What are the main points of large-span steel structure construction for different projects, and what should be done for rational design?

Many steel structure warehouses and steel structure exhibition halls use long-span steel structures, large-span structure is mainly in the work of self-loading, in order to reduce the structural deadweight, often suitable for the use of steel structure as the main structure. According to the problems encountered in the past construction, we are mainly summarized into 3 categories.

1、Design and optimization aspects

Large-span steel structure construction design should be optimized before construction, especially in the calculation and analysis. Many project departments do not know how to calculate, do not calculate, resulting in poor construction quality or high cost of the project. So which parts should be looked at in the calculation and analysis?

①graphic design

First of all, we should pay attention to the cooperative work of the superstructure and substructure, and the effect of multidirectional seismic action should be taken into account. The most reasonable way to consider the cooperative work of the superstructure and substructure is to calculate the seismic effect according to the overall structural model. The simplification of the substructure must be based on reliable and dynamic principles, that is, the effectiveness of the stiffness and mass equivalence should be taken into account.

The software is used to model the design model and carry out calculation and analysis. In particular, the calculation model should be rationally determined to ensure that the connection and structure of the roof and other structures and the main supporting parts are consistent. In addition, the force analysis should be considered. Calculation analysis, in addition to simulating the structure of the overall molding of the force situation, but also take into account the construction process of the special force situation, to avoid the structure before molding because of the local force exceeds the design value and damage. For the calculation and simulation of the construction process, it is necessary to take into account the lifting of components, the working conditions of different construction phases, the structural pre-deformation technology, the pre-assembly and unloading of components.

②structural arrangement

The structural arrangement should avoid the formation of weak parts due to local weakening or sudden changes, resulting in excessive concentration of internal forces and deformations. Measures should be taken to improve the seismic capacity of possible weak parts. Therefore, in the structural arrangement, it should be ensured that the mass and stiffness distribution is balanced and the structural integrity and force transmission is clear.

The seismic effect of the roof should be effectively transferred downward through the support; avoid the concentration of internal force or large torsion effect of the roof, for this reason, the arrangement of the roof, the support and the substructure should be uniform and symmetrical; ensure the structural integrity of the roof, so the space transmission system should be used in preference to avoid local weakening or sudden change of the weak parts; it is preferable to use a lightweight roofing system, so the unit self-weight of the roofing system should be strictly controlled.

2、Construction and installation

The complexity of large-span structures and the diversity of construction methods determine that the design process must be combined with the consideration of construction issues. This is also the design process is often ignored or incomplete consideration of the place. The construction mainly involves the following installation techniques.

Structural components and shaped node production technology

Various kinds of large-span, complex space shape of steel structure buildings require complex local stress, production of difficult steel components, therefore, in the construction of complex projects should be considered structural components and shaped nodes should be produced to meet the conditions of stress, to ensure the quality and safety of the project.

①Integral slip construction technology

The more critical problem in the construction of large-span steel structure is the stability of the structure before forming a spatial whole. The problem can be better solved by sliding construction technology by using traction equipment that can control synchronization to move the structure divided into several stabilizers horizontally to the designed position along a certain track from the assembled position. But in the use of its requirements for the structure of the out-of-plane stiffness, the need to lay tracks, multi-point traction synchronization control difficult characteristics.

②Overall lifting construction technology

The technology through the hydraulic jack as a power device, according to the requirements of the lifting force of each operating point, a number of hydraulic jacks and hydraulic valves, pumping stations and other combinations of hydraulic jack clusters, and synchronized movement under computer control, to ensure that the lifting or shifting process of the large-scale structure of the attitude of a smooth, balanced load.

②High-altitude unsupported assembly construction technology

High-altitude block expansion unit unsupported assembly technology, the construction principle is: the structural system of reasonable segments, choose the sequence of lifting, so that the construction process does not need to set up a support platform, the use of the structure's own stiffness to form a stable unit, through the continuous expansion of the unit to connect the installation, and finally the formation of the overall structure.

3、Quality measures control, the construction process, need to pay attention to the following issues

①Mounting accuracy control

Complex space steel structure should be measured and controlled when it is installed, due to the measurement and control of steel structure construction as a part of construction technology, the reasonableness and advancement of its engineering construction program is analyzed from a large amount of measurement and control data information, and the results are reacted and confirmed. For large-span steel structure, due to the deformation and force state of the structure in the construction process, there is a great difference between the structure and the molding, so it is necessary to use all kinds of support frames to ensure the accuracy of the structure.

②Disassembly control

As the large-span steel structure has the characteristics of large unloading tonnage, wide distribution of unloading points, large unloading force at a single point, large workload of unloading calculation and analysis, etc., if the support force is released unreasonably, it will damage the structure or make the scaffolding unstable step by step. Therefore, when unloading the steel structure, it is necessary to take the system conversion program as the principle, structural calculation and analysis as the basis, structural safety as the purpose, deformation coordination as the core, real-time monitoring as the guarantee, and operate strictly according to the requirements of the two unloading methods of isometric method and equidistant method.

③Lifting program

When lifting large-span steel beams, if reasonable calculation of lifting points is not carried out, and the traditional two-point lifting is still chosen, due to the long steel beam structure, large spacing of lifting points, and factors such as self-weight and variable load, the steel beams and cables are subjected to a large amount of axial force, and it is easy to appear lateral bending of steel beams, and even more serious deformation occurs.

The construction site of large-span steel structure should strengthen the management and increase the training of workers' business knowledge, so that they have a more concrete understanding of the force characteristics of the components and the knowledge of lifting. At the same time, the construction organization design should be strengthened to make reasonable argumentation for the lifting scheme, so as to choose a more reasonable lifting scheme.

④mounting sequence

As the large-span steel structure requires high installation order, if the installation order is not reasonably considered, and the steel components do not meet the needs of lifting, it may affect the safety of the structure. When designing the construction organization, the installation sequence should be arranged reasonably, and the factory processing, component transportation and on-site installation should be coordinated in a unified way, and be strictly implemented in the construction process. In addition to carefully formulate the installation sequence suitable for the project, should also choose experienced construction team for installation, to avoid quality hazards.

The large-span steel structure is applied more in specific projects, and for the problems in the construction process, the optimization of the construction organization design should be strengthened, the safety and quality red line should be strengthened, and the construction technology should be improved continuously.