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48 Figure 57. Surface asperity geometry variables. at half the depth d to define an effective angle . Because PRELIMINARY AESTHETIC the angled asperity is the most general, it is the type of sur- DESIGN GUIDELINES face asperity used in the parametric study to develop guide- All simulations in the parametric study to establish the pre- lines for the aesthetic treatment of concrete safety shape liminary aesthetic design guidelines were performed with the barriers. 2000P pickup truck impacting a rigid New Jersey safety For the purpose of this research, asperities were defined as shape barrier following Test 3-11 of NCHRP Report 350. the portion of the barrier that was recessed into the barrier sur- The impact conditions for Test 3-11 involve the 2000-kg face. In other words, an asperity is a depression in the surface pickup truck impacting the barrier at a speed and angle of of the barrier. Thus, another critical dimension to be included 100 km/h and 25 degrees, respectively. in the parametric study was the width of the asperity, W, The parametric study was performed using 45-degree, which was defined as the distance between the outer edges of 90-degree, and 30-degree asperity angles (). The asperity the asperity spacing, as shown in Figure 57. The distance width (W) and depth (d) were systematically varied for each of between two adjacent asperities was defined as the asperity these angles. The impact performance associated with each spacing (Ws). For the parametric studies presented in this simulation run was assessed based on the established surrogate chapter, an asperity spacing of 25 mm was used. OCD thresholds. As previously mentioned, the passing and The asperities were created by depressing the surface of failing internal energy limits were selected as 2,200 J and the barrier profile at the desired asperity locations. The orig- 10,700 J, respectively. The results were used to establish pre- inal barrier profile was, therefore, unchanged in the regions liminary relationships that identified asperity configurations between asperities, defined in Figure 57 as the asperity spac- having impact performance considered to be "acceptable," ing (Ws). The asperities began at the top of the "toe" of the "marginal/unknown," and "unacceptable." If for a simulated safety shape barrier and continued vertically to the top of the asperity configuration, the truck floorboard internal energy barrier. The toe of the barrier remained smooth, as shown in was more than 10,700 J, the configuration was marked as Figure 58. "unacceptable." Floorboard internal energy value between Figure 58. Truck with fluted New Jersey shape barrier.

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49 2,200 J and 10,700 J implied that the asperity configuration 45-degree, 90-degree, and 30-degree asperity angles have been was marked as "marginal/unknown." If the floorboard internal combined in Figure 62. energy was less than 2,200 J, the configuration was marked as The curves shown in Figures 59 through 62 provide only a "pass" or "acceptable." failure line, above which the asperity geometries were pre- Other than the baseline simulation with the New Jersey bar- dicted to fail to meet impact performance criteria and below rier without asperities, none of the simulated configurations which the impact performance was unknown. As discussed resulted in truck floorboard internal energy of less than previously, the existence of a region of unknown performance 2,200 J. Consequently, "unacceptable" and "marginal/ is due to a lack of crash tests of rigid barriers with measured unknown" were the only two regions identified in the prelim- OCD values corresponding to the regions below the failure line. inary guidelines. The "pass" region was later identified with This region of unknown performance was reduced through a the use of full-scale crash testing, details of which follow in the judiciously selected full-scale crash-testing phase, the details of next chapter. It is worth mentioning that asperity configura- which are presented in the next chapter. tions (with very small depths and large widths) can be selected Examining the shape of the guideline curves, the effects such that they would result in floorboard internal energies of of asperity width (W ) and depth (d ) on barrier performance less than 2,200 J. Such configurations can be used to establish appear logical. When the asperity width (W ) is small, the vehi- a "pass" region in the preliminary guidelines. However, the cle engages more asperities during its contact with the barrier. asperity depth and width values for such configurations would This in turn presents more resistance to vehicle sliding on the have no practical significance for the aesthetic surface treat- barrier and causes more snagging and damage to the vehicle. ment of concrete barriers and hence were not simulated. Consequently, we see a reduction in the allowable asperity Simulation results for the truck floorboard internal energy depth (d ) for these smaller widths. As the width (W ) of an for the 45-degree, 90-degree, and 30-degree asperity angles asperity increases, the allowable depth (d ) also increases up to are presented in Tables 4 through 6, respectively. Simulations a limiting or controlling value. with no depth refer to a smooth-faced New Jersey safety shape It can also be seen that as the angle becomes shallower, the barrier. The tables present floorboard internal energy for dif- failure line moves upward to higher asperity depths. Thus, ferent asperity configurations. Using the results for the simu- the 30-degree asperity angle results in a larger "marginal/ lated values of W and d, a curve denoting the failure threshold acceptable" region than the 45-degree asperity angle. Simi- was plotted for each asperity angle. The corresponding rela- larly, the "marginal/unknown" region significantly reduces tionships for the 45-degree, 90-degree, and 30-degree asperity with the increase in asperity angle from 45 degrees to angles are shown in Figures 59 through 61, respectively. For 90 degrees. For the 90-degree asperity angle, it can be seen convenience of use and comparison, the relationships for the that for asperity widths less than 500 mm, the internal energy TABLE 4 Parametric study results for a 45-degree angle of asperity Asperity Asperity Truck Floorboard Width (W) Depth (d) Internal Energy Run Vehicle [mm] [mm] [J] Pass/Fail 1 Truck 555 0 1,108 Pass 2 Truck 555 15 4,341 Marginal 3 Truck 555 27.5 6,986 Marginal 4 Truck 555 40 8,397 Marginal 5 Truck 555 52.5 12,835 Fail 6 Truck 555 65 15,939 Fail 7 Truck 555 90 18,318 Fail 8 Truck 280 0 1,108 Pass 9 Truck 280 15 8,965 Marginal 10 Truck 280 27.5 14,680 Fail 11 Truck 280 52.5 15,507 Fail 12 Truck 180 0 1,108 Pass 13 Truck 180 6.5 9,158 Marginal 14 Truck 180 15 11,844 Fail 15 Truck 80 0 1,108 Pass 16 Truck 80 6.5 8,900 Marginal 17 Truck 80 15 17,182 Fail 18 Truck 30 0 1,108 Pass 19 Truck 30 5 4,149 Marginal Passing Limit = 2,200 J Failure Limit = 10,700 J

