Directional sliding pendulum seismic isolation systems with articulated sliding assembly

A bi-directional sliding pendulum seismic isolation system for reducing seismic force acting on a structure by sliding pendulum movements, each system comprising a lower sliding plate forming a sliding path in a first direction, an upper sliding plate forming a sliding path in a second direction, and a sliding assembly for reducing the seismic force of the structure by performing a pendulum motion by sliding along the lower and upper sliding plates.

FIELD OF THE INVENTION

1. Field of the Invention

The present invention relates to directional sliding pendulum seismic isolation systems and articulated sliding assembly therefor, and more particularly, to directional sliding pendulum seismic isolation systems and articulated sliding assemblies therefore, that can reduce seismic load applied to structures, such as bridges or general buildings, through directional pendulum motion and frictional sliding.

2. Description of the Related Art

Recently, multi-span continuous bridges are widely used. In general, such a multi-span continuous bridge is designed to have a single fixed point in the longitudinal direction of the bridge.FIG. 1ashows an example of the conventional multi-span continuous bridge. In the conventional 4-span continuous bridge, a fixed support102is installed on a fixed support pier103, which is located in the middle of the 4-span continuous bridge, to restrict the longitudinal movement of the superstructure101of the bridge. Movable supports107are installed on movable support piers104,105and106to permit free longitudinal movement of the superstructure101of the bridge.FIG. 1bis a schematic view illustrating the deformation of the 4-span continuous bridge ofFIG. 1awhen a seismic load is imparted thereto. Referring toFIG. 1b, the seismic load is applied to the superstructure101of the bridge in the arrow direction “b” by an earthquake ground motion expressed in the arrow direction “Ug”. The superstructure101of the bridge moves in the longitudinal direction of the bridge due to the seismic load. If the frictional force is negligible at the movable supports, the seismic load imparted to the superstructure101of the bridge would be transmitted solely to the fixed support pier102through the fixed support103. The fixed support pier102provided with the fixed support103would withstand the whole seismic load transmitted from the superstructure101of the bridge, and finally be forced to deform as shownFIG. 1b. If an excessive seismic load is applied to the fixed support pier102, the bridge itself as well as the fixed support103of the fixed support pier102will be seriously damaged, consequently resulting in possible failure of the fixed support pier102.

In traditional earthquake resistant design of bridges and general structures, the structural members, components and systems are required to have adequate amount strength and ductility in the event of strong earthquakes. However, the structures designed according to this strength design principle tend to experience severe damage or excessive deformation in the event of very strong earthquake even though they may not collapse. Therefore alternative methods have been developed that can protect structures from earthquakes within predetermined deformation limit. One of the most widely used protection methods is seismic isolation system. Because it has been proved to be very effective in the reduction of seismic load in recent earthquakes, the use of seismic isolation systems is on an increasing trend.

The basic principle of the seismic isolation system will be explained in connection with the earthquake actions. However, the seismic isolation systems according to the present invention are not restricted to the earthquake motion, and can be applied also to various kinds of dynamic loads applied to the structures.

If a structure201is fixed to the ground202as shown inFIG. 2a, it can be modeled as a single degree of freedom system as shown inFIG. 2b. The response of the structure to the earthquake action, such as base shear force and relative displacement can be estimated using response spectra.

FIGS. 2cand2dshow graphs of acceleration response spectra and graphs of displacement response spectra respectively as examples. The drawings show response spectra for two values of damping ratio. In the graph ofFIG. 2c, the vertical axis indicates the spectral acceleration and the horizontal axis indicates the period. In the graph ofFIG. 2d, the vertical axis indicates the spectral displacement and the horizontal axis indicates the period. The base shear force acting between the structure and the ground by the horizontal ground motion can be estimated from the acceleration response spectrum shown inFIG. 2c. That is, if the natural period and the damping ratio (ξ1or ξ2) of the single degree of freedom are given, the spectral acceleration is read from the curves shown inFIG. 2c. If the obtained spectral acceleration value is multiplied by the mass of the structure, the base shear force is approximately found.

The relative displacement between the superstructure and the ground can be estimated from the displacement response spectrum shown inFIG. 2d. If the natural period of the single degree of freedom and the damping ratio are given, the spectral displacement is read from the curves shown inFIG. 2d. The obtained spectral displacement shows the relative displacement of the ground of the single degree of freedom.

As can be seen from the graph shown inFIG. 2c, generally, if the period becomes longer, the spectral acceleration is reduced. Moreover, in the same period, if the damping ratio becomes larger, the value of the spectral acceleration is reduced.

In the case of the spectral displacement, as can be seen from the graph shown inFIG. 2d, if the period becomes longer, the relative displacement is increased. Furthermore, in the same period, if the damping ratio becomes larger, the value of the spectral displacement is reduced.

In conclusion, if the period is longer and the damping ratio is higher, the spectral acceleration is reduced, and thereby the seismic force, i.e., floor shear force, becomes small. The seismic isolation systems adopt the above mechanical principle. For example, the seismic isolation system such as a high damping lead rubber bearing has mechanical properties that the horizontal stiffness is very small but the damping capacity is high.

As shown inFIG. 3a, if a seismic isolation system203is installed between the base frame and a ground202, the natural period of the whole structural system becomes even longer, and also the damping ratio increases. Like this, if the natural period T becomes longer period Teor the damping ratio ε is increased to a ration εe, then the seismic force can be reduced significantly, as can be seen from the graph shown inFIG. 3b.

