Design of Foundations for Large Dynamic Equipment in a High Seismic Region

摘要

Generally, foundations for large dynamic equipment are made of considerable amounts concrete, thus they contribute to a significant percentage of a project's total concrete quantity. Designing these dynamic foundations requires a series of static and dynamic analyses to meet the vibration requirement of the equipment and any seismic requirements of the local building codes. This article researches and compares different modeling methods, and then proposes an efficient approach for their design in high seismic regions. For design optimization, two different types of foundations should be considered for these areas: mats and piles. Liquefaction, downdrag on piles, bearing pressure, spring constants, soil stratification, water table, soil types, bearing depth, and settlement, can all affect a foundation. Reviewing the geotech report and performing a cost/risk analysis with the contractor should make it clear which type of foundation should be considered at a given locale. Engineers should design these foundations using a finite element modeling software that can handle dynamic loading. Modal analysis can be used to provide frequencies and displacement amplitudes to verify vibration performance criteria based on ACI 351 and the manufacture's requirements. Modal analysis can also be used to analyze seismic response spectrum per SAP time history analysis. In addition, a model based on static and quasi-static loads as required by the applicable building code should be analyzed. The ability to combine these models into one can help to solve these problems more quickly and efficiently. A case study for a foundation of steam turbine generator is presented, in which, the analysis features and design procedures used are described in detail. This may help design engineers understand the different advantages and results of finite element models, to pick the best modeling option for any given situation.