Search

Concrete hydraulic structures are of great importance in today's society. When situated in areas with hard bedrock, these structures may become extra vulnerable to seismic excitations as these here are dominated by high-frequency vibrations which can have disastrous consequences for slender structures. The aim of this thesis was to investigate special considerations that must be made when conducting analyses of such hydraulic structures during high-frequency excitations. Underground and on the ground structures were investigated separately. Underground concrete pipelines and concrete buttress dams were selected for the study because their behaviour when exposed to seismic excitations is dominated by their stiffness. The most effective models and modelling methods for the seismic analyses of such structures were implemented and evaluated. Two-dimensional finite element (FE) models were developed for the dynamic analysis of underground concrete pipelines loaded by seismic waves propagating from bedrock through soil. The interaction between the bedrock and the surrounding soil was investigated with respect to rock geometry and soil properties. The surface of dam foundations is commonly irregular, resulting in nonuniform motions at the dam-foundation interface. The free-field modelling methods for concrete dam foundations were adapted in order to accurately describe the propagation of earthquake vibrations from the source to the ground surface. The implementation of a threedimensional FE model for concrete buttress dams was investigated. Two different methods for free-field modelling are presented, which can be implemented independently of the software used. The seismic loads are applied as effective earthquake forces at non-reflecting boundaries. In the first method, the free-field motions at the non-reflecting boundaries are determined by the so-called domain reduction method using the direct FE calculation. In the second method, the free-field motions are analyticall, Betongkonstruktioner för vattenkraft och vattenförsörjning är av stor betydelse för dagens samhällen. I områden med hård berggrund kan dessa konstruktioner vara särskilt känsliga för seismiska händelser då de domineras av höga frekvenser, vilket kan leda till katastrofala konsekvenser för slanka konstruktioner. Syftet med föreliggande avhandling var att undersöka överväganden och antaganden som måste göras vid analyser av sådana strukturer för vattenkraft och vattenförsörjning vid excitationer med högre frekvenser. Strukturer under jord och på markytan undersöktes separat. Underjordiska rörledningar och lamelldammar av betong valdes till studien eftersom de vid seismiska excitationer domineras av deras styvhet. De mest effektiva modellerna och modelleringsmetoderna för de seismiska analyserna av sådana strukturer implementerades och utvärderades. Tvådimensionella finita element (FE) modeller utvecklades för dynamisk analys av underjordiska rörledningar av betong utsatta för seismiska vågor som utbreder sig från berggrunden och genom jordlager. Samspelet mellan berggrunden och den omgivande marken undersöktes med avseende på bergets geometri och markegenskaperna. Bergytan hos dammfundament är vanligtvis oregelbunden, vilket resulterar i ojämna rörelser vid gränsytan mellan damm och grundläggning. Modelleringsmetoderna med fria fält för betongdammars berggrundläggning har här anpassats för att korrekt beskriva utbredningen av jordbävningsvibrationer frånvibrationscentrum till markytan. Implementeringen av en tredimensionell FE-modell för betonglamelldammar undersöktes. Två olika metoder för frifältsmodellering presenteras, vilka kan användas oberoende av aktuell programvara. De seismiska belastningarna appliceras som effektiva jordbävningskrafter vid icke-reflekterande materialgränser. Med den första metoden bestäms de fria fältens rörelser vid de icke-reflekterande gränserna genom den så kallade domänreduktionsmetoden, med direkt FE-beräkning. I den andra metoden bes, QC230224