However, as shown inFIG. 3c, if the natural period becomes longer, the relative displacement increases. To restrict the increase of the relative displacement, dampers can be installed in addition to the conventional seismic isolation system having low damping capacity. One of the seismic isolation systems having high damping capacity and the long natural period, which do not require the additional dampers, is a sliding pendulum seismic isolation system. However, the sliding pendulum seismic isolation system used presently has a structure that a slider moves on a dish having a concave surface, and therefore if the seismic isolating period becomes longer, the diameter of the dish becomes even larger. In the case of bridges, generally, an area to install a seismic isolator on a pier or an abutment is extremely restricted. Therefore, a long span bridge requiring the seismic isolating period of a long-term has a difficulty in using the conventional sliding pendulum seismic isolation system of the dish type.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a sliding pendulum seismic isolation system having a new configuration, which can be easily installed without limitations in an installation area.

It is another object of the present invention to provide a sliding pendulum seismic isolation system, which does not use dampers additionally employed in a conventional seismic isolation system that has low damping capacity.

It is a further object of the present invention to provide a sliding pendulum seismic isolation system, which moves in predetermined directions and yet effectively induces seismic isolation effects in all horizontal directions for the earthquake motion that is applied in arbitrary direction.

It is a still further object of the present invention to provide a sliding assembly, which has newly structured sliders, used in a directional sliding pendulum seismic isolation system. Even though the sliding assembly is located at any position, the surfaces of upper and lower sliders in contact with a friction channel of the sliding pendulum seismic isolation system are kept uniform, and thus the compressive force is always transferred to the friction channel through the center of the sliders.

To achieve the above objects, the present invention provides a directional sliding pendulum seismic isolation system, which reduces earthquake effects on the structures using sliding pendulum motion in selected directions.

The present invention provides bi-directional sliding pendulum seismic isolation systems for reducing seismic force acting on a structure by sliding pendulum movements, each system comprising a lower sliding plate forming a sliding path in a first direction; an upper sliding plate forming a sliding path in a second direction; and a sliding assembly for reducing the seismic force of the structure by performing a pendulum motion by sliding along the lower and upper sliding plates.

In the present invention, the lower and the upper sliding plates have sliding channels for sliding of the sliding assembly respectively, and the sliding assembly includes a main body, lower sliders sliding along the lower sliding channel, and upper sliders sliding along the upper sliding channel.

According to the embodiment of the present invention, the lower and the upper sliding plates have sliding channels for sliding of the sliding assembly, and the sliding assembly includes an upper main body on which an upper slider is mounted on an upper surface thereof, a lower main body on which a lower slider is mounted on a lower surface thereof, and elastic or elasto-plastic objects inserted between the lower and upper main bodies. In one application, the upper main body and lower main body of the sliding assembly can rotate freely around vertical axis.

Further, in another embodiment of the present invention, the lower and the upper sliding plates have at least a pair of sliding channels for sliding of the sliding assembly, wherein the sliding assembly has a ratio of a predetermined width/height not to be overturned when the sliding assembly performs the pendulum motion, and wherein radius of curvature of an arc section of the upper sliding channel has a value smaller than radius of curvature of the first directional pendulum motion to prevent the upper slider from escaping from the upper sliding channel while the sliding assembly performs the pendulum motion in the lower sliding channel, and radius of curvature of an arc section of the lower sliding channel has a value smaller than radius of curvature of the second directional pendulum motion to prevent the lower slider from escaping from the lower sliding channel while the sliding assembly performs the pendulum motion in the upper sliding channel.

In the above embodiment, preferably, the elastic or elasto-plastic objects of the upper and lower separable sliding assembly are spheres having a predetermined elasticity and damping capacity, and the lower and the upper main bodies have hemispherical holes for mounting the spherical elastic or elasto-plastic objects respectively.

Further, in the above embodiment, preferably, the elastic or elasto-plastic objects of the upper and lower separable sliding assembly are spheres having a predetermined elasticity and damping capacity, and the lower and the upper main bodies have a hemispherical central hole for mounting the spherical elastic or elasto-plastic objects and a contour hole around the central hole respectively.

Further, in another embodiment, the lower and the upper main bodies have a hemispherical central hole and a contour hole around the central hole respectively, the spherical elastic or elasto-plastic object having a predetermined elasticity and damping capacity is mounted in the central hole, and annular elastic or elasto-plastic objects having a predetermined elasticity and damping capacity arc mounted in the contour hole.

In another embodiment, the elastic or elasto-plastic object of the upper and lower separable sliding assembly is a disc type having a predetermined elasticity and damping capacity, and the lower and the upper main bodies have a hole for mounting the disc type elastic or elasto-plastic object respectively.

In the present invention, the sliding channels may be formed in multiple, and an escape preventing sill may be provided between the sliding channels to prevent the sliders of the sliding assembly from escaping from the sliding channels.

Further, the present invention provides uni-directional sliding pendulum seismic isolation systems for reducing seismic force of a structure by earthquake motion of one direction, each system comprising a sliding plate having a sliding channel forming a sliding path in one direction; and a sliding assembly for reducing the seismic force of the structure by performing pendulum motion by sliding along the sliding channel.

The present uni-directional sliding pendulum seismic isolation systems may be installed in multi-level to induce seismic isolation effects in all horizontal directions by performing pendulum motion in two directions horizontally.

Further, the present invention provides a sliding assembly used in a bi-directional sliding pendulum seismic isolation system, the sliding assembly comprising: a main body; a lower slider provided at a lower portion of the main body, the lower slider sliding along a lower sliding channel of a lower sliding plate of the bi-directional sliding pendulum seismic isolation system; and an upper slider provided at an upper portion of the main body, the upper slider sliding along an upper sliding channel of an upper sliding plate of the bi-directional sliding pendulum seismic isolation system.

In the embodiment of the sliding assembly, the lower and upper sliders includes a slider support; and a slider core mounted at an end of the slider support to freely rotate with respect to the slider support, the slider core being in frictional contact with the sliding channels in such a manner that the area contacting the sliding channels remains unchanged even though the sliding assembly is located in an arbitrary position in the sliding channels.

