Sensing-Based Seismic Assessments
by Ardalan Sabamehr, P.Eng., Ph.D.
Seismic damage predictions can be an important key parameter for asset managers and engineers to increase the general life safety of a given building. One of the most useful and unique features of the Sensequake approach is the ability to directly predict damage levels of structures from sensing tests. This patented approach allows for rapid building screening and analysis without the need to create complete and complicated theoretical models. Once a test is done on a structure, there are two levels of damage analysis that can be done in our analysis software: a global approach of the entire structure and a component-based analysis for structural and nonstructural components.
After a rapid test of a structure, the modal properties of the structure can be identified based on the ambient vibrations collected. Once confirmed, these properties, with the help of our software 3D-SAM, can conduct a modified linear time-history analysis of the structure. From there, important engineering demand parameters (EDP) can be extracted from the analysis and used for the seismic damage prediction of the building.
Steps taken by our analysis software, 3D-SAM, to obtain global-level (HAZUS) and component-based (FEMA P-58) seismic damage analysis
Global-based Damage Analysis
A global-based damage analysis of a building includes a breakdown of the structure's engineering demand parameters per floor or per story to relate it to damage estimations. This kind of analysis gives an estimation of the level of damage on an entire floor, encompassing the entirety of all structural components or all non-structural components, which is beneficial if in-depth. This global estimate allows a building manager to quickly get a sense of the overall performance of a structure, to make an informed decision on how to manage and mitigate risk.
The analysis itself ranks the damage into 5 different categories and are defined by HAZUS as the following:
"Building damage varies from “none” to “complete” as a continuous function of building deformations (building response). Wall cracks may vary from invisible or “hairline cracks” to cracks of several inches wide. Generalized “ranges” of damage are used... to describe structural and nonstructural damage, since it is not practical to describe building damage as a continuous function. ... For example, the Slight damage state extends from the threshold of Slight damage up to the threshold of Moderate damage. Damage predictions resulting from this physical damage estimation method are then expressed in terms of the probability of a building being in any of these four damage states." (1)
The 5 HAZUS building damage levels
Component-based Damage Analysis
A component-based analysis of a structure requires additional knowledge about the types of components present in the structure to get specific damage predictions. This applies to both the structural and a collection of non-structural components commonly found in buildings. Each of these will be processed similarly to the global analysis: on a floor or story basis per individual component based on the engineering demand parameters determined for the building.
These predictions are based on FEMA-P58, a large-scale study conducted on many different components. Comparing the building's seismic reaction to the performance curves defined in FEMA-P58 allows for damage estimates to be determined. Different thresholds are shown and associated with different damage levels of the component. In the figure below, the three damages levels DS1, DS2 and DS3 are shown in green, yellow and red respectively. These are associated to the following damage levels for the component:
DS1:Beams or joints exhibit residual crack widths > 0.06 in. No significant spalling. No fracture or buckling of reinforcing.
DS2: Beams or joints exhibit residual crack widths > 0.06 in. Spalling of cover concrete exposes beam and joint transverse reinforcement but not longitudinal reinforcement. No fracture or buckling of reinforcing.
DS3: Beams or joints exhibit residual crack widths > 0.06 in. Spalling of cover concrete exposes a significant length of beam longitudinal reinforcement. Crushing of core concrete may occur. Fracture or buckling of reinforcement requiring replacement may occur. (2)
FEMA-P58 Damage Curves
Both of these methods are rapid and solely based on the actual building information obtained from physical sensing tests. As well, the damages are performance-based, leading to the many benefits discussed in our last blog post.
For more information on this structural testing and how it can benefit your structures, contact us today.
1. Multi-hazard Loss Estimation Methodology (HAZUS MR4), (2003). National Institute of Building
2. Science, Department of Homeland Security, Federal Emergency Management Agency (FEMA)
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