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Lathrop, CA, United States

Hanna K.,Con Fab California Corporation | Morcous G.,University of Nebraska at Omaha | Tadros M.K.,University of Nebraska at Omaha
Journal of Materials in Civil Engineering | Year: 2014

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. © 2014 American Society of Civil Engineers.

Morcous G.,University of Nebraska at Omaha | Hanna K.,Con Fab California Corporation | Deng Y.,University of Nebraska at Omaha | Tadros M.K.,University of Nebraska at Omaha
Journal of Bridge Engineering | Year: 2012

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. © 2012 American Society of Civil Engineers.

Patzlaff Q.,E construct.USA LLC | Morcous G.,University of Nebraska at Omaha | Hanna K.,Con Fab California Corporation | Tadros M.K.,E construct.USA LLC | Tadros M.K.,University of Nebraska at Omaha
Journal of Bridge Engineering | Year: 2012

The AASHTO standard bridge specifications require that nominal reinforcement should be placed to enclose prestressing steel at girder ends for at least a distance equal to the girder's height. The AASHTO LRFD bridge specifications state that the minimum requirements for this confinement reinforcement is No. 10 (#3) bars at a maximum spacing of 150 mm (6 in.) for at least 1.5 times the girder's height. Neither standard nor LRFD specifications justify the need for such reinforcement. The main objective of this study is to investigate the effect of confinement reinforcement on the performance of prestressed concrete bridge girders. Of particular interest is the effect on transfer and development length of prestressing steel and on the shear capacity of prestressed girders. The experimental investigation includes testing the flexural and shear capacities of 610 mm (24 in.) deep T-girders and 1,100 mm (43.3 in.) I-girders. The results indicate that (1) neither the amount or distribution of confinement reinforcement has a significant effect on the transfer length of prestress strands; (2) at the AASHTO calculated development length, the amount of confinement reinforcement does not have significant impact on either the nominal flexural capacity of bridge girders or bond capacity of the prestressing steel, however, the distribution of confinement reinforcement along the entire length of the girder results in improved ductility and reduced cracking under extreme loading conditions; and (3) confinement reinforcement improves the anchorage of strands at girder ends, and consequently, the shear capacity of prestressed girders. © 2012 American Society of Civil Engineers.

Hansen J.,University of Nebraska - Lincoln | Hanna K.,Con Fab California Corporation | Tadros M.K.,University of Nebraska - Lincoln
PCI Journal | Year: 2012

Precast, prestressed concrete adjacent box girders are regularly considered for short- to medium-span bridges on secondary roads. This corresponds to spans from 20 ft to 127 ft (6.1 m to 38.7 m), though typically no more than 40 ft (12.2 m). Many of these projects have limited funding or require rapid construction. Secondary roads are also subject to a certain amount of public criticism, particularly with regard to cost and aesthetic appeal. Research has shown that an appealing structure can be defined as having continuously flat soffits and high span-to-depth ratios-characteristics of an adjacent box system. Proper design and detailing of the transverse connection between girders is essential to minimizing both initial cost and long-term maintenance. Typical connections include diaphragms and cast-in-place concrete toppings, which directly increase both cost and time of construction. Inadequate post-tensioning is the primary cause of reflective cracking leading to ingress of chlorides and the consequent reinforcement deterioration, excessive girder deflection, and possible unexpected failures. This paper presents the results of testing on a posttensioned transverse system that eliminates the need for diaphragms and a concrete overlay. Post-tensioning was determined based on previous research on a similar system that was not post-tensioned. Results indicate that the system does not exhibit strain change or cracking under fatigue loading and would be an excellent candidate for practical applications.

Hasenkamp C.J.,Larson Engineering Inc. | Badie S.S.,George Washington University | Hanna K.E.,Con Fab California Corporation | Tadros M.K.,University of Nebraska - Lincoln
PCI Journal | Year: 2012

Precast, prestressed concrete bridge girders are widely used in the United States. Longitudinal web cracks, often called end-zone cracks, at the ends of pretensioned concrete girders are commonly observed at the time of strand detensioning. End-zone cracks differ from flexural cracks in conventionally reinforced beams and slabs and from tensile cracks in water storage structures. In practice, there is no consistent understanding of the effect of end-zone cracking on the strength and durability of the girders. Thus, the decisions made by bridge owners vary from doing nothing to total rejection of the girders. There is no consensus among owners as to acceptable crack widths. This paper gives a user's manual for acceptance and repair of web end cracking and details of end-zone reinforcement that will minimize the number and width of end-zone cracks. The user's manual and reinforcement details were developed in the NCHRP 18-14 report 654.

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