by Click “steel structure design” above to pay attention to the wide application of steel structure components in various steel structure buildings in China, including steel structure frame, steel truss, steel grid, steel cable structure, cold-formed thin-walled steel structure, light steel structure, steel pile and other types.
How should we evaluate the safety performance of steel components in a steel structure building? What is the difference between the safety appraisal control indexes of steel members in various steel structure buildings? According to relevant specifications (reliability appraisal standard for industrial buildings gb50144-2019 and reliability appraisal standard for civil buildings gb50292-2015), the safety appraisal of steel structure members shall be evaluated according to the three aspects of bearing capacity, structure and displacement or deformation unsuitable for bearing, and the grade of each tested member shall be evaluated respectively; the safety appraisal of steel structure joints and connection areas shall be evaluated according to the bearing capacity and deformation Construct two inspection items and evaluate the level of each node and connection domain respectively; For cold-formed thin-walled steel structures, light steel structures, steel piles, industrial areas with corrosive media, or steel structures in high humidity and coastal areas, the corrosion unsuitable for bearing shall be taken as the inspection item to evaluate their grade; Then take the lowest level as the safety level of the component.
1.
Bearing capacity when evaluating the safety grade of steel structure members according to the bearing capacity, the grade of each checking calculation item shall be evaluated respectively according to the provisions of Table 1, and the lowest grade shall be taken as the safety grade of the bearing capacity of the member.
The checking calculation of steel structure overturning, sliding, fatigue and brittle fracture shall be carried out in accordance with the provisions of relevant current national codes; The checking calculation of nodes and connection areas shall include the checking calculation of their plates and connections.
Table 1 safety grade of steel structure members assessed according to bearing capacity 2 When evaluating the safety grade of steel structure components according to the structure, the grade of each inspection item shall be evaluated respectively according to the provisions of Table 2, and the lowest grade shall be taken as the safety grade of the component structure.
Table 2 safety grade of steel structure members assessed by structure note: 1 structural defects also include defects left by construction: butt welds refer to slag inclusion, bubble, undercut, burn through, missing welding, insufficient welding, incomplete penetration and insufficient weld leg size; Rivets or bolts refer to missing rivets, missing bolts, dislocation, staggered arrangement and U-turn, etc; Other defects left by construction shall be determined according to the actual situation; 2.
Local surface defects of node and connection structure include slightly poor weld surface quality, slightly insufficient weld size, slight deviation of connecting plate position, etc; Obvious defects of joints and connecting structures include cracks at welding parts, looseness, deformation, fracture and falling off of some bolts or rivets, or cracks or significant deformation of gusset plates, connecting plates and castings.
3.
Displacement or deformation unsuitable for bearing when the safety of steel structural members is evaluated according to the displacement or deformation unsuitable for bearing, the following provisions shall be met: 3.1 for the deflection of truss, roof truss or bracket, when the measured value is greater than 1 / 400 of the calculated span of truss, its bearing capacity shall be checked and calculated according to this standard.
During checking calculation, the influence of additional stress caused by displacement shall be considered, It shall be rated according to the following principles: (1) when the checking calculation result is not lower than Bu level, it shall still be determined as Bu level, but it should be observed and used for a period of time; (2) When the checking result is lower than Bu level, it shall be determined as Cu level or Du level according to the actual severity.
3.2 for the lateral displacement of the truss apex, when the measured value is greater than 1 / 200 of the truss height and may develop, it shall be determined as Cu level or Du level.
3.3 for the evaluation of the deformation of other steel structure bending members that are not suitable for bearing, it shall be rated according to the provisions of Table 3.
Table 3 other steel structure bending members Evaluation of deformation unsuitable for bearing note: l0 in the table is the calculation span; LS is the short calculation span of space truss.
3.4 the evaluation of deformation of other steel structure flexural members that are not suitable for bearing shall be rated according to the provisions of Table 4.
(1) When the displacement is related to the whole structure, the same grade as the upper bearing structure shall be taken as the horizontal displacement grade of the column according to the evaluation results in article 7.3.10 of this standard; (2) when the displacement is only an isolated event, the influence of the additional displacement shall be considered in the checking calculation of the bearing capacity of the column and rated according to the provisions of this specification; (3) When the displacement is still developing, it shall be directly rated as Du.
Table 4 – Evaluation of lateral displacement grade not suitable for bearing.
3.5 for the bending of column and truss compression chord caused by out of limit deviation or other use reasons, when the measured value of bending vector height is greater than 1 / 660 of the free length of column, the influence of additional bending moment caused by it shall be considered in the checking calculation of bearing capacity and shall be in accordance with this specification Specified rating.
3.6 for double angle steel compression web members with overall bending deformation but no obvious local defects in the steel truss, when the overall bending deformation is not greater than the limit specified in Table 5, their safety can be rated as Au or bu according to the actual integrity; When the overall bending deformation has exceeded the limit specified in the table, it shall be rated as Cu or Du according to the actual severity.
Table 5 overall bending deformation limit of double angle steel compression web member of steel truss 4 Corrosion unsuitable for bearing when the safety of steel structure members is evaluated according to the corrosion unsuitable for bearing, the bearing capacity shall be checked according to the remaining intact sections, taking into account the stress eccentricity effect caused by corrosion, and shall be rated according to the provisions of table 6.
Table 6 evaluation of corrosion of steel structural members not suitable for bearing note: T in the table is the wall thickness of the original section of the member at the corrosion position or the plate thickness of the steel plate.
5.
Safety evaluation of steel cable components the safety evaluation of steel cable components shall be based on the project rating specified in this standard, It shall also be rated according to the following supplementary items: (1) if there are broken wires in the cable, it can be rated as Cu if the number of broken wires does not exceed 5% of the total number of steel wires in the cable; if the number of broken wires exceeds 5%, it shall be rated as Du.
(2) if the cable member is loose, it shall be rated as Cu or Du according to its actual severity; (3) it shall be directly rated as Du under the following circumstances: 1) cracks appear in the cable node anchorage; 2) The cable joints slip; 3) there is water seepage crack in the anchor plug of cable node.
6.
Joint safety evaluation of steel grid structure the safety evaluation of welded hollow ball joints and bolted ball joints of steel grid structure shall be in addition to the project rating specified in this standard, It shall also be rated according to the following items: (1) when the hollow spherical shell has visible deformation, it shall be rated as Cu; (2) when the hollow spherical shell has cracks, it shall be rated as Du; (3) when the barrel of the bolt ball joint is loose, it shall be rated as Cu; (4) when the bolt fails to screw into the bolt ball according to the length required by the design, it shall be rated as Du; (5) when the bolt ball has cracks, it shall be rated as Du; (6) If the bolt of the bolt ball joint is disconnected, it shall be rated as Du.
7.
Other supports, joints and connections (1) for friction type high-strength bolt connection, when the friction surface is warped and fails to form a closed surface, it shall be directly rated as Cu.
(2) For the bearing joint of long-span steel structure, when the hinged bearing can not achieve the rotation or slip required by the design, it shall be rated as Cu; when the weld of the bearing cracks and the anchor bolt deforms or breaks, it shall be rated as Du.
(3) For the rubber bearing, when the rubber plate is extruded and deformed with the bolt or anchor bolt, it shall be rated as Cu; when the rubber bearing plate slides relative to the top surface of the supporting column or beam, it shall be rated as Cu; when the rubber bearing plate is seriously aged, it shall be rated as Du..
