Browsing by Subject "Shear"
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Item Analysis of the shear behavior of prestressed concrete spliced girders(2016-08) Al-Tarafany, Dhiaa Mustafa T.; Jirsa, J. O. (James Otis); Bayrak, Oguzhan; Tassoulas, John; Hrynyk, Trevor; Ghannoum, Wassim; Wheat, HarovelImplementation of the spliced girder technology in bridges has been growing in recent years. Increased girder lengths can now be realized by splicing shorter precast segments to produce a long span. The research conducted in this dissertation is focused on an evaluation of spliced girders using a three dimensional finite element analysis. The project consisted of a series of tests that were conducted in two phases. In Phase I, the effect of post-tensioning ducts on the shear behavior and strength of prestressed concrete girders was evaluated. In Phase II, the focus was on the behavior of cast-in-place splice regions between precast segments. Since a limited number of full scale beams could be tested, a three-dimensional advanced finite element program is an effective alternative to expensive tests. The parameters considered were grout to girder concrete strength ratio, splice to girder concrete strength ratio, concrete shear key detailing, coupler diameter, duct to web width ratio, shear span to depth ratio, and concrete shrinkage losses. The findings are described in detail. Using the experimental and analytical results, it was found that the grout to concrete strength ratio for grouted ducts should not to be less than 0.3. The effect of increasing the duct diameter to web width ratio from 0.43 to 0.57 was minimal. Splice to girder concrete strength ratio should be greater than 0.6. The addition of a shear key had no effect on the shear capacity of the girder. The coupler diameter in the splice region had no effect on the behavior of the spliced girder for coupler diameter to web width ratio up to 0.55. Including concrete shrinkage in the analysis slightly improved the correlation with observed response.Item Anchorage-controlled shear capacity of prestressed concrete bridge girders(2012-05) Langefeld, David Philip; Bayrak, Oguzhan, 1969-; Ghannoum, WassimAs part of the ongoing research on shear at the Phil M. Ferguson Structural Engineering Laboratory (FSEL) located at The University of Texas at Austin, the anchorage controlled shear capacity of prestressed concrete bridge girders was in this research studied in two distinct ways, experimentally and analytically. The results of this research are an important step towards improving understanding of strand anchorage related issues. For the experimental program, two full-scale Tx46 prestressed concrete bridge girders were fabricated at FSEL. The Tx46 girders were topped with a concrete, composite deck. Both ends of the two girders were instrumented and tested. For the analytical program, a new Anchorage Evaluation Database (AEDB) was developed, by filtering and expanding the University of Texas Prestressed Concrete Shear Database (UTPCSDB), and then evaluated. The AEDB contained 72 shear tests, of which 25 were anchorage failures and 47 were shear failures. The results and analysis from the experimental and analytical programs generated the following three main conclusions: (1) A reasonable percentage of debonding in Tx Girders does not have a marked impact on girder shear capacity calculated using the 2010 AASHTO LRFD General Procedure. (2) The AASHTO anchorage equation is conservative but not accurate. In other words, this equation cannot be used to accurately differentiate between a shear failure and an anchorage failure. In regards to conservativeness, anchorage failures in AASHTO-type girders may lead to unconservative results with respect to the 2010 AASHTO LRFD General Procedure. (3) The 2010 AASHTO anchorage resistance model and its corresponding equation do not apply to Tx Girders. Because of the Tx Girders' wider bottom flange, cracks do not propagate across the strands as they do in AASHTO-type girders. This fact yields overly conservative results for Tx Girders with respect to AASHTO Equation 5.8.3.5-1. In summary, this research uncovered the short-sided nature of the AASHTO anchorage design method. Given its short-comings, there is an obvious need for a validated, comprehensive, and rational approach to anchorage design that considers strength and serviceability. To appropriately develop this method, additional full-scale experimental testing is needed to expand the AEDB, as currently there are not enough tests to distinguish major, general trends and variables. Any future additional research would be expected to further validate and expand the significant findings that this research has produced and so take the next step toward safer, more-efficient bridge designs.Item ASR/DEF-damaged bent caps: shear tests and field implications(2009-12) Deschenes, Dean Joseph; Bayrak, Oguzhan, 1969-; Folliard, Kevin