Investigating the seismic behavior of sandwich domes consisting of a light concrete core and reinforced outer layers

Master's Thesis in the field

Civil-Structural Engineering

Today, domes and arches have found wide applications in architectural and industrial structures due to the suitable covering of large openings. The use of today's technologies in styling and optimizing energy consumption in these types of structures is one of the important challenges facing engineers. Therefore, the need to investigate the seismic behavior of such structures is necessary and unavoidable. In this research, the seismic behavior of concrete sandwich domes consisting of a light concrete core and two layers of reinforced cladding has been evaluated by considering the geometric variables of height and thickness using finite element simulation. In order to investigate the behavior of their earthquakes, by dynamic analysis and normalization of the Tabas earthquake record, the desired structures have been modeled with Abaqus software and their seismic parameters have been investigated. In general, it can be concluded that the initial hardness and final strength of concrete sandwich domes increases by reducing the ratio of the height to the diameter of the dome, and on the other hand, by increasing the thickness of the concrete core, the hardness and final strength are improved to a very small extent.

1-1 Importance and Contexts

According to the size of Iran and the different climatic conditions in its different regions, it is necessary to formulate and implement construction methods that are suitable for specific regional characteristics. Considering that Iran is located on one of the active earthquake belts in the world, creating strong and safe structures is a special priority. Since the poor quality of construction has caused the rapid depreciation of existing buildings, this has increased the need for new buildings and also the retrofitting of existing structures. Considering the wide needs mentioned and the need to improve the quality of building production, as is common in most industrialized countries, it is necessary to seriously consider the methods of industrial production of buildings. One of these techniques proposed in the last two decades is the use of various types of composite structures [1], including the common example of it in housing construction projects in Iran is sandwich panels [2] consisting of two layers of reinforced concrete and a light core. Among all the possible design methods in composite structures, sandwich structures have become very widespread due to the advancement of cellular materials as core materials. Sandwich structures consist of a pair of hard and strong shells, a light and thick core to separate the shells and transfer power from one shell to another, and an adhesion system capable of transferring shear stress and axial loads from and to the core. In this type of structures, the separation of the shells from the core increases the bending resistance and hardness of the plate, and as a result, the panel becomes an efficient structure to withstand bending stresses and out-of-plane deformations [12]. Considering the climatic conditions of Iran and the importance of optimizing energy consumption, especially in public places, including meeting halls, the use of materials that are resistant to various atmospheric conditions and fire, and suitable insulation for heat and sound transmission, is of particular importance. that lightweight concretes, including Darba bubble concretes, having these characteristics have attracted the attention of many engineers in the construction industry in recent years. This type of concrete, which by increasing the density, obtains the required resistance for structural elements, can be considered a very suitable option as the core of sandwich plates.

Looking at the historical structures in Iran, it can be seen that arched structures, vaults and domes have played a special role in Iranian architecture. But today, the presence of steel, which has caused changes in building forms, has caused brick domes, which were considered architectural and construction masterpieces in their time, to be implemented without considering the main and real function of power transmission in the arch and without their detailed seismic investigation. The expansion of these types of structures, which are more decorative elements than structural elements, can be seen in the reconstruction and revival of religious places and mosques in our country in recent years. Now, due to the inability of traditional methods and materials to compete with new materials, in this research, an attempt has been made to evaluate the light sandwich system as a new and competitive structure economically and functionally in dome structures.. So that the applications of these types of structures can be revived in the areas that were previously used and are now abandoned and forgotten due to economic reasons and the existence of implementation problems. The use of arches in masonry structures and due to the very heavy weight of this type of material, the use of new and light materials such as sandwich panels and finding a new method to optimize their structural and economic performance can be one of the main goals of this project. According to the increasing need of the society for structures with large openings in sub-structures such as sheds, sports halls, mosques and religious places, amphitheatres and conference halls, railway stations and Airports, the revival of arched structures with regard to modern construction methods and the importance of lightening can justify the examination of the performance of these types of structures in scientific and research projects in our country.

According to the hot and dry climate of most regions of our country and considering the optimization of energy consumption in public places and its importance in our country in recent years, the examination of sandwich panels with a middle layer of light concrete that has acceptable thermal insulation can help us in this goal.

Obtaining a detailed analysis of the structural performance of arches and domes implemented with multi-layer light plates can make our engineering community more familiar with the performance of these types of structures.

Examining the mechanism of destruction of this type of structure under vertical and lateral loads to apply the necessary measures to identify weak points and how to strengthen them can provide a more appropriate view for the design of these types of structures. Arch deflection can be one of the other goals of this research.

Examining the seismic performance of the proposed system against the force of the earthquake and comparing it with traditional masonry structures can make this type of structure economically justifiable. First, the correctness of the modeling method was ensured by validating a laboratory model, and then the models were examined by changing the geometric parameters of the height of the dome and its cross-sectional thickness under incremental dynamic analysis[4]. By drawing force-displacement diagrams, seismic parameters such as ductility and behavior coefficient have been extracted from the diagrams and compared with each other. In the first chapter, as seen, an introduction to the needs of research and the general process of the project is mentioned. In the second chapter, studies on the technical literature of the research subject and studies of other researchers have been studied. The theories governing the research problem, the theories governing arches and lightweight concrete and shotcrete are reviewed in the third chapter. The process of modeling and achieving the desired results of the study is mentioned in the fourth chapter, and finally, the conclusion of the obtained results, summarization and suggestions for future studies are covered in the final chapter.

Chapter Two

A review of technical literature

2-1- Introduction

The scope of application and construction of shell roofs and domes in new and diverse forms, especially in the form of concrete shells and domes, is increasing. In terms of structure and architecture, shell buildings are among the economic and developed buildings, and from the mathematical point of view, the form of equations governing the mechanical behavior of these types of buildings is very complex. Among the structural components in masonry and historical buildings, special attention has been paid to arches and domes. Many historical structures are still in service all over the world and an important part of them have artistic and cultural value [1].