Measuring Displacement of Tall Concrete Columns during Construction

Multiple-span, segmental concrete bridges built by balanced cantilever construction demand precise geometric control so that adjoining tips align at the time the closure segment is cast. When this type of bridge superstructure is cast monolithically on tall piers, moment redistribution, as well as creep, shrinkage, and temperature effects, can cause excessive demand on the exterior end spans and piers of the structure. To compensate, designers often use horizontal forces (jacking) to induce a counteractive moment in the pier columns. However, designers often do not make the effort to ensure that the intended displacement is realized at the needed structural elements. A methodology for measuring deflections of tall pier elements with tiltmeters during construction is presented in this paper for the Jeremiah Morrow Replacement Bridge, Interstate 71, Lebanon, Ohio. Fast-sampling data collection systems and postprocessing algorithms, including thermal effect removal, are detailed. In addition to the deflections from unbalanced cantilever moment during the casting cycle, fast-sampling data for the first horizontal jacking event are discussed and compared with the data collected through traditional laser survey techniques. The data were valuable information. They allowed the designer to fine-tune the geometry setup during the segment casting cycles, and they provided real-time displacement readings that permitted field decisions about the final force application during the jacking event.