Further, in the embodiment of the sliding assembly, the slider core has an upper surface of a shape corresponding to radius of curvature of the sliding channels and a lower surface of a semicircular plate type having a predetermined thickness and radius of curvature, and rotates with respect to the slider support when the lower surface is mounted in the slider support.

In another embodiment of the sliding assembly, the slider core has an upper surface of a shape corresponding to radius of curvature of the sliding channels and a lower surface of a round shape having a predetermined radius of curvature, and rotates with respect to the slider support when the slider core is inserted in the slider support.

In another embodiment of the sliding assembly, the slider includes a slider support having a disc type supporting part of a predetermined thickness and radius of curvature of a convex form at an end; and a slider core having an upper surface of a shape corresponding to the radius of curvature of the sliding channels and a concave part corresponding to the disc type supporting part, the slider core being mounted on the slider support in such a manner that the disc type supporting part is inserted into the concave part. The slider core can rotate freely with respect to the slider support.

In another embodiment of the sliding assembly, the slider includes a slider support having a spherical supporting part of a predetermined radius of curvature, which is in the form of a convex at an end; and a slider core having an upper surface of a shape corresponding to the radius of curvature of the sliding channels and a concave part corresponding to the spherical supporting part, the slider core being mounted on the slider support in such a manner that the spherical supporting part is inserted into the concave part, the slider core freely rotating with respect to the slider support.

Preferably, in the sliding assembly, friction-reducing materials are coated on the surface of the slider core to reduce a friction between the slider core and the sliding channel and a friction between the slider core and the slider support.

The present invention also provides a sliding assembly used in a uni-directional sliding pendulum seismic isolation system, the sliding assembly comprising a main body; and a slider formed at an upper portion of the main body, the slider sliding along the sliding channel of the sliding plate of the uni-directional sliding pendulum seismic isolation system, wherein the slider includes a perpendicular slider support and a slider core mounted at an end of the slider support and being in frictional contact with the sliding channel, and wherein the slider core is mounted to rotate with respect to the slider support and maintains contact area with the sliding channels even though the sliding assembly is located in an arbitrary position in the sliding channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described in detail in connection with preferred embodiments with reference to the accompanying drawings.

FIG. 4shows a schematically perspective view of an embodiment of bi-directional sliding pendulum seismic isolation systems according to the present invention.

As shown inFIG. 4, the bi-directional sliding pendulum seismic isolation system1according to the present invention includes a lower sliding plate10forming a sliding path in the first direction, an upper sliding plate20forming a sliding path in the second direction, and a sliding assembly30sliding in the two directions and performing the pendulum motion between the lower sliding plate10and the upper sliding plate20.

FIGS. 5athrough5cshow the lower sliding plate10in more detail.FIG. 5ais a perspective view of the lower sliding plate10, andFIGS. 5band5care views taken along the lines C—C and D—D inFIG. 5a. As shown inFIG. 5a, the lower sliding plate10has lower sliding channels11for allowing the sliding assembly30to slide. As shown inFIG. 5b, the lower sliding channel11is in the form of a concave arc section of a predetermined radius of curvature (rT) and is in the form of an arc of a predetermined radius of curvature (RT) in a longitudinal direction, i.e., the first direction. The radius of curvature (rT) of the arc section has a value even smaller than the radius of curvature (RT) of the pendulum motion. InFIG. 4, the reference numeral12indicates coupling means12, such as a bolt, for fixing the lower sliding plate10to the structure.

In the embodiment, the lower sliding channel11is formed as a pair of parallel channels, but may be two or more channels without being restricted in the number of the channels. However, at least a pair of parallel channels should be formed to prevent the sliding assembly30from being overturned to a horizontal motion of an arbitrary direction.

In the bi-directional sliding pendulum seismic isolation system1of the present invention, in the same way as the lower sliding plate10, the upper sliding plate20is also in the form of a concave arc section of a predetermined radius of curvature (rL) and is in the form of an arc of a predetermined radius of curvature (RL) in a longitudinal direction (the second direction). The upper sliding plate20has a pair of parallel upper sliding channels21, on which the sliding assembly30slides. In the same way as the lower sliding plate10, the upper sliding plate20may also have two or more sliding channels, and must have at least a pair of parallel channels to prevent the sliding assembly30from being overturned.

The sliding assembly30, which slides along the sliding channels11and21, is mounted between the lower sliding plate10and the upper sliding plate20.FIGS. 6aand6bshow schematically perspective and sectional views of an embodiment of the sliding assembly30. The sliding assembly30includes a plate type main body31, a lower slider32provided at a lower portion of the main body31and sliding along the sliding channel11of the lower sliding plate10, and an upper slider33provided at an upper portion of the main body31and sliding along the sliding channel21of the upper sliding plate20.

The plate type main body31is not restricted to a disc form, but may be in various forms, such as a polygon including a rectangle, an oval, or the likes, as shown inFIG. 6c. Furthermore, the lower slider32and the upper slider33may be formed in a plural number corresponding to the number of the lower and upper sliding channels11and21. Modifications of another sliding assembly30will be described later.

A coupled relationship between the upper and lower sliding plates10and20and the sliding assembly30will be described hereinafter.

