Prestressed steel structures is increased in all kinds of steel structure high strength prestressed bar outages and tensioned prestressed bar give other artifacts and load in the opposite direction from the internal force of the prestressed, prestressed bar and get the same as the direction of load internal force caused by prestressing, both give full play to the role of the high strength prestressed bar, and make full use of the strength of steel members. The essence of prestressed steel structure is to replace a part of ordinary steel with a small amount of high strength steel and improve the bearing capacity of other components to obtain significant economic benefits.
At present, the application of steel structure in high building structure and super high-rise structure has been widely used in recent years, and it has become the main trend of super high-rise structure because of its good seismic performance. In addition, light steel structure building system for small and medium-sized factories, stores, supermarkets, because of its simple structure, single material, is conducive to the production of industrialization and standardization, and because of light weight, short construction period, good economy and rapid development.
First, the principle and state of prestressed steel structure
1, the basic principle of prestressed steel structure
Is the basic principle of prestressed steel structure according to the characteristics of ordinary steel structure, artificially in structure or component larger stress place, introduced in contrast to the loads symbol MaLi beforehand, make the structure bearing load, offset part or most of the components of internal force, deformation also reduced accordingly, achieve the goal of structure is more reasonable and more economical. According to the construction technology of prestressed steel structure, rigid structure and semi-rigid structure can be classified into one category, flexible structure is classified into another category. Rigid structure and semi-rigid structure have relatively independent stiffness of rod structure. When the prestress in the cable fails, the structural stiffness decreases. But the stiffness of the rod structure still exists. Therefore, the construction technology calculation model of rigid structure and semi-rigid structure can be decomposed into the action of cable on the partial structure of rod. The suspension system, the cable-stayed system, the prestressed grid structure, the prestressed reticulated shell structure and the tensioned beam roof frame all have the characteristics that can be divided into relatively independent partial structure of rod. Flexible structure is different from rigid structure and semi-rigid structure, it only forms a rigid structure under the action of prestress, can not be divided into relatively independent rod part of the structure, its design and construction calculation need to determine the shape of the structure, so flexible structure construction is completely different from rigid structure and semi-rigid structure construction.
2. State of prestressed steel structure
The state factor consideration of prestressed steel structure refers to the cable force and the geometric shape of the structure. For the convenience of analysis and narration, three different states of prestressed steel structure can be defined as follows:
(1) Zero state: the structure in zero state is the assembly of components after processing and lofting. In the zero state, there is no prestress, no external load and the function of dead weight, and the shape and geometric size of the rod part in the zero state of the structure are given by the design drawings.
(2) Initial state: Initial state refers to the state of self-balance only under the action of prestress and self-weight after the structure is installed and tensioned. The initial state of prestressed steel structure only has the function of pre-stress force and structure weight, which is actually the prestressed construction tension state, and the cable force and geometric shape of this state are the control value of cable tension and displacement monitoring value during construction tension respectively.
(3) Working state: Working state refers to the equilibrium state reached by the structure when it is put into use under the external action. Usually, the displacement of the working state under the external action is explained and required by the designer.
Second, the construction process and control design of prestressed steel structure
1. Construction process of prestressed steel structure
The exhibition hall of Changsha Convention and Exhibition Center is a complex space prestressed steel structure with the combination of cable and tensioned truss. The construction process is as follows :(1) assembling the truss span of the roof truss on the ground lift mold; Tensioning down the string, tensioning beam across the arch to the predetermined amount; (2) hoisting, installation of tensioned truss span, two-end welding connection; (3) Tension oblique cable, so that the roof displacement control point arch to a predetermined amount; (4) Remove the support, and then install the roofing panels and equipment.
From the above construction process, the following characteristics of prestressed steel structure construction can be concluded :(1) prestressed construction will have stages, which can be nested; (2) It is necessary to determine a shape control as the cable tension target, the cable force target when the target is achieved controls the cable force, and the displacement of the control point when the target is achieved is the target control displacement, that is, the initial state; (3) The control cable force is often a few, even more than a dozen. Due to the limited practical tensioning equipment, it is impossible for all cables to be tensioned at the same time, so a tensioning scheme must be developed to achieve the target controlled cable force and target controlled displacement using a small number of devices.
