Experimental and numerical investigation of dynamic rocking foundation behavior

Soil-structure interaction problems have long been a focus of researchers over a wide array of applications. Presented in this thesis are experiments and analyses of small-strain soil-structure vibration problems and large-strain soil-structure rocking behavior. A literature review is presented regarding the relevant bodies of work for both topics followed by two experimental investigations. The first is an investigation of multi-modal, small-strain vibrations of field-scale surface foundations on a natural cohesive soil deposit. For this investigation, the physical aspects of the soil-structure vibrating system, the excitation system, the measurement system, the measurement approach, numerical modeling, and comparison with experimental results are presented. The validity and efficiency of a hybrid-mode vertical-eccentric test is demonstrated via its equivalence to separate modal vertical and lateral-rocking tests. Critical insights from numerous past centrifuge scaled-model studies are verified and extended to this field-scale study. The second is an experimental investigation of large-strain rocking of a field-scale surface foundation resting on a cohesive soil deposit. The physical aspects of the soil-structure rocking system, the measurement system, the various actions imposed on the physical system, and a discussion of the experimental results are presented. The results of the field investigation show that energy may be dissipated at the soil-structure interface by means of soil hysteresis through moment-rotation and horizontal force-horizontal displacement. Rounding of the soil surface was observed due to yielding and plastic deformation of the soil from increased rotational strains. Yielding soil also introduced nonlinearity into the response of the soil-foundation system, which directly influenced the period. Lastly, an analytical model was developed to satisfactorily simulate dynamic properties of a rocking system from quasi-static experimentation

Vibration and soil-structure interaction tests of a nine-story reinforced concrete building

The Millikan Library Building, a nine-story reinforced concrete shear-wall structure at the California Institute of Technology, was tested dynamically by means of two eccentric mass vibration generators located on the ninth floor. The response levels ranged up to a maximum acceleration of 0:02 g. The natural periods of vibration, the mode shapes and the energy dissipation were measured for the first and second E-W translational modes, the N-S fundamental mode and the first torsional mode. Soil-structure interaction was investigated by measuring foundation motion and nearby soil surface movements during resonent vibrations in the N-S and E-W fundamental modes. Other tests included “man-excited” vibrations at low stress levels and a measurement of resonance of an air handling unit on the roof, which was found to magnify the roof response by a factor of 8.5. The measured fundamental periods were short compared to typical framed structures of this height, 0.50 sec in the N-S direction, 0.66 in the E-W direction and 0.46 in torsion. These values increased roughly 3 per cent over the range of testing. The energy dissipation as measured by a viscous damping factor, varied between 0.70 and 2.00 per cent of critical. This large variation over the testing range indicates that tests at higher stresses are needed to determine the energy dissipation expected during the response to strong earthquake motions. The soil-structure interaction measurements showed that the building responded very nearly as if fixed at the foundation; rocking contributed less than 1 per cent to the total roof motions of the structure and foundation translation about 2 per cent. Although negligible as far as the building motion is concerned, the results demonstrate the possibility of performing full-scale soil-structure interaction experiments

Soil-structure interaction: A state-of-the-art review of modeling techniques and studies on seismic response of building structures

The present article aims to provide an overview of the consequences of dynamic soil-structure interaction (SSI) on building structures and the available modelling techniques to resolve SSI problems. The role of SSI has been traditionally considered beneficial to the response of structures. However, contemporary studies and evidence from past earthquakes showed detrimental effects of SSI in certain conditions. An overview of the related investigations and findings is presented and discussed in this article. Additionally, the main approaches to evaluate seismic soil-structure interaction problems with the commonly used modelling techniques and computational methods are highlighted. The strength, limitations, and application cases of each model are also discussed and compared. Moreover, the role of SSI in various design codes and global guidelines is summarized. Finally, the advancements and recent findings on the SSI effects on the seismic response of buildings with different structural systems and foundation types are presented. In addition, with the aim of helping new researchers to improve previous findings, the research gaps and future research tendencies in the SSI field are pointed out

A Numerical and Experimental Investigation of a Special Type of Floating-Slab Tracks

