| The steel-concrete composite I-girder is an open cross-section composite structure composed of a concrete slab and parallel I-beams connected by transverse bracing system.It is a fairly common structural form of composite beam bridges.Because of its simple structure and clear form of stress,convenience of prefabrication and maintenance,and outstanding durability advantages,it is quite competitive in the selection of small and medium-span bridges,which has the potential to realize‘standardized design’,‘prefabricated assembly’,and ‘rapid construction’ of modern bridge construction.The development and application of steel concrete composite I-girder structure is relatively mature in the foreign countries.However,due to the late start of research,it is not that common in China,and there are many problems to be solved urgently.In this paper,with a medium-span I-steel concrete composite girder bridge as the background,the key stress problems of the steel concrete composite I-girder bridge are researched and studied from three aspects: transverse load distribution,overall stability,and the mechanical performance of the negative bending moment area.The detailed research work of the study is summarized as follows:(1)Based on the composite bridge constructed with ‘using double beams as a unit for hoisting’ technology,the transverse load distribution was studied against this situation that unequal layouts of transverse bracing systems within and between the units.The numerical simulation method was used to establish a finite element model for analysis,and the results were compared with the calculated values of the theoretical method.The results showed that the load distribution coefficient calculated by the theoretical method is relatively larger,which tends to be safe.Then,through numerical simulation,the influence the number and size of braces,the number of main beams,the thickness of bridge decks,on the transverse load distribution was analyzed.The analysis results can provide a reference for the design and construction of composite bridges.(2)Based on the ‘erecting steel beams first and constructing concrete decks’ construction technology,the infulence of number and size of transverse braces on stability of parallel steel beams was studied using the finite element analysis.The results showed that increasing the number of transverse braces can greatly improve the overall stability of the system.After the increase of lateral connections from 2 to 5,the critical buckling load factor increases by more than 4 times;the number of transverse braces has a greater impact than the brace size.(3)In order to explore the cracking and bending performance of UHPC in the negative bending moment area of the continuous composite bridge,the static loading test a steel-UHPC composite beam under the negative bending moment was completed.The main test results of the whole test process from loading to failure of the beam were obtained,and the crack development,cracking performance and ultimate bearing capacity were analyzed.The results showed that when the crack width is less than0.13 mm,the load-maximum crack width curve is approximately straight;the cracking strength of the UHPC slab calculated by the elastic analysis method is 48.7MPa,which is much greater than the maximum tensile stress of the deck under the load of the real bridge;the ultimate bending bearing capacity of the test beam calculated by the the simplified plastic theory analysis method considering UHPC tensile strength of is in good agreement with the test value;the distribution of the tensile stress of the bridge deck of the composite beam bridge is obtained through establishing a finite element model based on engineering and it is recommended to lay the UHPC in the longitudinal range of 0.15L～0.2L in the negative bending moment area. |
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