A Structural Engineer’s Approach to Efficient SFSI: Towards Performance Based Design

Performance-based design (PBD) involves designing structures to achieve specified performance targets under specified levels of seismic hazard. This involves analyzing the entire soil-structure system and requires structural and geotechnical expertise. This paper is focused on soil-foundation-structure interaction (SFSI) in relation to PBD. A Beam-on-Nonlinear-Winkler- Foundation (BNWF) model is developed to incorporate important SFSI aspects into structural analysis software. The model accounts for: nonlinearity due to soil yield and/or footing uplift; cyclic degradation of stiffness and strength due to variable-amplitude loading; distribution of soil resistance underneath the footing for different loading conditions; reduction in radiation damping with increased nonlinearity; and coupling effects between different responses of the foundation. The coupling between different responses is achieved by appropriate mathematically derived bounding surfaces. The model utilizes a rotation hinge governed by a bounding surface to model coupling between rocking (in two directions) and vertical responses, and a shear hinge governed by another bounding surface to couple the horizontal responses. These models are implemented in readily available structural packages, and hence allow structural engineers to properly account for SSI effects when performing PBD. The application of the developed models to analysis of experiments on model foundations showed good agreement between the calculated and observed behavior

Machine Foundation Design: Experimental and Analytical Soil Structure Interaction

A comprehensive dynamic testing program has been undertaken to establish the dynamic characteristics of existing fan foundations in order to evaluate their suitability to support new variable speed fans. The dynamic testing program encompassed two sets of tests: pull tests and steady-state vibration test. In addition, dynamic soil-structure interaction analyses were performed to evaluate the response of the foundation to the dynamic operating loads of the new fans

Monotonic and Cyclic Behavior of Helical Screw Piles Under Axial and Lateral Loading

The main objectives of this research paper are to: investigate the monotonic and cyclic behavior of helical pile foundation systems, develop new helical screw systems suitable for seismic retrofitting of existing foundations and new structures. The proposed new pile configurations proposed include: fiber reinforced polymer grouted helical screw piles (FRP-G-HSP); and reinforced grouted helical screw piles (RG-HSP) with steel fibers added to the grout. The research methodology involved conducting more than one hundred full scale field load tests on twenty three helical screw piles installed in cohesive soil and subjected to axial and lateral monotonic and cyclic loading in which twenty piles are instrumented. The test piles included: seven plain helical screw piles (P-HSP); four grouted helical screw piles (G-HSPs); eight FRP-G-HSPs; and four RG-HSPs. The axial cyclic performance of HSPs and G-HSPs experienced 5-10% capacity reduction after 15 loads cycles. However, their lateral capacity was low due to their slender shaft. The lateral capacity and stiffness of internally and externally grouted FRP-G-HSPs were twice the FRP-HSP with internal grout. The RG-HSP piles axial capacity was more than twice that for P-HSP, with minimal reduction after cyclic loading, and their lateral capacity was more than 3 times the P-HSPs capacity

Probabilistic Analysis of Wind Response of Tall Structures Supported by Flexible Foundations

The effect of soil-structure interaction on the response of structures to dynamic loads has long been recognized and the deterministic approach is usually used for its evaluation. In most soil-structure interaction analyses, the soil shear wave velocity is used to characterize the stiffness of the soil and the foundation system. In practice, the shear modulus of the soil is difficult to evaluate and the natural spatial variability and the measurement technique affect its measured value. Probabilistic concepts are used to evaluate the significant design parameters of tall structures and to examine the sensitivity of their wind response to the variation of the soil shear wave velocity used in the analysis. In this study, the dynamic response of tall structures and the base bending moment of R/C TV towers, as an example of a tall shell structure, are evaluated accounting for soil-structure interaction. A probabilistic approach is used to account for the uncertainties in the shear modulus of the soil underneath the foundation and the design wind speed on the calculated response and base bending

Vibration of Synchrotron Foundation Due to Ground-Transmitted Excitation

The Canadian Light Source (CLS) is a third generation synchrotron that will be capable of generating a wide spectrum of electromagnetic radiation used in the study of the atomic and sub-atomic structure of materials. The CLS facility will feature a 50 m diameter vacuum storage ring used to contain a highly focused stream of electrons. The accuracy required in aiming the electron beam and resulting radiation necessitates very stringent operational tolerances on foundation vibrations, with peak dynamic displacements being limited to less than 0.35 μm. To assess the level of seismic excitation at the site due to traffic on an adjacent roadway, an extensive “green field” ground vibration monitoring program was carried out. The analytical model used to calculate the dynamic characteristics of the foundation system is described. A Fourier analysis approach was used to predict the response of the foundation to the ground-induced vibrations. The results of the analysis showed that the proposed foundation system would perform satisfactorily

