Explain the specifications for assembling highway guardrail nets.
Dec 20,2022
Discuss the specifications for assembling highway guardrails
1. The problem of the relative height of highway guardrail installation. The precise installation height of the guardrail, especially when very high, relates to the safety and effective control of most vehicles. Generally, the height from the core of the continuous anchor bolt of the guardrail to the ground is 60cm. If the curb height is calculated as 12cm, then the core height of the continuous anchor bolt of the guardrail is 72cm. However, on some highways, without any curbs, the relative height of the roadside highway guardrails is all increased to 72cm, while the pole dimensions are not correspondingly changed. This puts the guardrail under harmful stress. In addition to the guardrail height not meeting requirements, during construction and installation, the guardrail height also varies significantly. This is due to the inconsistency between the guardrail construction elevation and the ground elevation. During guardrail construction, the top elevation of the post should be calculated based on the ground elevation and strictly controlled. Therefore, the top elevation of the guardrail post should match the building elevation. However, in reality, due to deviations in the asphalt pavement construction elevation, and the displacement of the original route's stakeout points from the guardrail construction points, different elevations result. In some places, the guardrail height exceeds 100cm, while in others it is only 40cm.
The above-mentioned situations lead to changes in the relative height of the guardrail settings, and in most cases, the guardrail height specifications are increased, which affects the original design conditions. This severely deteriorates the support conditions of the guardrail.
2. The problem of active lateral earth pressure on highway guardrail posts. The magnitude of vehicle collision force sustained by guardrail posts depends on various factors such as the compaction degree of the backfill, embedding depth, distance from the slope line, slope size, and soil characteristics. On some phase-built (full-frame) highways in China, due to the narrow road width, the posts of roadside guardrails are moved as far outwards as possible, some close to the slope line, and some even driven onto the slope. Coupled with insufficient compaction of the earth shoulder, this significantly reduces the ability of the guardrail posts to withstand vehicle collisions.
3. Lack of strict control over the steel used for highway guardrails. According to a survey report on the use of highway guardrails in China, a few manufacturers produce guardrail components with insufficient stainless steel thickness, and the steel quality does not meet specifications. Some are prone to cracks, some are too brittle, and lack sufficient rigidity, leading to a reduction in the overall strength of the guardrail.
4. The problem of the length of guardrail settings. As is well known, corrugated highway guardrails are considered infinitely long beam-column structures. When vehicles impact the guardrail uncontrollably, causing significant displacement, the maximum extent of impact can reach more than 12 spans. To ensure that highway guardrails can function normally during collisions, various countries have specific regulations on the length of guardrail settings. China stipulates 70m. On some highways in China, the required length for guardrail settings has not been followed, which may significantly reduce the overall resistance of the guardrail.
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