Quality control in grid structure engineering.

 1. Quality control in grid construction

（1）quality control of bolt ball grid structure the bolt ball is composed of bolt, pipe sleeve, pin, cone head or sealing plate, which is connected by high-strength bolt ball of reinforcement bolt to form a spatial truss structure, and the structure carries out the load of baseball grid. Any quality problem components will endanger the overall safety structure. This should be a good quality component. Strict quality grid components are required before assembly, and unqualified components are eliminated to ensure the quality of the most important part of the project network structure. The factory certificate shall be checked and acceptance records shall be made for grid members entering the site. Meanwhile, sampling test shall be carried out among each group according to the specification. In addition, the inspection and test of bars can not be ignored.

（2） quality control of grid assembly and hoisting, pre assembly is required to ensure the correctness of formal construction. During the pre assembly, the site shall be leveled and tamped, and the setting out shall be accurate. The specification of the bolt ball and the correct position of the pressure bar shall be determined carefully according to the design model of the drawing, so as to prevent the wrong position of the tension and compression bar. During assembly, the bottom chord should be assembled first, then the elevation and axis of the bottom chord should be corrected and tightened, and then the web member connection and the upper chord assembly should be carried out. During this period, it should be prevented from being too loose or too tight, so as to avoid the assembly residual stress.

（3） quality control of accessories installation during the installation of roof panel purlin support, it should be fixed on the bolt ball with bolts. The purlin support must not be fixed on the bolt ball by welding method. It is necessary to prevent the reduction of thread shear and sliding resistance caused by high temperature during welding and the performance degradation caused by cracking of cold steel after welding. For the suspended ceiling, fire pipe, catwalk, heavy equipment and temporary construction erection, it is necessary to adopt bolt connection to hang on the ball joint (it should be noted that all suspended objects need to be checked by design, and the weight and quantity can not be increased arbitrarily), and welding connection is not allowed. It is very dangerous to prevent the weight of the equipment directly hanging on the rod, especially in the middle of the pressure bar. If the equipment is suspended in the middle of the pole, it is equivalent to adding a concentrated force in the span of the pole. The heavier the equipment is, the greater the corresponding concentrated force will be, and the greater the harm to the member will be, which may cause the bending failure and the instability of the grid structure and the overall collapse failure.