FRP Reinforcement of Masonry Buildings in the Republic of China

If we look further into the long term, considering the long-term benefits, FRP has good durability and hardly needs maintenance in the later period, while other reinforcement methods require higher long-term maintenance costs. Therefore, considering comprehensively, FRP reinforcement method appears to be more economical.

There are a large number of masonry buildings in the ancient city of Nanjing. There are more than 200 masonry buildings in the period of the Republic of China alone. They are an important part of the architectural cultural relics of Nanjing and have important cultural relics, usage and scientific research values.

After nearly a century of baptism, these buildings in the Republic of China are gradually aging and denuding. The wanton transformation of the structure by the owner and the user also caused great damage to these buildings. In addition, at that time, the building structure did not consider the seismic fortification requirements, the seismic capacity of the structure can not basically meet the requirements of the current seismic design code.

In order to better protect and rationally develop these representative excellent buildings and leave rich architectural and cultural heritage for future generations, it is necessary to reinforce masonry buildings in the Republic of China.

In recent years, the Housing Administration Department of Jiangsu Provincial Authority has entrusted testing units to conduct a comprehensive monitoring of the National Heritage Buildings in the Presidential Palace of Nanjing, and is prepared to adopt effective plans for seismic reinforcement of the Presidential Palace based on the test results. The safety evaluation and seismic performance appraisal of the Presidential Palace complex were carried out by the testing unit. The following problems were found:

(1) The material performance of masonry structure is seriously deteriorated, and the compressive bearing capacity of most buildings, especially the first floor walls, can not meet the requirements.

(2) The mortar is basically denuded, and the strength of the remaining mortar is close to zero.

(3) The structure lacks the necessary anti-seismic measures;

(4) Many building stories exceed the current specifications, and the height-thickness ratio basically does not meet the requirements of the Code for Masonry Structural Design (GB 50003-2011). The conclusion is that the seismic performance of the buildings in the Presidential Palace of the Republic of China is very poor, so it is urgent to reinforce them.

Traditional masonry reinforcement methods generally have the following kinds: enlarged section method, enclosed steel reinforcement method, reinforced concrete mortar reinforcement method, external post-tensioned prestressing reinforcement method, cement grouting method and shotcrete reinforcement method. These methods have certain advantages despite a long period of practical engineering application. However, cultural relic buildings are different from general industrial and civil buildings, and have their own characteristics and particularities.

Excellent cultural relics buildings are required to maintain the original style of the building, not to change the superstructure, or even to modify the original facade, in order to avoid destroying the original style, the traditional reinforcement methods can not basically meet these harsh requirements. In recent years, the increasingly mature FRP (Fiber Reinforced Plastics, Fiber Reinforced Plastics, Fiber Reinforced Plastics), mainly composed of high-performance fibers, polyester or epoxy resins, the common materials are mainly carbon fibers, glass fibers and aramid fibers) reinforced masonry method has gradually entered the public's vision. The technology of FRP strengthening masonry structure has been paid more and more attention in recent years because it is suitable for the reinforcement of local cracks in the wall and the reinforcement of the wall under the condition of insufficient bearing capacity. Although there is still a gap compared with Japan, the United States and other advanced countries, but the technology in China still has a very large space for development.

Compared with traditional reinforcement methods, this new technology has unique advantages:

(1) High strength and high efficiency: can greatly improve the ductility and bearing capacity of components, improve the mechanical performance of components. The tensile strength of FRP material is about 10 times of that of steel, but its specific gravity is only 1/4 of that of steel.

(2) Good corrosion resistance and durability: It can make the reinforced components resist the corrosion of various acids, alkalis and salts, and improve the overall durability of buildings. It does not need regular maintenance after reinforcement, and it can protect the internal structure. It has enough ability to adapt to the change of temperature. Adding fire retardant coatings to FRP can also effectively prevent fire, enhance the adaptability of the structure to harsh external environment, and prolong the service life of the structure.

(3) Fatigue resistance: For structures that are often subjected to dynamic, cyclic and variable loads, strengthening can effectively ensure the overall fatigue resistance of the structure.

(4) Maintaining appearance: For various structural shapes such as circular, rectangular and irregular surfaces, joints, beams, slabs, columns and other structural parts, FRP material reinforcement can basically maintain the original appearance and shape of the structure, this advantage has absolutely irreplaceable significance for ancient cultural relics buildings. At the same time, because of the lightweight nature of FRP material itself, the weight gain per square meter after reinforcement generally does not exceed one kilogram, which basically can be considered as not changing the self-weight of the original structure, thus effectively guaranteeing that the seismic performance of the original structure will not be weakened by increasing the self-weight.

(5) Convenient construction: When FRP sheets are used on site, they can be cut arbitrarily according to the specific conditions and needs, without the need to prepare complex construction tools. Therefore, FRP reinforcement construction process has the advantages of short period, high efficiency and less land occupation. According to some data, FRP bonding is 4 to 8 times more effective than steel plate bonding. In addition, because FRP cloth is a flexible material, it can basically achieve 100% effective sticking rate. Even if there are bubbles in the local area, it is very easy to handle. The corresponding acceptance standard is to require 70% effective sticking rate, so it can effectively ensure the quality of construction and acceptance.

(6) The comprehensive economic benefit is good. Although FRP sheet is expensive, it consumes less materials, takes less construction time, does not need large-scale machinery, and the one-time investment cost may not exceed the traditional reinforcement method. If we look further into the long term, considering the long-term benefits, FRP has good durability and hardly needs maintenance in the later period, while other reinforcement methods require higher long-term maintenance costs. Therefore, considering comprehensively, FRP reinforcement method appears to be more economical.

Keywords:
Fiber-reinforced Polymer (FRP)
Composite materials
Polymer matrix
High-strength fibers
Lightweight
Strength
Durability
Structural applications
Engineering
Materials science
Civil infrastructure
Aerospace
Automotive
Manufacturing techniques
Processing methods

Fiber architecture

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