FIG. 7ais a sectional view taken along the line A—A ofFIG. 4andFIG. 7bis a sectional view taken along the line B—B ofFIG. 4. The lower slider32of the sliding assembly30is positioned at into the lower sliding channel11of the lower sliding plate10and the upper slider33is positioned at the upper sliding channel21of the upper sliding plate20, thereby being mounted perpendicularly. If a distance (B) from the center of the sliding assembly30to the center of the slider32or33and a ratio (B/H) of a height (H) of the sliding assembly30defined inFIG. 6bare larger than the friction coefficient between the slider and the sliding channel, a stability to the overturning can be maintained when the sliding assembly30slides along the sliding channel and performs the pendulum motion. The radius of curvature (rL) of the arc section of the upper sliding channel21formed on the upper sliding plate20has a value even smaller than that of the radius of curvature (RT) of the first directional pendulum motion, the upper slider33does not escape from the upper sliding channel21while the sliding assembly30performs the pendulum motion in the lower sliding channel11formed in the lower sliding plate10. If the radius of curvature (rT) of the arc section of the lower sliding channel11formed on the lower sliding plate10has a value much smaller than that of the radius of curvature (RL) of the second directional pendulum motion, the lower slider32does not escape from the lower sliding channel11while the sliding assembly30performs the pendulum motion in the upper sliding channel21formed in the upper sliding plate20.

Referring toFIGS. 8athrough8dshowing an example that the bi-directional sliding pendulum seismic isolation system1of the present invention is installed on a bridge, the operation of the present invention will be described. The upper sliding plate20is fixed on the deck101of the bridge in such a manner that the upper sliding channel21is in a longitudinal direction of bridge, i.e., the second direction becomes the longitudinal direction. The lower sliding plate10is fixed on a pier110and an abutment120of the bridge in such a manner that the lower sliding channel11is at right angles to the longitudinal direction of bridge, namely, the first direction is at right angles to the longitudinal direction of bridge. An example that the earthquake motion is applied will be described hereinafter.

In the seismic isolation system of the present invention, because the radius of curvature (RL) of the arc of the longitudinal direction of the upper sliding channel21is larger than the radius curvature (rT) of the arc section of the lower sliding channel11, if the horizontal force applied to the upper sliding plate20exceeds the friction force between the surface of the upper sliding channel21and the contact surface of the upper slider33, the upper slider33starts to slide along the upper sliding channel21.

Therefore, if the earthquake motion is applied in the bridge shown inFIG. 8cand the seismic force, which exceeds the friction force between the surface of the upper sliding channel21and the contact surface of the upper slider33, is applied to the superstructure101of the bridge in the longitudinal direction of bridge, the sliding assembly30moves along the upper sliding channel21(seeFIG. 8b). Thus, the superstructure101of the bridge moves in the longitudinal direction of bridge (seeFIG. 8c). That is, the upper sliding channel21on the sliding assembly30moves in the longitudinal direction of bridge, and then, the bridge deck moves as shown inFIG. 8c. In this process, the sliding assembly30maintains the stability to the overturning as described above.

Because the superstructure101of the bridge moves in a horizontal direction relative to the pier even though the earthquake motion is applied to the superstructure101of the bridge, very small amount of earthquake force will be transmitted to the pier in comparison with a case that a fixed bearing is used. Therefore, if the seismic isolation system a according to the present invention is installed on the structure, the influence of the earthquake motion directly applied to the structure is very small when the earthquake motion is applied.

FIG. 8dis an upside down view ofFIG. 8b. The sliding of the sliding assembly30duet to a lateral movement of the upper sliding plate20caused by an external load, such as earthquake, may be modeled as the pendulum motion of the sliding assembly30taken along the upper sliding channel21, as shown inFIG. 8d.

If the upper slider33moves from the neutral position to a predetermined angle (θ) by sliding along the upper sliding channel21, the restoring force (PT) for restoring to the neutral position by a pendulum effect is applied. The pendulum motion of the sliding assembly30is stopped by an energy loss due to the friction between the upper slider33and the upper sliding channel21, and thereby also the movement of the structure by the seismic force is stopped.

If the friction coefficient between the upper slider33and the upper sliding channel21is zero, the upper slider33performs a free pendulum motion along the upper sliding channel21inFIG. 8b. The period (T) of the pendulum motion can be calculated approximately by the following equation (1).T=2⁢⁢π⁢R⁢⁢cos⁢⁢θg(1)

In the equation (1), if the angle (θ) moved from the neutral position is a value close to zero, the period (T) is increased in proportion to the square root of the radius of curvature (RL) of the upper sliding channel21. In the equation (1), “g” means an acceleration of gravity.

Like the above embodiment, the seismic isolation system of the present invention is not restricted by the installation space because the upper sliding plate20is mounted on the superstructure101of the bridge and the lower sliding plate10is mounted on the pier. Therefore, the radius of curvature (RTand RL) of the sliding channel11and21formed on the sliding plate10and20can be increased.

It is an advantage that the radius of curvature (RTand RL) of the sliding channels11and21can be increased. In detail, in the above embodiment, if the radius of curvature (RL) of the upper sliding channel21is increased, the natural period of the whole structural system can be increased, as can be seen from the mathematical formula 1. If the natural period is increased from T to Te, the seismic force is reduced (seeFIG. 3b). At the same time, because high energy dissipation effects (damping effects) may be obtained by adjusting the friction coefficient properly, also the displacement may be restricted. The seismic isolation system according to the present invention can reduce the seismic force, significantly compared with the conventional seismic isolation systems.

The seismic force due to the earthquake may be applied in a direction perpendicular to a longitudinal axis of bridge. If the seismic force in the direction perpendicular to the longitudinal axis of bridge is applied to the superstructure101of the bridge, the lower slider32of the sliding assembly30performs the free pendulum motion along the lower sliding channel11similar to the above, thereby reducing the seismic force in the direction perpendicular to the longitudinal axis of bridge. The seismic isolation system of the present invention has independent seismic force reducing effects to the two directions simultaneously.

In the above embodiment, the seismic isolation system is installed to have seismic force reducing effects in the longitudinal direction of bridge and the direction perpendicular to the longitudinal axis, but the installation directions of the lower sliding plate10and the upper sliding plate20may be selected freely.

