In this paper, three kinds of shear walls with full sleeve grouting, fully defective sleeve and partially defective are designed for finite element analysis to analyze the influence of defects on the seismic performance of shear walls. The research shows that at the beginning of loading (5 s), the three models begin to appear compressive damage at the bottom of the wall in all three models. The damage of the defect-free model develops rapidly, and the damage of the fully defective model is basically the same as that of the partially defective model. With the gradual increase of displacement control (15 s), the compressive damages at the foot of the wall in the defect-free and partially defective grouting model are obvious, with plastic hinge formed in the foot of the wall, and the phenomenon of development along the pier body showing up. When the structure is damaged, the overall compressive damages of the wall in the defect-free and partially defective models are obvious, and the damage on the defective side of the partially defective model is slightly deficient. While the maximum stress of pre-stressed reinforcement in the defect-free model is concentrated at the top of the sleeve, the maximum stress of the pre-stressed steel bar in the fully defective model appears at the end of the steel bar in the sleeve. The hysteresis curve shape of the non-defect model and partially defective model are basically the same, showing a “shuttle” shape with a sound energy dissipation effect. The hysteresis curve shape of the fully defective model appears an obvious “pinch” phenomenon. The yield displacement levels of the defect-free and partially defective models are smaller than that of the fully defective model structure. The stiffness degradation curves of the three models basically overlap with one another. Before the limit displacement, the stiffness results of the non-defect model and the partially defective model are greater than that of the fully defective model. When the displacement is loaded to 20 mm, the stiffness degradation of the three models is equivalent.

The prefabricated building is constructed on site with premade factory components. The components are manufactured by the standardized production and processing of the factory, and their quality is easy to guarantee. The final assemblage of the components into the overall structure is completed on the site, especially the connection of the longitudinal force reinforcement which is the key to affecting the safety of the overall structure. Sleeve grouting connection is a common form of longitudinal reinforcement connection in prefabricated concrete structures. Sleeve grouting connection is to insert ribbed steel bars in the metal sleeve and achieves force transmission by hardening the grout mixture. Therefore, the fullness of the grouting material is very important to the force transmission effect. Sleeve grouting is a hidden project. Restricted by field construction method, management and testing means, there could still be some problems regarding grouting quality, such as defects. For example, Looseness of sealing plug at the grouting mouth or an untight sealing seam of the slurry layer may cause leakage of slurry, resulting in dropping of the sleeve top and defects at the end of the sleeve.

In developed countries such as the United States and Japan, to ensure the compactness of the grouting, measures taken include improving the working skills of the workers, adopting appropriate guidance norms and effective management. However, in China, with short development time, yet-to-improve factory production factory, insufficient on-site personnel training, guidance norms as well as supervision, the phenomenon of sleeve grouting being not dense happens frequently, which leads to the failure of steel bars to play a full role in the stress which introduces further potential safety risks.

Existed research on steel sleeve grouting mainly focuses on its mechanical properties and force transmission effects, etc. Kim [

In order to verify the rationality of the finite element model of shear wall, this paper analyzes the finite element model of TWL in [

Unit selection

The concrete part of the model adopts solid hexahedron element C3D8R. The reinforcement part adopts the space two node frame separation unit T3D2. The sleeve part adopts solid element.

Constitutive relation of materials

In this paper, the damage plastic model of concrete is used to simulate the concrete in the shear wall, with compressive stress-strain relationship determined according to the code GB50010-2010 (2011), such as

When

When

In the formula:

n-coefficient, when the calculated n value is greater than 2.0, it is taken as 2.0.

The tensile stress–strain relationship determined by ABAQUS in-built model, the tensile and compressive elastic modulus made equal before cracking, the tensile strength calculated according to the formula in literature [^{5} Mpa, and the Poisson's ratio is 0.3. C40 concrete GB50010-2010 [

Loading mode

When using the ABAQUS software to analyze the seismic performance of the shear wall structure, the structure is subjected to multiple cyclic reciprocating loads, resulting in nonlinear elastic-plastic deformation and failure. The horizontal displacement low-cycle reciprocating loading form is used to simulate the cyclic reciprocating periodic motion of the substructure of the wall under the action of seismic waves, and the anti-overturning ability of the assembled shear wall model is studied. Based on the above theory, two loading conditions that fit the actual wall force are drawn up.

Condition 1: Only apply the respective weight of the three models as well as the uniform load generated by the upper structure of the wall on the lower structure. In this paper, the axial compression ratio of the design model is 0.12. According to the axial compression ratio formula,

Condition 2: The structural dead weight and the upper uniform load applied in Condition 1 are transferred to Condition 2 in the form of a dead load, while a horizontal displacement is applied to the side of the loading cover beam.

