6.2 Special Session: Advances in Sesmic Retrofit of Reinforced Concrete Buildings
Performance Based Retrofit Strategies and Solutions for Pre-1970'S Reinforced Concrete Buildings: An Overview of Latest Developments
S. Pampanin, W.Y. Kam & U. Akgüzel
ABSTRACT: The need for simple and cost-effective retrofit solutions for existing reinforced concrete buildings, particularly those designed before the 1970s, thus prior to the introduction of modern seismic code provisions and capacity design principles, is no longer “just” an academic or scientific research statement, but it is eventually being recognized as a critical socio-political priority at international level.
Similarly to what pursued for the design of new structures, a performance-based approach should be adopted when assessing the vulnerability and defining the retrofit strategy for existing buildings. In this latter case, the target limit states or performance levels have to be more realistically adjusted to account for the difficulties encountered in the assessment phase, as well as for the several issues associated to costs, feasibility and invasiveness of the proposed strengthening/retrofit solution.
This paper provides an overview of alternative performance-based retrofit strategies and technical solutions for RC buildings developed and/or further refined in the past few years as part of a multi-year research project carried out at the University of Canterbury, with the final aim to prepare a Retrofit Handbook for daily use of practicing engineers. The feasibility and efficiency, in the contest of a performance-based retrofit approach, of adopting and/or combining different solutions such as a) Fiber Reinforced Polymers applied to exterior corner joints to limit the invasiveness of the intervention, b) low-invasive low-cost metallic diagonal haunches, c) post-tensioning concrete or timber frames or walls or d) selective weakening techniques, will be discussed, based on numerical and experimental evidences.
Presentation 198
Recent Tests on Seismically Damaged Reinforced Concrete Beam-Column Joints Repaired using Fiber-Reinforced Polymers
Bing LI & Tso-Chien Pan
SUMMARY: To prevent the casualties which can result from the potential collapse of earthquake damaged structures, it is important that structure can be rehabilitated as soon as possible. This paper proposes a rapid rehabilitation scheme for repairing moderately damaged reinforced concrete (RC) beam-wide column joints. Four non-seismically detailed interior beam-wide column joints were used as control specimens. All of these four sub-assemblages were subjected to similar cyclic lateral displacement so as to provide the equivalent of severe earthquake damage. The damaged control specimens were then repaired by filling their cracks with epoxy and externally bonding them with Carbon fiber reinforced polymer (CFRP) sheets and Glass fiber reinforced polymer (GFRP) sheets. These repaired specimens were then re-tested and their performance compared to that of the control specimens. This paper demonstrates that repair of damaged RC beam-wide column joints using FRP is able to restore the performance of damaged RC joints with relative ease, suggesting that the repair of beam-column joints is a cost effective alternative to complete demolition and replacement.
Displacement-Based Seismic Retrofit Design for Non-Ductile RC Frame Structures using Local Retrofit Interventions at Beam-Column Joints
W.Y. Kam & S. Pampanin
ABSTRACT: Seismic retrofit design using local retrofit interventions is often done using piece-meal iterative approach, in which the local retrofit design and global structural response are derived from iterative numerical models. Adopting a displacement-based seismic retrofit approach and following the capacity-design principles, local retrofit interventions’ effects can be correlated to the expected global deformation responses. Clearly acknowledging that displacement (or drift) is a better response parameter for structural and non-structural damages, a displacement-based methodology gives a more direct and rational seismic retrofit design. This paper will first introduce the concepts of displacement-based seismic retrofit. Then, the design procedure is illustrated for two local retrofit interventions for RC frames: a) selective beam-weakening retrofit, and b) post-tensioning retrofit and fibre-reinforced polymer jacketing. The design procedure is then verified using non-linear time-history analysis on a case study building retrofitted using the two local interventions.
An Update of Innovative Retrofitting Techniques for R/C and Masonry Building: From Experimental Investigations to Practical Applications
F.C. Ponzo, A. Di Cesare, D. Nigro & M. Dolce
ABSTRACT: Traditional approaches for the seismic retrofit of existing buildings consider the following assumptions: (a) the building is not damaged after a minor earthquake, (b) the building is reparable after a moderate earthquake, and (c) the building will not have collapsed after a severe earthquake. In recent times, following several destructive earthquakes which have occurred in past decades, the general public or building owner are no longer satisfied with the above performance objectives. In the last twenty years, several experimental investigations have been carried out by a research unit based at the University of Basilicata (UNIBAS), Potenza, Italy, in order to test the effectiveness of several innovative retrofitting techniques such as: (i) seismic isolation, (ii) energy dissipation bracing systems, (iiia) a Active Confinement of Manufactured materials (CAM) strengthening system consisting of a three-dimensional tie system for the upgrading of existing structures and (iiib) Dis-CAM based on the CAM system with added energy dissipation. Different anti-seismic devices, based on currently available technologies or innovative systems also have been considered. In this paper an overview of recent developments, from the numerical simulations and experimental investigations obtained by UNIBAS within several research projects, to their practical applications is reported.
Seismic Strengthening of a Non-Ductile RC Frame Structure using GFRP Sheets
U. Akgüzel, P.Quintana Gallo & S. Pampanin
ABSTRACT: An as-built reinforced concrete (RC) frame building designed and constructed according to pre-1970s code design construction practice has been recently tested on the shake table at the University of Canterbury. The specimen, 1/2.5 scaled version of the original prototype, consists of two 3-storey 2-bay asymmetric frames in parallel, one interior and one exterior, jointed together by transverse beams and floor slabs. Following the benchmark test, a retrofit intervention has been proposed to rehabilitate the tested specimen. In this paper, detailed information on the assessment and design of the seismic retrofit procedure using GFRP (glass fibre reinforced polymer) materials is given for the whole frame. Hierarchy of strength and sequence of events (damage mechanisms) in the panel zone region are evaluated using a moment-axial load (M-N) interaction performance domain, according to a performance-based retrofit philosophy. Specific limit states or design objectives are targeted with attention given to both strength and deformation limits. In addition, an innovative retrofit solution using FRP anchor dowels for the corner beam-column joints with slabs is proposed. Finally, in order to provide a practical tool for engineering practice, the retrofit procedure is provided in a step-by step flowchart fashion.
Seismic Retrofit of St. Joseph Hospital using Advanced Composite Materials for the Enhancement of Column, Slab, Wall and Beam Elements
S.F. Arnold, M. Chiewanichakorn & L. Toranzo
ABSTRACT: St. Joseph Hospital, in Orange, California, is one of hundreds of hospitals in the state with buildings built before 1973, that have been classified as Structural Performance Category 1 (SPC-1) as defined by Senate Bill 1953 (SB 1953). SPC-1 buildings are those that are considered hazardous and at risk of collapse or significant loss of life in the event of an earthquake. Two buildings at the facility will receive a SPC-2 upgrade based on a nonlinear analysis and specific design criteria for the use of fibre reinforced polymers (FRPs). The advanced composite materials were used for a variety of structural deficiencies, including, column shear, diaphragm shear, wall shear, diaphragm chords, collectors, shrinkage joint shear transfer and life safety catch mechanisms. The FRPs were selected in order to minimize disruption to the operating facilities and provide the most cost effective design solution. In order to be accepted by the Office of State-wide Health, Planning and Development (OSHPD), a strict specification and design criteria had to be reviewed and accepted. This paper will review the analysis of the buildings, the submittal requirements and the construction details implemented to complete the SPC-2 retrofit in accordance with State law.