RESULTS OF NUMERICAL ANALYSIS OF THE IMPACT OF SEISMIC LOADS ON MULTI-STORY REINFORCED CONCRETE FRAME BUILDINGS

ABSTRACT

When designing multi-story reinforced concrete frame buildings, it is important to select and implement the most technically efficient existing structural systems. The choice of the type that has the greatest reliability and the best economic indicators depends on the accuracy of the calculation and the quality of construction. The article considers four variants of structural systems of multi-story monolithic reinforced concrete frame buildings for construction in seismic areas, taking into account the requirements of current design standards. The most reliable structural system of the buildings under consideration was selected by comparing their resistance to seismic impacts based on the results of calculations performed using PC Lira 9.6.

Based on the results of the numerical experiments, recommendations are given for implementation in practice of designing multi-story monolithic reinforced concrete frame buildings constructed in seismically active areas. As a result, these structural systems make it possible to take into account planning solutions according to the wishes of customers not only in their design, but also in their construction and operation.

АННОТАЦИЯ

При проектировании многоэтажных железобетонных каркасных зданий важно выбрать и реализовать наиболее эффективные с технической точки зрения их существующие конструктивные системы. При этом выбор типа, который обладает наибольшей надежностью и наилучшими экономическими показателями, зависит от точности расчета и качества строительства. В статье рассмотрены четыре варианта конструктивных систем многоэтажных монолитных железобетонных каркасных зданий для строительства в сейсмических районах с учетом требований действующих норм проектирования. Выбор наиболее надежной конструктивной системы рассматриваемых зданий осуществлен сопоставлением их сопротивляемости сейсмическим воздействиям по результатам расчетов, выполненных с использованием ПК Лира 9.6.

По результатам проведенных численных экспериментов даны рекомендации для внедрения в практику проектирования многоэтажных монолитных железобетонных каркасных зданий, строящихся в сейсмически активных районах. В результате эти конструктивные системы позволяют учитывать планировочные решения по пожеланиям заказчиков не только при их проектировании, но и при строительстве и эксплуатации.

Keywords: reinforced concrete frame building, structural system, seismic resistance, numerical calculation, result, analysis, conclusion.

Ключевые слова: железобетонное каркасное здание, конструктивная система, сейсмостойкость, численный расчет, результат, анализ, вывод.

Introduction. Ensuring the seismic resistance of buildings of various structural systems has always been one of the main tasks in their design and construction in earthquake-prone areas. In this regard, the problem of developing anti-seismic measures is raised, which includes the development of a reliable structural system of buildings that have high technical and economic indicators and are capable of withstanding earthquakes of the expected intensity with minimal damage.

The construction of earthquake-resistant buildings and structures, taking into account the requirements of the present time, requires the implementation of their size-planning and design solutions based on the results of scientific research. For the construction of earthquake-resistant buildings and structures, the requirements of the current design documentation [1, 2, 3, 4] must be fully met by their individual elements (their connecting nodes) and themselves. Therefore, in order to build earthquake-resistant buildings, it is necessary to comply with the following rules established during their design:

- reduction of seismic loads through the use of lightweight building materials and structures;

- ensuring uniform distribution of loads and loads in buildings;

- the correct choice of a rational structural system of the building;

- placement of elements of buildings and structures on a solid and equally durable foundation;

- mitigation of the development of plastic deformations by increasing the load on structural elements.

Among the above rules, it is important to choose a rational structural system of the building. Knowing how to make the right choice provides the basis for ensuring a sound building design process.

Main part. Lira-PK 9.6 in numerical experiments to calculate the seismic impact of reinforced concrete frame systems selected on the topic of research and determine the optimal solution. the program was used.

As a research object, a multi-storey residential building with a reinforced concrete frame was systematically analyzed based on 4 different design solutions.

Option I. Frame building (without diaphragm) (clause 1b of Table 3.1 QMS 2.01.03-19), spatial monolithic reinforced concrete frame with a single frame node,

Option II. Frame building (with a diaphragm in 4 corners) (item 1b of Table 3.1, spatial monolithic reinforced concrete frame with one frame node,

Option III. If the elevator walls and diaphragm are located inside a frame building (item 1b of Table 3.1, spatial monolithic reinforced concrete frame with one frame node,

Option IV. Frame building (where the outer walls are filled with brick) (item 1-d of Table 3.1, frame that absorbs seismic effects (stone, block, brick).

One of the basic principles of earthquake resistance is the creation of a lightweight, flexible building structure, which in turn absorbs and absorbs seismic forces. To do this, it is necessary to select the right earthquake-resistant materials, that is, the concrete in reinforced concrete must have a certain strength and be reinforced with steel rods. For reinforcement of reinforced concrete structures, reinforcement should be used that meets the requirements of current standards [9]. In addition, for the use of reinforcement in seismically active areas, an indicator of the strength of its connection with concrete should be included [10], since it provides anchorage for the working reinforcement.       

