Overstrength and force reduction factors of multistorey reinforced‐concrete buildings

Abstract

This paper addresses the issue of horizontal overstrength in modern code‐designed reinforced‐concrete (RC) buildings. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. The lateral capacity and the overstrength factor are estimated by means of inelastic static pushover as well as time‐history collapse analysis for 12 buildings of various characteristics representing a wide range of contemporary RC buildings. The importance of employing the elongated periods of structures to obtain the design forces is emphasized. Predicting this period from free vibration analysis by employing ‘effective’ flexural stiffnesses is investigated. A direct relationship between the force reduction factor used in design and the lateral capacity of structures is confirmed in this study. Moreover, conservative overstrength of medium and low period RC buildings designed according to Eurocode 8 is proposed. Finally, the implication of the force reduction factor on the commonly utilized overstrength definition is highlighted. Advantages of using an additional measure of response alongside the overstrength factor are emphasized. This is the ratio between the overstrength factor and the force reduction factor and is termed the inherent overstrength (Ω i). The suggested measure provides more meaningful results of reserve strength and structural response than overstrength and force reduction factors. Copyright © 2002 John Wiley & Sons, Ltd.

Simulation-Based Fragility Relationships for Unreinforced Masonry Buildings

“…Conventional and adaptive pushover techniques are compared to IDA by Elnashai (2002), and in Papanikolaou andElnashai (2005, 2006) a test case of eight different reinforced concrete buildings of various plan, height, ductility, and directional effects are investigated to determine the ease of use and accuracy for each of these methods. Although it is shown that adaptive pushover methods yield more accurate results and have some advantages over conventional pushover curves, it is deemed that both techniques are adequate for structural systems free from significant irregularities in plan and elevation.…”

Seismic Overstrength of Shear Walls in Parking Structures with Flexible Diaphragms

“…According to previous researcher (e.g., Uang, 1991;Whittaker et al, 1999;Elnashai and Mwafy, 2002), the response modification factor can be expressed as the product of four factors:…”

“…Elnashai and Mwafy [2002] studied 12 reinforced concrete buildings designed and detailed in accordance with Eurocode 8. They addressed that three sources of overstrength, which lead to an overstrength factor being greater than 2.0, are material overstrength, using the elastic period in the design force calculation instead of the cracked period, and designing the columns in biaxial bending when analyzed uniaxially.…”

Assessment of the Response Reduction Factors of Plan-Irregular Rc Buildings

“…Recognized researchers have made observations on the analytical procedures based on response reduction factors and the validity of adopted values [3] and [4] recent studies have focused on evaluating the response reduction factors of different structural typologies, applying non-linear analysis, [6]and in this research, part of the FEMA P695 methodology [8] has been adopted to validate the reduction factors applied in the Venezuelan seismic code for low-rise RC buildings whose plants have different re-entrants, determining if they lead to satisfactory seismic behavior.…”