QC 20221025

Concrete buttress dams could potentially be susceptible to high-frequency vibrations, especially in the cross-stream direction, due to their slender design. Previous studies have mainly focused on low-frequency vibrations in stream direction using a simplified foundation model with the massless method, which does not consider topographic amplifications. This paper therefore investigates the nonlinear behaviour of concrete buttress dams subjected to high-frequency excitations, considering cross-stream vibrations. For comparison, the effect of low-frequency excitations is also investigated. The influence of the irregular topography of the foundation surface on the amplification of seismic waves at the foundation surface and thus in the dam is considered by a rigorous method based on the domain-reduction method using the direct finite element method. The sensitivity of the calculated response of the dam to the free-field modelling approach is investigated by comparing the result with analyses using an analytical method based on one-dimensional wave propagation theory and a massless approach. Available deconvolution software is based on the one-dimensional shear wave propagation to transform the earthquake motion from the foundation surface to the corresponding input motion at depth. Here, a new deconvolution method for both shear and pressure wave propagation is developed based on an iterative time-domain procedure using a one-dimensional finite element column. The examples presented showed that topographic amplifications of high-frequency excitations have a significant impact on the response of this type of dam. Cross-stream vibrations reduced the safety of the dam due to the opening of the joints and the increasing stresses. The foundation modelling approach had a significant impact on the calculated response of the dam. The massless method produced unreliable results, especially for high-frequency excitations. The free-field modelling with the analytical method led, QC 20220502

In this paper, seismic analyses of Pine Flat Concrete dam performed as part of theme A in the 15th benchmark workshop are presented. The results presented focuses on differences between mass and massless foundation and the influence from non-linear material behavior. The analyses performed with mass foundation using analytical free field input records and infinite boundary elements corresponded with the expected free surface results, for lower frequencies. For higher frequencies some discrepancies caused by the influence from the dam and the reservoir as expected. The corresponding analyses with massless foundation showed significantly higher accelerations but good agreement with the expected free surface displacement at the dam toe. To consider the influence from nonlinear material behavior, a dynamic push-over analysis (endurance time acceleration function, ETAF) was performed. It was possible to perform the analysis for the full duration of the record, despite significant non-linear material behavior. The initial damage occurred at the upstream toe and then showed significant induced damage as the level of excitation successively increased. In the end of the analysis, the top of the dam is cracked through which would cause an instability failure of the top of the dam., QC 20210409

Buried pipelines are tubular structures that cross large areas with different geological conditions. During an earthquake, imposed loads from soil deformations on pipelines may cause drastic damages. In this study two dimensional finite element models of pipelines and surrounding soils are usedfor simulation of seismic waves that propagate from the bedrock through thesoil. The models describe both longitudinal and transverse cross-sections ofpipelines and the soil-pipe interaction is described as a nonlinear behaviour.The effects of uniform ground with different burial depth and soil layer thickness, soil stiffness and non-uniform ground on the seismic response of reinforced concrete pipelines is studied. Two earthquakes, with high and low frequency contents, are employed for the dynamic analysis. The results show asignificant effect on the response due to non-uniform ground caused by inclined bedrock, especially for high frequency earthquake excitations., QC 20201019

Buried reinforced concrete pipelines are widelyused in e.g. water and wastewater systems. Failure of these infrastructures mayresult in drastic effects and recently they have been brought into focus asvital components in safety systems for nuclear power installations. The highlevel of safety has here lead to a demand for reliable earthquake risk analyses.In this paper, methods are compared and the use of seismic design loadsdemonstrated. FE analysis in 2D of soil-pipe interaction under seismic wavepropagation is performed. The performance of concrete pipes subjected toseismic waves with different frequency content is evaluated with respect todifferent soil condition but also water mass effect., QC 20150128

QC 20160226

Buried pipelines are tubular structures that cross large areas with different geological conditions. During an earthquake, imposed loads from soil deformations on concrete pipelines may cause severe damages. In this study, the use of two-dimensional finite element models of pipelines and surrounding soil for simulation of seismic waves that propagate from the bedrock through the soil are demonstrated. The models describe both longitudinal and transverse cross-sections of pipelines and the soil-pipe interaction is modelled as a nonlinear behaviour. The effects of uniform ground with different burial depths, soil layer thickness, soil stiffness and bedrock geometry on the seismic response of reinforced concrete pipelines is studied. Two earthquakes, with high and low frequency contents, are employed for the dynamic analysis. The results show that there is a much smaller risk of damage from high-frequency earthquakes, but that there is a significant effect on the response due to possible irregular ground with inclined bedrock., QC 20161014

QC 20230221