A rapid and economical vibrational tension measurement method is presented to detect distress in external tendons used in segmental posttensioned bridges. This method provides a complementary technique to traditional inspection methods currently employed in the field. The natural frequency and overtones produced by an impact excitation are measured and used to determine the tendon segment's tension and flexural stiffness using a differential equation describing a stiff string with clamped-clamped boundary conditions. The flexural stiffness is not negligible in tendons of this type causing the vibration modes to be inharmonically related. This method provides consistent (typically within 1%) and reasonably accurate (typically within 10%) estimates of tendon tension. Accuracy can be improved by lessening uncertainty in input constants such as the tendon mass and tendon length. Application examples from several in-service bridges have shown that detection of corrosion damage, improper tensioning, and force distribution effects from friction at deviation blocks can be detected.

Modeling at the structural scale most often requires the use of beam and shell elements. This paper compares two finite element formulations based on first-order shear deformation theory undergoing thermo-mechanical loading. One formulation is a two node beam element employing static condensation based on the work of Chakraborty et al. The second formulation follows a more traditional route using FSOD theory for a three node beam element. Both formulations are used to investigate the behavior of a functionally graded beam under axial and through-the-thickness temperature gradients. Both formulations work well for a constant uniform mechanical or temperature loading. However, for beam structures containing a thermal gradient in the axial direction, the two node beam element performs poorly as compared to the three node element in terms of transverse shearing stress calculated from the equilibrium equation.

To simulate a trunnion-hub-girder (THG) assembly for bascule bridges, two full-scale laboratory tests were conducted for quantifying stresses at previously observed failure locations and for identifying a favorable assembly procedure. One assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. Using AP#1, development of cracks on the hub was observed in one THG assembly, and, in yet another assembly, the trunnion got stuck in the hub before full insertion could take place. Large hoop stresses and low temperatures were observed at the trunnion-hub interface when the trunnion-hub assembly was cooled for insertion into the girder. Since fracture toughness of THG parts decreases with temperature, allowable crack lengths were small. In an alternative assembly procedure, AP#2, where the hub is shrink fitted into the girder first, followed by cooling the trunnion and shrink fitting it into the hub-girder assembly, the allowable crack length was determined to be double the allowable crack length of AP#1. Hence, for the given full-scale geometry and interference values, assembly procedure AP#2 was found to be better than AP#1.

This paper is a study of avoiding failures during the assembly of a trunnion-hub-girder (THG) for bascule bridges. The currently used assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. During assembly, using AP#1, development of cracks on the hub was observed in one THG assembly. Yet, during another assembly, the trunnion got stuck in the hub before it could be fully inserted. A complete analytical, numerical, and experimental study was conducted to understand these failures, and the results were used to develop specifications and recommendations for assembly. The causes of failures include development of high stresses at low temperatures during assembly, while noting that fracture toughness of THG material decreases with temperature. Recommended specifications included following an alternative assembly procedure that doubled allowable crack length, and lower cooling temperatures to avoid trunnions sticking in the hub.