The research presented in this paper deals with the seismic retrofitting of existing frame structures by means of passive energy dissipation. An iterative displacement-based procedure, based on capacity spectrum is described and some applications are discussed. The procedure can be used with any typology of dissipative device and for different performance targets. In this work the procedure has been applied to an existing r.c. frame building, which shows both vertical and plan irregularities. In the application presented the buckling restrained braces have been used in order to prevent damages to both the structure and non structural elements. The evaluation of commonly Nonlinear Static Procedures (NSPs) for seismic response of the existing and retrofitted structure is presented to check the suitability of the use of NSP in the design procedure: the use of conversional NSPs to be not suitable for the case of irregular building but, once this building is retrofitted, and therefore regularized, with a bracing system, the use of NSPs for seismic response of the braced structure is effective.
Existing reinforced concrete frame buildings designed for vertical load only could suffer severe damage during earthquakes. In recent years, many research activities have been paid to develop reliable and practical analysis procedure to identify the safety level of existing structures. The Incremental Dynamic Analysis (IDA) is considered to be one of the most accurate methods to estimate seismic demand and capacity of structures. But it requires the execution of many nonlinear response history analyses (NL_RHA) in order to describe the entire range of structural response. The research discussed in this paper deals with proposal of an efficient Incremental Modal Pushover Analysis (IMPA) to obtain capacity curves by replacing the NL_RHA of the IDA procedure by Modal Pushover Analysis (MPA). In this work, the basic idea of IMPA is presented and the step-by-step computational procedure is then summarized. This new procedure, accounting the higher modes effects, does not need the execution of complex NL-RHA, but only simpler nonlinear static analysis. Then, the new procedure is applied to an existing irregular building. The capacity curves obtained by different procedures (standard pushover analysis, IMPA and IDA) are presented and discussed.
A generalized cyclic steel model characterized by isotropic and kinematic hardening, inelastic buckling in compression and corrosion of rebars in reinforced concrete (RC) structures is presented. The model has been implemented in a fiber code, to perform seismic analyses of RC sections. The model is particularly accurate with respect to experimental cyclic behavior of rebars with buckling in compression when the strain does not exceed 1.5%. Twelve configurations of RC cross sections were selected as case studies for three geometries and different steel arrangements, assumed representative of RC columns or bridge piers (in a suitable scale). Each section was subjected to two groups of cyclic curvature histories representative of severe seismic loads, not far from collapse. Different axial loads and corrosion percentages (no corrosion, moderate, or high) have been selected to perform cyclic parametric analyses. One of the cases was taken from an experimental test on columns, deriving also steel characteristics used in all numerical cases. The results of the comparison among RC sections have been discussed. Numerical results show that the maximum compressive strain for steel rebars is always smaller than 1.5%, therefore the proposed steel model is accurate and represents a valid tool for structural assessment. Corrosion reduces RC section capacity, affecting various rebar mechanical characteristics, in particular buckling behavior.
A new strategy that repairs severely damaged reinforced concrete (RC) columns after an earthquake is proposed as a simpler and quicker solution with respect to the strategies currently available in the literature. The external concrete parts are removed from the column surface along the whole plastic hinge region to uncover the steel reinforcement. The transverse steel is cut away, and each longitudinal rebar is locally substituted by steel rebar segments connected by welding connections to the original undamaged rebar pieces outside the intervention zone. The new rebar segments have a reduced diameter achieved by turning to ensure plastic deformation only in the plastic hinge, protecting the original rebar and the welding connections. The connection is specifically designed to be effective and simple, and is directly realized on column reinforcement. Finally, the removed concrete is restored by a jacket built with high-performance concrete with steel or polymer fibers. The use of concrete with high volume fraction of polymer fibers to repair the column is investigated for the first time in this paper. This concrete was characterized by compression and flexural tests in the laboratory and its mechanical characteristics were compared with those of the concrete with steel fibers, which are being increasingly used in construction. The repair strategy was applied to two RC columns (1:6 scaled bridge piers), tested by asymmetric cyclic tests. The results show that the column strength, stiffness, and ductility were restored, and the energy dissipation capacity improved. The experimental evidence was investigated by fiber models in OpenSees.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.