Seismic improvement of foundations of reinforced concrete bridges with FRP

Dissertation for receiving a Master's degree

in the field of: Civil Engineering with a focus on structures

Abstract:

Today, many reinforced concrete structures that are in operation are more than 75 years old and have been damaged due to natural disasters such as earthquakes and wind, or due to material fatigue or corrosive factors. Maintenance of structures is very important due to the cost of construction and repair. By studying the behavior of concrete structures, it is determined that several factors such as design and calculation mistakes, lack of proper implementation, changing the use of structures reduces their durability, at the same time, changing building codes (causes changes in loading and reliability coefficients) also causes the design and structure to be re-evaluated and revised so that it can be improved and strengthened if necessary.

Various methods are used to repair and strengthen reinforced concrete structures. Among them, we can mention reinforcement with metal and concrete coating, which in comparison, steel coating has an advantage over concrete in terms of weight, but steel also has several disadvantages, including heavy cost and difficulty in implementation, as well as vulnerability in corrosive environments. The new FRP material has been used for many years due to its unique features, such as strengthening and strengthening existing structures in bending and shearing cases, and high resistance to corrosion. . . They are used in the strengthening and improvement of structures.

Reinforced concrete columns are the main members resistant to horizontal and vertical loads in concrete structures, so making columns resistant to earthquake forces can play an important role in strengthening the entire structure. As a result, the use of FRP composites for the strengthening of reinforced concrete columns has spread in the world, and studies in this field are carried out by many researchers. In this research, a bridge with real dimensions and its frames were subjected to gravity, wind, water and earthquake loads with the ABAQUS finite element software, and were subjected to non-linear static and dynamic analysis with three earthquake acceleration maps, Manjil, Northridge and Chi Chi of Taiwan, and by gluing the layer CFRPs according to the needs of each base, the change in the amount of maximum displacement, the amount of cutting and the energy loss of their foundation has been investigated and the difference in the results of two static and dynamic methods has been calculated.

Key words: reinforced concrete bridge, wind, water, acceleration mapping, improvement, FRP sheet

Introduction

Earthquake is a natural and unavoidable phenomenon that does not cause loss of life and money by itself, but it is in the action of earth movements with man-made environments that the lack of ability to resist structures causes serious damage. Following earthquakes, in addition to loss of life, national wealth is also wasted and a large financial burden is placed on the economy of countries, which has serious and long-term effects on countries with fragile economies (Natiq Elahi, 2018). In recent years, on average, every five years, a severe earthquake has occurred in a part of the country, which has caused many human and financial losses (Hamra, 2017). Bridges as strategic and important structures and because they are one of the important elements in vital arteries, they must be designed in such a way that they can function during the earthquake and after, not destroying the bridge and not taking it out of operation after a severe earthquake is one of the many life and economic losses after It will reduce accidents (Zare Barzashi, 2013).

In the past few decades, along with the development of the country's roads, a significant amount of relevant budgets have been allocated for bridges. Unfortunately, despite the technological advances in material engineering, these structures still suffer many failures over time due to various reasons, including inappropriate environmental conditions, heavy traffic, and natural accidents. If these failures are not paid attention to in time, in addition to reducing the level of exploitation and the useful life of the structure, the maintenance costs will increase greatly. which shows the importance of using logical and kinematic methods in the management of bridge maintenance in order to maintain the safety of bridge users and prevent the wastage of the country's funds (Rahgozar, 2017). Therefore, finding a method or methods for seismic improvement of bridges that are not sufficiently resistant to earthquakes can be very important (Moradi, 2013).

For improvement, there are various methods such as local restoration, use of concrete cover, use of steel cover, etc. under the title of "classical methods". One of the new methods that has attracted the attention of craftsmen in recent years is retrofitting or improving existing buildings using composites. A lot of research has been done in this field and preliminary regulations have been prepared for their use (Natiq Elahi, 2015). Due to their high tensile strength, these materials are a suitable tool for increasing the capacity of concrete and masonry members. Today, in advanced countries, a large amount of improvement and strengthening of concrete and masonry structures is done using these materials (Hamra, 2007).

1-2- Statement of the problem

In this thesis, the reinforcement of concrete bridge foundations with FRP sheets under dynamic earthquake load will be discussed, the bridge foundations with real dimensions and enclosed with FRR are modeled in ABAQUS software, for the analysis of the foundation under earthquake load. Non-linear dynamic analysis has been used to investigate the effect of FRP on bridge foundations that are under acceleration mapping. 1-3- Research background The technology of using FRP sheets in civil engineering was first proposed and tested in 1984 in Switzerland by Professor Meier, where Carbon FRP (CFRP) sheets were tested to strengthen concrete beams. The biggest advantage of FRP compared to steel is its high strength-to-weight ratio. In 1987 and 1988, Katsumata and his colleagues presented the method of using FRP to strengthen reinforced concrete columns. One of the usual methods to strengthen and increase the bearing capacity of reinforced concrete columns is to create a peripheral cover to limit the transverse expansion of the loaded column. In addition to preventing the buckling of the column's longitudinal reinforcements, this method also delays the destruction of the column by postponing the separation of the concrete shell.

Studies on the method of reinforcing reinforced concrete columns were conducted at the beginning of the 20th century and on columns reinforced with steel cladding. These studies showed that the presence of a screw around the column increases its load-bearing characteristics. The adverse effect of environmental conditions on steel claddings and the difficult and time-consuming steps involved in creating these claddings caused composite plates made of polymers reinforced with fibers known as FRP sheets to be gradually used as an alternative to steel claddings. Also done:

Barghi, Mostafa and Haddad, Maitham, 2017, evaluation of flexural strengthening of reinforced concrete bridge base by GFRP under periodic loading, Khajeh Nasir Tusi University of Technology.

In this research, a model of the actual dimensions of a bridge base with a circular section was created and its behavior under periodic uniaxial loading (simultaneous gravity and lateral loading, whose lateral loading is periodic) was investigated. The introduced column is wrapped by a GFRP sheet with a thickness of 1 mm (along the entire length of the column), the base cut hysteresis curve was drawn in two cases without confinement and with confinement by FRP. The results are as follows:

A. GFRP reinforcement cover (with a thickness of 1 mm) has increased the bending capacity of reinforced concrete bridges by 8%.

B. The main property of the GFRP reinforcement coating is an increase in the breaking strain by 50%, which leads to more ductility and energy loss, and also improves the seismic performance of the column.

Salehian, Hamid Reza and Esfahani, Mohammad Reza "Laboratory investigation of the strength of a concrete column enclosed with GFRP under the combined effect of axial force and bending anchor and comparison with theoretical models", 2018.

In this research, samples Columns with a square cross-section have been investigated. This research shows that the application of bending anchors on the samples of columns enclosed with FRP, in addition to the interaction of compressive load and bending anchor, has a reducing effect on the compressive strength of the enclosed concrete. Applying bending anchor to the column section causes non-uniform distribution of the compressive stress on the cross section and its transverse expansion, for this reason the use of relationships to estimate the compressive strength of confined concrete, with the increase of the bending anchor, leads to unrealistic and unreliable answers. A new composite has been presented.