Retrofitting and Reinforcement of Civil Airport

With the rapid development of the national economy, it has brought unprecedented development opportunities to the civil aviation industry. A large number of new and unique terminal buildings have been relocated and expanded in China, and how the original terminal buildings continue to be used normally is a major issue for the civil aviation management department. It involves many issues such as cost, function, coordination of new and old terminal buildings, utilization efficiency and social benefits.

The old terminal of Xi’an Xianyang International Airport was built in 1988 and was designed by China Northwest Architecture Design and Research Institute in accordance with 74 series of codes (seismic code TJ1178). The plane of the terminal building is fan-shaped (see Figure 1 for the schematic diagram of the building roof), and the main structure has 3 floors (2 floors on the north side), with a total construction area of 20697m2. The structure of the building is a cast-in-place reinforced concrete frame structure with two deformation joints to divide the structure into three parts. The column network is arranged regularly, the frame beams are arranged in the circumferential and radial directions, and the secondary beams are mainly arranged in the circumferential direction. The short span of the floor slab is mainly radial. The foundation is treated by dynamic compaction, and the foundation bearing capacity is 220kPa. The foundation adopts a reinforced concrete independent foundation, with reinforced concrete tension beams in both radial and circumferential directions, and the buried depth of the foundation is 2.9m.

The seismic fortification of this project is classified as Class B, the frame seismic class is Class II, the structural safety class is Class II, the foundation design class is Class C, the collapsible loess building is classified as Class C, and the construction site is Class II site. According to the "Report on the Earthquake Safety Evaluation of the Xi'an Xianyang International Airport Expansion Project Site" of the Shaanxi Earthquake Engineering Survey Center..., the peak ground acceleration of the ground motion with a probability of exceeding 10% in 50 years is 0.18g.

In 2001, a new terminal building full of times was built on the west side of the project, which achieved the predetermined goal and was well received by all parties. The new and old terminals are close to each other. How to use the old terminal and make the old terminal and the new terminal coordinated and unified, the following decisions have been made after multiple demonstrations:

① The building is still used as a terminal building, and appropriate adjustments have been made to the process flow and functional division.

②Add a roof garden and a sightseeing hall on the roof. Adjust the location of individual buildings and elevators, and transform kitchens and bathrooms to further improve the building's use functions and conditions.

③The old terminal building was still in normal use before the renovation, and no hidden safety hazard was found in the structure after the appraisal unit.

④The renovation of the facade and the addition of a driveway canopy on the land side are unified considerations and coordinate with the new terminal building.

The typical section of the building is shown in 2.

Owner's request: "According to the approval of the budgetary estimate of the renovation project, and subject to investment restrictions, the old terminal should try to avoid major adjustments while meeting various needs. The renovation plan of the old terminal building should be advanced, applicable, maneuverable and flexible."

In order to reduce the cost of reconstruction, the overall structure does not consider improving the safety and seismic capacity of the structure, try to maintain the original main structure, and make full use of the original structural components.

Ideas for reinforcement design

The overall idea of the renovation and design of the old terminal is considered in the following aspects:

First, only consider the load transposition without considering the addition of layers. In order to maintain the original structure as much as possible, make full use of the original structural members, and not increase the load, the measures adopted in the reinforcement design are as follows. When refurbishing walls and floors, remove the original base layer together. For internal partition walls in areas where the floor load is increased, light partition walls should be used as much as possible. For the reinforcement of the components, the method of sticking carbon fiber cloth and sticking steel plate should be adopted as much as possible. Its construction is simple and can effectively reduce the cost of reinforcement and reconstruction, and the added weight of the main structure and components is limited and can be basically ignored. Moreover, the strength is greatly improved, but the rigidity of the structural member is hardly increased. At the same time, using this kind of reinforcement method, it is easy to avoid leaving traces of reinforcement after decoration, and it is convenient to achieve the requirements of beautiful and generous indoor and outdoor terminal buildings.

Secondly, consider adding a sightseeing hall on the roof. The idea of this article is to make the impact on the terminal building as small as possible. For this, a steel frame system is used in the design to reduce the load. After calculation, the building materials above the structural slab of the roof layer are removed, and the load of this part is basically the same as the added load. For the connection between the Observation Hall and the terminal building, hinged joints are used in the design of the column feet. Its purpose is to reliably transfer the horizontal and vertical loads of the sightseeing hall to the roof of the original terminal building, and to ensure that the newly added sightseeing hall does not directly generate bending moments on the components of the terminal building. As a result, the entire structure does not significantly increase the weight due to the addition of the viewing hall, nor does it transmit the bending moment, but only transmits the shear force generated by the horizontal action of the viewing hall. Due to the small area of the Observatory, the design considers it as a tower and considers the whip effect. However, the amplification of the whip effect on the earthquake is only for the Observatory and does not pass to the lower floors. Therefore, the horizontal shear force of the tourism hall is very weak to the overall structure. In the end, it is ensured that the addition of floors has a small impact on the terminal building and is easy to meet the calculation requirements. According to the above ideas, the calculation and analysis of the overall structure meets the design requirements (only a few beams are insufficiently reinforced). The specific content of structural analysis and reinforcement design under the action of horizontal structure can be found in "Reconstruction and reinforcement of the old terminal of Xi'an Xianyang International Airport"

In addition, reconstruction and reinforcement of the foundation part are not considered. As time goes by, the bearing capacity of the foundation will generally increase to a certain extent. Seventeen years have passed from the completion of the project to the renovation. According to experience, the foundation bearing capacity will increase by 10% to 20%. Combining the several reasons explained above, the overall change of the internal force transmitted to the foundation of the superstructure according to the force transmission path of floor-beam-column is very small. Even if the local load has increased, the increase or decrease is extremely limited. Considering the increase in the bearing capacity of the foundation, the requirement can still be met without the need for foundation reinforcement.

in conclusion

(1) Reinforcement and reconstruction of existing building structures should comprehensively consider the changes in building functions and the fortification requirements of the building structure. The current building reliability appraisal standards, building seismic appraisal standards and building seismic design codes should not be applied singly.

(2) On the premise of meeting the objectives of reinforcement and reconstruction, check calculations should be carried out according to the three-level target of seismic fortification.

(3) When applying carbon fiber sheets to reinforce concrete structures in the design of reinforcement and reconstruction, attention should be paid to the construction quality.