Structural health monitoring of a 32‐storey steel‐frame building using 50 years of seismic monitoring data

Abstract

The case study, Los Angeles 32‐storey residential building, has an exceptionally long seismic observation history, spanning 50 years (1971‐2020), during which it has experienced many earthquakes, some causing extensive damage in the metropolitan area. Records of 13 earthquakes are analyzed, including San Fernando of 1971, to find out if permanent loss of stiffness occurred in the structure since 1971 and to describe statistically its nonlinear elastic behavior, not related to damage. It is a rare example of an instrumented pre‐San Fernando earthquake steel‐frame building, constructed with some on‐site welded column‐beam connections, type of construction that exhibited weaknesses after the Northridge, 1994 earthquake. The identification method consists of fitting equivalent uniform and four‐layer Timoshenko beams models by waveform inversion of bandpass filtered impulse responses, which results in piecewise constant profiles of shear wave velocity (the damage sensitive parameter) and the elastic moduli ratio, reflecting the distribution of structural stiffness along the height. The nonlinear elastic behavior derived from the smaller amplitude data constitutes strain‐dependent baseline for future structural health monitoring of this building. This behavior reveals more prominent strain dependency in the longitudinal direction and stronger variation with strain toward the base of the structure.

Wave propagation in a doubly tapered shear beam: Model and application to a pyramid‐shaped skyscraper

“…The average shear-wave velocity 𝑐 𝑆 of the model (Gnd to 49th floors) was found to be 𝑐 𝑆 ≈150-160 m/s for both directions (with the NS direction being slightly stiffer), indicating almost symmetric lateral resistance in both transverse directions, consistent with its physical characteristics 4 and within the range observed in other steel moment frame buildings. 36,82 The variations of 𝑐 𝑆 along the height detected by fitting a multi-layer model were significant. The analysis revealed very large wave velocity between Gnd and 5th floors, consistent with the larger stiffness and smaller mass density in that part of the structure, as compared with the other parts (see discussion in Sections 4.1).…”

“…Later the method was applied to horizontal response recorded in buildings, in which case 𝑄 and the corresponding damping ratio 𝜁 = 1∕(2𝑄) represent the effect of overall attenuation of vertically propagating waves in the structure, for frequencies inside the passband of the impulse responses, that is caused by material damping, scattering from internal inhomogeneities, geometric spreading, and other factors. 10,36,82,86 If the structure is on rigid soil and the attenuation is solely due to viscous material damping with constant 𝑄, then the 𝜁 = 1∕(2𝑄) from Equation ( 67) would be equal to the modal damping ratios. However, in reality, the two estimates are not necessarily the same.…”

Quantifying modeling uncertainty in simplified beam models for building response prediction

“…Therefore, at least in theory, their seismic responses can be accurately approximated by using simple beam models. Since the pioneering work of Biot 13 and several key studies that followed, 14–17 there have been quite a few efforts wherein various beam models are devised or used to represent building structures—for relatively recent examples, see literature 18–25 …”

“…Since the pioneering work of Biot 13 and several key studies that followed, [14][15][16][17] there have been quite a few efforts wherein various beam models are devised or used to represent building structures-for relatively recent examples, see literature. [18][19][20][21][22][23][24][25] As lateral systems of buildings are usually combinations of various types of structural elements/subsystems-such as frames, walls, and braces-researchers realized that a single shear or Bernoulli beam might not be adequate to capture the overall seismic response. In 1965, Osawa 26 introduced the concept of the coupling beam in which uniform shear and uniform flexure (Bernoulli) beams are connected with rigid lateral elements to have similar displacements.…”

Applying the damage assessment for rapid response approach to the august 24 M6 event of the seismic sequence in central Italy (2016)

“…The recorded signal in buildings allows assessing their response to earthquakes and monitoring changes to their structural health (e.g., Rahmani et al, 2015;Rahmani and Todorovska, 2021). Past studies have demonstrated the relevance of assessing the building's fundamental period (Goel and Chopra, 1997), which is a key parameter for estimating the expected performance of buildings during earthquakes (Michel et al, 2010).…”