Numerical analysis and experimental study of seismic performance of assembled concrete structures

Abstract

Studying the seismic performance of assembled concrete structures is an effective means to improve the quality of buildings. In this paper, the primary focus was on elucidating the research objectives. Initially, seismic performance experiments for assembled concrete structures were meticulously designed, and subsequently, concrete structural frames were assembled for comprehensive experimental analysis. A finite element model was developed for the nodes of the assembled concrete structure, incorporating the concrete principal structure model, concrete damage plasticity model, and steel principal structure model. Numerical simulations and finite element analysis were performed to verify the specific factors affecting the seismic performance of the assembled concrete structure. The results show that the hysteresis curves of the assembled concrete frame obtained from the simulation and the test curves basically match, and the difference in the maximum forward beam end displacement is only 1.76 mm, with an error rate of only 3.98%. When the axial compression ratio of the assembled concrete structural frame is within 0.3, there is no decrease in the bearing capacity when the assembled concrete is loaded to 2.3% lateral displacement. This shows that the seismic performance of assembled concrete structures can be effectively analyzed by using finite element models, and also provides a new research direction for improving the seismic quality of buildings.

Keywords

Finite element model concrete principal hysteresis curve seismic performance assembled concrete

1. Introduction

1.1 Research background

In recent decades, earthquakes have occurred frequently in various countries around the world, and seismic hazards have become one of the most important factors affecting the safety of human life and property as well as environmental safety [1, 2]. China is in a zone where earthquakes occur more frequently, and the seismic effects occur with shallow sources, high intensity, and wide distribution, and most areas are in seismic-resistant areas, which are among the countries with severe earthquake damage [3, 4, 5]. At the same time, earthquakes can cause serious damage to the ground surface, leading to disasters such as landslides, cracks in the ground and subsidence. Not only does it seriously affect the safety of people’s lives and properties, but also has a great impact on the country’s economy and modernization [6, 7].

The progression of assembled building structures is imperative for achieving construction industrialization. In contrast to assembled structures, cast-in-place reinforced concrete structures exhibit certain drawbacks in construction processes, necessitating in-situ formwork at the construction site, utilizing a substantial amount of formwork, and requiring on-site pouring. To address these issues and contribute to the advancement of construction methodologies, this research delves into alternative construction techniques that mitigate the limitations of cast-in-place structures. The study explores innovative solutions for formwork reduction, on-site pouring optimization, and other advancements aimed at enhancing the efficiency and applicability of assembled building structures in the context of construction industrialization [8, 9]. The number of work sequences is relatively high, the construction is difficult, the cycle time is also longer, the work intensity of labor workers is high, and the cost of construction labor is elevated leading to a significant increase in the total cost of construction work [10, 11]. In addition, the large volume of concrete and the poor quality of maintenance are particularly likely to lead to large areas of concrete cracking. The excessive consumption of construction resources, particularly in terms of energy usage and environmental impact, poses a significant risk of construction material wastage. Managing construction waste is challenging due to its sheer volume, presenting a contradiction to the overarching goals of energy conservation and environmental protection. To delve deeper into this issue, pertinent literature underscores the pressing need for sustainable construction practices, waste reduction strategies, and the adoption of eco-friendly materials. Research by the environmental implications of construction activities, urging the adoption of efficient waste management systems. Furthermore, investigates the challenges posed by construction waste and proposes innovative solutions for minimizing environmental impact. These studies collectively contribute valuable insights into the complex issue of construction resource consumption and the imperative for sustainable practices in the construction industry [12, 13].

1.2 Current status of research

The performance of concrete is an important way to guarantee the quality of buildings. Wang YH, Yu J et al. conducted composite beam tests on the casting method of concrete bridge decks as a way to investigate the static mechanical properties of assembled monolithic steel-concrete composite beams, and the results showed that assembled steel-concrete composite beams have better ductility and elastic stiffness [14]. Zhou Y, Hu X et al. tested the slump performance by designing RC and PC two different scales of moment substructure for collapse performance test, the results showed that the PC specimens have better bearing capacity than RC specimens, and the dynamic test results also indicate that RC specimens have better gradual collapse performance [15]. Shen S, Pan P et al. proposed a steel shear bond using steel shear plates combined with fillet and plug welds, and the RC precast shear wall specimens with different connection strengths were tested and the results showed that the shear wall incorporating SSK has better bearing capacity and elastic stiffness than the conventional shear wall [16].

