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2022.12.30

Construction Technology of Steel Space Frame Roof Project

steel truss gymnasium

The steel space frame roof structure is novel and beautiful because it integrates the advantages of building plane shape, support point, roof structure and facade. It is often used in the roof design of public buildings such as sports venues, large shopping malls, high-speed railway stations, and airport terminals. The quality control of the roof steel space frame structure is particularly critical in the construction process. Therefore, when carrying out the construction of this type of project, it is necessary to adopt strict construction technology and strengthen the management of the construction process to ensure that the construction process is strictly in accordance with the proposed construction technology and process requirements. To ensure the quality of the project and reduce the probability of safety accidents.

1. Project Overview

The indoor swimming pool of a sports center covers an area of 5481.19m², with a total construction area of 7808.97m², a basement area of 1238.44m2, and a capacity area of 6570.53m2. The total height of the building is 14.15m, the lower chord bottom building elevation of the roof steel space frame is 10.20m, and the depth of the swimming pool structure is 2.60m. The building mainly includes one basement floor and two floors above ground, which are a duty room, medical emergency room, competition management room, equipment warehouse, swimming pool venue, ticket office, consumer control room, athlete room, lighting control room, on-site broadcasting room, and venue. Operate functional rooms and facilities such as office space, journalist work area, and warehouse. The roof steel space frame of this project is a positive quadrangular pyramid space frame, the space frame support system is the upper chord point support, the support adopts the elastic support, and the safety level is second.

2. Construction sequence of roof steel space frame project

This project is required to be completed according to the contracted construction period, and careful construction arrangements and reasonable arrangements for the construction of each process should be carried out before construction. The construction sequence can be divided into:

(1)Inside the steel structure factory: drawing deepening design – drawing review and design disclosure – lofting, cutting – raw material entry and inspection – processing and manufacturing components (steel balls, rods, supports) – surface Anti-corrosion treatment (outdoor high-oxidizing enamel topcoat, the total thickness of paint surface is 160 μm), quality inspection- packaging and sending to the construction site;

(2)Construction site: the ground of the construction site is leveled and hardened, the scaffolding is erected and the operation panel is laid. (Up to 300mm lower chord of the space frame ) Installation preparation for a space frame -(check and measure whether the positioning size, elevation, and flatness of the embedded parts at the support of the space frame meet the requirements of the design drawings and construction acceptance specifications and make corresponding adjustments if necessary) -An elastic support is installed, space frame assembled, a space frame hoisted and fixed- Space frame connection node detection- acceptance – archiving.

10 measures to control welding deformation of steel structure

3 Construction points of steel space frame roof engineering

3.1 Inside the steel structure factory

3.1.1 Material procurement and inspection

The materials to be purchased for the quadrangular pyramid space frame in the project are mainly steel balls, seamless steel pipes, etc. Before the project starts, it is necessary to formulate a procurement plan for related materials according to the actual planning of the project; and combine the requirements in the engineering design drawings. The specific procurement and inspection work of materials in the steel structure factory has been improved to provide support for the smooth entry of subsequent materials.

 (1) The steel ball material is generally made of 45# steel, which should meet the Q235 material requirements specified in the “Carbon Structural Steel” (GB 700-88) standard. The seamless steel pipe should meet the requirements of the 20# steel standard of “High-Quality Carbon Structural Steel” (GB 699-88).

 (2) The cone head and the sealing plate need to be made of Q235 steel or 16 manganese steel, and the corresponding materials are selected for forging.

 (3) High-strength bolts are made of 40Cr steel. The processing requires four steps of forging, wire rolling, rolling and heat treatment. The strength level needs to reach 10.9S to meet the requirements of the “Construction Quality Acceptance Standards for Steel Structure Engineering” (GB50205-2020).

(4) Welding rod, the main metal material of the project is Q235, and the welding rod is E43 type.

(5) Anti-corrosion coatings, including anti-corrosion primers and topcoats, thinners, etc. The anti-corrosion materials used in this project mainly include epoxy zinc-rich paint, epoxy micaceous iron intermediate paint, and chlorinated rubber topcoat.