J.Over the last decade, a number of reinforced concrete bent caps within Houston, Texas have exhibited premature concrete damage (cracking, spalling and a loss of material strength) due to alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF). The alarming nature of the severe surface cracking prompted the Houston District of the Texas Department of Transportation to initiate an investigation into the structural implications of the premature concrete damage. Specifically, an interagency contract with the University of Texas at Austin charged engineers at Ferguson Structural Engineering Laboratory to: 1. Establish the time-dependent relationship between ASR/DEF deterioration and the shear capacity of affected bridge bent caps. 2. Develop practical recommendations for structural evaluation of in-service bridge bent caps affected by ASR and/or DEF. To accomplish these objectives, six large-scale bent cap specimens were fabricated within the laboratory. Four of the specimens (containing reactive concrete exposed to high curing temperatures) represented the most severe circumstances of deterioration found in the field. The remaining two specimens (non-reactive) provided a basis for the comparison of long-term structural performance. All of the specimens were subjected to a conditioning regimen meant to foster the development of realistic ASR/DEF-related damage. Resulting expansions were characterized over the course of the study through a carefully-planned monitoring program. Following a prolonged exposure period, three of the six bent cap specimens (representing undamaged, mild, and moderate levels of deterioration) were tested in shear. Observations made over the course of each test captured the service and ultimate load effects of ASR/DEF-induced deterioration. Six shear-critical spans were tested prior to this publication: three deep beam and three sectional shear tests. The remaining six shear spans (contained within the remaining three specimens) were retained to establish the effects of severe deterioration through future shear testing. Subsequent analysis of the expansion monitoring and shear testing data provided much needed insight into the performance and evaluation of ASR/DEF damaged bent structures. The results ultimately formed a strong technical basis for the preliminary assessment of a damaged bent structure within Houston, Texas.Item Behavior of slender beams without stirrups: effects of load distribution and member depth(2015-12) Klein, Joseph Robert; Bayrak, Oguzhan, 1969-; Hrynyk, Trevor DThough uniform loading is common in structures, the vast majority of all shear strength tests on slender reinforced concrete members without stirrups have been performed using concentrated loading. Furthermore, the uniform load tests that have been conducted typically involve members with smaller specimen depths (d) and larger reinforcement ratios (ρ) than are commonly used in practice. Previous studies usually agree that a noticeable increase in shear strength can be expected when a specimen is subjected to uniform loading as opposed to concentrated loading. Six shear tests were performed on four slender beams without stirrups at The University of Texas at Austin. Two of the specimens had approximately double the effective depth (d) as the other two. For a given depth, two concentrated load tests were carried out on either end of one specimen, and one uniform load test was carried out on the second specimen. Thus, four reinforced concrete beams were used to perform a total of four concentrated load tests and two uniform load tests, with the objective of determining the influence of load distribution as member depth (d) increases. To ensure that a direct comparison could be made between each load distribution, the ratio between maximum bending moment and maximum shear force was maintained for all tests. Additionally, to provide consistency with typical design practice, the reinforcement ratio (ρ) was selected to match that of a typical beam. The experimental results presented an influence of load distribution opposite to that of previous studies, with a range of increase in shear strength at first diagonal cracking of concentrated load tests of -16 to 50 percent, with an average increase of 18 percent, over uniform load tests. Additionally, the tests with smaller effective depths (d) saw a percent increase in shear strength of 31 to 68 percent, with an average increase of 50 percent, over tests with larger effective depths (d).