Borg, RC; (2015) The Deformation Capacity of Reinforced Concrete Elements Subject to Seismic Loading: Determination of Empirical Equations for Assessment. Doctoral thesis , UCL (University College London).

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Abstract

This project aims to enhance relationships that quantify earthquake induced damage in reinforced concrete (RC) structures, in terms of Engineering Demand Parameters (EDPs) and/or Damage Indices DIs. In the seismic vulnerability assessment process structures are classified onto Damage Scales (DS) based upon their expected performance. The damage level is quantified by Damage Indices (DIs) as a function of Engineering Demand Parameters (EDPs). This research aims to enhance the relationships that quantify damage in Reinforced Concrete (RC) structures in terms of empirically derived EDPs equations as a function of material properties, geometrical properties of sections and detailing aspects. Current relationships found in literature are generally defined at yield and ultimate damage states, or at the occurrence of a particular failure mechanism in terms of chord rotation. Assessment procedures have however evolved from these two limit states onto multiple state assessment. Relationships referring to intermediate states of damage are therefore proposed. EDP relationships are derived from datasets of low cycle fatigue tests on columns found in literature. The number of elements with design and detailing aspects referring to old design practices are limited. Recent earthquakes have shown that such structures are very vulnerable. Hence, an experimental campaign consisting in RC elements with varying detailing aspects, material properties and geometric properties, designed to old design codes was conducted to enhance the dataset, act as a benchmark, and to investigate failure mechanisms. Low cycle fatigue tests generally refer to monotonic or cyclic loading patterns without any direct reference to earthquake loading or response. A procedure describing the determination of the loading history based on earthquake demands is therefore considered. The experiments also indicate that the loading pattern is a function of chord rotation capacity. This effect is taken into account in the development of the EDP relationships. Multivariable stepwise regression was used for the development of the EDP relationships. The selection of the explanatory variables was based on significant parameters used in existing EDP relationships, parameters found in existing relationships describing particular failure modes, and dimensional analysis. A comprehensive model of chord rotation and stiffness are provided at yielding, maximum force, 10% maximum force reduction, 20% maximum force reduction and 50% maximum force reduction. Relationships that relate residual stiffness, chord rotation and energy dissipation are derived. The testing campaign on columns not only highlights the behaviour of reinforced concrete designed without seismic detailing, but adds to the database in literature. The beam-column connection tests indicate that the behaviour at the nodes affects the behaviour of RC structures, and stress the importance of their inclusion in further investigations. Finally, proposing a method to determine lowcycle fatigue loading regimes based on seismic response is an attempt to address an anomaly where tools that are used to quantify seismic damage are not linked in any way with earthquakes.

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