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Pages 6-47

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From page 6... ... . Concrete Strength Girder concrete compressive strength ranged from 3,500 to 7,000 psi at release and 4,000 to 9,000 psi at 28 days for normal mixes. Read the entire page →
From page 7... ... into the diaphragm and 3/4-in.-diameter coil tie rods were used to transmit the force from the end of the beams to the diaphragm. From the results of Phases I and II, a design method was proposed for positive moment connections using bent strand. Read the entire page →
From page 8... ... . A total of 12 strands were used in each I girder, while the box girders had 20 strands. Read the entire page →
From page 9... ... Mild reinforcement was extended from the ends of the girders into the continuity diaphragms to provide a positive moment connection. The positive moment connection reinforcement was hooked in the continuity diaphragm and was embedded into the end of the girder. Read the entire page →
From page 10... ... This bridge was located on US 280 in Lee County, Alabama. The bridge was constructed using AASHTO Type II girders with mild reinforcement extending into the continuity diaphragms to make a positive moment connection. Read the entire page →
From page 11... ... A parametric study was conducted on a two-span bridge consisting of AASHTO Type III girders. The spans were 65 ft, and the girder spacing was 8 ft. Read the entire page →
From page 12... ... Depending on the relative age and properties of the girder and deck, this initial negative moment may be larger than the positive restraint moments cause by girder creep, leading to a net negative moment at the connection. Read the entire page →
From page 13... ... specimen. TABLE 1 Details of positive moment connections in the stub specimens Specimen Number Type of Specimen Diaphragm Width (in.) Read the entire page →
From page 14... ... Figure 6. Details of the connections. Read the entire page →
From page 15... ... At an applied load of 7 kips, the dead load is relieved and the crack begins to open. Until the compressive stress from the dead load is relieved, the connection maintains a stiffness equal to the initial stiffness. Read the entire page →
From page 16... ... Stub Specimen 1: Bent Strand Specimen 1 was a bent-strand connection where the girder ends were not embedded in the diaphragm (see Figure 14) Read the entire page →
From page 17... ... ure 14) , so concrete could not completely surround the strand. Read the entire page →
From page 18... ... It was assumed that all the load was dead load; however, subsequent calculations revealed that thermal effects had caused the specimen to camber up and the end reactions had increased. This thermal effect was inadvertently added to the applied load, and the specimen was overloaded in the positive moment direction by approximately 35% on the first few load cycles. Read the entire page →
From page 19... ... An observation was made with respect to crack opening: in Specimen 1, crack openings on either side of the stub beam were the same, but this was not true of Specimen 2. As shown in Figures 6 and 16, the bars in the stub beam are closer to one side of the bottom flange than to the other. Read the entire page →
From page 20... ... Figure 18. Spalling of the diaphragm. Read the entire page →
From page 21... ... . These crack openings were not unusually large compared with those for other specimens. Read the entire page →
From page 22... ... Failure was due to fracture of the bars in the positive moment connection and by the girders pulling out of the diaphragm. At failure, there was significant spalling of the diaphragm concrete. Read the entire page →
From page 23... ... Then, any tension caused by positive moments will simply reduce the compression rather than cause tensile cracking. The partial diaphragm was poured when the girders were 28 days old. Read the entire page →
From page 24... ... At the time the deck slab was cast, the diaphragm was in tension because of creep, shrinkage, and temperature effects in the girders. The compressive stresses created when the deck slab was poured were not enough to overcome this tension, and the diaphragm still shows a net tension even after the deck slab is added. Read the entire page →
From page 25... ... The loss of load mimics the deck slab temperature graph. These responses are caused by the heat of hydration in the deck slab. Read the entire page →
From page 26... ... Both the top and bottom flange strains stay reasonably constant until just before the peak in the deck slab temperature, which is approximately the time of the final set for the concrete. The strains then approximately follow the temperature curve. Read the entire page →
From page 27... ... A similar shrinkage specimen had been made for the girder; and, during the same period, the girder -775 -750 -725 -700 57 57.5 58 58.5 59 Time - Days from beam fabrication B ot to m F la ng e St ra in - M ic ro st ra in 0 7 14 21 28 35 42 Te m pe ra tu re - De gr ee C Bottom Flange Strain Pour Slab Temperature Gradient Slab Temperature Figure 35. Bottom flange strain after deck slab pour. Read the entire page →
From page 28... ... Change in girder/deck slab strain with time. -1200 -1000 -800 -600 -400 -200 0 200 0 50 100 150 200 250 Time - Days from beam fabrication m ic ro st ra in Bottom Flange Strain Top Flange Strain Deck Slab Strain Pour Slab Strain at prestress transfer Bottom flange = -548 Top flange = 0 Pour Partial Diaphragm Read the entire page →
From page 29... ... The effective shrinkage strain in the deck can be found from εeffective = εsh(Ac /Atr) where εsh = unrestrained shrinkage strain for deck concrete; Ac = gross area of concrete deck slab; 27 Atr = area of concrete deck slab with transformed longitudinal deck reinforcement, Ac + As (n − 1) Read the entire page →