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 Effect of confinement on shear dominated reinforced concrete elements(Texas A&M University, 2005-02-17) Powanusorn, SuraphongIt has been demonstrated that transverse reinforcement not only provides the strength and stiffness for reinforced concrete (RC) members through direct resistance to external force demands, but also helps confine the inner core concrete. The confinement effect can lead to improved overall structural performance by delaying the onset of concrete fracture and allowing more inelastic energy dissipation through an increase in both strength and deformability of RC members. The objective of this research was to evaluate the effect of confinement due to the transverse reinforcement on enhancing the shear performance of RC members. A new constitutive model of RC members was proposed by extending the Modified Compression Field Theory (MCFT) to incorporate the effect of confinement due to transverse reinforcement by adjusting the peak stress and peak strain of confined concrete in compression. The peak stress of confined concrete was determined from the five-parameter failure surface for concrete developed by Willam and Warnke (1974). The peak strain adjustment was carried out using a relationship proposed by Mander et al. (1988). The proposed analytical model was compared with results from an experimental program on sixteen RC bent caps with varied longitudinal and transverse reinforcement details. Two-dimensional Finite Element Modeling (FEM) using the proposed constitutive model was conducted to numerically simulate the RC bent cap response. Results showed that the proposed analytical model yielded good results on the prediction of the strength but significantly overestimated the post-cracking stiffness of the RC bent cap specimens. The results also indicated that the confinement effect led to enhanced overall performance by increasing both the strength and deformability of the RC bent caps. Two potential causes of the discrepancy in the underestimation of the RC bent cap deformations, namely the effects of concrete shrinkage and interfacial bond-slip between the concrete and main flexural reinforcement in the bent caps, were discussed. Parametric studies showed that the tension-stiffening in the proposed constitutive models to implicitly take into account the bond-slip between the concrete and main flexural reinforcement was the major cause of the overestimation of the post-cracking stiffness of RC bent caps. The explicit use of bond-link elements with modified local bond stress-slip laws to simulate the slip between the concrete and main flexural reinforcement led to good predictions of both strength and deformation.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.Item Experimental investigation of shear transfer between concrete interfaces(2014-12) Massey, Joshua Brice; Bayrak, Oguzhan, 1969-; Jirsa, James OThis experimental program was focused on the effect of surface geometry (shear keys) on the transmission of shear forces between concrete cast against a hardened concrete interface. This research was part of a larger study at The University of Texas at Austin focused on several aspects of spliced precast concrete girder technology, particularly those concerning the interface between precast girders and cast-in-place splices. 14 push-through type specimens were tested with varying surface geometries, interface reinforcement ratios, and levels of prestress normal to the interface. The surface types considered included smooth, single shear keys, multiple shear keys, saw teeth of multiple depths and a monolithic specimen for comparison. The principle findings were that surfaces with properly detailed indentations could transfer significantly higher shear forces before slip occurred than smooth surfaces, and that shear keys generally displaced better performance than saw-teeth. Forces from prestress and yielding of reinforcement crossing the interface during failure were found to contribute to the strength in effectively the same manner. In addition, the shear friction based provisions of ACI 318-11, AASTHO LRFD 2012, and Eurocode 2 were found to provide satisfactory predictions of the ultimate strength of such surfaces with reinforcement ratios less than 0.75 %.Item Experimentally Validated Compatibility Strut and Tie Modeling of Reinforced Concrete Bridge Piers(2010-10-12) Scott, Reece MelbyA compatibility-based strut-and-tie model C-STM is proposed for analyzing deep beams and disturbed regions with particular emphasis on reinforced concrete bridge piers. In addition to the normal strut-and-tie force equilibrium requirements the model accounts for non-linear behavior through displacement compatibility using inelastic constitutive laws of cracked reinforced concrete. The model is implemented into widely used commercial structural analysis software and validated against results from previously conducted large scale experiments. A near full-scale experiment on a reinforced concrete sub-assemblage that represents cantilevered and straddle pier bents is conducted to investigate the shear-flexure performance of deep (disturbed) regions. Insights into the development of nonlinear behavior and the final collapse failure mechanism are then evaluated and accurately modeled using the C-STM. It is concluded that the proposed C-STM