Blast-Resistant Highway Bridges: Design and Detailing Guidelines (2010) / Chapter Skim
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30 3.1 Overview The experimental test programs for Phases I and II are presented in this chapter. Phase I included small-scale nonresponding columns tested in Vicksburg, MS, by the U.S.
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31 same explosive charge, which increases the accuracy of the comparison between round and square column loadings. 3.2.2 Data Acquisition and Instrumentation Plan Each non-responding column was instrumented with nine structure-mounted pressure gauges or instruments (SMI)
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32 The test program included ten half-scale, small standoff tests and six half-scale, local damage blast tests, as shown in Table 6. The goal of the small standoff tests was to observe the mode of failure (i.e., flexure or shear)
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capacity and failure limit states of concrete highway bridge columns. 3.3.1 Background on Parameters Selected for Testing The test specimens designed for this program incorporated design and detailing standards commonly used in practice in various regions of the country.
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34 While design guidance exists for blast-loaded building columns, there are currently no standards on how to design and detail a bridge column to resist blast loads. Bridge columns behave differently than building columns exposed to blast loads, preventing the direct application of current design guidelines for buildings.
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shape, length-to-depth (L/D) ratio, type of transverse reinforcement, volumetric reinforcement ratio, and splice location.
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36 There are four main column types: solid wall, singlecolumn, multi-column, and pile bents, as shown in Figure 26. The two most common column configurations, single-column and multi-column, were represented in this test program with two different column dimensions.
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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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3.3.2.1 Blast-Column Design A blast-loaded column design considers all potential plastic hinge locations to determine the maximum possible shear demand on the column. The maximum shear demand is a function of the boundary conditions and load distribution.
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The required pitch of transverse reinforcement can be determined by setting the maximum shear demand determined in the plastic hinge analysis equal to the shear design equations from the AASHTO LRFD, modified to account for strain rate effects (ASCE, 1997) , and solving for the spacing.
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clear cover (which corresponds to 2 in. of clear cover in fullscale columns)
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ground to prevent damage. Post-test measurements and pictures were taken to document damage conditions following each test.
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3.3.4.3 High-Speed Video Cameras One or two high-speed video cameras were used for each small standoff and close-in test. Video provided by these cameras was useful in observing aspects of behavior that were difficult to discern from the strain gauge data and other instrumentation.
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bolted to the reaction structure to provide the pinned connection near the top of the column. It should be noted that over the course of the test program the slab of the reaction structure experienced significant damage and may have allowed some rotation to occur at the base so that the assumed boundary conditions were not fully realized.
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3.4 Summary This chapter presented the design and instrumentation of columns tested during Phases I and II of this experimental research program. The small-scale, non-responding blast test setup was summarized.
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