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Literature Review I. Characteristics and future development of RC Frame Structures1. Features and advantages of frame structure:Today thereinforced concrete is one of the most widely used modern building materials, used in big quantities all over the world. We can cast the fresh concrete into almost any shape which is a very significant advantage of this material. however, its limited tension resistance prevented its wide use in building construction. To overcome this weakness, steel bars are embedded in concrete to form a composite material called reinforced concrete. The worldwide use of reinforced concrete construction stems from the wide availability of reinforcing steel as well as the concrete ingredients. Unlike steel, concrete production does not require expensive manufacturing mills. Concrete construction, does, however, require a certain level of technology, expertise, and workmanship, particularly in the field during construction. [1]Reinforced concrete (RC) frames consist of horizontal elements (beams) and vertical elements (columns) connected by rigid joints. These structures are cast monolithically - that is, beams and columns are cast in a single operation in order to act in unison. RC frames provide resistance to both gravity and lateral loads through bending in beams and columns. These structures have the following advantages: [2]1. Speedy construction due to simplicity in geometry, because they consist of only columns and beams or partially by the floor slab as main structural elements.2. Very rigid and stable: able to resist tremendous vertical (dead loads) and lateral loads (wind loads).3. Reduced dead load: absence of thick shear walls.4. Roofed over at an earlier stage: every floor slab being finished becomes a cover to protect the lower floors from sun and rain.5. Flexible utilization of space.6. Off-site preparation possible: especially for prefabricated construction using precast concrete or structural steel elements.7. Easy to design structurally including computer design , again due to its simple geometry.Reinforced concrete structures in China are the most commonly used structural types of multilayer frames. In recent years, the reinforced concrete multilayer frame structure around the world has developed rapidly and has been used a lot. [3]2.RC Frame structure development trend Nowadays the construction industry is developing fast along with the gradual increase ofmulti-story and high-rise buildings. Reinforced concrete frame structure is its main form. Although its steel and cement use are relatively large and the cost is higher than that of hybrid structure, but the beam and columns have very good load bearing. The wall only functions as a partition and enclosure. Partition brings flexibility for the size of rooms, door and windows. People can make full use of the space according to their preferences, meeting different requirements of users in use. Therefore, frame structure houses are more and more popular. The frame structure is a load-bearing system composed of beams and columns. The main beam, columns and foundation form a plane frame, and each plane frame is connected by a connecting beam to form a frame system. [4]The biggest feature of the frame structure is that there is a clear division of the loads between load-bearing members and secondary members. The internal and external walls of the building are very flexible and have a wide range of applications. Although this structural form appeared earlier, it did not develop rapidly until the emergence of steel and reinforced concrete. According to the direction of the frame arrangement, the frame system can be divided into three types: horizontal arrangement, vertical arrangement, and vertical and horizontal arrangement. The horizontal arrangement is the transverse arrangement of the main beam along the building, and the floor and connecting beams are arranged longitudinally. It has the advantage of good lateral stiffness of the structure, and it is actually used more. The longitudinal arrangement is the opposite of the horizontal arrangement, the lateral stiffness is poor, and the application is less. The vertical and horizontal arrangement is a load-bearing frame in both the vertical and horizontal directions of the building. [5]II. Design and calculation method of RC frame structure1. Frame calculation methodThe procedure for design of an RC frame structure (building) depends on the type of the building, its number of stories and complexity and will be done in a few steps. First the architectural drawing should be completed, structural system finalized and size of the structural members be decided then we can start the design. The structural arrangements of a building is chosen in a way as to make it efficient in resisting vertical as well as horizontal loads due to earthquake. The span of slabs and thickness of slabs are chosen based on design code and slab panels, floor beams, and columns, are all marked and numbered on the architectural plans. [6]Load analysis: the loading intensity of slab is calculated while we take intoaccount the dead load of the slab, finish plaster, etc. including partitions and the live load expected on each floor, depending on the usage of the floor or roof. The linear loading of beams, columns, walls, parapet. [7]Preliminary Sizes of structural members: Before proceeding for load calculation preliminary sizes of slabs, beams, the floor height is 3.3m, the foundation burial depth is 4.0m, the foundation height is 0.8m, and the indoor and outdoor height difference 0. 45m. According to Article 6.1.2 of the of the project in the 8-degree earthquake zone is Grade II.。
