JPS647192B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for installing concrete between the nodes of columns and beams of steel frame construction, or columns and beams of reinforced concrete construction, steel reinforced concrete construction, and precast reinforced concrete construction (hereinafter collectively referred to as "concrete columns and beams"). Approximately 1/2 of the yield stress is applied to steel braces built into reinforced concrete or precast reinforced concrete shear walls surrounded by columns and beams (hereinafter collectively referred to as "concrete shear walls"). By applying the initial tension with the necessary surplus left before the yield stress, it has high proof strength and excellent toughness, and prevents buckling of braces and damage of shear walls even when subjected to large horizontal loads due to earthquakes, typhoons, etc. The objective is to provide an economical, easy-to-construct, and rational frame that does not cause any damage.

To counter horizontal loads caused by earthquakes, wind, etc., it is effective to install braces between the nodes of columns and beams as shown in Figure 1a, but in general, braces are used between the nodes of columns, beams, etc. Compared to columns and beams, steel braces such as
When subjected to compressive loads, the contraction side braces immediately buckle under the compressive loads and become ineffective. Therefore, unless a section steel or steel pipe with a large cross section is used for the brace, perform structural calculations by ignoring the proof stress of the contraction side brace and assuming that only the tensile force of the extension side brace is effective. Generally, the cross section of the brace is determined and designed so as to have the tensile force T=P/cos θ. However, horizontal loads due to earthquakes and wind are dynamic loads that are applied repeatedly in positive and negative directions, so tension and compression are applied to the braces repeatedly as loads, and once the members are bent or locally deformed due to compression buckling. As shown in the history curve showing the relationship between load P and displacement δ in Figure 1C,
The strength of the frame will drop rapidly against repeated horizontal loads. The so-called "restoring force characteristics" are poor, making it difficult to effectively absorb earthquake energy, etc., and the "toughness" or tenacity of the building is low. Furthermore, as mentioned above, since only one brace is effective, the rigidity of the frame is low, and the building sways greatly due to earthquakes, wind, etc.

In addition to the same drawbacks as described above, this structure in which steel braces are built into concrete shear walls also has the following drawbacks. In other words, (a) Concrete is harder and more brittle than steel;
Although the initial rigidity is high, even slight deformation causes cracks to occur and the maximum yield strength is reached, and if the deformation progresses further, the cracks expand and the yield strength decreases rapidly. In comparison, steel braces have much lower rigidity, so the concrete shear wall will develop large cracks and collapse before it can deform enough to fully demonstrate its tensile strength.

(b) Also, when the steel brace buckles under compressive force, the force that tries to protrude out of the frame surface pushes out the cover concrete and causes it to fall off.

The present invention has been devised to eliminate all of the above-mentioned drawbacks, and will be explained in detail below with reference to the first invention.

Figure 2d is a graph showing the relationship between tensile stress T and strain (elongation) ε of steel brace materials.In this case, as shown in Figure 2a, both braces have a yield stress of 1/1 of the yield stress _Ty . An initial tension T ₀ of approximately 2 or more is given that leaves the necessary surplus strength up to the yield stress T _y . That is, this initial tension introduces compressive axial forces of T ₀ sin θ and T ₀ cos θ into the column and beam, respectively. When this frame receives a horizontal load P, as shown in Figure 2b, the tensile force on the extension side brace increases and becomes T ₁ = T ₀ + ΔT, whereas the tensile force on the contraction side brace decreases and becomes T ₂ = T ₀ −ΔT. The increase/decrease in the tensile force is ΔT=P/2×cosθ, which is 1/2 of the above T=P/cosθ, and not only the increase in the tensile force on the extension side brace but also the decrease in the tension on the contraction side brace ΔT , it can be seen that the compression brace contributes to the horizontal strength of the frame as if it were bulging at ΔT and resisting. Therefore, if we list the features and other features of this frame, it is as follows: (1) Since both braces work equally effectively, economical design is possible, and the rigidity of the frame is twice that of the case in Figure 1. The shaking of buildings caused by earthquakes and typhoons is halved.

