Field Experience Toward Validation of Performance-Based Assessment Procedures

Abstract eng:
Much intellectual capital has been invested in the pursuit of crafting increasingly more refined procedures that collectively comprise the performance based design and assessment methodology. Engineers who are educated at the public’s expense operate somewhere between banking and physics in their service to the public, and yet it is usually the banking that wins. If PBD is to turn the table in favor of the engineers, then its bag must be able to exhibit convincing cases that it performs well itself. Field confirmation is a pre-requisite for unconditional adoption. To our knowledge, no major building that has been explicitly designed according to PB anywhere in the world has ever experienced a strong-enough earthquake that would confirm the validity of the design path. Post-de-facto assessment exercises for existing buildings are inconclusive at best. Every theory must pass the test provided by nature serving engineering as a reliable instrument. Earthquakes are seldom events, and there is as yet little empirical evidence for existing RC building performance well in the nonlinear range except under infrequently occurring conditions or in the lab. Building stock elements are less perfectly known, so there is more uncertainty in modeling them. This study proposes to answer the rhetorical question of “do we have the tools for forecasting building performance under actual earthquakes of real buildings, given their blueprints and their input motion?” In Turkey, cast-in-place, older-type RC buildings were subjected to near-field strong ground motions from three major earthquakes. This occurred over a time span of eleven years. Three identical institutional buildings that had been built to the same design templates were shaken by three different M6.3 or larger earthquakes. The input ground motions recorded in the near-field (less than 10 km R jb ) were directly relevant for the buildings. Given the damage information, input motions, design drawings and material properties for all of the buildings; we indulged in replicating analytically the structural damage that occurred in these buildings. Three dimensional (3D) analytical models of the buildings were created using state-of-the-art procedures. Bi-directional excitations have been applied to the models using nonlinear dynamic analysis capability. The results illustrate that the analyses results overestimate the global damage level for all buildings. The overestimation is more significant in one case where the building sustained a pulse-type motion without significant distress. The lackluster performance of the prediction exercise is interpreted as a strong caveat against the irrational exuberance that PBD is the long-awaited nostrum for earthquake engineering.

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