JP5116707B2 - I-girder bridge repair method - Google Patents

Description

This invention relates to a method for repairing I-girder bridges, which involves replacing the supports installed in the cross beams of the steel piers of the I-girder bridge that support the load of each main girder, and reinforcing the area around the supports.

One type of steel bridge is the multi-girder I-girder bridge. One example of this type of multi-girder I-girder bridge is the three-girder I-girder bridge shown in Figures 16(a), (b), and (c) and 17, which is used as an elevated bridge in urban areas such as the Metropolitan Expressway.

This bridge is equipped with a gate-shaped steel pier 1 consisting of a pair of pillars 2 erected on both sides in the width direction of the bridge, and a cross beam 3 extending in the width direction of the bridge with both ends integrally attached to each of the pillars 2.

Furthermore, three main girders 4, 5, 6 consisting of I-girders are arranged at the required intervals in the width direction of the bridge, and of the main girders 4, 5, 6, the girder ends of the main girders 4, 6 at both ends in the width direction of the bridge (hereinafter referred to as outer main girders) are full web, and a notch 7 is provided on the lower side of the girder end of the main girder 5 in the center of the width direction of the bridge (hereinafter referred to as middle main girder). In addition, both sides of the girder edge part of the central girder 5 at a required distance from the girder end above the notch 7, and the upper inner side of the girder edge part of the outer main girders 4, 6 at a required distance from the girder ends located on both sides of the notch 7, are connected together via separate cross beams (hereinafter referred to as end cross beams) 8a, 8b that extend in the bridge width direction parallel to the cross beam 3, and the girder end of the central girder 5 where the notch 7 is provided and the positions near the outer ends in the bridge width direction of each of the end cross beams 8a, 8b are supported by the upper side of girder support brackets 9a, 9b, 9c protruding from the lower part of each bridge axis direction surface of the cross beam 3 of the steel pier 1 via supports (shoes) 10.

In an I-girder bridge having such a configuration, the cross beam 3 of the steel pier 1 can support the main girders 4, 5, 6 within the vertical dimension of the cross beam 3, so that the height positions of the upper and lower ends of the cross beam 3 and the upper and lower ends of the main girders 4, 5, 6 can be aligned, making it an advantageous configuration when girder height restrictions are imposed by building limits, etc. Note that for convenience of illustration, in Figures 16(a), (b), (c) and 17, the illustration of the deck slabs provided above the cross beam 3 and main girders 4, 5, 6 of the steel pier 1 has been omitted. (The same applies to the subsequent figures.)
In recent years, it has been pointed out that with I-girder bridges having the configurations shown in Figures 16(a), 16(b), 16(c) and 17, deterioration in the function of each support 10 and damage to the areas around the supports have occurred due to aging.

For this reason, so-called full-web construction of main girders has been conventionally carried out as a repair method that can restore functionality by replacing each of the above-mentioned supports 10 and reinforce the area around the supports (see, for example, Non-Patent Document 1).

The above-mentioned main girder full web construction work is carried out, for example, in the order shown in Figure 18 (a) (b) to Figure 20 (a) (b) (c). That is, first, as shown in Figure 18 (a) (b), a wide additional cross beam 11 is placed on the underside of the cross beam 3 of the steel pier 1 of an I-girder bridge having the same configuration as shown in Figures 16 (a) (b) (c) and 17, extending in the bridge axis direction to a position below the girder ends of each of the main girders 4, 5, and 6, and its upper end is attached integrally to the lower end of the cross beam 3, and both ends of the additional cross beam 11 in the bridge width direction are fixed integrally to both piers 2, respectively. At this time, jack-up pedestals 12a, 12b, and 12c are provided in advance at positions directly below the main girders 4, 5, and 6 on the bridge axis direction surface of the additional cross beam 11, protruding by the required distance along the corresponding main girders 4, 5, and 6. The jack-up pedestal 12b below the middle main girder 5 is protruded to a position below the full web part on the center side of the span from the cutout part 7 of the middle main girder 5, as shown in Figure 18 (B).

Next, as shown in Figures 19 (a), (b), and (c), the jacks 13 installed on the jack-up pedestals 12a, 12b, and 12c of the additional cross beam 11 are jacked up, and the lower flanges of the main girders 4, 5, and 6 are supported on the upper side of each jack 13, so that the load acting on each of the main girders 4, 5, and 6 is transmitted to and supported by the additional cross beam 11 via the jacks 13 and the jack-up pedestals 12a, 12b, and 12c.

Next, as described above, when the load acting on each of the main girders 4, 5, 6 is supported by the additional cross beam 11 via the jacks 13 and the jack-up pedestals 12a, 12b, 12c, the load from each of the main girders 4, 5, 6 is no longer applied to the girder support brackets 9a, 9b, 9c and the supports 10 above them that were installed on each of the bridge axis direction faces of the cross beam 3 of the steel pier 1, so in this state, the existing girder support brackets 9a, 9b, 9c and the existing supports 10 are removed from the cross beam 3.