[9]The designer calculates the three-story frame house, and the height of the first floor is 3.35m, it is assumed that the frame house is embedded at the top surface of the foundation tension beam at 0.05m. Obviously, it is inappropriate to choose such a calculation diagram. Because, firstly, the tension beams designed according to the structure cannot balance the column footing moment. Secondly, the Code for Design of Concrete Structures (GB50010. 2002 Article 7.3.11 stipulates that the height of the bottom pillar of the frame structure should be from the top of the foundation to the height of the top surface of the first floor. Engineering design experience shows that such a frame structure should be analyzed and calculated on the basis of 4 layers, that is, the foundation beam layer is input as layer l. If there is a load acting on the beam, the load should be input together. In this way, the first layer height for calculating the shear force is Hl = 4.8-0.05 = 3.15m, the height of layer 2 is 3.35m, and the height of layers 3 and 4 is 3.3m. According to the "Seismic Code" Article 6.2.3, the design value of the bending moment of the foot of the bottom column of the frame column shall be multiplied by the increase factor of 1. 25. When a beam layer is set, in general, it is necessary to compare the reinforcement of the bottom column by the top of the foundation. [8] 2.Frame load-bearing scheme2.1 Frame load-bearing scheme selectionThe shape of the frame structure should be simple and regular, so that each part is evenly symmetrical, reducing the possibility of twisting the structure, controlling the aspect ratio of the structure to reduce side shifts under horizontal loads, and making uniform the column grid and floor height as much as possible to reduce component types and simplify design and construction. The multi-layer frame structure is very flexible in terms of the plane layout. The frame structure is divided into the following three categories according to the load bearing method:(1) The load-bearing scheme of the horizontal frame: uses the frame beam as the main beam of the floor, and the floor load is mainly carried by the horizontal frame. Because the number of horizontal frames is often small, the main beam is arranged in the horizontal direction to enhance the lateral stiffness of the house. At the same time, the arrangement of the main beam along the transverse direction is also beneficial to the ventilation and lighting of the building. However, due to the large cross-section size of the main beam, when the house requires a large space, the headroom is small, and it is not conducive to the layout of the longitudinal pipes. [10](2) The longitudinal frame load bearing scheme uses the longitudinal beam of the frame as the main beam of the floor, and the floor load act on the longitudinal beam of frame. Due to the small cross-section size of the beam, it is conducive to the passage of equipment pipelines and can obtain a high indoor headroom. The lateral stiffness of the house is poor, and the depth scale is limited by the length of the prefabricated panel.(3) Longitudinal and horizontal frame hybrid bearing scheme: this arrangement is to arrange frame beams as the main beam of the floor in both directions, and the floor load is shared by both the longitudinal and transverse frame beams. (i.e. two-way slab).2.2 Frame beam and column arrangement principleThe layout of the frame column network must be considered from the four aspects of meeting the production process requirements, meeting the building plane requirements, making the structure reasonable, and facilitating construction. Columns are generally set at the intersection of the building's vertical and horizontal axes to reduce the influence of the column network on the use of the building. The column network is also related to the beam span. The large size of the column network can obtain a large space, but it will increase the beam and column section size. It should be considered in combination with the needs of the building and the structural cost. In the layout of the column network, consideration should be given to making the internal force distribution of the structure uniform and reasonable under the vertical load, and the strength of each component material can be fully utilized. At the same time, it should be as convenient as possible, speed up the construction progress, and reduce the project cost. As previously mentioned RC frames are roughly divided into three categories: horizontal frames, vertical frames, and vertical and horizontal frames. Horizontal frame: refers to the main beam of the frame which is arranged