Seismic Response And Failure Mechanism Of Single-layer Latticed Domes With Steel Columns And Braces As Substructures Considering Low Cycle Fatigue Of Steel

The single-layer latticed domes structure is the main form of long-span spatial structure.Because of its beautiful shape and reasonable force,it has been widely used all over the world,including earthquake-prone areas.Most single-layer latticed domes are built on the lower support structure.When an earthquake occurs,a single-layer latticed domes with a lower brace structure is often used as a refuge for people.Therefore,it is necessary to systematically study the failure mode and failure mechanism of single-layer latticed domes with steel columns and braces as substructures under strong earthquake,so as to ensure the safety of the structure under earthquake action.At present,the study on the strong earthquake response of single-layer latticed domes with steel columns and braces as substructures is to separate the lower brace structure from the upper latticed domes structure.But in fact there is an interaction between the lower brace structure and the upper single-layer latticed domes.Moreover,the existing research does not consider the effects of buckling of the members and low-cycle fatigue of the materials,which will result in inaccurate calculation results,and it is impossible to obtain accurate seismic response of single-layer latticed domes with lower brace structures under earthquake action.Therefore,the study of the collapse mechanism of the single-layer latticed domes with steel columns and braces as substructures should consider the effects of three factors:buckling of the members,low-cycle fatigue of the material and the lower brace structure.In this paper,the low-cycle fatigue performance of the circular steel pipe and the failure mode and failure mechanism of the single-layer spherical reticulated shell supported by the steel column under the action of strong earthquake are studied,and the following three aspects of work are accomplished:(1)The low-cycle fatigue test was carried out on the main rod-circular steel tube of the single-layer spherical reticulated shell.Through the analysis of the test phenomenon and the hysteresis performance of the specimen,it was found that the circular steel pipe specimen fractured under tensile loading,and the end section of the specimen breaks before the middle section of the span.The compressive bearing capacity of circular steel pipe specimens decreases sharply after compression buckling,and the decrease range is more than 70%of the maximum compressive bearing capacity,and the tensile and compressive bearing capacity is lower than that of the first cycle loading.Through low-cycle fatigue testing of round steel pipes,and the calculation formulas of key parameters in an existing low cycle fatigue constitutive model are fitted.The comparison between numerical simulation and experiment and mathematical statistics showed that the constitutive model can be compared.The constitutive model can well simulate the low cycle fatigue properties of circular steel tubes under axial reciprocating loading,and provides a valuable reference for the hysteretic simulation of common grades of steel circular steel tubes under axial reciprocating loading in China.(2)The finite element model of single-layer latticed domes with steel columns and braces as substructures was established by considering the buckling of member and low cycle fatigue of material.The failure mode and failure mechanism of single-layer latticed domes under strong earthquake are studied by IDA method.The results show that the low cycle fatigue of steel has little effect on the seismic response of single-layer latticed domes under small earthquakes,but the low cycle fatigue of steel has a great influence on the seismic response of single-layer latticed domes under strong earthquakes.Three failure modes of single-layer latticed domes are found:the failure of reticulated shell structure,the failure of lower supporting structure,the failure of reticulated shell structure and lower supporting structure;The PGA_u of single-layer latticed domes decreases or remains unchanged with the decrease of rise-span ratio,while PGA_y increases with the decrease of rise-span ratio;The increase of the brace section will increase the PGA_y,but at the same time reduce the ultimate bearing capacity PGA_u.The brace section should be determined according to PGA_y and PGA_u.(3)Using the above modeling method,the high-strength cable support is used instead of the circular steel pipe brace,and the seismic response of the single-layer latticed domes braced by the lower cable is studied by IDA method,and the seismic response of the lower cable-braced single-layer latticed domes is compared with that of the circular pipe-braced single-layer latticed domes.The results show that the first two order natural vibration periods of the lower cable braced single-layer latticed domes are larger than those of the circular pipe braced single-layer latticed domes,which indicates that the seismic force acting on the structure decreases after replacing the circular pipe brace with the high-strength cable brace.Its mechanical properties have been greatly improved;Under the action of large earthquake,the PGA_y of the lower cable braced single-layer latticed domes is obviously larger than that of the circular pipe braced single-layer latticed domes,which indicates that the seismic performance of the former is better than that of the latter,but there is no obvious regularity between the cable braced section and the latticed domes PGA_y.The optimal cable section should be calculated according to the seismic performance target.