Bench–shelf system dynamic characteristics and their effects on equipment and contents

Abstract

Economic losses during past earthquakes are strongly associated with damage and failure to nonstructural equipment and contents. Among the vast types of nonstructural elements, one important category, is scientific equipment in biological or chemical laboratories, These equipment are often mounted on heavy ceramic bench-tops of bench-shelf systems, which in turn may amplify the dynamic motions imposed. To investigate the seismic response of these types of systems, a series of shake table and field experiments were conducted considering different representative bench and shelf-mounted equipment and contents. Results from shake table experiments indicate that these equipment are generally sliding-dominated. In addition, the bench-shelf system is observed to be very stiff and when lightly loaded, has a fundamental frequency between 10 and 16 Hz. An approximate 50% reduction in the first and second fundamental frequencies is observed considering practical loading conditions. Insight into a broader range of system response is provided by conducting eigenvalue and time history analyses. Non-linear regression through the numerical data indicate acceleration amplification ratios Ω range from 2.6 to 1.4 and from 4.3 to 1.6, for fixed-fixed and pinned-pinned conditions, respectively. Both the experimental and numerical results support the importance of determining the potential dynamic amplification of motion in the context of accurately determining the maximum sliding displacement of support equipment and contents.