A six-story medical office building near the Fitzsimons campus had a problem. The structural engineers ran the numbers per ASCE 7-22 and the interstory drift on a conventional fixed-base design wasn't going to cut it—not with the stiff soils and the proximity to the Golden fault zone. That's where we came in. Base isolation seismic design flips the script: instead of bracing the building to fight ground motion, you decouple it. In Denver, where the subsurface transitions from weathered Pierre Shale to granular alluvium across a single zip code, the ground motion amplification can catch you off guard. We've seen it firsthand on projects from LoDo to DTC. The right isolation system—whether elastomeric bearings or friction pendulum—changes the conversation from “will it survive” to “will the occupants even notice.” For deeper soil profiling ahead of isolation design, we often pair this with a CPT test to map continuous stratigraphy without disturbing the sample, especially in the sandy lenses common along the Platte River corridor.
Base isolation doesn't fight seismic energy—it redirects it. In Denver's variable geology, that redirection can cut lateral force demands by half compared to fixed-base design.
Methodology and scope
Local considerations
Here's something you learn fast working Denver geotech: the static settlement behavior of the claystone tells you almost nothing about its dynamic response. We've pulled core samples that looked competent on the bench but degraded into a mess under cyclic triaxial loading. The biggest risk in base isolation seismic design isn't the isolator—it's the gap. If the moat around the isolated structure isn't sized for the full maximum considered earthquake displacement plus torsion, you're looking at pounding against the retaining wall, which defeats the whole point. Denver's temperature swings add another wrinkle; elastomeric bearings stiffen in January cold snaps, and we have to check the effective stiffness at 20°F against the design assumptions. Ignoring that seasonal shift can throw the isolation period off by enough to violate drift limits. And in floodplain zones near Cherry Creek, the water table complicates the isolation interface construction sequencing, demanding dewatering and solid waterproofing details that are easy to under-budget.
Applicable standards
ASCE/SEI 7-22: Minimum Design Loads and Associated Criteria for Buildings and Other Structures, Chapter 17, IBC 2021: International Building Code, Section 1705.13 (Seismic Isolation), AASHTO Guide Specifications for Seismic Isolation Design (LRFD Bridge), ASTM D4014: Standard Specification for Plain and Steel-Laminated Elastomeric Bearings for Bridges
Associated technical services
Full Isolation System Design & Nonlinear Time History
We develop complete isolation packages—bearing schedules, moat wall details, and utility crossings—backed by nonlinear time history analysis in ETABS or PERFORM-3D using site-specific ground motions matched to the Denver Basin's uniform hazard spectrum.
Peer Review & Construction Support
Independent design verification for isolated structures, plus construction-phase support including isolator prototype testing oversight, installation tolerances, and long-term monitoring plans for critical facilities.
Typical parameters
Frequently asked questions
What's the rough cost range for base isolation seismic design on a mid-rise Denver project?
For a typical mid-rise commercial or institutional building in the Denver metro area, the structural design and analysis package for base isolation seismic design generally falls between US$4,690 and US$8,340, depending on the number of isolators, complexity of the superstructure, and the level of peer review required by the jurisdiction. This covers the full design, not construction costs.
When does base isolation make more sense than a conventional moment frame in Denver?
It's a strong candidate when you have a Risk Category III or IV building, sensitive equipment inside, or a stiff structural system that attracts high seismic forces on a Site Class C or D profile. If continued operations after an earthquake matter—think hospitals, data centers, emergency operations centers—isolation often pays for itself in reduced damage and downtime.
How do Denver's specific soil conditions affect isolator selection?
The Denver Basin's interbedded claystone and sandstone layers create a stiff site profile that amplifies short-period motion. That pushes us toward isolators with longer effective periods—often friction pendulum systems or high-damping rubber bearings with a target period above 3 seconds. We also have to check near-fault effects from the Golden fault system, which can impose pulse-type demands that elastomeric bearings handle differently than sliding systems.
What testing is required for the isolators once designed?
ASCE 7-22 mandates prototype testing of at least two full-scale isolators per type, with dynamic testing to confirm effective stiffness and damping at design displacement. Production testing follows on every manufactured unit. We specify the testing protocol, review the lab results against our design values, and sign off before any bearing ships to the Denver site.