When the car hits the standard concrete guardrail, there is no real impact between the car and the concrete guardrail, but the impact kinetic energy of the car is consumed by climbing the front wheel of the car onto the slope of the concrete guardrail. The automobile structure does not contact the concrete guardrail, and there is no energy exchange between the automobile structure and the concrete guardrail. The semi-rigid guardrail is a real impact, and the vehicle structure and semi-rigid guardrail should contact and exchange energy. Generally speaking, the impact kinetic energy absorbed by semi-rigid guardrail is greater than that of the front wheel of the car climbing on the slope of concrete guardrail. Therefore, whether it is the HIC position of the occupant head or the peak value of the synthetic deceleration of the dummy's chest, the semi-rigid guardrail has lower value than the standard concrete guardrail, that is, the semi-rigid guardrail has better impact resistance than the standard concrete guardrail.
In addition, the problem of overturning is more easily existed when large vehicles hit the standard concrete guardrail, which is shown in the elevation of vehicle position. The example shows that when t = 5ooms, the shift center of the vehicle starts to rise sharply. When t = 903ms, the vehicle position reaches the limit position of 346.6m (the vehicle side inclination reaches 240), and then starts to decline (i.e. the rollover accident starts), and the rollover accident is inevitable. Because the contact between the car and the guardrail only shows the front wheel crawling on the slope of the concrete guardrail during the process of the automobile hitting the standard concrete guardrail, and there is no contact between the car body and the concrete guardrail, that is, the height of the concrete guardrail does not work for preventing the car from turning over. Only when the rollover has occurred, the car body hits the concrete guardrail When the height of concrete guardrail is used to inhibit the rolling over of vehicles that have already been overturned. It can be seen that concrete guardrail is not an ideal guardrail to protect large left vehicles. It is not scientific to adopt concrete guardrail in mountainous roads and dangerous sections, even if the height of concrete guardrail is increased.
When the car hits the semi-rigid guardrail, the calculation example shows that before t = 600ms, the height of the vehicle position does not change much. After t = 600ms, under the action of inertia force, the rear of the vehicle has the tendency to push the guardrail beam plate outward. However, under the block of the guardrail beam plate, because the vehicle is on the high side, the vehicle rolls outward with the upper edge of the beam plate as the supporting point. At this time, the carriage is pressed on the guard The upper edge of the guardrail plate is upward and the downward pressure is applied to the guardrail beam plate. Under the pressure, the guardrail beam plate starts to move downward, and the connecting bolts between the beam plate, the anti blocking block and the vertical are cut off gradually, which makes the beam plate gradually detached from the support. During this process, the vehicle a turns out rapidly due to the falling support point position of the roll out, and the vehicle position rises rapidly. When t = 905ms , the vehicle has risen 191.56mm and the vehicle's inclination angle is 14 °. It can be seen that the semi-rigid guardrail is far better than the standard of the rigid guardrail in preventing the overturning of heavy vehicles. However, the current semi-rigid guardrail will inevitably be crushed under the measure force of heavy vehicles, which shows the lack of integrity of the guardrail. Therefore, to solve the safety problems of the runaway large vehicles, a new guardrail design mechanism must be developed.