Background Art As well known to those skilled in the art, a guard rail functions to restrain a vehicle from leaving the road. The guard rail i s designed such that rails are fastened to a plurality of posts which are arranged at regular intervals and are fixed in the ground. The guard rail is provided along the center or shoulders of the roadway in a moving direction of a vehicle to prevent the vehicle from crossing the median or restrain the vehicle from leaving the road. There has been required a rail having a large cross-section to be suitable for restraining several kinds of vehicles, such as small-sized vehicles, medium-sized vehicles, and large-sized vehicles, regardless of traveling speeds of the vehicles.

However, when the rail has a large cross-section, the weight of the rail is increased, so it is difficult to install the rails to the posts. Further, although an impact force imposed on the guard rail is different according to the kind of vehicle, the rails of the conventional guard rail have the same structure. Thus, when a small-sized vehicle is in a collision, the conventional guard rail prevents the small- sized vehicle from crossing the median, but does not effectively absorb an impact due to a collision because the strength of the guard rail is excessively high.

Therefore, the small-sized vehicle may be bounced back, thus causing another traffic hazard. Meanwhile, when a large-sized vehicle is in a collision, the large- sized vehicle breaks through the guard rail to cross the median, so there may occur a head-on collision between the large-sized vehicle and an oncoming vehicle, thus resulting in a serious accident.

In order to solve the problems, there has been proposed Korean U. M.

Appln. No. 2002-12643, which was filed by the inventor of the present invention and is entitled"A GUARD RAIL WITH DOUBLE RAILS".

The above guard rail is designed such that two rails having different strengths, that is, upper and lower rails, are separately fastened to the upper and lower portions of posts. However, the guard rail has a problem that light beams pass through a gap between the upper and lower rails, thus obstructing the vision of oncoming drivers at night.

Disclosure of the Invention Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a differential strength guard rail, which is provided with a thin lower rail and a thick upper rail, and is designed such that a first extension upwardly extending along the upper end of the lower rail overlaps a second extension downwardly extending along the lower end of the upper rail and the overlapped first and second extensions are fastened to each other by a fastening means such that the upper and lower rails are integrated into a single structure.

In order to accomplish the above object, the present invention provides a differential strength guard rail, including a post, a spacer provided at a side or at both s ides o f t he p ost, a thin 1 ower r ail fastened at a fastening p art thereof t o a lower portion of the spacer by means of a first bolt, and a thick upper rail fastened at a fastening part thereof to an upper portion of the spacer by means of a second bolt, wherein a first extension extends along an upper end of the lower rail, and a second e xtension e xtends a long a 1 ower e nd o f the u pper r ail su ch t hat t he first

extension overlaps an outer surface of the second extension, the overlapped first and second extensions being fastened to each other by means of a fastening means.

Further, a vertical flange extends along the first extension of the lower rail in such a way as to overlap an outer surface of the fastening part of the upper rail, with overlapped portions of the vertical flange and the upper rail being fastened to the upper portion of the spacer by means of the second bolt.

The fastening means for fastening the overlapped first and second extensions is selected from a bolt, a rivet and a spot welding method. It is most preferable that the overlapped first and second extensions be fastened to each other using the bolt.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a perspective view showing a differential strength guard rail according to a primary embodiment of the present invention, with the guard rail being installed along a road; Fig. 2 is an enlarged sectional view showing the differential strength guard rail according to the primary embodiment of the present invention; and Fig. 3 is an enlarged sectional view showing a differential strength guard rail according to a second embodiment of the present invention.

Best Mode for Carrying Out the Invention Reference should now be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components.

Fig. 1 is a perspective view showing a differential strength guard rail according to a primary embodiment of the present invention. Fig. 2 is an

enlarged sectional view showing the differential strength guard rail according to the primary embodiment of the present invention. Fig. 3 is an enlarged sectional view showing a differential strength guard rail according to a second embodiment of the present invention.

The terms describing a guard rail's components are defined according to Korean Industrial Standard KSV 2617. The guard rail A of the present invention includes posts 1, lower rails 2a, upper rails 2b, and spacers 3.

The configuration of the guard rail A according to the primary embodiment of the present invention will be described with reference to Figs. 1 and 2.

