Patent Publication Number: US-2022228487-A1

Title: Npr anchor rod

Description:
TECHNICAL FIELD 
     The present disclosure relates to the technical field of concrete-related new materials, in particular to an NPR rock bolt. 
     BACKGROUND 
     In the prior art, in the support of coal mine roadways and tunnels, rock bolts are the most used support equipment in terms of both scope and quantity. With the continuous increase of coal mining depth, the roadway-surrounding rock often shows the characteristics of large deformation, such as large deformation of soft rock, large deformation of rock burst, large deformation of impact, large deformation of gas outburst. In the current supporting rock bolts, the bolt body has a low elongation and is not suitable for the nonlinear large-scale deformation and failure characteristics of surrounding rock in deep roadways. Under the action of impact loads, the rock bolt may reach its yield strength instantaneously, then fracture and failure occur, and its bearing and protection capabilities are lost, which leads to destructive situations such as repeated repairation of the roadway, distortion of the steel frame, and cracking of the poured concrete. 
     SUMMARY 
     An embodiment of the present disclosure provides an NPR rock bolt to solve the problem in the prior art that the conventional rock bolts have a low elongation and cannot meet the requirement of large deformation of the surrounding rock. 
     In order to achieve the above object, the present disclosure provides an NPR rock bolt, comprising a bolt body, a tray and a lock; the bolt body is an NPR spiral steel bar, an outer surface of the NPR spiral steel bar is provided with a number of convex spiral ribs, and the spiral ribs have a spiral structure; and the tray and the lock are directly sleeved on a tail of the NPR spiral steel bar. 
     Further, the tail of the NPR spiral steel bar is untreated. 
     Further, the NPR spiral steel bar has a yield strength of 800-950 MPa and a tensile strength of 900-1050 MPa, and a deformation displacement of the NPR spiral steel bar is 200-350 mm/m. 
     Further, a nominal diameter of the NPR bolt is 14-26 mm. 
     Further, the tray is a metal butterfly tray. 
     Further, the lock comprises a metal lock piece and a lock sleeve that cooperate with each other. 
     Further, the spiral ribs extend along an axial direction of the NPR spiral steel bar. 
     Further, the quantity of the spiral ribs is 3-6. 
     Further, a number of the spiral ribs are evenly disposed along a circumferential direction of the NPR spiral steel bar. 
     The NPR rock bolt according to the present disclosure can achieve uniform elongation (200-350 mm/m) when the roadway-surrounding rock deforms greatly, and maintain a substantially stable working resistance. Therefore, the NPR bolt according to the present disclosure can absorb the energy of the surrounding rock by means of transverse resistance and large deformation, so as to still have a good supporting effect under the condition of large deformation of the surrounding rock to ensure the stability of the roadway. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of the structure of an NPR rock bolt according to an embodiment of the present disclosure; and 
         FIG. 2  is a schematic diagram of a stress-strain curve of the NPR rock bolt according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described in further detail below with reference to the drawings and specific embodiments, but they are not intended to limit the present disclosure. 
     Referring to  FIG. 1  and  FIG. 2 , according to an embodiment of the present disclosure, a NPR rock bolt with constant resistance and large deformation is provided. The NPR rock bolt comprises a bolt body  1 , a tray  2  and a lock  3 . The bolt body  1  is an NPR spiral steel bar, an outer surface of the NPR spiral steel bar is provided with a number of convex spiral ribs, and the spiral ribs have a spiral structure. The tray  2  and the lock  3  are directly sleeved on a tail of the NPR spiral steel bar. 
     The NPR rock bolt according to the present disclosure can achieve uniform elongation (200-350 mm/m) when the roadway-surrounding rock deforms greatly, and maintain a substantially stable working resistance. Therefore, the NPR bolt according to the present disclosure can absorb the energy of the surrounding rock by means of transverse resistance and large deformation, so as to still have a good supporting effect under the condition of large deformation of the surrounding rock to ensure the stability of the roadway. 
     Preferably, the tail of the NPR spiral steel bar is untreated. For example, the tail of the NPR spiral steel bar is not subject to any treatment such as thread rolling. Such structure has the advantage of avoiding the stress concentration at the tail thread, thereby avoiding the occurrence of tail thread cracking, and effectively improving the elongation of the rock bolt. 
     Refer to the schematic diagram of stress-strain curve shown in  FIG. 2 , in the present embodiment, the NPR spiral steel bar has a yield strength of 800-950 MPa and a tensile strength of 900-1050 MPa, and the deformation displacement of the NPR spiral steel bar is 200-350 mm/m. The maximum stress of bolt body is &gt;210 KN, the elongation is &gt;20%, the anchoring force of bolt body is &gt;200 KN, the anchoring length is &gt;1 m, the bearing capacity of bolt lock is &gt;210 KN, and the bearing capacity of tray is &gt;210 KN. 
     Preferably, the nominal diameter of the NPR bolt is 14-26 mm. As shown in  FIG. 1 , the tray  2  is a metal butterfly tray. The lock  3  comprises a metal lock piece and a lock sleeve that cooperate with each other. A hole is formed at the center part of the tray  2  for the bolt body  1  to pass through. The metal lock piece is sleeved on the tail of the bolt body and cooperates with the lock sleeve to form a lock  3 . 
     The structure of the bolt body  1  is as follows. The spiral ribs extend along the axial direction of the NPR spiral steel bar. The quantity of spiral ribs is 3-6. A number of spiral ribs are evenly disposed along the circumferential direction of the NPR spiral steel bar. 
     The NPR bolt according to the present disclosure can realize constant resistance and large deformation, and in the roadway where the NPR bolt according to the present disclosure is used as a supporting equipment, when the roadway-surrounding rock is subject to a certain deformation, the NPR bolt will be evenly stretched and the deformation energy in the surrounding rock can be released, and when there is large tensile deformation, the relatively stable working resistance can be maintained, the stability of the roadway can be realized, and the hidden safety hazards such as roof fall and collapse can be eliminated. 
     It should be noted that the terminology used herein is only for describing specific embodiments and is not intended to limit the exemplary embodiments according to the present disclosure. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that when the terms “include” and/or “comprise” are used in this specification, they indicate there are features, steps, operations, devices, components, and/or combinations thereof. 
     It should be noted that the terms “first” and “second” in the specification, claims and drawings of the present disclosure are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way are interchangeable under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. 
     Of course, the above are only preferable embodiments of the present disclosure. It should be noted that those skilled in the art can make improvements and modifications without departing from the basic principles of the present disclosure, and these improvements and modifications shall also fall within the protection scope of the present disclosure.