Browsing by Subject "Reinforced concrete construction"
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Item A study of the differential deflections occurring in full-scale residential slab-on-ground foundations(Texas Tech University, 1985-08) Shih, Chaur-songNot availableItem 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 The anchorage behavior of headed reinforcement in CCT nodes and lap splices(2002) Thompson, Keith; Jirsa, J. O. (James Otis)The behavior of headed reinforcement in concrete was studied using full scale tests of CCT nodes and lap splices. The mechanics of the anchorage behavior were observed and recorded to evaluate the manner in which the capacity of a headed bar is developed. The measured data were used to evaluate existing models of headed reinforcement anchorage as well as the ultimate limit state for anchored bars in CCT nodes. Observations from the CCT node tests provided information on the stages of truss development in a simple strut-and-tie model as well as the stress state of the concrete in the node and adjacent struts. Observations from the lap splice tests provided information on the mechanism of stress transfer between lapped bars. The results indicate that strut-and-tie modeling can be successfully applied to understand the behavior of non-contact lap splices and is necessary in determining the anchorage length of lapped bars. Observations of headed bar anchorage have shown that the final anchorage capacity consists of peak head bearing and reduced bond. A model for anchorage capacity was produced based on this concept. Finally, recommendations for structural concrete design using headed reinforcement were made.Item Comparison between epoxy-coated steel and glass fiber reinforced polymer bars in a concrete highway bridge deck(Texas Tech University, 2002-12) Bice, JacobThe use of fiber reinforced polymer (FRP) bars as reinforcement in concrete highway bridges potentially provides a means that can extend the useful life of the bridges in selected cases. Resistance of glass fiber reinforced polymer (GFRP) rebars to corrosion associated with the use of de-icing salts on bridges makes these bars particularly attractive to the transportation industry. However, questions concerning the bars' relatively low modulus of elasticity, bond slip properties, and in situ corrosion resistance must be answered prior to widespread implementation in highway bridges. The Sierrita de la Cruz Creek Bridge near Amarillo, Texas provides a means of making a direct comparison between the performance of an epoxy coated steel (ECS) reinforced bridge deck and a fiber reinforced polymer (FRP) reinforced bridge deck. Short-term comparisons are presented in this thesis, and the long-term monitoring potential of the two bridge sections is also discussed. With the exception of a longitudinal crack that formed in the cast-in-place bay in the GFRP-reinforced span, this thesis found that the GFRP-reinforced sections perform almost identically to the steel-reinforced sections. The research performed for this thesis also determined that the FRP may be exposed to internal temperatures which may cause long-term deterioration of the FRP bars. The data collected in the live load tests set a benchmark for any future live load testing performed on the bridge. Long-term monitoring of the bridge will be required to assess the durability of the GFRP bars in the concrete bridge deck.Item Development of a CFRP system to provide continuity in existing reinforced concrete buildings vulnerable to progressive collapse(2007) Orton, Sarah Lynn, 1978-; Jirsa, James O.; Bayrak, Oguzhan, 1969-Reinforced concrete buildings may be vulnerable to progressive collapse due to a lack of continuous reinforcement. Progressive collapse is an extreme form of collapse that is disproportionate to the originating cause. Such collapses cause not only significant damage to buildings, but also greater loss of life and injuries. Carbon fiber reinforced polymer (CFRP) may be used to retrofit existing reinforced concrete beams and provide the missing continuity needed to resist progressive collapse. This research focuses on retrofitting the beams in a reinforced concrete building to provide sufficient continuity to reach catenary action. The catenary action may allow the beam to carry vertical loads at large displacements if a supporting column were removed. The CFRP can provide continuity through the negative moment reinforcement or through the positive moment reinforcement. The research was broken into three major components. Anchorage tests form the design basis of the CFRP retrofit and ensure that the capacity of the retrofit can be accurately predicted. Continuity tests determine if the CFRP retrofit is capable of providing continuity and if the retrofit will allow the beam to reach catenary action and sustain a load representing resistance to progressive collapse. The analysis model forms a set of equations for catenary action so the results can be applied to reinforced concrete beams in general. Forty anchorage tests, eight continuity tests, and one analysis model were constructed and evaluated. The anchorage tests found that carbon fiber anchors enabled improved utilization of the tensile capacity of a CFRP sheet and improved the efficiency of material usage in CFRP retrofits. The continuity tests found that beams without continuous reinforcement can reach catenary action (depending on design details) and a CFRP retrofit, if designed correctly (placed in locations that do not cause rebar fracture before catenary), may be able to reduce vulnerability to progressive collapse. The analysis model was able to accurately predict the load-deflection behavior of a reinforced concrete beam in catenary action. The overall conclusion is that a CFRP retrofit can reduce vulnerability to progressive collapse in reinforced concrete buildings.Item Effects of curing on shrinkage cracking in bridge deck concrete(Texas Tech University, 2003-12) Aamidala, Hari Shankar GShrinkage cracking is a critical factor affecting the durability of concrete bridge decks. Since cracks in reinforced concrete decks provide a path for corrosive agents to enter the concrete, thereby accelerating the deterioration of the reinforcing steel. Concrete undergoes volumetric changes due to variation in temperature and moisture. When concrete is prevented by a surrounding structure from undergoing these volumetric changes freely, tensile stresses are developed. Depending on the amount of restraint applied, these tensile stresses potentially lead to cracks in the structures. This type of cracking can be reduced by providing rebars in the form of mesh to take the tensile stresses and/or the use of shrinkage-reducing admixtures (SRAs). Recent studies performed on SRAs show that the use of such admixtures is an effective method to reduce shrinkage cracking. Simulating restraint experienced in highway pavements and bridge decks is a challenge to researchers. This challenge has led to the development of different methods to assess the potential of restrained shrinkage cracking. Currently, there exists no standard test to assess cracking due to restrained shrinkage, though several researchers have simulated the effects of restraint in various ways to better understand the behavior of concrete shrinkage. The objective of this research is the evaluation of the different concrete mix designs used in bridge decks in Texas. Specifically, the influence of curing duration on the cracking potential of concrete bridge decks has been investigated based on the unrestrained (free) linear shrinkage measurements of prismatic specimens. In addition to free shrinkage tests, tests have been performed to study the weight loss, modulus of elasticity and split tensile strength of the concrete mix designs. Using the data obtained from these tests, shrinkage stresses developed due to full-restraint (100%-restraint) have been estimated and compared with the split tensile strength to estimate the age at which a first crack can be observed in the concrete. The approach presented assists in better understanding the effect of shrinkage on the cracking of bridge decks under full-restraint. Using the weight loss measurements and weight of oven-dried specimens, internal moisture content was tracked. This data is used to compare the behavior of the material to the development of shrinkage strains. Comparing the different curing durations did not indicate a significant difference in the development of either modulus of elasticity or split tensile strength. However, a favorable correlation was observed between the tensile strength of concrete and shrinkage stresses developed due to full restraint based on different curing durations. The results did not show a significant delay in the age of first crack with increase in curing duration from 4 days to 7 days. Thus, based on the research to date, one can conclude that 4 day curing suffices for durability of bridge decks from a shrinkage cracking perspective.Item Rehabilitation of reinforced concrete slab-column connections for two-way shear(2006) Widianto; Bayrak, OguzhanItem 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.Item Structural analysis of aboveground storm shelters(Texas Tech University, 2002-12) Shamsan, Sanad Abdullah SallamNot available