Post-earthquake Reconnaissance Research Articles

Improved Image Analysis for Evaluating Concrete Damage

The use of images, whether in routine maintenance, or postearthquake reconnaissance, has quickly become the preferred approach to record and archive the exterior damage of existing infrastructure. Postsurvey analysis of these images, coupled with careful record keeping, provide invaluable data regarding the health of a structure. However, often significant amounts of data are obtained, especially for large structures, such as bridges. Therefore an automated procedure, which reliably and robustly reports on damage observed from these images, with minimal human intervention, is desirable. To this end, in this work, we present a statistical-based method for conducting image analysis, specifically for the purpose of evaluating concrete damage (cracks, spalling, etc.). We illustrate the derivation of the method, which is grounded in Bayesian decision theory and subsequently present results of the analysis of images with discrete cracks to illustrate its promise.

Seismic Response of a Composite Landfill Cover

The Olympic View Sanitary Landfill (OVSL) near Port Orchard, Washington, is a modern solid waste sanitary landfill covered, in part, by a composite cover system. The site was subjected to a free-field peak horizontal ground acceleration on the order of 0.16 g during the 28 February 2001 Moment Magnitude 6.8 Nisqually earthquake. To the knowledge of the writers, this is the first documented case history of a composite landfill cover shaken by strong ground motions. Postearthquake reconnaissance did not find any signs of earthquake-induced permanent displacement of the composite cover system. Accelerograms recorded within 1 km of the facility, the results of site-specific shear wave velocity measurements and laboratory interface shear testing, and these postearthquake observations provide a unique opportunity for a posteriori numerical analysis of this important case history. The seismic performance of the OVSL composite cover system was evaluated using four commonly used methods for seismic design of landfill cover systems. These methods include two simple screening procedures, a more rigorous screening procedure, and a decoupled equivalent-linear site response/Newmark-type permanent deformation analysis using the accelerograms recorded at the nearby strong motion station. The yield accelerations of the composite cover system, required for all four methods, were calculated using the results of construction quality assurance interface shear strength conformance testing. All four methods produce results consistent with the observed performance. However, the two simple screening procedures were significantly more conservative than the other two more rigorous methods.

Modelling failures in existing reinforced concrete columns

Experimental research and post-earthquake reconnaissance have demonstrated that reinforced concrete columns with light or widely spaced transverse reinforcement are vulnerable to shear failure, and in turn, axial failure during earthquakes. Based on experimental data, failure surfaces have been used to define the onset of shear and axial failure for such columns. After the response of the column intersects the failure surface, the shear or axial strength of the column begins to degrade. This paper introduces a uniaxial material model that incorporates the failure surfaces and the subsequent strength degradation. When used in series with a beam-column element, the uniaxial material model can adequately capture the response of reinforced concrete columns during shear and axial load failure. The performance of the analytical model is compared with results from shake table tests.Key words: shear failure, axial failure, beam-column elements, failure surface, earthquakes, reinforced concrete, columns, collapse, structural analysis.