| With the rapid growth of domestic electricity demand and the growth for power construction demand in countries along the “Belt and Road”,the foreign projects in the power industry are increasing,in order to enhance the international competitiveness of China’s EPC,it is becoming more and more important for the cost control of engineering investment and transmission towers,therefore,the refined design of transmission towers is also receiving more and more attention from the engineering community.The crossbracing is an important part of the transmission towers,we need to carry out more indepth and detailed tests and theoretical research on the cross-bracing to improve the construction standards,quality and economy.Two kinds of cross-bracing which commonly used in transmission tower sections are designed in this paper,12 groups of static loading tests are completed according to the different internal force ratio of the cross-bracing,the two kinds of sections cross-bracing are carried out numerical analysis by ANSYS,and compared the analysis results with the test results.The main conclusions are as follows:(1)Test results for only diagonal material section showed that when the cross-bracing was in tension-compression,the buckling failures around the minimum axis were occurred nearby the middle of the long part of the compression member(c-member),the bending axis was close to the parallel axis when the cross-bracing were both in compression.The smaller the tension-compression ratio(T-C ratio),the more obvious the S-type instability of the c-member was.T-C ratio has little influence on stability capacity of only diagonal material section,the maximum out-of-plane displacement of the section was always in the long part of the c-member.The calculation results of DL/T5154-2012 are a little conservative and correlate well with the test results;The calculation results of GB50017-2017 rapidly decrease with the increase of the T-C ratio,from insecurity to over-conservative;ASCE10-15 are close to the test results when the cross-bracing are in both compression and the T-C ratio is big,the rest results are unsafe;EN1993-3-1 are all conservative.(2)Test results for complex section with auxiliary material showed that when the cross-bracing was in tension-compression,the buckling failures around the parallel axis were occurred at the long part of the c-member,when the cross-bracing were both in compression,the buckling position moved towards the intersection with the increase of the T-C ratio,and the overall instability of the c-member was more obvious,the auxiliary material improve the stability of the section,and weaken the S-type instability of the cmember.T-C ratio has little influence on stability capacity of complex section when the cross-bracing are in tension-compression,T-C ratio has obvious influence when the crossbracing are both in compression.The maximum out-of-plane displacement of the section was between the intersection and the middle of the long part of the c-member,after reaching the stability capacity,the tension range of the c-member’s unconnected limb will expand with the increase of the T-C ratio.The calculation results of DL/T5154-2012 has the best agreement with the test results,but it is slightly conservative;GB50017-2017 and ASCE10-15 are unsafe when the section are in tension-compression,and are in good agreement with the test results when the section are both in compression,but GB50017-2017 is more conservative;EN1993-3-1 are unsafe only when the section are both in compression and the T-C ratio is large,the rest results are conservative.(3)The finite element results showed that the finite element in this paper can better judge the failure modes of the two sections under different T-C ratio,and calculated the corresponding stability capacity.The stability capacity of the two sections decrease with the increase of the T-C ratio,when the absolute value of the T-C ratio is large,the T-C ratio has little influence on the stability capacity.Increasing material strength,reducing slenderness ratio and width-thickness ratio,and increasing section size can increase the stability capacity of the two section,the increase of only diagonal material section is more obvious,when the two sections are both in compression,the improvement of the material strength is limited.The width-thickness ratio and other parameters have effects on the buckling position and the type of the bending axis.(4)According to the test results and the ANSYS analysis results,the correction coefficients of effective length of the compression member in the two sections were fitted,the relationship between effective length and the T-C ratio was quantified when the T-C ratio ≤-0.2,and proposed the modified calculation method,which effectively reduce the conservativeness of the calculation results of current code.The above conclusions can be used for reference in engineering design. |
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