Especially, the seismic force applied in an arbitrary direction may be decomposed into the longitudinal direction of bridge and the direction perpendicular to the longitudinal axis. Seismic force in each direction can be reduced by the above principle. In the bi-directional sliding pendulum seismic isolation system of the present invention, even though the lower sliding channel11is installed in the first direction and the upper sliding channel21is installed in the second direction, the upper sliding plate20and the lower sliding plate10can perform the relative motion in any directions to each other by the combination of the first direction and the second direction. Thus, effective seismic isolation actions in all horizontal directions are obtained.

Hereinafter, a modification of the sliding plate mounted on the seismic isolation system of the present invention will be described.

FIG. 9ais a perspective view of the lower sliding plate10having an escape prevention sill14for preventing the lower slider31of the sliding assembly30from escaping the lower sliding channel11when the sliding assembly30slides along the lower sliding channel11. The escape prevention sill14may be formed between two lower sliding channels11and/or at both sides of each sliding channel11.

The upper sliding plate20also has the escape prevention sill, like the lower sliding plate10.FIG. 9bschematically shows a coupled state of the lower sliding plate10and the upper sliding plate20having the escape prevention sills.

Referring toFIGS. 10athrough17b, various modifications of the sliding assembly30used in the seismic isolation system of the present invention will be described.

The sliding assembly30of the present seismic isolation system can be a type separable into upper and lower parts. The upper and lower parts may be manufactured separately and combined. The separable sliding assembly30includes an upper plate type main body35having the upper sliders33, a lower plate type main body34having the lower sliders32, and elastic or elasto-plastic objects36inserted between the upper and lower main bodies34and35.

FIGS. 10athrough10eshow examples of the separable sliding assembly30. In this embodiment, the elastic or elasto-plastic objects36are spheres having a predetermined elasticity and damping capacity. The lower and upper main bodies34and35have holes37formed in the form of a hemisphere respectively to house the spherical elastic or elasto-plastic objects36.FIG. 10dis a sectional view of the seismic isolation system that employs the separable sliding assembly30with the elastic or elasto-plastic objects36. The lower and upper main bodies34and35are not restricted to the disc shape, and may be made in various shapes, such as a polygon including a rectangle, an oval, or the likes (seeFIG. 10e).

If the separable sliding assembly30having the elastic or elasto-plastic objects36is used, because the elasticity and the damping capacity are given to the spheres, vertical seismic isolation effects can be induced and unexpected stress, which may be generated due to error in construction, can be absorbed. The spheres used as the elastic or elasto-plastic objects36may be solid spheres filled with appropriate materials (seeFIG. 11a), hollow spheres (seeFIG. 11b), dual shell type spheres filled with two kinds of contents (seeFIG. 11c), or triple shell type spheres filled with three kinds of materials (seeFIG. 11d). In the case of the shell type spheres, if the outermost shell is made of an elastic material and the inner shell is made of viscoelastic material, a three-dimensional seismic isolation system, which shows the vertical seismic isolation effects and damping effect, can be constructed.

FIGS. 12aand12bshow another example of the separable sliding assembly30. To show a contour hole38described later,FIG. 12ashows a partial cut lower main body34. In this embodiment, the lower and upper main bodies34and35have a circular contour hole38formed in the inner surface and a spherical hole39formed at the center, and the elastic or elasto-plastic objects36are inserted in the contour hole38and the circular spherical hole39. In the bi-directional seismic isolation system of the present invention, because the bi-directional motion is performed independently, unexpected torsional stress may be applied to the sliding assembly30. However, in the sliding assembly30shown inFIGS. 12aand12b, because the lower main body34and the upper main body35can rotate freely with respect to the vertical axis, development of the torsion stress can be prevented.

In the above modification, an annulus40is mounted in the contour hole38and a sphere41is mounted in the spherical hole39of the center thereof (seeFIGS. 13aand13b). In this case, the annulus40is a solid annulus filled with contents (seeFIG. 14a), a hollow annulus (seeFIG. 14b) or a multiple shell type annulus (seeFIG. 14c).

In another modification, as shown inFIGS. 15aand15b, it is possible that the lower and upper main bodies34and35have a hole42, and the elastic damper including a disc43is mounted in the hole42. The disc43is a solid disc filled with contents (seeFIG. 16a), a hollow disc (seeFIG. 16b), a multiple shell type disc (seeFIG. 16c), or a multi-floor disc made of elastic material of a plurality of floors (seeFIG. 16d). It is preferable that the disc type elastic or elasto-plastic objects are made to have a curved surface at upper and lower surfaces.

Also, in the embodiment shown inFIGS. 13athrough15b, the lower main body34and the upper main body35can relatively and freely rotate around a vertical axis.

In the sliding assembly30of the seismic isolation system according to the present invention, the lower and upper sliders32and33in contact with the lower and upper sliding channels11and21may be also modified in various ways.

FIGS. 17athrough17dshow various embodiments of the lower and upper sliders32and33used in the bi-directional seismic isolation system of the present invention. The surfaces of the lower and upper sliders32and33may be treated through a mechanical process (seeFIG. 17a) or coated with frictional material44having excellent high abrasion resistance, heat resistance and the predetermined frictional properties (seeFIG. 17b). The frictional material44may be selectively used from known various frictional materials according to a structural design.

Furthermore, the lower and upper sliders32and33can be constructed as a combination of the slider support45and slider cores46having excellent frictional materials (seeFIGS. 17cand17d). In this case, it is very economical since only the slider46is replaced without replacing the whole sliding assembly if the frictional properties of the slider are deteriorated. The slider support45may be manufactured in various shapes, such as a prism, a cylinder and an elliptical cylinder, and there are no limitations.

In the present invention, the bi-directional sliding pendulum seismic isolation system is described, but the sliding pendulum seismic isolation system can be modified into a uni-directional sliding pendulum seismic isolation system.

