Guardrail
An impact head for a guardrail includes cable routing means adapted to form a convoluted path through which a cable can be threaded. The convoluted path that the cables must follow through the impact head of the invention restricts movement of the cable through the head, thereby providing sufficient friction to slow down the movement of the impact head during a vehicle impact.
1. An impact head mounted to a terminal support post of a guardrail and having a cable routing means downstream of an impact face of the impact head, wherein the cable routing means comprises a bar member having a longitudinal axis and at least one cable entry port; wherein at least one cable extends from a fixed point at the terminal end of the guardrail and passes directly through the at least one cable entry port when said bar member is in a first non-cable gripping orientation; and wherein the bar member is pivotally mounted within the impact head such that upon rotation of said bar member through at least substantially 90 degrees about said longitudinal axis, a second cable-gripping orientation is reached which provides a cable routing means forming a tortuous path through which the at least one cable is threaded, wherein the tortuous path itself provides sufficient frictional resistance to movement of the at least one cable during impact of a force to facilitate impact energy dissipation.
2. An impact head, for a guardrail according to claim 1 wherein the cable routing means includes a member having two or more cable entry ports through which a cable may be threaded.
3. An impact head, for a guardrail according to claim 1 wherein the cable routing means is configured so that when a force is applied to the impact head the cables are forced through the cable routing means, such that resistance to cable movement provided by the tortuous cable path limits movement of the impact head caused by the force.
4. An impact head, for a guardrail according to claim 1 wherein the cables are under tension.
5. An impact head, for a guardrail according to claim 1 wherein at least one end of the cables is anchored to the ground.
6. An impact head, for a guardrail according to claim 5 wherein one end of the cables is anchored to the ground and the remaining end of the cables is anchored to a rail and/or a support post.
7. An impact head, for a guardrail according to claim 6 wherein the impact head is positioned substantially between the two anchor points.
8. An impact head according to claim 1 wherein the tortuous path is configured to absorb at least a portion of the kinetic energy of an impact on the impact head.
9. An impact head according to claim 1 wherein the cable routing means includes at least one substantially S or Z-shaped turn for the cable.
10. An impact head according to claim 1 wherein the tension of one or more cables can be adjusted so as to give a suitable resistant to movement.
11. A guardrail comprising: a plurality of support posts; a plurality of rails connected to the plurality of support posts; at least one cable wherein at least one end of the cable is fixed at a terminal end of the guardrail; an impact head mounted to a terminal support post of the guardrail and having a cable routing means downstream of an impact face of the impact head, wherein the cable routing means comprises a bar member having a longitudinal axis and at least one cable entry port; wherein the at least one cable extends from the fixed point at the terminal end of the guardrail and passes directly through the at least one cable entry port when said bar member is in a first non-cable gripping orientation; and wherein the bar member is pivotally mounted within the impact head such that upon rotation of said bar member through at least substantially 90 degrees about said longitudinal axis, a second cable-gripping orientation is reached which provides a cable routing means forming a tortuous path through which the at least one cable is threaded, wherein the tortuous path itself provides sufficient frictional resistance to movement of the at least one cable during impact of a force to facilitate impact energy dissipation.
12. A guardrail according to claim 11 wherein both ends of the cables are fixed in relation to the ground.
13. A guardrail according to claim 11 wherein the cable end located farthest from the cable routing means is anchored to the rail and/or support post.
14. A guardrail according to claim 11 wherein it includes one or more frangible posts comprising:
a first member substantially orthogonally connected to a second member,
wherein the at least one first member has a region of weakness.