After that, the lower flange provided around the cutout portion 7 of the middle main girder 5 is cut off, and then, as shown in FIG. 20(b), in the space where the girder support bracket 9b and the support 10 that supported the girder end of the middle main girder 5 have been removed, a full web reinforcement member 14 of a required shape that can fit into the cutout portion of the web is bolted to the remaining web of the middle main girder 5 to make the girder end of the middle main girder 5 into a full web. Furthermore, at the position above the additional cross beam 11 at the girder end of the fully webified middle main girder 5 and above the new support 16 described later, support stiffeners 15 are attached in a rib shape to both sides of the web and the lower flange to reinforce it. Similarly, as shown in FIG. 20(c), support stiffeners 15 are also attached in a rib shape to both sides of the web and the lower flange to reinforce it at the position above the additional cross beam 11 at the girder end of each of the outer main girders 4 and 6 and above the new support 16 described later.

After the girder end of the middle main girder 5 has been fully webbed in the manner described above, new supports 16 are installed below the girder ends of the main girders 4, 5, and 6 on the added cross beam 11, as shown in Figures 20 (a), (b), and (c), and then the jacks 13 are jacked down so that the girder ends of the main girders 4, 5, and 6 are supported by the added cross beam 11 via the new supports 16, completing the work of replacing the supports and reinforcing the area around the supports.

Then, the jacks 13 and the jack-up pedestals 12a, 12b, 12c are removed. Furthermore, if necessary, after the central girder 5 is fully webbed, the existing end cross beams 8a, 8b can be relocated or replaced before the jacks 13 are jacked down.

Tetsuhiro Shimosato, "Rejuvenation Strategy for Metropolitan Expressways", JSSC Journal, Japan Steel Construction Society, October 2003, No. 50, pp. 1-10

However, in conventional full web construction work, additional cross beams 11 must be installed below the existing cross beam 3 of the steel pier 1 to support the girder ends of the outer main girders 4, 6, which are originally full web, and the girder end of the middle main girder 5, which will be newly made full web, from below via new supports 16. However, the reality is that this cannot be applied to I-girder bridges, where the space below the existing cross beam 3 is limited by construction limits and there is not enough vertical space to install the additional cross beam 11.

Therefore, the present invention aims to provide a method for repairing an I-girder bridge that can replace each support and perform repair work by reinforcing the area around the supports for an I-girder bridge that has an outer girder with a full web end and an intermediate girder with a notch at the end, and has a girder support bracket protruding from a required location on the bridge axis side of the cross beam of the steel pier, and supports the girder end above the notch of the intermediate girder and the area near the outer end in the bridge width direction of the end cross beam that connects the girder end edges of the intermediate girder and each of the outer main girders via supports. Even if the space to attach reinforcing members to the underside of the cross beam of the steel pier is limited and the vertical space required to install an additional cross beam in the conventional full web construction cannot be secured, the present invention aims to provide a method for repairing an I-girder bridge that can replace each support and perform repair work by reinforcing the area around the supports.

In order to solve the above problem, the present invention, corresponding to claim 1, provides an I-girder bridge in which the girder ends of each outer main girder located at both ends in the bridge width direction are full webs, a notch is provided at the bottom of the girder end of the middle main girder located on the inside in the bridge width direction, and each girder support bracket protruding at a required location in the bridge width direction on the bridge axis direction surface of the cross beam of the steel pier supports, via bearings, the girder end where the notch of the middle main girder is provided and the location near the outer end in the bridge width direction of each end cross beam that connects the girder end edge portions of the outer main girder and the adjacent middle main girder, respectively. A notch is newly provided at the girder end of each outer main girder, and then a new girder support bracket that protrudes to the inside of the notch provided at the girder end of each outer main girder is provided at a location corresponding to each outer main girder on the bridge axis direction surface of the cross beam. Further, with each of the main girders jacked up using each of the jacks installed on each of the jack-up supports protruding from required locations on the bridge-axis surface of the cross beam, the existing girder support brackets for supporting each end cross beam and the existing supports above them are removed, and the existing supports above the girder support bracket for supporting the middle main girder are removed. After that, new supports are placed on the girder support bracket for supporting the middle main girder and on the upper side of each of the new girder support brackets, and then the jacks are jacked down so that the girder ends of the outer main girders with newly created notches are supported by the new girder support brackets, and the girder ends of the middle main girders are supported by the girder support bracket for supporting the middle main girder, each via the new supports.

In addition, in the above configuration, when creating a new cutout at the girder end of each outer main girder, reinforcement members with cutouts corresponding to the cutouts to be created in the outer main girder are attached to both sides of the girder end of each outer main girder in advance, and then the girder end of each main girder is cut along the cutouts of each reinforcement member to form a cutout at the girder end of each main girder.

Furthermore, in each of the above configurations, reinforcing members with a cutout that is one size larger than the existing cutout at the girder end of the central main girder are attached to both sides of the girder end of the central main girder, and then the web surrounding the existing cutout of the central main girder is cut along the cutout of each reinforcing member to provide a cutout reinforced by each reinforcing member at the girder end of the central main girder, and the girder end of the central main girder with the cutout reinforced by each reinforcing member is supported by the girder support bracket for supporting the central main girder via a new support.

