The strength of the materials used for high strength bolts is 4 ~ 5 times that of ordinary bolts, and the commonly used performance grades are 8.8 and 10.9. Grade 8.8 adopts high-quality carbon steel 35 or 45; grade 10.9 adopts alloy structural steel 20MnTiB, 40b and 35VB. There are two types of high strength bolts: large hexagon head bolts and torsion shear bolts. According to the specification of steel structure, the material of high strength bolt should conform to the current standard.

高強度螺栓的預拉力由材料的屈服度和螺栓的有效面積并考慮一定摩擦系數(shù)確定。高強度螺栓的預拉力是通過施工時緊固螺帽建立的，緊固(擰緊)螺帽的方法有如下幾種：

The pre tension of high strength bolt is determined by the yield of material, the effective area of bolt and the friction coefficient. The pretension of high-strength bolts is established by tightening nuts during construction. There are several methods for tightening (tightening) nuts:

(一)扭矩法

（1） Torque method

根據(jù)扭矩M與預拉力成正比的關系，先用普通扳手將螺帽初步擰緊，然后采用可顯示扭矩值的專用扳手擰規(guī)定的扭矩值。

According to the proportional relationship between the torque M and the pre tension, the nut is initially tightened with an ordinary wrench, and then the nut is screwed to the specified torque value with a special wrench that can display the torque value.

(二)轉角法

（2） Corner method

根據(jù)板層間緊密接觸后，螺母的旋轉角度與螺栓的預拉力成正比關系確定的一種方法。

According to the fact that the rotation angle of the nut is proportional to the pretension of the bolt after the close contact between the plates is a method.

緊固時，先用短扳手將螺帽擰不轉動的位置，然后再用長扳手將螺帽擰規(guī)定位置，以達到預拉力。

When tightening, first use a short wrench to screw the nut to the position that does not rotate, and then use a long wrench to screw the nut to the specified position to achieve the pre tension.

(三)擰斷螺栓尾部

（3） Screw off the bolt tail

用于扭剪型高強度螺栓，此螺栓有一特制的尾部。緊固時，用專用扳手套住螺栓和螺栓尾部，一個套筒正轉，另一個套筒反轉，在螺帽擰緊到一定程度時，螺栓尾部擰斷。由于螺栓尾部的槽口深度是按擰斷扭矩和預緊拉力之間的關系確定的，所以擰斷時就達到相應的預拉力值。

For torsion shear type high strength bolt, this bolt has a special tail. When tightening, use a special wrench to hold the bolt and the bolt tail, one sleeve rotates forward, the other sleeve reverses, and when the nut is tightened to a certain extent, the bolt tail will be broken. Because the notch depth of the bolt tail is determined by the relationship between the torque and the pre tightening force, the corresponding pre tension value is reached when the bolt is broken.

高強度螺栓連接中，摩擦系數(shù)的大小對承載能力的影響很大。試驗表明，摩擦系數(shù)與構件的材質、接觸面的粗糙度、反向力的大小都有直接關系，其中主要是接觸面的形式和構件的材質。為了增大接觸面的摩擦系數(shù)，施工時應將連接范圍內構件接觸面進行處理，處理的方法有噴砂、用鋼絲刷清理等。設計中，應根據(jù)工程情況，盡量采用摩擦系數(shù)較大的處理方法，并在施工圖上清楚注明。

In the high strength bolt connection, the friction coefficient has a great influence on the bearing capacity. The test results show that the friction coefficient is directly related to the material of the component, the roughness of the contact surface and the size of the reverse force, among which the form of the contact surface and the material of the component are the main factors. In order to increase the friction coefficient of the contact surface, the contact surface of the components within the connection range should be treated during construction. The treatment methods include sand blasting, wire brush cleaning, etc. In the design, the treatment method with larger friction coefficient should be adopted as far as possible according to the engineering situation, and it should be clearly indicated on the construction drawing.

除上述處理方式外，還有一種用手提式電動砂輪打磨接觸面的處理方法，打磨方向要與受力方向垂直，其抗滑系數(shù)相當于噴砂處理。

In addition to the above treatment, there is also a treatment method of grinding contact surface with portable electric grinding wheel. The grinding direction should be vertical to the force direction, and its anti sliding coefficient is equivalent to sandblasting treatment.