The main methods of steel structure reinforcement
Reduce the load, change the calculation of graphics, increase the original structure of the cross-section and the connection strength, to prevent crack propagation
When there is a mature experience, other reinforcement methods can also be used. Identification of the need to strengthen the steel structure, according to the scope of damage is generally divided into local reinforcement and comprehensive reinforcement.
Local reinforcement is a lack of carrying capacity of the bar or connecting nodes at the reinforcement, there are increased cross section method to reduce the free length of the rod method and the connection node reinforcement method.
Full reinforcement is the reinforcement of the overall structure, there is no change in the structure of the static calculation of the graphic reinforcement method and change the structure of the static calculation of the two types of graphic reinforcement.
Increase or strengthen the support system, but also an effective way to strengthen the structural system.
The method of reinforcement of the original component section is the most costly and most costly method (but often a viable method); the method of changing the calculation diagram is most effective and varied, and the cost is also greatly reduced
1. Before determining the reinforcement plan, the following information should be collected:
(1) the original structure of the completion of the map (including the change map) and acceptance records.
(2) the original steel material report copy or on-site material inspection report.
(3) the original structural components production, installation acceptance records.
(4) the original structural design calculations.
(5) structural or component damage inspection report.
(6) the actual load and reinforcement after the new load data.
Second, the main factors of steel structure damage and reinforcement technical measures
2.1 The main factors of steel structure damage are:
(1) structural changes in load, overdue service, norms and procedures lead to structural capacity is insufficient;
(2) components due to a variety of accidental deformation, distortion, disability, depression, etc., resulting in weakened cross-section, bar warping, connection cracking;
(3) under the action of temperature difference caused by component or connection deformation, cracking and warping;
(4) corrosion due to the erosion of chemical substances and electrochemical corrosion caused by weakened steel structure components;
(5) other including the design, production, construction errors and service during the illegal use and operation. This article origin steel alliance
2.2 steel structure reinforcement technology measures are mainly three:
(1) section reinforcement method: in the local or along the full length of steel components to strengthen, even as a whole to make the common force;
(2) to change the calculation diagram: additional support, adjust the load distribution, reduce the internal force level, the statically indeterminate bearing structure forcing displacement, reduce the stress peak;
(3) prestressed cable method: the use of high-strength cable reinforcement structure to enhance the weak links or improve the overall structure of the bearing capacity, stiffness and stability.
Third, the prestressed steel structure reinforcement technology
3.1 The traditional steel structure reinforcement problems:
When the welding is strengthened, the high temperature will cause the organization and performance of the welded parts to deteriorate; and the weld must be defective, will produce new cracks; welding structure within the residual stress, combined with other effects may lead to cracking. Welding so that the structure to form a continuous whole, once the instability of the crack expansion, it is possible to break in the end, causing a major accident.
The use of bolted connections in the vicinity of the damaged parts of the base material on the hole, weakened the cross-section, the formation of a new stress concentration area; ordinary bolts in the dynamic load under the loose, high-strength bolts prone to stress relaxation phenomenon, reducing the repair effect of the structure The Bonded steel reinforcement technology is in the steel surface with a special structure of the adhesive structure of the steel plate, relying on structural adhesive to make it together as a whole to work together to improve the structural capacity. The common drawback of these reinforcement methods is the increase in the weight of the structure, the steel is not easy to produce a variety of complex shapes, transport and installation is not convenient, and the steel plate is easy to rust, affecting the bond strength, high maintenance costs.
3.2 paste the characteristics of reinforced steel structure:
Paste the reinforcement of the steel structure is the use of adhesive will be affixed to the surface of the steel structure damage, so that part of the load through the adhesive layer to the upper, reducing the structural damage site stress. Paste reinforcement technology has obvious advantages:
(1) the specific strength and specific rigidity, after reinforcement does not increase the original structure of the original weight and the size of the original components;
(2) composite material has good anti-fatigue properties and corrosion resistance;
(3) Flexible composites have a particular advantage for any of the closed structures and the surface of the reinforced structures that are complex in shape. Good sealing, reducing the risk of leakage or even corrosion;
(4) simple, low cost, high efficiency, in a small space can also be construction, especially for on-site repair;
(5) no fire in the construction process, suitable for a variety of special circumstances.
