6.3　Connection of High-strength Bolts

6.3.1　High-strength bolt hole shall be formed by boring.The hole edge shall be free of flange and burr，etc.

6.3.2　The surface of the steel plate at the joint of the high-strength bolt shall be smooth，as well as be free of welding splash，burr and oil stains.The surface treatment method shall meet the requirements of the design document.

6.3.3　The friction surface of the treated high-strength bolt shall be taken protective measures and be free of contaminations，oil stains and any marks.

6.3.4　Anti-sliding coefficient test for the friction surface connected by the high-strength bolt shall be in accordance with the following requirements:

1　Manufacturer and installation organization shall take the anti-sliding coefficient test by taking the manufacturing batch of the steel structure as unit.Every 2000t or below shall be taken as the manufacturing batch according to the quantities of divisional work.Each treatment process shall be taken single test when two or more surface treatment processes are selected.There shall be three groups of test pieces in each batch.

2　The test piece for anti-sliding coefficient shall be processed by the manufacturer.3sets of test pieces shall be accompanied as per batch when the elements leave the plant.The installation organization shall be responsible for the review of the anti-sliding coefficient.The friction surface of the test piece shall not be damaged in the transportation process.

3　The test piece shall be the same as its representative material of element，treatment process of friction surface，batch of steel，performance level and diameter of bolt.The test method and result shall meet the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

6.3.5　Torque coefficient shall be reviewed for high-strength hexagonal headed bolt connection pair.The bolt for review shall be chosen randomly from the bolt batch to be installed on the installation site.8 suits of connection pairs shall be chosen from each batch for review and meet the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

6.3.6　Pretension force shall be reviewed for torsional shear type high-strength bolt connection pair.The bolt for review shall be chosen randomly from the bolt batch to be installed on the installation site.8 suits of connection pairs shall be chosen from each batch for review.The test method and result shall meet the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

6.3.7　When installing the high-strength bolt connection pair，the quantity of the temporary bolts and punching pins penetrating through each node bolt hole set shall be determined by calculating possibly undertaken load during installation and be in accordance with the following requirements:

1　It shall not be less than 1/3 of the quantity of the bolt holes.

2　It shall not be less than two temporary bolts.The high-strength bolt for connection shall not be used as the temporary bolt.

3　Punching pins penetrating quantity should not be more than 30% of the temporary bolts.

6.3.8　The high-strength bolt shall be freely penetrated into the bolt hole and must not be forced to beat.When it is unlikely to freely penetrate，a reamer shall be used for reaming and trimming.The maximum trimmed hole diameter shall be less than 1.2 times of the diameter of the bolt.All surrounding bolts shall be tightened and the steel plate shall be adhered to closely before reaming.The reaming shall not be subject to gas cutting.

6.3.9　The high-strength bolt shall be installed after the central position of the element is adjusted，its penetrating direction shall be subject to convenient installation，and the stress shall be consistent unless structural reason.When installing the torsional shear type high-strength bolt connection pair，one side of the nut with circular table shall face towards one side of a washer with chamfer.When installing the highstrength hexagonal bolt connection pair，one side of the washer with the chamfer below the bolt head shall face towards the bolt head.

6.3.10　When initially twisting，re-twisting and finally twisting the high-strength bolt，the bolt at the node shall be tightened in sequence of extending from center to periphery of the bolt group.After finally twisting the connection pair，2 threads to 3 threads of the bolt shall be exposed，and 1 thread or 4 threads of 10%of bolts may be exposed.

6.3.11　The friction surface of connection of high-strength bolt shall keep dry and clean and be free of flange，burr，weld splash，crater，scale and dirt，etc..The friction surface shall not be painted unless stated in the design document.The connection of the high-strength bolt shall not be operated in the rain.

6.3.12　Before construction，torque wrench for construction of high-strength hexagonal bolt shall be corrected，its allowable deviation of torque shall not be larger than±5%，and the torque wrench shall be reused till it has been qualified.

6.3.13　After finally twisting the high-strength hexagonal bolt connection pair between 1h and 48h，finally twisting torque shall be checked，and the inspection result shall meet the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

6.3.14　The twisting of the high-strength bolt shall be divided into initial twisting and final twisting.The twisting of the large node shall be divided into initial twisting，re-twisting and final twisting and shall meet the following requirement:

1　The initial twisting torque value of the torsional shear type high-strength bolt shall be adopted according to the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

2　The initial twisting torque value of the high-strength hexagonal bolt should be 50% of the construction torque.The construction torque value shall be adopted according to the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.

3　Re-twisting torque shall be equal to initial twisting torque.

6.3.15　After finally twisting the torsional shear type high-strength bolt，wabbler at the tail of the bolt shall be twisted during finally twisting unless structural reason.The bolt connection pair without twisting the wabbler during finally twisting shall be finally twisted and marked by a torque method or a corner method.In addition，the finally twisting torque shall be checked according to the relevant requirements of the current national standard GB 50205 Code for Acceptance of Construction Quality of Steel Structures.