64,993 research outputs found
Seismic Earth Pressure Development in Sheet Pile Retaining Walls: A Numerical Study
The design of retaining walls requires the complete knowledge of the earth
pressure distribution behind the wall. Due to the complex soil-structure
effect, the estimation of earth pressure is not an easy task; even in the
static case. The problem becomes even more complex for the dynamic (i.e.,
seismic) analysis and design of retaining walls. Several earth pressure models
have been developed over the years to integrate the dynamic earth pressure with
the static earth pressure and to improve the design of retaining wall in
seismic regions. Among all the models, MononobeOkabe (M-O) method is commonly
used to estimate the magnitude of seismic earth pressures in retaining walls
and is adopted in design practices around the world (e.g., EuroCode and
Australian Standards). However, the M-O method has several drawbacks and does
not provide reliable estimate of the earth pressure in many instances. This
study investigates the accuracy of the M-O method to predict the dynamic earth
pressure in sheet pile wall. A 2D plane strain finite element model of the
wall-soil system was developed in DIANA. The backfill soil was modelled with
Mohr-Coulomb failure criterion while the wall was assumed behave elastically.
The numerically predicted dynamic earth pressure was compared with the M-O
model prediction. Further, the point of application of total dynamic force was
determined and compared with the static case. Finally, the applicability of M-O
methods to compute the seismic earth pressure was discussed
Towards Landslide Predictions: Two Case Studies
In a previous work [Helmstetter, 2003], we have proposed a simple physical
model to explain the accelerating displacements preceding some catastrophic
landslides, based on a slider-block model with a state and velocity dependent
friction law. This model predicts two regimes of sliding, stable and unstable
leading to a critical finite-time singularity. This model was calibrated
quantitatively to the displacement and velocity data preceding two landslides,
Vaiont (Italian Alps) and La Clapi\`ere (French Alps), showing that the former
(resp. later) landslide is in the unstable (resp. stable) sliding regime. Here,
we test the predictive skills of the state-and-velocity-dependent model on
these two landslides, using a variety of techniques. For the Vaiont landslide,
our model provides good predictions of the critical time of failure up to 20
days before the collapse. Tests are also presented on the predictability of the
time of the change of regime for la Clapi\`ere landslide.Comment: 30 pages with 12 eps figure
The application of active controls technology to a generic hypersonic aircraft configuration
Analytical methods are described for the prediction of aerothermoelastic stability of hypersonic aircraft including active control systems. Thermal loads due to aerodynamic heating were applied to the finite element model of the aircraft structure and the thermal effects on flutter were determined. An iterative static aeroelastic trim analysis procedure was developed including thermal effects. And active control technology was assessed for flutter suppression, ride quality improvement, and gust load alleviation to overcome any potential adverse aeroelastic stability or response problems due to aerodynamic heating. A generic hypersonic aircraft configuration was selected which incorporates wing flaps, ailerons, and all moveable fins to be used for active control purposes. The active control system would use onboard sensors in a feedback loop through the aircraft flight control computers to move the surfaces for improved structural dynamic response as the aircraft encounters atmospheric turbulence
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