This document describes the protocol for the in situ rapid load testing of concrete structures and presents case studies that illustrate its execution and results. It is meant as a guide for engineers interested in assessment and load testing of structures. The motivation for considering the use of a rapid load test is twofold:

• Technological advances in equipment and instrumentation is allowing structural engineers to safely and economically determine the adequacy of members to resist given load conditions.
• Implementation of new construction and strengthening technologies can gain acceptance if verified by proof testing.

The key feature of a rapid load test conducted with hydraulic jacks is in the ability to progressively expose a structural member to loading-unloading cycles. This allows the engineer the opportunity to maintain a strict control on safety and, at the same time, determine response parameters that are key to structural assessment, namely: linearity of behavior, repeatability of response, and permanency of deformation.

In a rapid load test, loads applied to strategic locations are meant to induce the internal forces equivalent to those resulting from distributed loads. The engineer has to be able to analytically interpret this equivalency when establishing the load level to be applied during the in situ test.

This implies an understanding of boundary conditions (i.e., fixity), collaboration of adjoining members (i.e., load sharing), and composite action with structural and nonstructural components. A rapid load test consists of concentrated loads being applied in a quasi-static manner in at least six load cycles, with each cycle containing several load steps. The initial cycles achieve relatively low levels of load and are used to verify assumptions made in the preliminary analysis and ensure stability of the system.

The duration of a rapid load test can be significantly shorter than the 24-hour period that has been employed with traditional in situ tests. The cyclic nature of the rapid load test is considered a suitable substitute for the 24-hour sustained load. In any event, a rapid load test can last as deemed necessary by the engineer.

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