KR100396713B1 - The method of prestressed composite beam made by using the additional compressive materials - Google Patents

Abstract

In order to compensate for the loss of compressive force of the lower casing concrete due to the welding residual stress, concrete creep deformation, and dry shrinkage, which is inevitably generated during the production of the prestressed composite beam, the lower casing concrete is poured into the lower casing concrete during the composite beam manufacturing process. In addition, the present invention supplements the compressive stress reduction of the lower casing concrete by installing a compressive reinforcement on the upper flange while applying a force to introduce a compressive force and applying a force. According to the present invention, the steel consumption is significantly reduced compared to the conventional manufacturing method, and the inconvenience caused by the use of the additional tension material can be avoided.

Description

Prestressed composite beam made by compressive stiffener and its manufacturing method {The method of prestressed composite beam made by using the additional compressive materials}

The present invention relates to a prestressed composite beam using a compressive stiffener and a manufacturing method thereof.

Conventional prestressed composite beams have a phenomenon in which the compressive stress introduced in the lower casing concrete 40 of FIG. 1 decreases due to creep deformation and dry shrinkage of the weld residual stress concrete generated when the I-shaped steel is manufactured, and thus the lower casing concrete is often It is in tension and cracked. In order to prevent this cracking, many steel cross sections have to be taken, which is expensive. In this case, additional compressive stress may be introduced using the tension PC-PC as shown in FIG. 2 as a way to compensate for the reduction of the compressive stress of the lower casing concrete. However, if the tension material is added to the composite beam, it is not only cumbersome to produce, but additional costs such as the tension cost of the tension material are required, and even the composition of the composite beam combines two methods of introducing prestressing force, resulting in a complicated structure.

In addition, as shown in FIG. 3, additional compressive force may be introduced to the lower flange of the composite beam constructed in the field using the branch point, but this method requires additional cost when installing the branch point, and the use of the lower space is restricted due to the branch point installation. Will receive. For example, when applied to bridge construction, it prevents traffic flow of bridge spaces due to the ascending facilities of branch points, and it prevents the flow of flowing water in rivers, and when it is applied to buildings, Parallel work is disturbed and this requires additional air.

The present invention improves the above problems and has economical steel cross section than conventional prestressed composite beams, avoids the cumbersome process of tensioning additional tension members, or the inconvenience caused by the installation and operation of branches at the construction site. This paper proposes a prestressed composite beam and its manufacturing method using compressed reinforcement materials that are economical and easy to install.

This invention is applied to the casing concrete of the lower flange by assembling the compressive stiffener to the upper flange to compensate for the welding residual stress and the compressive stress loss of the lower casing concrete due to the concrete creep deformation and dry shrinkage. It is an object of the present invention to provide a prestressed composite beam using a compressive reinforcement for introducing an additional compressive force and a manufacturing method thereof. The present invention also provides an additional compressive force to the lower casing concrete of a composite beam so that tension is not generated in the lower casing concrete with an economical steel cross section. By doing so, it is possible to avoid the conventional tension installation process of the additional tension material or the installation process of the branch point at the construction site, thereby aiming at the ease of construction and at the same time to improve the economic loss due to the expansion of the conventional steel cross section.

Figure 1 is a conventional prestressed composite beam manufacturing process diagram

Figure 2 is a principle diagram for introducing additional compressive stress by prestressing the tension material in the conventional prestressed composite beam

Figure 3 is a manufacturing process diagram of prestressed composite beam using a conventional branch point Figure 4 is a prestressed composite beam manufacturing step using a compressive stiffener according to the present invention Figure 5 is a stress-strain diagram appearing in the prestressed composite beam according to the present invention

<Description of Drawing Major Symbols>

10: compression reinforcement 20: lower flange 30: upper flange 40: lower casing concrete

The conventional prestressed composite beam has been widely constructed so far because of advantages such as quickness of construction, high moldability, material reduction, and improvement of fatigue strength. The conventional prestressed composite beam is manufactured in the center of the steel I-beam as shown in Fig. 1 (a) so that the center rises, and as shown in Fig. 1 (b), the loads P and P are applied to be bent downward in the elastic range as shown in Fig. 1 (b). As shown in (c), when the casing concrete 40 surrounding the lower flange of the steel is poured and the load is removed as shown in FIG. 1 (d), the compressive force is introduced into the lower casing concrete 40 as the restoring force of the I-shaped steel.

