Application of Netslab for Remote Testing of Bridge Systems

An Internet based remote hybrid testing platform was developed for bridge systems. The testing platform, NetSLab, was developed based on client/server concept along with a proposed data model and communication protocols. The platform is capable of transferring control and feedback data and signals among remotely located structural testing laboratories or computers connected by Internet. The effectiveness of the proposed platform is demonstrated by remote hybrid tests of a six-span bridge system at the Hunan University, Harbin Institute of Technology, Tsinghua University, China and the University of Southern California, USA. The remote hybrid testing platform enables the shared use of testing resources by integrating single structural laboratories into a powerful and networked laboratory with advanced capability. Application of NetSLab in asymmetric bridge System under earthquake excitation is also discussed in this paper. . INTRODUCTION In the field of Earthquake Engineering, structural experiments are still important means for understanding behavior of structures and their components. As the scale and complexity of a modern structural experiment increase, existing structural laboratories, even large-scale ones, are facing increasing difficulties to satisfy various types of demands of experiments with their limited resources. Therefore, the concept of remote hybrid test was developed recently which integrates individual laboratories into large-scale Internet-based structural testing system. In a remote hybrid test, the prototype test structure is divided into substructures or sub-components, each of which can be tested at a different test site. The testing of all the sub-components is carried out concurrently in real-time to form a single experiment of the prototype system. The concept of remote hybrid test which facilitates more efficient utilization of test facilities at geographically distributed laboratories to conduct collaborative experiments via internet is more useful than improving facilities of individual structural laboratory. It can cost less and bring tremendous benefits of sharing and integrating laboratory resources. Several attempts have been made to carry out collaborative tests on structural system with remotely located laboratories connected by internet, such as NEES in US (Pauschke et al. 2002; Buckle et al. 2004), ISEE in Taiwan (Yang et al. 2007; Wang et al. 2007), ED-Net in Japan (Ohtani et al. 2002), KOCED in Korea (Kim. 2004). The aim of the current study is to develop a robust standardized platform for remote collaborative hybrid tests of bridge system at different locations developed by Hunan University (Xiao et al. 2004; Xiao et al. 2005 ). 1 Key Laboratory of Building Safety and Energy Efficiency, College of Civil Engineering, Hunan University; Changsha, Hunan, China 2 Dept. of Civil Engineering, University of Southern California; Los Angeles, CA, US 2 REMOTE HYBRID TESTING PLATFORM NETSLAB To facilitate the structural research collaborations between the University of Southern California and the Hunan University of China as well as other institutes, an Internet based remote hybrid platform, named as NetSLab (Networked Structural Laboratories) was established. The testing platform, NetSLab, was developed based on client/server concept along with a proposed data model and communication protocols. It is capable of transferring control and feedback data among remote structural testing laboratories or computers connected by Internet. Based on NetSLab, several application programs have been developed to realize hybrid tests on various structural model. Generally, these application programs always include four types of modules with different functions: ControlCtr, PhysicalTester, VirtualTester, and Observer. ControlCtr is essentially the core of the system and it plays a transfer post dispatching information to all clients. Therefore, there is only one ControlCtr in a test, but multiple testers and observers are allowed to join the test. For any client, all messages and data must be sent to and received from ControlCtr. The reason that clients do not connect directly to each other is to simplify the network topology and hence the communication flow. ControlCtr plays as the server of the platform. It organizes the testing procedure, controls the testing progress and data communication among all participants, and stores or publishes the testing results. PhysicalTester operates the actual testing equipment to generate testing results. VirtualTester uses computation to provide restoring force of substructures instead of physical equipments. It was used extensively during the development stage for debug purposes. Observer monitors the process and shares the testing results without any interference of the test join or quit a test at any time during testing. Each module is implemented by using the TCP connection for its simplicity and reliability. The TCP connection provides a connection-oriented services since a virtual circuit is established between two hosts and the connection exists until any side of a connection terminates it. Fig. 1. Controlling algorithm of remote hybrid testing The controlling algorithm of remote hybrid testing is shown in Fig.1. During a test, ControlCtr first reads an earthquake record. Based on the input information about testing structure, 3 ControlCtr calculates the displacement step for the testing element and the analytical element. ControlCtr then sends the displacement command to PhysicalTester for operating the actuator and VirtualTester if it is involved. After the actuator achieves the command position, PhysicalTester sends the measured restoration force to ControlCtr via NetSLab. Meantime, the calculated restoration force based on selected numerical model by VirtualTester is also sent to ControlCtr via NetSLab, and ControlCtr then decides the deformation command for next step of the testing. APPLICATION OF NETSLAB IN BRIDGE SYSTEM One of the initial trial applications of NetSLab for remote hybrid test was carried out using the large-scale testing frame at USC on a full-scale model of precast prestressed concrete pile to pile-cap assembly. As shown in Fig.2, the super structure is analyzed as a concentric mass which includes all the tributary masses from the neighboring spans. The bridge column is simulated by analysis which includes a hysteresis model and the lateral force and deformation envelop. The pile response is experimentally simulated. Fig. 2. Precast concrete pile to pile-cap assembly model Currently, one of the applications of NetSLab is to simulate the system responses of single column bent bridges as shown in Fig.3a. When simulating the transverse seismic response of this kind structure, it can be considered as an ideal SDOF system, as shown in Fig.3b. The length of specimen is equal to or scaled from the length of the column as shown in Fig.3c. Fig. 3. Transverse response of single column bent bridge Another application is to simulate longitudinal response of single column bent bridge and the transverse response of multi-column bent bridge system with different column length as shown in Fig.4a. As for the bridge system, a column can be tested in a remote site as a substructure. The loading methods are shown in Figs 4b and 4c. In Fig.4b, specimen length is half of the prototype or scaled column, measured from the top of footing to inflection point. When the column is L L