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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2.4. Local optimization solutions The seismic performance of the CA frames for low seismicity showed to be in general satisfactory. Identified failure mechanisms were often locally restricted and/or resolvable with reasonable effort. Concerning the CA direction, some of the main optimization proposals can be summarized as follows:  CS-1 : No specific measures needed.  CS-2 : Local strengthening of the lower chord of the roof truss.  CS-3 : No specific measures needed.  CS-4 : Strengthening of overstressed uprights at the bottom of the structure; strengthening of critically stressed spacers, or study/modification of boundary conditions and reassessment; stronger bolts for overstressed brace-to-upright connections (at the bottom of the structure).  CS-5 : Stronger cross sections for critical upright frame braces (higher bearing capacity). 3. Conclusions Automated Rack Supported Warehouses (ARSW) are special steel structures, which already have reached a significant market share. Because ARSWs provide several advantages over traditional warehouses, they will further gain interest with the ongoing rise of e-commerce. However, seismic design recommendations and guidelines tailored for ARSWs do not yet exist. Structural engineers, therefore, apply seismic design codes for regular steel structures and such for traditional steel pallet rack structures. Due to the special characteristics of steel rack supported warehouses the direct applicability of these guidelines and codes is questionable. The STEELWAR project (Advanced structural solutions for automated STEELrack supported WARehouses) aims to be a first step toward the development of specific seismic design provisions for the structural typology of steel rack supported warehouses. In this paper, current seismic design approaches as applied in practice have been assessed. Five rack manufacturers participating in the STEELWAR project were asked to design a double-depth automated steel rack supported warehouse for low seismicity conditions, employing their typical seismic design approach and their manufacturer-specific structural members. The resulting case studies were assessed by means of dynamic time history analyses. The current paper focuses on the seismic performance of the cross-aisle (CA) frames. The different design approaches were compared by evaluating the simulated seismic performance. The main focus was given to observed failure modes and the hierarchy of criticalities, i.e. the sequence of potential failure modes. For the investigated ARSW frames in cross-aisle direction, which were designed for low seismicity regions, the overall seismic performance was in general satisfactory. The identified overstress was limited to few details and specific restricted locations/elements of the structure. The assessment of the seismic performance lead also to the conclusion, that these details and/or restricted elements of the structure can be enhanced with reasonable effort by slight local modifications. Concerning design recommendations for the seismic design of ARSW cross-aisle frames, the following aspects should be considered during the design process: identification of the hierarchy of criticalities (demand to capacity utilization ratios); favoring ductile failure mechanisms over brittle ones; strengthening of local zones and realistic modeling of such zones (e.g. short spacers); respecting design rules to guarantee envisaged hierarchy of criticalities (capacity design); usage of increased safety coefficients for diagonal-to-upright connection verification, to force the damage into the braces rather than to the connections; specification of a limit value for the non-dimensional slenderness of the upright columns’ cross-sections; provision of overstrength to the uprights and their base connections so that their brittle failure does not precede the failure of other components; application of a reasonable behaviour factor q to the diagonal bracings and their connections (under consideration of the recommendations given above).