horizontally, and the connecting beam is arranged longitudinally; this frame arrangement is helpful to improve the lateral stiffness of the building, and it is also beneficial to daylighting. Longitudinal frame: refers to the vertical arrangement of the main beam of the frame, so the height of the beam is small, the pipelines are conveniently arranged, and a large headroom is obtained. Vertical and horizontal frame: generally used in the case of prefabricated floor covering. Arrangement principle: easy calculation, reasonable force transmission path, meeting the relevant requirements of the building, and considering the manufacturing process of some components. [11]3. Selection of frame beam-column sectionFrame beam section size: The frame beam section size should be determined based on a number of factors such as the size of the vertical load, the span of the beam, the space between the frames, whether to consider the requirements of seismic fortification, and the strength of the selected concrete material. In general, the cross-sectional size of a frame beam can be estimated by referring to the bending member as follows: beam height h = (1/8 ～ 1/12) l, where l is the span of the beam. Beam width b = (1/2 ～ 1/3) h. In an earthquake-resistant structure, the beam section width should not be less than 200mm, the aspect ratio of the beam section should not be greater than 4, and the ratio of the beam span to the section height should not be less than 4. [12]Frame column cross-section dimensions: The cross-sectional form of frame columns is usually square and rectangular. The width and height of the cross section of the column are generally taken from 1/15 to 1/20 of the layer height, and at the same time,l0 is the calculated length of the column. In multi-storey buildings, the width and height of the frame column section should not be less than 300mm; in high-rise buildings, the height of the frame column section should not be less than 400mm and the width should not be less than 350mm. The ratio of the height of the cross section of the column to the width is 1-2. The ratio of the column clear height to the section height should be greater than 4. In order to reduce the types of components and simplify the construction, the cross-section of columns in multi-storey buildings should not be changed along the height of the house.In the calculation, it should also be noted that the cross-sectional dimensions of the frame columns should comply with the requirements for the shear compression ratio, shear span ratio, and axial compression ratio (limit values of the specification). If the requirements are not met, the cross-sectional dimensions should be adjusted at any time to ensure the ductility of the column. In seismic, design Column cross-section size is mainly controlled by slenderness ratio limit。
[13]4. Design of Stairs Staircase is part of the secondary system of structures and it is one of the essential parts of the building because of its functional importance. Staircases not only serve better in case of an emergency like fire but also provides stiffness for the building. [14]The traditional slab staircase design method ignores the adverse effect of the staircase on the seismic design of the main structure, that is, when the structure calculation does not consider the staircase, the overall stiffness of the structure will be reduced, the maximum floor displacement, the floor displacement angle will increase, the period will increase, the floor Shear force, overturning bending moment reduction sliding bearing staircase design form is similar to the floor displacement, period, floor shear force, and overturning bending moment without considering the stairs. When the staircase participates in the overall calculation of the structure, it will cause the overall stiffness of the structure to increase, the maximum floor displacement to be reduced, the displacement angle and period between the floors to be reduced, and the floor shear and overturning bending moments to be increased. This shows that the staircase is not considered in the calculation of the structure, and the adverse effects of the staircase on the structure will be ignored, which will bury hidden dangers for the earthquake resistance of the structure. Therefore, when the influence of the frame stairwell on the structural calculation is not considered, a sliding support should be arranged in the stairwell to reduce the adverse effect of the staircase on the seismic resistance of the structure. [15]5. Measures to strengthen short columnsFrame structure staircases are usually provided with ladder columns, but the ladder columns will form a short column effect. The main method to solve this problem is to strengthen the structural measures of short columns: during the construction of the project, the ceiling may need to be suspended or other decoration. In order to save costs, Party A often requires that the walls be filled between the columns, or the door or window openings are arbitrarily opened on the wall. This often causes short columns. Due to the large stiffness of the short column, it absorbs earthquake action and causes it to be sheared. When the