In addition to this, Hadhood A et al. conducted an experimental database on the factors influencing the flexural strength of concrete and tested and analyzed several different types of concrete through this database, and the results showed a strong correlation between the strength values of concrete and those predicted by ERSB [17]. Huang D, Wei J et al. conducted ageing tests on assembled concrete and steel-concrete composite beams with Differences were tested for long-term performance and analyzed using an assembled composite beam performance model based on deformation coordination conditions, and the results showed that compressive stresses in assembled concrete develop into tensile stresses with time [18]. Wang JJ, Liu C et al. used high-fidelity finite element simulations of composite slabs against shear wall-concrete to construct a triaxial model of concrete, and by comparison, it was found that the triaxial model in terms of ultimate capacity, energy consumption, and other aspects to obtain reasonable accuracy [19].

1.3 Research methodology

This paper outlines the design of seismic performance experiments for assembled concrete structures, with subsequent fabrication and experimental analysis of assembled concrete structural frames. The analysis encompasses the mechanical properties of materials, along with a detailed examination of the experimental measurement contents and specific methodologies employed. Then, a nodal finite element model of the assembled concrete structure is constructed using the concrete principal structure model, the concrete damage plasticity model and the reinforced steel principal structure model jointly, and the model is meshed with the unit mesh, limited load and boundary conditions. Finally, numerical simulations and finite element analysis are performed for the assembled concrete structural frame, including hysteresis curve, skeleton curve, prestressing tendon area and axial compression ratio analysis. The results show that the seismic performance of assembled concrete is affected by the prestressing tendon area and axial compression ratio, which provides a new research path to improve the seismic performance of buildings.

2. Experimental design of seismic performance of assembled concrete structures

With respect to the construction method, concrete structures can be categorized into two types: cast-in-place structures and prefabricated assembled structures. Given that many Chinese cities are situated in seismic zones, considering the seismic performance of prefabricated concrete structures is imperative in both study and application. This chapter undertakes the experimental design for assessing the seismic performance of assembled concrete structures, laying the groundwork for constructing a finite element model for subsequent numerical simulation analysis.

2.1 Experimental design

For assembled monolithic concrete frames, beams, some columns and foundations are prefabricated. Within the height of 500 mm at the upper end of the column, part of the column above the elevation of the lower end of the beam is constructed with post-cast concrete to complete the connection between the beam and the column. A 30 mm thick gap was reserved at the bottom end of the column for later grouting to complete the connection with the foundation through grout sleeves [20]. The schematic diagram of the frame design is shown in Fig. 1.

2.2 Mechanical properties of materials

Material tests were performed on the concrete to determine the actual strength used in the tests. Five standard cubic specimens and five standard cylindrical specimens were reserved for each part of the specimen. The specimens and concrete material test blocks were maintained under the same conditions and cured for 30 days according to the Standard for Mechanical Properties Test Methods of Ordinary Concrete (GB/T50081-2016), and the mechanical properties of concrete indexes were obtained through the final tests, i.e., the concrete cube compressive strength of precast beams and precast columns was 48.34 MPa, the concrete axial compressive strength was 30.27 MPa, and the modulus of elasticity was The concrete cube compressive strength of the joint was 45.52 MPa, the concrete axial compressive strength was 33.62 MPa, and the modulus of elasticity was 35.16 GPa. The performance indexes of the reinforcement and steel involved in the experiment are shown in Table 1.

Table 1
Performance indicators of reinforcements and steel

Steel and steel plate grades	Diameter of reinforcement and thickness of steel plate/mm	Yield strength /MPa	Ultimate strength /MPa
HRB400	11	501.24	635.94
HRB600	16	701.48	876.19
HRB800	23	649.52	823.43
Q235	7	299.37	465.68
Q235	13	265.76	403.02
Q235	15	262.19	432.13
Q235	18	279.83	455.79

Figure 1.

