BDI uses two broad categories to describe the evaluation of a particular structure, using the length of field time as the reference.
In general, we refer to “testing” or “diagnostic testing” as temporarily installing a data acquisition system, recording live load responses, and then removing the system. Usually, this type of test can be completed in a day or two.
Conversely, we refer to “monitoring” (sometimes referred to as “structural health monitoring”) as installing a data acquisition system that will remain in place for weeks, months, or years and automatically collect and store data.
While there can be combinations of these two approaches, these are useful guidelines to remember when considering evaluation techniques. BDI works with the customer to determine what approach will work best for their particular application.
“What is Structural Health Monitoring?” There is really not an agreed-upon definition of this term, although it is used often by engineers, researchers, and politicians. In general, it refers to putting “some sort” of electronic box out on a structure that collects “some type” of data which can then be evaluated “somehow”. One example would be a datalogger that is connected to strain sensors which are, in turn, mounted on critical structural members. Then, if an unusually high strain/stress level is detected (like from an overloaded truck crossing a bridge or perhaps a pier is tilting due to scour), the system can alert the owner. There are hundreds of other examples. Prior to installing any monitoring system, the end user should clarify exactly what they would like to accomplish with the data, what decisions are to be made given a particular response, and what is the shortest amount of time required to answer the questions at hand. The difference in cost between a temporarily installed system and a permanently-installed system can be an order of magnitude.
“What is Diagnostic Load Testing?” No matter how sophisticated, modern analytical techniques cannot replace field testing for understanding how a structure will respond under load. As an example, parapets, sidewalks, and asphalt overlays can make a bridge much stiffer than originally designed. Or, a navigation lock gate may be distributing load much more efficiently than anticipated. By installing strain and deflection sensors on primary structural members and recording responses while a load is applied, a clear picture can be developed of how that load is distributed. Depending on the project, it may be enough to know that some members are being loaded and what stress levels are being reached. Other projects require a more sophisticated comparison between the field data and finite element models.