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50 TABLE 5 Parametric study results for a 90-degree angle of asperity Asperity Asperity Truck Floorboard Width (W) Depth (d) Internal Energy Run Vehicle [mm] [mm] [J] Pass/Fail 1 Truck 5 40 2,157 Pass 2 Truck 30 0 1,108 Pass 3 Truck 30 2.5 3,257 Marginal 4 Truck 30 15 6,077 Marginal 5 Truck 30 40 6,049 Marginal 6 Truck 55 0 1,108 Pass 7 Truck 55 2.5 17,497 Fail 8 Truck 55 40 25,000+ Fail 9 Truck 125 6.5 18,250 Fail 10 Truck 280 0 1,108 Pass 11 Truck 280 6.5 24,240 Fail 12 Truck 280 15 30,000+ Fail 13 Truck 400 0 1,108 Pass 14 Truck 400 6.5 12,000+ Fail 15 Truck 500 0 1,108 Pass 16 Truck 500 6.5 8,653 Marginal 17 Truck 500 12.5 21,000+ Fail 18 Truck 580 0 1,108 Pass 19 Truck 580 15 8,909 Marginal 19 Truck 580 27.5 14,000+ Pass Passing Limit = 2,200 J Failure Limit = 10,700 J of the truck floorboard exceeds the failure limit for almost all forces below levels that would be induced by a rigid asperity. practical asperity depths. In the simulations, the 90-degree The degree of snagging reduction was difficult to quantify with- asperity angle induces more severe snagging and resistance to out additional test data. sliding, which causes more damage to the vehicle. An analogy For the 90-degree asperity angle, as the asperity width (W ) can be drawn between the 90-degree asperities and splices in increases beyond 500 mm, the allowable depth (d ) increases up tubular steel rail members that have demonstrated the potential to a limiting or controlling value. Another interesting point to for severe snagging and increased OCD in full-scale crash tests. note is that as the width (W ) decreases to a value of 30 mm One must bear in mind that all simulated asperities (45-degree, or less, a significant increase in the asperity depth (d ) can be 90-degree, and 30-degree asperities) were modeled as rigid. In achieved. This is because even though d is large, the small an actual impact, spalling or fracture of the concrete asperities width of the asperity reduces the potential for vehicle parts may occur. This spalling can serve to reduce the snagging to intrude into the asperity. Thus, the opportunity for vehicle TABLE 6 Parametric study results for a 30-degree angle of asperity Asperity Asperity Truck Floorboard Width (W) Depth (d) Internal Energy Run Vehicle [mm] [mm] [J] Pass/Fail 1 Truck 100 0 1,108 Pass 2 Truck 100 25 4,476 Marginal 3 Truck 200 0 1,108 Pass 4 Truck 200 25 6,238 Marginal 5 Truck 200 50 7,652 Marginal 6 Truck 400 0 1,108 Pass 7 Truck 400 25 4,465 Marginal 8 Truck 400 50 7,538 Marginal 9 Truck 400 75 11,341 Fail 10 Truck 600 0 1,108 Pass 11 Truck 600 25 3,952 Marginal 12 Truck 600 50 4,701 Marginal 13 Truck 600 75 5,985 Marginal 14 Truck 600 100 6,724 Marginal Passing Limit = 2,200 J Failure Limit = 10,700 J

