1、 For the quality of steel, the chemical composition analysis and mechanical properties sampling re inspection shall be carried out for the steel under one of the following conditions: 

(1) Imported steel products;

(2) Steel mixed batch;

(3) Thick plates with thickness equal to or greater than 40mm and designed with Z-direction performance requirements;

(4) The safety level of the building structure is grade I, and the steel used in the main load-bearing components of the long-span steel structure;

(5) Steel with retest requirements;

(6) Steel of questionable quality.

         1.Chemical composition analysis (main control item)

(1) Test index: carbon, silicon, manganese, sulfur, phosphorus and other alloy elements

(2) According to the standard: sampling and preparation of samples for the determination of chemical composition of steel and iron GB / t20066-2006 technical standard for the detection of building structures GB / t50344-2004

(3) Sampling method and quantity: chemical composition analysis of steel, full component analysis or main component analysis can be carried out as required.The sampling method used shall ensure that the analytical sample can represent the average chemical composition of the sample product.The analytical specimens shall be free from surface coating, dehumidification, dust removal, and other forms of contamination.The analytical specimens shall be free from porosity, cracks, porosity, burrs, folds or other surface defects as far as possible.The quality of the prepared analytical sample shall be large enough to permit the necessary retesting.For chip or powder samples, the mass is generally 100g.The chip sample can be made by drilling, cutting, turning and punching.When the chip like sample cannot be prepared by drilling method, the sample should be cut down or broken, and then crushed by crusher or vibration mill.There are disc mill and ring mill.All samples for powder analysis shall pass through the sieve with specified aperture.Analysis of chemical composition of steel, 1 sample for each batch of steel.

         2.Mechanical property test (main control item)

(1) Test index: yield point, tensile strength, elongation, cold bending, impact energy

          2、 Connection quality of fasteners and grid joints

          1.High strength large hexagon head bolt connection pair (main control project) high strength large hexagon head bolt connection pair shall be subject to torsion rejection coefficient and mechanical performance test before delivery, and re inspection of torsion rejection coefficient shall be conducted after the bolt enters the site.

(1) Inspection indexes: torque coefficient (compulsory inspection items), wedge load, minimum tensile load of bolt, guarantee load of nut, hardness of nut and washer

(2) According to the standard: Code for acceptance of construction quality of steel structures (GB50205-2001) technical conditions of high strength bolts, nuts and washers with large hexagon head for steel structures (GB / t1231-2006)

(3) Sampling method and quantity: bolts of the same performance grade, material, heat number, thread specification and length (when the bolt length is ≤ 100mm, the length difference is ≤ 15mm; when the bolt length is > 100mm, the length difference is ≤ 20mm, it can be regarded as the same length), machining, heat treatment process and surface treatment process are the same batch; bolts of the same performance grade, material, heat number, thread specification and machining are the same batch.The nuts with heat treatment process and surface treatment process are the same batch; the gaskets with the same performance grade, material, heat number, specification, machining, heat treatment process and surface treatment process are the same batch.The connection pairs composed of bolts, nuts and washers in the same batch are the same batch.Every 3000 sets are regarded as a batch, less than 3000 sets are regarded as a batch, and 8 sets of each specification and batch are taken.The high strength bolts submitted for inspection shall be in factory condition (within 3 months after delivery), and the surface shall be clean and the thread shall be free from damage.

          2. torsional shear type high-strength bolt connection pair (main control item) the torsional shear type high-strength bolt connection pair shall be subject to fastening pre tension and mechanical performance test when leaving the factory, and the bolt must be subject to fastening pre tension re inspection after entering the site.