Ground Improvement to Reduce Liquefaction Potential Using Vibrocompaction and Stone Columns

With the rapid pace of industrialization, structures are being designed and constructed in the flood plains of major rivers. In earthquake prone areas, a fundamental issue in the design and construction of structures on saturated sandy soils is weather or not the design earthquake could initiate liquefaction in the form of lateral spreading, sand boils, settlement, or cracking. Many different methods, including vibrocompaction, deep dynamic compaction, compaction piles, geopiers, deep mixing, vibratory probes, displacement/compaction grout, etc., have been used to reduce the liquefaction potential at various sites. Use of vibrocompaction to densify cohesionless soil is becoming more common and cost effective. For projects in the New Madrid seismic zone (NMSZ) another challenge to perform site specific analysis is the lack of recorded ground motions. Therefore, synthetic time histories need to be generated using the attenuation models applicable to the region. This paper provides details about a site specific study performed for a site in the bootheel area of Missouri, and results of liquefactions analysis and ground modification achieved using vibrocompaction

How to optimize frames using plastic design concept

An optimal design procedure using plastic design concept was presented. For low-rise building frames, optimal plastic designs can be made using the plastic limit load as a basis of design. However, the design of multistory building frames is complicated by the incidence of frame instability, and rigid-plastic methods of design must be modified to allow for this

Ground motion and site specific studies for bridges in West Tennessee

This paper describes the methods and results of a research project to produce a set of acceleration contour maps to be used in the design of Tennessee Department of Transportation (TDOT) facilities. The investigation is composed of three major tasks: (1) develop procedures to generate horizontal bedrock motions in West Tennessee from a seismologically based model. The model must include the effects of attenuation, characteristics of the source zone, recurrence interval (500 and 2500 years), and seismotectonic setting of the region, (2) perform seismic field investigation to determine the dynamic properties of soil in West Tennessee, and (3) propagate the soft bedrock motion through the layered soil deposits using the computer program SHAKE to determine the earthquake motions at the ground surface of a site. Methods employed and the results are discussed and described in this paper. © 2004 ASCE

Optimal design of nonlinear framed structures under multiple loading conditions based on a stability criterion

An optimization-based design methodology is presented for improving the strength and overall stability of framed structures. The design methodology is a multiple-objective optimization procedure whose objective functions involve the buckling eigenvalues and eigenvectors of the structure. Designs are constrained to have constant weight. An iterative optimality criterion method is used to solve the optimization problem. The method provides a general tool for designing complex structures with nonlinear behavior and generally leads to designs with better limit strength and stability while avoiding nonlinear analysis in the optimization cycle. The approach is indirect, but is effective and efficient.The design procedure is developed for 2-D and 3-D nonlinear framed structures. Development and application of the optimization procedure for planar framed structures is presented first and is then extended to space-frame structures. Three-dimensional design problems are more complicated, but they yield insight into the real behavior of the structure and can help avoid some of the problems that might appear in the planar design procedure such as the need for out-of-plane buckling constraints.To control the vibration characteristics of the designs, frequency weighting functions are introduced and incorporated into the objective function. These weighting functions provide information about the vibrational characteristics of the design and can be used to avoid undesirable dynamic effects, such as resonance, by pushing the structure away from it while improving the overall stability and strength of the design.One of the novelties of the new design methodology is its ability to efficiently model and design structures under multiple loading conditions. These loading conditions include different factored loads, components of an earthquake, and geometric imperfections and can be applied to the structure simultaneously or independently.Several examples are presented to evaluate the validity of the underlying assumptions and to examine the performance of the procedure. By way of example it is shown that by improving the overall stability characteristics of structure under static loading, the dynamic performance of the structure is also improved.U of I OnlyETDs are only available to UIUC Users without author permissio

Optimal design of nonlinear framed structures under multiple loading conditions based on a stability criterion

