Author : Yuanzhi Chen
Publisher :
ISBN 13 :
Total Pages : 188 pages
Book Rating : 4.:/5 (14 download)
Book Synopsis Effect of Near-fault Ground Motion Characteristics on Bridges with Footing Uplift by : Yuanzhi Chen
Download or read book Effect of Near-fault Ground Motion Characteristics on Bridges with Footing Uplift written by Yuanzhi Chen and published by . This book was released on 2017 with total page 188 pages. Available in PDF, EPUB and Kindle. Book excerpt: Urban areas have experienced tremendously growth in seismically active zone since last century. Only in recent decades it has been realised that the shaking closely adjacent to a fault (e.g. within 20 km) produced a different effect on the seismic loading from far-source induced shaking. The immense cost of damage due to the near-fault earthquakes emphasized the importance of studying near-fault ground motions and their effects on structures. In conventional seismic design, footing uplift is not permitted, thus the energy can only dissipate though the damping of the structure and plastic hinge development at a specific location. Plastic hinge development, within limits, helps to improve the safety of people. However, recent research indicates that plastic hinging due to near-fault earthquakes is more significant than that caused by far-field excitations, which has a substantial impact on economics and functionality. Therefore, the research reported in this PhD thesis considers an innovative low-damage seismic design philosophy: mitigate the damage resulting from near-fault excitations by incorporating footing uplift. Previous research on footing uplift focused on the structural response. The footing response, including the contact forces at the interface of the footing and support, is investigated in this study for the first time. The outcomes of this research provide the basis of holistic low-damage seismic design. This research starts with a simple experimental system to provide a rational interpretation of the structure and footing response including the effect of uplift. The effects of the supporting soil, the characteristics of the earthquake excitations and the structural plastic hinge development were then incorporated to enhance the understanding of this topic. To achieve this objective, a series of shake table experiments were conducted on physical models with different scales. The series of testing consisted of three groups of experiments with consideration of varying support and loading conditions: (1) a bridge pier with footing uplift on a rigid base under free-vibration induced by an initial vertical footing displacement, harmonic and strong earthquake base excitations, (2) a bridge pier with soil-foundation structure interaction under near-fault and far-field excitations, (3) a single bridge span with footing uplift on a rigid base and with strong vertical excitations included for the first time. The correct similitude of an uplifting structure on a rigid base, within the scaling laws, were addressed and applied to the experiments. Sensors were attached at the interface of the footing and support, i.e. load cells, a pressure mapping sensor and strain gauges, to reveal the contact forces due to footing uplift. The results shown in this thesis provide an experimental verification for existing theoretical models of structures with uplift. This research showed that near-fault horizontal excitation with strong pulses dominated the footing response. However, under horizontal ground motion without a pulse, the vertical component had the main effect on uplift. Uplift sometimes caused a lower contact force compared with the fixed base case. Moreover, a system designed with multiple energy dissipating mechanisms, i.e. foundation soil yielding, footing uplift and structural plastic hinge development, were likely to avoid the excessive rotation sometimes observed in structures with a single nonlinear mechanism.
