ALBERT

Description: Delays in the postearthquake safety estimations of important buildings significantly increase unnecessary disorder in economic and social recovery following devastating earthquakes. Providing promptness and objectivity in evaluation procedures, damage detection through a structural health monitoring system using sensors attracts attention from building owners and other stakeholders. Nonetheless, local damage on individual structural elements is not easily identifiable, as such damage weakly relates to the global vibrational characteristics of buildings. The primary objectives of this research are to present and verify a method that quantifies the amount of local damage (i.e.,fractures near beam-column connections) for the health monitoring of steel moment-resisting frames that have undergone a strong earthquake ground motion. In this paper, a novel damage index based on the monitoring of dynamic strain responses of steel beams under ambient vibration before and after earthquakes is firstly presented. Then, the relation between the amount of local damage and the presented damage index is derived numerically with a parametric study using a nine-story steel moment-resisting frame model. Finally, the effectiveness of the damage index and an associated wireless strain-sensing system are examined with a series of vibration tests using a five-story steel frame test bed. © 2014 John Wiley & Sons, Ltd.

Description: Seismic monitoring system provides opportunities to observe possible damage or failure and weakening of structural components and to evaluate serviceability performance of a structure during an earthquake. This can be achieved by comparing structure recordings before and after the event or by identifying significant change in characteristics of structural response that may serve as indicators of failure or damage in progress. Excessive vibration on some parts of structure may become a serviceability concern for some buildings, and this also can be detected from continuous monitoring. Several factors such as characteristics of ground motion, soil condition, and geometry of the structure could cause excessive localized structural vibration, and by evaluating the responses, one can take remedial action. For a base-isolated building in particular, reduction of response of upper stories is critical to protect nonstructural elements or sensitive equipments on the building. In this paper, we describe a case study on seismic monitoring of a base-isolated building with the main focus on evaluation of serviceability performance. The study emphasizes on a influence of building asymmetricity on the seismic response. Results of the study are based on a long-term building seismic monitoring program for over 3years between 2010 and 2012 under various amplitudes of earthquake including the March 11, 2011 Great East-Japan Earthquake. © 2014 John Wiley & Sons, Ltd.

Description: Energy dissipation devices are necessary for base-isolated buildings to control the deformation in the isolation system and to dissipate the earthquake-induced energy. U-shaped steel dampers (also known as U-dampers) dissipate energy through plastic deformation of specially designed U-shaped steel elements. This type of device can be installed at several locations in the isolation system. U-dampers have been widely used in Japan for different types of isolated structures, such as hospitals, plants and residential buildings, since the 1995 Kobe Earthquake. Previous research has used static tests to estimate the performance of U-dampers. However, the ultimate plastic deformation capacities and hysteretic behaviors of full-scale U-dampers under dynamic excitations still remain unclear. In addition, it is unclear whether the initial temperature has an effect on the hysteretic behavior and plastic deformation capacity of U-dampers. In this paper, two series of dynamic loading tests of U-dampers were conducted to evaluate the issues described earlier. The major findings of the study are (i) the loading speed has little effect on the plastic deformation capacity of U-dampers; (ii) method to evaluate the ultimate plastic deformation capacities of U-shaped steel dampers of different sizes is established using a Manson–Coffin relation-based equation that is based on the peak-to-peak horizontal shear angle γt, which is defined as the lateral deformation amplitude (peak-to-peak amplitude) divided by the height of the dampers; (iii) the loading rate and the initial temperature have a minimal effect on the hysteretic behavior of the U-dampers; and (iv) a bilinear model is proposed to simulate the force-deformation relationships of the U-dampers. Copyright © 2014 John Wiley & Sons, Ltd. Copyright © 2014 John Wiley & Sons, Ltd.

Description: [No abstract available]

Description: In current seismic design, structures that are essential for post-disaster recovery, and hazardous facilities are classified as risk category IV and are designed with higher importance factors and stringent drift limits. These structures are expected to perform better in an earthquake event because a larger base shear and more stringent drift limit are used. Although this provision has been in the seismic design code over the last three decades, few studies have investigated the performance of essential structures. The aim of this study is to quantify the impact of higher importance factors and stringent drift limits on the seismic performance of steel moment resisting frames. A total of 16 steel structures are designed for Los Angeles and Seattle. Different risk categories are used for the design. The effects of the risk categories on the structural periods, and thus on the seismic force demand, are investigated. A suite of inelastic time history analyses are carried out to understand the probability of exceeding a specified limit state when the structures are subjected to different levels of earthquake events. The results show that the periods of the structures in risk category IV decrease by a factor of 0.5 to 0.8, and the strengths increase by a factor of 1.5 to 3.2. Seismic fragility analysis shows that the structures in risk category IV generally satisfy the probabilistic performance objectives. © 2014 John Wiley & Sons, Ltd.

