Ultimate Load Capacity of Single Steel Angles

Abstract

Design of single-angle members has been a controversial subject for some time. The design specifications differ considerably with regard to design of these members. The authors are to be thanked for their effort to shed more light in this area that clearly needs additional research. By considering a large range of slenderness ratios (60, 90, 120, 150, 180, and 210) in their experiments, the authors have covered a wide spectrum of single-angle struts. The experimental results are compared with ASCE Manual 52 (1988) for design of latticed transmission towers. This comparison indicates that the manual overpredicts angle capacity by a significant margin for both (L/r 120) struts. As has been emphasized by the authors, full-scale tests are often made on lattice transmission towers in the power industry. These tests indicate that the capacity of the towers is very close to that predicted by ASCE Manual 52. This is a clear indication that individual member tests, while serving a very useful purpose of verifying analytical methods, often fail to model the behavior of members assembled as a structure. The strut tests reported use ball end connections, thus removing all beneficial end restraint effect present in a tower. This may be the reason for the significant difference in capacity predicted by the tests and Manual 52. The paper reports L/r values for the tests. It would be useful to know the location of the points in the test setup between which the length L was measured. This will have an impact on the comparison with Manual 52, particularly for shorter angles. In the design office, typically, L is taken from work point to work point. Another point of interest would be any information about the lateral behavior of the members. Were the lateral deflections and rotations along the length measured in the study? It is the experience of the writers that steel single angles, when loaded through one leg in compression fail by exhibiting a bending (buckling) behavior predominantly about one leg only. This appears to be true whether the loading is through long leg or short leg. Perhaps the authors would like to throw some light on this subject. The tables showing the test and calculated ultimate load of single angles appear to have an error. For example, the test capacities shown in kips in Figs. 4 and 9 for test number 4 and I, respectively, do not convert to the corresponding capacities shown in the tables. The authors might wish to clarify the point. It is also interesting to compare the results of these tests with recently reported tests by Elgaaly et al. (1992) that were performed on the web members of a truss. Tests 18, 19,50,51, and 52 in Elgaaly et al. are similar in slenderness, angle size, and steel strength to test 21 by the authors as shown in Table 10. Manual 52 capacity shown in Table 10 is based on nominal section properties and nominal yield strength (248 MPa). Nominal values are used as will be the case in the design office. It is noteworthy that test 21 has lower slenderness ratio and higher F, and yet, has a test capacity significantly lower than that for the corresponding tests by Elgaaly et al. (1992). This perhaps is because the tests reported by the authors include the detrimental