engleski

The effect of some parameters on behaviour and bearing capacity of multi-drum stone columns under static load and earthquake

In this thesis, the effect of several important parameters on the behaviour and bearing capacity of multi-drum stone columns loaded by short-term static loads and earthquakes was investigated. These parameters have not been investigated to date or have been investigated only sporadically. All of the experiments were conducted on small-scale column models using modern equipment for testing and measuring. Dynamic testing of the models was performed using an established earthquake platform. The effects of the column block number and joint type were investigated, as well as several parameters for the bolts used in the column joints (material, length, bolt diameter and the diameter of the bolt hole). Static tests were conducted separately for centric compressive loads and for bending loads with longitudinal compression. During the dynamic tests, the samples were exposed to the acceleration of three different earthquake types with a successive increase in acceleration to failure. During the action of all loads, the characteristic displacements, accelerations and strains of the model were recorded. The motion of the model was recorded with a precision camera. The aim of this research was to contribute to the development of science in the subject area, which has been accomplished through the publication of five scientific papers in relevant worldwide journals. The purpose of this research is to provide conclusions regarding the investigated effects of important multi-drum stone column parameters, and the results should find practical application in the restoration/strengthening of existing multi-drum stone columns and the creation of new multi-drum stone columns. The most important conclusions of the research are listed below. Increasing the number of blocks (joints) in the multi-drum column reduces the column’s stiffness and increases its deformability. The consequence of this is a significant reduction in the column’s bearing capacity for static loads, as well as for longer duration earthquakes, which entered great energy in the construction. For impact-type earthquakes, increasing the number of blocks in a column can result in a greater bearing capacity because the column stiffness is reduced, and smaller earthquake forces are generated in the column. Soft joints (dry, joints made from stone powder and weaker mortar), compared to rigid joints and single-block column, result in a softer column with a lower bearing capacity for static loads and long lasting earthquakes with greater generated energy. However, for impact-type earthquakes, column with soft joints can have a greater bearing capacity than columns with rigid joints or single-block columns. Bolts in multi-drum stone columns significantly contribute to their bearing capacity during earthquakes. The bolt material has no major impact on the column bearing capacity during earthquakes if the column collapse is predominantly followed by bending and less by shear, i.e., if the failure is caused by the bolts pulling out and not by shear failure. The diameter of the bolt has no major effect on the column bearing capacity when it is loaded with smaller transverse forces. In that case, a thick bolt can be unfavourable for some earthquakes, as a thick bolt increases the stiffness of the column, and pull on it larger earthquake forces. In this case, the column failure is followed by the bolt pulling out but not by its failure. When the column is subjected to large shear with respect to bending, increasing the bolt diameter increases the column capacity. The bolt length does not have a greater effect on the column bearing capacity when the bolt has no adhesion with the block, i.e., when the bolt cannot withstand tensile forces. Increasing the bolt hole diameter in relation to the bolt diameter and having a bolt that cannot withstand tensile forces decreases the column bearing capacity during an earthquake. With the same maximum amplitude, the type of earthquake (duration and predominant period) has a considerable effect on all column parameters considered in this research. Therefore, in practice, it is crucial to know what type of earthquake can be expected at the considered location.

multi-drum stone column, experiment, block height, joint type, bolts parameters, bearing capacity, static load, earthquake

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