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............................65 Figure 7.1 Diagram of Hoyer Effect [65].............................................................................................72 Figure 7.2 Variation of Steel Stress =-=[3]-=-................................................................................................73 Figure 8.1 Beam Nomenclature ...........................................................................

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...ms. 11.3.1.1 Moment Comparison Three methods of calculating the theoretical moment capacity were used: the AASHTO STANDARD Method, the Whitney Stress Block method, and the Stress Block Factors Method =-=[24]-=-. A factor of φ = 1.0 156was used in each method. All of these methods are based on the assumption of strain compatibility and give virtually identical results for these beams. The results of these c...

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...up to and including 6000 psi [47]. The tensile strength of normal strength concrete is around 15% of the compressive strength [72]. Typical reinforced concrete will use a minimum of 3500 psi concrete =-=[46]-=-, and is in widespread use in the construction industry. Prestressed concrete often uses strengths in the 6000 psi range for many applications, although recent years have seen increased use of much hi...

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...ms. Mixes F-6 through F-9 were aimed at solving the 8000 psi strength problem. Mixes F-7 through F-9 were based upon a mix used in an earlier high-strength normalweight concrete project by John Myers =-=[57]-=-. The volume of normalweight aggregate was replaced by an equal volume of lightweight aggregate. 3.3.1.2 Chemical Admixtures For this sequence of the project, Daratard-17 and ADVA Superflow were again...

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...relation between the amount of draw-in at the free end of the strand, ∆d, the initial strain in the strand, esi, and the transfer length. The original equation formulated by Guyon is given as Eq. 7.6 =-=[30]-=-. 2 77Lt α ⋅ ∆ d = Equation 7.6 In this equation, α is a term that accounts for either a constant load stress distribution, α=2, or a linear load stress distribution, α=3. Balazs states that Polish r...

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...oject. 7.3.4.1 Martin, L. & Scott, N. – [49] The researchers in this study indicate that the values for transfer and development length in the ACI Code were determined from a study by Kaar and Magura =-=[31]-=-. All the tests that Kaar and Magura performed were on normalweight concrete specimens. The researchers contended that in the Kaar and Magura study only one test beam failed as a result of bond failur...

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...t of normalweight concrete. The creep and shrinkage of lightweight concrete are comparable to that of normalweight concrete, and the same multipliers and coefficients in the code can be used for both =-=[47, 72]-=-. The use of lightweight concrete in bridge applications has been gaining popularity since 1955, particularly in California and Norway. Bridge girder and deck applications, as well as slabs in buildin...

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...1. This study evaluated experimentally the applicability of the AASHTO-calculated minimum development length for lightweight concrete. 3Table 1.1 Development Length Equations Author ACI 318 / AASHTO =-=[2,1]-=- L d Development Length Equation ⎛ 2 = ⎜ f ps − f se ⎝ 3 ⎞ ⎟ ⎠ Zia & Mostafa [18] Buckner (FHWA) [5] L = L + 1. 25( f − f ) d d d t t pu L = L + λ( f − f ) d ps se se b b Mitchell [13] L d = L t + ( f...

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...for determining this value are: 76L ⎛ ⎞ e ⎜ 135 L ≤ ≤ + 31⎟ e 80d b f ps Equation 7.1 80 1/ 6 d b ⎝ d b ⎠ L 135 80d f 6 0. 39L e e b ps 1 / d d b b + ≤ ≥ Equation 7.2 7.3.4.2 Mitchell, D., et. al. – =-=[54]-=- This team of researchers examined the influence of concrete strength on the transfer and development length for pretensioned strand in normalweight concrete. They performed tests of 22 precast preten...

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....................... 8 2.1.5 Nilsen and Aïtcen (1992) [59].............................................................................................................. 9 2.1.6 Zhang and Gjørv (1991) =-=[80]-=-............................................................................................................... 9 2.1.7 Mircea, Ioani, Filip, and Pepenar (1994) [53]......................................

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... coarse aggregates can lead to significant reductions in the selfweight of the concrete. Materials used as lightweight aggregate include slate, slag, palletized fly ash, and expanded clays and shales =-=[58]-=-. The clays and shales are mined from the ground and then placed in a kiln. As they are heated, gases are introduced and the materials expand into a hard, yet porous, material. The porosity (voids in ...

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...................................... 9 2.1.7 Mircea, Ioani, Filip, and Pepenar (1994) [53]...................................................................................... 9 2.1.8 Reichard (1967) =-=[64]-=-.......................................................................................................................... 10 2.2 PERFORMANCE OF LIGHTWEIGHT CONCRETE IN PRESTRESSED MEMBERS...............

