JPS647193B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an earthquake-resistant frame suitable for flexible structures such as high-rise buildings, which has high yield strength, is rich in toughness, and is less prone to cracking.

In order to withstand horizontal loads caused by earthquakes and typhoons, it is most effective and economical to install shear walls and braces at key points in a building, but ordinary reinforced concrete shear walls are constructed of columns and beams. Compared to a rigid frame, it has high rigidity and low toughness, in other words, it is hard and brittle, which is disadvantageous because the input that occurs to the building during an earthquake increases, making it more likely to break or fall. As shown, stress is excessively concentrated in the shear wall, and that part cannot follow the deformation and breaks first, which reduces the overall strength and causes the building to collapse.

On the other hand, with steel braces, unless large cross-sectional steel sections or steel pipes are used, the compression side braces will quickly buckle and become ineffective, and their rigidity is lower than that of reinforced concrete columns and beams, so reinforced concrete structures are Even when the maximum strength is exceeded, the tension in the braces is still low, and the concrete will crack and lose its overall strength before it reaches its full strength.

The present invention has been improved to overcome all of these drawbacks, and will be explained below with reference to Examples.

Figure 1 is an example of an earthquake-resistant frame using this shear wall. 1 is a precast reinforced concrete wall plate (hereinafter abbreviated as "PCa plate") that incorporates one or more high-strength steel braces 2. ). The brace 2 is a prestressed steel rod or prestressed steel wire that has a high tensile strength and yield point, a wide elastic deformation range, and easy introduction of tension, and is inserted into a thin-walled steel pipe sheath 2a or unbonded with an unbonded coating 2a. Keep tension possible by using tendons. or
The periphery of the PCa version, that is, the side surface 1a of the boundary with the left and right pillars
The upper and lower surfaces 1b of the boundaries between the walls and the beams are smooth or moderately rough surfaces, without using any shear bolts, shear reinforcing bars, dowels, etc. to transmit shear force, as seen in general precast shear walls. By leaving the concrete surface as it is, when the horizontal earthquake force causes the structure to deform, it will prevent shear failure while maintaining an appropriate frictional resistance between the columns and beams (hereinafter referred to as "frames"). Allow the person to slip without waking up.

This PCa version 1 is erected in a predetermined position, and concrete is poured around the four circumferences of the reinforced concrete or steel reinforced concrete frame, that is, the columns 3 on both sides, the lower beam or foundation beam 4, and the upper beam 5. Generally, the lower beam or foundation beam 4 is cast in advance at the same time as the lower frame, so in that case, as shown in Fig. 1, the lower part 2' of the brace 2 is connected to the column 3 by attaching the fixing fitting 2b to the lower end. They are buried in advance at the nodes of the lower beam 4, and after the PCa plate 1 is erected, the braces 2 and 2' are connected using a joint fitting 2j such as a coupler.

The upper part of the brace 2 is made by penetrating the node between the column 3 and the upper beam 5, which is located opposite the node between the column 3 and the lower beam 4, with a thin-walled steel pipe sheath or an unbonded coating 2a, and attaching the fixing fitting 2c to the upper end thereof. After the concrete has achieved the required strength, the upper end of the brace is pulled with a jack or the like to create tension and fix it. The tension at that time is such that the brace tension after setting is approximately 50% of its yield point load, and the initial tension of this brace causes the concrete of the PCa plate and surrounding columns and beams to , prestress will be introduced in the in-plane horizontal and vertical directions.
Note that this initial tension value is an example that is considered to be the most appropriate, and does not necessarily reflect the yield point load.
It is not limited to around 50%, but for example 30 to 40
% or even 60 to 70%, the present invention includes all such ranges.

In the case of a continuous shear wall, similar shear walls are stacked on the upper floor as shown in Figure 1, and in the case of a continuous span shear wall, a similar shear wall is installed continuously on the adjacent span.

The outline of this shear wall and the standard construction method have been described above.Next, we will analyze each effect and explain its characteristics and effects in detail.

() Regarding tension braces, a general shear wall with built-in X-shaped braces is shown in Figure 2a.
If a horizontal force P is applied to the frame from the state shown in Figure b, the brace will receive the compressive force and immediately buckle and become ineffective. The structural strength suddenly decreases and the restoring force is lost. Moreover, the buckled braces get caught out of plane and push out the cover concrete, causing it to fall off and destroy the wall concrete.

On the other hand, as shown in Figure 3c, the present shear wall, in which an initial tension To of about 50% of the yield point load Ty is applied to the high-strength steel braces, has the following characteristics.

