Rocking Response of Free-Standing Rigid Blocks on Slopes

Structure, equipment, statue or storage cask may experience free-standing rocking on slopes because of the nonuniform settlement of the base, construction error or foundation failure. The free-standing rigid block on a slope subjected to one-sine pulse excitation and earthquake motions is examined in this paper. First, considering the free-standing rigid block on a slope, the overturning acceleration spectrum under one-sine pulse is built. The spectrum covers two overturning modes, i.e. overturning with one impact either before or after the excitation and overturning without impact. Then the influences of the slope on the overturning acceleration spectrum are discussed in depth. The analytical solution is compared with the numerical solution based on both linear and nonlinear formulations. It reveals that the safe region of the minimum overturning acceleration spectrum between mode 1 and mode 2 depends on the angle of the slope. Further, the block on a slope is subjected to the Tianjin, Kobe and Northbridge earthquake motions. By simplifying the main pulse of the motions to one-sine pulse, although the overturning acceleration spectrum fails to predict the overturning acceleration of the block subjected to real earthquake motions, it can provide some guidelines to predict the practical performance of the rocking structures.

Geophysical investigation of foundation failure at Medina Estate, Lagos, Southwestern Nigeria

Integrated geophysical investigation involving Ground Penetrating Radar (GPR) and Electrical Resistivity methods were carried out at Medina Estate, Lagos southwestern Nigeria to map the subsurface lithology in order to delineate its peat stratigraphy that has been causing foundation failure in the area. Twenty-one traverses (varying from 35-880 m in length) of Ground Penetrating Radar (GPR) survey were conducted along the streets of Medina trending NE-SW and NW-SE directions using the Mala 250 MHZ bi-static shielded antenna. Thirty-six Vertical Electrical Soundings (VES) were carried out using Schlumberger electrode array at some selected points along the established traverses within the area. The GPR data were processed into radar section using Rad Explorer software. The VES data were interpreted quantitatively using the partial curve matching method and 1-D forward modeling with Win Resist Software. Available litho-logs from boreholes drilled within the area were compared with the geophysical results. Results of the GPR survey delineated three geologic layers which include the topsoil with high amplitude, parallel to sub parallel, horizontal reflections, with thickness varying from 1 to 2 m across the entire profiles and composed of lateritic clay; peat layer with low amplitude, parallel sinuous/wavy reflections with depth of occurrence ranging from 2.0 to 8 m and clay with low amplitude, planar, horizontal, sub-parallel reflections underlying the peat layer. Vertical Electrical Sounding results revealed the presence of three geological layers which are the topsoil, peat and clay and sandy clay with layer resistivity values ranging from 20- 225 Ωm, 5 – 90 Ωm and 36 to 366 Ωm and thickness values ranging from 0.5 – 2 m, 4.0-29.0 m and infinity respectively. Borehole information confirms the occurrence of shallow peat with depth ranging from 1.5 to 9 m and clay layer with depth ranging from 9 to 21 m beneath the area. The GPR survey results correlates with the well logs acquired in the study area. Based on the correlation of the geophysical results with the well logs, the GPR gives better information about the peat layer compared to the Electrical ResistivityMethod. The information obtained from this study shows that the soils at shallow depth are organic soils which are difficult foundation materials because they exhibit very high compressibility, as such making shallow foundation impossible except some form of soil improvement is carried out. The alternative approach is the adoption of deep foundations in form of piles. Keywords: Foundation Failure, Geophysical Investigation, Ground Penetrating Radar, Vertical Electrical Sounding, Peat.

Alternative foundation for reducing building losses due to foundation failure in soft soil

Much damage to buildings occurs in areas that have soft soil layers due to the failure of the foundations. Besides, foundations in soft soils generally require very expensive construction. For this reason, proper research needs to help develop strong foundations that can be used on soft soils with relatively low cost. In this research, foundations with various diameters and depths were tested on soft soil. The foundations were made of PVC pipes with diameters of ½ ", 1", 2 " or 2.5" and the same depth. Soft soil in the form of clay with particle-sizes that passed filter No. 200 was used. Before testing the foundations, carrying capacity analysis was done using the classical method on each pipe with a closed head so that the optimum carrying capacity of each foundation (PVC Pipe) was known. From this test the influence of the size of the foundations on the carrying capacity of soft soil could be seen. The results of this research will help reduce building loss/damage in areas dominated by soft topsoil

Repair and retrofitting of buildings post earthquake

This paper discusses the damage types, repair methods and retrofitting of buildings post an earthquake. Data were taken by conducting surveys and assessment of buildings directly, both engineered and non-engineered buildings affected by the West Sumatra earthquake in 2009. Some causes of damage, among them is the detailing of reinforcement that do not follow the existing standard, soft-story effect, foundation failure, low material quality and does not meet the requirements, design and implementation of the construction do not follow the rules and technical provisions of the building earthquake resistant. Improvement and buildings retrofitting can be done after the buildings damage types or its components/parts and the quality of the building materials used were known. The structural analysis was done in order to know the cause of the building elements damaged and if the results of analysis with the latest regulations earthquake load, the building structures is able to withstand the earthquake loads and a repair is not required, but if not, the retrofitting is required.

Assessment of Failure Occurrence Rate for Concrete Machine Foundations Used in Gas and Oil Industry by Machine Learning

Concrete machine foundations are structures that transfer loads from machines in operation to the ground. The design of such foundations requires a careful analysis of the static and dynamic effects caused by machine exploitation. There are also other substantial differences between ordinary concrete foundations and machine foundations, of which the main one is that machine foundations are separated from the building structure. Appropriate quality and the preservation of operational parameters of machine foundations are essential, especially in the gas and oil industry, where every disruption in the technological process is costly. First and foremost, there are direct repair costs from damage to foundations, but there are also indirect costs associated with blockages of the production process. Foundation repairs can temporarily shut down a given part of the refining process from operation. Thanks to cooperation from our partner, we obtained data from 510 concrete machine foundations from a refinery. Our database included many parameters, such as concrete cover thickness, machine gravity center distortion, the angular frequency of vertical self-excited vibrations, the angular frequency of horizontal self-excited vibrations, amplitudes of oscillation, foundation area, foundation volume, and information on occurring failures. Concrete machine foundation failure is not yet fully understood. In our study, we assessed what affects the failure occurrence rate of concrete machine foundations and to what extent. We wanted to find out whether there are correlations between the foundation failure occurrence rate and the mentioned parameters. To achieve this goal, we utilized state-of-the-art machine learning techniques.

MATHEMATIC MODEL OF A BEAM PARTIALLY SUPPORTED ON ELASTIC FOUNDATION

The paper presents the methodic for analytical determining of stress-strain state of a beam partially supported on elastic foundation at sudden damage of foundation structure (partial failure). Bending equation for a beam is written using dimensional parameter and solved with the initial parameters method. Such approach al­lows to obtain dimensional analytical solution to static and dynamic problems for universal boundary conditions of a beam since it always leads to equations’ system of second order. Using numerical analysis for various values of generalized stiffness parameter of a system “beam - foundation”, we established affecting of the length of failure foundation part to stress-strain state of the beam for two supporting variants: partial supporting and sup­porting by two ends with foundation failure in the middle part of the beam.