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...d concern that the equations developed by Kaar and Hanson were not accurate. To determine the transfer length they used the slope-intercept method. They used the equation developed by Zia and Mostafa =-=[83]-=- as the model for their equation. They concluded that the transfer length should be a function of the initial stress in the steel, fsi, and concrete compressive strength at transfer, f’ci. The square ...

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...0.020 (15) x x zip ties LW8000-20-S 0.038 0.054 (3) 0.021 (16) x x LW8000-1-N 0.045 0.057 (1) 0.040 (12) 0.050 0.044 LW8000-1-S 0.042 0.067 (8) 0.015 (12) 0.041 0.042 LW8000-2-N 0.039 0.051 (9) 0.034 =-=(4,7)-=- 0.050 0.042 2 bad LW8000-2-S 0.042 0.054 (9) 0028 (5) 0.045 0.042 LW8000-3-N 0.044 0.060 (8) 0.027 (2) 0.036 0.046 LW8000-3-S 0.044 0.061 (2) 0.030 (4) 0.059 0.040 3,7-8 bad LW6000 0.052 0.045 0.049 ...

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...se facts. Combining this equation with the transfer length equation yielded the development length equation given as Eq. 7.11: L = L + 1. 25( f − f ) d Equation 7.11 d t pu se b 7.3.4.6 Buckner, C. – =-=[21]-=- This report was commissioned by the FHWA to review the recent studies being completed at that time on transfer and development length, analyze the data, and formulate design equations and guidelines....

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................................7 2.1.1 Martinez Morales (1982) [50].............................................................................................................. 7 2.1.2 Shideler (1957) =-=[70]-=-............................................................................................................................. 8 2.1.3 Zhang and Gjørv (1993) [81]..........................................

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...ided for a relatively crack-free structure. Overall performance of the bridge was expected to be more than adequate, providing increased seismic resistance for a smaller cost. 2.2.2.4 Vaysburd (1996) =-=[78]-=- In his article in Concrete International, Vaysburd reported a study of durability of lightweight concrete structures. By comparing the mechanical properties of lightweight concrete to normalweight co...

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...ad stress distribution, α=3. Balazs states that Polish researchers had conducted tests which found this constant equal to 2.86 [84] while research performed by den Uijl obtained a value of 2.46 for α =-=[6]-=-. Balazs states that the problem with Guyon’s equation is that the coefficient takes into account the assumed shape of the bond stress distribution. He develops an equation that did not have this prob...

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...ed by calculations and in fact did not occur in the actual beams 838.3 DEVELOPMENT OF 40-FT DESIGNS The use of a 40-ft length for the test beams was determined by their effectiveness in past studies =-=[15]-=-. This allowed two tests to be performed on one beam without the damage from one test unduly influencing the next test. By using one beam for two tests it was possible to control the independent varia...

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...minimum development length for lightweight concrete. 3Table 1.1 Development Length Equations Author ACI 318 / AASHTO [2,1] L d Development Length Equation ⎛ 2 = ⎜ f ps − f se ⎝ 3 ⎞ ⎟ ⎠ Zia & Mostafa =-=[18]-=- Buckner (FHWA) [5] L = L + 1. 25( f − f ) d d d t t pu L = L + λ( f − f ) d ps se se b b Mitchell [13] L d = L t + ( f − ps f se ) d b 4. 5 f ' c 1.6 OBJECTIVES TxDOT commissioned this research proje...

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...d development lengths. This section reviews the past and present literature pertaining to the models used for comparison of the test results in this research project. 7.3.4.1 Martin, L. & Scott, N. – =-=[49]-=- The researchers in this study indicate that the values for transfer and development length in the ACI Code were determined from a study by Kaar and Magura [31]. All the tests that Kaar and Magura per...

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...concrete beams was evaluated by Kolozs [43]. A portion of the testing of the development length of strand in lightweight concrete beams was also reported by Kolozs [43], and was completed by Thatcher =-=[75]-=-. Transfer length of strands in precast deck panels was studied by Sylva [85]. Additionally, strains, deflections, strand elongation, 2crack patterns, cracking and ultimate loads and moments, and fai...

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... 9.13. This figure compares the ACI 318 Code equation using fse as a variable in the equation for transfer length (Eqn. 2.14). The value for fse was calculated based on the recommendations of ACI 318 =-=[82]-=-. All the normalweight data falls below the line that signifies complete agreement between equation and measurement. This equation is not conservative for most of the lightweight concrete data, except...

