International Journal of Advanced Structural Engineering
Volume:1 Issue: 1, Winter 2009

Near-fault ground motions with long-period pulses can place severe demands on structures near an active fault. These pulse-type ground motions can be represented by pulse sequences with simple shapes. Half-sinusoidal pulse sequences are used to approximate recorded ground motions and dynamic responses of SDOF system under the excitation of these pulse sequences are studied. Four cases are considered: (1) variation in duration of successor sub-pulse; (2) variation in duration of predecessor sub-pulse; (3) variation in amplitude of successor sub-pulse; and (4) variation in amplitude of predecessor sub-pulse. The corresponding acceleration, velocity and displacement response spectra of these pulse sequences are studied. The analysis on SDOF system shows that in some cases the responses are strongly affected by the changes of duration and/or amplitude of the sub-pulse. The study can be useful to understand the influences of sub-pulse in the near-fault pulse-type ground motions.

Reliable stress-strain behavior of concrete is necessary particularly when a member is subjected to combine bending and axial load and confinement effects should be accounted for. A unified theory for confinement of circular hollow sections is proposed herein, that can be extended to the case of solid and noncircular sections. The main aim of the model is to trace step-by-step the evolution of the three dimensional stresses in confined concrete and confining devices (i.e. FRP externally bonded jackets). The iterative model is able to estimate confinement effectiveness and to plot stress-strain relationships, which are different in the case of solid and hollow sections. Through the proposed improved model, a simplified closed form solution has been also derived to directly determine ultimate confined concrete properties and stress-strain curves. At present, theoretical results based on the proposed concrete circular hollow sections confinement model, in satisfactory agreement with the experimental data available in scientific literature, show that FRP jacketing can enhance the ultimate load and ductility significantly, also in the case of hollow concrete cross sections.

This study contains the identification of modal dynamic properties of a 3-story large-scale steel test frame structure through shaking table measurements. Shaking table test is carried out to estimate the modal properties of the test frame such as natural frequencies, damping ratios and mode shapes. Among many different model structures, ARX (Auto Recursive Exogenous) model structure is used for modal identification of the frame structure system. The unknown parameters in the obtained ARX model structure are estimated by Least-Square method by minimizing the AIC criteria with the help of a program coded in advanced computing software MATLAB®. The adopted model structure is then tested out in time domain to verify the validity of the model with the selected model parameters. Then the modal characteristics of test frame and the story stiffness are estimated using the white noise shakings. An attempt is done to determine the change of modal characteristics and the story stiffness of test frame according to the velocity, which the test frame structure experienced during the shaking schedule and also during the input shaking of El Centro 1940 NS. Results shows that there is an increase in damping ratio and a decrease in both story stiffness and natural frequency for all modes when the damage forms at cementitious device and the test frame structure itself during the shaking schedule.

This article presents the seismic vulnerability assessment of the S. João de Loure bridge, inPortugal. The single span steel bridge has riveted joints, commonly affected by corrosion,which can lead to a significant stiffness reduction. With the objective of evaluating theinfluence of the joints stiffness in the structural response of the bridge, a structural model of the bridge was created, and natural frequencies, maximum axial forces and maximum stresses, and maximum mid-span deflection were analysed. Four possible element rupture scenarios where also studied. Two of them where proved to be a risk for the structural safety of the bridge. A commonly used strengthening solution intending to reduce the bridge’s mid-span deflection with external pre-stressing cables was studied.

In this paper the optimal design of a dissipator made of aluminium and steel and principally subjected to shear forces and the preliminary results of the characterization tests are described. The device has been designed on the basis of an optimization procedure with the objective to maximize the energy dissipated in the device. The response of a 3D frame equipped with the device and subjected to 7 earthquakes compatible with the response spectrum of Eurocode 8 is shown. The optimal response obtained from the characterization tests exhibits a good dissipative behaviour of the device, highlighted by a wide enough hysteresis cycle.