Mechanic Behavior Of Cable-Braced Grid Shells With Bolted Joints

Cable-braced grid shell is a new type of single-layer latticed shells, especially suitable for glass roofs. Because the connection of tubes and the constraint of cables should be considered in joint construction, bolted joints are adopted in cabled-braced grid shells. Bolted joints have significant effect on mechanic behavior of cable-braced grid shells. However, mechanic behavior of cable-braced grid shells with bolted joints is a lack of research.Based on the theory of series springs stiffness, the formula of bolted joints'spring stiffness was derived. According to the experimental result, bolted joints'spring stiffness was calculated, and the correctness of series springs model was verified.Elliptic paraboloid cable-braced grid shells with bolted joints are taken as research examples. Based on the mechanic behaviors of bolted joints which have been obtained by experiments, the springs were used to simulate the rotational stiffness of bolted joints. Compared with cable-braced grid shells with rigid joints or traditional bolted joints, the mechanic behaviors of cable-braced grid shells with bolted joints have been researched. The effect of rise to span ratio, mesh size and span on the buckling load of cable-braced grid shells with bolted joints has been researched. The results show that too small stiffness of bolted joints will lead to the change of the buckling mode of grid shells. The distribution of the maximal compression stress of the tubes was similar to that of the structural displacement when the cable-braced grid shell collapsed. The deeper the concave dimple was, the higher the stress of the tube was. Compared with cable-braced grid shells with rigid joints, the buckling loads and structural stiffness of the grid shells with the bolted joints decreased to different extent. The buckling loads and structural initial stiffness of cable-braced grid shells with bolted joints are about 80% of those of cable-braced grid shells with rigid joints. Compared with the cable-braced grid shells with bolted joints, the buckling loads and structural initial stiffness of cable-braced grid shells with traditional bolted joints decrease by 15%and 8%. Ratio of rise to span, mesh size and span have little effect on the ratio of buckling load of cable-braced grid shell with bolted joints to that of cable-braced grid shell with rigid joints. Mechanic behavior of bolted joints has significant effect on the buckling load of cable-braced grid shell with bolted joints.The effect of mechanic behavior of bolted joints on the buckling load of grid shells with bolted joints was studied in details. The results prove that:with the decrease of the joint stiffness, the number of the half-wave in the buckling mode of the grid shells increases and the buckling mode changes from overall failure to local failure, and the space integrity is reduced. As the ultimate moment of bolted joints increases, buckling load of the grid shell increases, but the degree is limited. The effect of plastic displacement of bolted joints on buckling load of cable- braced grid shell is small. The smaller the plastic displacement of bolted is, the worse ductility of grid shells is. The results suggest that the joint stiffness of elliptic paraboloid cable-braced grid shells should not be less than 20% of the rigid joint stiffness and the ultimate moment of the bolted joints should not be less than 30% of that of the rigid joint. Estimation formula of the elliptic paraboloid cable-braced grid shells with bolted joints was given at last.