Analytical Modeling of Performance For Evaluation of Structural Safety

For structural design, the anticipated loads and the life of the structure are defined. Load and resistance factors are used to account for uncertainties in the magnitude and type of loading and for variations in material performance, section sizes, and construction details. However, many unforeseeable events can occur over the life of a structure, which may require an evaluation for the true structural capacity as a basis for evaluating structural safety. The ever-increasing demand for surviving larger and larger seismic events is a good example. In addition, structures are often asked to perform much longer than the original design basis and the effects of aging must be quantified. Sometimes, material performance issues, such as alkali aggregate reaction in concrete, can pose structural safety issues.

On occasion, the structural design itself may be inadequate if assumptions are used in the design calculations that do not actually develop in the completed structure. These situations require detailed, nonlinear modeling to evaluate the true performance and limit states of a structure for safety evaluation. ANATECH, a Structural Integrity Associates company has performed many such performance and limit state analyses using advanced modeling capabilities for concrete and steel.

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Loading Beyond the Design Basis

  • Increased probability of extreme loads such as earthquake or floods

  • Increased frequency or magnitudes of normal operational loads

Structural Life Extension and Effects of Aging

  • Freeze and thaw cycles

  • Corrosion of embedded steel

  • Concrete spalling and section loss

  • Deterioration of supporting soil or rock foundation

  • Rebar and grouted anchor bond performance

Material Degradation Over Time

  • Alkali aggregate reaction in concrete

  • Stress corrosion and erosion pitting in steel sections

  • Inadequate strength development

Inadequate Design or Construction Control

  • Unexpected resistance for thermal cycles

  • Inadequate welds or detailing at joint connections

  • Vibrations from loads near resonance frequencies

Maintenance Problems

  • Frozen or misaligned mechanical components

  • Failure of detection or override equipment

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