The transverse dimension of the building is 19.8 m along axes 1-10, the longitudinal dimension is 33.2 m along axes A-I, the column spacing is 3.2; 4.0; 6.0; It consists of 6.4 m. The total height of the building is 33.5 m. The height of the basement is 4.35 m, the height of the first and upper floors is 3.5 m.

The city of Tashkent was chosen as the construction site; the seismicity of the construction site is 8 points. For columns and beams, concrete class is B30, for foundations and concrete walls - B25, working reinforcement - class A-400, transverse reinforcement - reinforcement class A-240 [2].

Structural systems used in residential and public buildings are divided into load-bearing wall, frame, volume-block, single-core and shell [5, 6, 7, 8]. Today, multi-story reinforced concrete frame buildings are used in many cases.

Loads acting on the building [3]:

Load 1. Specific gravity of the structure.

Load 2. Constant load.

Load 3. Long-term load. Payload (for a residential building)

Load 4. Short-term load. Snow and attic space

Load 5. Short-term load. (wind acting on the X axis)

Load 6. Short-term load. (wind acting along the Y axis)

Load 7. Seismic load acting along the X axis.

Load 8. Seismic load acting along the Y axis.

Option I. Frame building (without diaphragm)

Option III. If the walls and elevator diaphragm are located inside a frame building

Table 1.

Data obtained as a result of calculations

To analyze the frame systems under consideration, a symbol was introduced for these frame systems as follows:

Figure 5. Comparison diagram of the maximum seismic force (N, t) produced in the direction of X and Y-axis.

Figure 6. Comparison diagram of maximum seismic moment (Mu, t*m) generated in X and Y-axis direction

Figure 7. Comparison diagram of the maximum seismic transverse force (Qz, t) generated in the direction of X and Y-axis

Figure 8. A comparison diagram of the maximum displacements produced in the direction of the X and Y-axis

Figure 9. A diagram comparing the reinforcement percentage of the frame systems considered in the research topic

Analysis of results. Based on the results of numerous experiments conducted in the Lira-PK 9.6 program:

- The amount of longitudinal force N generated by seismic forces in the III-variant frame system: on average, it is 45% less than the I-variant frame system, 92% less than the II-variant frame system, and 21% on average compared to the IV-variant frame system found to be low;

- The amount of moment Mu generated by seismic forces in the III-variant frame system: on average, it is 16.0% larger than the I-variant frame system, 23.0% larger than the II-variant frame system, and 23.0% larger than the IV-variant frame system was found to be 39.0 percent larger on average;

- The amount of transverse force Qz generated by seismic forces in the III-variant frame system: on average, the I-variant is 10.0% larger than the frame system, the II-variant is 32.0% larger than the frame system, and the IV-variant is larger than the frame system and it was determined to be 41.0% larger on average.

- As a result of the influence of seismic forces, the values ​​of the displacements generated in the frame systems considered in the subject of the study in the III-variant frame system: on average, the I-variant is 30.0% less than the frame system, the II-variant is 4.0% less than the frame system, IV- it was determined that the option is 13.0 percent more than the frame system. However, it was found that the values ​​of the displacement caused by seismic forces in the frame system of the IV option exceeded the permissible displacement by 45 percent on average according to QMQ 2.01.03-19 [1].

- The percentage of reinforcement in the columns and beams of the frame systems considered in the research topic is in the III-variant frame system: on average, it is 2 times less than the I-variant frame system, 37% less than the II-variant frame system, and 23% on average compared to the IV-variant frame system was found to be low.

Conclusion. According to the results of this number of experiments, compared to the rest of the frame systems, it was determined that the frame system with elevator walls and diaphragm placed inside the frame building is the most optimal structural solution in terms of seismic effects. It is recommended to use this frame system in the design and construction of multi-story frame buildings in seismic areas.

One of the main conditions for earthquake-resistant construction of multi-storey reinforced concrete monolithic frame buildings using an effective structural system is the use of materials of the required quality that meet current standards. In our opinion, the use of reinforced concrete structures with steel reinforcement, which has high adhesion strength to heavy concrete, structural expanded clay concrete and basalt fiber reinforced concrete using local materials, should be considered as earthquake-resistant materials . The main indicator of the successful use of these materials as part of load-bearing reinforced concrete structures is that they provide high adhesion strength to locally produced reinforcement, which has a periodic profile with a crescent-shaped surface [11]. With an increase in this indicator, the resistance of reinforced concrete structures to seismic influences increases, which is associated with an increase in the level of cracking and the possibility of the fullest use of the strength of concrete.

The use of high-strength concrete (compressive strength classes B40 and higher) creates the condition for reducing the dead weight of the structure and its cross-section. In addition, the basis for the widespread use of basalt fiber reinforced concrete in load-bearing reinforced concrete structures is that its tensile strength is higher than that of conventional concrete. For the widespread and successful use of basalt fiber reinforced concrete, there is currently a simple and rational technology for its preparation based on local materials and basalt fiber [ 11].

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