Application of energy dissipation and damping structure in the reinforcement of shear wall in concrete engineering

2.1 Detection of anti-vibration coefficient of the concrete shear wall

In this design, in order to ensure the effectiveness and pertinence of the reinforcement part, the anti-vibration coefficient of the concrete shear wall is first tested. The seismic evaluation of shear wall is a direct method to test the current use of shear wall, determine the feasibility of shear wall transformation scheme, and plan for the future use of the building. The existing seismic appraisal of a reinforced concrete structure needs to detect multiple seismic factors of the structure. The comprehensive seismic capacity analysis of the test results leads to the appraisal conclusions, including: the rationality of the overall layout of the structure, the concrete strength test, the mechanical properties of the reinforcement and the corrosion degree test, the component connection test, the component seismic bearing capacity test, etc. According to the current standard “standard for seismic evaluation of buildings” [11], the general steps for seismic evaluation of existing buildings are to check the original data of buildings, such as the calculation sheet of architectural design drawings and the completion acceptance documents. If the data are not complete, the buildings to be evaluated shall be surveyed on site. It is necessary to check whether the existing service conditions of the building are consistent with the design documents, the construction quality of the site survey, and the maintenance of the building, and find out the defects of the building in terms of earthquake resistance. According to the characteristics of the structural type of the building, the on-site inspection shall be carried out for the material strength, component reinforcement, and structural layout of the building. According to the test results and seismic bearing capacity analysis, the seismic evaluation report has to be made. If the appraised building conforms to the requirements of the standard for seismic evaluation of buildings, the subsequent service life of the building shall be stated and the handling method shall be proposed for the non-conformities. At present, there are many common methods to determine the anti-vibration coefficient of a shear wall. In order to ensure the feasibility of this design method, the method of comparing the advantages and disadvantages of the measurement method will be used to obtain the form suitable for concrete shear wall [12].

Through the above comparison results, in this design, the ultrasonic-rebound method is used to complete the wall anti-vibration test. In the process of reinforcement, the rebound instrument is used to deal with the shear wall in the project according to the above set detection steps. In order to effectively control the data in the detection and ensure its accuracy and operability, a special rebound instrument is selected to complete the work in this detection. The specific model of a rebound instrument is shown below (Figure 2).

Figure 2

Model and appearance of a rebound tester selected in the paper.

The anti-vibration coefficient of shear wall is tested by the above instrument. The evaluation of anti-vibration coefficient of existing buildings is based on the evaluation of anti-vibration measures and the calculation of anti-vibration bearing capacity. The identification of anti-vibration measures includes the arrangement of anti-lateral force members, abrupt change of stiffness distribution, identification of structural system, and strength detection of structural materials [13]. When the anti-vibration intensity is more than six degrees, it is necessary to check the anti-vibration bearing capacity, and at least check the anti-vibration bearing capacity in two directions of the main shaft. It is known that the strength of concrete is proportional to the elastic modulus when the type and proportion of concrete aggregate are fixed, while the propagation speed of wave in the medium is related to the elastic modulus and density, as shown in the following formula.

In the above formula, A is the design value of shear wall internal force, R is the design value of shear wall bearing capacity, and ∂ CE is the adjustment coefficient of shear wall anti-vibration. Through the above formula, the originally measured data are processed. The anti-vibration coefficient of shear wall is calculated by combining the processed data with ultrasonic method.

The ultrasonic method is used to measure the propagation time of the wave in the concrete medium by the method of sending and receiving two probes, then calculate its velocity, and determine the concrete strength by the numerical curve. The specific calculation process is as follows [14].

In the above formula, E _C is the dynamic modulus of elasticity, ρ is the density, and μ is the Poisson’s ratio. The specific value of shear wall strength V can be calculated by the above formula. It should be noted that when using the above formula to measure the measuring points, the measuring points of the shear wall should not be less than the average value of 10 pairs of speed, and the measuring points must avoid the reinforcement in the concrete, so as to avoid greatly affecting the measurement results. The anti-vibration coefficient of shear wall can be obtained from the above calculation results and the measured value of the rebound instrument. In this method, the rebound instrument and the ultrasonic instrument are used to work together to measure the rebound and wave velocity values of the same test piece. Then with the adjustment coefficient of different materials, the measurement results are substituted into the following formula to calculate the anti-vibration coefficient of the concrete shear wall of the test piece. The specific formula is as follows.