FIGS. 18athrough18cshow the uni-directional sliding pendulum seismic isolation system having one sliding channel and one slider.FIGS. 19athrough19cshow the uni-directional sliding pendulum seismic isolation system having two sliding channels and two sliders.

The uni-directional sliding pendulum seismic isolation system according to the present invention includes a sliding plate100having a sliding channel111forming a uni-directional sliding path, and a sliding assembly300performing a pendulum motion by sliding along the sliding channel11.

The sliding plate100of the uni-directional sliding pendulum seismic isolation system has the same structure as the lower or upper sliding plate10or20of the bi-directional sliding pendulum seismic isolation system described above, and therefore, the detailed description will be omitted.

The sliding assembly300includes a plate type main body310and a slider320sliding along the sliding channel111of the sliding plate100. The surface of the slider320of the uni-directional sliding pendulum seismic isolation system is also treated by the mechanical process or coated with appropriate material, like the bi-directional sliding pendulum seismic isolation system. Moreover, a separate slider46separated from the main body may be used.

The operation of the uni-directional sliding pendulum seismic isolation system is the same as the bi-directional sliding pendulum seismic isolation system, besides that the sliding pendulum motion is performed in one direction, and therefore, the description of the operation will be omitted.

The uni-directional sliding pendulum seismic isolation system can be used to structures requiring uni-directional seismic isolation.FIG. 20ashows an example that the sliding plate100is installed on the structure and the sliding assembly300is installed as a base, andFIG. 20bshows another example that the sliding plate100is installed as the base and the sliding assembly300is installed on the structure.

The uni-directional sliding pendulum seismic isolation system may be used even when multi-axial seismic isolation is required. The uni-directional sliding pendulum seismic isolation system is installed in multi-level, wherein the sliding assembly is installed at a lower level to slide in the first direction and the sliding assembly is installed at an upper level to slide in the second direction (seeFIGS. 21aand21b). If the uni-directional sliding pendulum seismic isolation system is installed in multi-level, seismic isolation effects in all horizontal directions are shown as the sliding assemblies slides in the first and second directions.

InFIG. 21a, the sliding plates100are installed to have the channels facing down while the channels may be facing up in another installation method as shown inFIG. 21b.

An embodiment of an articulated sliding assembly used in the directional sliding pendulum seismic isolation system of the present invention will be described.

FIG. 22ais a perspective view of an embodiment of the sliding assembly30used in the bi-directional sliding pendulum seismic isolation system.FIG. 22bis a sectional view of a shape that the sliding assembly30ofFIG. 22ais mounted on the bi-directional sliding pendulum seismic isolation system.

The sliding assembly30includes the plate type main body31, the lower slider32formed at the lower portion of the main body31and sliding along the sliding channel11of the lower sliding plate10mounted on the sliding pendulum seismic isolation system, and the upper slider33formed at the upper portion of the main body31and sliding along the sliding channel21of the upper sliding plate20mounted on the sliding pendulum seismic isolation system.

In this embodiment, the respective lower and upper sliders32and33include a rectangular slider support45, and a semi-disc type slider core46inserted and mounted into the end of the slider support45. The semi-disc type slider cores46are directly in contact with the sliding plates10and20.

FIG. 22cis an exploded perspective view of an embodiment of the slider according to the present invention. In this embodiment, the slider core46mounted on the slider support45is in the form of a semi-disc of a predetermined thickness. The shape of the upper surface47in direct contact with the sliding channel of the sliding pendulum seismic isolation system is made to correspond to the radius of curvature of the sliding channel of the sliding pendulum seismic isolation system. The lower surface48of the slider core46inserted into the end of the slider support45is made in the form of a semi-cylinder of a predetermined diameter to rotate freely with respect to the slider support.

FIG. 22bis a sectional view of a state that the sliding assembly of this embodiment is mounted on the bi-directional sliding pendulum seismic isolation system.FIG. 22dis an enlarged detailed sectional view of an “A” portion ofFIG. 22b.FIG. 22eis an enlarged detailed sectional view of the slider part when the sliding assembly is located at one end of the sliding channel.

InFIG. 22d, RTSmeans the radius of curvature in the longitudinal direction (the x-axis direction inFIG. 22c) of the surface47of the slider core in contact with the channel11of lower sliding plate10. The radius of curvature (RTS) of the surface47of the slider core, which is a portion of the slider in direct contact with the sliding channel11, is the same as or smaller than the radius of curvature (RT) of a longitudinal direction of the sliding channel11of the lower sliding plate10. The radius of curvature of the surface47of the slider core, which is a portion of the slider in direct contact with the sliding channel21of the upper sliding plate, is denoted as RLS. It is the same as or smaller than the radius of curvature (RL) of a longitudinal direction of the sliding channel21of the upper sliding plate20. InFIG. 22d, ΦTSmeans the inner angle of the arc of the upper surface47of the slider core in contact with the channel11. The inner angle of the arc of the upper surface47of the slider core in contact with the channel21in the upper sliding channel20will be denoted as ΦLS. DMSmeans the depth that the slider core46is buried in the slider support45and EMSmeans a value that the depth (DMS) is subtracted from a height of the whole slider core46. RMSmeans the radius of curvature of the surface48(seeFIG. 22c) of the slider core47.

InFIG. 22c, the surface48of the slider core is inserted into the end of the slider support45of the sliding assembly and in the form of a semi-cylinder in such a manner that the slider core46freely rotate around an axis at right angles to the sliding channel inside the slider support45, i.e., around y-axis ofFIG. 22c. The slider core46has a predetermined radius of curvature in an axial direction perpendicular to the sliding channel, i.e., in the thickness direction (in a y-axis direction inFIG. 22c).

