Patent Application
20120151860
1. Field of the Invention
The invention in question, is a new design of ductile shear reinforced bar layout and it's application on reinforced concrete shear wall structures, and in particular to structures containing reinforced concrete which improves it's capacity to absorb seismic energy.
2. Description of the Prior Art
At 2:45 in the afternoon on May 12, 2008; the city of Sichuan in Mainland China had a strong earthquake registering a magnitude of 8. This caused nearly 70,000 casulties as well as hundreds of thousands of injuries. The earthquake caused approximately 216,000 buildings to collapse, including 6,898 education facilities. The destruction caused by the Wenchuan earthquake's has highlighted the lack of anti-seismic buildings, and the need for more effective anti-seismic building design. Through the occurrence of the earthquake in Sichuan, two problems were highlighted: insufficient anti-seismic building design and a lack of disaster prevention work. To prevent the level of destruction experienced after the Sichuan earthquake from happening again, disaster prevention design and the development of seismic resistant technology needs be studied.
Most buildings in Mainland China are constructed by reinforced concrete (RC), therefore the shear walls are also made from reinforced concrete (RC). According to post-disaster statistics, the factors which lead to the damage of houses and school buildings include: pillars that are too small, an inferior quality of concrete, a lack of main reinforced bars, insufficient force of the bonding reinforced bars on the pillars, bad joining of main reinforced bars, insufficient RC shear walls, and an insufficient amount of bonding reinforced bars at the joint parts of pillars, etc. This demonstrates that the prior design standard is not flexible enough to resist earthquakes. Therefore, the anti-vibration and reinforcement design should aim to improve this non-flexible behavior or to promote seismic capacity.
For low-rise buildings, the RC walls or RC shear walls may greatly improve the seismic capacities. When such buildings receive a horizontal load, such as a seismic force, the RC shear wall can withstand the shearing force so as to increase the effect of anti-earthquake. The RC shear wall is generally a square solid component or a rectangular solid member, which is much rigid in comparison to pillars and columns. Major seismic forces resisted by the traditional RC shear walls will often produce many giant diagonal cracks after absorbing the seismic tension. In traditional RC shear walls, it is inconvenient to arrange the reinforced bars in any direction other then horizontally or vertically. Since the direction of the largest shear stress of any point in the RC shear wall is dependent on different corresponding positions, the cracks in the RC shear wall cannot be effectively controlled. After earthquakes, the cracks in the RC shear wall are mostly diagonal; furthermore, the irregular vibrations from earthquake, the accelerations and directions of the seismic forces are capricious over time, and on top of that, the direction of a shear force is not constant. However, as previously mentioned, the domestic arrangement of the reinforced bars are mostly horizontal and vertical, which is convenient for applying in-situ but not for suppressing cracks with various directions.
Since RC shear walls are much stiffer than columns, RC shear walls are able to absorb most horizontal forces whilst columns can only absorb a few horizontal forces. While designing the RC shear wall, the dimensions of the columns can be decreased in order to save costs. However, in practice, the RC shear wall not only has the superior seismic capacity but also saves costs while in construction. The major application of the RC shear wall is an infilling wall to a connecting column that is disposed between elevators or an independent mount; and the RC shear force is much thicker than a general concrete wall, sometimes the most thickness is more than 50 cm. The other application is to dispose the RC shear wall in a column with a larger diameter. Nevertheless, the position to the RC shear wall may be disposed to a place which may not interfere the usage.
Damage to RC shear walls are usually brittle damage caused by seismic forces, which it makes obvious that its ductility is worse; owing mainly to the fact that most seismic forces are absorbed by the RC shear wall and delivered to a building above the ground. Thus the arrangement and application of the RC shear wall should be designed in detail and a torsional effect to buildings may be avoided in order to match with the characteristic of stiffness balance of a building and exert the functions of an RC shear wall.
The principles of earthquake-resistance are simple, regularity and symmetricallity. In many earthquakes, poor structural systems are the main factor. To improve such structural systems, the horizontal surfaces, vertical surfaces, and the delivering path of seismic forces, etc. should be focused so that stress concentration and torsional effect, may be prevented. For old buildings that are weak, the solution is to add vertical construction materials, such as RC shear walls, to resist horizontal forces. This also raises the lateral stiffness and strength of a high building, and it is the most economic way to reinforce inferior structural systems.
The stiffness of an RC shear wall is very large for the wall, capable of handling most seismic forces. Hence, a detailed design is required to prevent torsional effects which are caused by the uneven distributions of the horizontal surfaces or vertical surfaces of a building. Besides, in many earthquakes, the cracks damaging an RC shear wall are mostly in diagonal directions and are caused by brittle/shortness forces. On the other hand, reinforced bars of a general RC shear wall are arranged horizontally, which is convenient to build but not suitable for shear forces with variable directions; as a result, cracks with different directions are hardly controlled. Components of a force along a 45-degree direction is the largest for a shear force caused by earthquake, and a reinforced bar net with vertical and horizontal arrangement cannot effectively resist diagonal cracks. When an oblique tension stress is larger than the tensional strength of the concrete, oblique/diagonal cracks happen.
