Corrugated beam guardrails are generally classified according to their installation location and impact resistance level, as shown in the table below. According to installation location, they can be divided into roadside guardrails and median guardrails. According to impact resistance level, they can be divided into Class A and Class S (Am and Sm indicate installation in the median). Class S guardrails are reinforced and suitable for use on particularly dangerous roadside sections, while Class A is used for dedicated highways.
Roadside Corrugated Beam Guardrails
(1) Transverse Layout
The transverse layout of roadside corrugated beam guardrails should not allow the guardrail surface to encroach into the highway construction clearance limits, and should not significantly reduce the lateral earth pressure on the outer side of the guardrail posts. The minimum distance from the outer edge of the post to the edge of the shoulder is: not less than 25cm when the shoulder width is 75cm; and not less than 14cm when the shoulder width is 50cm.
(2) End Treatment
The starting and ending points of the roadside corrugated beam guardrails should be treated. The ends of the roadside guardrails can be rounded or anchored. In the early stages of highway construction in my country, round-headed guardrail ends were commonly used, connected to the standard section of guardrail by a transition section. This transition section was typically parabolic, with the posts gradually shifting outwards while maintaining a constant height. The spacing between the posts near the ends increased to 2 meters. Concrete foundations and cable-stayed anchors were used; this method is called end-beam extension, with round-headed end beams. This type of end was widely used abroad because it was easy to manufacture and install, and provided good guidance at small collision angles. However, if an out-of-control vehicle collided head-on with the end, the guardrail could penetrate the vehicle body. Therefore, ground-anchored end ends were adopted. These end ends extend gradually towards the ground via an angled beam and are anchored at the end with a concrete foundation. In a head-on collision, the out-of-control vehicle would climb up the angled corrugated beam to absorb energy. In a side collision, it also provided good guidance.
The ends of the guardrail have different treatment methods upstream in the oncoming traffic direction and downstream in the flow of traffic direction. The end treatment methods described above refer to the upstream end in the oncoming traffic direction. The downstream end in the flow of traffic direction is laid in a straight line with the standard section of guardrail. The downstream end is generally treated as a round-headed end beam. When the vehicle reaches the downstream end, the guardrail installation is complete, and the danger on the roadside is considered to be minimal.
(3) Construction of the anti-blocking block
The anti-blocking block of the roadside corrugated beam guardrail is the load-bearing component between the corrugated beam and the post, and can be manufactured using various shapes of steel. It can be divided into two types: Type A and Type B. Type A is suitable for round posts and is a hexagonal structure; Type B is suitable for channel posts or other steel posts. Adding anti-collision blocks between the corrugated beam and the posts offers several advantages:
① The anti-collision block itself acts as an energy-absorbing mechanism, allowing the guardrail to gradually deform upon impact, facilitating energy absorption and reducing occupant injuries.
② The anti-collision block, fixed between the post and the corrugated beam, suspends the beam from the post. In the event of a collision, an out-of-control vehicle will not have its front wheels stuck at the post due to the beam being too close to it.
③ The anti-collision block contributes to the overall function of the guardrail, distributing the impact force across a wider span, resulting in more even stress distribution, a smoother collision trajectory, improved vehicle guidance, and increased overall guardrail strength.
④ When anti-collision blocks are installed on sections with curbs, the distance between the corrugated beam and the curb surface is reduced, mitigating or even eliminating the adverse effects on the guardrail caused by an out-of-control vehicle bouncing after hitting the curb.
(4) Post Installation
Roadside guardrail posts should be installed in solid earthen shoulders. The interaction between the post and the roadbed soil causes the post to bend and deform, while the soil compresses and deforms; this is part of the guardrail's energy absorption process. However, in three situations-where guardrail posts cannot be driven into bridges, passageways, culverts, or where there are underground pipelines or rocky sections beneath the post-the guardrail posts should be installed in concrete foundations. If possible, replaceable guardrail posts should be used.
There are three methods for installing guardrail posts in concrete: one is to pre-drill holes in the concrete foundation, fill them with dense sand after the post is placed, and seal the top and bottom with asphalt. In the event of a collision, the post can deform to a certain extent without damaging the concrete foundation, and replacement is also easier. Another type uses a flange base with bolted connections. The flange has an elongated hole; in the event of a collision, the flange will shift slightly along the elongated hole, making repairs easy if the anchor bolts are not damaged. A third type uses a replaceable road safety barrier device. This device is suitable for round posts, made of cast steel, with the outer base embedded in concrete. The inner sleeve is bolted to the outer base. The barrier post is inserted into the inner sleeve, and when the bolts are tightened, the inner sleeve locks the post in place. In the event of a collision, the post may bend or deform; simply tightening the bolts allows for easy removal and replacement.
