Long-Span Truss Structures for Low-Vibration Environments

With the advancement of science and technology, vibration control becomes an increasingly significant requirement in facility design. Historically, waffle slabs have been widely used in the process floor design in semiconductor production facilities (Fabs), where a vibration level of VC-D (6.25 μm/sec) is often required to host all sorts of vibration-sensitive fabrication tools [1]. In a less stringent vibration environment, for example, in hospitals and general optical labs, concrete joist slab with stiffeners could be a suitable design option. In both of the two approaches, the effectiveness of vibration control in floor structures would be substantially reduced when the column span becomes larger. As a result, it is technically difficult and financially inefficient to adopt conventional waffle slab or stiffened joist slab in a long-span facility design. The article presents the vibration analysis and test results of a long-span truss facility recently constructed in Asia. With 5 x 3 bay finite element (FE) models, the midbay stiffness and fundamental resonant frequency of the process floor are evaluated. The mechanical and walker-induced vibration velocities of the floor are subsequently predicted and compared with the proposed vibration criteria. The model results are further substantiated with field data, which are measured at a number of locations randomly distributed over the process floor to represent the average-plus-one-standard-deviation level of the vibrations [3].