Introduction to Flexible Guardrails
The guardrails and concrete barriers are designed to protect the vehicle’s occupants and prevent them from being damaged in case of highway accident. Their main function is to alleviate the severity of traffic accidents in cars that deviate from the main route, so that it diverts the vehicle away from the steep slopes of the roadside embankment or fixed barriers and lowers its kinetic energy.
However, it is useful when hitting guardrails have less risk than colliding with fixed roadside barriers or slipping off the existing slope. Therefore, the guardrail should not be installed until we ensure its increased safety. This is achieved by gradually reducing the vehicle speed and lowering its kinetic energy, and sometimes by changing the direction of the diverted vehicle from a path leading to collision with barrier and making it a safe stop.
The current guardrails in many cases cause accidents or are not efficient. An integral part of road safety plans and measures is to alleviate accidents through cost-effective engineering operations in accident-prone locations. The huge cost of accidents on major freeways and roads around the world has made road safety improvement a top priority for transportation.
Nowadays, three common systems are used in construction and installing road protection barriers:
1-1-Flexible (elastic) barriers:
These barriers are resilient and show flexible properties when hit by a vehicle. These barriers are categorized in three groups of three-rope barriers, two-waved barriers and three-waved barriers.
1-2-Semi-rigid barriers:
The flexibility of these barriers are less than other types, and so they show little flexibility while hit by a vehicle. Examples are the box- shaped shield and two-waved shield with strong base.
1-3-Rigid barriers:
These barriers are fragile and vulnerable in severe accidents, so all aspects must be examined in great detail when these are produced and installed so that the barriers are installed in a solid and precise way. The New Jersey separator is a known standard type of these barriers that when installed appropriately is capable of supporting loads up to 18 tons. The example could be the concrete barrier with variable section.
The most significant problems of current systems are:
1-4-Metal Guardrails:
This barrier can support vehicles weighing 8 to 8.1 tons and when hit by a 1800 kg vehicle with a 25 degrees angle and 95 km/h speed, the lateral deformation of 2.2 meters is recorded. The highest service level of this barrier is when it is hit by a 2100 kg caravan running 95km/h in a 24 degrees angle. This system is sensitive to installation height and roughness of the ground, so great care must be given to the installation height while it is installed.
Disadvantages:
- High Initial cost
- Expensive installation costs
- Relative long distance needed for sublation
- Separation in joints
- Damage to the vehicle and passengers due to breaking up the cars body and entering its interior space
- Overturning in case of inappropriate performance of bases or improper angle of horizontal plates
- Corrosion in humid climates
- Unsuitable for using in precipices
1-5-Cable barriers:
A rope protection barrier that consists of steel cables place on a weak base and could support vehicles of 2 to 8 tons weight. S-shaped base metal barrier can completely change the course of a 1800 kg caravan. When installed in curves, the designers must take into account higher lateral deformation in their computations. For example, a three-rope barrier with metal S-shaped bases of 75*5.8 dimensions with a 9.4 long space between bases is suitable for a curve with a 135 meter radius.
Disadvantages:
- The need for replacement of a long part of barrier when It’s hit
- The big space needed behind the barrier because of its large deformations Few application in curves
- Separated and torn up ropes when hit by a vehicle
- Tearing up the car’s body when hit by a vehicle
1-6-Concrete barriers:
The design of concrete barriers is done in such a way that when hit by car side, it acts as a rebound surface due to the small angle of the edges and stops the vehicle. All pieces contain male and female connections which makes the installation easy. Usually, two holes are designed above the barrier pieces for passing pipes or easy displacement. To build these barriers, a 350kg cement used and the higher this ratio gets, the resulting concrete will be stronger. These barriers are designed for different types of vehicle considering various speeds and angles in impact.
Disadvantages:
- Very heavy weight
- The need to heavy equipment to install
High installation costs - The possibility of fatalities because of high rigidity
- Inappropriate performance in Snowy or sandy places because of snow-sand accumulation
- Difficulty in simultaneous installation of traffic signs and road lights and their protections
- Difficulty of correction in case of a problem in concrete panels
- Delicate connections in prefabricated concrete pieces
2- Pervious inventions:
Publication Number: 206859121, Safe crashproof highway guardrail, The utility model discloses a safe crashproof highway guardrail, including base, backup pad, buffering cylinder and fixed axle, the base is fixed to be set up subaerial, the one end of fixed axle is passed hollow through hole and will be cushioned the cylinder and fix on the base, the backup pad is connected with the other end of fixed axle, constitutes the highway guardrail jointly with buffering cylinder, base. During the installation, earlier fix the base in the highway both sides, is connected fixedly on right rear fixing shaft and the base, cushion on the cylinder penetrates the fixed axle, install the backup pad on the fixed axle at last, when bumping, the sponge parcel layer of buffering on the cylinder at first with the automobile contact, absorb partly kinetic energy and prevent that the automobile body from being scraped, cushion orientation that the cylinder can be naturally go along with the automobile after that and take place rotatory, absorb most impact energy with the mode that changes the impact orientation through extrusion deformation, the safety of property and life has been guaranteed to the at utmost. The utility model discloses still have simple structure, simple to operate, the easy advantage of changing.
3- Prior arts
Publication Number: 206859121, Safe crashproof highway guardrail, The utility model discloses a safe crashproof highway guardrail, including base, backup pad, buffering cylinder and fixed axle, the base is fixed to be set up subaerial, the one end of fixed axle is passed hollow through hole and will be cushioned the cylinder and fix on the base, the backup pad is connected with the other end of fixed axle, constitutes the highway guardrail jointly with buffering cylinder, base. During the installation, earlier fix the base in the highway both sides, is connected fixedly on right rear fixing shaft and the base, cushion on the cylinder penetrates the fixed axle, install the backup pad on the fixed axle at last, when bumping, the sponge parcel layer of buffering on the cylinder at first with the automobile contact, absorb partly kinetic energy and prevent that the automobile body from being scraped, cushion orientation that the cylinder can be naturally go along with the automobile after that and take place rotatory, absorb most impact energy with the mode that changes the impact orientation through extrusion deformation, the safety of property and life has been guaranteed to the at utmost. The utility model discloses still have simple structure, simple to operate, the easy advantage of changing.
4- Description of invention:
In order to improve vehicles and occupant’s safety when crashing with guardrails and barrier, this impact attenuator controls the impact acceleration during three steps. After collision, in addition to imposing less damage to existing New Jersey barrier, it allows the vehicle to be driven to the main track. The three steps mentioned include failure, displacement, and traction, which cause the energy to be depreciated.
This guardrail is made up of fibers that fails after a severe collision during an accident, and then the horizontal support beams are seamlessly wrapped around the car and it is subjected to displacement along with impact. If the impact intensity exceeds the displacement limit, then the mechanism of the existing traction cables starts and prevents the vehicle from straying off the main track, thereby it returns to the main track with minimum damage
Fig 1 – General view of the interior and exterior parts of the Guardrail
4-1-Brief Description of the Drawings
The main benefits of this plan are as follow:
- Increasing the impact strength and impact attenuation
- Reducing the damages to vehicles and passengers in traffic accidents
- Increasing the safety of roads in the accident areas
- Reducing operating costs due to obviating great parts displacement and installation compared to existing concrete and steel shields used in steel guardrails.
- The possibility of in situ replacement of panels in the shortest possible time and reducing maintenance costs
- Despite the strengths of similar samples, their weaknesses are masked in this design
- Lower manufacturing and installation costs than present samples