serves as an advanced method of analysis that can predict with suitable accuracy the force-deformation response of both D- and B- regions, deep beams, and beam-columns. This provides engineers with a supplementary analysis tool that can be used to assess the nonlinear behavior of bridge piers with stocky members and/or large disturbed regions.Item In-plane shear strength and stiffness of precast concrete panels(2015-12) McCammon, Victoria Elizabeth; Helwig, Todd Aaron, 1965-; Clayton, PatriciaPre-Cast-Panels (PCP) have been used for decades as stay-in-place forms to support the wet concrete during the placement of bridge decks and as part of the composite slab for typical straight bridges. The typical connection detail in Texas is to set the panel on a foam bedding strip, leaving a ledge for the slab concrete to flow under; this ledge provides the long-term support for the panel. The PCP is not structurally connected to the bridge until the slab has set up; it provides no in-plane shear resistance under construction loads, when the superstructure is the most vulnerable to lateral forces. If the PCP is connected to the girders during deck casting they can provide bracing to the top flanges of the beams and forces in the traditional lateral resisting system can be reduced, potentially leading a reduction in the number of cross-frames and top lateral truss member sizes. The objective of this research is to measure the in-plane shear strength and stiffness of PCP attached to girder systems using different connections and to determine the stability of the traditional connection method with respect to in-plane shear movement. The research included testing conventionally reinforced full scale PCP in a shear frame. The typical Texas detail was tested at three different bedding strip heights. Variations of two additional connection methods were tested to determine their behavior. Bolting the PCP to the shear studs provides only a small in-plane shear stiffness and strength. Welding the PCP to a steel shape that is welded to the top flange of the beam provides a much stronger and stiffer connection.Item Permeability characterization of shear zones in the Hickory sandstone member, Riley Formation, Texas(Texas A&M University, 2005-02-17) Nieto Camargo, Jorge EnriqueReservoir compartments, typical targets for new infill locations, are commonly created by faults that may reduce or enhanced permeabilities. Faults often contain narrow zones of intense shear comprised of geometrically complex elements that reduce permeability and compartmentalize blocks as a function of time and pressure. This thesis characterizes the permeability structure of shear zones and the relationship between fault permeability, host rock properties and the relative degree of deformation. The main objectives of this work are to (1) characterize the geometry and permeability of deformation elements within shear zones; (2) determine permeability anisotropy in shear zones according to fault characteristics and host lithology; and (3) develop a process to predict permeability anisotropy of faults in reservoirs using probabilistic approaches. The study results give a better understanding of fluid flow behavior of shear zones and their potential to create reservoir heterogeneity and compartmentalization. Fluid flow in a reservoir with faults is controlled by variables such as fault throw, shear-zone thickness, undeformed and deformed rock permeability and the geometry of all deformation elements. Methodology to predict permeability structure was developed using analytical and numerical simulation of selected core samples and laboratory measurements. We found useful relationships between permeability of the host rock and highly deformed elements according to the amount of throw of the fault. The high lateral continuity of the highly deformed elements and their predictable low permeability make these elements most important in controlling permeability in shale-free and low-shale shear zones created by low displacement (subseismic) faulting. Probe permeameter data is a precise, inexpensive and non-destructive source of permeability information that can be effectively incorporated in detailed models to investigate the effect of individual deformation elements in the whole shear zone permeability and their effect at the field scale.Item Preliminary analysis of doubler plate attachment details for steel moment resisting frames(2011-05) Shirsat, Priyanka Saiprakash; Engelhardt, Michael D.; Engelhardt, Michael D.; Helwig, Todd A.In steel moment resisting frames, the region of the column located within the beam-column joint is known as the panel zone. When a steel moment resisting frame is subjected to lateral load, due to wind or seismic loads, the panel zone is subject to high shear. In some cases, the shear in the panel zone is sufficiently high that the panel zone must be reinforced to increase its stiffness and/or