According to an ROC (Republic of China) patent number 585207, the characteristics of the prior shear wall are pre-casting shear wall and has a rectangle member formed by pouring concrete, a plurality of bonding reinforced bars are vertically disposed in the member, each bonding reinforced bar has a plurality of vertical reinforced bars, the bonding reinforced bars are intersected. Since vibrations from earthquake are irregular and the magnitudes and directions of the vibrations are variable with time, the changes of the magnitudes and directions may cause that the maximum shear stress to change over time. However, because the arrangements of the reinforced bars of the RC shear wall are mostly vertical and horizontal for the convenience of applying in-situ, it cannot adapt to the dynamic changes required for the maximum shear stress. Therefore the cracks of the RC shear wall are diagonal, as shown in
The inventor of the present invention has spent years to developing shear reinforced bar structures and applying them to shear walls made from ductile reinforced concrete so as to work out the deficiencies in prior designs.
The main objective of the present invention is to provide a ductile shear layout to reinforced concrete shear wall structures, which is better than the traditional RC shear walls. Because of the new arrangements of the shear reinforced bar, the ductility performance of RC structures is enhanced and the possibility of causing huge cracks decreases. Hence, the seismic capacity of the structure increases as well.
The secondary objective of the present invention is to provide the shear reinforced bar structure applied to the shear wall with ductile reinforced concrete so that different arrangements/figures of the shear reinforced bars are possible for different types of walls.
The shear reinforced bar structure includes many vertical reinforced bars, a plurality of horizontal reinforced bars, many connecting reinforced bars, a shear reinforced bar, and many reinforced bars, wherein the vertical reinforced bars and the horizontal reinforced bars are intersected to form a plane, then the shear reinforced bar structure and the reinforced bars are firmly disposed on the plane, two adjacent planes are connected by the connecting reinforced bars; continuously pouring concrete to the shear reinforced bar connected on the planes and then the shear reinforced bar structure being wrapped around by the concrete are to form the shear wall with the content of the reinforced concrete (RC). Due to irregular vibrations from earthquake, the surface of the wall may be cracked along the directions with larger shear forces which causes huge diagonal cracks. As a result, the seismic capacity of the structure is suddenly lost, which makes it vital, adding the shear reinforced bar structure which makes it capable of avoiding earlier cracks and promoting the flexibility and ability to anti-vibration.
Other features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings are incorporated in and constitute a part of this application and, together with the description, serve to explain the principles of the invention in general terms. Like numerals refer to like parts throughout the disclosure.
The objects, spirits, and advantages of the preferred embodiments of the present invention will be readily understood by the accompanying drawings and detailed descriptions, wherein:
The following preferred embodiments and figures will be described in detail so as to achieve aforesaid objects.
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The present invention can be in mass produced in a pre-casting factory in order to shorten the construction period and to promote a efficiency for rapidly building up an RC shear wall. This is beneficial to post-disaster rebuilding efforts, which can be completed efficiently, as well as meeting desired seismic building standards; so that people can obtain basic essential creature comforts as quickly as possible.
Earthquakes shake the ground, twist, rise and fall in ground movement. The movement and size of an earthquake can change at any moment. In the absence of vibrations, displacement to a structure may occur when cracks are happening, furthermore, if cracks continue to appear, total collapsation may be the next step. For an anti-earthquake building, the most common way is to add an RC shear wall to make the swing of the building smaller. The function of RC shear wall is to absorb the majority of vibration forces from earthquakes, so that the RC shear wall can be the first defense against earthquakes. After the earthquake, the failure mode of the RC shear wall is mostly represented by oblique cracks. Due to irregular vibrations from the earthquake, the amplitudes and directions of earthquake are variable over time. The changed amplitudes and directions of seismic force of earthquake means that the maximum shear stress also changes over time. Presently, the common way is to arrange the reinforced bars horizontally and vertically. This way is more convenient, but it is incapable of adapting to dynamic changes in demand for the maximum shear stress, as a result the cracks of the RC shear wall are diagonal.
Cracks of RC shear walls are mostly diagonal. The angles of the cracks are related to the ratio of the height and width of the RC shear wall, the detail bars disposed inside the RC shear wall and the amplitude of earthquake. To avoiding such diagonal/oblique cracks, the best way is to dispose reinforced bars that are vertical to the cracks. Then, circular bars are added into the RC shear wall. The circular bar is a spiral, a plurality of geometry polygons, a plurality of concentric circles, etc. in order to control the possibility of causing cracks.
Compare to prior designs, the ductile shear reinforced bar layout applied to reinforced concrete shear wall structures provided by the present invention has the advantages listed below:
Although the invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments that will be apparent to persons skilled in the art. This invention is, therefore, to be limited only as indicated by the scope of the appended claims
