Structure Foundation Soil Research Articles

Effect of structural inertia on liquefaction-induced settlements of shallow foundations

The majority of published research on the performance-based design of shallow foundations on liquefiable soil focuses on seismic settlement accumulation by neglecting soil-structure-interaction (SSI) effects. On the other hand, SSI effects prove dominant when the foundation soil is non-liquefiable. Thus, the aim of this paper is to investigate the dynamic response of structure-foundation-soil (SFS) systems by examining the role of structural inertia on the performance of shallow foundations on liquefied soil, through a series of 3D fully coupled nonlinear numerical analyses of SFS systems. As a first step, the nonlinear fundamental period of vibration of the SFS system is correlated to the key system and excitation parameters. Next, in order to isolate the effects of structural inertia, shear-induced seismic settlements of SFS systems in liquefied soil are compared with the respective settlements of conjugate foundation-soil (FS) systems that apply the same static contact pressure on the foundation soil. Finally, approximate relations are proposed for the effects of structural inertia on liquefaction-induced settlements of shallow foundations, based on a multivariable statistical analysis of the numerous parametric numerical estimates.

Influence of structure–foundation–soil interaction on ground motions recorded within buildings

The present work investigates the effect of soil–structure interaction (SSI) on foundation motion recorded at accelerometric stations installed at the lowest level of buildings. For this purpose, two sites of instrumented buildings, for which foundation and free-field strong motion recordings are available, are studied in terms of transfer functions as well as strong motion intensity and frequency content. The importance of such an instrumentation scheme is highlighted, especially when it comes to assessing the filtering action of the foundation on moderate to high frequency components of free-field motions. The effect of ground motion filtering at the soil–foundation interface is further quantified in terms of amplitude and frequency content. The recordings are supplemented by a parametric analysis of the sub-structured soil–structure system leading to regression expressions that associate the intensity and frequency parameters of the recordings obtained at the base of the instrumented buildings and the corresponding free-field ones. It is shown that kinematic and inertial decoupling of SSI is not only a useful but also a necessary task for correcting earthquake records obtained at building basements particularly for high frequency-dominated ground motions.

The collapse of Space building

On 12 October 2013, the 24-storey high ‘Space’ building collapsed in Medellín, Colombia. The building had a reinforced concrete structure founded on large-diameter piles with enlarged bases. During and after construction the building exhibited structural problems and excessive settlements of some piles. Because of the evidence of structural damage, the building was evacuated on 11 October 2013, 1 day before the collapse. Isolated large-diameter piles excavated in a firm, high-plasticity saprolitic residual clay, supported building columns. Building collapse was triggered by a significant increase of the vertical load transmitted by some columns, which, in turn, is explained by widely different settlements experienced by neighbouring piles and the resulting loading transfer mechanisms. The first part of the paper presents the results of the field exploration and laboratory tests, as well as the structural and architectural layout, including the construction process and other forensic aspects that could influence the collapse of the structure. Afterwards, the joint structure–foundation–soil numerical model developed and its predictions are described. Matching the records of pile settlements, measured during construction and afterwards until building collapse, with model predictions allowed the validation of the model. The causes that triggered the collapse were identified and some other lessons were learned.

Analysis for the Variety of Piled Raft Foundations Rigidity and Subgrade Stress Based on Earthquake

The pile raft foundations has very good earthquake resistance effect. Different from usually separating foundation calculation from subgrade calculation, pile-soilstructure interaction system combines pile raft foundations with ground soil for rigidity conformity, obtains total rigidity matrix of rigid foundations, and makes rigid foundations and the superstructure work together to analyze the characteristic of structure. Analyzing the variety of rigidity for structure foundation soil in earthquake action, it can be obtained the variety of characteristic value of subgrade bearing capacity. Considering pile-soil-structure interaction system, we can calculate stress and strain for subgrade and foundations, and estimate stabilization condition of subgrade and foundations.

Improved bearing resistance of soil foundations of buildings with injectable polyurethane composites

The article deals with the analysis of SPT®polyurethane materials and maintenance technologies based on them, and an analytical review of literature on the topic. Solidification with SPT®materials and technologies makes it possible to compact unstable foundation soils of structures and buildings. The solidification is implemened through a guided increase of polymeric material injected into a foundation. As a result, polymeric root-like reinforcing bodies are formed in the foundation, and the water is extruded out of the soil, thus considerably increasing the bearing capacity of the foundation. In order to assess the actual efficiency of the material the authors conducted the full-scale research into the general overhaul technology of the pipe culvert, the static and the dynamic tests on the models of solidified soil was conducted and compared with the results of the tests on the models of non-solidified soil. The authors investigated into the life ratio of SPT®material and the soil solidified with it. By comparing characteristics of SPT®materials and technologies with those of conventional materials, the basic analogies and differences were established. And the possibility to use them for construction, refurbishment and maintenance of rail facilities was determined.

