Browsing by Subject "Post-tensioning"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Assessment of long-term corrosion resistance of recently developed post-tensioning components(2012-08) Moyer, Kevin Lee; Breen, J. E. (John Edward), 1932-; Wood, Sharon L.; Wheat, Harovel G.The forensic analysis of fourteen post-tensioned beam specimens after six years of aggressive exposure testing is the focus of this thesis. Funding for this research came from TxDOT and FHWA. Current post-tensioning materials and construction practices have been deemed inadequate due to fairly recent corrosion failures. Recently developed post-tensioning components and systems were assessed to determine their suitability to prevent durability concerns that had been found in older structures. Testing was conducted on the following variables: Strand Type, Duct Type, Duct Coupler Type, Anchorage Type, Electrically Isolated Tendons. Non-destructive and destructive testing methods were used to study the specimens and were evaluated on their effectiveness in predicting corrosion. Service life analysis was done on a structure using the strands and ducts study in the project. Galvanized duct showed substantial pitting and area loss. The majority of the plastic ducts had no observed damage. However, tendon grout chloride concentrations in most cases were extremely elevated with both galvanized and plastic ducts. This indicated that moisture had entered the duct, through either the couplers and/or grout vents. Except for strands from one specimen, the strands had minor corrosion with occasional mild pitting. The exception had heavy mild pitting confined to a small portion of the strand due to a hole in the duct. Backfill quality was good but it did not bond well with the base concrete. Therefore, moisture and chlorides entered the anchorage region. The electrically isolated tendon did not perform as well as expected. The grout chloride concentrations and level of corrosion damage were comparable to the concentrations and corrosion damage from the more conventionally protected specimens.Item Behavior of the cast-in-place splice regions of spliced I-girder bridges(2015-08) Williams, Christopher Scott; Bayrak, Oguzhan, 1969-; Jirsa, J. O. (James Otis); Ghannoum, Wassim M; Hrynyk, Trevor D; Wheat, Harovel GSpliced girder technology continues to attract attention due to its versatility over traditional prestressed concrete highway bridge construction. Relatively limited data is available in the literature, however, for large-scale tests of post-tensioned I-girders, and few studies have examined the behavior of the cast-in-place (CIP) splice regions of post-tensioned spliced girder bridges. In addition to limited knowledge on CIP splice region behavior, a wide variety of splice region details (e.g., splice region length, mild reinforcement details, cross-sectional geometry, etc.) continue to be used in the field. In response to these issues, the research program described in this dissertation was developed to (i) study the strength and serviceability behavior of the CIP splice regions of spliced I-girders, (ii) identify design and detailing practices that have been successfully implemented in CIP splice regions, and (iii) develop design recommendations based on the structural performance of spliced I-girder test specimens. To accomplish these tasks, an industry survey was first conducted to identify the best practices that have been implemented for the splice regions of existing bridges. Splice region details were then selected to be included in large-scale post-tensioned spliced I-girder test specimens. Two tests were conducted to study splice region behavior and evaluate the performance of the chosen details. The failure mechanisms of both test girders were characterized by a shear-compression failure of the web concrete with primary crushing occurring in the vicinity of the top post-tensioning duct. Most significantly, the girders acted essentially as monolithic members in shear at failure. Web crushing extended across much of the test span and was not localized within the splice regions. To supplement the spliced girder tests, a shear-friction experimental program was also conducted to gain a better understanding of the interface shear behavior between precast and CIP concrete surfaces at splice regions. The findings of the shear-friction study are summarized within this dissertation. Based on the results of the splice region research program, design recommendations were developed, including recommended CIP splice region details.Item Experimental investigation of crushing capacity of I-girder webs containing post-tensioning ducts(2012-12) Wald, David Michael; Jirsa, James O. (James Otis); Bayrak, OguzhanThe shear capacity of a post-tensioned, concrete I-girder may be influenced if the crushing capacity of the web is reduced by ducts for the tendons. An experimental investigation was conducted on compressively-loaded, high-strength concrete panels with embedded post-tensioning ducts to better understand the parameters influencing girder web crushing behavior. The panels were intended to represent portions of a girder web subjected to shear-induced, principal compressive stresses. Material properties and construction procedures utilized in the fabrication and erection of bridge members in the field were considered. The primary goal of this study was to assess the impacts of various parameters on web crushing capacity. The results were needed to determine which variables should be considered for shear testing of full-scale girders. The parameters considered in the panel test program were duct type, grouting, member thickness, and the inclusion of confining reinforcement near the ducts. Notable findings from this study indicate that 1) elements with plastic ducts exhibit lower capacities than those with steel ducts, 2) a significant size effect exists when determining crushing capacity, and 3) the presence of a small amount of reinforcement placed near a duct through a member’s thickness can greatly improve its capacity. Results indicated that American design codes may be severely unconservative in their handling of ducts when designing for shear. Recommendations to refine and expand the standard approach for reducing web crushing capacity were developed. Additionally, a new means of estimating web crushing capacity was introduced.