strength. This is normally accomplished by welding doubler plates to the column in the panel zone region. Doubler plates can be a costly feature in steel moment resisting frames because of the substantial amount of welding involved. There has been a large amount of past research that has investigated the required shear strength and stiffness of the panel zone region to establish a basis for sizing doubler plates. However, very little past research has investigated the details of attaching doubler plates to columns. These attachment details can have a significant influence on the structural performance of panel zone and on cost. The overall goal of this research was to conduct preliminary finite element studies that provide insight into several key issues related to the attachment of doubler plates to columns and to identify issues that require further research. The research involved finite element modeling of a simplified representation of beam-to-column joint subjected to monotonic loading. A total of twenty-one analysis cases with different doubler plate attachment details were studied. Issues that were investigated included the effect of welding different edges of the doubler plate to the column (horizontal edges only, vertical edges only, and all four sides), the effect of extending the doubler plate beyond the panel zone region, and the effect of providing two thinner doubler plates of equivalent total thickness on both sides of the column web instead of one thick doubler plate on one side of the column web. In addition, the forces developed in the doubler plate welds were computed from the finite element analysis and compared with current building code requirements for the design of these welds. Observations and preliminary design recommendations on these issues are provided in this thesis, along with recommendations for further research.Item Pretensioned box beams : prestress transfer and shear behavior(2011-12) Avendaño Valderrama, Alejandro Raul; Bayrak, Oguzhan, 1969-; Jirsa, James O.; Wood, Sharon L.; Breen, John E.; Ezekoye, OfodikePretensioned concrete box beams have been used in highway bridges for more than half a century. Due to their geometry, they have often been used as a viable alternative to the classic I-shaped girders. Box beams are highly effective in cases where speed of construction is a priority. However, the detailing and design of box beams are more complicated than that of I-shaped girders. The flow of forces at the beam’s end blocks must be understood in order to detail reinforcement adequately. The following were the objectives of this research study: (i) quantify the demands placed on box beam end blocks upon prestress transfer, (ii) characterize the demands placed on box beam end blocks upon the application of superimposed loads, (iii) evaluate the effects of alternative void geometries at skewed ends of box beams on curing temperatures, (iv) based on the knowledge gained in (i), (ii) and (iii), improve the box beam end blocks, (v) test the improved end block under worst case scenario demands at prestress transfer and under extreme loading conditions, and (vi) validate currently used shear strength design methodologies in their application to pretensioned box beams. In order to achieve these objectives, an experimental program was conducted. The experimental program included the load testing of ten 4B28 and five 5B40 box beams, for a total of twenty nine load tests. The influence of several factors that distinguish box beam behavior from the better-understood I-shaped girder behavior was studied. Additionally, the experimental program included the fabrication, instrumentation and early-age behavior study of five 5B40 box beams. The first three beams were used to vii assess the behavior of box beams fabricated with the current TxDOT standard details (from December 2006). The fourth beam incorporated modifications to the standard reinforcement details based on the observations made through the study of the first three 5B40 box beams. The last specimen corresponded to a new box beam cross section (5XB40) optimized to be used in a spread-box beams configuration.Item Shear behavior of reinforced concrete bridge pile cap girders strengthened with carbon fiber reinforced polymer (CFRP) strips and CFRP anchors(2016-08) Shekarchi, William Asad; Ghannoum, Wassim M.; Jirsa, J. O. (James Otis); Hrynyk, Trevor D; Juenger, Maria C.G.; Wheat, Harovel GExternally bonded CFRP strips are ideal for rehabilitating existing members due to their high tensile strength-to-weight ratio, relatively low cost, formability, and expedited installation times. However, without proper anchorage, CFRP strips debond from the concrete surface before the strength of the CFRP can be mobilized. Consequently, CFRP spike anchors are used to delay debonding and develop the fracture strength of the CFRP strips. Previous research conducted on large-scale T-beams have shown