Acceleration‐based damage indicators for building structures using neural network emulators
In this paper we propose the use of artificial neural network (ANN) emulators for an acceleration‐based approach to evaluating building structures under earthquake excitation. The input layer of the ANN is a forced vibration, described as ground acceleration and the acceleration data of several floors. The approach is improved by using the acceleration at later time steps as the output of the neural network (NN). This time delay is optimized as a tunable band to provide the most sensitive signals.
Identification of Structural Parameters Using Symbolic Time Series Analysis and Intelligent Algorithms
Structural Health Monitoring (SHM), a field inaugurated in aerospace engineering in the late 20 th century through mechanical engineering towards civil engineering communities. As the process of implementing a damage detection strategy, SHM has received increasingly attention and interest in the civil engineering with prominent technology development and promising economic attraction. Even as research on SHM chugs along, challenges remain before they can be applied to civil engineering structures. This dissertation presents a new approach for damage identification of structures using symbolization-based intelligent algorithms. To implement the concept, a two-phase approach is proposed. In the first phase, a "Symbolization-based Negative Selection" (SNS) algorithm that combines the advantages of symbolic time series analysis (STSA) and negative selection (NS) is proposed for detecting the abnormal states of a building structure. In SNS, no prior knowledge of the structure's abnormal state is needed. Only the response of the structure in a current normal state is used as input data. In addition, this approach works fine even with one sensor, so it is highly practical and flexible. In the second phase, after knowing the damage occurrence, we need to determine the damage location and quantity. The method for this stage was named as “Symbolization-based Differential Evolution Strategy” (SDES). Differential evolution List of publications (DE) strategy employed here is intended to minimize the distance between SSHs (state sequence histogram) that are transformed from raw acceleration data of a real structure and candidate models. Accuracy of the method is theoretically studied and explained including the effects of parameters. SDES was numerically compared with Particle Swarm Optimization (PSO) and DE with raw acceleration data. These simulations revealed that SDES provided better estimates of structural parameters when the data was contaminated by noise. Moreover, in order to prove that the method is indeed applicable to realistic problems, the computing strategy for SHM is experimentally verified. Two different structural models, small model and large steel model, are utilized to verify the proposed approach. Experiments using the small model were conducted at our Laboratory, damage cases were considered for different locations and degrees of damage. Data of the experiments using the steel model (carried out under the US–Japan cooperative structural research project on Smart Structure Systems) was used to further verify the proposed methodology. Finally, the conclusion is given. The damage identification using symbolic time series analysis and intelligent algorithms is proposed, and it can detect, localize and quantify the damage accurately. The symbolization of data alleviates the effects of harmful noise, employment of the intelligent algorithms make the whole procedure adaptively and efficiently. Comparisons with existing methods show that our proposed methodology is indeed a powerful tool for damage identification of building structures.
Emerging Needs in Japan for Health Monitoring Technologies in Civil and Building Structures
The needs for health monitoring systems are recently emerging in Japan for many industrial structures including civil and building structures. The trend has been accelerated after the 1995 Hyogo-Ken Nanbu Earthquake in which the damages of beam-column joints in many steel buildings were found only after conducting elaborate one-by-one eye-inspections. Difficulty to evaluate the damages in pile foundations was also reminded by this event. In addition, recognition of the importance of renovation and rehabilitation markets associated with huge accumulation of infrastructur es and buildings during the booming era is demanding urgent development of sophisticated health monitoring systems for minimizing costs and time by obtaining proper damage status. Two national projects launched by the Ministry of International Trade and Industries and the Ministry of Construction indeed reflect the strong needs for the technology. Noteworthy and important advances in fiber optic sensors and a network technology that will play an important role are briefly explained.