Installation Height of Corrugated Beam Guardrails
When an out-of-control vehicle collides with a guardrail, it is desirable for the guardrail to act on the effective part of the vehicle, preventing it from going over the guardrail or going under the guardrail beams. Ideally, the guardrail's overall action should force the vehicle to gradually steer back to its normal driving direction. However, the world's automobiles vary greatly, from heavy-duty trucks to tiny microcars, with significant differences in weight and shape. Modern cars are trending towards miniaturization, becoming lighter and with lower, more streamlined hoods to reduce air resistance. Such vehicles are more likely to go under the corrugated beam guardrail beams upon collision, causing serious consequences.
Another situation is the increasing size and weight of vehicles. Large vehicles may experience jumping problems upon impact with guardrails. Especially when colliding with a "W-shaped" corrugated beam guardrail, the vehicle's bumper may twist into an inclined plane due to the impact with the top of the guardrail's crossbeam. This is even more dangerous at large collision angles and high speeds. Once this occurs, the bumper may tilt downwards and backwards, and under the force of the vehicle's impact, it can easily slide onto the inclined plane of the guardrail, leading to an accident where the vehicle jumps over the guardrail.
Both of the above-mentioned scenarios-the vehicle crawling under the guardrail and the vehicle jumping over the guardrail crossbeam-are undesirable. This necessitates a careful study and determination of the appropriate installation height for the guardrail. The guardrail installation height can be determined through three factors: full-scale collision tests between the vehicle and the guardrail; traffic accident investigation data on guardrails in use; and analysis of the geometric characteristics of modern vehicles. Generally, the center height of the crossbeam of the corrugated beam guardrail, measured from the road surface, should be 60cm from the center of the connecting bolt holes. When a curb is present, the center height of the crossbeam, measured from the top surface of the curb, should also be 60cm from the center of the connecting bolt holes. When a corrugated beam guardrail has anti-blocking blocks, its center height remains unchanged.
Strength of Corrugated Beam Guardrails
The strength of a corrugated beam guardrail is mainly determined by the stiffness of the posts, the bearing capacity of the soil, and the tensile strength of the beam. In particular, the relationship between the horizontal bearing capacity and displacement of the posts is a crucial factor in determining their strength. When the posts are embedded in the soil foundation, considering factors such as potentially insufficient compaction of the shoulder fill and reduced lateral earth pressure due to excessive proximity of the posts to the slope line, the post embedment depth should not be less than 110cm, and for posts with curbs, the embedment depth should not be less than 125cm. When the posts are embedded in a concrete foundation, the embedment depth should not be less than 40cm. Since the maximum bending moment of the posts occurs at the root, it is important to consider how to make repairs easier after damage. For ease of maintenance, a flange-mounted connection method can be used. The dimensions of the concrete foundation and the connection strength of the flanges should be determined by calculation based on different situations. When conditions permit, it is best to use a replaceable guardrail post device. Its characteristic is that the post holes are pre-drilled using rigid plastic pipes. The burial depth can vary from 40 to 80 cm as needed, mainly to allow for future height adjustments. The bearing is fixed in the concrete foundation. During installation, loosen the clamping screws, insert the post, and after adjusting the height, tighten the three bolts to lock the post in place. This device has a simple structure and is easy to install and maintain.
Standards for Components of the Corrugated Beam Guardrail: The corrugated beam, posts, anti-collision blocks, crossbeams, end caps, and other components should comply with relevant product standards.
① Corrugated Beam: The corrugated beam is the first point of contact with an out-of-control vehicle. Through the corrugated beam, the impact force is distributed to multiple posts, which then transfer the force to the foundation soil. The interaction between the out-of-control vehicle and the guardrail will continuously change its position over time. The corrugated beam primarily bears tensile force. Under the impact of a colliding vehicle, the corrugations unfold, absorbing energy. In addition to meeting tensile strength requirements, the corrugated beam also has good guiding and energy absorption properties.
② Posts: A corrugated beam guardrail can be approximated as a continuous beam supported at points on an elastic foundation. The impact force of a vehicle acting on the guardrail at a certain angle (θ=10°～20°) can be decomposed into forces acting perpendicularly to the guardrail and forces acting parallel to the guardrail. The perpendicular force causes deformation of the guardrail and posts, while the parallel force causes the impact to continuously change direction and position. The corrugated beam, posts, and foundation soil jointly bear this impact force, with the corrugated beam primarily bearing tensile force and the posts primarily bearing bending moment. During the collision, the posts play a crucial supporting role. To improve the strength of the posts, the moment of inertia can be increased; however, the moment of inertia is affected by the shape and area of the post's cross-section. In practice, different countries use different shapes of steel for the posts. For example, Australia uses rectangular and H-shaped posts, the United States uses square wooden posts and I-beam posts, the United Kingdom uses I-shaped posts, the Netherlands uses flat round posts, the United States uses channel steel, Germany uses I-beams, and Japan uses round tubular steel, all with excellent results. On my country's dedicated roads for automobiles, guardrail posts mainly come in two forms: round posts and channel posts.