Nonlinear time domain seismic response and performance evaluation of A-frame jumbo-size container cranes

Abstract

Seismic responses of A-frame jumbo-size container cranes are comprehensively studied by exciting them as realistically as practical to evaluate the adequacy of the conventional static approach routinely used for their design. Multiple design earthquake time histories corresponding to the structure and site-specific earthquake design spectra corresponding to specific return periods are selected for the nonlinear time domain dynamic analyses. Cranes are considered to be in service (i.e., boom down), (2) at rest (i.e., boom up or stowed) with a friction contact support condition, and (3) at rest with tie-downs installed conditions. They are represented by finite elements, and appropriate dynamic properties are used following the practices commonly used in the profession. The seismic responses, in terms of base shear force, vertical wheel load, main member stress, portal drift ratio, and uplift, are estimated to define several performance objectives and their corresponding limits. Two container cranes with different dynamic properties and their responses are used to make the final recommendations. The in-service operating condition appears to be the most critical. The variation in the stress responses between the cranes in the at-rest and in-service conditions is about 17 %. However, the uplift in the stowed crane can be about 82 % higher than that in the in-service crane. The commonly used lateral load method using the static concept may not always be conservative, especially for the base shear force and vertical wheel load. For example, the method significantly underestimates the base shear force by about 52 % for the slender crane and 26 % for the relatively stiffer crane. Thus, the nonlinear time domain approach proposed here should always be used. It will satisfy the performance-based seismic design concept under development at present.