This compressive force is intended to reduce the tensile stress due to dead and live loads. However, this manufacturing method is to reduce the compressive stress due to the welding residual stress and the concrete creep deformation and drying shrinkage during the curing process of the lower casing concrete (40).

In order to compensate for the reduced compressive force, the conventional prestressed composite beam needed to enlarge the steel section. That is, the conventional prestressed composite beam is to enlarge the cross section of the steel to balance the upper and lower flanges in order to compensate for the reduction of the compressive force of the concrete in the steel fabrication of Figure 1 (a), as a result of the enlarged part of The cross section of the steel becomes an unnecessary part. Also, as shown in FIG. 2, a method of additionally introducing a lost compressive stress using a tension PC-PC is used, but this method is cumbersome in the manufacturing process, and is used to tension the tension material. The additional process cost and the combination of the two methods of introducing prestressing force complicate the structure of the composite beam.

Alternatively, as shown in FIG. 3, the prestressed composite beam fabricated in the same process as in FIG. 1 is raised by installing a branch point as shown in FIG. 3 (a), and then the upper casing concrete and the abdominal concrete as shown in FIG. After pour curing and remove the branch point as shown in Figure 3 (c) additional compressive force is introduced to the lower casing concrete. However, this method requires an additional cost to install branch points at the site of the composite beam, and when branch points are installed, the use of the lower space is impeded. When it is applied to buildings, parallel work is hindered by the installation of branches, which causes delays in the process.

As such, in the conventional method, the cross section of steel, an additional tensioning member, or a branch point are installed to compensate for the compressive force loss, which is a disadvantage of the conventional prestressed composite beam. The process is performed as described above. , Drawbacks such as complicating the cost, answering additional costs, impeding the use of subspaces, and prolonging air.

The present invention is to solve the above-mentioned shortcomings, and to compensate for the compressive stress loss of the composite beam lower casing concrete that occurs during the production of conventional prestressed composite beams using a compressive reinforcement. In relation to this, when applying the force to apply prestressing force, the equilibrium state of the upper and lower flanges is unnecessary, and only the steel for introducing the compressive stress of the lower casing concrete is assembled to the upper flange as the compressive stiffener, which is very economical and effective. The compressive stress of the lower flange casing concrete is to be compensated for. In FIG. 4, a prestress composite beam manufacturing method using the present invention compressive stiffener was used.

As shown in FIG. 4 (a), the I-shaped steel is made to rise upward and mounted at both ends. Then, as shown in FIG. 4 (b), the load is applied to the lower flange 20 according to the bending force by applying the loads P1 and P1 within the elastic range. do. In this state, as shown in Fig. 4 (c) is poured the lower casing concrete 40 surrounding the wrapped in the lower flange 20 is cured. Next, as shown in Figure 4 (d) to remove the load P1, P1 by the compressive stress is introduced into the lower casing concrete 40 as a restoring force of the I-shaped steel. At this time, the welding residual stress and the creep deformation and the dry shrinkage force of the concrete act on the lower casing concrete 40, thereby reducing the compressive stress of the concrete 40 by a certain amount. In order to further introduce the reduced compressive stress, as shown in FIG. ) To the compression stiffener 10 by welding or the like to attach and assemble. Steel compression materials such as steel sheets are used as the compression reinforcing materials, and are assembled in the area of the center 1 / 2L or more of the upper flange. After assembling the compressive stiffener 10 and removing the loads P2 and P2 as shown in FIG. 4 (f), the compressive stiffener 10 resists against dead load and live load acting downward, thereby introducing additional compressive force to the lower casing concrete 40. do.