that uni-directional (vertical) and bi-directional (vertical and horizontal) applications of CFRP strips and anchors increased the cracking load and ultimate shear capacity of members with transverse steel reinforcement, thin webs, and span-to-depth ratios above three (i.e., sectional behavior). However, the ability of the CFRP to strengthen wide-webbed members remained unknown. The objective of this research was to investigate the feasibility of strengthening wide-webbed reinforced concrete pile cap girders in shear using CFRP strips and CFRP anchors and to develop comprehensive design and detailing recommendations for CFRP shear strengthening. An experimental test program, consisting of nine tests, was created to investigate: 1) the effects of loading conditions, 2) retrofitting uncracked and cracked sections, 3) placing anchors in tension zones, and 4) uni- and bi-directional CFRP layouts on the shear performance of 32-in. deep by 32-in. wide reinforced concrete pile cap girders. The test results indicated that the uni-directional CFRP layouts were able to increase the shear capacity by as much as 56% while the bi-directional layouts increased the cracking shear load by as much as 22%. Anchored CFRP layouts were found to be as efficient as fully wrapped layouts despite anchors being placed in tension zones. Moreover, at the onset of the loss of shear strength, the measured lower bound average CFRP fracture strain was 0.007, which is significantly larger than the permitted effective strain in current ACI 440.2R-08 design guidelines (i.e., 0.004). A database of test results from relevant CFRP strengthened specimens was collected, in addition to using the pile cap girder experimental results, to develop a rational design approach and detailing recommendations for CFRP shear strengthening.Item Shear behavior of reinforced concrete T-beams strengthened with carbon fiber reinforced polymer (CFRP) sheets and CFRP anchors(2011-12) Kim, Yun Gon, 1977-; Ghannoum, Wassim M.; Jirsa, J. O. (James Otis); Wood, Sharon L.; Bayrak, Oguzhan; Liechti, KennethThe objective of this research is the evaluation of shear behavior of full-scale reinforced concrete T-beams strengthened with carbon fiber reinforced polymer (CFRP) sheets and CFRP anchors. Although the CRFP material has high tensile strength, premature failure due to debonding CFRP sheets prevents utilizing that strength. The use of CFRP anchors prevents this failure, so the CFRP sheets are able to reach ultimate strain. The current shear design is based on plasticity, which assumes that all steel (ductile material) stirrups, across the critical section yield at ultimate. However the strain in the CFRP (brittle material), is essential to estimate the shear contribution of CFRP. To evaluate the validity of CFRP strengthening for shear, 24 tests were conducted with several parameters including shear-span-to-depth ratio, depth of beams, different transverse reinforcement ratios, and the layout of CFRP strips. In addition, a simple shear behavior model was developed to explain the differences between ductile and brittle material. From test observation, the use of CFRP anchors resulted in U-wrap application to perform like continuous wrapping which implies that a CFRP strip reached rupture strain because the anchors prevented debonding failure. However, all FRP strips did not rupture simultaneously because the strain distribution across a critical crack was not uniform. The average strain across the critical crack was about 0.005. Therefore a conservative value of effective strain (0.004) was selected for design purposes. In addition, when a beam is strengthened with CFRP, interactions between the contributions of the CFRP, steel or concrete must be taken into account. Factors ka, ks, and kf were introduced in the proposed shear design equations. Factor ka reflects the change in the material contributions as the shear span to depth ratio (a/d ratio) changes in deep beams. Factors ks and kf account for the change in steel or CFRP shear contribution due to the change in the critical crack angle as well as the interactions between the steel and FRP transverse reinforcement. As the amount of either steel or FRP material increase, the efficiency of the other material decreases.Item Shear behavior of spliced post-tensioned girders(2014-08) Moore, Andrew Michael, 1984-; Bayrak, Oguzhan, 1969-; Ghannoum, Wassim M.By its nature a spliced girder must contain a number of post tensioning tendons throughout its length. The focus of the experimental program described in this dissertation is the evaluation of the strength and serviceability of post-tensioned girders loaded in shear, and, more specifically, how a post-tensioning duct located in the web of a girder affects the shear transfer mechanism of a bulb-tee cross-section. Due to the limited number of tests in the literature conducted on full-scale post-tensioned girders, eleven shear