Find the right way to reinforce steel structure!
Main methods to reinforce steel structure:
Reduce the weight, change graphics of calculation, increase the original structure of the cross-section，enhance the connection strength and avoid crack propagation on steel structure.When you have plenty of experiences, other reinforcement methods can also be taken. Steel structure which need to be reinforced by identification can be divided into local reinforcement and comprehensive reinforcement referred to its damage scope.
Local reinforcement usually be used on rods or connecting nodes with insufficent bearing capacity. Methods such as increasing bars' cross section, reducing free length of the rod and strengthen the connection nodes. Comprehensive reinforcement refers to overall structure consolidation, which including two methods. One is calculating graphic reforcement methods without changing the structure static, another is calculating graphic reforcement with structure static changed.
Another effective way to fasten structural system is increasing or strengthening the support system.
The reinforcement method of increasing original component is the most material-cost and labor-cost (meanwhile also the most feasible method): changing calculation diagram is the most effective and varied, but also reduce a lot of costs.
You should collect materials before the final reinforcement method settled down.
The following information shall be collected before determining the strengthen scheme:
1) Completion work chart of the original structure (including the changing chart) together with examining and receiving 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) Inspection report on damage of structure or component
6) The existing actual load and the data of newly added load after reinforcement.
The main factors can damage steel structure.
1.Load change, extended service, rules and regulations change which lead to the insufficient bearing cap of the structure.
2.A variety of accidents caused by deformation, distortion, disability, depression, resulting in weakened component sections, bar warping, and connection cracking;
3.Temperature difference caused the deformation, cracking and warping of component or connection.
4.Corrosion and electrochemical corrosion caused by the erosion of chemical substances, which weakened the cross section of the steel structure.
5.Other factors including design, production, construction errors and illegal use and operation in service.
There are three main technical measures to strengthen the steel structure:
1) section reinforcement method: in the local or along the full length of steel components to strengthen with steel materials, even as a whole to make the common force;
2) change the calculation diagram: add support, adjust the load distribution, reduce the internal force level, the statically indeterminate bearing structure forcing displacement, reduce the peak stress;
3) Prestress cable method: using of high-strength cable reinforcement structure to enhance the weak link or improve the overall structure of the bearing capacity, stiffness and stability.
Prestressed Reinforcement Steel Structure Technology
Problems existed in the traditional steel structure reinforcement:
When the welding strengthened, the high temperature will make the organization and performance of the welded parts deteriorate, and the weld joint must have defectives, such as new cracks; residual stress within the welding structure, combined with other effects may lead to cracks. Welding leads to the formation of a continuous whole thing, so once the instability of the crack expansion, it is possible to break down, causing a major accident.
Using 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 under the loose in the dynamic load, 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, the steel plate is easy to rust, affecting the bond strength, high maintenance costs.
Advantages of prestressed reinforcement:
1) Reinforcement work can be carried out in conditions without unloading and non-stop.
2) The application of prestressing can directly reduce the deformation, rapidly eliminate stress and exceeded internal forces
3) Compared with the non - prestressed way, the phenomenon of stress hysteresis can be eliminated, and the high - strength characteristics can be fully utilized to improve the reinforcement efficiency.
4) Combined with reliable anchoring can reduce the adhesive interface of the peel stress, also can avoid the overall peeling and improve the reliability of reinforcement;
5) Reduce the cost of reinforcement and the costs