Dapeng Town Industrial Park, Tongshan District, Xuzhou City, Jiangsu Province, China
Bolted ball mesh frame is a kind of large-span steel mesh frame, which is more common in large-scale building construction, the use of the mesh frame for large-span construction can effectively shorten the construction time, the construction process is relatively simple, can reduce the welding workload at the construction site, welding error is small and easy to adjust. However, in recent years, with the popularity of bolted ball mesh frame structure in the building, the phenomenon of mesh frame structure collapse often occurs, therefore, the control of the quality of bolted ball mesh frame, the stability of bolted ball mesh frame use, safety enhancement has an important role.
1.Bolt ball net frame project quality common problems
(1) Insufficient strength of high strength bolts
The tensile strength of high-strength bolts in bolted ball node mesh frame structure is the main factor affecting the bearing capacity of the node, and its strength is related to the surface hardness, so the quality of high-strength bolts can be guaranteed by hardness control, and the surface hardness test for high-strength bolts can guarantee the quality of bolts.
(2) High-strength bolts screwed into the bolt ball bolt length does not meet the requirements
During the installation and construction, the thread length of the high strength bolt screwed into the bolt ball has been hidden and cannot be measured, so it is impossible to judge the length of the screwed bolt, and if the screwed length is insufficient, there will be a hidden safety hazard, which directly affects the strength and stiffness of the net frame node connection.
(3) Excessive deviation of bolt ball processing
Bolt ball diameter, roundness, milling surface imbalance and thread deviation is too large, will make the net frame installation more than the permissible deviation, so that the net frame dimensions, axes, etc. can not meet the design requirements, affecting the net frame force performance, reduce the bearing capacity, resulting in a potential safety hazard.
(4) Dimensional deviation of pole processing and verticality deviation of cross-section
Quality problems and hazards: the length of the net frame rod processing, section of the verticality of the pipe axis and the axis of the mouth of the pipe deviation exceeds the specification allowed, will make the net frame assembly and installation of the difficult to install, assembly and installation or barely installed, resulting in geometric dimensions, the axis of the rod deviation is not in line with the design requirements, affecting the performance of the net frame, reduce the structural load-bearing capacity.
(5) Deflection and axis deviation of net frame installation
After the total assembly of
bolted ball net frame is completed, there are cases that the connection of high strength bolts and ball nodes is not tight, there are gaps, loosening, not tightened, and the overall deflection of the net frame exceeds the specification (i.e., exceeds the design value by 1.15 times), which will reduce the overall strength and stiffness of the net frame structure, and affect the safety of use.
(6) Large deflection and surface coating peeling and rusting during the use of net frame.
After the installation of the net frame structure, in the use of additional hanging load, deflection increase, and even beyond the design value of 1.15 times more than the specification, resulting in serious safety hazards. Mesh frame surface in 5~10 years or so serious painting flaking, rust and corrosion phenomenon, resulting in poor perception, but also threaten the structural safety of the mesh frame.
2.Quantity and method of steel mesh frame bolt ball detection
(1) Bolt ball and the materials used for manufacturing bolt ball nodes, their varieties, specifications, performance, etc. should be in line with the current national product standards and design requirements.
Inspection quantity: full inspection.
Inspection method: according to the product quality documents, Chinese labelling and inspection report.
(2) Bolted ball net frame in the product shall not have cracks and creases, etc..
Inspection quantity: 5% of the corresponding quantity of each specification, and should not be less than 3.
Inspection method: observation with 10 times magnifying glass and surface flaw detection.
(3) The bolt ball thread size should be in accordance with the current national standard GB/T 196 ‘Basic Size of Common Threads’, and the thread tolerance should be in accordance with the current national standard GB 197 ‘Common Thread Tolerance’ in the provisions of the 6H level of accuracy.
Inspection quantity: 5% of each specification is sampled according to the quantity, and it should not be less than 3.
Inspection method: choose to use the basic form of standard thread.
(4) bolt ball mesh frame on the adjacent bolt hole centre line diameter, structural roundness, size and angle of the allowable deviation should be consistent with the provisions of GB 50205-2020.
Inspection quantity: 5% of the number of each specification, and not less than 3.
Inspection method: check with calipers and indexing head instrument.
(5) Allowable deviation of bolt ball processing
Inspection quantity: 10% of the number of each specification, and should not be less than 5 .
3. The importance of bolt ball grid detection
Bolted ball mesh frame structure due to its excellent performance, so that the development and application of its speed and wide range. As the bolted ball node mesh frame does not need on-site welding, it is convenient to make, and the installation can be completed by erecting a small part of scaffolding, which saves materials and human resources, and at the same time shortens the construction period, with remarkable economic and technical benefits. However, if no attention is paid to the processing and installation process, it will lead to various quality problems such as rod deformation, deflection value is too large, and the harm produced is also very great, if not given enough attention to eradicate it will bring great safety hazards to the steel frame structure.