Assembled monolithic concrete frame.

2.3 Experimental measurement content and methods

The specimen loading phenomena were recorded mainly including the cracks in the beam end, column end and node core area under each loading condition. The specific practice is to use lime slurry to paint white in the node core area, and draw a positioning grid on both sides of the node core area and the beam end with a grid size of 40 mm $\times$ 40 mm, and the grid markings are marked sequentially from the left beam loading end to the right beam loading end. During the test, the cracks were depicted with a red marker for positive loading and a black marker for negative loading, and the crack development was depicted on the square paper in real time.

The strain test of experimental reinforcement and steel plate mainly includes beam longitudinal reinforcement, column longitudinal reinforcement, node core area hoop reinforcement, flange connection plate, web connection plate, column side steel plate, horizontal connection plate and cross partition, the deformation of beam end is measured by displacement meter, the calculation of the corner value of each plastic hinge area is obtained by taking the mean value of LVDT at the corresponding position, and two intersecting displacement meters are placed in the node core area to measure the core area Two intersecting displacement gauges are placed at the core of the node to measure the shear deformation at the core.

3. Finite element model of assembled concrete structure nodes

The study of complex structures of assembled concrete is based on certain experiments and then combined with suitable finite element analysis software. The correctness of the modeling is verified by comparing the finite element calculation results with the experimental results, and then the finite element software is used to carry out more complex studies that are difficult to achieve experimentally, and the data obtained are analyzed to derive the corresponding theoretical findings. This chapter focuses on the finite element model under assembled concrete structures as a way to provide theoretical support for the numerical analysis of the seismic performance of concrete to be carried out later on.

3.1 Material ontology relationship model

The selection of the material intrinsic relationship model is the key to further research using finite element software on the basis of prefabricated node tests, and it is an important factor in determining the accuracy of the calculation results and the convergence of the calculation. The finite element calculation of the node model of assembled concrete structure frame in this paper involves the intrinsic structure relationship models of concrete, reinforcement, steel, prestressing tendons, high-strength bolts and other materials.

3.1.1 Concrete principal structure model

There are three commonly used concrete instantiation models in ABAQUS, namely, concrete damage plasticity model, concrete dispersion cracking model, and concrete cracking model. For different models, the choice of material instantiation has a great influence on the calculation results, so it is especially important to choose the appropriate material instantiation model. For the low circumferential reciprocal loading in this paper, the concrete damage plasticity model is more appropriate. The model takes into account the influence of concrete damage factors in tension and compression, and can simulate the phenomenon of model stiffness degradation more realistically. In this paper, the concrete adopts the principal structure relationship in the “Concrete Structure Design Guilan” (GB50010-2010).

(1) Concrete uniaxial compressive stress-strain relationship

$\displaystyle\sigma=({1-{d}^{\prime}_{c}})E_{c}\varepsilon$ (1) $\displaystyle{d}^{\prime}_{c}=\left\{{{\begin{array}[]{ll}{1-\frac{\rho_{c}n}{% n-1+x^{n}}}&{x\leqslant 1}\\ {1-\frac{\rho_{c}}{\alpha_{c}(x-1)^{2}+x}}&{x>1}\\ \end{array}}}\right.$ (2) $\displaystyle\rho_{c}=\frac{f_{c,r}}{E_{c}\varepsilon_{c,r}}$ (3) $\displaystyle n=\frac{E_{c}\varepsilon_{c,r}}{E_{c}\varepsilon_{c,r}-f_{c,r}}$ (4) $\displaystyle x=\frac{\varepsilon}{\varepsilon_{c,r}}$ (5)

The uniaxial compressive stress-strain curve of concrete is shown in Fig. 2.

Figure 2.

Uniaxial compressive stress-strain curve of concrete.

