An effective method for in-situ strength evaluation for structures

Typical load testing methods consist of applying uniformly distributed dead loads to the structure in the form of water, sand, concrete blocks, or similar materials. These techniques provide an indication of a structure's ability to carry a particular load. However, they do not provide adequate information for the engineer to evaluate the stability and response of the structural components. In addition, these methods carry the risk of possible structural failure during testing and are often expensive, time consuming, and are often not conclusive.

In an effort to provide an alternative in-situ load testing tool, Structural Preservation Systems' Strengthening Division offers RapidLoad™, a procedure that uses a proven technology developed to provide a non-destructive yet conclusive demonstration of the performance of structural elements.

The key feature of RapidLoad™ is the use of hydraulic jacks placed at strategic locations to induce internal forces equivalent to those resulting from any load condition, which are commonly created by distributed loads. RapidLoad™ has the ability to progressively expose a structural member to loading/unloading cycles. The RapidLoad™ method allows for better control of the applied load as well as an ability to maintain a strict control of structural safety. Key information such as loads, strains and deformations are obtained during the testing and are used to determine response parameters that are key to structural assessment. In comparison to typical load testing methods, RapidLoad™ is faster, safer, more economic, and more conclusive.

An appraisal by Concrete Innovations Appraisal Services (CIAS), a wholly owned subsidiary of the Concrete Research and Education Foundation (ConREF) of the American Concrete Institute (ACI), stated that:

"The panel's opinion is that the proposed RapidLoad™ Test protocol has great potential value to the construction industry. The method has potential for making load testing of new structures, deteriorated structures, and repaired structures more practical and more meaningful than the present 24-hours static load test presented in the American Concrete Institute 'Building Code Requirements for Structural Concrete (ACI 318-99),' Chapter 20."

Procedure for RapidLoad™ Testing

The RapidLoad™ test involves applying load in six load cycles with the procedure shown on the figure to the right. Each individual load cycle (defined on the chart by a circled letter) includes four to six load steps. As shown on the figure, each load cycle is repeated at least one time using the same load steps and load levels. Comparison of the two successive, identical cycles provides information to determine the linearity of behavior, repeatability of response, and permanency of deformation, which is key information to evaluate the structural response to the applied loads. Instrumentation consisting of linear variable deformation transducers (LVDT), strain gauges, extensometers, and load cells, are used to measure deflections, strains, crack widths, and loads, respectively.

Real-time monitoring of the response using a customized data acquisition system allows for strict control of safety against collapse.

A comprehensive report is submitted to the owner/engineer that summarizes the test procedure, response measured during the load test, and the load carrying capacity of the structural member based on this test.