Keywords

1 Introduction

The development of prefabricated building will become an inevitable way for the transformation and upgrading of the construction industry. However, in the process of development, assembly building also has its disadvantages, among which the grouting sleeve connection quality problem is the most prominent [1]. The primary problem of precast concrete structures is the connection between precast components such as beams, columns, plates and shear walls, which must be effectively integrated to ensure the safety, ease of use and durability of the structure under various load conditions [2] 53/5000.

Andrea Belleri et al. [3] (2012) showed through experimental research that grout steel sleeve is suitable for columnal-foundation connection in earthquake area. ZhengLu et al. [4] (2017) studied the seismic performance of prefabricated concrete columns with grouting sleeve joint. The test results show that the precast column has good energy dissipation capacity and stiffness degradation is slower than the cast-in-place column, and meets the requirements of interstorey displacement ratio during large earthquakes. GuoshanXu et al. [5] (2017) found that the assembled concrete shear wall sample was similar to the cast-in-place shear wall sample in terms of failure mode, interlayer displacement Angle, ultimate force, ductility and dissipated hysteretic energy. In this paper, ABAQUS is used to conduct numerical simulation of prefabricated concrete columns with defects under the action of low cyclic load, and the influence of size and location of grouting defects on the seismic performance of prefabricated concrete columns is analyzed.

2 Concrete Column Model

2.1 Column Size and Reinforcement

Figure 1 is the schematic diagram of this modeling model: The assembled concrete column consists of three parts: concrete base, concrete column body and loading column cap.

Fig. 1.
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Schematic diagram of size and reinforcement of prefabricated concrete column

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Fig. 2.
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Control diagram of specimen loading system

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2.2 Loading System

Two loads are applied during the experiment: axial pressure and horizontal thrust. The axial pressure belongs to the monotone static load and remains unchanged during the test after it is applied. In this experiment, the design value of axial compression ratio is 0.3, and the design value of compressive strength of C35 commercial concrete is 16.7 mpa. Therefore, the axial pressure of the specimen was 801.6 kN. The axial pressure of the specimen is loaded, and the axial force is slowly loaded to the predetermined design value. Thereafter, the axial pressure is kept unchanged during the test. The loading regime is shown in Fig. 2.

2.3 Specimen Number and Defect Setting

Four models are established this time. The defect Settings are shown in Table 1, and the naming rules are shown in Table 2.

Table 1. Defect settings
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Table 2. Naming rules of specimens
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3 Model

3.1 Reinforcing Steel Bar

The steel bar adopts an ideal elastic-plastic tripline model, in which the yield strength, ultimate strength, yield platform length and ultimate strain of the steel bar are taken from the Code for Design of Concrete Structures (GB50010-2010) [6].

3.2 Concrete

Concrete constitutive model adopts the concrete damage plastic model (CDP) of ABAQUS. See the detailed introduction. It should be noted that although stirrups are created in the finite element model in this paper, the Truss unit does not take into account the tangential action between stirrups and concrete. Therefore, in order to consider the restraint effect of stirrup on concrete in the core area of section, this paper adopts Mander constraint concrete constitutive model for concrete constrained by stirrup [7]. Peak strain and peak stress are calculated using the formula suggested by Dr. Hu Qi [8] of Tongji University.

3.3 Optimization of Grouting Sleeve in the Model

In this paper, the effect of grouting sleeve with end defects on seismic performance of assembled concrete column is studied. The key is how to deal with grouting sleeve and grouting defects. The former can not better simulate the mechanical behavior of the defective sleeve from tension to compression through the spring element, and the latter is easy to cause “over-constraint” and inconsistent with the actual force. Therefore, a more convenient and easy to operate method is adopted in this paper. The grouting sleeve connecting steel specimens are treated as equivalent steel bars, and the grouting defects are simulated by cutting off the corresponding steel bars.