As shown inFIG. 22b, the surface47of the slider core in contact with the channel of upper sliding plate has the radius of curvature of rLSin the thickness direction, wherein the radius of curvature (rLS) of the thickness direction of the surface has a value that is the same as or smaller than the radius of curvature (rL) of the thickness direction of the sliding channel21. The surface48of the slider core may be formed without the radius of curvature in the thickness direction. InFIG. 22b, BLSmeans a thickness of the slider core46.

Detailed dimensions of the slider core46that is in contact with the channels21in the upper sliding plate20, i.e., the radius of curvature (RLS, rLS) of the surface47, the radius of curvature (RMS) of the surface48, the arc angle (ΦTS) of the upper surface, the thickness (BLS) and the buried depth (DMS), are determined according to dimensions of the sliding channel of the sliding pendulum seismic isolation system. Detailed dimensions of the slider core46that is in contact with the channels11of the lower sliding plate10can be determined in the same way. To reduce friction between the slider core46and the sliding channel11and friction between the slider core46and the slider support45, preferably, each friction surface is coated with coating material of a small friction coefficient, which can be obtained in the market, for example, “TEFLON®.”

In this embodiment, because the surface48of the slider core46freely rotates inside the slider support45, when the sliding assembly30slides in the sliding channels11and21, the surface of the slider core46of the sliding assembly being in contact with the sliding channels11and21can remain unchanged. That is, as shown inFIG. 7e, because the slider core46rotates even though the sliding assembly30moves from the sliding channels11and21to both ends of the sliding channel, a contact area between the slider core46and the sliding channel is kept uniform, and thus compressive force (P) is always transferred through the center of the slider. Therefore, the movement of the sliding assembly30is performed in a more stable state.

Referring toFIGS. 23athrough23d, another embodiment of the sliding assembly of the present invention will be described.

FIG. 23ais a perspective view of a hemispherical slider core50having a hemispheric lower part.FIG. 23bis a perspective view of a shape that the hemispherical slider core50is mounted on the slider support45.FIG. 23cis a sectional view of a state that the sliding assembly is mounted on the bi-directional sliding pendulum seismic isolation system, andFIG. 23dis an enlarged view of an “A” portion ofFIG. 23c.

In the hemispherical slider core50of this embodiment, the surface51in direct contact with the sliding channel11of the lower sliding plate10has the radius of curvature (RTS) in the x-axis direction, which is the same as or smaller than the radius of curvature (RT) of the longitudinal direction of the sliding channel11of the lower sliding plate10. The surface51in direct contact with the sliding channel21of the upper sliding plate10has the radius of curvature (RLS) in the x-axis direction, which is the same as or smaller than the radius of curvature (RL) of the longitudinal direction of the sliding channel21of the upper sliding plate20and the radius of curvature (rLS) in the y-axis direction, which is the same as or smaller than the radius of curvature (rL) of perpendicular direction of the sliding channel. In the slider core50of this embodiment, a surface52inserted into the slider support45is in the form of a sphere of a predetermined radius (RMS) (seeFIG. 23d).

As shown inFIG. 23b, the hemispherical slider core50is mounted on the slider support45. Because the lower surface of the slider core is in the form of a hemisphere, the slider core50can rotate freely in all horizontal directions with respect to the slider support45.

InFIG. 23d, ΦTSmeans an inner angle of arc of the surface51of the slider core that is in contact with the channel11of the lower sliding plate10. The inner angle of arc of the surface51of the slider core that is in contact with the channel21of the upper sliding plate20will be denoted as ΦLS. DMSmeans the depth that the slider core50is buried in the slider support45and EMS means a value that the depth (DMS) is subtracted from a height of the whole slider core50. BLSmeans a thickness of the upper surface of the slider core50of the perpendicular direction of the sliding channel21of the upper sliding plate20.

Because the slider core50having the hemispheric lower surface can rotate in all directions with respect to the slider support45, a contact area between the slider core50and the sliding channel is maintained uniform regardless the sliding assembly is located at any position of the sliding channel, and thereby the compressive force (P) is always transferred through the center of the slider. Therefore, the movement of the sliding assembly is performed in the more stable state.

Referring toFIGS. 24athrough24d, an embodiment of the sliding assembly including a slider support having a disc type supporting part of a convex shape and a slider core of a concave shape corresponding to the convex supporting part.

FIG. 24ais a perspective view of a shape of the disc type supporting part56formed at an end of the slider support45.FIG. 24bis a perspective view of a shape of the concave slider core53put on the disc type supporting part56and directly in contact with the sliding channel.FIG. 24cis a sectional view showing a state that the sliding assembly is mounted on the bi-directional sliding pendulum seismic isolation system.FIG. 24dis an enlarged view of an “A” portion ofFIG. 24c.

In this embodiment, the slider support45has the disc type supporting part56of a predetermined radius of curvature (RFS) at an end thereof. As shown inFIG. 24b, the concave slider core53has a concave part54of a shape formed at a lower portion to correspond to the disc type supporting part56. The disc type supporting part56is mounted on the slider support45to be inserted into the concave part54.

The surface55of the concave slider core53directly in contact with the sliding channel11of the lower sliding plate10has a radius of curvature (RTS) in the x-axis direction, which is the same as or smaller than the radius of curvature (RT) of the longitudinal direction of the sliding channel11of the lower sliding plate10. The surface55of the concave slider core53directly in contact with the sliding channel21of the upper sliding plate20has a radius of curvature (RLS) in the x-axis direction, which is the same as or smaller than the radius of curvature (RL) of the longitudinal direction of the sliding channel21of the upper sliding plate20and has a radius of curvature (rLS) in the y-axis direction, which is the same as or smaller than the radius of curvature (rL) of the perpendicular direction of the sliding channel21of the upper sliding plate20.

