Seismic Response and Damage Detection Analyses of an Instrumented Steel Moment-Framed Building

Abstract

The seismic performance of steel moment-framed buildings has been of particular interest sjnce bdttle fractures were discovered at the beam{olum[ colnections in a number of buildings following the M 6.7 Norrhridge earlhquake of January 17, 1994. A case study ofthe seismic behavior of an extensively instrumented 13-story steel moment tiame building located in the greater Los Algeles aroa of California is described herein. Response studies using frequency domain, joint time frequency, system identification, and simple damage detection an:rlyses are performed using an extensive strong motion dataset dating from 1971 to the present, suppofied by engineering drawings and results of postearthquake inspections. These studies show that the building's response is more complex than would be expected liom its highly symmetrical geometq,. The response is characterized by low damping in the fundamental mode, larger accelerations in the middle and lower stories than at the roof and base, extended periods of vibration after the cessation of stong input shaking, beating in the response, elliptical pafiicle motion, and significant torsion du ng strong shaking at the top of the concrete piers which extend fiom the basement to the second floor The analyses conducted indicate that the rcsponse of the structure was elastic in all recorded earthquakes to date, including Nofthridge. Also, several simple damage detection methods employed did not indicate any shctural damage or connection fracturcs. The combination of a large, real stucture and low inshl-lmentation density precluded the application of nany recently proposed advanced damage detection methods in this case study. Overall, however, the flndings of this study are consistent with the limited code compliant postearlhquake intrusive inspections conducted after the Nofihridge earthqunke, which found no connection fractures or other structural damage.

Dynamic Characteristic Identification of Seismic-Excited Multi-Story Buildings through Response-Only Technique

“…Earthquakes shook these two buildings, and their acceleration responses during these ground motions were measured and documented. This paper presents results of investigations on dynamic characteristics of these multi-story buildings under three earthquake ground excitations, respectively; for the 14-story building the earthquakes investigated in this study a) The epicentral distance was measured from the earthquake epicenter to the building location, b) PGA presented in this table was peak acceleration measured in the basement of the building in the E-W direction [2,6] a) The epicentral distance was measured from the earthquake epicenter to the building location, b) PGA presented in this table was peak acceleration measured in the basement of the building in the E-W direction [2,6] investigated in this study, and peak acceleration response recorded in the building's basement in the EW direction [2][3][4][5][6]. These buildings' seismic responses were chosen since these response data have been well documented so that they were readily available for the study presented in this paper.…”

Dynamic Characteristic Identification of Seismic-Excited Multi-Story Buildings through Response-Only Technique

“…The performance of a multi-story building under seismic loadings was studied, and the results were discussed in [4,5]. In [4], the authors utilized the building's measured response to compute its dynamic characteristics using the method employed in [1][2][3].…”

“…Finite element analyses were carried out to obtain an appropriate numerical model for simulating the structure's time response under these loadings. The ARX method was also applied in [5] for structural system identification of a 13-story steelmoment resisting frame building to extract damping ratios and natural frequencies of the building under different earthquake excitations. Damage detection methods including frequency changes and presence of high frequencies were applied to detect fractures that occurred in the building due to the seismic ground motions.…”

“…Earthquakes shook these two buildings, and their acceleration responses during these ground motions were measured and documented. This paper presents results of investigations on dynamic characteristics of these multi-story buildings under three earthquake ground excitations, respectively; for the 14-story building the earthquakes investigated in this study a) The epicentral distance was measured from the earthquake epicenter to the building location, b) PGA presented in this table was peak acceleration measured in the basement of the building in the E-W direction [2,6] investigated in this study, and peak acceleration response recorded in the building's basement in the EW direction [2][3][4][5][6]. These buildings' seismic responses were chosen since these response data have been well documented so that they were readily available for the study presented in this paper.…”

“…However, finite element analyses of the buildings investigated in this study had been conducted in studies reported in [4,5,7]. Those studies were performed with the intent of obtaining numerical models for the buildings where their time responses were similar to the buildings' time responses recorded during earthquake excitations.…”