CEE Seminar: Base Isolation for Industrial Structures; Design and Construction Essentials

Abstract: Improved seismic performance objectives (immediate occupancy and continued operation) set by owners of high-tech manufacturing facilities have resulted in increased use of supplemental damping and base-isolation designs. This presentation reviews the design and construction process of industrial base-isolated buildings with focus on code requirements, design and analytical methodologies, and constructability challenges. Due to velocity/displacement-dependent behavior of base-isolation systems, the building code (IBC/ASCE-7) requires performing a Non-Linear Time History (NLTH) analysis to determine the seismic loading on the base-isolated structure. However, due to the complexity of NLTH and because the superstructure must be essentially elastic, the code also permits performing a staged analysis. The staged analysis consists of: 1) performing a linear (modal) analysis of the superstructure to determine the lumped-mass dynamic characteristics of the building, 2) performing a NLTH analysis of the isolation system and superstructure to determine system forces, displacements and base shears, 3) performing superstructure design using a linear (modal) analysis with scaled-base shear forces, and 4) designing the base isolator footings and support framing to resist the system design displacements and resulting forces. The required series of time history analyses are performed for a suite of time history records, each scaled to the Design Earthquake (DE) and the Maximum Considered Earthquake (MCE), variations of upper bound and lower bound isolator properties, and position of center of mass at each floor. A case study of a multistage analysis, design and construction of three concrete industrial buildings built on a single-base isolation slab is presented to discuss details and challenges related to design and construction of isolator selection, mounting and support, as well as the design criteria for utility displacement compatibility at the isolator moat, and reduced equipment and contents anchorage requirements.

Bio: Altoontash has more than 10 years of experience as a structural engineering consultant and more than five years of academic research experience in the field of structural analysis and design. He has performed analysis, design and evaluation for a variety of healthcare, industrial, commercial and high-tech projects working with a variety of building materials, including concrete, steel, masonry, wood, acrylic and glass. His expertise includes linear or non-linear structural analysis, new or remedial analysis and design, seismic design/retrofit/vulnerability assessment, base isolation, equipment anchorage, fragility and reliability analysis, geometrically complex structures, structural investigations and use of a variety of computer software packages related to structural engineering. He is a registered Structural Engineer in the state of California and holds a doctorate from Stanford University. In addition to his engineering practice, he is a part-time lecturer and has taught the structural steel design course at UCI.