Nonbuilding and Special Structures
Modular construction for both facilities and process skids becomes popular due to its benefits, such as efficiency, speed, safety, quality, economy and convenience. Modular design mostly for process equipment, power delivery module (PDC), pipe-racks and other equipment which can be built together. Modularization also provides challenged tasks for structural engineers, such as supporting system of modules themselves; consideration of transportation; erection plan; anchorage, and foundation systems.
In the article, the system of modularized structures will be discussed. Just like buildings, we may consider moment frame, brace frame, shear wall system, or non-building structures based layout of equipment. Tubes, channel, W shape and angle are mostly used. The module size and weight depend on transportation, lifting plan or even the sizes of galvanized tank. No all modularized structures will be installed on a mat foundation directly. Based on type of modularized, PDC requires crawl space for electrical conduits, chemical or process modules require to collect water or chemicals in case for emergency situations. Therefore, pedestals, tall columns, or more complicated elevated structures may be needed to support the modules. At the boundary line of module and foundation, the seismic shear forces are significantly larger than that of stick-built system because all support structures are included in the modules. Considering the fabrication tolerances and loads, the anchorage details and types, such as welding embedded plates, post-poured anchor bolts, shear slugs on grout pockets will be illustrated in the article.
For high seismic region, the structure system should follow building codes such as ASCE 7-16. Because the modules are designed by equipment vendors who are not foundation engineers, it may be too late to be adjusted if a combined system is required to be analyzed. For example, the cantilevered column support is not a foundation, but a supporting structure. Following ASCE 15. 3, a combined analysis is actually required. The requirements for ASCE 15. 3 are: Type 1: the non-building structure is less than 25% of the combined structures. Type 2: the non-building structure is larger or equal to 25% of the combined structures, where fundamental period, T of non-building structure is less than 0. 06 S. For both Type 1 and Type 2, the module (non-building) can be considered as a rigid element per Chapter 13. Type 3: the non-building structure is larger or equal to 25% of the combined structures, where the fundamental period, T of non-building structure is 0. 06 S or greater, the non-building structure and supporting structure shall be modeled together in a combined model. All three types of system are provided in case study of this article. For the most typical modules, the finite analysis of combined system is analyzed base on Section 15. 3 of ASCE 7-16. Summarized table will be provided. Engineers can utilize the data for more economic design.
Additionally, the foundation structures of oil or water containments, fire walls modularized pile supported pedestals, columns will also be discussed in the article.