In the above formula, f ec c is the anti-vibration coefficient of shear wall, V _o is the ultrasonic velocity measurement, R _o is the rebound value of wall, and o , b , c is the concrete strength. In the process of strength measurement, the rebound value and sound velocity value should be measured before the ultrasonic test. Based on the layout of the test area, engineers shall select three ultrasonic test points in the test plane and then calculate the average value of the sound velocity according to the following formula.

In the above formula, V is the average value of ultrasonic wave, l measurement distance, and y 1 , y 2 , y 3 is the time value of three measurement points. The above formula is used to control the ultrasonic speed measurement.

2.2 Construction of a shear damping wall with energy dissipation structure

In this method design, the damper is used to complete the design of energy dissipation and damping structure of concrete buildings. According to the characteristics of concrete, dampers are selected to realize the energy dissipation and damping performance of shear walls. In order to ensure the effectiveness of reinforcement, a viscous damper is selected to complete the design. The viscous damper can be divided into fluid resistance type (hydraulic cylinder type) and shear resistance type according to the different damping methods of viscous materials. The shear resistance type can also be divided into (three-way) tubular viscous damper and viscous damping wall, as shown in the figure below (Figure 3) [15].

Figure 3

Classification of viscous dampers.

According to the above classification, the viscous damping wall is selected as the design basis of the energy dissipation and damping structure. Viscous fluid damper is mainly composed of steel, damping materials, and sealing materials. Due to the rustproof treatment of steel and the chemical stability of sealing materials, the durability of a viscous fluid damper depends on the durability of damping materials. A damping material is not easy to age, and there is almost no change during normal use: under the action of cyclic stress, the characteristics of a damping material do not change, and its fatigue resistance is good; a damping material is extremely stable for ozone and ultraviolet, and its weather resistance is good; a damping material does not undergo change when it is immersed in water, and its water resistance is excellent. Through the installation of dampers in shear wall joints, the energy dissipation and damping performance of shear wall is strengthened. The damper models selected in this paper are as follows (Figure 4).

Figure 4

Viscous damper.

The above dampers are used for energy dissipation and vibration reduction of shear walls. The location optimization of dampers is an important problem in energy dissipation design. Its purpose is to use the least number of dampers to make the structural system achieve the corresponding damping objectives or even a better damping effect. Therefore, the selection of optimization objectives becomes particularly important. At present, the common objective control functions are mainly the maximum interfloor displacement angle, floor lateral displacement, absolute acceleration, and their weighted combination of the structure. According to the characteristics of viscoelastic dampers, there are five kinds of damper optimization design methods with different objective control functions: Taking interlayer displacement as control function; taking control force as control function; taking interlayer displacement and floor lateral displacement as control function; taking interlayer displacement and top floor displacement as control function; and taking vibration mode as control function. According to the relevant characteristics of concrete shear wall, in this design, interlayer displacement and top floor displacement are selected as the control function in the design scheme of the damper. According to the given different damping, the optimal damping is the optimal configuration when the optimal control effect is obtained; through genetic algorithm, the optimal damping is sought to reduce the total damping when the seismic performance of the structure is basically the same. Based on the theory of structural control, the optimal position with the control force as the objective is studied from the two criteria of “safety” and “comfort”. It is concluded that the optimal position is at the maximum displacement of the first mode when the variance of the control force and the variance of the structural response are the minimum.

According to the measured anti-vibration coefficient of shear wall, the damping coefficient of damper is set and applied to the reinforcement of shear wall. In this design, the Maxwell model is used to set the damping coefficient of damping wall [16], which is a more accurate mechanical calculation model expressed by the continuity of pure damping element and damper’s own stiffness. In this model, the damper has a strong dependence on the frequency. In this model, if we define the damper’s own stiffness as a spring element, and its damping model can be made up of a pure damping element and a spring element in series, then the damping coefficient can be obtained through the data changes before and after the deformation of the pure damping element and the spring element. If the displacements of damping element [17] and spring element are ∂ 1 ( t ) and ∂ 2 ( t ) , respectively, the relationship can be expressed as follows:

The integration of the above two formulas is as follows:

In the above formula, F ∂ ( t ) is the output of the damper, Q o is the linear damping constant at zero frequency, P o is the stiffness coefficient of the damper itself, and ℑ is the relaxation time coefficient of the damper. Using the Fourier transform and Euler formula for the above formula, and making F ∂ ( ϖ ) = P o ( ϖ ) Q o ( ϖ ) , we can get the following expression of the complex Maxwell model:

If the above two formulas are combined, they are:

Through the calculation of the above formula, the energy storage coefficient and energy dissipation coefficient of the shear wall after the damper is installed can be obtained. The formula can be expressed as follows [18]:

Considering the damper–damping relationship, there are:

Combining the above with the damper energy dissipation coefficient y 2 ( ϖ ) , the damping coefficient of the damping wall after the energy dissipation structure is:

The damping parameters of the damper used in the shear wall are controlled by the above formula and applied to the concrete shear wall.

2.3 Strengthening of the concrete shear wall

Compared with the traditional structural strengthening technology, this design uses the buckling brace reinforcement technology to install the buckling brace in the wall. The technology cannot damage the use function of the original structure, does not affect the size of the structure space, and is easy to maintain. Compared with the traditional reinforcement technology, the repair work after a major earthquake is more simple and recyclable. Buckling restrained brace is a new seismic method developed in recent decades. The essence of the anti-seismic technology of buckling brace is to set the buckling brace between the structural members. When an earthquake occurs, the buckling brace members yield before the main structure, which plays the role of energy dissipation and shock absorption, and can effectively reduce the damage of the main structure caused by the earthquake. As a result, the technology of buckling proof brace has become the main direction of building reinforcement. In this project, it is difficult to ensure the safety of the structure under a strong earthquake. The structure with buckling proof support has a great energy consumption capacity due to the buckling proof support. According to the domestic and foreign engineering examples, the cost of a buckling proof support technology can be reduced by about 5–10% compared with the traditional reinforcement technology [19]. As it shows good economy, the project has adopted the buckling support technology for reinforcement. The setting of a buckling brace used in this design is as follows (Figure 5).

Figure 5

Design drawing of a buckling proof supporting apparatus.

In order to make the reinforcement part play a better role and put into use more quickly, the selection of reinforcement materials is also very important. In order to reduce the size and material use, high-strength steel can be used. Considering the bonding of the combination surface of reinforcement and the integrity of the reinforcement components, when selecting materials to make concrete, the raw materials with high strength, small shrinkage, and good bonding with the original components are used. In addition to adding dampers and buckling brace devices, the shear wall is strengthened by sticking steel. The load-carrying capacity of the members is enhanced by sticking the 2–6 mm thick steel sheet on the surface of the concrete structure with a certain adhesive strength [20]. The construction process of this reinforcement method is simple and generally used to strengthen the flexural and tensile members. The structural adhesive used has strict shear and tensile strength, which can combine the strength of steel plate and concrete as a whole to resist the load. The shear wall structure after sticking steel is as follows (Figure 6).

Figure 6

Results of shear wall reinforcement with steel. (a) Design results of sticking steel method. (b) Wall structure after pasting steel.

The glued steel plate and the coated structural adhesive are exposed to the air. If the anti-corrosion and maintenance measures are not carried out in time, the bearing capacity of the steel plate will be greatly reduced, and the structural adhesive will lose its adhesion. It is necessary to set the protective measures as general application of waterproof materials and apply 15–20 mm M15 cement mortar to complete the reinforcement process [21,22]. Combining the above settings with the energy dissipation structure, the design of a shear wall reinforcement method based on the energy dissipation structure is completed.

3.1 Experimental preparation

Considering that the viscous damper used in this paper is a velocity-dependent damper, and its normal working frequency is usually between 1 and 3 HZ, it is not allowed to use any general simulation experimental equipment or conduct any static test. It is better to use the dynamic loading test with a dynamic control system. Therefore, the simulation seismic vibration table is selected to add the seismic wave and sine wave to the concrete experimental sample. For the load test, the basic parameters of the vibration table are shown in the table below (Tables 1–3).

