Retrofit Design Methodology for Response Modification of Substandard RC buildings Thermou, G.E., Pantazopoulou, S.J. Department of Civil Engineering Reinforced Concrete Laboratory, Demokritus University of Thrace (DUTh), Vas. Sofias 12, 67100 Xanthi, Greece, Emails: gthermou@civil.duth.gr; pantaz@civil.duth.gr Elnashai, A.S. Department of Civil and Environmental Engineering - Newmark Labs, University of Illinois at Urbana-Champaign (UIUC), 205 North Mathews Avenue, Urbana, IL 61801, USA, Email: aelnash@uiuc.edu INTRODUCTION The majority of the existing building stock exhibits a number of deficiencies rendering them susceptible to damage from future earthquakes. The only viable solution is retrofitting, despite the difficulties that may arise from socio-economic constraints and the lack of an established code framework. The main objectives of rehabilitation are to modify the structural response by rearranging the modes of failure and correcting any deficiencies related to localization of damage. In quantifying damage at the structural level, lateral drift is one of the more representative indecies; performance objectives that define the various structural limit states ranging from “immediate occupancy” to “collapse” are related directly to lateral deformation. Therefore the conceptual framework of displacement-based design is compatible with the stated objectives of retrofitting. In developing a rehabilitation strategy for a given structure the most important decisions made by the designer are: (a) Identification of the need to implement global interventions in addition to local measures to increase deformation capacity of individual member, (b) Selection of the pertinent intervention scheme from among the array of alternative solutions and technologies, and (c) Dimensioning of the global intervention option chosen so as to meet the rehabilitation objectives. Calculations required in order to implement and fine-tune a solution can be demanding and tedious, often involving iterative procedures. In this paper a design methodology for seismic rehabilitation of old substandard construction is proposed. A key element in the proposed methodology that differentiates it from other alternative displacement-based strategies [1, 2, 3, 4] is reliance on a desirable pattern of lateral deflection, referred to hereafter as the target response shape. In the proposed method, response modification is effected through a weighted distribution of added stiffness along the height, so as to simultaneously reduce demand in the critical regions as well as to enhance the force and deformation supply. An important tool in controlling the extent of damage through the proposed strategy is engineering the fundamental and predominant vibration mode shape of the upgraded structure so as to achieve a target distribution of interstorey drift. Pertinent stiffness weighting factors are derived for characteristic shear frame structures in order to enable attainment of a target deflection shape [5]. A methodology for deriving Drift Dependent Spectra (DDS) which relate the stiffness demands to the target drift demands as well as design charts which relate the characteristics of established global intervention methods to stiffness demands are developed. The objective of this effort is to obtain automated application rules by which to gauge the implications on drift demands effected by changes in the characteristics of the intervention methods. The design charts provide a fast conceptual procedure for selection of the appropriate retrofit scheme. Design calculations are performed at yield; stiffness and strength are considered interdependent parameters. Members are dimensioned to match the required stiffness and a target interstory drift at yielding. Reinforcement detailing at the member level is based on the direct displacement-based design approach [6]. Keywords: retrofit strategy, seismic upgrading, rehabilitation, displacement-based design, drift