Central Median Corrugated Beam Guardrails: Corrugated beam guardrails installed in the central median are classified into Am and Sm levels based on their impact resistance. Sm level guardrails are reinforced and suitable for sections of the central median containing important structures where lateral displacement of the guardrail needs to be restricted. Am level guardrails are suitable for general sections of dedicated vehicular roads. They can be classified into separate and combined types based on their construction. Separate guardrails are suitable for road sections with relatively wide median strips, numerous structures within the median strip, and underground pipelines. Combined guardrails are suitable for road sections with narrower median strips, fewer structures within the median strip, or fewer underground pipelines.
(1) Cross-sectional Layout
The cross-sectional layout of corrugated beam guardrails for median strips should be determined based on the width of the median strip, its cross-sectional shape, and the layout of underground communication pipelines.
When the median strip is laid out in a separate manner, the guardrail surface should not encroach upon the road construction boundary. If separate guardrails are installed in a median strip with curbs, the corrugated beam guardrails should have anti-blocking blocks. If installed in a median strip where communication, power, or other pipelines are laid, the minimum value C of the corrugated beam guardrail's curb surface can be reduced to 25cm (generally C=50cm). When using composite corrugated beam guardrails in the central median, the centerline of the guardrail posts should ideally coincide with the road centerline. If there are structures or underground pipelines within the road centerline, the centerline of the guardrail posts can be shifted to one side, or the composite type can be changed to a separate type to bypass the structures at the centerline. Composite corrugated beam guardrails consist of posts, crossbeams, corrugated beams, and fasteners. Posts can be made of round or channel steel. Crossbeams consist of two channel steels, installed on both sides of the post, with each end connected to the corrugated beam. The maximum combined width of the two corrugated beams is 100cm, which can be adjusted according to the width of the central median.
(2) End Treatment
Guardrails installed at the start, end, and openings of the central median should have their ends treated. Untreated ends are extremely dangerous; when a vehicle collides with a metal guardrail, the end beam may pierce the passenger compartment; when a vehicle collides head-on with a reinforced concrete guardrail, it will generate enormous impact force. In a head-on collision, the end-end anti-collision device must not have spikes, cause bulging, or induce vehicle rollover. The vehicle's acceleration during the collision must not exceed the required limits. When an out-of-control vehicle collides between the end-end and the standard section, the end-end structure should have the same vehicle-changing performance as the standard section of the central divider guardrail.
End-end type: Two types can be considered: separate and combined. For separate corrugated beam guardrails, the end-end should be consistent with the alignment of the central divider. Within a certain length (e.g., 16m), the corrugated beam guardrail gradually narrows inward from two parallel lines towards the divider at a certain ratio, generally in a parabolic shape. The post spacing is 2m, and the radius of the rounded end should be consistent with the alignment of the divider opening, generally 25cm.
Research on end-end treatment technology in my country is limited. The above-mentioned treatment methods basically connect the corrugated beams on both sides with rounded ends, without employing disassembly of energy-dissipating posts or sliding bases, and the corrugated beams do not incorporate energy absorption or displacement designs. Therefore, the energy absorption effect at this end is not very good, but this structure is easy to manufacture and install, and has a low cost, so it is still widely used.
Traffic Diversion Triangle Area Guardrails: The triangular areas at the entrances and exits of interchange ramps, service areas, and parking lots on dedicated motorway roads are considered danger triangle areas and should be equipped with specially designed guardrails. The guardrail structure at this location should be consistent with the roadside corrugated beam guardrails and should be laid out according to the alignment and terrain of the triangle area. During installation, reinforced (S) guardrails should be used within 8 meters of both ends on the side closest to the main road and within 8 meters of both ends on the side closest to the ramp. Six spans of Class A guardrails should be connected in the middle of the reinforced guardrails, and the guardrails on both sides of the triangle area should be connected with rounded ends. When conditions permit, crash barriers should be installed within the danger triangle area. Crash barriers can effectively absorb collision energy and reduce the speed of vehicles in a frontal collision. In the event of a side collision, crash barriers can change the collision angle of the vehicle and guide the vehicle to the center of the road; therefore, they are widely used in the danger triangle areas of traffic diversion.