AN INVESTIGATION OF ACCURACY OF INERTIAL INTERACTION ANALYSES WITH FREQUENCY-INDEPENDENT IMPEDANCE COEFFICIENTS Yilmazok, &Ouml / zg&uuml / n M.S., Department of Civil Engineering Supervisor: Assoc. Prof. Dr. B. Sadik Bakir November 2007, 79 pages The inertial interaction between the soil and structure alters dynamic response characteristics of a structure due to foundation deformability, such that the flexibility and energy dissipation capability of surrounding soil may lead to a significant increase in period and damping of structural oscillations. The inertial interaction analyses can be accomplished through utilisation of frequency dependent foundation impedance coefficients that are reported in literature for various soil conditions and foundation types. However, such analyses should be performed in frequency domain, and applicable to only cases that linear structural response is considered. Alternatively, equivalent frequencyindependent foundation impedance coefficients can be employed, such that a constant excitation frequency is assumed in calculation of these coefficients. In this study, it is assumed that the fundamental frequency of a fixed-base structure, which can be obtained through employing available empirical relationships or a modal analysis, can be substituted for excitation terms in impedance expressions. The error induced in calculation of peak structural distortions is investigated through comparisons of structural response due to frequency-dependent and frequency-independent foundation impedance coefficients. For analyses, a linear single-degree of freedom oscillator is considered for modeling the structure. The frequency-dependent impedance of a rigid disk foundation resting on elastic halfspace is simulated by a limited number of discrete elements. The response calculations are performed in frequency domain, through employing 72 acceleration records. It is concluded that, the natural frequency of fixed-base building can be considered as effective excitation frequency for calculation of foundation impedance coefficients, when the effect of inertial interaction on structural response is moderate. Through employing equivalent-linear approximation for the structural response, it is shown that the conclusion is also valid in cases that nonlinear structural response is considered. However, when the inertial interaction has more profound effects on the structural response, the use of natural frequency of flexible-base structure, which is calculated iteratively due to its dependence on foundation-impedance factors is recommended.

La presente investigación, desarrollará la interacción dinámica suelo estructura IDSE con y sin amortiguamiento aplicado a 3 modelos denominados modelo A, modelo B y modelo C con 4, 8 y 12 pisos respectivamente. Estos modelos serán evaluados en tres tipos de perfiles de suelo S1, S2 y S3 con características (peso específico, coeficiente de poisson y carga admisible) obtenidas de los libros del Sr. Braja M. Das y Willian Rodriguez Serquen. La evaluación de la IDSE se realizará mediante las ecuaciones simplificadas propuestas por la Norma Americana (EEUU) NIST GCR 12-917-21 Soil-Structure Interaction for Building Structures donde se desarrolla la interacción inercial que se hace referencia a los desplazamientos y rotaciones en la base de la estructura (fundación) debido a la respuesta de la estructura cuando da lugar un sismo. Asimismo, la flexibilidad de la fundación y suelo son representados mediante 6 rigideces (3 de traslacionales y 3 de rotación) con y sin amortiguamiento. Para cada modelo se realizará una comparación de cortante basal, momento, desplazamientos, derivas, periodos, frecuencias, modos de vibración, fuerzas internas máximas, y fuerzas internas en un pórtico con la finalidad de observar el comportamiento de las estructuras en los distintos tipos de suelo y tamaños de las modelos propuestas. / This research will develop dynamic floor structure IDSE interaction with and without damping applied to 3 models called model A, model B and model C with 4, 8 and 12 floors respectively. These models will be evaluated in three types of soil profiles S1, S2 and S3 with characteristics (specific weight, poisson coefficient and permissible load) obtained from the books of Mr. Braja M. Das and Willian Rodriguez Serquen. The evaluation of the IDSE will be carried out using the simplified equations proposed by the American Standard (USA) NIST GCR 12-917-21 Soil-Structure Interaction for Building Structures where inertial interaction is developed that refers to displacements and rotations at the base of the structure (foundation) due to the response of the structure when an earthquake occurs. In addition, the flexibility of the foundation and soil are represented by 6 rigidities (3 translational and 3 rotation) with and without damping. For each model, a comparison of basal shear, timing, displacements, drifts, periods, frequencies, vibration modes, maximum internal forces, and internal forces will be made on a gantry in order to observe the behavior of structures in the different soil types and sizes of the proposed models. / Tesis