An optimization-based design methodology is presented for improving the strength and overall stability of framed structures. The design methodology is a multiple-objective optimization procedure whose objective functions involve the buckling eigenvalues and eigenvectors of the structure. Designs are constrained to have constant weight. An iterative optimality criterion method is used to solve the optimization problem. The method provides a general tool for designing complex structures with nonlinear behavior and generally leads to designs with better limit strength and stability while avoiding nonlinear analysis in the optimization cycle. The approach is indirect, but is effective and efficient.The design procedure is developed for 2-D and 3-D nonlinear framed structures. Development and application of the optimization procedure for planar framed structures is presented first and is then extended to space-frame structures. Three-dimensional design problems are more complicated, but they yield insight into the real behavior of the structure and can help avoid some of the problems that might appear in the planar design procedure such as the need for out-of-plane buckling constraints.To control the vibration characteristics of the designs, frequency weighting functions are introduced and incorporated into the objective function. These weighting functions provide information about the vibrational characteristics of the design and can be used to avoid undesirable dynamic effects, such as resonance, by pushing the structure away from it while improving the overall stability and strength of the design.One of the novelties of the new design methodology is its ability to efficiently model and design structures under multiple loading conditions. These loading conditions include different factored loads, components of an earthquake, and geometric imperfections and can be applied to the structure simultaneously or independently.Several examples are presented to evaluate the validity of the underlying assumptions and to examine the performance of the procedure. By way of example it is shown that by improving the overall stability characteristics of structure under static loading, the dynamic performance of the structure is also improved.U of I OnlyETDs are only available to UIUC Users without author permissio

Estimation of the coda-wave attenuation and geometrical spreading in the new Madrid seismic zone

Using the single backscattering method, coda quality factor functions through coda window lengths of 20, 30, 40, 50, and 60 s have been estimated for the New Madrid seismic zone (NMSZ). Furthermore, geometrical spreading functions for distances less than 60 km have been determined in this region at different center frequencies exploiting the coda normalization method. A total of 284 triaxial seismograms with good signal-to-noise ratios (SNR \u3e 5) from broadband stations located in the NMSZ were used. The database consisted of records from 57 local earthquakes with moment magnitudes of 2.6-4.1, and hypocentral distances less than 200 km. Q-factor values were evaluated at five frequency bands with central frequencies of 1.5, 3, 6, 12, and 24 Hz. Vertical components were utilized to estimate vertical coda Q-factor values. Horizontal coda Q-factor values were determined using the average amount of the Q-factor values estimated from two orthogonal horizontal components. The coda Q-factor increases with increasing of the coda window length implying that with increasing the depth, the coda Q-factor increases. The intermediate values of the Q-factor and intermediate values of the frequency dependency indicate that the Earth’s crust and upper mantle beneath the entire NMSZ is tectonically a moderate region with a moderate to relatively high degree of heterogeneities. The geometrical spreading factors of S-wave amplitudes are frequency dependent and determined to be −0:761, −0:991, −1:271, −1:182, and −1:066 for center frequencies of 1.5, 3, 6, 12, and 24 Hz, respectively, at hypocentral distances of 10-60 km. The geometrical spreading factors for lower frequencies are not recommended to be used due to the greater impact of the radiation pattern and directivity effect on low frequencies, as well as the greater sensitivity of band-pass-filtered seismograms of small earthquakes to the noise in low frequencies

Machine learning–based ground motion models for shallow crustal earthquakes in active tectonic regions

