Optimum Ductility Assessment of Earthquake Resistant Structures

TLDR: In this article, a comparison of two 4-storey reinforced concrete buildings designed as high ductility classes (DCH) and medium ductility class (DCM) upon a strong rock (ground type A, Eurocode 8 soil classification) according to the Eurocode8.

Abstract: Provision of ductility in the structures according to the modern design codes lead to more economic constructions, while safety levels reach higher rates. The philosophy is based into allowing some damage to occur in predetermined elements where enough ductility has been provided in order to ensure the member’s capacity during an earthquake. This research focuses on investigating optimum ductility provisions for buildings to achieve the desired performance. The aim is to assess the parameters which affect ductility demands and overall present a comprehensive methodology for evaluating the structural performance. Analytical work was based on the comparison of two 4-storey reinforced concrete buildings designed as high ductility class (DCH) and medium ductility class (DCM) upon a strong rock (Ground type A, Eurocode 8 soil classification)according to the Eurocode 8. For a fair comparison both buildings were designed to have same vibration frequencies in order to experience same energy release rates under a number of earthquakes with varied ground acceleration amplitudes and frequency spectrums. The main criteria for the comparison were: (i) the inter-storey drifts, (ii) the energy distribution among the floors, (iii) the structural damage in terms of plastic hinges initiation and ductility demand rates, (iv) total energy dissipation and (v) top floor displacements. The damage rates in the structures were found to be directly correlated to the earthquake’s frequency range. Low frequency seismic events corresponding to high periods in the elastic response spectrum used for the design of the structures were more catastrophic. The paper proved that DCH buildings perform generally better than DCM for high ground acceleration amplitudes, while for smaller GAA where the responses are governed by the stiffness in the elastic response range the DCM structures have functional superiority. Higher ductility provisions have been found beneficial for the structural performance, especially for higher ductility demands caused by higher intensity earthquakes with increased return periods and ground acceleration amplitudes.