The I-girder bridge repair method of the present invention exhibits the following excellent effects.
(1) In an I-girder bridge in which the girder ends of each outer main girder located at both ends in the bridge width direction are made full web, a notch is provided at the bottom of the girder end of the middle main girder located on the inside in the bridge width direction, and each girder support bracket protruding from a required location in the bridge width direction on the bridge axis direction face of the cross beam of the steel pier supports, via bearings, the girder end where the notch of the middle main girder is provided and the location near the outer end in the bridge width direction of each end cross beam that connects the girder end edge of each outer main girder and the adjacent middle main girder, each outer main girder is newly provided with a notch at the girder end of each outer main girder, next, new girder support brackets that protrude to the inside of the notch provided at the girder end of each outer main girder are provided at locations corresponding to each outer main girder on the bridge axis direction face of the cross beam, and further, each main girder is supported by using each jack installed on each jack-up support platform protruding from a required location on the bridge axis direction face of the cross beam. With the girder jacked up, the existing girder support brackets for supporting the end cross girders and the existing support above them are removed, and the existing support above the girder support bracket for supporting the middle main girder is removed. After that, new support is placed on the girder support bracket for supporting the middle main girder and on the upper side of each new girder support bracket, and then the jacks are jacked down, so that the girder ends with the newly created notches of each outer main girder are supported by the new girder support brackets, and the girder ends of the middle main girder are supported by the girder support bracket for supporting the middle main girder, respectively, via the new support. Therefore, the existing support in the I-girder bridge of the above type can be replaced with a new support, and the support location can be changed from the end cross girders to the girder ends of the outer main girder, thereby restoring the function of the support and the surroundings. Furthermore, if the girder support bracket for supporting the middle main girder is reinforced, it is possible to further restore the function of the surroundings of the support.
(2) Furthermore, the girder ends of each outer main girder, with newly created cutouts, are placed and supported via supports on new girder support brackets that protrude to correspond to the cutouts of each main girder on the bridge axis direction surface of the cross beam of the steel pier. Therefore, even if a large space cannot be secured below the cross beam of the steel pier due to building limits, etc., it is possible to replace the existing supports and reinforce the area around the supports.
(3) When creating new cutouts at the girder ends of each outer main girder, reinforcements with cutouts corresponding to the cutouts to be created in the outer main girder are attached to both sides of the girder end of each outer main girder, and then the girder ends of each main girder are cut along the cutouts of each reinforcement to form cutouts at the girder ends of each main girder, thereby preventing a temporary decrease in rigidity near the girder ends of each outer main girder. This makes it possible to replace each of the supports and carry out construction work to reinforce the areas around the supports while the I-girder bridge is in service.
(4) Reinforcements with cutouts that are one size larger than the existing cutouts at the girder end of the intermediate main girder are attached to both side sides of the girder end of the intermediate main girder, and then the web around the existing cutout of the intermediate main girder is cut along the cutouts of each reinforcing material to provide a cutout reinforced by each reinforcing material at the girder end of the intermediate main girder.The girder end of the intermediate main girder with the cutouts reinforced by each reinforcing material is supported by a girder support bracket for supporting the intermediate main girder via a new support.Even if fatigue damage has occurred around the existing cutouts at the girder end of the intermediate main girder, the damaged portion can be removed and the girder end of the intermediate main girder can be reinforced.

This shows the procedure for one embodiment of the I-girder bridge renovation method of the present invention, where (a) is a schematic plan view showing the state in which a notch is provided at the girder end of the outer main girder, and a new girder support bracket, a temporary jack-up cradle, and a jack-up cradle are provided on the cross beam, (b) is a view seen in the A-A direction of (a), and (c) is a view seen in the B-B direction of (a). This shows the state in which each outrigger and one of the existing end cross beams have been jacked up using the repair method of the present invention, where (a) is a schematic plan view and (b) is a view taken in the C-C direction of (a). This shows the steps after jacking up in Figure 2 in the repair method of the present invention, where (a) corresponds to Figure 2(b) and shows the state after the existing girder support brackets and supports on both sides of the bridge width have been removed, (b) shows the state after the existing other end cross girder has been removed, and (c) shows the state after a new other end cross girder has been installed. This shows the procedure after Figure 3(c) in the repair method of the present invention, and corresponds to Figure 2(b) which shows a state in which a new end cross beam has been jacked up in place of the existing one end cross beam, and a state in which the jack that was supporting the existing one end cross beam has been removed. This shows the procedure after Figure 4(b) in the repair method of the present invention, where (a) corresponds to Figure 2(b), showing the state after the existing end cross beam has been removed, and (b) shows the state after a new end cross beam has been installed. This is a schematic cross-sectional side view showing the state in which the girder support bracket in the center of the bridge width direction has been reinforced using the repair method of the present invention. This shows the state in which new supports are installed and then the outriggers and the new other end cross beam are jacked down using the repair method of the present invention, where (a) is a schematic plan view and (b) is a view taken in the direction of the arrows D-D in (a). These figures show the state after the temporary jack-up support platform, jacks, outriggers, and temporary cross beams have been removed and the repair method of the present invention has been completed, with (a) being a schematic plan view, (b) being a view seen in the E-E direction of (a), and (c) being a view seen in the F-F direction of (a). This shows the reinforcement procedure when a cutout is provided in the outer main girder using the repair method of the present invention, where (a) is a schematic oblique view showing the state in which an outer main girder outer reinforcement member is attached to the outer surface of the outer main girder in the bridge width direction, and (b) is a schematic oblique view showing the state in which the existing stiffening material has been removed from the inner surface of the outer main girder in the bridge width direction. This shows the step after Figure 9 (b) in the reinforcement procedure when a cutout portion is provided in the outer main girder in the repair method of the present invention, where (a) is a schematic oblique view showing the state in which the outer main girder inner reinforcement material is attached to the inner surface of the outer main girder in the bridge width direction, and (b) is a schematic oblique view showing the state in which a notch is provided at the girder end of the outer main girder. This shows the step after Figure 10 (b) in the reinforcement procedure when a cutout portion is provided in the outer main girder in the repair method of the present invention, and is a schematic oblique view showing the state of attaching the outer main girder inner girder end reinforcement material to each outer main girder. This shows the procedure for reinforcing the girder ends of the central main girder using the repair method of the present invention, with (a) being a schematic oblique view showing the state after the existing stiffening material on one side of the central main girder in the bridge width direction has been removed, and (b) being a schematic oblique view showing the state after the central main girder reinforcement material has been attached to one side of the central main girder in the bridge width direction. This shows the step after Figure 12 (b) in the procedure for reinforcing the girder end of the middle main girder in the repair method of the present invention, where (a) is a schematic oblique view showing the state after the existing stiffening material on the other end face of the middle main girder in the bridge width direction has been removed, and (b) is a schematic oblique view showing the state after the middle main girder reinforcement material has been attached to the other side face of the middle main girder in the bridge width direction. This shows the procedure after Figure 13 (b) in the reinforcing procedure for the girder end of the intermediate main girder in the repair method of the present invention, and is a schematic oblique view showing the state in which the intermediate main girder end reinforcement members are attached to each side of the intermediate main girder in the bridge width direction. This is a schematic side view showing the step after Figure 14 in the reinforcing procedure for the girder end of the central main girder in the repair method of the present invention, showing the state in which the web around the existing cutout portion at the girder end of the central main girder has been cut to form a new cutout portion. This shows an example of a three-main I-girder bridge conventionally used on the Metropolitan Expressway and other roads, where (a) is a plan view, (b) is a view taken in the G-G direction of (a), and (c) is a view taken in the H-H direction of (a). FIG. 17 is an enlarged perspective view showing the support structure portion of the main girder in the three-main I-girder bridge of FIG. This shows the state in which an additional cross beam has been installed below the cross beam of a steel pier in the conventional full web construction work for main girders, (a) is a schematic plan view, and (b) is a view taken in the direction of the arrows I-I in (a). This shows the state of each main girder jacked up during full web construction work, where (a) is a schematic plan view, (b) is a view taken in the J-J direction of (a), and (c) is a view taken in the K-K direction of (a). This shows the state in which each main girder is placed on top of the new supports after the intermediate main girder has been made fully web-made during the full web construction work for main girders, where (a) is a schematic plan view, (b) is a view taken in the L-L direction of (a), and (c) is a view taken in the M-M direction of (a).

