Nonlinear analysis of reinforced concrete structures on two-parameter soil model and visual computer software

The developments in computer technology in recent years result significant changes in design methods and codes. As a result, the structure can be analyzed with more complex and accurate methods, so project control mechanisms require more calculations and details. In addition, since the material quality and production opportunities increases, higher and more slender structures are designed. These topics such slenderness and soil structure interaction in structural design is therefore becoming more important cases. This case for the superstructure, also applies to the foundation and ground system. Traditionally, soil stress under foundaton is calculated using Winkler hypothesis, which means the stress is directly proportional with and only the displacemet of foundation nodes. The interaction between the soil nodes are neglected in Winkler hypothesis. As a result, the soil system outside the foundation can not be calculated. The continuty of soil system, other structures and external loads can not be taken into account in Winkler type soil. This usually results exaggerated soil stress on foundation edges, so the structure designer needs to add piles to foundation system or strengthen the soil, both means extra cost for building contractor. On the other hand, Pasternak type soil can take into accout the interaction between the soil nodes by using a shear parameter. The compression and shear parameters can be calculated by using Vlasov soil analysis. The effects of multiple soil layers and thickness of compressive soil system are taken into considiration in Vlasov analysis. When the continuity in soil enviroment is take into account, the displacements on foundation edges generally decreases and the effect of surrounding structures can be taken into account. This always results more realistic analysis and usually results more economical design. In this study, the structure performance was determined using Incremental Response Spectrum Analysis (IRSA) procedure, which is based on the approximate development of the modal capacity diagrams, which are defined as the backbone curves of the modal hysteresis loops. Modal capacity diagrams are used for the estimation of instantaneous modal inelastic spectral displacements in a piecewise linear process called pushover-history analysis. IRSA procedure can estimate with a reasonable accuracy the peak inelastic response quantities of interest, such as story drift ratios and plastic hinge rotations as well as the story shears and overturning moments. In this study, a tensionless soil model with bearing capacity is developed and its effect on soil, foundation and superstructure was investigated. The new model uses Vlasov type soil so the effects of multiple soil layers and thickness of compressive soil system are taken into considiration. The effects of neighbour structures and the effect of bearing capacity on tensionless soil is investigated on several examples. In the prepared thesis, a performance evelation method is developed to compare the performace of structures with different soil types, soil properties, foundations and superstructure systems. The existing methods mentioned in codes are targetting the structure safety, so any number of columns in collapse state results collapse performance performance. On the other hand, number of columns and their seismic importance must be taken into account for performance comparision. In the suggested performance method, the structure performance is represented numerically and the damege in structural members are accumulated by cosiderig their importance to determine overall structure performance. As a result, the importace and shear ratio of collapse state columns also taken into account. The structures are compared according to their numerical damage that represents the damage density. The yield surfaces representing the the yield conditions idealised with frequent divided triangles to be used in multimode adaptive pushover analysis. As a result, the nonlinear yield conditions lineariezed in a very sensitive way. During the pushover process, the plastic hinge parameter occured in new step is taken into considiration by condensating in frame rigidity matrix by using a special algorihim. This keeps the system rigidity matrix in the same size so the number of uknowns remain same. After the system displacements are solved, by using the frame condensation matrix, the plastic hinge parameter is calculated. The hinge parameter is used to determine the curvature and the damage in plastic hinge. The nonlinear behaviour of foundation system is also investigated in structural performance analysis. The mat-foundation slab was idealised with grid system. The bending moment and torsional moment interaction was taken into account in grid idealisation. Vlasov soil analysis and soil finite element is seperated from foundation finite element, so the foundation can be modelled as slab system or grid system freely. Plastic hinges are introduced in grid frames according to material, section and reinforcement properties of foundation. The plastic hinge parameters and curvature in grid plastic hinges are calculated to determine the damage in foundation system. In the prepared thesis, a computer software system that allows examining the structure of different types of analysis has been developed. In the prepared software, 12 degrees of freedom frame, 24 degrees of freedom shell and 48 degrees of freedom solid members can be defined in three dimensional space. Different types of restraints or springs can be assigned to the structure, rigid diaphragms can be defined to the joints. After generating finite element model, several analysis like linear analysis, free vibration analysis, response spectrum analysis, static pushover analysis, detachment analysis, multi-mode adaptive pushover analysis, performance analysis, Vlasov soil analysis, second order analysis, buckling modes analysis and time history analysis can be performed. The program can calculate the vertical loads automatically and can generate mass for joints. The software can optimize large matrices to use less memory and make fewer calculations, and the matrices can be stored in sparse format. Stress-strain curves for steel and concrete material can be defined in section properties, the capacity surfaces can be generated according to defined material and geometry automatically. General purpose structural analysis and design programs can not consider the second parameter of the Vlasov model, but this parameter may be indirectly considered by the adaptation of Mindlin plate elements as soil elements in the libraries of the mentioned programs by changing the elastic properties of the materials. In this time however, the second parameter cannot be correctly considered as some soil parameters may change between the time intervals of time history analysis. In the computer code which is devoloped for time history analysis of structures on Vlasov foundation, necessary soil parameters may be updated between the time intervals and more realistic results may be obtained. For the comparison, choosen structural systems are analyzed by the developed computer code and the results are compared with those obtained by a general purpose structural analysis program before, so as to show the effects of the mentioned soil parameters on time history analyses. In this study, a complete computer code is developed for time-history analysis of multistory buildings on Vlasov foundation. The computer code can perform the analysis of interacting multistory buildings under the real earthquake records. As the mode shape parameter proposed by Vlasov is depended on the soil deformation, the computer code calculates the mentioned coefficient in each time integration step and plots the displacement and internal force histories. According to the primary investigations, the buildings on Vlasov foundation can lead unfavourable dynamic reply to earthquakes depending on the distance between the buildings and uncompressible soil depth, comparing to the buildings on Winkler foundation. Several examples solved with the software for verification, also some problems like Vlasov soil model and structure interaction is examined. Furthermore, two-parameter soil model is used in time integration for soil-structure interaction. The suggested tensionless soil model with bearing capacity adopted to the computer software to compare various structures. Different compressable soil thickness and soil bearing capacities selected in order to determine the effect of soil properties on structural performance. Similarly, some solutions like pushover analysis, non-elastic behavior of foundation and soil, adaptive pushover analysis and structure performance from the literature used for verification of the software, and new problems like the effect of soil performance on structure performance is inspected. Also a new score system used to determine the performance of soil and structure system. The software has a graphical interface to investigate mathematical model and analysis results. The outputs can be generated in various formats and exported to several programs. The software is designed as a library, which means that it can be called from other programs, the outputs can be generated by sending commands to the library. The operations and objects in the library is described in detail, and two examples are prepared for Visual Basic NET and C# programming languages.