Seismic Analysis of Retrofitting of RC Regular Frame with V-Braced Frame

Retrofitting of the existing buildings helps to reduce the serious damages under the strong ground motions. In retrofitting techniques, steel bracings are used to resist the lateral load effectively. In this study, the author aimed to investigate the four-story RC frames without and with steel bracings to understand the seismic performances of the buildings. The authors select the V bracings having 7 different thickness of steel bracings ( t= 2.5, 4, 6, 8, 10, 14 and 20mm) and observed the effect in seismic behaviors of the structures in terms of maximum story displacements, inter-story drift (ISD), base shear, fundamental time period (FTP) and capacity curves. In addition, it observed the failure behaviors of the structures. To study the seismic behaviors, the response spectrum analysis and nonlinear static analysis are performed in ETABs software. The result indicates that V bracing improves the seismic performances of the RC frames as well as improves the strength capacity and stiffness of the buildings. Adding bracing in RC frames decreases the top story displacements and inter story drift of the buildings. To get the expected failure mechanism in the braced frames and suitable uniform energy dissipation behaviors, the bracings are designed in such a way that the RC columns should be the main line of defense in the dual systems. Expected failure mechanism is obtained when stronger column, weak beam and weaker bracings design philosophy is used and it is only possible when the columns are designed to resist at least 50% lateral base shear in dual systems. A suitable thickness of bracings which is economical and structurally good should be selected.

Seismic Behavior Investigations of the Haunched Joint with Ribbed Anchor Webs in CFDST Structures

The haunched joint with ribbed anchor webs in the concrete-filled double steel tubular (CFDST) structure was proposed in this study. The CFDST column and the steel beam were connected by vertical ribbed webs, which were anchored inside the column and connected to the beam web by the bolted connection, and haunches were welded to shift plastic hinges from the joint core to beam ends. The cyclic loading test was conducted on three beam-to-column joint specimens. Seismic behaviors including failure modes, strain and stress responses, hysteretic curves, ductility, and energy dissipation capacity were respectively analyzed. Besides, a finite element (FE) modeling was completed by ABAQUS in consideration of geometric and material nonlinearity. The validity of FE modeling was checked by comparisons between FE results and test results, and research results confirmed that the beam-to-column rotation and the shear deformation in the joint core were small owing to the restriction from the configuration of haunches. Then parametric investigations on connection constructional details, geometric dimensions, material strength, and axial compression ratios, were made to study seismic behaviors of the haunched joint with ribbed anchor webs. It showed that the selected parameters except concrete strength had certain influences on bearing capacity, ductility, and energy dissipation, and corresponding practicable design suggestions were proposed for the application of haunched joints with ribbed anchor webs in CFDST structures.

Relationships between deformation and morphology of forearc wedges and earthquake ruptures

<p>Over the last decade, we have accumulated evidence that, along subduction zones, a significant part of the seismic cycle deformation is permanently acquired by the medium and reflects the variation of rupture properties along the megathrust. Assuming a persistence of the megathrust segmentation over several hundred thousand years, this permanent deformation and the forearc topography could thus reveal the mechanics of the megathrust. Numerous recent studies have also shown that the megathrust effective friction appears to differ significantly between aseismic or seismic areas. From mechanical modelling, I will first discuss how such differences in effective friction are significant enough to induce wedge segments with varying morphologies and deformation patterns. I will present examples from different subduction zones characterized by either erosive or accretionary wedges, and by different seismic behaviors. Secondly, I will present how this long-lived deformation can in turn control earthquake ruptures. I will show, that along the Chilean subduction zone, all recent mega-earthquakes are surrounded by basal erosion and underplating. Therefore, the deformation and morphology of forearcs would both be partly linked to the megathrust rupture properties and should be used in a more systematic manner to improve earthquake rupture prediction.</p>