Blast-Resistant Highway Bridges: Design and Detailing Guidelines (2010) / Chapter Skim
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From page 60... ...
60 5.1 Overview Observations from analytical research and experimental test programs are presented in this chapter. The experimental research was divided into two phases.
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From page 61... ...
the shock front strikes the column increases, resulting in significantly decreased pressure and impulse near the top of the column as the standoff distance decreases. Figure 45 shows the difference in geometry for two different standoff distances with the same scaled standoff, and one can see that the ratio R′2/R′1 is significantly greater than the ratio R′2/R′1.
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From page 62... ...
peak pressure and impulse for all three of the front gauges, and the overestimation increases along the height of the column. Initially, the case of a shock wave striking a column may seem similar to that of a shock wave striking a wall; however, the fact that BEL and BlastX increasingly over-predict pressure and impulse as the distance from the column base increases may be evidence that clearing for a column is more complex than previously thought.
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From page 63... ...
standoff, and this difference depends on the actual standoff distance and the location of interest along the height of the column. In some cases, the pressures and impulses at the bottom gauge of the circular column are equal to or greater than their corresponding values for the square column.
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From page 64... ...
off distances, resulting in pressure–time histories that are difficult to compare directly. Nevertheless, these observations are interesting and merit additional investigation, and future work should address these issues.
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From page 65... ...
flexural response of the column, whereas the loading due to the pressures recorded during the Phase I tests would most likely result in a shear-dominated behavior early in time. Moreover, because BEL increasingly over-predicts pressures as the height of the location of interest on a column increases, the error of the proposed method will also increase with the height of the location of interest on a column.
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From page 66... ...
ment, and #4 deformed discrete ties and hoops. The stress– strain plot for each bar type is illustrated in Figure 49.
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required a booster (a small quantity of C-4) to ensure reliable detonation.
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proximity of the charge to the specimen. Also, the data in Table 12 suggests that as the charge gets closer to the target, efficiency increases in terms of pressure and decreases in terms of impulse.
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Column 1A2, as seen in Figure 52. A permanent deflection of 5 in.
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5.1.2.3.4 Column 2A1. The first 30-in.
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standoff as Column 2A2. Again, a 3.3w size charge was placed near the column at a standoff of 2.4z.
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5.1.2.3.9 Column 3A. Column 3A, a 30-in.
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5.1.2.3.11 Summary of Column Failures. The small standoff tests enabled the observation of the mode of failure for ten concrete columns with eight different column designs over a range of different scaled standoffs (i.e., blast scenarios)
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From page 74... ...
below the blast location resulted in significant permanent deformation and imminent failure of the column.
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gravity design column with discrete ties at 6 in. on-center that sustained extensive damage from the small standoff tests.
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5.1.2.5 Discussion of Test Variables The test program included ten half-scale, small standoff and six half-scale, local damage blast tests on eight different column designs. Column specimens were constructed with consideration given to five main test variables, including scaled standoff, column geometry, amount of transverse reinforcement, type of transverse reinforcement, and splice location.
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From page 77... ...
pressure seeks relief toward lower pressure regions (free edges) through a rarefaction (or relief)
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increasing the amount of transverse reinforcement, requiring continuous spiral reinforcement or discrete hoops with sufficient anchorage, and avoiding splices. These design provisions are covered in detail in the following sections.
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shown in Figure 72, was assumed to form two hinges before failure. The plastic hinge analysis determined a maximum shear of: where: MP = plastic moment capacity (kip-ft)
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80 Table 15. Pitch of transverse reinforcement.
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where: f ′c = specified compressive strength of concrete at 28 days (psi) fy = yield strength of reinforcing bars (psi)
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with better anchorage into the concrete core. The column with discrete hoops in Figure 75 experienced a shear failure at the column base because the bottom three hoops were pulled open.
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consist of a 135° bend, plus an extension of not less than the larger of 20.0 db or 10 in. 5.1.2.5.5 Location of Longitudinal Splices.
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84 -5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 0 10 20 30 40 50 60 70 80 90 100 Time (msec) µS tra in Strain Data Filtered Strain Data Figure 79.
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85 -1500 -1000 -500 0 500 1000 1500 2000 2500 0 10 20 30 40 50 60 70 80 90 100 Time (msec) µS tra in Filtered Strain Data Rolling Average Filtered Strain Data Figure 81.
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From page 87... ...
The magnitude of the maximum moment was assumed to be equal to the plastic moment or column capacity from the moment–curvature plots. The moment at each strain gauge was then calculated using the gauge location and assumed moment diagram.
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