Problems needing attention in technical scheme design of guardrail

1、Structural Form of Anti-collision Guardrail

  Highway engineering anti-collision barriers are generally wall-type barriers. Although the cross-section forms and sizes of each project are different, they can be roughly divided into the following two structural forms:

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1. The inner and outer sides are above the beam flange 2. The outer side of the beam flange is used as drip design.

Figure 1. Cross-sectional view of wall crash barrier





2、 Construction of Anti-collision Guardrail Formwork

  Installation of anti-collision guardrail is usually to install inner formwork first. The reinforcement of inner formwork usually uses steel bar spot welding to support the inner formwork panel. The outer side uses steel pipe to support the formwork, so that the inner and outer sides become the form of inside and outside double clamps. The size and elevation between the inner and outer formwork are made by two pairs of pull bolts and bolts. The top is connected horizontally, and the verticality of the formwork is adjusted by the diagonal braced steel pipe and the drawing bar (or flower basket bolt) on the inner side of the guardrail (the side of the central line of the bridge). The construction section of the crashproof guardrail is shown in the following figure:

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Figure 2. Cross-sectional drawing of anti-collision guardrail construction

3、 Design of Anti-collision Guardrail Template

  1. The appearance of concrete on the surface of anti-collision guardrail must be beautiful, so the design of guardrail formwork should have enough strength and rigidity. It is suggested that the turnover times of formwork should be more than 40 times. (Because the internal space is too small, it is not easy to observe the staggered platform of adjacent templates. Generally, it is easier to ensure the assembly quality with a stable pin design, but the general distribution work is difficult and labor-intensive. See if there are any anti-error control measures which are good for both processing and use.

2. If Party A has not made any special requirements for the section of the template, it is recommended that the general section length be 2 m. If the bridge is on the plane curve, when the radius of the plane curve is greater than or equal to 400 m, the section of the template is 2 m. If the radius of the plane curve is less than 400 m, the section of the template is 1 m.

3. It is suggested to adopt 6-cap 4-cushion or 4-cap 4-cushion to fix the spacing of the formwork in the inner part of the formwork, so as to prevent the structural dimension of the upper part of the formwork from changing. The scheme with suspension outside formwork hanger is suggested at the top of the inside. )

4. In order to facilitate the turnover of the lower tension bolt, the PVC pipe for the tension bolt usually needs to pass through the panel, so the diameter of the hole punched on the concrete tension panel of the formwork panel should not be less than 22 mm (with a diameter of 16 mm) for the tension bolt. When the pull-down position is in the oblique plane, the formwork must set up vertical measures to the pull point, so that the pull nut can be subjected to average force.

5. The lower part of the inner formwork should be designed to be 20-30 mm short, so as to prevent the formwork from being unable to adjust when the concrete of the box girder is higher than the design elevation. The lower treatment method is to leveling the high-grade mortar to the design elevation. (For the outer formwork on the beam, the same design should be done. For the lower wing-clad plate, the same design length should be used as the shorter design. For the single vertical plate in dripping water, the vertical long hole design should be set up with the main L-shaped plate. )

_6. It is suggested to drill holes in the back ribs near the upper mouth of the inner formwork to make it convenient for the drawing rod or basket bolt to tighten the guardrail formwork for site construction, so as to achieve the purpose of "one pull and one support" for the fixing of the inner formwork.

7. Generally, the setting of false seam should be considered in guardrail formwork. The width of false seam is generally 20 mm. Semi-circular steel plate or round steel plate is used to weld on the formwork panel. Artificial joints are usually 5 m in length or in the middle of the span of the beam (refer to the design drawings for the specific location). When making scheme exchanges, they should communicate with each other's communicators on such issues.

8. Whether the face with chamfer at the top needs to be grooved, the design value is whether the inner side of the face is level with the other side, or the outer side is level with the other side, which is clearly defined as shown in the following figure. If beveling is required, 2mm blunt edge shall be reserved for the beveling, and transportation protection measures shall be designed.

9. The spacing between left and right sides of some bridges is too small, and the spacing between the anti-collision guardrail at the central partition zone of the bridge is only 1-2 cm. When encountering this type of anti-collision guardrail, we should consider the problem that the left and right construction formwork can not be installed, and communicate this kind of problem with Party A to see if it is replaced by wooden formwork or made into steel plate.





4、Standardization of template design for collision barrier

  Anti-collision guardrail formwork is generally designed in the following two cross-sectional forms:

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Figure 3. Cross-section design of anti-collision guardrail template


  

It is suggested that standardized design should be adopted in the future fence template design to meet the standardized requirements of products.

1. Orthotropic plate design is adopted for the template structure of anti-collision guardrail. 5 mm (minimum not less than 4 mm) steel plate is used for the panel, 6*63 steel strip for the back rib, 8*63 steel strip for the connecting edge, 6.3_channel steel for the back rib, M16*40 for the connecting bolt and T16 for the pulling bolt.

2. According to previous design data and guardrail design cross-section, the upper and lower ports of common cross-section anti-collision guardrail are generally 200 mm and 500 mm respectively. According to the statistics of pull bolts of guardrail formwork over the years, it is found that the length of upper and lower pull bolts is M16*550 and M16*900 respectively. Therefore, in future design, the length of pull bolts should be designed on the above two lengths as far as possible in order to use spare parts.

3. The along-bridge spacing of tension bolts is usually set together by 500-1000mm. In case of special circumstances, the pulling distance can be adjusted appropriately.

4. Template processing should be pre-assembled in the factory. After pre-assembled and qualified, the number and number should be marked at the prominent position of the template. (It is suggested that the numbering method of each template can be distinguished uniquely according to the stipulation, so that the workshop number and the design description number are unified, and the goods are not delivered to the site and can not be found. The design of which template to use and where to use) should be indicated in the technical instructions of the drawings.




5、 Picture reference of guardrail formwork construction

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