Atorod Azizinamini

FLEXURAL CAPACITY OF COMPACT AND NONCOMPACT HIGH-PERFORMANCE STEEL PLATE GIRDERS

As a result of a cooperative research program between FHWA, the U.S. Navy, and the American Iron and Steel Institute, high-performance steels (HPSs) with yield strengths of 485 MPa [70 kips/in.2 (ksi)] (HPS-70W) and 690 MPa (100 ksi) (HPS-100W) were developed. During the past 2 years, several bridges in the United States have used these new grades of steel. Because of a lack of test data, AASHTO specifications placed several limitations that prevent bridge designers from taking full advantage of HPSs. In response to AASHTO limitations, which preclude full use of the advantages that the HPS-70W and HPS-100W steels have to offer, research investigations were initiated at the University of Nebraska–Lincoln, Lehigh University, and the Georgia Institute of Technology. Partial results of research activities under way at the University of Nebraska–Lincoln and Lehigh University to remove design limitations related to the use of HPSs are presented.

Experimental Evaluation of Repair Options for Timber Piles

An experimental investigation compared repair methods that could be used to repair timber piles in timber pile bridges. Five full-scale timber pile specimens with different levels of damages were prepared. The damage in each specimen was repaired with fiberglass-reinforced plastic wrap to encapsulate the damaged region, which was filled either with resin or grout or with resin and gravel. Ultimate load tests were carried out on the specimens to evaluate the effectiveness of the repair methods. Test results showed that grout was more effective than resin in repairing large cavity-type damage. Resin appeared to be more effective in repairing cracks and small cavities in timber piles. The failure load of the repaired pile specimens was at least five times greater than the design load capacity of the timber piles and indicated that the repair methods effectively restored the capacity of the damaged timber piles.

BEHAVIOR OF TENSION SPLICES FOR REINFORCING BARS EMBEDDED IN HIGH-STRENGTH CONCRETE

Safety concerns and a lack of test data on bond capacity of deformed reinforcing bars embedded in high-strength concrete (HSC) have been reasons that the American Concrete Institute (ACI) 318 building code has imposed an arbitrary limitation of 69 MPa (10,000 psi) in the calculation of tension development and splice lengths. This limitation was first introduced in the 1989 revision of the ACI 318 building code. In an attempt to evaluate the impact of this limitation and develop provisions for its removal, a two-phase investigation was carried out at the University of Nebraska-Lincoln. During both phases of the investigation, 70 beam splices were tested. The parameters studied included diameter, length, and deformation type of the reinforcing bars; amount of transverse reinforcement over the splice length; casting position; and concrete compressive strength. Results of the investigation are used to discuss the differences that exist between normal concrete and HSC, develop hypotheses to explain these observed differences, and suggest alternatives for removal of the current concrete compressive strength limitations existing in the ACI 318 building code for calculating tension development and splice lengths.