Construction Monitoring—The Greatest Stress Is Not Always What Is Measured

Structural monitoring has been an important aspect of bridge construction for many years and has generally been considered a form of quality control. While ensuring compliance of material and design specifications is essential to quality construction, most monitoring programs have not been considered mission critical by the contractor; rather, it has been a necessary means to check boxes off a list. With advances in measurement technology coinciding with innovative construction methods, the role of structural monitoring has changed in recent years where measurements are an integral part of the erection process. For example, forces in hanger rods or cables during erection of complex suspended bridge structures is often part of the tensioning sequence along with geometric checks. These measurements can be made with permanent inline sensors or temporarily installed sensors which are critical to the completion of each stage of construction. This transition in monitoring goals has changed the nature of measurement importance, required system reliability, system quality control methods, and installation requirements. This paper will highlight several bridge projects where construction decisions and procedures were highly dependent on structural monitoring. The discussion will include the importance of the measurements along with the associated risks with measurement quality. When quality and safety of a finished structure is dependent on the quality of data in a litigious environment, quality assurance programs become critically important regarding validation, documentation, system reliability, and overall cost. This paper will include both technical and operational information for structure owners, designers, and contractors. The topic will be relevant to all professionals dealing with complex construction methods.