Below, the embodiment of the present invention will be described with reference to the drawings.

Figures 1(a), (b), (c) through 15 show one embodiment of the I-girder bridge repair method of the present invention, which is as follows:

In other words, as shown in Fig. 16 (a), (b), (c) and Fig. 17, the outer main girders 4, 6 have full web ends, and the central main girder 5 has a notch 7 at the end. The girder end above the notch 7 of the central main girder 5 and the locations near the outer end in the bridge width direction of each end cross beam 8a, 8b that connects the girder end edge of the central main girder 5 and each outer main girder 4, 6 are supported by girder support brackets 9a, 9b, 9c protruding from the bridge axis direction surface of the cross beam 3 of the steel pier 1 via supports 10. In the lower part of the girder end of each of the outer main girders 4, 6, a notch 17 is provided as shown in Fig. 1 (a) and (b).

Next, new girder support brackets 18 are provided at the lower positions of the locations corresponding to the outer main girders 4, 6 on the bridge axis direction surface of each cross beam 3 of the steel pier 1, protruding in the bridge axis direction inside the cutouts 17 provided in the outer main girders 4, 6.

As shown in Figures 1(a) and 1(c), temporary jack-up supports 19a, 19b are provided at the lower positions of the cross beams 3 at the bridge axis direction faces of the cross beams 3 at locations corresponding to the inner ends of the end cross beams 8a, 8b in the bridge width direction, protruding to a position below the end cross beams 8a, 8b.

Furthermore, as shown by the two-dot chain lines in Figures 1(a) and 1(b), outriggers 20 extending to the vicinity of the cross beam 3 are temporarily installed on the outer surface of each of the outer main girders 4, 6 in the bridge width direction at a required distance from the girder end. Meanwhile, at the lower position of the required location near both ends in the bridge width direction corresponding to each of the outriggers 20 on the bridge axis direction surface of each of the cross beams 3, a jack-up support pedestal 21 protruding to a position below each of the outriggers 20 is installed, for example as an integral part with the new girder support bracket 18.

Furthermore, as shown by the two-dot chain lines in Figures 1(a) and 1(c), temporary cross girders 22 extending in the bridge width direction are placed between the inner side surfaces in the bridge width direction at a location a required distance away from the girder ends of the outer main girders 4 and 6 and both side surfaces in the bridge width direction at a location a required distance away from the girder ends of the middle main girder 5, and both ends of the temporary cross girders 22 are attached to the inner side surfaces in the bridge width direction of the outer main girders 4 and 6 and both side surfaces in the bridge width direction of the middle main girder 5, respectively.