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... values that had been presented in valid tests to give a safe approximation of the transfer length. This expression is given as Eq. 7.5 (units in ksi): L f se t = db Equation 7.5 7.3.4.4 Balazs, G. – =-=[14]-=- A theoretical approach can be taken to find a correlation between the amount of draw-in at the free end of the strand, ∆d, the initial strain in the strand, esi, and the transfer length. The original...

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...ht aggregate can weigh 40-50% less than normal coarse aggregate, and the hardened concrete using lightweight coarse aggregate can weigh 20% less than concrete cast using normalweight coarse aggregate =-=[33]-=-. The typical unit weight of normalweight concrete is about 145 to 150 lb/ft 3 . The unit weight of lightweight concrete is usually about 120 to 125 lb/ft 3 , and can range as low as 90 lb/ft 3 [58]. ...

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...ype of strain curve. A value of α=2 is used for a bilinear strain profile while α=3 is used for a parabolic strain profile. Lt α ⋅ ∆ d = Equation 9.3 ε si As discussed in Chapter 7, Russell and Burns =-=[66]-=- use a value of α=2 in their formulation of the transfer length. The notation is different from Equation 9.3, but the equation is essentially the same. The value of α=2 will be used for comparison in ...

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...length for lightweight concrete. 3Table 1.1 Development Length Equations Author ACI 318 / AASHTO [2,1] L d Development Length Equation ⎛ 2 = ⎜ f ps − f se ⎝ 3 ⎞ ⎟ ⎠ Zia & Mostafa [18] Buckner (FHWA) =-=[5]-=- L = L + 1. 25( f − f ) d d d t t pu L = L + λ( f − f ) d ps se se b b Mitchell [13] L d = L t + ( f − ps f se ) d b 4. 5 f ' c 1.6 OBJECTIVES TxDOT commissioned this research project (Project 0-1852)...

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.............. 8 2.1.3 Zhang and Gjørv (1993) [81]............................................................................................................... 8 2.1.4 Burg, Cichanski, and Hoff (1998) =-=[23]-=- ................................................................................................ 8 2.1.5 Nilsen and Aïtcen (1992) [59]....................................................................

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...concrete has been widely used in bridges in the United States since the 1960s. Most experiences have been good as lightweight concrete has performed similarly to normalweight concrete. 2.2.2.1 Hanson =-=[32]-=- Hanson wrote an early paper discussing the use of lightweight concrete for prestressed concrete construction. He focused on the expanded shale aggregate that was available in the Rocky Mountain area....

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...he concrete; the Hoyer effect, adhesion, and mechanical interlock. The Hoyer effect is the tendency of the prestressing strand to increase in diameter as the stress in the strand decreases at release =-=[35]-=-. Initially, before casting of the concrete, when the strand is in open air and is being stressed to its initial pretensioning stress, fpi, its diameter will decrease due to the Poisson’s ratio effect...

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...Also, measured chloride levels in the lightweight concrete were lower than in normalweight concrete structures. The performance was satisfactory for all the bridge structures. 2.2.1.2 Laamanen (1993) =-=[45]-=- Laamanen discusses the Sundbru bridge in Eidsvoll, Norway which used high-strength lightweight concrete. The bridge, built in 1991-1992, utilized natural sand and lightweight aggregate Leca, an expan...

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...................................................................7 2.1 GENERAL RESEARCH ON HIGH-STRENGTH LIGHTWEIGHT CONCRETE............................................7 2.1.1 Martinez Morales (1982) =-=[50]-=-.............................................................................................................. 7 2.1.2 Shideler (1957) [70]................................................................

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...... 9 2.1.6 Zhang and Gjørv (1991) [80]............................................................................................................... 9 2.1.7 Mircea, Ioani, Filip, and Pepenar (1994) =-=[53]-=-...................................................................................... 9 2.1.8 Reichard (1967) [64]........................................................................................

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...the coarse aggregate. Florida officials chose to handle this problem by sprinkling the stockpiled aggregate for 24 hours prior to production of the concrete. 2.2.2.3 Murillo, Thomas, and Smith (1994) =-=[56]-=- Another advantage of lightweight concrete for segmental bridges is in the seismic area. Lightweight concrete can alleviate two problems faced by normalweight segmental concrete bridges; the lateral f...

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...as steps are taken to monitor the bridge, since durability of lightweight concrete is not fully understood, then lightweight concrete makes a good choice for a bridge material. 2.2.1.4 Sandvik (1993) =-=[67]-=- Sandvik provided an overview of bridges built in Norway with lightweight concrete since 1987. Eight bridges had been constructed using high-strength lightweight aggregate concrete. All are found in m...

