Kromel E Hanna

Mechanical and Bond Properties of 18-mm- (0.7-in.-) Diameter Prestressing Strands

For several years, 18-mm- (0.7 in.-) diameter strands have been successfully used in cable bridges and for mining applications. The use of these large diameter strands in pretensioned concrete girders could allow approximately 35% increase in the prestressing force compared to the same number of 15-mm- (0.6 in.-) diameter strands and 92% increase compared to 13-mm- (0.5 in.-) diameter strands. Consequently, this process will allow for longer spans, shallower structural depth, and/or wider girder spacing in bridge construction. For the same prestressing force, the use of 18-mm- (0.7 in.-) diameter strands results in fewer strands to jack and release, fewer chucks, and greater flexural capacity due to lowering the center of gravity of the strands. Despite the advantages of using large diameter strands in pretensioned concrete girders, the lack of data on their mechanical and bond properties hinder their wide use in bridge construction. In this paper, the mechanical and bond properties of 18-mm- (0.7 in.-) diameter strands are evaluated. One hundred and two strand specimens were obtained from different strand producers and production cycles to evaluate the ultimate strength, yield strength, modulus of elasticity, and elongation at two different laboratories. Test results indicated that all strands adequately met the requirements of the ASTM standard A416-06, with the exception of the minimum yield strength requirements (90% of the specified ultimate strength). The power formula for stress-strain relation- ship was used to provide an accurate predictor of the behavior of strands. Also, 58 strand specimens were tested for their bond in mortar and concrete using the North America Strand Producers (NASP) test method. Test results demonstrated that the bond of 18-mm- (0.7 in.-) diameter strands is proportional to the concrete strength. A formula for predicting the NASP pull-out test value as a function of concrete strength was also developed. In addition, NASP test results for clean and rusted strands were measured and compared at different slip values. DOI: 10.1061/(ASCE)MT.1943-5533.0000424.

Concrete-Filled Steel Tubular Tied Arch Bridge System: Application to Columbus Viaduct

The tied arch bridge system provides a unique solution to the several challenges associated with the construction of railroad overpasses and water crossings, such as restricted vertical clearance, undesirable or impractical arrangement for intermediate piers, and extremely limited traffic control during construction. The paper presents the design and construction challenges pertinent to a novel concrete-filled steel tubular tied arch system that was first introduced in the Ravenna viaduct (53 m) and applied later to the Columbus viaduct (79 m). The main structural components of the Columbus viaduct are described in detail and the advantages of the system are summarized. The detailed analysis of the system at different construction stages and design checks of main components and connections under various loading conditions are discussed. Experimental investigations conducted on concrete-filled steel tubular arch and tie specimens to validate their theoretical capacities are demonstrated. The three-dimensional nonlinear finite element model developed to analyze the tie-to- arch connection and evaluate the lateral stability of arches is presented. Finally, the main construction procedures and challenges of the three tied arches of the Columbus viaduct are highlighted. DOI: 10.1061/(ASCE)BE.1943-5592.0000205.

Effect of Supplementary Cementitious Materials on the Performance of Concrete Pavement

Supplementary cementitious materials (SCMs) have been used in portland cement concrete pavements (PCCP) to increase their resistance to deterioration mechanisms, such as alkali-silica reaction (ASR), freeze and thaw, and permeability. In addition, SCMs are mostly by-products that can effectively reduce material cost and improve concrete sustainability. This paper presents the results of an experimental investigation carried out to evaluate the effect of Class C fly ash, Class F fly ash, and ground granulated blast furnace slag (GGBFS) on the performance of PCCP. Laboratory testing of multiple mixes with different combinations and percentages of SCMs is presented. This testing includes slump, unit weight, air content, time of setting, compressive strength, flexural strength, alkali-silica reactivity, freeze/thaw, length change, chloride ion penetration, and wet/dry test specified by Nebraska Department of Roads (NDOR). Field applications of four candidate mixes at two separate locations are also presented. Test results from laboratory and field investigations indicated that using a combination of Class C fly ash (15-20%) and Class F fly ash (20-25%), or all three SCMs in the range of 15-20% each, improves concrete durability and overall performance. DOI: 10.1061/(ASCE)MT.1943-5533.0000862.