(2) Uniaxial stress-strain relationship of concrete in tension

$\displaystyle\sigma=({1-{d}^{\prime}_{t}})E_{c}\varepsilon$ (6) $\displaystyle{d}^{\prime}_{t}=\left\{{\begin{array}[]{ll}1-\rho_{t}[{1.2-0.2x^% {5}}]&x\leqslant 1\\ 1-\frac{\rho_{t}}{\alpha_{t}(x-1)^{1.7}+x}&x>1\\ \end{array}}\right.$ (7) $\displaystyle x=\frac{\varepsilon}{\varepsilon_{t,r}}$ (8) $\displaystyle\rho_{t}=\frac{f_{t,r}}{E_{c}\varepsilon_{t,r}}$ (9)

The uniaxial stress-strain curves for concrete subjected to uniaxial tension are shown in Fig. 3.

Figure 3.

Uniaxial stress-strain curve of concrete under tension.

Where $\alpha_{c},\alpha_{t}$ is the parameter value of the falling section of the uniaxial compressive and tensile stress-strain curve, respectively, taken according to the specification. $f_{c,r},f_{t,r}$ is the uniaxial compressive and tensile strength of concrete, respectively, taken according to the actual requirements. $\varepsilon_{c,r},\varepsilon_{t,r}$ is the peak compressive and tensile strain of concrete corresponding to $f_{c,r},f_{t,r}$ , respectively, taken according to the specification. ${d}^{\prime}_{c},{d}^{\prime}_{t}$ are the uniaxial compressive and tensile damage evolution parameters of concrete, respectively.

3.1.2 Concrete damage plasticity model

The concrete damage plasticity model defines that concrete is finally damaged by cracking failure due to tensile action and by crushing due to compressive action. By introducing the damage factor to simulate the stiffness degradation of concrete after plastic deformation, the concrete strain after considering the damage factor is calculated as follows:

(1) When concrete is subjected to compression

$\displaystyle\varepsilon_{c}^{{in}}=\varepsilon_{c}-\varepsilon_{c}^{{el}}$ (10) $\displaystyle\varepsilon_{c}^{{el}}=\frac{\sigma_{c}}{E_{0}}$ (11)

(2) When concrete is under pressure

$\displaystyle\varepsilon_{t}^{{in}}=\varepsilon_{t}-\varepsilon{}_{t}^{{el}}$ (12) $\displaystyle\varepsilon_{t}^{{el}}=\frac{\sigma_{t}}{E_{0}}$ (13)

Where $\varepsilon_{c}^{{el}},\varepsilon_{t}^{{el}}$ is the elastic compressive and tensile strain of concrete, $\varepsilon_{c}^{{in}},\varepsilon_{t}^{{in}}$ is the inelastic compressive and tensile strain of concrete, and $E_{0}$ is the initial elastic modulus of concrete.

At this point, the conversion relationship between inelastic strain $(\varepsilon_{c}^{{in}},\varepsilon_{t}^{{in}})$ and plastic strain $(\varepsilon_{c}^{{pl}},\varepsilon_{t}^{{pl}})$ is as follows

$\displaystyle\varepsilon_{c}^{{pl}}=\varepsilon_{c}^{{in}}-\frac{d_{c}}{({1-d_% {c}})}\frac{\sigma_{c}}{E_{0}}$ (14) $\displaystyle\varepsilon_{t}^{{pl}}=\varepsilon_{t}^{{in}}-\frac{d_{t}}{({1-d_% {t}})}\frac{\sigma_{t}}{E_{0}}$ (15)

Where, $d_{c},d_{t}$ is the damage factor in compression and tension, respectively.

According to Sidoroff’s energy equivalence principle it is known that the elastic energy of the damaged material due to the nominal stress is equivalent to the residual energy of the undamaged material of the same geometry due to the effective stress. The resulting expression for the calculation of the damage factor $d_{c},d_{t}$ is

$\displaystyle d=1-\sqrt{\frac{\sigma}{E_{0}\varepsilon}}$ (16)

3.1.3 Hysteresis rule

When the concrete is subjected to cyclic loading, the cross-section is cracked under tensile stress, and the cross-section is subjected to compressive stress when reverse loading, which enables the aggregate at the crack to re-occlusion. Following this, it is able to continue to transmit compressive stresses, and after being subjected to multiple cyclic loading effects, the concrete is eventually damaged due to the cracking surface effect. After adding the damage index, the linear elastic stiffness of concrete under tensile and compressive effects is reduced to a certain extent, which can simulate the phenomenon that the unloading stiffness of concrete decreases due to the increase of damage, thus responding to the accumulation of damage of concrete under cyclic loading.