(1) When a horizontal force P is applied to the frame, the tensile force on the extension side brace increases from the state shown in Figure 3a to the figure b, and becomes T1 = To + △T, whereas the contraction side brace The tensile force decreases and becomes T ₂ =T ₀ −T△. In this case, not only the increase in tensile force “+△T” on the extension side brace, but also the decrease in tension “−△T” on the contraction side brace, is as if the compression brace were being stretched and resisting at △. This contributes to the horizontal strength of the frame. In other words, since both braces work equally advantageously, the rigidity of the frame due to the braces is twice that of the case shown in Figure 2 where no initial tension is applied.In other words, the amount of deformation δ2 is 1/2 of δ1, so it is difficult to prevent earthquakes. The shaking of buildings caused by typhoons is halved.

(2) The axial force of the brace is 0 and Ty with T ₀ as the center.
Since it only moves up and down within the tension region between ≒T1max and compressive force is not applied to the contraction side brace, buckling does not occur, and the cover concrete will not be pushed out and the wall concrete will not be destroyed.

(3) Therefore, even if subjected to repeated horizontal loads due to earthquakes, the proof strength will not decrease and the restoring force will not be lost.

(4) Since the brace uses PC steel rods or PC stranded wires whose yield point load and tensile strength are several times higher than ordinary rigid materials, and whose Young's modulus is equal to or lower than that of ordinary steel, the initial tension can be reduced. Even if the range from 0 to εy in Figure 3C is divided into two, the elastic deformation region (ε0→0 and ε0→
εy) is wide, and even in the event of a large earthquake, the brace axial force can be kept within the positive elastic range (0 to εy).

() Effects of prestressed concrete (1) The initial tension of the braces tightens the columns, beams, and walls both vertically and horizontally, introducing prestress into the concrete, which increases the shear, tension, and bending strength of the columns and beams. and the shear strength of the wall is improved. In other words, the seismic strength of the frame increases by the difference between a general reinforced concrete structure and a prestressed reinforced concrete structure.

(2) As a result, cracks are less likely to occur in the concrete of walls and frames, and even if cracks do occur, their expansion and growth is suppressed, and once the external force is removed, the crack width closes and almost disappears. It has been confirmed through experiments that it can be restored to the point where it is invisible to the naked eye.

(3) Figures 4a and 4b represent the relationship between load P and deformation δ in a general reinforced concrete structure (hereinafter abbreviated as "RC") and this shear wall structure, respectively, in which the dotted line R indicates a rigid frame Dot-dashed line W
is the shear wall and experiment Σ is the total, and comparing the two is as follows.

In other words, a general RC shear wall, like W in Figure 4a, has high initial stiffness and shear strength, but is hard and brittle and rapidly loses its strength after the maximum strength. There is a discrepancy at the time when the strength is reached, and the maximum strength of both cannot be added.

In comparison, this shear wall delays and reduces the occurrence of cracks in the concrete by prestressing due to brace tension, as shown by W in Figure 4b, and the concrete shear wall reaches its maximum bearing capacity in the process of interstory deformation. By delaying the onset of the load and bringing it closer to the point at which the steel brace reaches its yield load, the maximum yield strength of both can be effectively synergized. This restraint prevents the strength from decreasing due to the expansion of the crack even after the maximum strength.
As shown in Figure b, when combined with Ramen R, the maximum yield strength of both can be added.

() Slip effect Conventionally, it was considered essential to integrate the PCa wall slab and cast-in-place frame, and a shear slipper was used at the interface between the two to completely transmit shear stress without causing relative displacement. At present, a considerable amount of shear reinforcing bars, dowels, etc. are painstakingly constructed, taking much time and expense, but this shear wall breaks from this common sense and completely eliminates such shear reinforcement, making it possible to prevent earthquake hydraulic power. In the event of a slippage, it is designed to naturally slip at the boundary surface. In other words, by changing our way of thinking, we can proactively create a number of new advantages that were not possible with conventional earthquake-resistant walls, such as the following.

(1) Since the initial stiffness is lower than that of a monolithic RC wall, the natural period of the building becomes longer and the input to the building during an earthquake becomes smaller.
In other words, it is a flexible shear wall similar to the shear walls with slits that are often used in conventional high-rise buildings, but unlike the shear walls with slits, it does not have the troublesome and unsightly slit in the center of the wall.
This is very convenient as you only need to slip it in an inconspicuous spot around the wall.

(2) According to the experimental results, there was almost no decrease in the strength even after the maximum strength was reached, and the strength was maintained until large inter-story deformation occurred, and a shear wall with a high plasticity ratio was obtained, thereby increasing the toughness of the building. be able to.

(3) Also, at the interface between the PCa wall area and the inner wall of the frame, the internal and external concrete is pressed against each other by the tightening force of the tension brace and rubs against each other while resisting the frictional force. Sometimes a large amount of energy is consumed. In other words, the energy that enters the building due to an earthquake can be effectively absorbed and damage can be prevented, but unlike conventional earthquake-resistant walls and braces, this energy absorption can be caused by cracks in the concrete, plastic deformation or buckling of the brace steel, etc. Since it does not leave behind any aftereffects and only causes slippage at the interface, it is advantageous in that it does not require repairs after an earthquake.

