ATTEN: Manager Liu
ADD: Longhua Development Zone, Jing County, Hengshui City, Hebei Province
Example 1: A factory with a span of 315 meters and a length of 78 meters has a square pyramid bolted spherical grid supported by the upper chord. During the construction of the roof grid of the main factory building, the main joint suddenly collapsed as a whole, which is a major accident. Field adjustment found that many lower chord tendons were broken and bent, some high strength bolts were broken, belly tendons were buckled, bolts were bent or broken more commonly, ball tendons were broken, and the reasons of grid support falling were analyzed: (1) processing reasons, material management was confused, no necessary testing was carried out on the materials entering the field, and the carbon content of individual rods was low, and individual high strength. Bolt strength can not reach the qualified mark (2), construction reasons, construction does not follow the construction organization design is the main reason for the overall site of the grid. When the space truss is installed, it is assembled as a whole, and then it is loaded in bulk from one end to the other. When assembling and forming a stable unit system, there is no observation and measurement of the displacement and deflection of the support seats of some space trusses, no adjustment and fixing of the support seats of the space trusses, no necessary support in the span of the space trusses, and high-altitude bulk loading and roofing construction, resulting in the inadequacy of individual tight countries of the space trusses, large deflection of the space trusses, changes in overall dimensions, stalks and mule bolts. The stress of the joints is not in accordance with the design conditions, and the shear stress of the bolts of the joints is too large to break, which leads to the collapse of the space truss.
When the web rod at the support is connected with the mule bolt ball, individual bolt holes do not correspond to each other. Simple welding is adopted, and its bearing capacity only reaches about 40% of the design value. Construction has not been carried out in accordance with the procedures and specifications. Due to the tight construction period, without the completion of the main body of the grid and the welding of the supports, the roof construction team began to work on the roof. The roof load increased, and the overall collapse of the grid was also criticized. Engineering Example 2: The structure of an industrial factory building is a portal steel frame, 120 meters long, 72 meters wide, 24 meters long, three-way spanning truss, 12 meters high eaves, 6 meters apart from columns, hinged column foot. During the construction of the main steel frame, the whole collapse occurred suddenly, resulting in the collapse deformation of the main structure installed, and the crane was smashed. Cause analysis: (1) Design reasons, because of the main consideration of cost savings, relatively small cross-section of beams and columns, not fully considering the impact of construction load, leading to the overall collapse of buckling of individual components. For this kind of long-span rigid frame, the design of construction stage is very important, and the irrationality of construction organization should be taken into account.
In addition, for the Shen-long-span space truss, the use of swing columns in the middle column is not prohibited by the code, but it is impossible to achieve in practical engineering. This design is not conducive to the stability of the beam in and out of plane. Especially in the construction stage, the support system of the whole structure is incomplete, and the rigid connection of the middle column appears to be of great significance. (2) Construction reasons, from the construction point of view. The analysis silk truck girder has been installed, but the whole support system is extremely inadequate, and the tie rod and the corner support are not installed. Due to the incomplete support, there is a huge difference between the design state and the actual state, especially in the out-of-plane calculation length. After installing two spans, purlins and supports - scissors braces should be corrected and installed in time. Horizontal braces form an integral framework. That is to say, the state before the fall is in an unstable state. At this time, there is no need for too much lateral force, which is enough to make it overturn completely.