At the 2018 AEES annual conference in Perth, the recipient of the first Charles Bubb Postgraduate Award was announced as Omar El-Hawat from the University of Technology, Sydney.
Omar’s application described his reason for interest in Scholarship and the potential beneficial contribution to earthquake engineering in Australia. The details of his application are below, and we look forward to the ongoing publication of the results of his research. Omar published his first AEES paper in 2019, available here.
Overview
Over the past few decades, several destructive earthquakes have stricken in cities from around the world including low seismic countries such as Australia. To this day, damage is still observed in structures such as buildings and bridges, and hence I have taken a strong interest in the research of earthquake damage mitigation solutions. Damage is usually allowed to occur in performance based design of structures. However, structures such as bridges and hospitals are classified as important structures and are required to remain functional and damage free after earthquakes for the safe passage of emergency services. Conventional design of bridges worldwide require their piers to develop plastic hinging at the ends of the piers as its main earthquake resisting system. This is effective in surviving the earthquake but leads to excessive damage which can lead to expensive repairs or even demolition of the structure. Several solutions have been proposed; however, none have been effective in completely eliminating damage from the system while providing a cost effective solution, especially in developing countries where cost is governing issues regarding design. Recent literature has proved that by allowing the foundation to uplift (rocking foundations), the seismic demand on the structure are reduced and a damage free bridge can be achieved. However, this design leads to excessive settlements, large deck displacements leading to abutment and bearing failure, and instability of the structure leading to overturning. My interest in earthquake engineering has allowed me to develop a novel foundation system that will address these issues and allow the bridge structure to experience no damage whereby other conventional methods of design would fail. This is an improvement of a rocking foundation where the foundation is allowed to uplift about piles to reduce settlement. The uplift motion is also restricted with the use of post-tensioned tendons that are connected to the pile and the pile cap. This will ultimately control the period of the structure, and hence attract smaller inertial forces in the bridge structure and smaller deck displacements. Additionally, the restraining tendon offers a re-entering force to the rocking foundation,
increasing its stability to overturning.
By receiving this scholarship, it brings many advantages to both my personal research and the AEES committee. The twelve month research support would allow me to investigate further applications of the proposed seismic foundation system to other structures such as tall buildings. As a result, more publications can be produced and presented to professional engineers working in the industry. The money provided from the scholarship can also be used to conduct a shake table test to validate the proposed novel foundation system.
Additionally, by having the opportunity to attend the AEES conference for three consecutive years gives me the chance to present my research and interact with professional engineers from both academic and industry backgrounds. This could lead to potentially adopting my foundation concept in future projects to come in Australia.
Project Proposal
In regions where strong seismic activities are expected, it is uneconomical to conventionally design bridges that perform elastically under large earthquakes. For this reason, bridges are allowed to have their piers designed to form plastic hinges at their ends, providing energy dissipation while preventing collapse at the cost of damage. For the same bridge and seismic loading, recent research has shown that by allowing the foundation to uplift, the bridge can be designed to behave completely elastic. However, this may result in large non-linear deformations which could lead to deck unseating, bearing failure and abutment damage. This study investigates the effects of controlling the rocking behaviour of the foundation by connecting the pile caps to the piles using post-tensioned strands. This will limit the lateral deflections of the bridge deck and improve the seismic performance of the bridge. The results are compared to two identical bridges with different foundations, namely (i) foundations that
rock on unconnected piles (rocking pile foundations) and (ii) fixed bridge foundations that are conventionally designed to allow the development of plastic hinges at the pier base as per the European code.
The bridges are numerically modelled using three-dimensional finite element software to capture the geometric and material non-linear behaviour of the bridge, and the soil-structure interaction between the soil medium and the foundation. Dynamic non-linear time history analysis will be performed for the different foundation systems to compare the seismic displacement of the bridge decks, pier drifts, bearing displacements, pier forces and other nonlinear behaviour experience by the structure. Four strong motion earthquakes with both their horizontal components are selected and scaled to two different hazard levels of shaking with return periods of 475 and 2475 years.