(4) However, since this slip also absorbs the structural deformation, no cracks occur in the central part of the PCa wall slab up to a large interlayer deformation angle, and experimental results show that many cracks occur in walls of general structures. Compared to a slip shear wall that would cause major damage, even at the final loading stage, only one diagonal crack occurred in the center of the wall, and there were almost no other cracks, and the damage to the wall was much smaller. It showed a remarkable feature.

In other words, even in the event of a fairly large earthquake, this shear wall will only suffer from slips around the wall that cannot be discerned unless you look closely, and small-scale local collapses at the wall corners, instead of cracks that occur within the wall. It turns out.

(5) Even if a slight crack occurs during the same earthquake, the width of the crack will be closed by the tightening force of the tension brace as mentioned above once the external earthquake force is removed, so all in all, it will be maintenance-free. It can be said to be a seismic wall.

(6) Also, from a construction perspective, there is no need for labor-intensive and costly shear bolts, shear reinforcing bars, or dowels between the PCa wall slab and the frame.
Since there is no need to do anything troublesome, it is extremely simple, easy, economical, and advantageous in terms of construction period.

() Summary We have described the characteristics and effects of each item above, but it is believed that if these items are combined and devised, they will have a synergistic effect and produce various new benefits. The main points are as follows.

(1) By incorporating this shear wall into the structural framework of a building or other building using high-strength, high-quality steel and concrete, it is possible to construct a strong, tenacious, highly accurate, and reliable frame.

(2) By appropriately selecting the concrete thickness of the shear wall, the amount of PC steel braces built into it, and the strength of the concrete and steel used, the initial tension of the braces and the resulting frame and PCa wall can be adjusted. It is possible to freely change the prestress amount of concrete slabs and the seismic horizontal force sharing ratio of shear wall concrete and steel braces, thereby increasing the strength and strength of the building as a whole.
It is possible to adjust the stiffness and toughness as desired. In other words, it is possible to design anything from a highly rigid, strength-oriented building to a tenacious, toughness-oriented building.As an extreme example, we can design an RC building with no concrete for shear walls or concrete for shear walls and frames. Columns/beams”＋
"PC steel tension brace" or "steel frame column/beam"
＋Flexible structures such as "PC steel tension braces" are also possible.

(3) As mentioned above, if this precast slip shear wall with built-in tension braces is effectively incorporated and properly designed, (i) the building will not sway easily and will be comfortable in the event of an earthquake or typhoon of the magnitude normally considered; (ii) Even if an unprecedented earthquake were to occur, compression buckling would not occur in the braces, and there would be almost no cracks in the concrete of the shear walls; Even if a leak occurs, it closes immediately and has a resilient force that prevents harmful damage to the building.
Safety is ensured and there are no repair costs.

(iii) Tension braces give the frame high horizontal strength, toughness, and appropriate rigidity, while precast concrete shear walls with slips around the periphery overcome the drawbacks of ordinary RC or PCa shear walls. It eliminates certain hardness and brittleness and exhibits moderate rigidity and high toughness, so by combining the two, a strong and durable building can be economically obtained.

[Brief explanation of drawings]

Figure 1 shows an example of an earthquake-resistant frame using this shear wall, and Figures 2 a and b show the shape of a general shear wall with built-in X-shaped braces and its deformation when subjected to horizontal loads, respectively. The relationship with the brace tension is shown in Figure 3a,
b and c are diagrams showing the initial state of this shear wall with initial tension applied to the built-in braces, the relationship between deformation and brace tension when subjected to horizontal loads, and the relationship between tension and strain of the brace material, respectively. Figures 4a and 4b show and compare the relationship between the load and deformation of the rigid frame and shear wall in a general reinforced concrete structure and this shear wall frame, respectively. 1... Precast reinforced concrete wall plate,
1a... Wall plate side surface, 1b... Wall plate top and bottom surface, 2...
Brace, 2'... Lower part of brace, 2a... Thin-walled steel pipe sheath or unbonded coating, 2b, 2c...
...Fixer fitting, 2j...Joint fitting, 3...Column, 4...
...Lower beam or foundation beam, 5...Upper beam.

Claims (1)

[Claims] 1. The surrounding area will be left with a smooth or moderately rough concrete surface so that it will slip when earthquake horizontal force is applied, and precast reinforced concrete wall slabs with built-in high-strength steel braces will be erected at designated locations, and the surrounding area will be Place concrete for reinforced concrete or steel-framed reinforced concrete columns and beams, and fix one end of the brace to the node of the column and beam.
After the required strength of the concrete has been achieved, the other end of the brace that has passed through the nodes of the opposing columns and beams is fixed under tension to give the brace an initial tension of approximately 50% of the yield point load, or more or less than that. The wall slab and the pillars around it. Precast with built-in tension braces that introduce prestress into the concrete of the beam. Slip shear wall.