Structural Components and Systems

For The Seismic Retrofit of Tilt-up Buildings

Seismic Performance Levels

FEMA356 contains information on structural and non-structural performance levels that should be referred to when determining Seismic Performance Objectives for all seismic retrofit projects, including Tilt-Up and concrete block building retrofits. The following tables summarize some of the performance objectives that are discussed in FEMA356. Please refer to FEMA356 for more information.

Structural Performance Levels and Ranges

S-1
Immediate Occupancy
The post-earthquake damage state that retains the pre-earthquake design strength and stiffness, and is safe to occupy. Some minor structural repairs may be appropriate but not necessary to make the building safe to occupy.
S-2
Damage Control Range
The continuous range of damage states between the Life Safety Structural Performance Level (S-3) and the Immediate Occupancy Structural Performance Level (S-1). This range may be desirable to minimize downtime and repair time, to protect equipment that depends on the survival of the structure for its functionality, or to preserve historic features of the building when its too costly to design for the S-1 damage state.
S-3
Life Safety
The building will retain at least some of its strength against collapse and should prevent loss of human life. However, there may be injuries and the building could potentially be damaged beyond the point of economical repair. Some business owners may desire to have a higher standard of design safety for their building. This is especially true in the case of business’ s that would suffer dramatically if business was interrupted after a seismic event. Obviously any building that collapses proposed significant risks to life safety and would not satisfy this design objective.
S-4
Limited Safety Range
The continuous range of damage states between the Life Safety Structural Performance Level (S-3) and the Collapse Prevention Structural Performance Level (S-5).
S-5
Collapse Prevention
The building experience damage to structural components that weaken it so that it retains little or no lateral resistance against collapse either in part or in full. However, it will still continue to support its own weight provided that there is no further ground motion. Aftershock activity could cause collapse, but the initial event did not bring down the building.
S-6
Not Considered
A building rehabilitation that does not address structural performance at all, but instead focuses entirely on non-structural hazards associated with the building such as anchoring equipment and preventing damage to tenant property and improvments.

The following table summarizezs non-structural performance levels and ranges. For more information please refer to FEMA356.

Non-Structural Performance Levels and Ranges

N-A
Operational
The post-earthquake damage state where non-structural building components retain pre-earthquake function. Most nonstructural systems required for normal building use such as lighting, HVAC, and plumbing are functional. Some minor cleanup and a few repairs on non-critical components may be required.
N-B
Immediate Occupancy
Includes some damage to non-structural components but building access and Life Safety systems such as doors, stairways, elevators, emergency lighting and fire alarms and suppression systems, generally remain available and operational provided power or other required utilities are avialable.
Minor window breakage and slight damage could occur to some components. If the building is structurally safe, occupants should be able to safely remain in the building. Mechanical and electrical components should maintain function but some misalignments and internal damage may occur. Risk of life threatening injury from nonstructural components is very low.
N-C
Life Safety
Post Earthquake damage state that includes damage to nonstructural components but the damage is not life threatening. Damage can be significant and costly but damaged components have not become falling hazards. Egress routes within the building are not extensively blocked.
N-D
Nonstructural Hazards Reduced
The Hazards Reduced Nonstructural Performance Level includes damage to nonstructural components to the point of potentially creating falling hazards. High hazard components have been secured and will not fall into areas of public assembly. Egress routes and life support systems such as fire suppression systems and other similar life safety issues are not addressed.
N-E
Nonstructural Performance Not Considered
A building rehabilitation that does not address nonstructural performance at all that be classified as Nonstructural Performance Not Considered.