Sensor networks nowadays are widely used for structural health monitoring; for example, the sensor monitoring system deployed on the Guangzhou New TV Tower, China. While wired systems still dominate, it is commonly believed that wireless sensors will play a key role in the near future. One key difficulty for such systems is the data transmission from the sensor nodes to the base station. Given the long span of the civil structures, neither a strategy of long-range one-hop data transmission nor short-range hop-by-hop communication is cost-efficient. In this paper, we propose a novel scheme of using the elevators to assist data collection. A base station is attached to an elevator. A representative node on each floor collects and transmits the data to the base station using short range communication when the elevator stops at or passes by this floor. As such, communication distance can be minimized. To validate the feasibility of the idea, we first conduct an experiment in an elevator of the Guangzhou New TV Tower. We observe steady transmission when elevator is in movement. To maximize the gain, we formulate the problem as an optimization problem where the data traffic should be transmitted on time and the lifetime of the sensors should be maximized. We show that if we know the movement pattern of the elevator in advance, this problem can be solved optimally. We then study the online version of the problem and show that no online algorithm has a constant competitive ratio against the offline algorithm. We show that knowledge of the future elevator movement will intrinsically improve the data collection performance. We discuss how the information could be collected and develop online algorithms based on different level of knowledge of the elevator movement patterns. Theoretically, given that the links capacity assumptions we made, we can prove that our online algorithm can guarantee data delivery on time. In practice, we may set a buffer zone to minimize the possible data delivery violation. A comprehensive set of simulations and MicaZ testbed experiments have demonstrated that our algorithm substantially outperforms conventional multihop routing and naive waiting for elevator scheme. The performance of our online algorithm is close to the optimal offline solution.

There are heavy studies recently on applying wireless sensor networks for structural health monitoring. These works usually focus on the computer science aspect, and the considerations include energy consumption, network connectivity, etc. It is commonly believed that for the current resource limited wireless sensors, system design could be more efficient if the application requirements are incorporated. Nevertheless, we often find that, rather than integration, assumptions have to be made due to lack of knowledge of civil engineering; for example, to evaluate routing algorithms, the sensor placement is assumed to be random or on grids/trees. These may not be practically meaningful to the respective application demands, and make the great efforts by the computer science community on developing efficient methods from the sensor network aspect less useful. In this paper, we study the very first problem of the SHM systems: the sensor placement and focus on the civil requirements. We first study the current general framework of structure health monitoring. We redevelop the framework that includes a new sensor placement module. This module implements the most widely accepted sensor placement scheme from civil engineering but focusing on its usefulness for computer science. It provides such interfaces that can rank the placement quality of the candidate locations in a step by step manner. We then optimize system performance by considering network connectivity and data routing issues; with the objective on energy efficiency. We evaluate our scheme using the data from the structural health monitoring system on the Ting Kau Bridge, Hong Kong. We show that a uniform and a state-of-the-art placement are not very meaningful in placement quality. Our scheme achieves almost the same sensor placement quality with that of the civil engineering with five-fold improvement in system lifetime. We conduct an experiment on the in-built Guangzhou New TV Tower, China; and the results validate the effectiveness of our scheme.