Design And Research On The Welded Hollow Spherical Joints Strengthend By Rib Stiffeners Out Side The Ball

Collapse of the grid structure of welded hollow spherical joints causes great threat topeople’s life and property, however there are no alternative strengthen method on joints, inpresent specification. Rib stiffener was proved to be an effective method to significantlyimprove the strength and stiffness of the welded hollow spherical joint. But it is verydifficult to set rib stiffener inside the hollow sphere of an existing ball grid joint system.So, an alternative method is to set rib stiffener outside the existing hollow ball. In thispaper, a comparable analysis of the hollow sphere with rib stiffener and withoutstrengthening was presented by test method. The result shows that the method is feasibleand can improve the compression and tension bearing capacity of welded hollow sphere.Furthermore the capacity increasing coefficient is derived.A numerical analysis that contains welding seam and non-welding seam is presented,the deformation and failure process of the welded hollow spherical joints strengthenedwith outside rib stiffeners were analyzed. The numerical simulations took into accountboth geometric and material nonlinearity, the influence of welding seam on the bearingcapacity of welded hollow spherical joint was studied. The result shows welding seam hadan influence on bearing capacity of welded hollow spherical joint, so the resultconsidering welding seam is more accessible to reality. A comparable analysis of thehollow sphere with rib stiffeners and without strengthening was presented when a hollowsphere was under uniaxial stress state and complex space stress state. Furthermore, thecapacity increasing coefficient is derived based on numerical simulation and verified byreinforcing conventional size welded hollow sphere.The bearing capacity of strengthened welded hollow sphere is relative to width of ribstiffeners, thickness of rib stiffeners, thickness of hollow sphere and outer diameter ofsteel pipe. By keeping the other parameters unchanged and changing one parameter, theinfluence of single parameter on capacity increasing coefficient was analyzed. The resultindicated bearing capacity increased as the thickness and width of rib stiffeners increased,and both of them are substantially linear; the bearing capacity decreased with the add ofwelded spherical thickness, and they were substantially inverseproportion. Under above conditions, compression bearing increasing coefficient was higher than tension; it provedrib stiffeners strengthened method was more effective for compressive welded hollowsphere.Two problems are encountered in actual construction process, one is sometime awelded hollow sphere can only be welded by three rib stiffeners, the other is rotating45degree in one of welded rib stiffeners of welded hollow sphere. After analyzing aboveproblems, we found capacity increasing coefficient was lower that four welded ribstiffeners and was important to increase the size of rib stiffeners, in the first case; in thelater case, turning45degree in one welded rib stiffeners had not affected on the increasingcoefficient. Based on above analyses, strenth design of welded hollow spherical gridstructure was presented.