$\displaystyle E=(1-d)E_{0}$ (17) $\displaystyle(1-d)=({1-s_{c}d_{t}})({1-s_{t}d_{c}})\quad 0\leqslant s_{c},s_{t% }\geqslant 1$ (18) $\displaystyle s_{t}=1-\omega_{t}r^{\ast}(\bar{\sigma}11)\quad 0\leqslant\omega% _{t}\leqslant 1$ (19) $\displaystyle s_{c}=1-\omega_{c}({1-r^{\ast}(\bar{\sigma}11)})\quad 0\leqslant% \omega_{c}\leqslant 1$ (20) $\displaystyle r^{\ast}(\bar{\sigma}11)=H(\bar{\sigma}11)=\left\{{{\begin{array% }[]{*{20}c}{1,}&{\bar{\sigma}11>0}\\ {0,}&{\bar{\sigma}11<0}\\ \end{array}}}\right.$ (21)

Equations (19) and (20) $\omega_{t},\omega_{c}$ is the stiffness recovery factor, which reflects the recovery of concrete stiffness in compression and tension under cyclic loading. When the concrete is transformed from tensile to compressive state, if the compressive stiffness is fully recovered then $\omega_{c}=1$ , and vice versa $\omega_{c}=0$ . When the concrete is transformed from compressive to tensile state, if the tensile stiffness cannot be recovered then $\omega_{t}=1$ , and vice versa $\omega_{t}=0$ .

The stress-strain relationship of concrete under reciprocating load is shown in Fig. 4.

Figure 4.

Stress-strain relationship for concrete under reciprocal loading.

Figure 5.

Reinforcement hysteresis model curve.

3.2 Reinforcement and steel ontology model

3.2.1 Reinforcement principal structure model

Since there is a bond-slip effect between concrete and reinforcement when they act together in practice, and in ABAQUS the reinforcement is usually built into the concrete without considering the bond-slip effect between the reinforcement and concrete, the resulting hysteresis curve is not “pinched and shrunk”, which is not consistent with the actual test. Therefore, this paper adopts the Clough reinforcement intrinsic model, which considers the bond slip effect between reinforcement and concrete by reducing the unloading stiffness of reinforcement, and the hysteresis model curve is shown in Fig. 5.

The hysteresis model curve under re-circulating load of steel reinforcement is calculated by the following expression:

$\displaystyle\sigma=\gamma({\bar{\varepsilon}^{3}-\bar{\varepsilon}^{2}})+(1-% \alpha)\sigma_{m}\bar{\varepsilon}+\alpha\sigma_{m}$ (22)

Among them,

$\displaystyle\gamma=E_{{sh}}({\varepsilon_{m}-\varepsilon_{1}})-(1-\alpha)% \sigma_{m}$ (23) $\displaystyle\bar{\varepsilon}=\frac{\varepsilon-\varepsilon_{1}}{\varepsilon_% {m}-\varepsilon_{1}}$ (24) $\displaystyle\alpha=\left\{{{\begin{array}[]{ll}0.5,&{(\beta\leqslant 1)}\\ {(20-\beta)/38,}&{(1<\beta<20)}\\ 0,&{(\beta\geqslant 20)}\\ \end{array}}}\right.$ (25) $\displaystyle\beta=\frac{\varepsilon_{m}-\varepsilon_{0}}{\varepsilon_{y}}$ (26) $\displaystyle E_{{sr}}=\left\{{{\begin{array}[]{ll}{E_{s}},&{(\beta<1)}\\ {(1.05-0.05\beta)E_{s}},&{(1\leqslant\beta\leqslant 4)}\\ {0.85E_{s}},&{(\beta>4)}\\ \end{array}}}\right.$ (27)

Where $\sigma_{m},\varepsilon_{m}$ is the maximum tensile stress and tensile strain, and $E_{{sh}},E_{{sr}},E_{s}$ is the hardening stiffness, unloading stiffness and initial stiffness of the reinforcement, respectively.