3.1.2 Rod processing

The positive quadrangular pyramid space frame structure of this project mainly adopts the method of interconnecting welding nodes with relatively complicated process. For the specific processing of all the rods used in this project, it is necessary to select a steel structure factory with professional technical level, and it is required to have relevant equipment that can meet the actual requirements of the processing of the project components, such as steel pipe bending equipment.

3.1.3 Rust removal and anti-corrosion treatment

(1) The quality judgment basis of rust removal.

The rust removal judgment basis involved in this project is mainly based on the Swedish rust removal standard Sa2.5 level as the actual basis. There is a direct relationship between the quality of rust removal and the selection of methods, so it must meet the design requirements and the requirements of the rust removal grade specified in the national standard “Rust Grade and Derusting Grade on Steel Surfaces Before Painting” (GB 8923-88).

(2)Rust-removal

In view of the basic requirements for components in this project, the specific rust removal method is shot blasting and rust removal. The specific process mainly includes the following aspects: The compressed air as a kind of power, drive the need to remove rust components, make it through the special nozzle, the use of friction, impact force, rust removal on the surface of components. After the completion of rust removal, it is necessary to clean the surface dust in time and carry out anti-rust coating after passing the inspection.

(3) Environmental requirements for anti-corrosion paint and brushing.

The steel pipe truss and space frame roof structure paint of this project is painted twice with epoxy zinc-rich paint, twice with epoxy micaceous iron intermediate paint, and twice with chlorinated rubber topcoat. Based on the characteristics of the brushing materials selected for this project, during the construction process, it is necessary to ensure that the outdoor temperature is 5C°~35C°, and the humidity should preferably be less than 85%, and it is necessary to avoid rain, snow, and strong winds greater than level 5. weather. In summer, the temperature is higher than 40 ℃ and construction is strictly prohibited under strong direct sunlight.

 (4) Treatment of surface defects on the base layer of components.

Before the anti-corrosion paint is applied, it is necessary to carry out basic reinforcement treatment on the gaps and uneven parts of the components, and at the same time, it is necessary to ensure that the surface of the steel is flat and there are no sharp edges and corners. On the surface that has been primed, it is necessary to carry out secondary rust removal treatment, and the rust removal standard is Swedish St3 level; for the surface coated with zinc-rich primer, if the surface has been exposed to the air for a period of time, a dialogue is also required. rust and other dirt; the powdered surface needs to be polished, and the dust on the surface needs to be removed after the treatment is completed.

3.1.4 Quality reinspection and material delivery

After all the above work is completed, the materials that have passed the inspection can be bundled and packed, and transported to the construction site according to the actual requirements of the project.

3.2 Construction site

3.2.1 Ground treatment and scaffolding construction

In this project, full-floor scaffolding is adopted and the wooden formwork is fully paved on the top as the operation platform for assembling the steel roof truss. Therefore, the erection of full-floor scaffolding is a prerequisite for the installation of steel space frame. This project is an indoor swimming pool project. Most of the ground area below the roof steel space frame is the swimming pool. Most of the scaffolding falls on the bottom of the swimming pool, and some of the scaffolding falls on the platform of the viewing seat.There is a certain height difference, which causes certain construction difficulty and unsafe factors for the erection of scaffolding. Before the roof steel mesh frame is installed, the concrete structure of the swimming pool has been completed, and the ground on the viewing seat has not been hardened. The ground on the viewing table must be hardened before the installation, and the drainage ditch should be set up to ensure that the foundation of the frame body will not be submerged by rain and cause safety hazards. The requirements for the full-house scaffolding are: the bearing capacity needs to meet >250kg/m2, the scaffolding step distance is 1.53m, the vertical and horizontal vertical rod spacing is 1.20m, the vertical and horizontal horizontal rod spacing is 0.60m, the wall parts are set in three steps, and the scaffolding board is 18mm thick plywood, in the form of a full lay on the scaffolding. The sweeping pole set on the ground is 300mm away from the ground, and the wooden base is set at the bottom of the pole. Set scissor braces on the side, and set up a pair of scissors braces in the middle every four rows of vertical bars along the east-west longitudinal direction. The inclination angle between the scissor braces and the ground is 45°~60°. All scissor braces and diagonal braces are continuous from the base to the top. Set up horizontal scissor braces on the top, bottom and every three steps to improve the stability of the scaffold.

