Advanced concrete structures and design methods
Non-linear behavior of a concrete gravity dam during seismic excitation: A case study of the Pine Flat dam
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.
Seismic response of large diameter buried concrete pipelines subjected to high frequency earthquake excitations
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 used for simulation of seismic waves that propagate from the bedrock through the soil. The models describe both longitudinal and transverse cross-sections of pipelines 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 a significant effect on the response due to non-uniform ground caused by inclined bedrock, especially for high frequency earthquake excitations.
Numerical simulations of a concrete bridge deck loaded to shear failure
Numerical simulations of the shear failure of a bridge slab previously tested in full scale on an existing bridge is presented. Using the non-linear finite element method, a model of the bridge is assembled with the purpose to simulate the test procedure and realistically capture the failure load and behaviour. This in order to conclude what type of shear failure that occurred. Furthermore, the shear capacity of the bridge is calculated according to current design codes. A parametric study is conducted on the FE model with the aim to study the influence of key variables on the outcome of the analyses. From the studied parameters, it is observed that a combined reduction of the tensile strength and fracture energy, together with a low fixed crack coefficient has the largest influence. It is also observed that the location of the failure and the ultimate load is dependent on how the loading was applied to the model, i.e. via load control or deformation control. In the final FE analysis, the model fails at a load which slightly exceeds the experimental ultimate load. The mode of failure obtained in all the analyses are the result of a large shear crack propagating from the edges of the loading plate, through the slab to the slab/girder-intersection. This indicates that the type of failure that occurred in the full scale test was primarily due to a one-way shear mechanism with a secondary punching effect. The design values calculated with current codes results in very conservative values when compared to the obtained failure load from the experiment.
Contact: Mikael Hallgren (profile pages)