This thesis presents a research study on the dynamic behavior of a special type of FST used in recently built subway system in Doha, Qatar. The special FST has a continuous concrete slab with periodic grooves for which the track can be modeled as periodic structure with a slab unit having two elements with different cross sections. Extensive numerical and experimental investigations were conducted on a multi-unit full-scale mockup track. The numerical investigations were carried out using both a fast running model based on the Dynamic Stiffness Method and a detailed Finite Element model. In the experimental campaign, experimental vibration test was performed to identify the actual vibration response of the mockup track. Results from the experimental investigations were then used for verifying the numerical models and carrying out a model updating exercise for the fast running model. The model updating process was carried out according to an automated hybrid optimization approach. Finally, the updated model was extended to an infinite model and used in a parametric study to investigate the influence of varying groove’s thickness on the dynamic behavior of the special track with infinite length for both bending and torsion scenarios. The parametric study suggested that reducing the thickness below 50% of the full thickness of the slab significantly affects the dynamic behavior of the special FST

The stresses in granular material due to applied vibration

The dissipation and spread of stresses in a granular material due to an applied disturbance is investigated. A single impulse was applied to a granular material to help understand its behaviour when disturbed by an oscillating vertical force. Measurements were made of the effect of the impulse at the surface of the beds of sand of various heights. The spread of the disturbance in a direction normal to that of application was measured by a radial traverse of the surface of each bed, The behaviour of a granular material when acted upon by a force is comprehensively discussed in the literature survey. The effect on the structure throughout the material of a disturbance applied at a distant point is then assessed. [Continues.

Advances in Geotechnical Earthquake Engineering

This book sheds lights on recent advances in Geotechnical Earthquake Engineering with special emphasis on soil liquefaction, soil-structure interaction, seismic safety of dams and underground monuments, mitigation strategies against landslide and fire whirlwind resulting from earthquakes and vibration of a layered rotating plant and Bryan's effect. The book contains sixteen chapters covering several interesting research topics written by researchers and experts from several countries. The research reported in this book is useful to graduate students and researchers working in the fields of structural and earthquake engineering. The book will also be of considerable help to civil engineers working on construction and repair of engineering structures, such as buildings, roads, dams and monuments

Dynamic and Static Performance of Large-Capacity Helical Piles in Cohesive Soils

Large-capacity helical piles can provide immense construction and performance advantages over the conventional concrete and steel piles. Nowadays, there is significant interest in using large-capacity helical piles to support foundations that would be subjected to both dynamic and static loading. The main objectives of this thesis are to: investigate the dynamic response and impedances of large-capacity helical piles; develop an analysis methodology for their dynamic response; and investigate their static axial compression and lateral behaviour, considering installation effects on their dynamic and static performances. The thesis presents the first full-scale vertical and horizontal dynamic field testing program executed on large-capacity helical piles, which involved 190 full-scale field load tests on nine instrumented large-capacity helical piles and two driven steel piles with different geometrical configurations installed in cohesive soils. Six piles were tested two weeks after installation and four piles were tested after allowing a recovery period of nine months following installation. One hundred and seventy six field experiments were conducted to evaluate the dynamic response characteristics of single helical piles and driven piles under different levels of vertical and horizontal harmonic excitations. The effects of various parameters, namely: pile length, number of helix plates and inter-helix spacing, excitation intensity, and soil thixotropy on the dynamic response were investigated. The experimental results were compared to the theoretical predictions of the continuum theory considering linear and nonlinear approaches. Reasonable match was found between the predicted response using the nonlinear approach and the measured response for both vertical and horizontal vibrations. The results demonstrated the significant effects of pile installation on forming weak soil zone around the pile, which stiffened with time following installation. This stiffening was manifested in an average increase in pile stiffness of about 43% and in pile damping of 25 to 90% within a nine month period. In addition, the dynamic response of the helical piles was similar to that of the driven piles. The load transfer mechanism of large-capacity helical piles was found to be predominantly through the helical plates and pile toe end bearing. Based on the results of the pile load tests, it is proposed to define the ultimate load of helical piles as the load that corresponds to pile head movement equal to the pile elastic deformation plus 3.5% of helix diameter. The helical piles displayed a superior axial performance with capacities higher than driven pile by about 17 to 85% based on pile configurations. The effects of attached helices and inter-helix spacing were found to be negligible on the pile lateral capacity and performance. The lateral pile load tests were examined numerically using the p-y approach incorporated in LPILE program. The mobilized soil shear strength parameters and soil moduli of subgrade reaction were back-calculated