3.3 Advantages of prestressed reinforcement:
(1) reinforcement work can be carried out without unloading, non-stop conditions;
(2) the application of prestress can directly reduce the deformation, the rapid elimination of stress and internal force beyond the peak;
(3) Compared with the non-prestressed way, can eliminate the phenomenon of stress hysteresis, make full use of high-strength characteristics, improve the reinforcement efficiency.
(4) combined with reliable anchoring, can reduce the adhesive interface of the peel stress, to avoid the overall peeling, improve the reliability of reinforcement;
(5) reduce the cost of reinforcement and the use of cost.
Fourth, fiber cloth installation process
4.1 Surface treatment:
(1) first with coarse sandpaper grinding components of the bonding area, clean up the surface layer, with acetone or alcohol solution to scrub the surface, remove contaminants, dry dry, impregnated with a binder surface.
(2) in the design requirements of the location of drilling, should be away from the site to be reinforced in order to avoid secondary damage;
(3) in the fiber cloth surface of the plastic, the gap between the fiber bundle initially closed, slightly dry and then filling;
(4) glue a little dry after the second application of prestressed to the design of the control stress (the use of extrusion effect, improve the quality of paste), with plastic fiber bundles fully saturated, improve common performance.
(5) After 48 hours at room temperature (when the temperature is low should be appropriate to extend the time), glue fully hardened, cut off the excess screw, according to the actual requirements of the structure of surface protection. This article origin steel alliance
4.2 Prestressed reinforcement design and calculation principles Prestressed reinforced steel structure in addition to compliance with the general steel structure reinforcement guidelines and regulations, but also has the following characteristics:
(1) the static calculation must first determine some of the parameters related to the adjustment of stress, such as auxiliary balance force size, prestressed strength, prestressed unloading moment value, the bearing elevation of the displacement value;
(2) to determine the reasonable load stress or stress level, in other words, to determine whether to determine the reinforcement structure of the need to uninstall, or unload to a certain level.
4.3 The following principles shall be observed in the design calculation of the reinforcement structure:
(1) the reinforcement and the reinforcement are within the elastic range of the material force, both at the same time under the load to achieve the strength of the material design value;
(2) give full play to the potential strength of the material, the reinforcement of the pre-stress can be added to the stress of the reinforcement to the extreme value of its reverse stress;
(3) Prestressed reinforcement design should also consider the prestressing load factor, prestress loss coefficient, working condition coefficient, load factor and so on.
Construction Technology and Steps of Prestressed Reinforced Steel Structure
Prestressed reinforced steel structure can be divided into two kinds,
First, the direct paste method, the two ends of the anchor and the application of prestressed, through the adhesive paste on the surface of the steel structure; generally applicable to the surface of the workpiece more flat rod, the components or their local reinforcement;
Second, the beam as a prestressed cable to adjust the stress, generally applicable to the overall structure of the overall reinforcement.
5.1 Selection: Carbon fiber for structural reinforcement is mainly selected PAN-based carbon fiber, the ultimate strength of up to 3500MPa, elastic modulus of about 2.35 × 109MPa. Resin system using epoxy materials.
5.2 Design: According to the force characteristics of the structure to be patched, force transmission path and stress - strain field, determine the amount of cloth, size and laying direction. The direction of the fiber should be consistent with the direction of maximum force in the damaged component. If the injured site is in a complex stress state, the fiber orientation and laying sequence should be consistent with the direction of the control principal stress.
5.3 Embedded prestressed tensioning technology: the special nature of steel structure reinforcement, the need for a simple pre-stress application, the traditional pre-stress application is often the first post-tensioning anchor, the need for relatively complex tensioning machine, and the corresponding Of the reaction device. In the anchor when the prestress loss is also relatively large. Embedded prestressed tensioning technology, which is characterized by the first anchor after the tension to the component itself and the previous anchor as a tension force device, without the need for complex tensioning machine. The embedded prestressing tensioning technique can apply prestressing force to produce the extrusion effect on the adhesive layer and improve the reliability of the paste. At the same time, due to the use of the first anchor after the tensioning technology, the prestress loss is small, the method is simple and effective.