Cyclic behaviour of saturated sands subject to previous horizontal shear stresses

The dynamic behaviour of saturated sands has been studied from different perspectives. However, most experimental research on this field does not take into account the shear stress conditions existing prior to the application of dynamic loads; i.e., a null initial static shear stress (τo = 0) is assumed. The main objective of this work is to report on the influence that static shear stresses (τo) have on the behaviour of saturated sands under cyclic shear loads. This article presents the results and analysis of part of a wider experimental programme involving 30 monotonic and 26 cyclic simple shear tests for different combinations of static shear stress (τo) and cyclic shear stress (τc) (all undrained), besides identification and classification tests. The tested samples have been taken from the area of the North Entrance Mouth at the Port of Barcelona (Spain).

Dynamic & Cyclic behaviour of ballast in the long term as determined in Cedex's track box

The 6 cylinder servo-hydraulic loading system of CEDEX's track box (250 kN, 50 Hz) has been recently implemented with a new piezoelectric loading system (±20 kN, 300 Hz) allowing the incorporation of low amplitude high frequency dynamic load time histories to the high amplitude low frequency quasi-static load time histories used so far in the CEDEX's track box to assess the inelastic long term behavior of ballast under mixed traffic in conventional and high- speed lines. This presentation will discuss the results obtained in the first long-duration test performed at CEDEX's track box using simultaneously both loading systems, to simulate the pass-by of 6000 freight vehicles (1M of 225 kN axle loads) travelling at a speed of 120 km/h over a line with vertical irregularities corresponding to a medium quality lin3e level. The superstructure of the track tested at full scale consisted of E 60 rails, stiff rail pads (mayor que 450 kN/mm), B90.2 sleepers with USP 0.10 N/mm and a 0.35 m thick ballast layer of ADIF first class. A shear wave velocity of 250 m/s can be assumed for the different layers of the track sub-base. The ballast long-term settlements will be compared with those obtained in a previous long-duration quasi- static test performed in the same track, for the RIVAS [EU co-funded] project, in which no dynamic loads where considered. Also, the results provided by a high diameter cyclic triaxial cell with ballast tested in full size will be commented. Finally, the progress made at CEDEX's Geotechnical Laboratory to reproduce numerically the long term behavior of ballast will be discussed.

Health monitoring of web plastifying dampers subjected to cyclic loading through vibration tests

This article investigates experimentally the application of health monitoring techniques to assess the damage on a particular kind of hysteretic (metallic) damper called web plastifying dampers, which are subjected to cyclic loading. In general terms, hysteretic dampers are increasingly used as passive control systems in advanced earthquake-resistant structures. Nonparametric statistical processing of the signals obtained from simple vibration tests of the web plastifying damper is used here to propose an area index damage. This area index damage is compared with an alternative energy-based index of damage proposed in past research that is based on the decomposition of the load?displacement curve experienced by the damper. Index of damage has been proven to accurately predict the level of damage and the proximity to failure of web plastifying damper, but obtaining the load?displacement curve for its direct calculation requires the use of costly instrumentation. For this reason, the aim of this study is to estimate index of damage indirectly from simple vibration tests, calling for much simpler and cheaper instrumentation, through an auxiliary index called area index damage. Web plastifying damper is a particular type of hysteretic damper that uses the out-of-plane plastic deformation of the web of I-section steel segments as a source of energy dissipation. Four I-section steel segments with similar geometry were subjected to the same pattern of cyclic loading, and the damage was evaluated with the index of damage and area index damage indexes at several stages of the loading process. A good correlation was found between area index damage and index of damage. Based on this correlation, simple formulae are proposed to estimate index of damage from the area index damage.