JP2533830B2 - Girder section stress improvement method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for improving stress of girder section in a bridge structure.

[0002]

2. Description of the Related Art Conventionally known methods for improving stress in a girder cross section are roughly classified into methods for reinforcement such as strengthening the girder cross section, and methods for changing the supporting conditions of the girder. Specifically, the former is a method of increasing the cross-section to the upper and lower flanges of the girder and the method of using an external cable, and the latter is a method of supporting and supporting.

The cross section strengthening method for the upper and lower flanges of the girder is
This is a method of increasing the cross-sectional rigidity of the girder by attaching reinforcing steel materials to the upper and lower flanges of the girder by welding or high-strength bolting, respectively.

In the method using the outer cable, a cable made of a new material such as steel or carbon is arranged on the lower surface or side surface of the girder in the bridge axis direction, and a tension is applied to this to give a negative bending moment to the girder to load it. It is a method of improving the stress generated in the girder by canceling the positive bending moment generated by the applied load.

[0005] The method of supporting work is a method of reducing the stress generated in the girder by supporting the girder span portion by supporting work to shorten the span length.

Due to the increase in traffic volume and the increase in size of vehicles in recent years, bridge slabs are often damaged, and damaged floor slabs are being replaced in various places. Normally, the floor slab and girder act as a composite cross section and have a large bending rigidity, but when the floor slab is removed, the floor slab disappears and acts as a cross section of the girder only, resulting in only a small bending rigidity. . Therefore, these stress improving methods are used as a countermeasure.

Although all of these methods have advantages and disadvantages, the present invention proposes a more effective method by eliminating the disadvantages of these methods.

The method using the outer cable is, specifically, as shown in FIGS. 6 and 7, a pair of brackets 4 facing the lower surface or the side surface of the girder 1 are attached with bolts 5, and the bracket 4 is attached.
A cable 3 made of PC steel is arranged in between, and a negative bending moment is given to the girder by introducing prestress.

In the supporting method, as shown in FIG. 8, the supporting members 20 support the vicinity of the center between the girder supports.

[0010]

According to these methods, there are the following problems. First, in the method of reinforcing the cross section, there are problems of (1) drilling when bolted and (2) heat effect when welded. Next, in the method using the external cable, (1) when the steel material is used because the cable is exposed to the outside, the durability is lost due to corrosion over time. Therefore, complete corrosion protection of the cable is required. (2) Since the bracket for fixing the cable uses the flange of the bracket to form bolt holes in the flange or web of the girder and is joined by bolts or welded, the material and cross section of the girder are affected. In addition, in the method using the support work, the support work 20 may not be installed depending on the crosslinking conditions. The present invention solves such a problem and, as a more effective one, utilizes a method using an outer cable.

[0011]

[Means for Solving the Problem] First, the prestress necessary for producing a negative bending moment in the girder is introduced, the precast floor slab is placed on the upper surface of the girder, and after the girder and floor slab are combined, By the means for releasing the stress, it is possible to solve the problems when the steel material is used for the cable and the problems due to the supporting work.

Here, the introduction of the prestress necessary to generate a negative bending moment in the girder is carried out by using a high tension vise in place of the known bolt connection or welded connection for the cable fixing bracket to rub the flange. By means of joining
Since this is performed, the problems caused by bolt joining and welding joining can be solved.

[0013]

In this means, first, the synthesis of the girder and the precast floor slab is carried out while the stress introduced into the girder is kept enclosed, so the prestress introduced into the non-synthetic section is released after the synthesis of the girder and the precast floor slab. Then, a positive bending moment and a tensile force act on the composite cross section. Therefore, the stress balance is very good. Since the fixing bracket of the cable is frictionally joined to the girder by using the high tension vise, the existing member is not damaged by holes, welding, or the like. Also, no holes remain after removal.

[0014]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing a procedure of a stress improving method for a girder section, and FIG. 2 is an explanatory diagram of a stress degree in a girder.
(B) is the stress level when prestress is introduced (state 2), (c) is the stress level when prestress is introduced and the floor slab is installed (state 3), and (d) is after floor slab synthesis. 4 is an explanatory view of the stress level (state 4) when the prestress is released, and FIG. 3 is a detailed view of the fixing portion showing a state in which the fixing placket is indirectly attached to the girder by using a high tension vise.
FIG. 5 is a sectional view taken along line AA in FIG. 3, and FIG. 5 is a schematic view of the fixing unit showing a state in which the fixing bracket is directly attached to the girder by using a high tension vise.

The procedure of the method for improving the stress in the cross section of the girder will be described with reference to FIG. 1 and the degree of stress generated in the girder will be described with reference to FIGS. 2 to 5, 1 is a digit, 2 is a floor slab, 3 is a cable, and 4 is a fixing bracket.

First, preliminary tension is performed (A). Specifically, a known steel cable is fixed to a bracket attached to the lower surface or the side surface of the girder. The cable used may be a new material such as carbon other than steel. The bracket is attached to the girder using a high tension vise, which will be described later. This pre-tensioning is performed by introducing pre-stress for the excess when the girder has a non-composite cross section when the floor slab is dismantled and the stress level of the girder exceeds the existing slab dismantling or the installation of a new slab.