(2) For earthquakes and typhoon loads that normally occur, the tensile forces T ₁ and T ₂ of the brace are designed to be below the yield stress T _y and within the range of elastic deformation. By designing so that ΔT≦T ₀ , that is, T ₂ =T ₀ −ΔT≧0, even under a huge horizontal load equivalent to an earthquake, no compressive force is applied to the contraction side brace and buckling is prevented. It doesn't happen.

(3) On the other hand, the tensile force T ₁ of the extension side brace may exceed the yield stress T _y at the maximum load mentioned above and enter a slight plastic deformation region, but even in that case, the tensile force T 1 of the extension side brace will continue to be higher than the yield stress and the yield strength will be increased. does not decrease, and when the external force is removed, the residual strain corresponding to the plastic deformation (elongation of the brace) occurs as shown by the dotted line in Figure 2 d.
, and return to the original state. This residual strain is very slight and does not affect anything else, but if you retighten just the stretched portion, it will be completely restored to its original state with the initial tension, and this work is easy. .

(4) The hysteresis curve showing the relationship between the load P and displacement δ on the structure due to repeated horizontal loading has a spindle shape as shown in Figure 2C, indicating that the structure can effectively absorb seismic energy and has excellent restoring force characteristics. I understand.

(5) In other words, if this braced structure is used, the building will not sway even in the event of an earthquake or typhoon that would normally be expected, and a comfortable living environment will be maintained, even if an unprecedented large earthquake were to occur. Since the brace does not undergo compression buckling and has a restoring force, it does not leave any damage to the building, ensuring safety and reducing repair costs. And since all the braces work effectively, it is durable, economical, and easy to install.

(6) It is an earthquake-resistant and wind-resistant structure that can be used in a wide range of applications, from super high-rise buildings to general medium- and low-rise buildings.

(7) Since no compressive force is applied to this brace, its cross-sectional shape can be freely chosen as long as it has the necessary cross-sectional area to withstand the tensile force, and any steel material can be used, and it can withstand tension. Materials other than steel may be used if available, but from a structural standpoint, PC steel rods and PC steel stranded wires (PC cables), which have high strength, a high yield point, a wide elastic deformation range, and easy to introduce tension, are suitable. It is considered to be optimal, well-designed, economical, and easy to use.

As an example, Fig. 3 shows a joint between a PC steel bar brace and a steel column/beam.

(8) Above we have described the case where braces are arranged in an X-shape within a unit frame of columns and beams as the most basic form, but in actual buildings, etc., the braces are multi-layered and multi-span. As shown in the framework diagram in the figure, braces can be arranged to connect the nodes of columns and beams through two layers or two spans, or more multilayers or multiple spans.

The second invention is one in which this steel brace is built into a shear wall made of reinforced concrete or precast reinforced concrete, and is basically the same as the first invention, and has the structure described in the first invention. Since it has all of the following characteristics, we will omit the explanation of these points, but furthermore, by cooperating with concrete shear walls, the following synergistic effects can be achieved.

(1) By introducing initial tension into the steel braces, prestress is applied to the concrete shear walls and concrete columns and beams in both vertical and horizontal directions within the frame plane, and the concrete shear walls are tightened strongly from all sides. Therefore, even if shear force or tensile/bending load is applied to the frame, cracks are unlikely to occur in the concrete, and the shear resistance of the concrete shear wall increases in proportion to the tightening and compressive force.

(2) The restraint delays and reduces the occurrence of cracks in concrete, delays the time at which concrete shear walls exhibit their maximum strength during the progress of interstory deformation, and delays the time at which steel braces reach their yield load. Since they can be brought close together, the maximum strength of both can be effectively synergized.

(3) Even after the concrete shear wall reaches its maximum strength, strong restraint from all four sides will prevent a sudden drop in strength due to crack expansion and crack separation.

(4) Since no compressive force is generated on the contraction side brace, the cover concrete will not be pushed out of the plane and cause failure due to the protrusion of the brace due to compression buckling.

