Metallic fabric jackets: an innovative method for seismic retrofitting of substandard RC prismatic members

This paper presents the results of a recent experimental research study where metallic (high-strength steel cord) fabric jackets (MF jackets) were utilised for the seismic upgrading of substandard reinforced concrete members. The proposed intervention method and its practical application are described in detail. Specimens were cantilevers with a square cross-section, representing a typical building column at half scale. The length of the test region corresponded to half the span of a typical storey building column under lateral sway. Due to lack of adequate seismic detailing the specimens were susceptible to various modes of failure such as web shear failure, buckling of compression reinforcement or failure in the lap splice region. The as-built specimens were first damaged up to failure after being subjected to combined axial loading and cyclic lateral displacement reversals simulating seismic loading. In the next phase, specimens were retrofitted with both composite and metallic fabric jackets and then tested again under the same load history. The results of this preliminary experimental research programme show that the metallic fabric jackets performed in an excellent way compared to glass- and carbon-fibre reinforced polymer jackets, increasing substantially both the strength and the deformation capacity of the repaired members. The excellent mechanical performance of the metallic fabrics combined with many of the advantages of the synthetic wraps (easy handling, no change in member dimensions) and the intrinsic favourable properties of steel (fire resistance), underline the potential of this novel material in repair/strengthening of reinforced concrete as an alternative option for jacketing applications

Seismic rehabilitation of substandard R.C. buildings with masonry infills

Seismic deformation demands are localized in areas of stiffness discontinuity, such as in soft-storeys of frame structures, where disproportionate damage is often reported in post-earthquake reconnaissance. In many parts of the world this damage pattern is mitigated using strengthening schemes that include addition of stiffness in the structure so as to limit the magnitude of drift demands. A low-cost retrofitting method is the addition of masonry infills to increase the stiffness of soft storeys in low- to mid-rise reinforced concrete (R.C.) structures. This is an easily replaceable remedy in the event of damage that may prove advantageous over R.C. structural systems, owing to the lower forces imparted to the foundation in this retrofit option as compared to more thorough interventions, thereby avoiding extensively invasive retrofit operations in the foundation. Behavioural mechanisms mobilized by masonry infills in successful retrofits are shown to emulate confined masonry behaviour. It is also shown that despite their brittleness, well connected infills can successfully mitigate the occurrence of catastrophic damage by diverting damage localization from the vulnerable regions of the building. The main objective of the current paper is to present a rapid retrofit design methodology, where masonry infills are utilized for strengthening existing substandard constructions in order for their R.C. load bearing elements to behave elastically in the event of the design earthquake. To facilitate the retrofit design, practical design charts have been derived, to link drift demand to the ratios of infills' area in plan to the total plan area in the critical floor of the structure. Performance criteria, such as target distributions of interstorey drift demand, a target estimate of the fundamental period, as required by the designer, and a limit on acceptable displacement ductility in terms of demand for the retrofitted structure, are necessary design decisions that guide the proposed retrofit strategy. Application of the retrofit design through infills is demonstrated through example case studies

Seismic deformation capacity indices for concrete columns: Model estimates and experimental results

The transition to displacement-controlled methods for seismic design relies on explicit measures of deformation capacity, Although conceptually clearly defined, the various alternative indices such as displacement ductility, drift and plastic rotation capacity calculated with the available analytical tools in the literature are marked by excessive scatter when tested with well-controlled experimental results, indicating that the validity of the underlying physical models is questionable. This problem is explored systematically in the current paper, by evaluating the parametric performance of the analytical models, as well as through comparison with the experimental trends. An important result of the present study is that well-confined members designed as per the ATC-32 requirements have large dependable deformation capacities regardless of the axial load ratio, a finding with significant implications in practical bridge seismic design. © 2007 Thomas Telford Ltd

Flexural Behavior of Brittle RC Members Rehabilitated with Concrete Jacketing

The composite flexural action of prismatic reinforced concrete (RC) members repaired/strengthened by RC jacketing was modeled with a dual-section approach. The model considers the relative slip at the interface between the existing member and the jacket and establishes the mechanisms that are mobilized to resist this action, thereby supporting composite behavior. An iterative step-by-step incremental algorithm was developed for calculating the overall flexural response curve. Consideration of frictional interlock and dowel action associated with sliding at the interfaces as well as the spacing and penetration of flexure-shear cracks are key aspects of the algorithm. The proposed procedure was verified through comparison with published experimental data on RC jacketed members. The sensitivity of the upgraded member’s flexural response to jacket design variables was investigated parametrically. Monolithic response modification factors related to strength and deformation indices were evaluated and the sensitivity of the model was assessed