Boundary conditions

In the contact attribute, the penalty element is used to define the tangential attribute, with the friction coefficient set up as 1, the normal attribute adopting “hard” contact element, and the constraint execution method selected as default. Base and shear wall, loading beam and shear wall are connected through tie. The binding constraint is used to bind two regions in the model together so that there is no relative movement between them. The two contact surfaces in this connection form are equivalent to rigid connections in stiffness data transmission, and there is no relative motion and deformation in the binding area.

The steel mesh and sleeve elements are embedded into the shear wall entity element via embedded region. This model assumes that the co-working performance of steel and concrete is sound. Both the sleeve and the grouted steel do not slip with the surrounding concrete. The steel skeleton is embedded in the concrete solid unit via embedded region. The embedding constraint can specify a set of units to be embedded in a set of main units. The nodes of the embedded unit located in the main unit will be removed from translational degrees of freedom and become “embedded nodes”. The translational degrees of freedom of the embedded nodes are constrained by the difference of the corresponding degrees of freedom of the main element. The embedded unit allows rotation, but its rotation is not restricted by the embedded region.

The finite element analysis of this paper is compared with the experimental results of reference [

Comparison of failure modes

Comparison of bearing capacity

Comparison of hysteretic energy consumption

This article mainly analyzes the seismic performance of shear wall models with different level of defects. The degree to which the structure is influenced is analyzed by setting different locations and quantities of such grouting defects. The size of the shear wall is shown in

The steel bars of the shear wall are all HRB400 grade, and according to the elastic modulus _{S}^{5} MPa, Poisson's ratio is 0.3. The loading cover beam, base, and shear wall are all made of C40 concrete with a Poisson's ratio of 0.2; the sleeve is made up of steel, with an elastic modulus of 370 MPa, and a Poisson's ratio of 0.3. The sleeve grouting material is a high-strength non-shrinkage cement grouting material, using C80 high-strength concrete constitutive, with a Poisson ratio of 0.2. The material performance parameters of the test samples are shown in

Materials | Compressive strength/MPa | Yield strength/MPa | Ultimate strength/MPa |
---|---|---|---|

C 14 | — | 470.2 | 627.11 |

C 12 | — | 467.08 | 619.35 |

C 8 | — | 465.31 | 618.81 |

Grouting material | 89.35 | — | — |

Concrete | 40.15 | — | — |

The finite element model of the shear wall is established according to the method described in

The simulation of the grouting defects in the sleeve is the key part. First, a hole should be reserved in the defective wall so that the steel bar at the defect can be separated from the grouting when the rebar is embedded in the grouting, which will cause stress concentration at the hole during analysis and so needs to be dealt with separately during grid division. The division situation is shown in

The base plane split geometric element tool in the ABAQUS part element is used to split the defective steel bars. When the contact element steel bars are embedded in the shear wall entity, the defective parts are not embedded in the wall, as shown in

Shear wall is the main lateral resistance component of a building structure. Ductility is an important index to measure the seismic performance of shear wall, and its ductility is obtained by the formation and development of plastic hinge. The plastic hinge rotates under horizontal load of shear wall, so that the wall can obtain ductility. By studying the generation and variation mechanism of plastic hinges in the three models, including fabricated shear wall sleeve with full grouting (QM), sleeve with fully defective grouting (QD) and sleeve with partially defective grouting (BD), the differences of the three models in deformation and failure under reciprocating load are compared in detail. When the axial compression ratio of the shear wall is controlled to be constant, the field distribution of the damage parameter cloud of the structure under horizontal reciprocating load is shown in

From the comparative analysis of

From

It can be seen from

It can be seen from

It can be seen from the prestressed steel stress cloud chart

The energy consumption capacity of the three working conditions can be analyzed through the hysteresis curves, as shown in

The hysteresis curve shape of the defect-free and partially defective models is basically the same, and both show a “shuttle” shape. Before the cracking failure of wall concrete occurs, the horizontal load and displacement show a linear relationship, and the slope of hysteresis curve remains basically unchanged with the increase of load value, indicating that the wall is in an elastic stage. It shows that when the component is in the elastic stage, the energy consumption is small, the residual displacement of the two models is not obvious after unloading, and the stiffness has no significant degradation. With the increase of load, plastic deformation occurs in the wall. The slope of the hysteresis curve decreases gradually with the increase of load, but the increasing trend gradually slows down. The stiffness of the wall degenerates with the wall gradually developing from the yield state to the failure state, showing up more obvious stiffness degradation. Some defects have little effect on the energy dissipation of the whole structure, as the defect-free prestressed reinforcement plays a key role.