shear strength of concrete is insufficient, cross cracks and brittle fractures will occur, which will cause damage or even collapse of buildings or structures. Therefore, the following measures should be taken in the design: reduce the floor constraints of the short columns as much as possible, such as reducing the height of the connecting beams, using hinges between the beams and columns, etc .; increase the configuration of the stirrups, and the spacing of the stirrups in the range of the short columns should not be greater than 100mm , The column's longitudinal steel bar spacing is ≤150mm; adopt good stirrup type, such as spiral stirrup, composite spiral stirrup, double spiral stirrup, etc. [16]III. Computer Modeling Design analysisCAD (Computer Aided Design)CAD software is one of the contemporary software used for drawing architectural plans, the software is convenient and easy to use. The CAD drawing has good precision, on the other hand we can store the data very conveniently. It also has the dimensional drawing functionality which is a bonus with very good drawing effect that can enable use to see more details of our drawing from three dimensions.1. What other software can be used for RC frame structure design and what are the characteristics?2. What role can BIM technology play in design?1. How to realize the failure mechanism of RC frame structure?Failure mechanism is one of the most important parts of the design of a frame structure, in order to design a durable and safe structure we should know the failure mechanism of the structure and design the building based on that knowledge. In order to have a correct structural analysis and design we have to carefully consider the contribution of floor slabs to the stiffness of floor slabs and bearing capacity of the beam, and also the floor out-plane stiffness should be taken into consideration. It is absolutely necessary to consider the beams and design them as T shaped.2. How is the effect of stairs on the internal force calculation of the overall structure considered?To answer this question we can say that, stairs in the building increase the rigidity of the frame structure, reduces the natural frequency and side shift of the structure, it also causes a significant change in theinternal force of most components. The effect of the stairs on the natural vibration period of the structure and the internal force of the components is mainly in the direction of the ladder. The influence on the direction of the vertical ladder run can be ignored; the plane layout of the stairs may change the rigidity center position of the structure, which has an impact on the torsional period of the structure; the overall effect of the stairs on the frame-shear wall structure is relatively small, which affects the shear force. The influence of the wallcan be ignored; when the stairwell is a frame, the surrounding members are greatly affected, the columns form short columns, and withstand large torsional effects; the stair plates and stair beams are also different from ordinary simply supported beams.References[1] A. R. J. a. Y. Y. Grider, Structural Concrete Design, Raton: CRC Press LLC, 1999. [2] J. C. R. H.Brown., Design of Reinforced Concrete 9th edition, 2014. [3] J. G. M. James K. Wight, Reinforced Concrete: Mechanics and Design. 5th Edition, Prentice Hall, 2008. [4] Concrete software solutions, "Structural Analysis of Reinforced Concrete Frames," 2018. [5] E. b. X. Xiuli, Design of concrete frame, Beijing: China Construction Industry Press, 2016. [6] J. B. T. a. C. W. Richard Liew, Multistory Frame Structures, Boca Raton: CRC Press LLC, 1999. [7] R. M. Dy, "Structural Design of Rcc Building Components,," Vols. vol. 232, no. M, , p. pp. 172. [8] Z. W. G. J. Edited by Dong Jun, Civil Engineering Major Graduation Design Guide-Building Construction Volume, Beijing: China Water Resources and Hydropower Press, 2002. [9] GB 50011-2010. Code for seismic design of buildings. [10] I. Ntroduction, "Comparative Study of Analysis and Design of R.C. and Steel Structures, .," Vols. vol. 6, no. 2, , pp. pp. 256267,, 2015. [11] e. o. S. Q. Liang Xingwen, Guidance for graduation design of civil engineering specialty, Beijing: Science Press, 2005. [12] C. Jichang., "Method for determining the cross-section dimensions of frame beams and columns," Shanxi Architecture, pp. 52-53, 2010. [13] GB 50010-2010. Code for design of concrete structures. [14] M. Z. M. S. A. M. a. A. B. M. Danish, "Effect of Staircase on Rc Frame," p. 1893, 2013. [15] L. N. W. H. Li Jin, "Analysis of the influence of stairs on the overall design of the structure," Value Engineering, pp. 115-117, 2016. [16] Y. W. F. 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Guoxing, Guide to graduation design of housing structure, Beijing: China Construction Industry Press, 2004. [26] A. B．S．Smith, Tall Building Structures Analysis and Design, 1999. [27] GB 50009-2012. Building Structure Load Specification. [28] GB 50007-2011. Code for design of building foundation. [29] GB50352-2005. Civil building design general principle. [30] GB / T 50104-2010. Architectural drawing standards.
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