tests were performed on seven prestressed concrete bulb-tee girder specimens. Of these tests, ten were conducted on specimens that contained a post-tensioning duct within their web and additional pretensioning reinforcement in their bottom and top flanges. The remaining shear test was conducted on a control specimen that did not have a post-tensioning tendon but contained the same pretensioning reinforcement as the post-tensioned girder specimens. The behavioral characteristics of these eleven test specimens at service level shear forces and at their ultimate shear strengths were evaluated in regards to five primary experimental variables: (i) the presence of a post-tensioning duct, (ii) post-tensioning duct material (plastic or steel), (iii) web-width, (iv) duct diameter, and (v) the transverse reinforcement ratio. The findings of this experimental study are described in detail within this dissertation, but can be summarized by the following two points. (i) No differences were observed in the ultimate or service level shear behavior in girders containing plastic grouted ducts when compared to those containing steel grouted ducts and (ii) The current procedure of reducing the effective web width to account for the presence of a post-tensioning duct is ineffective because it addresses the incorrect shear transfer mechanism. A method that correctly addresses the reduction in shear strength due to the presence of a post-tensioning duct was developed and verified using the tests performed during this experimental program and tests reported in the literature.Item Shear database for prestressed concrete members(2011-05) Nakamura, Eisuke; Bayrak, Oguzhan, 1969-; Jirsa, James O.Development of shear databases attracted a great deal of attention in the shear research community within the last decade. Although a few shear databases have already been developed by several research groups, there is no comprehensive shear database that is focused on prestressed concrete members. This thesis aims to develop a shear database for prestressed concrete members with an intensive literature review. This literature review resulted in a database that contained a total of 1,696 tests reported in North America, Japan, and Europe from 1954 to 2010. The database was used to evaluate shear design provisions available in North America, Japan, and Europe. The variations in measured versus calculated shear strength using twelve shear design equations were analyzed. The analysis results indicated that design expressions based on the Modified Compression Filed Theory (MCFT) produced the best performance to estimate the shear strength of prestressed concrete members with sufficient shear reinforcement. The MCFT-based design expressions, however, provided unconservative strength estimations for members that failed in shear but exhibited signs of horizontal shear damage and/or anchorage zone distress. The ACI 318-08 detailed method was found to be less conservative than the MCFT-based design expressions. Additionally, on the basis of a careful examination of test results included in the database, a new limit for the minimum shear reinforcement was proposed. The database was also used to investigate the shear behavior of prestressed concrete members. This investigation revealed that there was no evidence of size effect in the shear strength of prestressed concrete members with sufficient shear reinforcement. Additionally, it was found that prestress force and shear reinforcement increased the shear strength although there was an upper limit on the effectiveness of shear reinforcement.Item Shear performance of ASR/DEF damaged prestressed concrete trapezoidal box bridge girders(2010-08) Wang, Tz-Wei; Jirsa, J. O. (James Otis); Bayrak, Oguzhan; Ghannoum, Wassim M.; Wheat, Harovel G.; Zhu, JinyingConcrete bridges in Texas have developed large cracks in bent caps and pretensioned trapezoidal bridge girders. The bridges show premature concrete deterioration due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF). There is concern that deterioration due to ASR/DEF may lead to a loss of structural capacity. However, there are no quantitative guidelines to relate the level of concrete deterioration due to ASR/DEF to structural performance. Using such guidelines, the need for rehabilitation of beams with ASR/DEF cracking can be assessed. The goal of this research was to determine the shear capacity of pretensioned trapezoidal box girder specimens exhibiting varying degrees of ASR and/or DEF cracking and to use the shear testing results to evaluate the severity of the problem that may exist in Texas bridge structures. To achieve this goal, beams that were severely deteriorated due to ASR/DEF over a period of more than ten years were transported to the University of Texas for testing to failure. Both severely deteriorated and uncracked beams were tested in shear. The test results were used to evaluate the shear