After that, as shown in Figures 2(a) and 2(b), jacks 23a, 23b, and 23c are installed on the jack-up pedestals 21 located below the outriggers 20 and the temporary jack-up pedestal 19a installed below the one end cross beam 8a, and the main girders 4, 5, and 6 are jacked up by the jacks 23a, 23b, and 23c via the outriggers 20 and the one end cross beam 8a above. As a result, the loads of the main girders 4, 5, and 6 that were applied to the supports 10 on the existing girder support brackets 9a, 9b, and 9c are supported by the jacks 23a, 23b, and 23c. In this state, the girder support brackets 9a and 9c on both sides of the bridge width direction and the supports 10 above them are removed as shown in Figure 3(a). Furthermore, by jacking up the jacks 23a, 23b, and 23c, the other end cross girder 8b is removed from the load transmission path that transmits the loads of the main girders 4, 5, and 6 to the cross beam 3. As a result, the other end cross girder 8b is no longer subjected to the loads of the main girders 4, 5, and 6. As shown in FIG. 3(b), both ends of the existing other end cross girder 8b are removed by cutting them off from the outer main girder 6 and the middle main girder 5, respectively. After that, the removed portion of the existing other end cross girder 8b on the outer main girder 6 and the middle main girder 5 is reinforced as described below, and then, as shown in FIG. 3(c), a new other end cross girder 24b extending in the bridge width direction is attached integrally between the reinforced girder end edges above the cutouts 17 and 7 of the outer main girder 6 and the middle main girder 5.

After the existing other end cross beam 8b has been replaced with the new other end cross beam 24b as described above, as shown in FIG. 4(a), another jack 23d is installed on the temporary jack-up support 19b located below the new other end cross beam 24b, and the new other end cross beam 24b is jacked up by the jack 23d, so that the load of each of the main girders 4, 5, 6 can be supported by the jack 23d supporting the new other end cross beam 24b and the jacks 23a, 23b supporting the outriggers 20. This allows the jack 23c supporting the existing one end cross beam 8a to be jacked down, and then the jack 23c is removed after being jacked down, as shown in FIG. 4(b).

When the jack 23c that was supporting the existing one end cross girder 8a is jacked down, the existing one end cross girder 8a is removed from the load transmission path that transmits the loads of the main girders 4, 5, and 6 to the cross beam 3. As a result, the existing one end cross girder 8a, which is no longer subjected to the loads of the main girders 4, 5, and 6, is removed by cutting off both longitudinal ends from the outer main girder 4 and the middle main girder 5, as shown in Figure 5 (A). After that, the outer main girder 4 and the middle main girder 5 are reinforced as described below, and then a new one end cross girder 24a extending in the bridge width direction is attached integrally between the upper girder end edges of the outer main girder 4 and the middle main girder 5 cutouts 17 and 7, as shown in Figure 5 (B).

Furthermore, with the loads of the main girders 4, 5, 6 being received by the jacks 23a, 23b, 23d, as shown in FIG. 6, the existing support 10 installed on the upper side of the girder support bracket 9b in the center of the bridge width direction is removed, and a girder support bracket reinforcing member 25 extending continuously through the lower side of the lower flange of the cross beam 3 is placed on the lower side of each girder support bracket 9b in the center of the bridge width direction provided on both sides of the cross beam 3 in the bridge axis direction, and the upper end of the girder support bracket reinforcing member 25 is attached integrally to the lower side of each girder support bracket 9b in the center of the bridge width direction and the lower flange of the cross beam 3, thereby reinforcing each girder support bracket 9b.

After that, as shown in Fig. 7 (a) and (b), new supports 26 are installed on the upper side of the reinforced girder support bracket 9b at the center of the bridge width direction on the bridge axis direction surface of the cross beam 3 of the steel pier 1, and on the upper side of each of the new girder support brackets 18 near both ends in the bridge width direction. Then, by jacking down the outriggers 20 and the jacks 23a, 23b, and 23d supporting the new other end cross beam 24b, the upper girder end of the notch 7 of the middle main girder 5 and the upper girder end of the notch 17 newly provided in each of the outer main girders 4 and 6 are placed on the upper side of each of the supports 26, so that the load of the middle main girder 5 and each of the outer main girders 4 and 6 is transmitted and supported by the cross beam 3 of the steel pier 1 via the new supports 26, the reinforced girder support bracket 9b at the center of the bridge width direction, and the new girder support brackets 18 near both ends in the bridge width direction.

After the load of each of the main girders 4, 5, 6 has been supported by the cross beam 3 via the new supports 26, and the girder support brackets 9b and new girder support brackets 18 in the manner described above, the temporary jack-up supports 19a, 19b, the outriggers 20, and the temporary cross girders 22 are removed to complete the repair work on the I-girder bridge. As a result, as shown in Figures 8(a), (b), and (c), the girder ends of the outer main girders 4 and 6 with the newly provided notches 17 are supported by the upper side of the new girder support brackets 18 provided at the required locations on the lower part of the cross beam's bridge axis direction surface via new supports 26, and the girder end of the middle main girder 5 with the notch 7 is supported by the upper side of the reinforced girder support bracket 9b in the center of the bridge width direction via new supports 26, and further, the existing girder support brackets 9a and 9c that supported the outer main girders 4 and 6 are removed to construct a renovated I-girder bridge structure.

