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66 CHAPTER 7 FINAL DESIGN GUIDELINES GUIDELINES FOR AESTHETIC SURFACE It can be observed that for a given asperity width, the TREATMENTS OF SAFETY SHAPE acceptable asperity depth varies with the asperity angle. For CONCRETE BARRIERS example, at an asperity width of 500 mm, the acceptable asperity depths are 6 mm, 35 mm, and 99 mm for 90 degree, As described in the previous chapter, the internal energy 45 degree, and 30 degree asperity angles, respectively. of the floorboard of the pickup truck was used as a surrogate The guidelines do not include asperity spacing as an addi- measure of OCD. Due to limited test data, the internal energy tional design parameter. In the opinion of the researchers, the threshold associated with the maximum allowable OCD was degree of variation in the asperity configurations that are not well defined. Consequently, the preliminary guidelines acceptable for the two asperity spacings investigated did not contained a large region of asperity configurations for which justify adding another level of complexity to the guidelines. impact performance was unknown. Even though wider asperity spacing results in less spalling of The crash test data were evaluated and used to make the concrete between asperities, the net change was a reduction adjustments to the preliminary guidelines. Each asperity con- in overall snagging severity. Therefore, the final guidelines, figuration that was crash tested has an associated level of which were based on an asperity width of 25 mm, are slightly truck floorboard internal energy that was derived from the conservative for wider asperity spacings. simulation study. A summary of these data is presented in Table 8. The verification crash test with the 820-kg passen- ger car (Test 6) is excluded from the table because the small COMPARISON WITH GUIDELINES FOR SINGLE- car is not critical in terms of the performance assessment of SLOPE AND VERTICAL-FACE BARRIERS AND STONE MASONRY GUARDWALLS the asperities. Test 2 evaluated the same asperity configura- tion used in Test 6. Guidelines developed for the safety shape barriers under The tentative energy failure threshold upon which the pre- this research were compared, to the extent possible, with the liminary guidelines were based was 10.7 kJ. Test 2 and Test 7 previously developed guidelines for single-slope and vertical- confirmed that this level of floorboard internal energy was face barriers and stone masonry guardwalls. In the case of indeed unacceptable. The highest level of energy associated guidelines for safety shape barriers, the use of finite element with a successful test can conservatively be used as a pass/ simulation studies in conjunction with crash testing enabled fail threshold. Based on this rationale, a floorboard internal the researchers to define relationships over a range of asperity energy of 8.5 kJ was selected as the pass/fail threshold. With parameters. Previously existing guidelines for single-slope reference to Table 8, the asperity configurations used in and vertical-face barriers and stone masonry guardwalls were Test 3, Test 4, and Test 5, which were all successful tests, had developed using crash testing alone and therefore were not in internal floorboard energies ranging from 8.4 kJ to 8.9 kJ. the form of relationships defined over a range of asperity pa- Given that the highest OCD among these successful tests was rameters. Moreover, a significant portion of the information 120 mm, using 8.5 kJ as the internal energy threshold pro- contained in these guidelines cannot be displayed graphically. vides good confidence in the validity of the "acceptable" or Figure 83 shows an overlay of the guidelines developed crashworthy region of the guidelines. for the safety shape barriers and some of the information The failure curve associated with each asperity angle (i.e., from the guidelines for single-slope and vertical-face barriers 30, 45, and 90 degrees) was shifted to correspond to the revised that could be displayed graphically. This figure shows lines energy threshold of 8.5 kJ. The final design guidelines for aes- for 45- and 90-degree asperities that were suggested for thetic surface treatment of safety shape concrete barriers based single-slope and vertical-face barriers. on the revised threshold are presented in Figure 82. For each For the 90-degree asperities on single-slope and vertical- asperity angle, the guidelines show regions of "acceptable" face barriers, the maximum depth and width allowed were asperity configurations and regions of asperity configurations 13 mm and 25 mm, respectively. At the same time, the that are "not recommended" due to a high probability of failure guidelines allow gaps, slots, grooves, or joints of any depth during a design impact event resulting from excessive OCD. with a maximum width of 20 mm. This amounts to the ver-
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67 TABLE 8 Floorboard internal energy associated with slope and vertical-face barriers, a single maximum asperity crash-tested asperity configurations depth value of 25 mm was set, irrespective of the width of the Test No.* Internal Energy Test Outcome asperities. The comparison thus shows that for smaller widths, (kJ) guidelines for safety shape barriers allow for shallower asper- 1 6.9 Pass 2 11.8 Fail ities, whereas for larger widths, deeper asperity widths are 3 8.4 Pass acceptable when compared with the guidelines for the single- 4 8.9 Pass slope and vertical-face barriers. 5 8.9 Pass The two guidelines are reasonably similar to each other. 7 10.3 Fail The differences highlighted above stem from the differences * Test 6 with 820C excluded in the development approach. In the case of safety shape bar- riers, finite element simulations allowed for developing rela- tionships as a function of asperity parameters. Moreover, tical line shown in Figure 84 for 90-degree asperities (see a greater number of crash tests were conducted for the Figure 85 for English units). A similar vertical line has been 45-degree asperities so as to allow verification and readjust- suggested for the safety shape barriers, but with a slightly ment of these relationships. The single-slope and vertical- larger maximum asperity width (30 mm as opposed to 20 mm). face barrier guidelines, however, were developed primarily In addition to an "acceptable" region for asperity widths of through crash testing, and finite element simulations were not less than 30 mm, guidelines developed for the safety shape performed. This restricted the guidelines to single maximum barriers show an "acceptable" region at higher asperity asperity depth values for different asperity angles. widths, which was identified through simulation and later Initially, the comparison was done so as to generate a verified by crash testing. single graph of relationships between asperity depths and For the 45-degree asperities on safety shape barriers, the widths for all types of barriers. However, such a generalized asperity depth versus width relationship allows for smaller graph can become very confusing for the designer. In addi- depths when asperity widths are small. The acceptable maxi- tion, a significant portion of the information contained in the mum asperity depth increases with the increase in width for guidelines for single-slope and vertical-face barriers and these guidelines. However, in the case of guidelines for single- stone masonry guardwalls can only be displayed textually. Figure 82. Final design guidelines for aesthetic surface treatment of safety shape concrete barriers.
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68 Figure 83. Comparison of guidelines for single-slope and vertical-face barriers and stone masonry guardwalls. Figure 84. Final design guidelines for aesthetic surface treatment of safety shape concrete barrier (metric).
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69 Figure 85. Final design guidelines for aesthetic surface treatment of safety shape concrete barrier (English). For the convenience of an aesthetic barrier designer, all three whereas the guidelines for single-slope and vertical-face and guidelines have been consolidated into a single, standalone stone masonry guardwalls have been presented in textual section, which appears in the appendix. The guidelines for form. This appendix also includes examples of the use of the safety shape barriers have been presented in graphic form, guidelines developed for safety shape barriers.