I. Steel Column Reinforcement Method
1. Section of reinforced column. Generally, the section of reinforced column is made of steel plate or section steel. Welded or high strength bolts are used to connect the original column into a whole.
2. Adding support. Supports are added to reduce the free length of columns and improve the bearing capacity. The stability of the column is improved when the section size is unchanged.
3. Change the calculation sketch to reduce the external load or internal force of the column.
4. Reinforcing the steel column with reinforced concrete around it can obviously improve the bearing capacity.
II. Column unloading method
When strengthening or replacing new columns under unloading condition, the method of "supporting beam replacing column" must be adopted. When only the upper columns need to be strengthened, the roof truss can be supported by crane girder bridge frame to unload the columns. When the lower column needs to be strengthened or the lower column needs to be truncated, a long-term supporting beam can be set under the crane beam to share the load of the upper column (including the load of the crane beam) with the adjacent column (the adjacent column must be checked and strengthened, as well as the checking basis).
When using this method, it should be considered that the bracket beam will produce a certain deflection after replacing the lower column with the bracket beam, which will force the original roof truss to sink, thus possibly damaging the connection joints of the components connected with the roof truss. For this reason, temporary load can be added to the bracket beam in advance to make the bracket beam deflect in advance. The sequence of using this method is to reinforce adjacent columns, weld supporting beams and adjacent columns, add temporary loads, weld supporting beams and central columns, unload temporary loads, reinforce or truncate lower columns.
III. Column foot reinforcement method
1. Reinforcement Method of Insufficient Thickness of Column Base Plate
Adding stiffening ribs at column foot can reduce the calculation bending moment of floor. Concrete is poured between the column-foot steel sections to make the bottom plate of the column-foot become a rigid block. In order to increase the bonding force, the surface paint and rust of the column foot should be cleaned up.
2. Reinforcement Method of Insufficient Anchorage at Column Foot
Additional anchor bolts are added. When the concrete foundation is wider, it is adopted. On the basis of concrete, holes are drilled, additional bolts are inserted, epoxy mortar is poured, and the whole column foot is wrapped with reinforced concrete. The new reinforcement should be inserted into the foundation and welded with the original reinforcement.
Up to now, the stress redistribution after reinforcement by steel structure manufacturers has not been fully confirmed by experiments (at least in the elastic stage), but for static load structures, when a part of the section enters the plastic state, the stress will eventually redistribute, so the static load structure can be calculated according to the principle of the new and old sections working together; when the dynamic load is applied, the static load structure can be calculated according to the principle of the new and old sections working together. In the case of structure, it is difficult to form plastic zone. Without considering the redistribution of stress, the situation before and after reinforcement will be calculated separately, and then the sum of them will be calculated.