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...degrees Fahrenheit. Although no temperature measurement was taken, the concrete was estimated at 110 degrees. This is a sign that the concrete was too hot and could lead to trouble. Soroka and Ravina =-=[73]-=- documented this phenomenon. They showed that slump loss in concrete is accelerated by temperatures over 86°F. Although no temperature was taken of the concrete, the ambient air temperature that day w...

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..... 104 9.6.3 Comparison to Transfer Length Equations ...................................................................................... 106 9.7 TRANSFER LENGTH IN LIGHTWEIGHT CONCRETE DECK PANELS =-=[85]-=- ........................................112 9.7.1 Transfer Length Test Setup.............................................................................................................. 113 9.7.2 Te...

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...0 LW6000-2-N 0.047 0.059 (3) 0.032 (2) 0.037 0.049 LW6000-2-S 0.050 0.062 (1,6) 0.042 (5,7) 0.053 0.050 9-12 bad LW8000-20-N 0.036 0.064 (10) 0.020 (15) x x zip ties LW8000-20-S 0.038 0.054 (3) 0.021 =-=(16)-=- x x LW8000-1-N 0.045 0.057 (1) 0.040 (12) 0.050 0.044 LW8000-1-S 0.042 0.067 (8) 0.015 (12) 0.041 0.042 LW8000-2-N 0.039 0.051 (9) 0.034 (4,7) 0.050 0.042 2 bad LW8000-2-S 0.042 0.054 (9) 0028 (5) 0....

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...he girders is greatest for lightweight concrete bridges, although a limiting factor is the deflection limit under service load. 7.3.1.2 Yang, Y. & Holm, T. – [79] This paper reviews a T.Y. Lin report =-=[27]-=- and the progress made since its publication. The researchers found that replacement of normalweight concrete decks with lightweight concrete decks increased the live load capacity of bridges studied ...

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...gure 9.1 DEMEC Points and Measurement of Concrete Strains 93It was determined from past use of this system that a spacing of 1.97 in (50 mm) would provide enough data to give a smooth strain profile =-=[15,40]-=-. The spacing and layout of the DEMEC points is shown in Figure 9.2. The distance that the DEMEC points extended along the beam was determined from calculations of the theoretical transfer length. For...

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...material properties of lightweight concrete are found in the work by Heffington [33]. The transfer length of the pretensioned strands in prestressed lightweight concrete beams was evaluated by Kolozs =-=[43]-=-. A portion of the testing of the development length of strand in lightweight concrete beams was also reported by Kolozs [43], and was completed by Thatcher [75]. Transfer length of strands in precast...

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...o the bond at release of the initial prestress. 71fri n i Strand Draw-In f se fs = 0 Increasing f s f s = 0 Transfer Length Steel Stress, f s Distance Along Strand Figure 7.1 Diagram of Hoyer Effect =-=[65]-=- Mechanical interlock is another mechanism by which the strand transfers stress to the concrete. This mechanism only occurs with twisted strand and is due to the tendency of the strand to want to unwi...

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...t of normalweight concrete. The creep and shrinkage of lightweight concrete are comparable to that of normalweight concrete, and the same multipliers and coefficients in the code can be used for both =-=[47, 72]-=-. The use of lightweight concrete in bridge applications has been gaining popularity since 1955, particularly in California and Norway. Bridge girder and deck applications, as well as slabs in buildin...

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...s the modulus of elasticity of the concrete as a variable. As shown earlier, the concrete compressive strength does not seem to affect the transfer length in a way that is expected from past research =-=[54,77]-=-. Specifically, as concrete strength increases, the transfer length should decrease. In the Zia and Mostafa model the concrete compressive strength is in the denominator (Table 9.8). Therefore, since ...

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...e strength, the maximum span distance of the girders is greatest for lightweight concrete bridges, although a limiting factor is the deflection limit under service load. 7.3.1.2 Yang, Y. & Holm, T. – =-=[79]-=- This paper reviews a T.Y. Lin report [27] and the progress made since its publication. The researchers found that replacement of normalweight concrete decks with lightweight concrete decks increased ...

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...s section briefly summarizes previous literature regarding possible use and testing of normalweight and lightweight pretensioned concrete beams. 737.3.1 Use of Lightweight Concrete 7.3.1.1 Zia, P. – =-=[84]-=- This study indicates that commercially available HSLC using natural sand fines was available in compressive strengths ranging from 5,000 – 7,000 psi. Also, by using fly ash and water reducing agents,...