Description: This paper presents the development and validation of several novel data-driven damage sensitive features. The proposed features are based on the Continuous Wavelet Transform of both the input acceleration signal to the structure and the output acceleration response. The combination of the input and output wavelet coefficients and the derivation of the features is presented. The features are applied to experimental data obtained from shake table tests on reinforced concrete bridge columns. The results are compared against typically used damage metrics, such as hysteretic energy, and exhibit high correlation with damage. The performance of the features in binary damage detection is evaluated using numerical simulations of reinforced concrete columns under earthquake loading. A damage classification scheme based on the developed features and established damage indices is proposed and validated through Monte Carlo simulation. The proposed features are applied to experimental and simulated data from a multistory frame, illustrating the features' capabilities for damage localization in civil structures. Due to its data-driven nature and use of strong motion recordings, the proposed damage detection scheme can be tailored to a wide variety of applications and deliver damage information immediately after an earthquake. © 2014 John Wiley & Sons, Ltd.

Description: This paper introduces and evaluates a methodology for the aftershock seismic assessment of buildings taking explicitly into account residual drift demands after the mainshock (i.e., postmainshock residual interstory drifts, RIDR o ). The methodology is applied to a testbed four-story steel moment-resisting building designed with modern seismic design provisions when subjected to a set of near-fault mainshock-aftershock seismic sequences that induce five levels of RIDR o . Once the postmainshock residual drift is induced to the building model, a postmainshock incremental dynamic analysis is performed under each aftershock to obtain its collapse capacity and its capacity associated to demolition (i.e., the capacity to reach or exceed a 2% residual drift). The effect of additional sources of stiffness and strength (i.e., interior gravity frames and slab contribution) and the polarity of the aftershocks are examined in this study. Results of this investigation show that the collapse potential under aftershocks strongly depends on the modeling approach (i.e., the aftershock collapse potential is modified when additional sources of lateral stiffness and strength are included in the analytical model). Furthermore, it is demonstrated that the aftershock capacity associated to demolition (i.e., the aftershock collapse capacity associated to a residual interstory drift that leads to an imminent demolition) is lower than that of the aftershock collapse capacity, which mean that this parameter should be a better measure of the building residual capacity against aftershocks. © 2014 John Wiley & Sons, Ltd.

Description: Recent events of significant seismic activity (L' Aquila 2009, Christchurch 2011), have highlighted the importance of accurately assessing the properties of structures, for estimating their risk in future earthquakes as well as detecting and quantifying damage following an event. This demand may be fulfilled through implementation of SHM methodologies, which offer a means of assessing structural condition through the use of sensor data. Furthermore, the emergence of various sensor technologies has improved the quality of collected signals and made the idea of fusing heterogeneous data more appealing. Similar steps were achieved in advancing system identification algorithms. Several methods such as the Autoregressive Moving Average, Least Squares Estimation, Eigensystem Realization Algorithm, and Subspace State-Space System Identification (SSID) perform well in identifying elastic properties. However, the resulting matrices are often not obtained with respect to the physical basis, which is often desirable. Such a representation is obtained by default in Bayesian estimation methods, as the Unscented Kalman Filter and Particle Filters, which have recently been applied in the literature for data fusion problems. In this work, an experimental structure mounted on a shake table is monitored using accelerometers and displacement sensors. A method is developed (T-SSID) to transform the results of the SSID onto the physical basis. The introduced method and the Unscented Kalman Filter are employed identifying the structural properties and detecting an artificially induced in the original system damage. The performance of various sensor setups, which include fusion of heterogeneous sensors, are investigated to illustrate the performance of both methods, their ability to localize damage, and the benefits of data fusion. © 2014 John Wiley & Sons, Ltd.

Description: The force-displacement behavior of the Friction Pendulum™ (FP) bearing is a function of the coefficient of sliding friction, axial load on the bearing and effective radius of the sliding surface. The coefficient of friction varies during the course of an earthquake with sliding velocity, axial pressure and temperature at the sliding surface. The velocity and axial pressure on the bearing depend on the response of the superstructure to the earthquake shaking. The temperature at an instant in time during earthquake shaking is a function of the histories of the coefficient of friction, sliding velocity and axial pressure, and the travel path of the slider on the sliding surface. A unified framework accommodating the complex interdependence of the coefficient of friction, sliding velocity, axial pressure and temperature is presented for implementation in nonlinear response-history analysis. Expressions to define the relationship between the coefficient of friction and sliding velocity, axial pressure, and temperature are proposed, based on available experimental data. Response-history analyses are performed on FP bearings with a range of geometrical and liner mechanical properties and static axial pressure. Friction is described using five different models that consider the dependence of the coefficient of friction on axial pressure, sliding velocity and temperature. Frictional heating is the most important factor that influences the maximum displacement of the isolation system and floor spectral demands if the static axial pressure is high. Isolation system displacements are not significantly affected by considerations of the influence of axial pressure and velocity on the coefficient of friction. © 2014 John Wiley & Sons, Ltd.