ShiTeng Traffic Facilities Co.,Ltd.

Effective Height Of Crash Barrier Effective Height Of Crash Barrier

I. The crash barrier should not only have enough height to block the vehicle from crossing but also prevents the vehicle from tilting or passing through. In the past, we thought the height of the guardrail was the height from top to the ground. In the beam column guardrail system and the combined guardrail system, the resistance R of the guardrail is usually not located at the top of the guardrail, but slightly lower. The effective height of the crash barrier is the height of the guardrail resistance R away from the ground. Therefore, considering the influence of vehicles tilting by guardrail’s height, the effective height of the guardrail is more important than the total height of the guardrail. The United States discovered that many guardrails were crossing through by vehicles from the barrier crash accident. It is not due to the strength of guardrail, but the insufficient effective height.

The effective height of the safety roller barrier is directly related to the design type. There are many kinds of cars produced in the world. From heavy duty automobile to mini cars, the weight and the shape of vehicles vary greatly. But for a specific type of vehicle, such as cars or trucks, all countries have a certain limitation on its outer side. Moreover, with the opening up of all countries and international standardization, the regulations on vehicle types are similar. Therefore, we can refer to foreign regulations on the effective height of the crash barrier.

According to the collision test analysis and field statistical investigation by the United States, the effective height of the guardrail is shown in table 8.1.3-2 and table 8.1.3.3. The minimum height of the crash barrier is 1.0m and the main longitudinal effective component (effective height) is 53.5cm~68.5cm in British regulation. The maximum height of the secondary vertical effective component is 38.5cm. The standard of the Japanese crash barrier stipulates that the central height of the main beams is 60~80cm, generally higher than 70cm. The height of the secondary beam below the main beam is 25~55cm. Japan is a country where there are most trucks (cars occupy 40% share of the market, trucks occupy 60% share of the market, in European and American countries, cars occupy 85%~93% share of the market). In European and American countries, cars share the are the majority in the market. But from the height of the safety crash barriers that should be suitable for the cars and trucks, the regulations on the effective height of crash barrier are similar in various countries.


The relationship between the anticollision grade and the effective height table 8.1.3-2

Anticollision grade

PL1

PL2

PL3

PL4

Effective height(m)

<0.68

0.68~0.86

>0.86

>0.86


The effective height of the guardrail required to prevent vehicle tilting table 8.1.3.3

Type of cars

Collision conditions

Minimum effective height(cm)

817kg~2043kg car

V=9.6km/h,θ=25°

61.0

9080kg car

V=9.6km/h,θ=15°

86.3

14530kg bus

V=9.6km/h,θ=15°

76.2


II. In addition to meeting the intensity requirement of the vehicle collision, the crash barrier should also give road users a sense of psychological safety. According to the experience of bridge railing in China for a long time, when the surface of the bridge is above the ground or above the water surface of 3 meters, the top of the handrail should be higher than the body's center of gravity. We all know that the height of the body's center of gravity is equivalent to the two third to three-fifths of height. For example, a person’s height is 1.7 meters, his body's center of gravity is 1.0 to 1.1 meters. So the general guardrail’s height is not less than 1 meters. Besides, drivers sitting in the driver's room have a sense of high altitude fear.

There are two methods to increase the height of traffic safety barriers when the crash barrier is used for the pedestrian guardrail. The first one is using a thrie-beam type anti-collision guardrail system, and the second one is increasing the longitudinal non-effective component in the top surface of the crash barrier.

III. The height of crash barrier should adapt to the requirements of bridge surface clearance. For example, the design of some bridge guardrails in Tianjin is based on the standard that the height of guardrail is below 1 meter when the width of the bridge is below 10 meters, the height of the guardrail is around 1.2 meters when the width of the bridge is in 10 to 30 meters.

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