Field Experiments for Monitoring the Dynamic Soil–Structure–Foundation Response of a Bridge-Pier Model Structure at a Test Site

Summary results from a series of field experiments at a test site in Greece are presented, involving an in situ instrumented bridge-pier model built on realistic foundation conditions, to study the dynamic behavior of structure-foundation-soil system. It was attempted to link the variation of its dynamic characteristics to certain changes in its structural system, including the development of structural damage. This measured response was next utilized to validate numerical tools capable of predicting influences arising from such structural changes as well as from soil–foundation interaction. This bridge-pier model was supported on soft soil deposits allowing the study of structure–foundation–soil interaction effects during low-to-medium intensity artificial excitations. The in situ experiments provided measurements that were used to verify fundamental analytical solutions for soil–structure interaction. They were also used to validate numerical simulations that were developed to predict the response of the studied structure and thus, back-evaluate modeling assumptions. The obtained accuracy of the numerical predictions must be partly attributed to sound knowledge of the mechanical properties of the pier model and of the soil, not necessarily the case in all practical applications. It is evident that more complex finite-element models can improve the quality of the prediction only in cases where their parameters can be defined equally well. A special study further focused on the radiation of the waves generated by the vibration of the bridge-pier model through the soil medium. It is deemed that this comprehensive experimental investigation of soil–structure interaction provides measurements of the system response and enhances our understanding of the physical phenomenon as a whole.

Soil Structure Interaction Effect on an Asymmetrical R.C. Building with Shear Walls

Earthquake in populated areas throughout the world causes extensive damage to the various structures that result in catastrophic loss of human life and enormous economic losses. However, the damage can be attributed to the inadequate design of the structures. Sometimes for low to medium rise structures, the analysis and design with respect to lateral forces has generally been a process of checking the vertical load resisting system for its ability to resist lateral forces. However, for tall buildings, the vertical load resisting system cannot resist lateral forces efficiently, it is well recognized that the incorporation of lateral force resisting systems in the form of shear walls, bracing systems etc. improve the structural performance of building subjected to lateral forces due to earthquake excitation. Further, the position of shear walls in a building alters the response of structure. It is desirable to decide the position of the of the shear walls judicially, so that maximum benefit can be derived. Similarly, adopting realistic approach for structure foundation soil behavior, a flexible approach analysis considering soil structure interaction, also alters the response of structure in terms of bending moment, axial thrust, etc. therefore response of building in terms of forces and bending moment in members, is required to be ascertained, with the placement of shear walls at different possible locations and also with the consideration of soil structure interaction effect. The phenomenon of soil-structure interaction is more pronounced in multi-storied building frames especially, when resting on poor soil, due to possibility of large unequal column loads. Neglecting SSI is reasonable for light structures in relatively stiff soil such as low rise buildings and simple rigid retaining walls. The effect of SSI, however, becomes prominent for heavy structures resting on relatively soft soils for example high-rise buildings, nuclear power plants and elevated-highways on soft soil.

Seismic response and simulations of reinforced concrete bridge using OpenSees on high performance computing

Nonlinear seismic analysis is becoming increasingly significant to grasp the performance of structures under earthquake. A nonlinear finite element model of existing bridge at Karad, India, including the bridge structure, pile groups, and the supporting foundation soil, is developed under 2D and 3D conditions in Gid (a pre and postprocessor software). The computational model is analyzed using Parallel OpenSees. OpenSees is open source software for carrying out earthquake engineering simulations, developed by Pacific Earthquake Engineering Research Centre, USA. The earthquake simulations were carried out using C-DAC’s high performance computing facilities. The ground motion selection and modification technique-predicting median interstory drift response of building, ground motions are selected by M and R and scaling to Sa(T1), is used for seismic response of combined large scale soil-structure interaction of Karad bridge. The idealized model properly represents the actual geometry; boundary conditions, gravity loads and mass distribution. Nonlinear modeling and analysis allows more accurate determination of stresses, strains, deformations and forces of critical components. The present work involves the effects of specially varying input excitation (earthquakes) at an existing bridge site. A nonlinear finite element model of this bridge site including the bridge structure, pile group and supporting foundation soil is developed in 2D plane strain conditions and in 3D 20 noded brick element. Carefully calibrated nonlinear stress–strain models are employed for both bridge and soil materials, in order to realistically reproduce actual site conditions. Seismic input motions are defined as forces using the boundary layer force method (zero length element approach). The earthquake simulation of bridge structure includes large scale interaction between structure–foundation–soil system and deformations at various locations of the bridge. The results include deformations at base of piers and at various spans of the bridge. Performing the bridge simulation on C-DAC’s Param Yuva facility results in accuracy and saving in computing efforts.

Structure-foundation interaction and soil creep : Brown, P T Sydney Univ, School of Civil Engineering, research report R300, Dec 1976, 16P

An examination of the effect of soil creep on structure foundation soil interaction with regard to variation of differential settlement of columns, bending moments in the structure and column loads is presented. The structures considered are three bay portal frames with pin based columns, the foundations considered are strip footings of finite length, and the soil is regarded as being a linear viscoelastic continuum of infinite depth. The adopted cree function is almost linear with log time and thus has the same general form as that commonly observed in laboratory tests. The purpose of the paper is to indicate, in terms of the relative stiffnesses of the structure, foundation and soil, which situations will lead to significant deterioration in conditions for the structure with elapse of time. The effects of changes in most of the parameters of the problems are discussed. Thus the results presented should enable estimates to be made of the changes in the various interaction effects with time, when the creep properties of the soil have been determined.