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Metal brackets are commonly used in 18~24kg/m rails and 16~20 I-beams. However, since the rails are not structural steels, this usage is not reasonable enough in terms of the material itself. Ideally metal stent made of steel I-beam are mineral and - steel, and their cross-sectional geometry of the cross section parameters.
B. Structural Types of Metal Brackets All brackets can be divided into rigid structures and shrinkable structures. The left side of the figure is a rigid trapezoidal metal bracket. Trapezoidal metal supports require strong joints, reliable operation, simple structure, and easy assembly and disassembly. Commonly used joints are shown on the right. The base of the column base has a round, rectangular and trapezoidal shape. 
The general structure of a shrinkable metal arched bracket. The free single is composed of a curved top beam of R1 and two column legs with an upper end curvature of R2 . Both ends of the curved top beam are inserted and overlapped on the curved portion of the column leg to form a three-hearted arch. The lap length l is about 300~400mm , which is fixed by two clamps (each clamp includes a U -shaped screw and a U -shaped plate, two nuts). The column leg is welded 150 * 150mm 10mm thick iron plate is used as a base. In order to strengthen the stability of the bracket along the axis of the roadway, the metal tie rods can be locked with each other by bolts and clamping plates, and the metal brackets can be supported by the cross braces.
When the bracket is subjected to the surrounding rock pressure, the member begins to deform, so that R1 gradually becomes larger, and R2 gradually shrinks. After the local pressure reaches a certain limit, the curved top beam is relatively slipped along the leg portion, and the bracket is shrunk, thereby slowing down. The pressure of the surrounding rock on the support. If the pressure is continuously increased, the amount of shrinkage of the stent will also increase, so as to adapt to each other until the shrinkage of the stent is exhausted. At this time, R1 < R < R3, the stent has been transformed into a rigid stent.
The shrinkage of this kind of bracket can generally reach 30~35cm . If 18~22cm round logs are placed under the metal base of the column legs, an additional shrinkage of 12~14cm can be obtained .
The relationship between the bearing capacity and the shrinkability of the shrinkable metal bracket depends firstly on the geometry of the main components of the bracket and the elastic deformation of the joint, the friction surface fit and relative slip, and also on the bracket. The distribution of ground pressure and the deformation state of the support under ground pressure.
It is worth mentioning that when designing and using such a bracket, special attention should be paid to the direction of slippage of the bracket joint, so that it should be adapted to the direction of the main pressure of the roadway or the maximum direction of movement of the surrounding rock. Will deform quickly and lose its stability.
Assembled bracket - metal bracket
A. Large metal scaffold metal stent strength, small size, strong, durable, fire, is an excellent roadway support, recovered after shaping can be reused, so that despite the large initial investment, and the final calculation is economical. However, it should be avoided in the case of acidic water.
The shrinkage of the metal bracket is generally obtained by inserting the wooden mat at the interface or inserting the leg into the bottom plate. It has been proved that the insertion amount can reach 10 to 30 cm . Plasticity can also be obtained by using a curved column foot buckle on a log, which can be reduced to 10~15cm .
The bracket is characterized in that when the roadway is pressed, the bracket can provide a relatively large retractability by its own structure. Shrinkable clamp tightness can be adjusted and controlled, generally requires tightening nut on the clamp force is equal to 147Km, in order to ensure the setting load of the stent. The relationship between the radius of curvature R1 of the arch beam and the radius of curvature R2 of the arc segment of the column leg is