3.2.2 Installation of the space frame support at the upper chord point 

(1) Preparations.

Before the structure is installed, the positioning axis, elevation, plane position and flatness of the embedded parts should be reviewed again. The allowable deviation should meet the requirements of the specification, the plane position error should be guaranteed to be less than 15mm, and the quality should meet the “Construction Quality Acceptance Standards for Steel Structure Engineering” (GB 502052020) and construction drawing requirements. In addition, the concrete frame columns should meet the following requirements: First, the strength of the concrete before installation must meet the design requirements. Second, use a level, steel tape measure, and steel wire to measure the column axis distance, column span size, elevation and section size, and use red paint to mark the axis after the steel plate and column are measured. Third, the verticality of the concrete frame columns meets the requirements of design and construction standards.

(2)The elasticity support

The elastic support is an important force-bearing component between the roof steel space frame and the embedded parts. The one-way sliding support is used in this project. The main installation and construction techniques for elastic support are as follows: First, during installation, the elevation and levelness of the embedded parts at the top of the frame should be reviewed to meet the design requirements, and the height difference between the four corners of the support should not be greater than 1mm. Second, the center line of the support should coincide with the center line of the embedded parts and the installation line of each truss. Third, after the support is installed in place, the welding of the bottom plate and the embedded steel plate should meet the design requirements. Once the entire truss is installed, the temporary connections should be removed immediately.

(3)The spaceframe assembly upper string point supports.

Measure and locate the center position of the lower chord bolt ball of the space frame, arrange the support platforms that can be adjusted up and down, and connect each platform together to ensure that the position of the center axis does not change after meeting the requirements. Then use the tower crane according to the positioning axis, put the bolt ball on the platform, use the total station to determine the position, and temporarily fix the ball with the limit block after the position is accurate. In the process of splicing the space frame, a standard axis is needed as the basis to carry out the specific assembly work. In the assembling process, the bottom chord network is generally assembled first, and then the abdominal rod and the top chord rod are assembled in sequence, and measurement and positioning are performed while assembling.

(4)Hoisting and lifting equipment.

The hoisting equipment used in this project is to use the hoisting on the construction site to hoist the rods to the scaffolding operation platform, and use the tower crane to lift each truss unit assembled on the operation platform to the top support of the frame column at both ends for positioning and fixing.

(5) The space frame assembly upper string point supports.

 The truss assembly work has been completed on the scaffolding platform. The hoisting sequence of each truss is strictly in accordance with the construction sequence determined by the component approach plan and the construction plan. The installation points are as follows: First, use the tower crane to hoist each assembled truss in place, and then weld and fix the supports at both ends of the upper chord of the truss and the elastic support at the top of the column. After installing the first unit, you need to use sleepers between the bottom ball and the operating platform to fix it, and then each operation needs to be padded with sleepers for operation. Second, after installing the mid-span connection position, the rigidity of the space frame has been basically formed. At this time, all the high-strength bolts can be tightened. The bolt tightening direction generally extends from both sides to the middle, and the upper and lower strings should be tightened at the same time, Only in this way can we truly ensure the stability of the space frame. Third, during the installation process, the position, elevation, surface flatness, straightness, etc. of the truss must be controlled in time, and the deviation must be adjusted in place in time. Fourth, after the installation is completed, the connection point needs to be checked and accepted, and the existing problems should be adjusted in time. After ensuring that all installations have been completed, the installation project can be checked and accepted, and all materials involved in the entire project will be sorted and archived.

The roof steel space frame structure is an important project in the indoor swimming pool project of the sports center, and also an important link that affects the overall quality of the project. This project is located in a place with abundant rain, so more attention should be paid to the construction quality of roof steel space frame engineering, to ensure that there will be no quality problems of water seepage and leakage after delivery.