| For the development of State Grid and ultra-high voltage(UHV) projects in China, traditional latticed transmission tower could not meet the current demand, furthermore, adding another steel angle is a common way to mend and reinforce existent latticed tower for the simple reason that it is convenient in constructing . The generally accepted design technique treats such built-up cruciform section member formed by two equal-leg angles as a solid web cruciform section member, however, problems occur in full scale transmission tower tests and engineering applications. The test loads do not match with the design bearing capacity, and the failure mode of members is different from the design method. There is no detail design information in domestic and overseas codes for this kind of two equal-leg angle cruciform section member which could explain the different or guide the design. In consideration of the reasons mentioned above, a further research is made for built-up cruciform section member formed by two equal-leg angles, and the investigating work focuses on the following aspects:(1) Three different sectional dimension types of Q420(yield strength: 420MPa) steel single angle are used to form two equal-leg angle cruciform section member, which is L160×12, L160×14 and L160×16, respectively. The members are tested under axial and eccentric loading, and the total test number is 26. The unstable failure mode and failure mechanism are affirmed during the test and a comparison is made toward design method in current codes. A finite element analysis is conducted for more sectional dimension, boundary condition and slenderness ratio. Based on the experiment and finite element analysis, the applicability of nowadays codes is validated, column curves for single internode and double internode members are obtained, and the slenderness ratio correction factor for eccentric load test is calculated. A local stability limit value is gained through computing the reduction of elasticity modulus for single and double internode members.(2)The Q420(yield strength: 420MPa) steel single angles whose sectional dimension is L160×14 are used to run axial and eccentric load test, and the total test number is 12. Based on the finite element analysis of more sectional dimension and test results, stability coefficients and the slenderness ratio correction factor for double internode members are obtained.(3)The mechanism performance of filler plates is analysis by test results and finite element method. By the research on relationship between filler plates and members' bearing capacities, the parameters which affluence the members' bearing capacities remarkably are separated out. Different forms of filler plates and intervals are adopted in finite element analysis to find the relationship toward members' bearing capacity, and the influence of filler plates arrangement with a series of members' slenderness ration is test. Based on the test result and analysis, a filler plates design method is formed for two equal-leg angle cruciform section members.(4)Based on the comparison of experimental data and finite element analysis on lateral bracing in double internode members, the variation rule of lateral bracing axial force and member's loading is obtained, and the influence of lateral bracing slenderness to member's bearing capacity and lateral bracing axial force is found. A relational expression containing lateral bracing axial force, member's loading, slenderness ratio of lateral bracing and members is given.(5)A simplification of double internode member is made which change the actual boundary condition to that of simply supported beam, and calculation equation is established based on the three-moment equation. The bearing capacity involving lateral bracing stiffness in elastic-plastic stage is computed. The calculation results are comparison with current design method, and bearing capacity modified formula is given for double internode members.
|
PDF Full Text Request