The hysteresis curve shape of the fully defective model has an obvious “pinching” phenomenon, mainly because the prestressed steel bar slips during the loading process due to grouting defects. With an increased energy consumption level, decreased resistance and horizontal displacement, the wall is gradually full of hysteresis.

The ultimate bearing capacity of the defect-free model is the highest, that of the partially defective model is slightly reduced, and that of the fully defective model is significantly reduced, indicating that the number of defects has a significant impact on the bearing capacity of the wall.

Displacement ductility factor is calculated by

The displacement ductility coefficient is used to represent the rotation ability of the plastic hinge section to resist the reciprocating load, which is similar to the solution formula of the displacement ductility coefficient. The ratio of the ultimate displacement to the yield displacement is the displacement ductility. The larger the displacement ductility coefficient, the better the rotational performance of the plastic hinge region, and the stronger its ability to resist earthquake action. The seismic performance parameters of three shear wall models are calculated in

Wall |
Load |
Yield |
Ultimate |
Displacement ductility |
---|---|---|---|---|

W-QM | Forward | 6.9 | 12.4 | 1.80 |

Backward | 4.2 | 12.3 | 2.93 | |

W-QD | Forward | 12.8 | 20.0 | 1.56 |

Backward | 9.2 | 20.1 | 2.18 | |

W-BD | Forward | 8.6 | 16.2 | 1.88 |

Backward | 4.5 | 14.9 | 3.31 |

Analysis of the data in

The skeleton curves of the three models are shown in

Wall |
Load |
Cracking |
Yield |
Maximum |
Ultimate |
---|---|---|---|---|---|

W-QM | Forward | 532.7 | 862.3 | 1108.2 | 942.0 |

Backward | 544.9 | 765.3 | 1022.4 | 869.0 | |

W-QD | Forward | 633.3 | 789.1 | 939.4 | 798.5 |

Backward | 642.2 | 774.6 | 918.8 | 781.0 | |

W-BD | Forward | 540.3 | 865.3 | 1071.4 | 910.7 |

Backward | 551.2 | 718.5 | 958.0 | 814.3 |

In this paper, three kinds of shear walls with full sleeve grouting, fully defective sleeve and partially defective sleeve are designed. The mechanical properties are analyzed by ABAQUS finite element software, and the following conclusions are obtained.

At the beginning of loading (5 s), compressive damage appears at the bottom of the wall in all three models. The damage of the defect-free model develops faster, and the damage of the fully defective model is basically the same as that of the partially defective model. With the gradual increase of displacement control (15 s), the compressive damages at the foot of the wall in the defect-free and partially defective grouting model are obvious, with a plastic hinge formed in the foot of the wall, and the phenomenon of development along the pier body showing up. The wall damage of the fully defective model is mainly concentrated in the 350 mm range from the bottom of the wall where it gets most serious. When the structure is damaged, the walls in the defect-free and partially defective models are obviously damaged under pressure, and the defective side of the partially defective model is slightly damaged. The defect-free model has tensile damage at the top of the sleeve, while the tensile damage in the partially defective and fully defective model is not obvious.

The maximum stress of the prestressed steel bar in the defect-free model is concentrated at the top of the sleeve, indicating that the prestressed steel bar does not slip; The maximum stress of the prestressed steel bar in the fully defective model appears at the end of the steel bar in the sleeve, indicating that the prestressed steel bar slips in the sleeve; the failure mode of the prestressed steel bar in the partially defective model is consistent with the previous two models.

The hysteresis curves of the defect-free model and the partially defective model are basically the same, showing a “shuttle” shape. The energy consumption effect is sound, and some defects have little effect on the energy consumption of the overall structure. The reason is that the defect-free prestressed steel bars play a key role. The hysteresis curve shape of the fully defective model has an obvious “pinching” phenomenon, mainly because the prestressed steel bar slips during the loading process for the grouting defects, resulting in increased energy consumption and decreased resistance. As the horizontal displacement increases, the hysteresis loop of the wall gradually becomes full.

The yield displacement results of the defect-free and partially defective models are smaller than that of the fully defective model. As the displacement increases, the secant stiffness of the samples decreases. The stiffness degradation curves of the three models are basically overlapped with one another. The stiffness levels of the defect-free model and partially defective model before the limit displacement is greater than that of the fully defective model. When the displacement is loaded to 20 mm, the stiffness degradation results of the three are equivalent.