VICKSBURG, Miss. – There are many ways to test the load-bearing capability of structures, and fortunately, the U.S. Army Engineer Research and Development Center (ERDC) has a unique facility to accomplish this task.
When building structures, from bridges to parking garages to office complexes, it is important to know that the structures will withstand the loads they were designed to bear. Usually, this is accomplished by following building codes and design guides, but new designs constructed of novel materials can require additional testing.
The ERDC’s Structural Strong Floor, operated by the Geotechnical and Structures Laboratory (GSL), is a 120-foot by 40-foot indoor space with a floor constructed of two-foot-thick reinforced concrete. It has anchor points located every three feet on-center to facilitate full-scale testing.
Additionally, the floor is equipped with six actuators, each with a capacity range of 110,000 to 550,000 pounds. These actuators can run independently or together, using a computer-controlled manifold to simulate complex loading patterns.
“Although there are other strong floors around the country, the ERDC’s Structural Strong Floor is completely modular,” said Dr. Kennan Crane, research civil engineer in ERDC-GSL’s Structural Engineering Branch (StEB). This allows us to re-configure the actuators based on the test we are performing. We can test a variety of structures under varying load scenarios.”
The purpose of the Structural Strong Floor is to be able to push or pull on structures in any direction, with up to one million pounds of force. The floor is capable of fatigue/durability testing, impact testing, quasi-static testing and dynamic testing.
Two general scenarios are evaluated using the Structural Strong Floor. In some tests, the ERDC engineers and scientists use designs based on previous knowledge. These tests take pre-existing data and look to build upon existing design codes and models.
Other experiments evaluate new or cutting-edge structural designs or materials that have never been tested before. The ERDC uses the Structural Strong Floor to ensure the new designs and concepts will perform as expected in the real world.
“The work we do with the Strong Floor is in conjunction with high-fidelity computational models,” Crane said. “We use the physical test to ensure that the computational model is accurately capturing the behavior of the structure. This validation allows for greater confidence than computational modeling alone.”
A good example of utilizing the ERDC’s Structural Strong Floor is a partnership with Army Product Manager Bridging (PdM Bridging) to conduct testing on several iterations of military bridges. These bridges must withstand thousands of crossings by large military vehicles. The results of ERDC’s testing allow for more rapid decision-making concerning further development of new government designs versus moving to commercial designs. It also supports the development of guidance for the usage of new high military load classification vehicles on current military bridges.
The GSL-StEB team has also worked with the ERDC’s Civil Works Program on repairing lock walls. Ship channel locks used by large barges to navigate rivers experience significant impacts and abrasion. The GSL-StEB team used the Structural Strong Floor to simulate scraping, rubbing, and impacting to demonstrate the superior performance of new lock wall materials and designs.
Materials are not only sensitive to load, but also to how fast the load is applied. A material may behave one way when having a 500-pound load slowly placed on it and very differently when that load is being dropped on it.
“Testing full-scale structures is very expensive,” said Crane. “In most cases, we use the Strong Floor to test critical, individual pieces of structures, allowing us to test the most crucial pieces of a structure without incurring the high cost of testing an entire structure.”
Currently, the GSL-StEB team is working to add more functionality to the Structural Strong Floor. In the near future, the research team will be able to simulate rapid loading scenarios created by something like an explosion. While this is not as accurate as full explosive testing, it can much more rapidly test a variety of materials under a high strain rate.
“This capability will allow for high-strain-rate testing of materials while collecting data in a way that is safer, faster and more cost-effective as opposed to numerous explosive tests,” Crane said.
The team is also working on new ways to present data from the Structural Strong Floor to sponsors and stakeholders. Through a series of closed-circuit cameras, test videos and data streams can be broadcast to monitors around the facility, allowing an immediate visualization of the data and greater real-time involvement from sponsors and stakeholders.
“The Structural Strong Floor is an important asset to GSL, ERDC and USACE. It provides a unique structural testing capability that supports USACE’s Military Engineering and Civil Works missions,” said Mariely Mejias-Santiago, chief of GSL’s Structural Engineering Branch.