Recommended Guidelines for Curb and Curb-Barrier Installations (2005) / Chapter Skim
Currently Skimming:
Pages 5-24
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 5... ...
Combinations of impact speed and angle falling to the left of the curve would result in redirection, and those falling to the right would result in mounting the curb. The boundary between redirection and mounting can be described by K = V sin α where V is the impact velocity and α is the impact angle.
|
From page 6... ...
Note that the required height of the curb increases as the radius of the tires increases, the velocity of the vehicle increases, the angle of impact increases, or the friction coefficient increases. Vehicle Dynamics Codes The first computer simulation program used for the analysis of vehicle-curb impacts was the Cornell Aeronautical Laboratory Single Vehicle Accident program (CALSVA)
|
From page 7... ...
; nine full-scale tests were conducted on each curb type at speeds of 48, 72, and 97 km/h and at 5-, 12.5-, and 20-degree encroachment angles. The HVOSM computer program was used to simulate vehicle impact with three different curb types: AASHTO curb types B, D, and G
|
From page 8... ...
Whether the vehicle penetrates behind the barrier or is redirected is, of course, influenced by other fac8 tors, including barrier configuration, lateral stiffness properties of the barrier, and impact conditions, as well as vehicle characteristics, such as bumper shape and vehicle kinematic properties. The trajectory of the vehicle after mounting a curb must allow the vehicle to contact the guardrail, or other roadside device, at the appropriate height.
|
From page 9... ...
The maximum vertical rise of the vehicle impacting the type G curb was less than 50 mm. Furthermore, the maximum rise height did not increase an appreciable amount for speeds greater than 48 km/h, indicating that the maximum rise height during impact with the type G curb is relatively independent of vehicle speed and impact angle.
|
From page 10... ...
Impact angle (deg) Max roll angle (deg)
|
From page 11... ...
For low-angle impacts on the 100-mm curbs with the 817-kg vehicle, the maximum roll and pitch angles increased as the impact velocity increased; values ranged from 5.6 to 9.0 degrees and 0.7 to 1.4 degrees for roll and pitch angles, respectively. For the moderate- and high-angle impact tests, the maximum roll angle increased as the impact speed increased, while the maximum pitch angle decreased with an increase in impact speed.
|
From page 12... ...
The impact speed was 100 km/h and the impact angle was 20 degrees. There was significant deflection of the guardrail, and the wheels of the vehicle contacted the curb.
|
From page 13... ...
During the test, the right front tire contacted the curb 20 milliseconds after initial contact with the guardrail and mounted the curb soon after. The maximum roll angle was negative 14 degrees (the roll angle was away from the system)
|
From page 14... ...
guardrail system. Test NEC-1 was conducted with impact conditions recommended by NCHRP Report 350 TL-3, which involves a 2000-kg pickup truck (1991 GMC 2500)
|
From page 15... ...
Test NEC-2 was conducted with impact conditions recommended in NCHRP Report 350 TL-3. The test vehicle was a 2000-kg pickup truck (1994 GMC 2500)
|
From page 16... ...
• In most (50% to 80%) of the rollover accidents, the vehicles were skidding out of control at a large yaw angle prior to overturning.
|
From page 17... ...
17 Figure 13. Summary of results of TTI Test 404201-1 from Bullard and Menges.
|
From page 18... ...
18 Figure 14. NCHRP Report 350 Test 3-11 impact with modified G4(1S)
|
From page 19... ...
The friction between the tires and the road surface was reduced by applying soap film to the roadway. In order to more accurately represent the impact conditions of vehicles in real-world accidents, where an initial roll of the vehicle would be produced from the tireground interaction, a roll angle of 2.5 degrees was built into the test vehicles by extending the left suspension with wood blocks.
|
From page 20... ...
. Curb impacts produced very high decelerations, usually in excess of 10 Gs.
|
From page 21... ...
Curbs along low-speed roadways are not likely to result in serious injuries and are commonly used in urban areas where speed limits are in the range of 40 to 48 km/h. Curbs along high-speed roadways have been discouraged by AASHTO for many years because of the potential hazard caused by high-speed impact with curbs (1)
|
From page 22... ...
Design parameters for curb impacts as defined by AASHTO (38)
|
From page 23... ...
It was not reported whether or not friction between the tires and ground surface was included in the simulations. Friction between the tires and ground will affect the initial roll angle and roll rate of the vehicle prior to impact, which may increase the vehicle's tendency to rollover.
|
From page 24... ...
There has been a great deal of advancement in computation power and in code development over the past few years that has enabled computer simulation programs to become a very efficient means of analysis. Both tracking and nontracking impact on curbs may be investigated using vehicle dynamics codes, such as VDANL, and finite element analysis (FEA)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.