3.2.2 Steel principal structure model

Commonly used intrinsic relationship models for steel include ideal elastoplastic model, isotropic strengthening model, follower strengthening model and hybrid strengthening model. Under low circumferential reciprocal loading, a follower strengthening model considering the Von Mises yield criterion, the follower strengthening criterion and the associated flow law should be used. In this paper, the steel plates, prestressing tendons and high-strength bolts are used in the double-folded random strengthening model, whose intrinsic parameters are shown in Table 2 and the stress-strain relationship curves are shown in Fig. 6.

Table 2
Steel principal structure parameters

Name	Yield strength	Ultimate strength	Modulus of elasticity	Modulus of reinforcement
	$f_{y}/\textit{MPa}$	$f_{u}/\textit{MPa}$	$E/\textit{MPa}$	${E}^{\prime}_{s}/\textit{MPa}$
Q235	315	452	2.05*10⁵	0.02
1860 grade steel strand	1645	1935	1.96*10⁵	0.02
Grade 11 high-strength bolts	946	1020	2.05*10⁵	0.02

Figure 6.

Steel stress-strain relationship curve.

3.3 Cell meshing and load boundary conditions

3.3.1 Concrete structure cell meshing

In the finite element modeling of prefabricated assembled frame beam and column nodes, the concrete material, column longitudinal reinforcement and steel sleeves are modeled using eight-node linear hexahedral cells. The beam reinforcement, column hoop reinforcement, and slab reinforcement are simulated using two-node linear three-dimensional truss units. In order to take into account the two aspects of node refinement calculation and model calculation efficiency, the mesh size of nodal beam, slab and column concrete units is 60, the mesh size of floor reinforcement unit is 100, the mesh size of beam and column reinforcement unit is 100, and the mesh size of steel sleeve unit is 30.

3.3.2 Loads and boundary conditions

Based on the nodal tests conducted in previous studies on assembled concrete structural frames, the test column is designed with a specified axial force of 10,560 kN, featuring ball-hinged connections at both ends. Preceding the test, a vertical load is applied to the predetermined axial pressure of the test column using a jack, ensuring its constancy throughout the experiment. According to the proposed static test loading system, the beam end loads were controlled by force-displacement mixing, and the beam end loads were applied to simulate the seismic forces in order to obtain the boundary conditions of the assembled concrete structural frame.

4. Numerical simulation and finite element analysis of assembled concrete structures

In order to investigate the seismic performance of the frame in depth, a simulation analysis of the pre-stressed prefabricated assembled frame structure in this test was performed. The finite element software OpenSEES is used to obtain the calculated values of hysteresis curve, skeleton curve, and prestressing tendon combined force, respectively, and compare the calculated values with the test results to illustrate the seismic performance of the assembled concrete structure.

4.1 Analysis of numerical calculation results

4.1.1 Hysteresis curve

The finite element model of the assembled concrete frame structure is established according to the aforementioned method, and the calculated values obtained from the software simulation are compared with the real values of the test. Figure 7 shows the hysteresis curves of the comparison between the test and calculation.

Figure 7.

Comparison of calculation and test hysteresis curve.

From the hysteresis curve comparison graphs, it can be seen that:

(1)

The hysteresis curves of the assembled concrete frame obtained by OpenSEES low circumferential reciprocal simulation and the experimental curves basically match, and the difference between the maximum positive beam end displacements is only 1.76 mm, with an error rate of only 3.98%, thus indicating that the assembled concrete frame can consume considerable energy. In addition, observing the hysteresis curve contours and trends of both positive and negative loading, it is found that the calculated and test values are both close to each other, so it can be considered that the hysteresis curve of the structure can be simulated more accurately if reasonable parameters can be selected in the modeling.

(2)

In the actual test, there are inevitable inhomogeneous characteristics of the material and loading errors, so the calculated and actual values have some errors, which are within the acceptable range.

