectra were compared to the design spectra. Comparisons show significant discrepancy between two spectra, and highlight the need to revise the current design guideline

Cone penetration test in clayey soil: Rate effect and application to pile shaft resistance calculations

This research focuses on the evaluation of the factors affecting cone resistance measurement during cone penetration in saturated clayey soils and the application of the result to pile shaft capacity analysis. In particular, effects of drainage conditions around the cone tip were studied. In order to investigate the effects of drainage during cone penetration test, penetration tests were performed with various velocities in the field and in a calibration chamber and the obtained data were analyzed. For the field tests, two sites which have homogeneous clayey soil layers under the groundwater table were selected and CPTs were performed with various penetration rates. Penetration tests in calibration chamber were performed to investigate the transition points between undrained and partially drained, partially drained and fully drained conditions based on cone penetration rate and the coefficient of consolidation. A series of flexible-wall permeameter tests were conducted for various mixing ratios of clays and sands to obtain consolidation coefficient which is important to determine mixing ratios of chamber specimens. Nine piezocone penetration tests were conducted for different rates in calibration chamber specimen P1 (mixture of 25% clay and 75% Jumun sand) and eight penetration tests were carried out in calibration chamber specimen P2 (mixture of 18% clay and 82% Jumun sand). From the results of the penetration tests in the calibration chamber, a correlation between cone resistance and drainage condition was established. Cone factor was evaluated based on collected CPT data having appropriate soil parameters. The correlations between Nk and selected soil properties were examined and the new Nk correlation was proposed. The new shaft capacity analysis method for piles driven in cohesive soil was proposed based on the suggested correlation between cone resistance and undrained shear strength and the α method. The α factor associated with the normalized cone resistance ratio and length effect was established based on statistical correlation based on 15 closed-ended pile load test results