(5) The improved performance of concrete shear wall structures surrounded by columns and beams can be seen as equivalent to the difference between prestressed reinforced concrete structures and ordinary reinforced concrete structures, and can be seen as preventing and reducing cracks, A wide range of improvements can be expected, ranging from increases in shear strength and bending strength to improvements in toughness and ultimate strength.

(6) The type, cross-sectional shape, and material of the brace are free as mentioned above, but in order to incorporate it into concrete columns/beams and earthquake-resistant walls, high-strength steel PC steel bars and PC steel stranded wires must be bonded and insulated. A suitable method is to bury an unbonded tendon covered with concrete, and then tension it after concrete is poured and the required strength is achieved to introduce tensile force into the brace.

(7) As mentioned above, in addition to the X-shaped arrangement of braces within the unit frame of columns and beams, multi-layer or multi-span through arrangement is also possible. They do not necessarily have to be connected to the nodes of columns and beams; for example, a diamond-shaped arrangement that connects the midpoint of the column height and beam span as shown in Figure 4a is effective. The reason for this is that when a concrete shear wall cracks and fails due to a large horizontal shear force, the surrounding columns and beams are generally pushed from the inner shear wall and bend outward, but inside the columns and beams Connecting points with braces and applying strong tension not only restricts the deformation of the columns and beams, but also tightens the concrete shear wall strongly both vertically and horizontally from the center of the four sides, introducing prestress, which prevents cracks. It is extremely effective in improving the performance of earthquake-resistant walls by increasing the shear strength and preventing damage. This is similar to how diamond-shaped diagonal hoops serve as shear reinforcement for columns.

This shear wall with built-in braces arranged in a rhombus pattern can be used alone, but it can also be easily used in multi-layer, multi-span structures, such as the framework shown in Figure 4b.

(8) There are other types of built-in braces, such as ∨ type, ∧ type, and combinations thereof, as shown in Figure 5 a, b, and c of the frame diagram, and K type and reverse K type as shown in Figure 6.
There are various combinations of types, and all of them improve the performance of concrete shear walls by introducing initial tension, so they can be used depending on each case.

[Brief explanation of the drawing]

Figures 1 a, b, and c show the shape of a general frame with steel braces arranged in an X shape, the relationship between deformation under horizontal load and brace tensile force, and hysteresis curves, and Figures 2 a, b , c, and d are the initial state of the frame of the present invention with initial tension applied to its steel braces, the relationship between deformation and brace tension when subjected to a horizontal load, the history curve, and the stress and stress of the brace material, respectively. FIG. 3 shows an example of a brace joint, FIGS. 4a and 4b show the shape of a frame in which braces are arranged in a diamond shape, and a frame diagram using the same. Figures 5 and 6 show schematic diagrams of other brace arrangements.

Claims (1)

[Scope of Claims] 1. A steel brace provided between the nodes of a column and a beam is provided with an initial tension that is approximately 1/2 or more of the yield stress and leaves a necessary surplus up to the yield stress, In addition, the cross-sectional strength of the brace, that is, the product of the yield stress of the brace steel and the cross-sectional area of the member, is determined by calculating the cross-sectional strength of the brace, that is, the product of the yield stress of the brace steel and the cross-sectional area of the member, at the time of the maximum horizontal load on the contraction side brace whose tension decreases from the initial tension when the frame receives a horizontal load due to an earthquake, etc. The brace structure is large enough not to generate compressive force. 2. Apply an initial tension in advance to the steel brace built into a shear wall of reinforced concrete or precast reinforced concrete surrounded by columns and beams that is approximately 1/2 or more of the yield stress and leaves the necessary surplus up to the yield stress. The cross-sectional strength of the brace, that is, the product of the yield stress of the brace steel and the cross-sectional area of the member, is the maximum on the contraction side brace where the tension decreases from the initial tension when the frame receives a horizontal load due to an earthquake, etc. A shear wall with built-in braces that is large enough not to generate compressive force even under horizontal loads.