Implementation of the recently developed Nebraska University I-girders (NU girders) in bridge design and construction was initiated under this research project. The University of Nebraska's research team, in cooperation with Nebraska Department of Roads, Bridge Division, the local precast concrete industry representatives, and local engineering firms transformed the UN girders from concept to reality. Several production concerns by bridge designers and fabricators were investigated by casting trial segments of NU 2000. The concerns included: 1) flowability of concrete throughout all girder parts especially the bottom flange; 2) the possibility of aggregate segregation during casting; 3) the difficulty of stripping the forms with the relatively small slope of the bottom surface of the top flange; and 4) the use of welded wire fabric versus conventional reinforcement bars. Standard reinforcement details using welded wire fabric were developed for the girders. Design aids in the form of charts, tables, and simplified equations were developed to help engineers in the preliminary selection of girder sizes for both pretensioned and post-tensioned girder bridges. For post-tensioned girders, a new haunched section was developed for use in spliced post-tensioned girder bridges. The new haunched section significantly increases the span capacity of the NU post-tensioned girders. The AASHTO Standard Specifications which require all vertical shear reinforcement to be extended into the cast-in-place deck slabs were investigated and found unnecessary for satisfaction of horizontal shear requirements. This conventional practice significantly increases the effort required for future removal of concrete slab. As a result of this study, this requirement was eliminated by the AASHTO Subcommittee on Bridges and Structures.

The effect of confining entire members or parts of members, such as beams and columns, is known to strengthen the bond between the concrete and reinforcement. In this paper, the effect of confining the grout that surrounds isolated, single reinforcing bars on the bond strength between the bar and the grout is investigated. Grout-filled steel pipe splices with differnet parameters and geometrical design were prepared and loaded in axial tension until failure. The test specimens are described and the test results are presented, with discussion and analysis in light of existing theory. The experimental results show that a generic and inexpensive reinforcing bar splice for field connection of precast concrete members can be achieved using grout-filled standard steel pipe.

Two new methods for creating continuity in precast concrete girders have been developed and are compared here with the two currently used methods. The two existing methods are full-length post-tensioning and continuity through reinforcement in the cast-in-place deck. Although these new methods are presented here for use with I-girders, they are equally applicable to other precast girder types. The new methods involve the creation of continuity in the girders prior to casting the deck. In addition to cost savings, these two methods offer other advantages over existing methods. One of these methods uses pretensioned top strands, and the other uses high-strength threaded rods in the top of the girder at negative moment regions.

A new precast concrete sandwich panel system with a high thermal resistance and optimum structural performance has been developed. A hybrid truss provides the connector in this panel system - the diagonals are fiber-reinforced plastic bars and the chords are prestressed steel strands. Each connector consists of a fiber-reinforced plastic bar fabricated in a deformed spiral shape through which a pair of prestressing strands is threaded to provide anchorage in the concrete wythes. The developed shear connecting system is described together with its advantages. An experimental and analytical investigation of the connecting system was conducted. The experimental program included testing of small scale specimens by push-off loading, small scale panels by flexural loading. The analytical investigation included finite element modeling of the tested small scale specimens and comparisons with theory of elasticity solutions. Experimental and analytical results from finite element modeling and from theory of elasticity equations correlated well and showed that the developed panel system meets the objectives of the research and is expected to have a promising future.

This paper presents a new technique for creating continuity in prestressed concrete members. The essence of the system is the creation of continuity at interior supports by coupling top end strand extensions. This coupling is followed by introducing compression into cast-in-place joints and tension in the coupled strands. This system has all the benefits of a continuously post-tensioned system without actually implementing the full post-tensioning operation. Members made continuous with this system are expected to exhibit enhanced seismic resistance, superior structural integrity and substantially lower deflection levels than other continuous and non-continuous prestressed concrete members in current use.

Maher K. Tadros Cheryl W. Prewett Professor of Civil Engineering and Director Center for Infrastructure Research University of Nebraska Omaha, Nebraska Precast Concrete Sandwich Panels (PCSP), used as exterior walls in multi-unit residential, commercial, and warehouse buildings, are structurally and thermally efficient building elements, and they are in use worldwide; yet, there is very limited available information on the various design, production and construction philosophies. This paper presents the PCSP systems most widely used in North America and Europe as exterior walls for low rise commercial and warehouse buildings. The constituents of these panels are described, and some of the limited available research results are discussed. The theory of analysis for volume change effects is explained and numerical examples are given. A discussion of issues in need of further research is provided. Some widely used PCSP systems in North America and Europe are described in Appendix A, and the names of producers are included for further reference.