As such, the present invention can be replaced with the need for the expansion of the steel cross section, which is a disadvantage of the prestressed composite beam, the assembly of the compressive stiffener 10, avoiding the uncomfortable and expensive additional tension member installation and tensioning process, the site of the composite beam Since the compression reinforcing material 10 is assembled before construction, all the problems such as inconvenience caused by the conventional branch point installation, additional cost burden, inconvenience of using the space for teaching, etc. are solved at once. Installation is not carried out as an additional process, but the compression stiffener installation process is inserted into the sequential process in the process, and the assembly process of the compressed stiffener can be carried out at low cost. Therefore, this invention can significantly reduce the construction cost compared to the conventional prestressed composite beam construction process. Hereinafter, the present invention will be described according to the stress-strain diagram shown in FIG. Since the lower flange of I-shaped steel in the state of 4 (a) has no strain, the stress-strained state is located at zero point in FIG. 5, and the lower flange stress becomes zero. As shown in FIG. 4 (b), when the load P1 is applied, the stress-strain state of the lower flange becomes point A, and the lower flange is in a tensile force σ sf state. As shown in Fig. 4 (c), after the lower casing concrete is poured and cured, the stress in the unreleased state of the I-shaped steel is the tensile force σsf, and the stress-strain state of the lower casing concrete is located at the point F of Fig. 5. C = 0. When the load P1 is removed and released as shown in Fig. 4 (d), the stress-strain state of the lower flange of the I-shaped steel is located at point B in Fig. 5 due to the compression resistance of the lower casing concrete. Therefore, the tensile force becomes σsp 'state, and the stress-strain state of the lower casing concrete is located at point E of FIG. 5, and the compressive force of the lower casing concrete is σcp'. As shown in Fig. 4 (e), the lower casing concrete compressive force reduced by the concrete creep dry shrinkage deformation is added by adding P2 to the lower casing concrete stress-strain state. After placing the compressive stiffener (10) and removing P2 after placing it at the point G, the lower casing concrete stress-strain state moves to the point H. At this time, the lower casing concrete is added as much as Δσc to σcp 'manufactured by the conventional method. The compressive force σcp is introduced and the lower flange tension decreases by Δσs to become σsp, which is advantageous when loading loads. However, I-shaped steel for applying prestressing force is manufactured by using the property of steel that is more compressive than tensile. In general, a 30m bridge composite beam has 20 to 25% cross-sectional deviation of the upper and lower flanges. When I-shaped steel is manufactured to have a cross-sectional deviation, compressive force is introduced into the lower casing concrete, and then, when the steel sheet with the cross-sectional deviation is used as the compressive reinforcing material, the compressive force reinforcement is about 4-7㎏ / ㎠ than the conventional manufacturing method of the same cross-sectional composite beam. Is done. This value corresponds to the effect of improving 12% to 22% of the lower casing concrete allowable tensile strength of 32㎏ / ㎠. This improvement is also a measure to ensure that the bottom casing crack is prevented. In addition, after installing the auxiliary material that can withstand the compressive force on the upper flange with a larger cross-sectional deviation, apply the load P1, and after placing and curing the lower casing concrete, remove the auxiliary material installed on the upper flange, and then apply the loaded reinforcement (P2). If you install 10) you can see more cone effect.

As described above, the present invention can significantly increase the tensile stress of the lower casing concrete by introducing a compressive force into the lower casing concrete using the compressive reinforcing material. Accordingly, the present invention provides a prestressed composite beam and a manufacturing method thereof, which can significantly reduce the steel consumption as compared with the conventional prestressed composite beam. In addition, the present invention is very easy to improve the process hassle and structural complexity compared to the conventional method of using an additional tension material to introduce additional compressive force, even if compared to the method of introducing an additional compressive force by the branch point It is possible to avoid the burden of the cost and inconvenience in using the lower space, there is an effect that can be very simple and easy to construct at low cost.

Claims (2)

In order to compensate for the reduction of the compressive stress of the lower casing concrete generated during the production of prestressed composite beam, the addition of the additional means for compressive stress, After the curing of the lower casing concrete of prestressed composite beam, after the curing is finished, the load is applied upward to add the compressive force to the lower casing concrete, and the compressive stiffener is attached to the center 1 / 2L of the upper flange while applying the upward load. Prestressed composite beam using compressive stiffeners that are assembled to introduce additional compressive force to the lower casing concrete. In adding the additional compressive stress introduction process in order to preserve the compressive stress reduction of the lower casing concrete generated during the production of prestressed composite beam, After placing the lower casing concrete of the prestressed composite beam, apply the load upwards to apply the additional compressive force to the lower casing concrete after curing, and attach the compressive stiffener to the center 1 / 2L of the upper flange while applying the upward load. Prestressed composite beam manufacturing method using a compressive stiffener consisting of the process of introducing additional compressive force to the lower casing concrete.