Lumped Damage Mechanics: Tubular Steel Structures

14.1 Local Buckling Damage Model For Planar Mono-Sign Loadings

The steel frame structure is the other major alternative in the civil engineering construction industry. During test on both, tubular steel elements and RC frame members, the same phenomena: degradation of stiffness and strength are observed when the specimens are subjected to overloads; however, their fundamental causes are radically different in each case. As it has been discussed at length in the previous chapters, cracking is the phenomenon responsible for these effects in reinforced concrete structures; this is not the case of steel structures. Tubular steel elements are usually built with relatively thin walls; overloads on these components generate the appearance of small waves or wrinkles (see Figure 1a) that do not disappear after unloading the element; this phenomenon is called local buckling. For instance, Figure 1b shows the damage in a crane of the port of Kobe resulting from the 1995 great earthquake. In the picture it can be clearly appreciated the presence of local buckling in its columns.

Figure 1.

a) Local buckling in a tubular steel member of square cross-section b) Buckled crane legs after the 1995 Kobe earthquake Port Crane legs buckled due to soil spreading (UCB-EERC 1995/01) Courtesy of NISEE-PEER, University of California, Berkeley

14.1b Crane legs buckled due to spreading. (1995). Kobe Geotechnical Collection, Japan. University of California, EERC 1995/01 Aug. 1995: 39. Retrieved February 28, 2014 from http://nisee.berkeley.edu/elibrary/Image/K0127 .

Therefore, it must be concluded that the use of the Griffith criterion and the concepts of fracture mechanics should not be used in the modeling of the behavior of tubular frame members since crack propagation is not the main cause of structural degradation in this case. However, some of the other ideas described in chapter 9 still apply.