Seismic response of a structure is influenced by the inertial interaction between structure and deformable medium, on which the structure rests, due to flexibility and energy dissipation capability of the surrounding soil. The inertial interaction analyses can be performed by utilizing simplified soil-structure interaction (SSI) analyses methods. In literature, it is noted that varying soil conditions and foundation types can be modeled by using these SSI approaches with springdashpot couples having certain stiffness and damping. In this study, the seismic response of superstructure obtained by using simplified SSI methods is compared with those of the fixed base systems. For this purpose, single and multi degree of freedom structural systems are modeled with both spring&ndash / dashpot couple and fixed base models. Each system is analyzed for varying structural and soil stiffness conditions under the excitation of three different seismic records. Next, the total base shear acting on the structural system and internal forces of load bearing members are investigated to observe the inertial interaction and foundation uplift effects on the superstructure. It is also aimed to examine the compatibility of the simplified SSI approaches utilized in the analyses. It is concluded that the structural and soil stiffness parameters are the most influential parameters that affect seismic structural response. Structures becomemore sensitive to varying soil properties as the structural stiffness increases. On the other hand, decreasing soil stiffness also increases the sensitivity of the structure to the seismic excitation. Calculated values of total base shear and internal member forces revealed that the inertial interaction might be detrimental for the superstructure. Contrary to general belief, the fixed base approach does not always yield to the results, which are on the safe side. Considering the analysis results, it is concluded that SSI analysis is very useful for more precise and economical design for the seismic behavior.

Esta investigación busca evaluar la Interacción entre el Suelo y la Estructura (ISE) en reservorios elevados tipo INTZE de tres diferentes capacidades, cimentados en diferentes tipos de suelos, ubicados en la zona con más peligro sísmico en el Perú. Para esto se planteó realizar una muestra de 27 configuraciones estructurales, con variaciones de altura y diámetro del fuste, y diámetro de losa de cimentación, las cuales están cimentadas en cuatro tipos de suelos de acuerdo con la norma Sismorresistente E.030-16. Se evaluará la influencia de la carga sísmica, mediante un análisis dinámico espectral definido por los lineamientos de las normas nacionales E.030-16 y complementariamente por códigos y estándares internacionales como el ACI 350.3-06. Para el dimensionamiento de los reservorios se aplicó el criterio de Otto Intze, análisis estático de esfuerzos y criterios del código ACI 350.3-06 y ACI 307-48. Estos reservorios fueron modelados en el software SAP2000, contando con 216 simulaciones en total. Se aplicó el modelo de Housner (1963) para la Interacción Fluido-Estructura y para la ISE se aplicó el modelo recomendado por el código FEMA P-750. Para analizar los resultados de interés, como las fuerzas internas en el fuste, la cortante basal, momento de volteo, desplazamientos y periodos, se aplicó la prueba de normalidad de Shapiro Wilk para la variación porcentual que se genera al evaluar la ISE, con el fin de determinar intervalos de variación con una probabilidad del 95%. Además, se aplicó la prueba de independencia Chi-Cuadrado para determinar cuantitativamente si la ISE influye en la reducción de las respuestas de interés. Se concluye de la prueba de independencia que, para un nivel de significancia de 15% la ISE influye en la reducción de la fuerza cortante basal y momento de volteo. Así mismo, para un nivel de significancia de 5% la ISE influye en la reducción de las fuerzas internas locales de fuste. / This research seeks to evaluate the soil structure interaction (SSI) in elevated water tanks of three different capacities, founded on different types of soil, all located in the most seismic hazard zone in Peru. Twenty-seven models were evaluated, all with different structural adjustments, including variations in the capacity, height, and diameter of the foundation slab, which are founded on four types of soil, according to the Peruvian Code for Earthquake Resistant Design E.030-16. We are going to analyze the seismic load influence through a spectral dynamic analysis, according to the Peruvian Code E.030-16, and the ACI 350.3-06 code for elevated tanks. For the sizing of the elevated tanks, the Otto Intze criterion, the static stress analysis, the ACI 350.3-06 and the ACI 307-48 code were applied. These elevated water tanks were modeled in the SAP2000 software, with 216 simulations. The Housner model (1963) was applied for the Fluid Structure Interaction, and for the Soil-Structure Interaction (SSI), we applied the model recommended by the FEMA P-750 code. To analyze the results of interest, such as internal forces in the shaft, base shear, rocking moment, displacements and periods, we applied the Shapiro Wilk normality test for the percentage variation that is generated when we evaluate the SSI, in order to determinate variations intervals with a probability of 95%. Also, we applied the Chi-Square test of independence to determinate, quantitatively, if the results are influenced by the SSI. We concluded, from the independence test that, for a significance level of 15%, the SSI influences the reduction of the basal shear force and the rocking moment. Likewise, for a significance of 5%, the SSI influences the reduction of the internal shaft forces. / Tesis