InFIG. 24d, ΦTSmeans the inner angle of arc of the upper surface55of the slider core in contact with the channel11of the lower sliding plate10. The inner angle of arc of the upper surface55of the slider core in contact with the channel21of the upper sliding plate20is denoted as ΦLS. DFSmeans the depth that the disc type supporting part56of the slider support45is buried in the concave part54of the slider core53, and EFSmeans a value that the depth (DFS) is subtracted from a height of the slider core53. InFIG. 24c, BLSmeans a thickness of the slider core53of the perpendicular direction of the sliding channel21of the upper sliding plate20and BFSmeans a thickness of the disc type supporting part56of the perpendicular direction of the sliding channel. ΨFSmeans an angle of a neck portion of the disc type supporting part56.

Also, in this embodiment, because the concave slider core53and the slider support45rotate freely with respect to each other, when the sliding assembly30slides on the sliding channels11and21, the surface of the slider core53of the sliding assembly in contact with the sliding channels11and21can be maintained uniform, and thus the compressive force (P) is transferred through the center of the slider. Therefore, the movement of the sliding assembly30is performed in the more stable state.

Referring toFIGS. 25athrough25d, an embodiment including a spherical slider support having a spherical supporting part and a concave slider core corresponding to the spherical supporting part.

FIG. 25ais a perspective view of a shape of the spherical support61formed at an end of the slider support45.FIG. 25bis a perspective view of a shape of the concave slider core62covered on the spherical supporting part61and directly in contact with the sliding channel.FIG. 25cis a sectional view showing a state that the sliding assembly is mounted on the bi-directional sliding pendulum seismic isolation system.FIG. 25dis an enlarged view of an “A” portion ofFIG. 25c.

In this embodiment, the slider support45has the spherical supporting part61of a predetermined radius of curvature (RFS) at an end thereof. As shown inFIG. 25b, the concave slider core62has a concave part63at a lower portion to correspond to the spherical supporting part61. The spherical supporting part61is mounted on the slider support45to be inserted into the concave part63.

The surface64of the concave slider core62directly in contact with the sliding channel11of the lower sliding plate10has a radius of curvature (RTS) in the x-axis direction, which is the same as or smaller than the radius of curvature (RT) of the longitudinal direction of the sliding channel11of the lower sliding plate10. The surface64of the concave slider core62directly in contact with the sliding channel21of the upper sliding plate20has a radius of curvature (RLS) in the x-axis direction, which is the same as or smaller than the radius of curvature (RL) of the longitudinal direction of the sliding channel21of the lower sliding plate20and has a radius of curvature (rLS) in the y-axis direction, which is the same as or smaller than the radius of curvature (rL) of the perpendicular direction of the sliding channel.

InFIG. 25d, ΦTSmeans an inner angle of arc of the surface64of the slider core in contact with the sliding channel11of the lower sliding plate10. The inner angle of arc of the surface64of the slider core in contact with the sliding channel21of the upper sliding plate20is denoted as ΦLS. DFSmeans a depth that the spherical supporting part61of the slider support45is buried in the concave part63of the slider core62, and EFSmeans a value that the depth (DFS) is subtracted from a height of the slider core62. InFIG. 25c, BLSmeans a thickness of the slider core62of the perpendicular direction of the sliding channel21of the upper sliding plate20, and BFSmeans a thickness of the slider core62in the perpendicular direction of the sliding channel21of the upper sliding plate20. ΨFSmeans an angle of a neck portion of the spherical supporting part61.

In case of the slider support45having the spherical supporting part61, because the slider support45has the spherical end, the concave slider core62can rotate freely in all horizontal directions with respect to the spherical supporting part61. Thus, even though the sliding assembly is located at any position, the contact area between the slider core62and the sliding channel is maintained uniform, and thereby the compressive force is always transferred to the center of the slider. Therefore, the movement of the sliding assembly is performed in the more stable state.

As described above, because the upper sliding plate of the bi-directional sliding pendulum seismic isolation system of the present invention is attached the girder or a slab of the bridge deck in the longitudinal direction of bridge and the lower sliding plate is mounted on the pier or the abutment in the direction perpendicular to the longitudinal axis of bridge or in an inclined direction, the seismic isolation system is not restricted in the installation space.

Moreover, because the seismic isolation period is freely selected in the longitudinal direction of bridge and in the direction perpendicular to the longitudinal axis of bridge or in the direction inclined with respect to the longitudinal axis of bridge, the isolation system most suitable for dynamic characteristics of the bridge can be designed. Furthermore, also after the earthquake, the orientation of the bridge can be always maintained in an initial state.

Especially, in the bi-directional sliding pendulum seismic isolation system of the present invention, because the lower sliding channel is installed into the first direction and the upper sliding channel is installed into the second direction, the upper sliding plate and the lower sliding plate can perform a relative motion in any directions to each other by the combination of the first direction and the second direction, and thus an effective seismic isolation action is obtained with respect to all horizontal directions.

The bi-directional sliding pendulum seismic isolation system of the present invention can have the seismic isolation effects not only of the horizontal direction but also of the perpendicular direction.

Moreover, if the uni-directional sliding pendulum seismic isolation system is used, only the seismic isolation effects of the uni-directional direction is obtained, but, if the uni-directional sliding pendulum seismic isolation system is installed in the multi-level, the seismic isolation effects of all horizontal directions are obtained, like the bi-directional sliding pendulum seismic isolation system.

Furthermore, in the sliding assembly of the present invention, because the slider core directly in contact with the sliding channel of the sliding pendulum seismic isolation system can rotate with respect to the slider support, the surface of the slider core being in contact with the sliding channel is maintained uniform even though the sliding assembly is located at any positions. The compressive force transferred through the upper sliding plate is always transferred through the center of the slider.

Thus, in the directional sliding pendulum seismic isolation system, the sliding assembly can move in the more stable state.