From page 30... ... Figures 39 and 40 show the variation of crack opening with time for cracks at the bottom of west girder. The crack openings appear to show some softening of the connection during the monitoring period as the crack opening amplitude increases with subsequent cycles. Read the entire page →
From page 31... ... After the initial testing, the cracks at the diaphragm were opened by simulating the positive moment that would develop from creep and shrinkage of the girders if continuity was established at an early age. To do this, a post-tensioning bar was placed through the bottom flange of the girder, and a post-tensioning force was applied (see Figures 44 and 45) Read the entire page →
From page 32... ... Ch an ge in R ea ct io ns (p ou nd s) East End West End End Reaction if Simple Spans End Reaction - Loaded Span - Continuous - One Span Loaded End Reaction Continuous - Both Spans Loaded End Reaction - Unloaded Span - Continuous - One Span Loaded East Beam Loaded West Beam Loaded Both Beams Loaded Figure 42. Read the entire page →
From page 33... ... This positive load would cause an additional positive moment of 395 k-ft. Added to the 400 k-ft caused by the post-tensioning, the total positive moment was 795 k-ft or 1.90 Mcr. Read the entire page →
From page 34... ... Ch an ge in R ea ct io n (p ou nd s) East End West End End Reaction - Loaded Span - Continuous - One Span Loaded End Reaction if Simple Spans End Reaction - Continuous - Both Spans Loaded End Reaction - Unloaded Span - Continuous - One Span Loaded East Beam Loaded West Beam Loaded Both Beams Loaded Figure 47. Read the entire page →
From page 35... ... Ch an ge in R ea ct io ns (p ou nd s) East Reaction West Reaction East = -38k West = 0 East = 0 West = -38k East = -38k West = -38k East = 10k West = 0 East = 10k West = 10k East = 30k West = 10k East = 30k West = 30k East = 40k West = 30k East = 40k West = 40k East = 40k West = 42k East = 0 West = 40k East = -38k West = 0 East = 0 West = -38k East = -38k West = -38k Applied Loads Negative Load = Negative Moment Positive Load = Positive Moment Read the entire page →
From page 36... ... Ch an ge in B ot to m F la ng e St ra in s (m icr os tra in) East Beam West Beam East = -38k West = 0 East = 0 West = -38k East = -38k West = -38k East = 10k West = 0 East = 10k West = 10k East = 30k West = 10k East = 30k West = 30k East = 40k West = 30k East = 40k West = 40k East = 40k West = 42k East = 0 West = 40k East = -38k West = 0 East = 0 West = -38k East = -38k West = -38k Applied Loads Negative Load = Negative Moment at joint Positive Load = Positive Moment at joint Figure 51. Read the entire page →
From page 37... ... Ch an ge in R ea ct io ns (p ou nd s) East Rxn West Rxn East Beam Loaded West Beam Loaded Both Beams Loaded End Reactions if Simple Span End Reaction - Loaded Span Continuous - One Span Loaded End Reaction - Continuous Both Spans Loaded End Reaction - Unloaded Span Continuous - One Span Loaded Figure 52. Read the entire page →
From page 38... ... Ch an ge in B ot to m F la ng e St ra in (m icr os tra in) West Beam East Beam Strain if Simple Spans Strain - Loaded Span Continuous - One Span Loaded Strain - Unloaded Span Continuous - One Span Loaded Strain - Continuous - Both Spans LoadedEast Beam Loaded Both Beams Loaded West Beam Loaded Figure 53. Read the entire page →
From page 39... ... Ch an ge in B ot to m F la ng e St ra in (m icr os tra in) West Beam East Beam Strain if Simple Spans Strain - Loaded Span Continuous - One Span Loaded Strain - Continuous - Both Spans Loaded Strain - Unloaded Span Continuous - One Span Loaded East Beam Loaded Both Beams Loaded West Beam Loaded Figure 55. Read the entire page →
From page 40... ... , the cracked section is now reasonably close to the cracked section used in the models and the expected drop in continuity is seen. Since the system was also to be tested for negative moment capacity, the positive moment testing was stopped at this point so that connection would not become excessively damaged. Read the entire page →
From page 41... ... This was less than the cracking moment of 930 k-ft calculated using the design concrete compressive strength for the deck slab, which was 4 ksi. Using the measured material properties, the expected cracking moment increased to 1,580 k-ft. Read the entire page →
From page 42... ... Comparison of change in bottom flange strains: initial and final loading. Read the entire page →
From page 43... ... Deck slab reinforcement. Slab Web Cracks Top Flange b cks Figure 62. Read the entire page →
From page 44... ... Time and budget consideration prevented further FEM studies. Crushing at Bottom Girder Diaphragm Figure 65. Read the entire page →
From page 45... ... Lo ad (K ) Bent Strand FE Bent Bar FE No Positive Moment Connection FE 14 536 2 Figure 67. Read the entire page →
From page 46... ... 44 0 500 1000 1500 2000 2500 0 0 .0005 0 .001 0.0015 Curvature M om en t ( kip -ft ) Response Program Present FE Analysis Bent Strand Specimen -400 -300 -200 -100 0 100 200 300 400 -0.0001 0 0.0001 0.0002 0.0003 0.0004 Curvature M om e n t ( ki pft ) Read the entire page →
From page 47... ... 45 0 150 300 450 600 750 0 0.0002 0.0004 0.0006 0.0008 0.001 Curvature M om en t ( kip -ft ) Response Program Present FE Analysis Bent Bar Specimen -450 -300 -150 0 150 300 450 -0.0002 -0.0001 0 0.0001 0.0002 Curvature M om e n t ( ki pft ) Read the entire page →

From page 6...

... . Concrete Strength Girder concrete compressive strength ranged from 3,500 to 7,000 psi at release and 4,000 to 9,000 psi at 28 days for normal mixes.