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51 Figure 59. Depth versus width guideline for a 45-degree asperity angle. Figure 60. Depth versus width guideline for a 90-degree asperity angle.

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52 Figure 61. Depth versus width guideline for a 30-degree asperity angle. Figure 62. Overlaid depth versus width guideline curves.

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53 snagging and cumulative vehicle damage is reduced. Even if design, the barrier may need to be widened beyond the width some intrusion into the asperity occurs, the depth of the intru- required to satisfy strength requirements. sion is again limited by the small width of the asperity. This The exact nature of the curves beyond an asperity width effect is illustrated by the vertical failure line in Figure 60. of 600 mm (denoted with a dashed line) is not completely In summary, simulation results for the 90-degree asperity defined. However, the curves should reach a limiting asper- angle indicate that only a very limited set of asperity configu- ity depth as the asperity width increases. As the asperity rations with this angle can be used for aesthetic barrier design. width continues to increase, a point will be reached where Further investigation was performed with a full-scale crash the vehicle is only engaging or interacting with a single test, details of which are presented in the next chapter. asperity during redirection. At this point, there will be a crit- It can be seen that for shallower asperity angles, much ical asperity depth that will no longer be influenced by greater asperity depths can be achieved. Note that some of asperity width. the simulated asperity depths for the 30-degree asperity It is worth noting that the failure lines shown in Figures 59 angle may not be practical from a design standpoint. How- through 62 are placed at the midpoint between simulated sur- ever, because not all desired aesthetic surface treatments face asperity depths at a given asperity width that resulted in can be anticipated, a wide range of asperity depths has been marginal and unacceptable OCD (as defined by the internal included in the analysis to more completely define the rela- floorboard energy). However, the increase in internal floor- tionship between asperity depth and width for shallow-angle board energy is not linearly related to asperity depth. This can asperities. be observed by comparing the internal energy values for dif- It is noted that a standard concrete barrier design will have ferent asperity widths and depths. a functional limit on the maximum asperity depth that can be The truck floorboard internal energy data for the 45- accommodated without exposing the reinforcing steel or leav- degree, 90-degree, and 30-degree asperity angles is pre- ing insufficient concrete cover. In order to maintain the desired sented in three-dimensional graphs in Figures 63 through clear cover (typically 37.5 mm to 50 mm) for reinforcement 65, respectively. For a given asperity width, the increase in steel when significant asperity depths are incorporated into the internal energy with increase in the asperity depth can be Figure 63. Truck floorboard internal energy values at different configurations for a 45-degree asperity angle.

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54 Figure 64. Truck floorboard internal energy values at different configurations for a 90-degree asperity angle. Figure 65. Truck floorboard internal energy values at different configurations for a 30-degree asperity angle.

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55 visualized. It can be seen that as asperity width decreases, 15 mm, the internal energy increases from 4.3 kJ to 17.2 kJ as the relative difference in internal energy between two simi- the asperity width decreases from 555 mm to 80 mm. lar asperity depths increases. For example, with reference to Since the internal energy of the truck floorboard is believed Figure 63, it can be observed that for an asperity width to be related directly to the OCD, these graphs were helpful in of 555 mm, the internal energy increases 63% (from 4.3 kJ understanding the relationships and trends associated with the to 7.0 kJ) as the asperity depth increases from 15 mm to asperity parameters. Such information was considered when 27.5 mm, respectively. For an asperity width of 80 mm, the developing the full-scale crash test plan. internal energy increases by 93% (from 8.9 kJ to 17.2 kJ) Having gained a reasonable insight into the effect of differ- when the asperity depth increases from 6.5 mm to 15 mm. ent asperity parameters on OCD and having established the Similarly, for a specific asperity depth, the floorboard inter- preliminary guidelines presented above, the researchers initi- nal energy increases as the asperity width decreases. For ated the crash-testing phase of the project. Details of this phase example, with reference to Figure 63, for an asperity depth of of the project are presented in the next chapter.