Passenger Special Line Bearing Vertical And Horizontal Beam System Simply Supported Steel Truss Girder Bridges

Deck-through steel truss-concrete deck composite bridges with the concrete deck combining with stringers and cross beams so that they act together favors the bridge designers because they have big stiffness, low architecture height, low vibration, simple forces of main truss and so on. With the construction of passenger dedicated lines in China, this kind of bridge has been applied more and more often. In this paper, three bridges with span of 64 meters, 80 meters and 106 meters respectively were taken as examples. Two composite forms of deck system of each bridge were studied, the one is the concrete deck combining with stringers and cross beams (SCSC for short), and the other is the concrete deck combining only with stringers (SCOS for short). With space finite element method, the displacements, stresses and internal forces of the three bridges under primary forces and temperature difference were calculated and analyzed. The main research work is as follows:1. Deformation and mechanical behavior of three bridges with span of 64 meters, 80 meters and 106 meters respectively of SCSC and SCOS under the combination of primary forces were analyzed. The results show that rigidity and strength of all bridges are satisfied.2. The problem whether the rigidity of stringers, cross beams and lower chords matches well or not was analyzed. The results show that rigidity of the three members matches well, because the stress level of the three members is near. As to 106-meter-span bridge, stress lever of cross beams is larger than that of stringers and lower chords, after changing the two crossbeams in the end region of bridge for box section, the stress, especially, out-of-plane bending stress has dropped considerably.3. Mechanical behavior of three bridges with span of 64 meters, 80 meters and 106 meters respectively of SCSC and SCOS under temperature difference was analyzed. The results show that when temperature of main truss is 15 degrees larger than that of members of deck system, large tensile stresses of the cross of stringers and cross beams and on the edge or along the external stringers of concrete deck were caused. Therefore, adverse effect of temperature difference must be taken into account.4. The effect of the concrete deck combining with cross beams or not on rigidity and strength of bridges was analyzed. The results show that vertical rigidity of SCSC and SCOS of the same span bridge are very close; and lateral rigidity of SCSC of the same span bridge is larger than that of SCOS, and the difference of lateral rigidity between SCSC and SCOS of 80-meter-span bridge is largest, 64-meter-span, 106-meter-span bridge takes second, third place. Stresses of members of main truss of SCSC and SCOS are near, but stresses of cross beams of SCSC are larger than those of SCOS, however, stresses of stringers and longitudinal tensile stress of concrete deck of SCSC are smaller than those of SCOS. So the effect of the concrete deck combining with cross beams or not is small on members of main truss and is large on members of deck system.5. The co-action of deck system and main truss was analyzed. The results show that the degree for deck system to undertake longitudinal forces of SCSC is larger than that of SCOS, and decreases little by little from end panels to middle panels in the same composite form of deck system. However, it is largest in panel 2 of 80-meter-span bridge, due to the largest out-of-plane flexural rigidity of crossbeam 2.The research results of this paper can provide a design basis for the deck-through steel truss-concrete deck composite bridges with the concrete deck combining with stringers and cross beams and reference for other similar bridges.