Next, the existing floor slab is dismantled and removed (B). Here, since the girder has a non-composite cross section, the stress of the girder often exceeds the allowable value when the existing floor slab is removed using a temporary heavy machine, but due to pre-tensioning, the load applied to the girder ( (Temporary heavy equipment, etc.) Since stress is generated with the opposite sign, the stress is offset and it is possible to dismantle without exceeding the allowable value.

After disassembling the existing floor slab, the girder flange is prepared and a precast floor slab is installed (C). When the floor slab 2 is installed on the girder 1 without introducing prestress,
A dead load bending moment is generated as shown in (a), but when prestress is introduced, a negative bending moment is generated in the girder 1 and the stress level is as shown in FIG. 2 (b). Figure 2 shows the stress level when the floor slab 2 is erected.
The state shown in (c) is obtained. The procedure so far is a known procedure.

The amount of preliminary tension introduced before the removal of the existing floor slab is
The floor slab will be removed and changed at each stage of erection. Therefore, the amount of finally required prestress is introduced to the lower digit (D). In other words, it will be introduced when the stress is exceeded in the completed form.
At this stage, the external force acting on the cross section of the main girder is Md + Mp
It becomes + P. Md: Positive bending moment due to floor slab / girder Mp: Negative bending moment due to prestress introduced by eccentricity P: Amount of prestress introduced

With the required amount of prestress introduced into the girder, concrete is placed in the box-extracted portion of the precast floor slab to synthesize the girder and floor slab (E). At this point, the stress introduced into the girder remains encapsulated and is combined with the deck.

After the synthesis of the deck and the girder is completed, the prestress under the girder is released (F). At this time, the bending moment and the tensile force opposite to those in which the prestress was introduced are applied. However, since this external force resists as a composite cross section, it becomes an indirect life and death load composite girder in the entire bridge. Figure 2 shows the state of the stress level when prestress is removed after floor slab synthesis.
As shown in (d), the balance between tension and compression is good.

Next, an embodiment in which the fixing bracket of the cable is frictionally joined to the girder in the above-described invention will be specifically described with reference to FIGS. 3 and 4. First, the girder 1 and the girder bracket 11 are connected to the upper flange 11 of the girder bracket 11.
a and the lower flange 1a of the girder 1 so that both flanges 1
1a and 1a are friction-welded using a high tension vise 7.

The fixing bracket 4 has a tensioning device 13 including a center hole jack 8, a ram chair 9 and a load cell 10 which are well-known tensioning devices, and is joined by bolts 12 to the girder bracket 11b via the upper flange 4a. There is. Here, although not shown, the fixing brackets facing each other at the other end of the girder 1 are also indirectly attached via the girder lower flange. Reference numeral 11c is a reinforcing plate. It goes without saying that the fixing bracket 4 may be directly friction-bonded to the girder 1 using a high tension vise.

Next, another embodiment will be described with reference to FIG. In this embodiment, the lower flange 1a of the girder 1 and the upper flange 4a of the fixing bracket 4 of the cable 3 by bolt joining in the above-mentioned conventional example are directly joined by friction by using high tension vise 7 instead of bolt joining. It is a thing.

In this way, the bracket for fixing the cable for introducing the prestress necessary for producing the negative bending moment in the girder is attached to the girder, and the prestress is performed under the girder by the procedure described above. , The precast slab is installed on the girder, the prestress under the girder is released after the girder and the slab are combined, and the stress in the girder section is improved.

[0026]

Since the present invention is constructed as described above,
It has the following effects. Since negative prestress is introduced to the girder and the prestress is released after the floor slab and girder are combined, a positive bending moment and tensile force work after releasing the prestress, but the external force is combined. Since it resists as a cross section, it becomes an indirect life and death load composite girder in the entire bridge, improving the stress balance. Also, no support work is required when changing the composite girder.

Further, releasing the prestress means removing the cable, so that problems such as corrosion of the cable can be eliminated as in the past. Besides, the bracket can be removed, so the appearance is neat.

Since the bracket is attached to the girder by friction joining using a high tension vise, not by bolt joining or welding joining, no damage is caused by drilling or welding the girder. .

Since the girder and the bracket are frictionally joined by the high tension vise, the bracket can be easily removed from the girder by releasing the frictional joining.
Therefore, after releasing the prestress, the high tension vise, the bracket, the cable, etc. can be diverted to other places, and the construction cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a procedure of a method for improving stress in a girder section.

FIG. 2 is an explanatory diagram of a stress level in a girder.

FIG. 3 is a detailed view of an embodiment in which a fixing bracket is frictionally joined to a girder via a girder bracket with a high tension vise.

4 is a sectional view taken along line AA of FIG.

FIG. 5 is a schematic view of another embodiment showing a state in which a fixing bracket is frictionally joined to a girder using a high tension vise.

FIG. 6 is a schematic view of a conventional example in which prestress is introduced under the girder.

FIG. 7 is a schematic view of a conventional example in which a fixing bracket for a cable is attached under a girder.

FIG. 8 is a schematic view of a conventional example of supporting work.

[Explanation of symbols]

 1 digit 2 floor slab 3 cable 4 fixing bracket 7 high tension vise

Claims (1)

(57) [Claims] 1. The introduction of prestress necessary for producing a negative bending moment in the girder is fixed to the cable fixing bracket.
To the girder using a high tension vise and frictionally welded in the transverse direction.
A method for improving stress in a girder section, which is characterized in that a precast floor slab is placed on the upper surface of the girder, and prestress is released after the girder and the floor slab are combined.