Browsing by Subject "Prestressed concrete beams"
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Item Alternate vertical steel reinforcement in prestressed concrete beams(Texas Tech University, 2001-08) Cedeno-Rosete, RafaelThe Texas Department of Transportation (TxDOT) widely uses prestressed concrete I-beams for constructing bridges. Currently, TxDOT prestressed concrete I-beam standard permits the substitution of an equal area of Welded Wire Fabric (WWF) for the traditional standard steel bars used as the vertical steel reinforcement. However, no details are provided to insure the standardization of this allowed substitution. The common practice is to simply make a one-for-one substitution using deformed wire for each conventional deformed bar. A research project was conducted at Texas Tech University (TTU) to study the behavior of the WWF as a vertical steel reinforcement, specifically the anchorage capacity of the WWF. In addition, alternate vertical steel reinforcement details were proposed using a simplified steel area and an equivalent strength steel area of WWF. The results of this study are reported in this work. WWF consists in deformed wire bars in the transverse direction and plain wires in the longitudinal direction welded at each intersection using an electrical resistance welding procedure to form flat sheets of WWF. These flat sheets of WWF are bent into the desired shapes and placed into position as units. The vertical shear reinforcement must be properly anchored at its ends in order to be capable of developing its fiiU shear design strength. Two longitudinal plain wires welded to each vertical leg on the WWF detail and spaced vertically two inches apart are provided to develop this anchorage behavior. This detail requires that the two longitudinal wires and their welds be capable of properly anchoring the vertical wires. This two cross-wire anchoring detail in the WWF has been used in several other similar applications. However, there are some differences between these similar applications and Texas prestressed I-beam details. One of the main objectives of this research work has been to study the effectiveness of this anchorage detail. The current TxDOT vertical reinforcement detail for I-beams at the ends consists of bars with diameter 1/2 inches (No. 4) spaced at 4 inches, called "R" bars, and bars with diameter 5/8 inches (No. 5) spaced at 4 inches, named "S" bars. Both of these sets of bars must be Grade 60. This project also studied a simplified WWF alternative of reinforcement consisting of using an equivalent wire diameter providing the same steel area. This simplified approach has the advantage of reducing the production cost of the WWF cages, due to the fact that only one wire diameter is needed to be fed during the production process. In addition to this alternative vertical steel reinforcement, another reinforcement proposal was studied. An equal strength substitution was proposed using Grade 80 wires with a smaller area in such a way that the total strength developed by the vertical WWF reinforcement will be the same of the traditional reinforcement using No. 5 and No. 4 bars of Grade 60. This change in policy would allow the use of the higher yield strength common in WWF material, leading to reduced areas of steel and an associated reduction in cost. Finally, with the onset of High Performance Concrete, the strength of concrete possibly used in the TxDOT I-beams has increased from 5,000 psi to 10,000 psL Because of this shift, concrete strength was also another study parameter consider in this research. In order to study the performance of the WWF steel substitution in the particular use of vertical steel reinforcement in the TxDOT I-beams, 14 full-scale tests were conducted at the Texas Tech University (TTU) structural testing laboratory. The concrete strength ranges used were 5,000-7,000 psi for normal concrete strength and 10,000-12,000 psi for high strength concrete. The beams were tested to observe their performance failure load. The results of this study were used to state recommendations about the current TxDOT policies of using WWF as vertical shear reinforcement.Item Camber analysis and design of continuous prestressed concrete beams(Texas Tech University, 1969-05) Horn, Howard RichardNot availableItem Characterization of cracks in bridge beams with welded wire fabric reinforcement using image processing(Texas Tech University, 2001-12) Turkyilmaz, SelimThe Texas Department of Transportation (TxDOT) widely uses prestressed concrete I-beams as bridge girders. The current TxDOT policies allow the substitution of an equal area of Welded Wire Fabric (WWF) for the traditional vertical steel reinforcement. However, TxDOT does not provide details for the WWF substitution. A research project was conducted to study the behavior of WWF as shear reinforcement m the high shear regions of prestressed concrete beams. The main purpose of the project was to test the anchorage capacity of the WWF bars. As alternatives, a simplified WWF design and an equivalent strength WWF design were also proposed. Another main objective of this research was the study of the cracks to have a better understanding for the performance of these alternative designs. The crack controlling behaviors of different WWF vertical shear reinforcement details were studied by using "digital image processing" techniques. Image processing techniques provide a faster and easier analysis of concrete cracks than manual crack measurement methods. A fast and accurate technique has been tried to provide for this analysis. The digital images of the crack regions were taken of the beams with different shear reinforcement details under common loads near failure. These digital images were converted into binary images by using a series of digital image processing techniques. Then the crack properties such as areas, lengths, and average widths were computed automatically. The results showed that the crack properties of the different WWF reinforcement designs were consistent with those of the standard reinforcement design. The equivalent strength designs exhibited the widest cracks and largest total crack areas.Item Statistical evaluation of transfer and development length of low-relaxation prestressing strands in standard I-shaped pretensioned concrete beams(Texas Tech University, 1999-05) Kose, Mehmet MetinThe Federal Highway Administration (FHWA) placed a moratorium on the use of 0.6-inch diameter prestressing strand for pretensioned concrete beams in October of 1988. This moratorium was imposed because of some apparent unconservatism in the code requirements addressing transfer and development lengths of seven-wire prestressing strand. The research conducted at Texas Tech University (TTU) and the results reported herein are an integral part of a larger, joint research project conducted with The University of Texas at Austin (UT) designed to provide additional test data for consideration toward Iifl;ing the FHWA moratorium. This joint study involved 36 fullscale AASHTO Type I (Texas Type A) I-beams. Six of these beams were tested at TTU. Concrete strengths in three ranges were investigated in the joint TTU / UT project. The three concrete strength ranges were 5,000-7,000 psi, 9,500-11,500 psi, and 13,000-15,000 psi. The strand surface conditions of the 0.6-inch diameter strand were mill bright or msty. For each combination of concrete strength and strand surface condition, beams were tested for three other variations in the strand; all strand fully bonded, 50% of the strand debonded, and 75% of the strand debonded. TTU portion of the study covered transfer and development length tests of 0.6-inch prestressing strand with rusty surface condition in fully bonded, 50% debonded and 75%) debonded pretensioned concrete beams with low strength concrete 5,000-7,000 psi. Results from this study were used to evaluate the current ACI, AASHTO-Standard and AASHTO-LRFD requirements for the transfer and development lengths, as well as the transfer and development equations proposed by C. Dale Buckner and Susan N. Lane. Research results showed that ACI and AASHTO-Standard code equations for transfer length are slightly unconservative. AIso, it showed that Buckner and AASHTO-LRFD equations are less conservative compared to Lane equation for both transfer and development length. Due to these observations, it was determined that a new transfer and development length equation needed to be developed. The new transfer and development length equation should provide conservative results for all concrete strength and prestressing strand diameter of 0.5 and 0.6-inch but yet not be overiy conservative for high-strength concrete. The new equations for the transfer and development lengths were formulated based on the resuhs obtained from this study and the results from other research studies to make sure that the equations would be representative of large number of data.