Data-driven ground motion models (GMMs) for the average horizontal component from shallow crustal continental earthquakes in active tectonic regions are derived using a subset of the Next Generation Attenuation (NGA)-West2 data set, including 14,518 recordings out of 285 earthquakes recorded at 2347 different stations. We use four different nonparametric supervised machine learning (ML) algorithms including Artificial Neural Network (ANN), Kernel-Ridge Regressor (KRR), Random Forest Regressor (RFR), and Support Vector Regressor (SVR) to construct four individual models. Then, we use a weighted average ensemble approach to combine these four models into a robust model to predict various ground motion intensity measures such as peak ground displacement (PGD), peak ground velocity (PGV), peak ground acceleration (PGA), and 5%-damped pseudo-spectral acceleration (PSA). The model input parameters are moment magnitude, rupture distance, VS30, and ZTOR. The ensemble modeling attempts to remove the drawbacks or deficiencies of different ML algorithms while capturing their advantages and accounts for epistemic uncertainty. Although no functional form is provided, the model can capture salient features observed in ground motions such as saturation as well as geometrical spreading, anelastic attenuation, and nonlinear site amplification. The response spectra and the magnitude, distance, VS30, and ZTOR scaling trends are consistent and comparable with the NGA-West2 GMMs including several additional input parameters. We used a mixed-effects regression analysis to split the total aleatory uncertainty into between-event, within-station, and event-site–corrected components. The model is applicable to magnitudes from 3.0 to 8.0, rupture distances up to 300 km, and spectral periods of 0 to 10 s

Improved velocity and displacement time histories in frequency domain spectral-matching procedures

Existing spectral-matching techniques in the frequency domain distort the displacement time history of the ground motions. In the time domain spectralmatching procedures, scale functions (wavelets) are additive and, with an appropriate scale functional form, extra displacement will not be imposed to the record. However, matching in the frequency domain with a multiplicative scale function applied to the Fourier spectrum requires a special attention in the matching process to have control on the displacement time history. This study shows that the velocity value at the end of the record is not affected by the Fourier amplitude spectrum scaling, but the displacement may linearly increase (or decrease) boundlessly. Two numerical solutions are proposed to solve the displacement drift problem in the frequency domain. Following the proposed frequency domain baseline correction procedure, one does not need to perform baseline correction in the time domain after completing the spectral matching. As a result, acceleration, velocity, and displacement time histories will remain fully compatible, and the boundary conditions of the velocity and displacement time histories will be preserved. The proposed procedure is not limited to spectral-matching methods and can be used with any general filtering process to retain the final displacement of the record. The possibility of applying a zero-padding technique to the spectral-matching filter is also discussed. It is shown that applying an appropriate window along with the zero-padding technique can lead to a reasonable displacement time history. The proposed procedures can be easily added to the existing or new frequency domain spectral-matching algorithms without significantly disrupting the spectral-matching process

Partially nonergodic empirical ground-motion models for predicting horizontal and vertical PGV, PGA, and 5% damped linear acceleration response spectra using data from the Iranian plateau

We present new ground-motion prediction equations (GMPEs) to estimate horizontal and vertical strong ground motion intensity measures (GMIMs) generated by shallow active crustal earthquakes occurring within the Iranian plateau. To this end, a dataset containing 688 records from 152 earthquakes with moment magnitudes ranging from 4.7 to 7.4 and Joyner-Boore distances up to 250 km has been used. The effects of the local site condition are taken into account using the timeaveraged shear-wave velocities in the upper 30 m (VS30). We decided not to include the style-of-faulting term in the final functional form because the total standard deviation is reduced 10% by removing this term from the functional form. We used a nonlinear mixed-effects regression to determine the coefficients of the functional form and to separate out the between-event and between-station standard deviations from the total standard deviation. Significant standard deviation of site-to-site variability demonstrates that the ergodic assumption is not able to account for the spatial variability of ground motions. We introduced random-effects coefficients to capture regional variations between different tectonic regions of the Iranian plateau, such as Alborz and Zagros, in the regression analysis to investigate the effects of regionalization on GMPEs. The results showed that, although the effects of regional variations for considered regions are negligible at close distances, they are significant at longer distances. The complexity and performance of the final functional form is justified by comparing Akaike and Bayesian information criteria values over many trial functional forms. Moreover, the distribution of between-event, site-to-site, and event-station corrected residuals demonstrates that no trends are evident, implying satisfactory performance of the proposed GMPEs. Therefore, the derived GMPEs can be employed to predict GMIMs and to do seismic-hazard assessments within the Iranian plateau