Aesthetic Concrete Barrier Design (2006) / Chapter Skim
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Pages 32-55
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From page 32... ...
The primary objective of this research was to develop guidelines for the aesthetic surface treatment of New Jersey and F-shaped concrete barriers (herein generally referred to generically as safety shape barriers) based on barrier impact performance.
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From page 33... ...
Most of the effort devoted to the validation effort therefore focused on the vehicle models. The validity of the improved 820-kg passenger car and 2,000-kg pickup truck vehicle models was established by comparing the results of simulations with the results of fullscale crash tests.
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From page 34... ...
In addition to the Caltrans fluted barrier, a smooth singleslope barrier was used as a baseline system to validate the modified Geo Metro model. A comparison of vehicle dynamics between crash tests and finite element simulations of the Caltrans fluted single-slope barrier and those of standard single-slope barrier follows.
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Figure 36. Comparison of roll angles from crash data with vehicle simulations for the angle fluted barrier.
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Figure 38. Comparison of yaw angles from crash data with vehicle simulations for the angle fluted barrier.
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Figure 39. Comparison of roll angles from crash data with vehicle simulations for the single-slope barrier.
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While the validation effort for the 820C vehicle was going on, TTI researchers were working in parallel on the 2000P vehicle model validation, details of which follow in subsequent sections in this chapter. As mentioned previously, the 2000P pickup truck design vehicle is believed to be more critical than the 820C in regard to evaluation of OCD and stability in impacts with concrete barriers.
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From page 39... ...
TTI researchers then simulated these crash tests using the NCAC detailed pickup truck model. This model, which contains approximately 54,800 elements, incorporates a deformable front suspension.
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Figure 45. Comparison of pitch angles of crash data with detailed pickup truck vehicle simulation on the single-slope barrier.
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Figure 47. Comparison of roll angles of crash data with detailed pickup truck vehicle simulation on the New Jersey safety shape barrier.
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Figure 49. Comparison of pitch angles of crash data with detailed pickup truck vehicle simulation on the New Jersey safety shape barrier.
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Part of the pilot study conducted under this project was devoted to assessing the ability of existing vehicle models to predict OCD, either through direct measurement of the maximum deformation inside the passenger compartment (similar to the procedure used in a crash test) , or by means of a surrogate measure correlated against the OCD measurements obtained in full-scale crash tests.
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From page 44... ...
These "passing" crash tests provide confidence in establishing a "passing" threshold for the selected surrogate OCD criterion. Results The first and most obvious measure of OCD was to take a direct measurement of the maximum deformation to the floorboard and toe pan of the vehicle in a manner similar to that used in crash test evaluation.
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From page 45... ...
As mentioned above, much of the OCD in a barrier crash test results from the wheel and suspension assembly being deformed and shoved back into the toe pan area. An option was set into the model to collect the direct impact forces between the wheel and barrier.
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From page 46... ...
Impulse [N-s] Name Oregon Fail Fail Fail Fail Pass Pass Cobblestone Single Slope Cobblestone with Reveal New Jersey Modified T203 Shallow Cobblestone Oregon Cobblestone Single Slope Cobblestone with Reveal New Jersey Modified T203 Shallow Cobblestone Pass/Fail Pass Pass Pass Pass Pass Pass Pass Pass 475 160 98 140 130 133 475 160 140 130 133 98 Not Reported Not Reported 1,290,000 1,340,000 1,290,000 1,176,000 276,000 498,000 228,000 263,000 901,000 278,000 229,000 290,000 910,000 510,000 459,000 450,000 195,000 164,000 197,000 231,000 459,000 455,000 438,000 195,000 196,000 164,000 123,000 449,000 28,800 29,900 34,500 10,700 15,200 14,500 14,800 12,100 12,800 12,800 21,100 18,700 18,700 27,700 28,300 31,900 35,900 14,300 14,600 10,600 15,100 12,000 12,700 11,900 19,800 18,000 18,000 40,100 TABLE 3 Internal energies for truck OCD study Crash Test OCD [mm]
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From page 47... ...
The outcome of impacts with solid barriers in which the internal energy of the floorboard is between 2,200 N-m and 10,700 N-m is largely unknown due to lack of crash test data with a sufficient range of OCD values. As is described in Chapters 6 and 7, the full-scale crash tests were designed to adjust these energy thresholds and reduce the size of the region with unknown performance.
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From page 48... ...
The toe of the barrier remained smooth, as shown in Figure 58. PRELIMINARY AESTHETIC DESIGN GUIDELINES All simulations in the parametric study to establish the preliminary aesthetic design guidelines were performed with the 2000P pickup truck impacting a rigid New Jersey safety shape barrier following Test 3-11 of NCHRP Report 350.
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From page 49... ...
However, the asperity depth and width values for such configurations would have no practical significance for the aesthetic surface treatment of concrete barriers and hence were not simulated. Simulation results for the truck floorboard internal energy for the 45-degree, 90-degree, and 30-degree asperity angles are presented in Tables 4 through 6, respectively.
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From page 50... ...
An analogy can be drawn between the 90-degree asperities and splices in tubular steel rail members that have demonstrated the potential for severe snagging and increased OCD in full-scale crash tests. One must bear in mind that all simulated asperities (45-degree, 90-degree, and 30-degree asperities)
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Figure 60. Depth versus width guideline for a 90-degree asperity angle.
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Figure 61. Depth versus width guideline for a 30-degree asperity angle.
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For a given asperity width, the increase in 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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Figure 65. Truck floorboard internal energy values at different configurations for a 30-degree asperity angle.
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From page 55... ...
when the asperity depth increases from 6.5 mm to 15 mm. Similarly, for a specific asperity depth, the floorboard internal energy increases as the asperity width decreases.
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