4 Results Analysis

4.1 Seismic Performance of Concrete Columns with Different Anchorage Lengths

  1. (1)

    Load-displacement curve

Fig. 3.
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Hysteresis curve and skeleton curve of BM, 4D-D-1 and 5D-D-1 specimens

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Figure 3 shows the hysteretic curves and skeleton curves of BM, 4D-D-1 and 5D-D-1 specimens. By comparison, it is found that the bearing capacity of the positive and negative directions decreases when the grouting defects are located only on the side of the section of the stressed direction column, and the bearing capacity of the side with grouting defects decreases more obviously than when the grouting is full. The larger the defect is, the smaller the anchorage length is, the lower the bearing capacity is and the more obvious the stiffness degradation is. Table 3 lists the bearing capacity of each specimen at the characteristic point.

Table 3. Bearing capacity information of each specimen
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  1. (2)

    Ductility and deformation performance analysis

In this study, displacement ductility coefficient is expressed, which is defined as the ratio of the ultimate failure point displacement ∆f of the specimen to the yield displacement ∆y of the specimen.inflection point method is adopted for yield point and 85% peak load method is adopted for limit point.

Table 4. Ductility information of each specimen
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It can be seen from Table 4 that the positive direction of each specimen is dense, and the yield point, limit point displacement and ductility coefficient are close. In the negative direction, the limit displacement and displacement ductility coefficient decrease due to grouting defects.

  1. (3)

    Energy dissipation capacity analysis

Figure 4 shows the relationship between energy dissipation and displacement of prefabricated concrete column specimens connected with grouting sleeve under the condition of end defects of different anchoring lengths. It can be seen from the Fig. 4 that the energy dissipation of concrete specimens increases gradually with the increase of displacement. In the horizontal displacement is small, when the graph is less than or equal to 40 mm, basic no grouting defects of energy dissipation of the specimens, even stronger than when grouting full energy dissipation ability, but when more than 40 mm, namely, with the increase of horizontal displacement concrete column is affected by grouting defects is more and more big, the filling defect, the greater the energy dissipation of the specimens.

Fig. 4.
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Energy dissipation curves of 4D-D-1 and 5D-D-2 specimens

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4.2 Effect of Different Defect Locations on Seismic Performance of Concrete Columns

  1. (1)

    Load-displacement curve

Fig. 5.
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Hysteresis curve and skeleton curve of 5D-D-1 and 5D-D-2 specimens

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Figure 5 shows the hysteresis curves and skeleton curves of 5D-D-1 and 5D-D-2 specimens. It can be seen from the Fig. 5 that the location of grouting defects has a certain influence on the seismic performance of concrete columns when the number and size of defects are the same. The positive and negative directions of the hysteretic curves are symmetric when the grouting defects are found on both sides of the stress direction. Table 5 lists the bearing capacity of each specimen at the characteristic point.

Table 5. Bearing capacity information of each specimen
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  1. (1)

    Ductility and deformation performance analysis

Table 6. Ductility information of each specimen
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As can be seen from Table 6, when the number and size of defects are the same, for a certain side of the column section in the stress direction, when the number of grouting defects on this side is larger, the displacement ductility coefficient of this side is smaller and the ductility is worse.

  1. (3)

    Energy dissipation capacity analysis

Figure 6 shows the relationship between energy dissipation and displacement of prefabricated concrete column specimens connected with grouting sleeve at different positions with the same defects. The Fig. 6 shows that when the horizontal displacement is less than or equal to 40 mm, for the same displacement, flaws in the column on both sides of the energy dissipation ability is slightlyless than a full energy dissipation along the side of the column, when more than 40 mm, with the increase of the horizontal displacement, the defects in the column on both sides of the energy dissipation capacity will gradually all energy dissipation along the side of the column above defects. It can be seen that all the defects on one side of the column are more unfavorable to the seismic performance of the prefabricated concrete column.

Fig. 6.
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Energy dissipation curves of 5D-D-1 and 5D-D-2 specimens

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5 Conclusion

In this chapter, ABAQUS finite element software is used to simulate the influence of different defect sizes and positions on the seismic performance of concrete columns, and the main conclusions are as follows:

  1. (1)

    In the case of the same defect location and number, the larger the defect size, the lower the bearing capacity, the more obvious the stiffness degradation, the smaller the displacement ductility coefficient, the worse the ductility, the weaker the energy dissipation capacity;

  2. (2)

    In the case that the number and size of defects are the same, when the defect position is symmetric in the force direction, the hysteresis curve is symmetric in the positive and negative directions, and its energy dissipation capacity is higher than that of the defect located on one side of the column section Force.