performance of trapezoidal box beams affected by ASR/DEF. In addition, three different types of forensic analyses were conducted on the beams to understand the nature of the ASR/DEF cracks and severity of the deterioration. After testing, it is found that the shear capacity of the test specimens was not significantly reduced even with heavy ASR/DEF cracking. Assessment using current US design provisions for bridges or buildings (ACI 318-08 and AASHTO LRFD 2008) and the proposed provision from an earlier project (TxDOT Project 5253) yielded conservative estimates of strength. Results from forensic analyses provided a qualitative indication of ASR/DEF damage but did not correlate with the observed levels of ASR/DEF deterioration.Item Shear strengthening of reinforced concrete beams with bi-directional carbon fiber reinforced polymer (CFRP) strips and CFRP anchors(2014-08) Alotaibi, Nawaf Khaled; Jirsa, J. O. (James Otis); Ghannoum, Wassim M.The use of externally bounded Carbon Fiber Reinforced Polymer (CFRP) for strengthening existing RC structures has shown promising results. Although CFRP materials have high tensile strength, the ability to utilize that strength is limited by debonding of the CFRP laminates from the concrete surface. In order to prevent or delay debonding, CFRP anchors were used to provide an alternative means of transferring forces from CFRP strips to the concrete. Previous tests on prestressed I-girders strengthened with uni-directional and bi-directional CFRP strips showed that bi-directional CFRP application resulted in significant shear strength gain in comparison to a uni-directional application. The objective of this thesis is to evaluate the behavior of reinforced concrete beams strengthened in shear with bi-directional CFRP strips and CFRP anchors so that the findings from the previous work can be understood and implemented. Four 24 in. deep T-beams were fabricated at the Phil M. Ferguson Structural Engineering Laboratory at The University of Texas at Austin. Eight tests were conducted on these specimens to examine the effect of the bi-directional layout of CFRP on the shear strength. Specimens with 14-in. web width were selected as a part of the experimental program to allow for direct comparison with test results from the previous project. Additional beams with a web width of 8 in. were included to evaluate thinner webs similar to those in the I-girders. Test results indicate a significant increase in shear strength due to the bi-directional application of CFRP strips with CFRP anchors installed on beams with a shear span-to-depth ratio (a/d) of 3. Substantial shear strength gain up to 62% was achieved in beams with 14-in. webs. and up to 43% for beams with 8-in. webs. However, negligible shear strength gain was observed in beams with a/d of 1.5 (deep beams). Experimental test results demonstrate an interaction between the contribution of concrete, transverse steel and CFRP to the shear resistance of a reinforced concrete beam. The findings of this research contribute to a better understanding of the shear behavior of reinforced concrete members strengthened with externally bonded CFRP applied bi-directionally. Experimental results from this research project provide data needed in the field of CFRP shear strengthening since limited data are available on large-scale tests.Item Shear strengthening of reinforced concrete beams with carbon fiber reinforced polymer (CFRP) and improved anchor details(2009-12) Quinn, Kevin Timothy; Ghannoum, Wassim M.; Jirsa, J. O. (James Otis)Fifteen tests were conducted to evaluate the shear performance of beams with carbon fiber reinforced polymer (CFRP) laminates and CFRP anchors. The specimens consisted of 24-in. deep T-beams. The specimens were strengthened in shear with CFRP laminates that were anchored using several different CFRP end anchorage details. Load was applied to the reinforced concrete members at three different shear span-to-depth ratios. Observations of the behavior and data from the tests were used to evaluate the performance of the CFRP laminates and CFRP anchors. Overall, a 30-40% increase in shear strength was observed when anchored CFRP laminates were installed on members loaded at a shear span-to-depth ratio greater than two. The CFRP strengthening system performed well when properly detailed CFRP anchors were installed. Design recommendations regarding the installation of the CFRP anchors were developed. The CFRP anchorage detail developed in this study provided additional CFRP material in critical locations to reinforce the anchor and prevent premature failures from occurring due to anchor rupture. Theoretical calculations predicting the shear strength of the retrofitted concrete members were carried out and compared to the measured strengths of the members. Based on this analysis, a design equation was developed that produced conservative results for all of the specimens tested.