By using the above platform as the basic platform of this simulation experiment, through setting the relevant experimental instruments to connect with the platform, we need to complete the component work of the complete experimental platform. In this experiment, the effect of earthquake on the shear wall of a concrete structure is simulated by an electronic tensile instrument, and the instruments used in the experiment are as follows (Figure 7).

Figure 7

Electronic universal testing machine.

By using the above-mentioned instruments, the simulation experiments are carried out on the experimental specimens after the original reinforcement method and the design reinforcement method in this paper, and the seismic effects of the experimental specimens after the original method and the design method in this paper are compared.

3.2 Experimental specimen design

For the purpose of this experiment, the corresponding concrete shear wall model is made. The size and reinforcement of the test piece are determined according to the requirements of the “code for design of concrete structure reinforcement” and the “code for design of concrete structure,” combined with the conditions of test equipment in the simulation laboratory. The model test piece is composed of a base beam, wall, and loading beam. The height from the top of loading beam to the bottom of foundation beam is 1,500 mm. The height of loading beam is 200 mm, the height of base beam is 400 mm, the height of wall is 900 mm, the section length of wall limb is 800 mm, the thickness of unreinforced wall is 70 mm, and the total thickness of reinforced wall is 140 mm. The specific section size and reinforcement parameters of a shear wall model are as follows (Figure 8).

Figure 8

Experimental sample design results.

According to the above parameters as the design basis of the experimental samples, in order to ensure the uniformity of the experimental process, the concrete and steel bars used in the experiment are set to complete the design process of the shear wall on the basis of a certain proportion. The production processes are: steel processing, strain gauge pasting, steel binding, skeleton production, formwork installation, concrete pouring, specimen maintenance, reinforcement treatment, and reinforcement specimen maintenance. Each construction procedure shall be carried out in strict accordance with the code for construction of concrete structures (GB50666-2011), so as to ensure the quality of test pieces. The concrete proportions are as follows.

Due to the limited experimental conditions, in the process of the experiment, C35 concrete strength material is used as the basic part of the experimental sample, and the proportion set above is used to complete the production of the experimental sample. In this experiment, the number of simulated earthquake intensity experiments is set to 30, and the intensity of each earthquake increases by 5% compared with the previous experiment. The displacements of the experimental specimen after using the design method and the original structure method are compared.

The parameters of seismic simulation are designed as follows: the shear wall load is 2.5 kn/m², the seismic grade of shear wall is grade 8, the peak value of basic seismic acceleration is 0.2 g, and the characteristic period is 0.45 s.

3.3 Analysis of experimental results

According to the above test settings, the displacement data of the strengthened test pieces are obtained from the structural laboratory, and the comparison results between the proposed method and the reference [5] method are shown in Table 4.

According to the above test data, the reinforcement effect of the proposed method is obviously better than that of the reference [5]. In the above table, the displacement data of the specimen strengthened by the two methods will be reflected in detail. The data show that the floor shear force of the structure with damping is significantly smaller than that before use; when the damper is set in the middle, the displacement value is significantly smaller than the displacement distance of the reference [5] method. The displacement difference between the reference [5] method and the proposed method is obvious. When the seismic simulation level is the same, the displacement distance of the designed method is shorter than that of the reference [5]. At the same time, in the test process of reference [5], the crack appeared earlier, the crack developed faster, the width was larger, and the penetration was earlier. But because the energy dissipation structure can effectively restrain the development of the original wall concrete inclined cracks and avoid the premature fracture of the concrete inclined cracks, the development trend of the cracks in the test pieces designed in this paper is obviously slowed down, and the number and width of the concrete damage are reduced, which shows that the reinforcement method of energy dissipation structure shear wall can improve the seismic performance of the shear wall to a certain extent. This paper slows down the development speed of time cracks after reinforcement according to the design method and reduces the number and width of main cracks. The results show that the damper reinforcement can restrain the development of cracks, and the ductility of the wall is larger than that of the single reinforcement. Most of the cracks in shear wall specimens start from the two sides of the wall and develop into inclined cracks, which are basically concentrated in the middle and lower part of the wall, and the concrete is crushed at the bottom. According to the development process and failure characteristics of the cracks in the test pieces, it is suggested to take corresponding structural measures for the middle and lower part of the wall in the process of reinforcement. In conclusion, this design method is superior to the reference [5] design method.