Prestressed Box Beam Bridges Research Articles

Effects of State Legal Loads on Bridge Rating Results Using the LRFR Procedure

The main objective of this research was to study the effects of different specified trucks on bridge rating with the load and resistance and factor rating (LRFR) procedure. Twelve specified trucks were selected for this study, which include one AASHTO design truck, three AASHTO legal trucks, and eight state legal trucks. These rating trucks were applied on 16 selected Tennessee Dept. of Transportation bridges to obtain the LRFR ratings. The selected bridges covered four commonly used bridge types, including prestressed I-beam bridges; prestressed box beam bridges; cast-in-place T-beam bridges; and steel I-beam bridges. The research results revealed that (1) LRFR AASHTO legal load ratings factors were enveloped by the LRFR HL-93 truck ratings factors, thereby confirming the validity of the LRFR tiered approach with regard to AASHTO legal loads; (2) the lighter state legal trucks were enveloped by the HL-93 loads, whereas the heavier state trucks with closer axle spacing typically resulted in load ratings t...

Investigation of Damaged 12-Year Old Prestressed Concrete Box Beams

An investigation was conducted of unexpected damage to a pair of three-span continuous-spread prestressed box beam bridges after 12 years of service. Routine inspection had revealed cracks in the box beams near the piers and abutments. An investigation was conducted to assess the condition of the beams in the bridges as well as their as-built properties and remaining strength. The investigation showed that the beams were built in accordance with the design drawings and specifications. One beam was tested under a combination of flexure and shear. These tests showed that the effective prestress was lower than standard design estimates. Measurable slip of the strands initiated as shear or flexure-shear cracks developed; however, the bond strength was sufficient for the strands to fail by fracture. The measured ultimate strength exceeded the analytical estimates by 7 to 9%. The conclusion of the investigation is that the cracks in the beams developed from a combination of conditions created by the design, detailing, and production of the beams.

Performance of Full-Depth Shear Keys in Adjacent Prestressed Box Beam Bridges

Bridge decks supported by adjacent, precast, prestressed concrete beams have become increasingly popular in recent years due to their ease of construction, shallow superstructure, and aesthetic appeal. In New York State prior to 1992, such structures were built by placing a number of precast beams alongside one another and connecting them through 12 in. (0.305 m) deep grouted keyways called shear keys to transfer shear forces across the structure. After the grout hardens, the beams are transversely post-tensioned and a composite, cast-in-place deck is poured over them. Prompted by the frequent appearance of longitudinal deck cracking over these partial-depth shear keys soon after the construction, full-depth shear keys with more transverse tendons were adopted in 1992. A follow-up study evaluated the performance of this new full-depth shear key/transverse tie system. Results indicate that this method has reduced the frequency of shear key related deck cracking.