(3)

The residual deformation of the frame calculated by the software is smaller than the actual test value, which shows more obvious pinching and shrinking characteristics. This is because the role of polypropylene fiber mortar at the beam-column joint surface and the crushing process of pressurized concrete are difficult to be accurately simulated in the software.

4.1.2 Skeleton curve

The computed skeleton curves of the assembled concrete structural frame specimens obtained from the software simulation were compared with the experimental skeleton curves, and their comparison curves were obtained as shown in Fig. 8.

Figure 8.

Comparison of calculation and test skeleton curve.

From the comparison of the skeleton curves, it can be seen that the calculated skeleton curves are very similar to the experimental skeleton curves in terms of size, shape and change process. When the displacement is small, the node has good initial stiffness and the curve is relatively steep. With the further increase of loading displacement, the increase of skeleton curve gradually tends to be flat, and the load capacity of the assembled concrete structural frame is 352 kN, which is 1.14% error compared with the experimentally derived load capacity. This shows that the numerical simulation can effectively realize the load capacity analysis for the assembled concrete structure frame, which can provide data support for the quality of construction projects.

4.2 Finite element parametric analysis

The force performance of beam-column joints significantly impacts the overall force behavior of assembled concrete structural frames, subsequently influencing their seismic performance. Addressing this, the paper conducts a parametric simulation analysis, scrutinizing key design factors that impact the force performance of beam-column joints in assembled concrete structural frames. The analysis yields valuable insights, and the paper provides practical design suggestions based on the findings for reference in future projects. This comprehensive approach aims to contribute to a deeper understanding and improved design considerations for beam-column joints in assembled concrete structures.

4.2.1 Area of prestressing tendons

The prestressing tendon area is one of the important factors affecting the force performance. Taking 300 mm² as the reference, the force performance of the structure when the prestressing tendon area Ap is 150 mm², 300 mm² and 400 mm² is analyzed, and the hysteresis curve comparison results are obtained as shown in Fig. 9.

Figure 9.

Hysteresis curve of prestressing tendon area.

From the comparative results of hysteresis curves of prestressing tendon area, with the increase of prestressing tendon area, the residual deformation decreases, and the corresponding positive load capacity of assembled concrete structure increases from 302 kN to 394 kN, which increases by 23.35%, while the negative load capacity decreases from $-$ 217 kN to $-$ 252 kN, which decreases by 16.13%, and the positive load capacity increases faster than the negative load capacity. This indicates that the increase of prestressing tendon area will lead to the increase of restoring force and seismic performance of the assembled concrete structure.

4.2.2 Axial pressure ratio analysis

The axial pressure ratio refers to the ratio of the design value of axial pressure of the section to the product of the full cross-sectional area and the design value of axial compressive strength of concrete, which is an important parameter affecting the bearing capacity and displacement ductility of the member. The axial pressure ratio is divided into design axial pressure ratio and test axial pressure ratio, and this section takes the test axial pressure ratio of 0.1, 0.2, 0.3, 0.4 and 0.5 for five working conditions respectively. Both load and prestress will affect the axial pressure ratio. In the analysis, it is assumed that the magnitude of prestress remains unchanged, and the axial pressure ratio is changed only by changing the magnitude of axial pressure. In order to save computational cost, the following analyses are performed with displacement-controlled monotonic loading, and the obtained vertex displacement-base shear curves are shown in Fig. 10.

Figure 10.

Influence of axial compression ratio on the pushover curve.

From the load-displacement curves, it can be seen that increasing the axial compression ratio will significantly increase the load carrying capacity of the assembled concrete structure. The initial stiffness and yield displacement of the model are insensitive to the change of axial pressure ratio, because the yielding of the connecting reinforcement marks the concrete into yielding and is only related to the position of the connecting reinforcement. When the axial pressure ratio was within 0.3, the assembled concrete loaded to 2.3% lateral displacement did not show any decrease in bearing capacity. When the axial pressure ratio was 0.5, the load capacity of assembled concrete loaded to 1.36% lateral shift began to decrease, indicating that the ductility of the member will gradually decrease with further increase of the axial pressure ratio, which in turn will also lead to the reduction of the seismic performance of assembled concrete.

Figure 11.