Review of Available Methods for Evaluation of Soil Sensitivity for Seismic Design

Sensitivity describes the effect of soil disturbance/remoulding on shear strength. Cyclic stresses during seismic events may lead to varying levels of disturbance and remoulding of brittle sensitive clays. The Canadian Foundation Engineering Manual (CFEM) recommends site-specific evaluation of the seismic hazard, including site response analysis, for sites that have quick or highly sensitive clays. Different levels of soil sensitivity have been shown in different versions of CFEM and their errata. The current manual CFEM (2006) classifies clay as highly sensitive if its sensitivity is greater than 40 (classified as Class F soil). However, there is considerable variation within the literature with respect to descriptions of sensitivity and more importantly, the related seismic risks that different soil states represent. This can have a significant impact on determination of the appropriate seismic forces on supported structures according to the seismic provisions of the current National Building Code of Canada, NBCC (2005). This paper reviews the different methods used to evaluate soil sensitivity and the sensitivity classifications in the literature. Based on this review, suggestions are provided for improvements of this approach to seismic design

Seismic landslide hazard mapping for Greater Vancouver, British Columbia

The lower Mainland of southwest British Columbia (BC) hosts about 3.5 million people and significant infrastructures of national importance. Southwestern BC has the highest seismic risk in Canada with significant potential to cause earthquake-induced hazards including tsunamis, liquefaction and landslides. A Cascadia mega-thrust (MW 9) earthquake is predicted to generate $75 billion Canadian dollars in losses. This damage can be resulted from ground shaking or its secondary phenomena like landslides; ground shaking during earthquakes may trigger landslides that can damage or destroy buildings, bury roads and highways and kill and injure people. In Canada, during the past century and a half, landslides have caused more fatality than all other natural hazards combined. Seismic hazard mapping for landslides integrates topographic, geotechnical and seismological information to develop the earthquake-induced slope displacements map which is indicator of seismic landslide potential. In this study we use a pseudo-probabilistic Newmark displacement analyses for regional landslide susceptibility mapping and its application will be illustrated with developing earthquake induced landslide hazard map for the quadrangle in Greater Vancouver area. The predicted displacements are assigned to the defined grids to come up with the final seismic landslide hazard map. The seismic landslide hazard map predicts very low hazard level (displacementcm) for the selected region which is in agreement with the observations in our field survey in July 2018 where no signs of deformation were recorded (e.g. cracks, settlements, previous landslides, scarps)

Impact of Ground Motion Duration and Soil Non-Linearity on the Seismic Performance of Single Piles

Pile foundations strongly influence the performance of supported structures and bridges during an earthquake. In case of strong earthquake ground motion, soft soils may be subjected to large deformation manifesting aspects typical of the non-linear behaviour such as material yielding, gapping and cyclic degradation. Therefore, nonlinear soil-pile interaction models should be able to capture these effects and improve the prediction of the actual seismic loading transferred from the foundation to the superstructure. In this paper, a beam on nonlinear Winkler foundation (BNWF) model is used, which can simulate cyclic soil degradation/hardening, soil and structural yielding, slack zone development and radiation damping. Incremental Dynamic Analyses (IDAs) are performed to evaluate the effects of Ground Motion Duration (GMD) and soil non-linearity on the performance of single fixed-head floating piles. Various homogeneous and bilayer soil profiles are considered, including saturated clay and sand in either fully dry or saturated state and with different levels of compaction. In order to evaluate the effect of nonlinearity on the response, the results of the nonlinear analyses are compared with those obtained from linear soil-pile analysis in terms of bending moment envelope. Results show the relevance of considering the GMD on the performance of the single pile especially when founded on saturated soils. For low intensities and dry sandy soils, the linear soil-pile interaction model can be used for obtaining reliable results

STR-990: SUSTAINABLE GROUTED HELICAL PILES: MATERIALS AND PERFORMANCE

Cementitious materials are widely used as a construction material all over the world. However, cement industry has high environmental impact such as the release of CO2 and the consumption of natural resources for its manufacturing energy. Therefore, reducing cement consumption is vital to achieve sustainable green construction practices. In this study, the effects of using treated oil sand waste (TOSW) as a partial replacement of cement in grouted helical pile applications were investigated. Fresh and hardened properties of the green grout incorporating different percentages of TOSW were evaluated. In addition, a model scale grouted helical pile with the green grout was tested to characterize its performance. The experimental results show that the properties of TOSW grout mixes were comparable to conventional grout and satisfy the strength and construction requirements of grouted piles. Moreover, tested grouted helical pile using the developed mixture exhibited similar geotechnical performance as those installed using conventional grout mix. Hence, TOSW can be implemented in grouted helical pile applications, which would assist in achieving sustainable construction