PSI - Issue 44

Marius Pinkawa et al. / Procedia Structural Integrity 44 (2023) 2342–2349 Marius Pinkawa, Cristian Vulcu, Benno Hoffmeister / Structural Integrity Procedia 00 (2022) 000–000

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Diagonal braces connecting the uprights to form the upright frame have a utilization ratio from 0.52 (CS-3) to 0.95 (CS-1). Member stability is the governing failure mode, besides for case study CS-5, where member stability and cross section capacities are almost identical. Given that all brace utilization ratios are smaller than 1.0, no buckling in compression and no plastic action in tension is expected to take place for the given seismic hazard (10% probability of exceedance in 50 years or 475 years return period). The connections at the joints of upright frame braces to uprights have a utilization ratio of well below 1.0 for case studies CS-1, CS-2 and CS-3. For case study CS-4 the maximum utilization ratio is 1.06. However, only connections of two braces at the very bottom of the structure are overstressed. All other brace-to-upright connections have a maximum utilization factor of 0.93. Thus, this overstress is probably insignificant for the overall behavior of the structure. Case study CS-5 on the other hand has moderate to very large utilization factors, depending on which thickness is applied for one of the brace cross sections. Some inconsistencies existed in the provided data, why two different options have been evaluated. In the numerical model the smaller thickness has been applied. With the larger assumed option, the utilization factor is still 1.27. Thus, the connection is overstressed, and its failure might be expected. Spacers are defined as the members interconnecting the single upright frames. They are built as trusses (CS-1), Z shaped bracing (CS-3) or single horizontal braces (CS-2, CS-4, and CS-5). The single horizontal bracings are either hinged at both ends (CS-2) or rigidly connected to the uprights (CS-4 and CS-5). While the truss, Z-shaped bracings or hinged horizontal braces are stressed in axial forces, the rigidly connected horizontal braces are stressed in shear and bending. These different philosophies of spacer design are clearly visible in the utilization ratios. While for the former approach spacers are barely stressed, very large utilization ratios occur for the latter approach. Due to large shear and bending demands, spacers are overstressed for case studies CS-4 and CS-5. While overstress is only slight for case study CS-5 (utilization ratio of 1.08), a very large overstress of 3.60 is evaluated for the spacers of case study CS-4. Moreover, overstress is present at many spacers throughout the structure. Thus, failure of these spacers is to be expected for case study CS-4 if their connections are assumed as perfectly rigid. In reality, their connection behavior is probably not perfectly rigid, which would decrease the seismic demand on spacers. Finally, the roof truss is overstressed only for case study CS-2. The overstress takes place at the lower chord between the upright frames, due to introduced large shear forces. For the other case studies, the utilization ratio of the roof truss is rather low. An illustration of the hierarchy of criticalities in CA direction for CS-2 frame is shown in Fig. 5. One of the main goals of this evaluation was to assess which structural members are the first to fail during the earthquake excitation. The demand to capacity ratios (D/C) within Fig. 5 are reported for two steps (i.e.: D/C = 1.1 to 1.0 and D/C = 1.0 to 0.9), illustrating the state of the CS-2 frame as well as the location of the critical members corresponding to each of the two steps.

D/C = 1.1 to 1.0

D/C = 1.0 to 0.9

Roof truss (lower chord)

Roof truss (lower chord)

Brace to upright connection

Diagonal brace

Base plate (combined pullout and concrete-cone failure+ anchor failure in shear)

Lower upright

Connection failure in the current D/C range Connection already failed within larger D/C ranges

Element failure in the current D/C range Element already failed within larger D/C ranges

Fig. 5. Hierarchy of criticalities in CA direction for Case Study 2 (CS-2).