In the above, when a notch 17 is newly provided at the girder end of each of the outer main girders 4, 6, which is the full web, it is necessary to reinforce the vicinity of the girder end of each of the outer main girders 4, 6 around the newly provided notch 17 in order to ensure that the rigidity required to withstand the load applied to each of the outer main girders 4, 6 is secured at the girder height sudden change portion formed by providing the notch 17. In consideration of this point, in the present invention, the area around the notch 17 provided in each of the outer main girders 4, 6 is reinforced in the procedure shown in the following Figures 9 (a) (b) to 11.

That is, first, as shown in FIG. 9(a), the outer surface in the bridge width direction of each of the outer main girders 4, 6 is provided with a notch 17a corresponding to the shape of the notch 17 to be formed, and an outer main girder outer reinforcement 27 with a lower flange 28a is attached integrally along the notch 17a on the outer surface in the bridge width direction near the girder end.

Next, as shown in FIG. 9 (b), the existing rib-shaped stiffeners 29 attached to the area on the side farther from the girder end than the end cross beams 8a, 8b near the girder end of the inner side of the outer main girders 4, 6 in the bridge width direction are cut and removed, and the cut surface of the existing stiffeners 29 is flattened with a grinder or the like. Then, as shown in FIG. 10 (a), an outer main girder inner reinforcement 30 having a cutout 17b according to the shape of the cutout 17 to be formed at the girder end of each of the outer main girders 4, 6 and a lower flange 28b along the cutout 17b is attached integrally to the area from which the existing stiffeners 29 were removed near the girder end of the inner side of the outer main girders 4, 6 in the bridge width direction.

Next, as shown in Figure 10 (b), the lower part of the web at the girder end of each of the outer main girders 4, 6 (only the outer main girder 6 is shown in Figure 10 (b)) is cut along the shape of the cutouts 17a, 17b of the outer reinforcement 27 and inner reinforcement 30 for the outer main girders 4, 6 to form the cutouts 17 at the girder ends of each of the outer main girders 4, 6.

Then, when removing the other end cross girder 8b (see Figure 3) attached to the inner side of the outer main girder 6 in the bridge width direction as shown in Figure 3 (b), as shown in Figure 11, an outer main girder inner girder end reinforcement 31 having a lower flange 28c along the upper side of the newly formed cutout 17 is attached integrally to the area from the removed part of the other end cross girder 8b on the inner side of the outer main girder 6 in the bridge width direction to the girder end via a filler plate 32, with the edge portion of the outer main girder inner girder end reinforcement 31 opposite to the side positioned closer to the girder end of the outer main girder 6 being overlapped by the required amount with the edge portion of the outer main girder inner reinforcement 30 on the side positioned closer to the girder end of the outer main girder 6. Also, although not shown, when removing one end cross girder 8a attached to the inner side of the outer main girder 4 in the bridge width direction as shown in FIG. 5 (A), the outer main girder inner girder end reinforcement 31 with the lower flange 28c along the upper side of the newly formed notch 17 is attached integrally to the area from the removed part of the one end cross girder 8a on the inner side of the outer main girder 4 in the bridge width direction to the girder end via a filler plate 32. As a result, the notch 17 is provided at the girder end of each of the outer main girders 4 and 6, and the girder height sudden change part formed by the notch 17 can be firmly reinforced by the reinforcements 27, 30, and 31 attached to both sides in the bridge width direction.

In addition, in the present invention, in order to be able to reinforce the area around the support even if fatigue damage occurs around the existing cutout portion 7 of the intermediate main girder 5, the girder end of the intermediate main girder 5 is also reinforced using the procedure shown in Figures 12 (a) and (b) through 15.

Specifically, as shown in FIG. 12(a), first, the existing rib-shaped stiffener 33a attached to the area on the side farther from the girder end than one end cross girder 8a near the girder end of one side of the middle girder 5 in the bridge width direction is cut and removed, and the cut surface of the existing stiffener 33a is flattened with a grinder or the like. Then, as shown in FIG. 12(b), a first middle girder reinforcement 34a having a notch 35a one size larger than the existing notch 7 of the middle girder 5 and a lower flange 36a around the notch 35a is integrally attached to the area on the side farther from the girder end than one end cross girder 8a near the girder end of one side of the middle girder 5 in the bridge width direction.

Furthermore, in the area near the girder end of the other side of the middle girder 5 in the bridge width direction, which is farther from the girder end than the other end cross girder 8b, the existing rib-shaped stiffener 33b is cut and removed in the same manner as above, as shown in FIG. 13(a), and the cut surface of the existing stiffener 33b is flattened with a grinder or the like. Then, as shown in FIG. 13(b), a second middle girder reinforcement 34b is attached integrally to the area near the girder end of the other side of the middle girder 5 in the bridge width direction, which is farther from the girder end than the other end cross girder 8b, which has a notch 35b that is slightly larger than the existing notch 7 of the middle girder 5 and has a lower flange 36b around the notch 35b.

Next, as shown in Figure 3 (B) and Figure 5 (A), when the end cross girders 8b and 8a attached to both sides of the middle girder 5 in the bridge width direction are sequentially removed, as shown in Figure 14, the middle girder end reinforcements 37a, 37b each having the lower flanges 36a, 36b of the middle girder reinforcements 34a, 34b and the corresponding lower flanges 36c, 36d are sequentially attached integrally to the area from the removed parts of the end cross girders 8b and 8a on both sides of the middle girder 5 in the bridge width direction to the girder end, with the edge of the middle girder end reinforcements 37a, 37b opposite to the side located closer to the girder end of the middle girder 5 being overlapped by the required distance with the edge of the middle girder reinforcements 34a, 34b located closer to the girder end of the middle girder 5 being overlapped by the required distance with the edge of the middle girder reinforcements 34a, 34b.

