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Seismic retrofitting sits at the heart of earthquake engineering—it's where theory meets the urgent reality of protecting lives in existing structures. You're being tested on your understanding of force transfer mechanisms, energy dissipation principles, and structural load paths. The techniques in this guide represent different engineering philosophies for the same fundamental problem: how do we keep buildings standing when the ground beneath them starts moving?
Don't just memorize what each technique does—understand why it works and when engineers choose one approach over another. Exam questions will ask you to compare methods, evaluate trade-offs between stiffness and flexibility, and recommend appropriate solutions for specific building types. Know the underlying mechanics, and you'll be able to tackle any scenario they throw at you.
These techniques work by separating the structure from ground motion or allowing controlled movement between building components. Rather than fighting seismic forces head-on, they let the building "go with the flow."
Compare: Base isolation vs. seismic joints—both accommodate movement rather than resist it, but base isolation separates the entire building from the ground while seismic joints separate parts of the building from each other. FRQs may ask when each is appropriate: base isolation for critical facilities, seismic joints for complex plan geometries.
These devices convert kinetic energy into heat or other forms, actively reducing the seismic demand on structural elements. Think of them as the building's shock absorbers.
Compare: Damping devices vs. moment-resisting frames—both dissipate energy, but dampers are supplemental systems added to a structure while moment frames are primary structural systems. Dampers can be replaced after a major event; moment frames may require inspection and repair of yielded connections.
These techniques work by increasing the structure's capacity to resist lateral forces directly. They add strength and rigidity to prevent excessive drift and deformation.
Compare: Shear walls vs. steel bracing—both add lateral stiffness, but shear walls provide continuous resistance along their length while bracing provides concentrated resistance at specific bays. Shear walls are better for fire and acoustic separation; bracing preserves more usable floor area and allows for openings.
These methods enhance the capacity of individual structural elements rather than adding new systems. They're particularly valuable when the overall structural configuration is sound but individual members are deficient.
Compare: Concrete jacketing vs. FRP wrapping—both strengthen existing members, but jacketing adds significant mass and stiffness while FRP adds almost no weight. Jacketing is better for severely deficient members; FRP excels when moderate strength gains are needed without altering dynamic properties.
The strongest superstructure means nothing if the foundation fails. These techniques ensure adequate load transfer to the ground and prevent foundation-level failures.
Compare: Foundation retrofitting vs. base isolation—both address the building-ground interface, but foundation retrofitting strengthens the connection to resist forces while base isolation weakens the connection to filter forces. The choice depends on building type, soil conditions, and performance objectives.
| Concept | Best Examples |
|---|---|
| Movement accommodation | Base isolation, seismic joints |
| Energy dissipation | Damping devices, moment-resisting frames |
| Lateral stiffness | Shear walls, steel bracing |
| Load path completion | Diaphragm strengthening |
| Member strengthening | Concrete jacketing, FRP wrapping |
| Foundation improvement | Foundation retrofitting, soil stabilization |
| Lightweight solutions | FRP wrapping, steel bracing |
| Minimal architectural impact | Base isolation, damping devices |
Which two retrofitting techniques work by accommodating movement rather than resisting forces, and how do their applications differ?
A hospital needs to remain fully operational after a major earthquake with minimal structural damage. Which retrofitting approach would best achieve this performance objective, and why?
Compare and contrast concrete jacketing and FRP wrapping: when would an engineer choose one over the other for column strengthening?
An FRQ describes a 1950s concrete frame building with inadequate lateral resistance and a flexible roof diaphragm. Which combination of techniques would address both deficiencies, and in what order should they be analyzed?
Explain why adding shear walls to an existing building might actually increase seismic forces on the structure, and what complementary technique might address this issue.