Key Factors in Seismic Design for Industrial Facilities

In regions prone to frequent earthquakes, ensuring the safe and stable operation of industrial facilities has become a critical challenge. Seismic protection design has emerged as an indispensable component of modern engineering projects. This article examines key elements of earthquake-resistant design for industrial infrastructure, focusing on seismic restraint systems, vibration isolation equipment, and protective measures for pipelines and machinery.

At a Canadian nuclear power plant, seismic restraint devices were installed on feeder pipes, anchoring them to the calandria shield tank surface beneath the reactor face. These threaded shaft assemblies, classified as support structures under ASME B&PV Code NF design rules, limit feeder movement during seismic events to reduce earthquake-induced loads. Post-installation "cold spring" treatment ensures optimal performance during actual earthquakes.

Equipment with vibration isolation in high-seismic zones requires specialized restraint systems that don't compromise isolation performance. While some isolators integrate restraint capabilities, most require separate three-dimensional restraint systems. Light suspended equipment may use slack braided steel cables, with all systems requiring structural engineering review and code compliance.

Spring-mass isolation systems assume rigid supports, making it crucial to construct sufficiently stiff support systems relative to isolator deflection. For lightweight structures like roof-mounted equipment, independent steel beam systems supported by foundation columns are preferred. When using concrete pads on thin roof slabs (less than 4.5 inches), dimensions should exceed equipment footprints by 12 inches to distribute loads effectively.

Rotating equipment with significant mass or high starting torque benefits from concrete inertial bases supported by spring isolators. While not improving isolation efficiency, these bases reduce displacement from driving forces and stabilize tall equipment. Typical pump bases weigh 2-3 times the supported equipment, while unbalanced compressors may require 5-7 times their weight.

Pipes transmit noise and vibration from fluid movement and connected equipment. Critical isolation measures include:

• Isolating the first three support points (approximately 50 feet for large pipes)
• Using flexible connectors for pipes over 5 inches diameter
• Accommodating thermal expansion in risers and long pipes
• In high-pressure systems, pulse attenuators with gas-filled bladders help dissipate fluid-borne vibration.

High-pressure ductwork (≥4 inches water static pressure) requires isolation for 30 feet from fans, supported by spring hangers with 3/4-inch minimum deflection. Sensitive locations like studios need isolation matching connected equipment for the first three supports, with reduced requirements beyond.

Maintaining acoustic ratings requires careful sealing around pipe penetrations. Holes should exceed pipe diameter by 1 inch, filled with insulation or fireproofing and sealed. Different sealing methods apply to concrete versus wood structures, with commercial pipe sleeves available for standardized solutions.

Rigid electrical conduits to isolated equipment must include flexible sections with sufficient slack to form 360° loops, preventing vibration transmission through electrical pathways.

Seismic events, caused by sudden crustal movements, can deliver devastating loads in seconds. Modern codes require structures to withstand minimum lateral loads (V) considering inelastic response, system redundancy, and ductility. With approximately 300,000 annual earthquakes worldwide, proper design is essential for facilities in active zones.

Mechanical, electrical, and architectural components require design for equivalent static forces and relative displacement demands. The seismic design category typically matches the supporting structure, with special considerations when non-building structures comprise less than 25% of combined weight.

Critical facilities like LNG plants require independent design review by seismic specialists, including analysis of site-specific spectra, nonlinear behavior under cyclic loading, and component performance verification. Additional measures address liquid sloshing, connection flexibility, and displacement accommodation.