A lower rail 2a is fastened at its fastening part 21 a, by means of a first bolt 4, to the lower portion of a spacer 3 which is fastened to a post 1 of the guard rail A. The lower rail 2a is designed to be projected outward at a predetermined curvature so that a first arc-shaped shock absorbing part 24a is formed. A first extension 22a upwardly extends along the upper end of the lower rail 2a in such a way as to be integrated with the first shock absorbing part 24a.

An upper rail 2b is fastened at its fastening part 21b, by means of a second bolt 4, to the upper portion of the spacer 3 which is mounted to the post 1 of the guard rail A. The upper rail 2b is designed to be projected outward at a predetermined curvature so that a second arc-shaped shock absorbing part 24b is formed. A second extension 22b downwardly extends along the lower end of the upper rail 2b in such a way as to be integrated with the second shock absorbing part 24b. In this case, the second extension 22b is overlapped with the first extension 22a.

According to the present invention, the upper rail 2b is designed to be thicker than the lower rail 2a so that the upper rail 2b is stronger in strength than the lower rail 2a. Preferably, the thickness ratio of the lower rail 2a to the upper rail 2b is 1: 2-2. 5. Alternatively, the lower and upper rails 2a and 2b may be made of different materials so that the lower and upper rails 2a and 2b have different strengths.

In a brief description, the present invention provides the guard rail, which

is provided with the lower and upper rails 2a and 2b having different strengths, and is designed such that the first extension 22a of the lower rail 2a overlaps the outer surface of second extension 22b of the upper rail 2b, and the overlapped first and second extensions 22a and 22b are fastened to each other by means of a fastening means 5.

A guard rail A according to the second embodiment of the present invention will be described with reference to Fig. 3.

As shown in the drawing, a vertical flange 23 upwardly extends along the first extension 22a which integrally extends along the upper end of each lower rail 2a.

The vertical flange 23 functions to fasten the lower rail 2a to the upper rail 2b without the fastening means 5. That is, the vertical flange 23 extends along the upper end of the first extension 22a of the lower rail 2a to reach the fastening part 21b of the upper rail 2b, so that the vertical flange 23 of the lower rail 2a is directly fastened to the spacer 3 together with the fastening part 21b of the upper rail 2b by means of the second bolt 4.

The spacer 3 fastened to the post 1 is used for absorbing an impact force transmitted to the post 1. When a vehicle is in a collision, an impact force imposed on the lower rail 2a is absorbed by a shock absorbing hole 31 of the spacer 3 to some extent, thus reducing a shock applied to the post 1 of the guard rail and the vehicle. The shock absorbing hole 31 is formed in the spacer 3 to which the lower rail 2a is fastened. Further, a reinforcing piece 32 is provided at an upper portion of the spacer 3, thus preventing a shock from being transmitted to the post 1.

The lower and upper rails 2a and 2b may be directly fastened to the post 1 by the bolts 4 without the spacer 3, as necessary.

Fig. 1 shows the guard rail according to the present invention, when it is installed along the road.

When the guard rail is installed along the median of the road to be used as a center divider, the lower and upper rails 2a and 2b are fastened to each side of the posts 1 which are fixed in the ground of the median. In this case, the spacer 3

is fastened at a surface thereof to each post 1 and at another surface thereof to the lower and upper rails 2a and 2b, thus enhancing the shock absorbing capability of the guard rail.

First, the spacer 3 is fastened to the post 1. The upper rail 2b is fastened to the upper portion of each side of the spacer 3 by means of the bolt 4.

Thereafter, the lower rail 2a is fastened to the lower portion of each side of the spacer 3 in the same manner as the upper rail 2b.

When the lower and upper rails 2a and 2b are fastened to the spacer 3 in this way, the first extension 22a of the lower rail 2a overlaps the outer surface of the second extension 22b of the upper rail 2b. Next, the overlapped first and second extensions are fastened to each other by means of the fastening means 5, so the assembly of the guard rail is completed. The assembled guard rail is used as the center divider.

The lower and upper rails 2a and 2b are fastened to each other at positions with regular intervals by means of the fastening means 5, thus allowing the guard rail to be easily assembled.

Industrial Applicability As described above, the present invention provides a differential strength guard rail, which is provided with upper and lower rails having different strengths, thus reducing a unit weight, therefore allowing the entire length of the guard rail to be increased, allowing the guard rail to be easily installed on a road. The guard rail may be designed such that the upper and lower rails are directly fastened to a spacer without a fastening means, thus reducing the number of components used to install the guard rail, therefore reducing the installation cost of the guard rail.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.