Single column bents on extended pile shafts are widely used in bridges for their economical and technical advantages. Nevertheless, this system is strongly affected by Dynamic Soil- Pile-Structure Interaction. In addition to the lengthening of the fundamental period of the structure, the compliance of the foundation induces a rocking component of the seismic motion experienced by the overall system that cannot be considered by following the procedures of a common seismic design practice. Although advanced models have been developed in order to account for Soil-Pile-Structure Interaction both in the linear and nonlinear range, Winkler-type models represent one of the most feasible approaches. In this work, a Beam on Nonlinear Winkler Foundation model is used to investigate the importance of features typical in soil nonlinear behaviour such as yielding, gapping, soil cave-in and cyclic hardening/degradation effects on the performance of extended pile shafts. A procedure to estimate the model parameters from geotechnical soil characterization is presented. Incremental Dynamic Analyses are performed to evaluate the effects of Ground Motion Duration and soil nonlinearity on the performance of extended pile shafts in various homogeneous and two-layered soil profiles, including saturated clay and sand in either fully dry or saturated state with different levels of compaction. A procedure to perform Incremental Dynamic Analysis, including effects on both site response analysis and on the structural performance, is established. Nonlinear kinematic and inertial interaction effects are analyzed by means of an exhaustive parametric investigation. The significant effects of the rocking component and the Ground Motion Duration on the seismic response of extended pile shafts are demonstrated. Comparisons with results obtained with a linear model are also presented. Finally, some considerations are drawn pointing out grey areas of the common design practice.
Il sistema pila-palo è largamente diffuso nelle strutture da ponte grazie ai suoi vantaggi economici e tecnici. Tuttavia questo sistema è fortemente influenzato dagli effetti dell’interazione dinamica terreno-palo-struttura. In aggiunta all’allungamento del periodo fondamentale della struttura, la cedevolezza della fondazione induce una componente rotazionale del moto sismico sul sistema globale che non può essere considerata mediante le comuni procedure di progettazione sismica. Sebbene siano stati sviluppati modelli avanzati per considerare l’interazione terreno-palo-struttura sia in campo lineare e non lineare, i modelli alla Winkler rappresentano uno degli approcci più versatili. In questo lavoro, un modello nonlineare di trave su suolo alla Winkler è stata utilizzato per indagare l’effetto sulla risposta della struttura dei principali aspetti legati al comportamento nonlineare del sistema terreno-fondazione, come ad esempio la plasticizzazione del terreno , la formazione di distacco all’interfaccia palo-terreno, il collasso delle pareti del foro e il degrado o incrudimento ciclico del terreno in prossimità del palo. Sono state eseguite analisi dinamiche incrementali per valutare gli effetti della durata del moto sismico e le non linearità del terreno sulle prestazioni della pila-palo in vari profili di terreno omogeneo e bistrato sia di argilla satura che di sabbia nello stato asciutto o saturo considerando differenti livelli di compattazione. Si è stabilita una procedura per eseguire le analisi dinamiche incrementali considerando gli effetti sia sulla risposta sismica locale sia sulle prestazioni strutturali. Gli effetti dell’interazione cinematica ed inerziale in campo non lineare sono stati analizzati mediante un’ampia indagine parametrica. Le analisi hanno evidenziato il ruolo determinante della componente rotazionale e della durata del moto sismico sulla risposta sismica della pilapalo. I risultati ottenuti sono inoltre stati confrontati con quelli ottenuti mediante un modello lineare. Infine, vengono fatte alcune considerazioni evidenziando le aree grigie della comune pratica di progettazione.
Seismic response of extended pile shafts considering nonlinear soil-pile interaction
TOMBARI, ALESSANDRO
2013
Abstract
Single column bents on extended pile shafts are widely used in bridges for their economical and technical advantages. Nevertheless, this system is strongly affected by Dynamic Soil- Pile-Structure Interaction. In addition to the lengthening of the fundamental period of the structure, the compliance of the foundation induces a rocking component of the seismic motion experienced by the overall system that cannot be considered by following the procedures of a common seismic design practice. Although advanced models have been developed in order to account for Soil-Pile-Structure Interaction both in the linear and nonlinear range, Winkler-type models represent one of the most feasible approaches. In this work, a Beam on Nonlinear Winkler Foundation model is used to investigate the importance of features typical in soil nonlinear behaviour such as yielding, gapping, soil cave-in and cyclic hardening/degradation effects on the performance of extended pile shafts. A procedure to estimate the model parameters from geotechnical soil characterization is presented. Incremental Dynamic Analyses are performed to evaluate the effects of Ground Motion Duration and soil nonlinearity on the performance of extended pile shafts in various homogeneous and two-layered soil profiles, including saturated clay and sand in either fully dry or saturated state with different levels of compaction. A procedure to perform Incremental Dynamic Analysis, including effects on both site response analysis and on the structural performance, is established. Nonlinear kinematic and inertial interaction effects are analyzed by means of an exhaustive parametric investigation. The significant effects of the rocking component and the Ground Motion Duration on the seismic response of extended pile shafts are demonstrated. Comparisons with results obtained with a linear model are also presented. Finally, some considerations are drawn pointing out grey areas of the common design practice.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14242/95753
URN:NBN:IT:UNIVPM-95753