Axial pressure ratio and joint slip.

Figure 11 shows the effect of axial pressure ratio on joint slip. The joint slip is defined as the horizontal relative misalignment between the upper joint end plate and the lower joint end plate at the outer edge of the compressed side during monotonic pushover loading. The misalignment primarily arises due to the shear slip occurring between the upper and lower wall plates at the joints, constituting an adverse deformation mode for the structure.

From the data in the figure, it can be seen that the frictional resistance between the upper and lower joint end plates is relatively small when the axial pressure is relatively small, which is not enough to resist the horizontal external load and will produce a certain amount of shear slip. The amount of slip increases linearly with the increase of lateral deformation of the model and decreases with the increase of axial pressure ratio. When the assembled concrete structure reaches 3% lateral shift, the beam end slip does not exceed 2.5 mm, and the joint structure of the assembled concrete structure can be considered to have sufficient slip resistance. When the axial pressure ratio increases to 0.5, the slip decreases rapidly and no longer increases with the increase of lateral deformation, so the effect of joint slip can be ignored.

5. Conclusion

Studying the seismic performance of assembled concrete structures is instrumental in enhancing their resilience against earthquakes. In light of this, experimental designs are formulated to assess the seismic behavior of assembled concrete structures. Numerical simulation results reveal a close match between the hysteresis curves of the assembled concrete frame and the test curves. The disparity in the maximum forward beam end displacement is a mere 1.76 mm, equating to an error rate of only 3.98%. Furthermore, finite element analysis indicates that augmenting the prestressing tendon area amplifies the restoring force of assembled concrete structures, thereby improving their seismic performance. Notably, within an axial compression ratio of 0.3, the load capacity of the assembled concrete remains unaffected even when subjected to a 2.3% lateral shift. This underscores the potential for enhancing the seismic performance of assembled concrete structures by increasing the prestressing tendon area. Nevertheless, careful consideration of a reasonable range for setting the axial compression ratio is essential to ensure optimal seismic performance.

5.1 Outlook

In this paper, a preliminary seismic performance study of the assembled concrete structural frame is done, but there are still several aspects that need further improvement as follows:

(1)

Only the axial force is applied to the column in the test and the axial pressure ratio is 0.3. In the actual project, the beam also has to bear the self-weight and external load and the axial pressure ratio is more than 0.5. The analysis of the structure in this paper is limited to the two-dimensional plane, while the actual three-dimensional structure in space is more complex. Whether the number of spans and floors of the structural frame have an impact on the seismic performance of the structure needs to be further studied.

(2)

The seismic performance of the assembled concrete frame structure is affected by many factors, so it should also be studied comprehensively by changing the material grade, member size, prestressing degree, angle steel parameters, etc. This new prestressed prefabricated assembled frame structure should be studied comprehensively, especially the analysis of prestressing tendons and angle steel should be paid attention to.

(3)

Dynamic time analysis is very important to study the performance of the assembled concrete frame structure, and the dynamic time analysis of the frame through finite element software can provide more in-depth understanding of its seismic performance.

Footnotes

Funding

This research was supported by National Natural Science Foundation of China (57108038).

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Numerical analysis and experimental study of seismic performance of assembled concrete structures

Abstract

Keywords

1. Introduction

1.1 Research background

1.2 Current status of research

1.3 Research methodology

2. Experimental design of seismic performance of assembled concrete structures

2.1 Experimental design

2.2 Mechanical properties of materials

Table 1 Performance indicators of reinforcements and steel

3. Finite element model of assembled concrete structure nodes

3.1 Material ontology relationship model

3.1.1 Concrete principal structure model

3.2.1 Reinforcement principal structure model

Table 2 Steel principal structure parameters

3.3.1 Concrete structure cell meshing

3.3.2 Loads and boundary conditions

4. Numerical simulation and finite element analysis of assembled concrete structures

4.1 Analysis of numerical calculation results

4.1.1 Hysteresis curve

4.2.1 Area of prestressing tendons

5.1 Outlook

Footnotes

Funding

References

Table 1
Performance indicators of reinforcements and steel

Table 2
Steel principal structure parameters