Then, as shown in Figure 15, the web around the existing notch 7 at the bottom of the girder end of the middle main girder 5 is cut at a position along the lower flanges 36a, 36b around the notches 35a, 35b of the middle main girder reinforcements 34a, 34b and the lower flanges 36c, 36d of the middle main girder end reinforcements 37a, 37b, so that a new notch 7a whose periphery is strongly reinforced by the reinforcements 34a, 34b and the girder end reinforcements 37a, 37b for the middle main girder 5 can be formed at the girder end of the middle main girder 5. Note that when a new notch 7a one size larger than the existing notch 7 is formed at the girder end of the middle main girder 5 as described above, the girder height at the girder end of the middle main girder 5 becomes smaller than the original girder height. Therefore, the reduction in girder height is compensated for by setting the thickness dimension of the new support 26 that supports the upper girder end of the newly formed cutout 7a thicker than the original thickness dimension, or by increasing the thickness dimension of the sole plate (not shown), so that the height position of the upper end of the middle main girder 5 does not change.

As described above, when the existing end cross girders 8b and 8a are removed one after another, the girder end reinforcements 31, 37a, and 37b are attached integrally to the removed portions of the end cross girders 8b and 8a on the inner side of the girder end of each of the outer main girders 4 and 6 in the bridge width direction and on both sides of the girder end of the middle main girder 5 in the bridge width direction. Therefore, when new end cross girders 24a and 24b are installed after the existing end cross girders 8b and 8a are removed as shown in Figures 3(c) and 5(b), both ends of the new end cross girders 24a and 24b are attached to the girder end reinforcements 31, 37a, and 37b, respectively.

When providing new girder support brackets 18 integrated with each jack-up support base 21 on each bridge axis direction surface of the cross beam 3 of the steel pier 1, as shown in Figure 1 (b), the new girder support brackets 18 integrated with each jack-up support base 21 are attached to a specified location on the lower part of each bridge axis direction surface of the cross beam 3, positioned so that their lower ends protrude below the cross beam 3 by the required distance, and connecting members 39 extending in the bridge axis direction through the underside of the cross beam 3 are arranged between the lower end protruding parts of each new girder support bracket 18 that correspond to each other in the bridge axis direction, sandwiching the cross beam 3, and both longitudinal ends of the connecting member 39 are attached integrally to the lower end protruding parts of each new girder support bracket 18, respectively, and the upper end of the connecting member 39 is attached integrally to the underside of the lower flange of the cross beam 3. Furthermore, a cross beam internal reinforcement 40 extending in the bridge axis direction within the cross beam 3 is placed between required locations on the inner web surface of the cross beam 3 that is inside the mounting locations of the new girder support brackets 18 on each bridge axis side of the cross beam 3, and both longitudinal ends are integrally attached to required locations on the inner web surface of the cross beam 3, respectively. The lower end of the cross beam internal reinforcement 40 is integrally attached to the upper side of the lower flange of the cross beam 3, so that the installation locations of the new girder support brackets 18 on the cross beam 3 that are around the support can be reinforced.

In this way, according to the I-girder bridge repair method of the present invention, the existing bearings 10 in an I-girder bridge equipped with outer main girders 4, 6 with full web ends and a middle main girder 5 with a notch 7 at the end can be replaced with new bearings 26, and functionality can be restored. The girder end above the notch 7 of the middle main girder 5 and the outer side of the end cross girders 8a, 8b connecting the girder end edges of the middle main girder 5 and the outer main girders 4, 6 are supported by girder support brackets 9b, 9a, and 9c protruding from the bridge axis direction face of the cross beam 3 of the steel pier 1 via bearings 10.

In addition, a notch 17 is provided in each of the outer main girders 4 and 6, and the girder end above the notch 17 is placed via a support 26 on a new girder support bracket 18 that protrudes from a required location on the lower part of the bridge axis direction face of the cross beam 3 of the steel pier 1. Therefore, even if the space below the cross beam 3 of the steel pier 1 for installing an additional cross beam that needs to be added in the conventional full web construction work cannot be secured due to building limits, etc., each of the existing supports 10 can be replaced with a new support 26 and the area around the support can be reinforced.

Moreover, before removing the existing stiffener 29 on the inner side in the bridge width direction, each of the outer main girders 4, 6 is reinforced by integrally attaching the outer main girder outer reinforcement 27 to the outer side in the bridge width direction near the girder end of each of the outer main girders 4, 6, so that the risk of a temporary decrease in rigidity near the girder end of each of the outer main girders 4, 6 can be prevented in advance. In addition, for the middle main girder 5, after removing the existing stiffener 33a on one side in the bridge width direction, the middle main girder reinforcement 34a is integrally attached to the one side in the bridge width direction, and then the existing stiffener 33b on the other side in the bridge width direction is removed, so that the risk of a temporary decrease in rigidity near the girder end of the middle main girder 5 can be prevented in advance. Therefore, it will be possible to replace each of the existing supports 10 with new supports 26 and carry out reinforcement work around the supports while the road on the deck (not shown) located above the cross beam 3 and each of the main girders 4, 5, and 6 remains in service.

