Fatigue strength test of casting material GS-20Mn5V
The Small-sample up and down fatigue test method was used to test the fatigue limit of casting GS-20Mn5V which is the most popular casting material in civil engineering. The symmetric tension-compression fatigue test was on the high frequency fatigue tester. Ten useful test values were obtained through twelve tests with standard specimens. The mean value of fatigue limit of GS-20Mn5V is 202.8MPa after a statistic of the test results. The test provides the available data for engineering application.
Elastoplastic analysis and experimental study on spherical cast-steel joint of reticulated shells
Elastoplastic analysis and full scale experiment of a spherical cast steel joint used in steel reticulated shells of Chongqing Olympic Stadium was carried out. By forming finite element model and performing elastoplastic analysis, the stress and strain distribution of the cast steel joint were obtained. The stresses on test points in the surface of the cast steel joint were gained from prototype experiment. Combining theoretical analysis with the prototype experiment, static behavior and stress transfer pathway of the cast steel joint are analyzed, and the‘high low high low’variation regularity of stress distribution from pipe shaft to surface of spherical joint are pointed out. Based on the Von Mises strength criterion, the security and load bearing capacity of the joint are evaluated. In addition, the ratio of stresses on pipe shaft and pipe foot, as a main factor to measure the degree of the stress concentration, is also analyzed. It is indicated that the distribution of stresses on large spherical cast steel joint can be improved by controlling the ratio of stresses.
Ermüdungsverhalten von Stahlgussknoten in Brücken aus Stahlhohlprofilen
Due to their aesthetic and structural advantages, tubular space truss structures are enjoying increasing popularity in modern bridge construction. The use of cast steel nodes for the joints between the circular hollow section members is also becoming increasingly popular. The fatigue design of such joints however requires additional knowledge with respect to their fatigue resistance. The present work deals with the global fatigue behaviour of cast steel nodes used in longitudinal truss girders of steel-concrete composite bridges. The global fatigue behaviour of cast steel nodes in a truss girder is quantified on the basis of experimental investigations. The relative influence of the resistance of the cast steel node and the resistance of the welds is analysed as a function of various parameters. An economically optimal fatigue design consists of adapting the fatigue resistance of the cast node to that of the welds. The experimental results show very clearly that the fatigue behaviour is governed by the welds in all tested configurations. Their fatigue behaviour is therefore investigated in a research program conducted simultaneously. The present work concentrates on the adaptation of the resistance of the cast steel nodes to that of the welds. Consequently, allowable initial casting defect sizes must be defined as a function of the required fatigue resistance of the welds. Using a numerical boundary element model, they are calculated for cast steel nodes in a typical steel-concrete composite bridge. The results show that brittle failure of a node containing cracks does not occur. A crack depth equal to 90 % of the wall thickness at the crack location is therefore chosen as the failure criterion, assuming that a through-thickness crack is unacceptable. Varying between 28 and 88 % of the wall thickness, the resulting allowable initial casting defect sizes are very large. Aiming at a general application for steel-concrete composite bridges, the results of the numerical investigations are represented by an approximate formula for the stress intensity factor based on a constant correction factor. This approximation results in a considerable simplification of the procedure for the fatigue design of cast steel nodes established for the aforementioned typical composite bridge. The approximate formula is used to perform a parametric study. The influences of the utilisation ratio under traffic and fatigue loads, the cast steel fracture toughness and yield strength and the node dimensions on the defect size are described. Assuming a fracture toughness likely to be encountered in practice and a mean utilisation ratio of the node as well as a range of node dimensions, the allowable initial casting defect sizes are quantified. The present work shows that the fatigue resistance of the welded joints needs to be improved substantially in order to benefit from the high fatigue resistance of the cast nodes. Weld details including a backing ring offer a higher fatigue resistance than those without. Using the proposed design concept, allowable initial defect sizes in cast steel nodes can be estimated as a function of the required fatigue resistance.