Void Networks in Collapsed Structures as a Guide for Development of Rescue Millirobots

Natural disasters such as earthquakes and hurricanes often cause buildings to collapse and trap people underneath. This research project investigates the use of millirobots as a safe and potentially more effective alternative to human search and rescue mission after a natural disaster. Current new advances in millirobots allow the production of small and simple robots at relatively low cost and have the potential to safely access trapped survivors through void networks; however, very little is known about the environment in which they would need to function. CITRIS researchers are investigating and modeling the void size, shape and connectivity that can be expected after a seismic event, the most likely locations for survivors based on the type of structure and its collapse mechanism, and the type of mobility that is required of the millirobots to be effective.

A working relationship was formed between the research group and the local FEMA Urban Search & Rescue (US&R) Task Force 3 located in Menlo Park, CA. US&R teams are responsible for locating, extricating, and stabilizing victims trapped in confined spaces following a variety of emergency or disaster situations including earthquakes, hurricanes, typhoons, storms, tornadoes, floods, dam failures, technological accidents, terrorist attacks, or explosions.

The research team visited the FEMA US&R Task Force 3 training site in Menlo Park, CA. At the site we were able to see the rubble mock-up used for training and speak with several senior members of the task force about the project. Plans were made to return to the site for a practice search drill to be conducted later this year.

Physical testing of robots on different debris mock-ups will soon be conducted based on photos of real collapse cases and the Menlo Park site. Robot mobility will be tested and analyzed on beds of concrete debris, with the main variable being debris particle size. This test setup can be used for other common rubble components (masonry, steel bar, structural steel, wall pieces, etc.), and different debris mock-ups will allow the robots to be developed for most conceivable rubble situations.

The Biomimetic Millisystems Lab (BML) and the task force see promise in using millirobots as a tool to aid in searching for victims. Some of the properties of these robots that make them particularly suited for search and rescue are their size, durability, cost, and functional capabilities.

  1. Size – These robots can be fabricated small enough to access spaces in debris or rubble that traditional human or canine first responders would not be able to access. Regions of the collapsed structure where victims may be trapped (based on canine or sensor detection) could be unsafe or inaccessible to first responders from the exterior. Small robots have the ability to enter small openings and could be deployed through holes cut in debris. Robot size could be specialized based on the maneuverability requirements of the site.
  2. Durability – Prototype robots developed by BML were able to survive falls up to eight stories and still function. Hazards that affect human and canine first responders including: steep drops, falls, dust, smoke, toxic vapors, fire, moisture, and unstable or unsafe confined spaces. Millirobots can function in many of these hazardous environments, although several (dust, fire, moisture) add new design demands.
  3. Economy – The millirobots being developed by the BML are less expensive than traditional search and rescue robots by several orders of magnitude (i.e. $100 vs. $100,000). Their low cost allows for the possibility of deploying many of these robots at a given site. Even if some robots are damaged or ineffective, multiple deployments provide wider search capability and redundancy.
  4. Functional Capabilities – These robots have taken many forms with different systems of mobility and sensors; robot deployment could be tailored to the needs of the specific site and rescue operation. Robots could be prefabricated with different types of sensors (gas, radio, camera, sound, vibration, etc.) and deployed as needed by rescuers.

Information on collapse patterns that links building details to the probably location and distribution of voids is important for defining the environment where millirobots will be deployed. Based on FEMA guidelines, some of the key parameters that will affect the distribution of voids in collapsed structures are building type, type of load, building function, and construction quality.

  1. Building Type – The type of lateral and vertical framing systems and materials used in the building are directly related to the type of voids that might develop if the building collapses.
  2. Type of Load – The type of loading which led to collapse of the structure can often dictate the state of the debris, rubble, and remaining building. Types of loading with specific collapse patterns include: earthquake; blast or explosion; hurricane, windstorm, or tornado; and storm surge or flooding.
  3. Building Function – The internal distribution of voids in a building prior to collapse is important as many of these spaces will be preserved after collapse. Buildings of different functions have different space requirements (schools, offices, churches, residences).
  4. Construction Quality – In underdeveloped areas or regions with poor building standards, building damage due to earthquakes and other hazards may be more severe; poor quality construction will affect the collapse mechanism of such structures.