The present invention is not limited to the above embodiment. In the above embodiment, of the jacks 23a, 23b, 23c, and 23d used to sequentially jack up the existing end cross girders 8a, 8b so that the load is no longer acting on them, jacks 23a and 23b are installed above each jack-up support 21 protruding from a predetermined location on each bridge axis direction face of the cross beam 3 of the steel pier 1, and are shown to jack up the outriggers 20 temporarily installed on the outer surface of each outer main girder 4, 6 in the bridge width direction. However, each of the jacks 23a and 23b may also be installed on a new girder support bracket 18 to jack up the girder ends where the newly provided cutout portions 17 of each outer main girder 4, 6 are provided. In this case, the girder ends of the outer main girders 4, 6 and one end cross girder 8a are jacked up by the jacks 23a, 23b on the new girder support brackets 18 and a jack 23c installed on the temporary jack-up cradle 19a, thereby removing the existing girder support brackets 9a and 9c and the existing supports 10 above them, removing the existing other end cross girder 8b, and installing the new other end cross girder 24b. Also, the girder ends of the outer main girders 4, 6 and the new other end cross girder 24b are jacked up by the jacks 23a, 23b on the new girder support brackets 18 and a jack 23d installed on the temporary jack-up cradle 19b, thereby removing the existing one end cross girder 8a and installing the new one end cross girder 24a. After that, the two jacks 23c and 23d on the temporary jack-up pedestals 19a and 19b are used to jack up the newly installed end cross beams 24a and 24b, and the loads on all of the main girders 4, 5, and 6 are supported by the jacks 23c and 23d. This replaces the jacks 23a and 23b on the new girder support brackets 18 with supports 26, and then the jacks 23c and 23d are jacked down, allowing the girder ends of the outer main girders 4 and 6 to be supported on the upper side of the new supports 26 installed on the new girder support brackets 18.

In addition, if the I-girder bridge is of a type that has outer main girders 4, 6 with full web ends and a middle main girder 5 with a notch 7 at the end, and the girder end above the notch 7 of the middle main girder 5 and the outer side in the bridge axis direction of the end cross girders 8a, 8b that connect the girder end edges of the middle main girder 5 and each of the outer main girders 4, 6 are supported by girder support brackets 9b, 9a, and 9c protruding from the bridge axis direction surface of the cross beam 3 of the steel pier 1 via supports 10, then the bridge can be applied to I-girder bridges other than viaducts on the Metropolitan Expressway, and various other modifications can of course be made within the scope of the present invention.

1 Steel pier 3 Cross beam 4 Outer main girder 5 Middle main girder 6 Outer main girder 7 Cutout 9a, 9b, 9c Girder support bracket 8a, 8b End cross girder 10 Support 17, 17a, 17b Cutout 18 New girder support bracket 19a, 19b Temporary jack-up support base (jack-up support base)
21 Jack-up support 23a, 23b, 23c, 23d Jack 26 Support 27 Outer main girder outer reinforcement material (reinforcement material)
30. Inner reinforcement material for outer main girder (reinforcement material)
34a, 34b Intermediate girder reinforcement (reinforcement)
35a, 35b notch

Claims (3)

In an I-girder bridge, the girder ends of each outer main girder located at both ends in the bridge width direction are made full web, a notch is provided at the bottom of the girder end of the middle main girder located on the inside in the bridge width direction, and each girder support bracket protruding at a required point in the bridge width direction on the bridge axis direction surface of the cross beam of the steel pier supports the girder end where the notch of the middle main girder is provided and the location near the outer end in the bridge width direction of each end cross beam that connects the girder end edge of each outer main girder and the adjacent middle main girder via a support, respectively. A notch is newly provided at the girder end of each outer main girder, and then a new girder support bracket that protrudes to the inside of the notch provided at the girder end of each outer main girder is provided at a location corresponding to each outer main girder on the bridge axis direction surface of the cross beam, and further, a new girder support bracket is provided at a required point in the bridge axis direction surface of the cross beam. This is a repair method for I-girder bridges, characterized in that, with each of the main girders jacked up using jacks installed on each of the jack-up supports protruding from the bridge, the existing girder support brackets for supporting the end cross beams and the existing supports above them are removed, and the existing supports above the girder support bracket for supporting the middle main girder are removed. After that, new supports are placed on the girder support bracket for supporting the middle main girder and on the top of each of the new girder support brackets, and then the jacks are jacked down, so that the girder ends of the outer main girders with newly created notches are supported by the new girder support brackets, and the girder ends of the middle main girders are supported by the girder support bracket for supporting the middle main girder, each via the new supports. The repair method for I-girder bridges according to claim 1, in which, when creating new cutouts at the girder ends of each outer main girder, reinforcement members with cutouts corresponding to the cutouts to be created in the outer main girder are attached to both sides of the girder end of each outer main girder in advance, and then the girder ends of each main girder are cut along the cutouts of each reinforcement member to form cutouts at the girder ends of each main girder. The repair method for an I-girder bridge according to claim 1 or 2, in which reinforcement members with a cutout that is one size larger than the existing cutout at the girder end of the middle main girder are attached to both sides of the girder end of the middle main girder, and then the web around the existing cutout of the middle main girder is cut along the cutout of each reinforcement member to provide a cutout reinforced by each reinforcement member at the girder end of the middle main girder, and the girder end of the middle main girder with the cutout reinforced by each reinforcement member is supported by a girder support bracket for supporting the middle main girder via a new support.

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