Keywords

1 Research Background

The prefabricated construction cost refers to the total cost generated during the whole construction process of the prefabricated building, which is mainly reflected in the sum of the costs generated by the design and production of prefabricated components, the transportation and on-site installation of finished components. The costs of prefabricated construction include: direct costs (labor costs, material costs, machinery costs), management costs, profits and taxes. The production cost, transportation cost, installation cost and related mold cost of prefabricated parts are important components [1].

Compared with cast-in-situ construction, there are four costs in the construction process: mold design cost, component manufacturing cost, component transportation cost and component construction cost. In summary, the cost of composite construction mainly includes four aspects: design cost, manufacturing cost, transportation cost and construction cost. Manufacturing costs include labor costs, materials costs, machinery costs, mold costs, transportation costs, storage costs and management fees for manufacturing components [2]. The mold cost is closely related to the specification, quantity and operation of the parts, which greatly increases the manufacturing cost of the parts. The installation cost of prefabricated parts mainly consists of the cost of labor, materials and machinery for the installation of prefabricated parts. As shown in Fig. 1.

Fig. 1.
figure 1

Cost composition of prefabricated buildings

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2 Analysis of Influencing Factors of Prefabricated Construction Cost

At present, many scholars in our country have made a deep discussion on it from multiple perspectives, multiple approaches and multiple examples [3]. For example, Zhao Liang et al. [4]. Studied the impact of assembled construction costs from four aspects: design, technology, management and policy. Through AHP method, they obtained the impact factors of construction costs, among which the most important ones are: prefabrication rate of construction, construction management, coordination among various types of work, reasonable splitting of components and turnover number. When Zhou Jingyang et al. [5]. Analyzed the cost of prefabricated buildings, they used the constructed explanatory structure model and found that these factors can be divided into five levels: The first is the surface influence factor (labor cost, tax, transportation distance, material market price, equipment), the second is the middle-level dynamic factor (safety inspection, production scale, production quantity of prefabricated components, production industrialization degree), the fourth is the deep guidance factor (construction site planning, assembly rate and prefabrication rate, construction plan formulation). Zhu Ying et al. first investigated the influence of all parties on the composite construction cost from five aspects: design, production, transportation, management and society, and then conducted a study using decision experiment and evaluation laboratory methods, and concluded that the prefabrication rate, the degree of component disassembly, transportation efficiency, the degree of component standardization and the efficiency of resource allocation are the main factors determining the composite construction cost. Zhao Weishu et al. used analytic hierarchy process to analyze the factors affecting the cost of prefabricated buildings, and concluded that the construction level of technical personnel, coordination and communication among various types of work, prefabrication rate and assembly rate, template design and secondary design, and mold standardization are the main reasons affecting the construction cost. Yao Weitao et al. identified the factors affecting the cost of prefabricated buildings mainly from the three perspectives of design, procurement and construction stage, and on this basis established a structural model based on system engineering. Finally, the main influencing factors such as prefabrication rate and assembly rate, reuse of prefabricated components, splitting of prefabricated components, production plan of prefabricated components and production management mode are analyzed [6].

While combing and analyzing the literature related to prefabricated buildings, the cost impact factors of 34 prefabricated buildings were determined from five levels according to specific representative cases, and the investigation was conducted accordingly [7].

3 Empirical Analysis of Influencing Factors of Prefabricated Construction Cost

3.1 Questionnaire Design

This paper analyzes the main factors affecting the construction cost of the combination from the angles of design, manufacturing, transportation and installation. Because latent variables cannot be directly observed, they can only depend on their observed data The questionnaire uses Likert’s 5-level scoring method to evaluate the impact factors on the combined construction cost, and divides them into 5 levels according to their importance, and the respondents score each factor according to their own experience.

3.2 Questionnaire Distribution

Through QQ, wechat and face-to-face intervicategoryews, questionnaires were conducted among people involved in assembly construction, researchers studying and working in universities, and people working in government departments. The research objects include universities, government departments, construction enterprises, construction enterprises, consulting institutions, component manufacturing enterprises, etc.

3.3 Questionnaire Collection and Sorting

A total of 100 questionnaires were issued in this survey, and 97 valid questionnaires were actually recovered. The statistical results of the survey objects are shown in Table 1.

Table 1. Collect questionnaire survey statistics
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3.4 Reliability Test

Klonbach formula is used to test its reliability [8]. In the measurement result, if a is less than 0.6, it is generally regarded as not meeting the measurement standard; The results show that the scale has good reliability in the range of 0.7–0.8. The A-value range is 0.8–0.9, indicating that the scale has good reliability. Among the 97 valid questionnaires, 34 indicators were tested for reliability, and the reliability value of each dimension was more than 0.8, which is sufficient to indicate that the reliability of the questionnaire is good and the reliability of the data of all dimensions is good (Table 2). Through the reliability test of the questionnaire, it can be seen that the questions in the questionnaire have high reliability, and the internal consistency among the influencing factors meets the demand.

$$\alpha = \frac{{N \cdot \overline{c}}}{{\overline{v} + (N - 1) \cdot \overline{c}}}$$
(1)

Here N is equal to the number of items, c-bar is the average inter-item covariance among the items and v-bar equals the average variance.

Table 2. Reliability verification of variables
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3.5 Content Validity Test

KMO and Bartlett’s test were used to carry out KMO and Bartlett’s test on the survey data [9], and the KMO value obtained was 0.899, higher than 0.8. The approximate chi-square value of Bartlett’s test was 3032.927, and the degree of freedom was 561. And the significance is less than 0.01, which indicates that the questionnaire data of influencing factors of prefabricated construction cost is applicable, and it is suitable for factor analysis.

$${\text{KMO}} = \frac{{\sum {\sum\limits_{i \ne j} {{\text{r}}_{{\text{ij}}}^2 } } }}{{\sum {\sum\limits_{{\text{i}} \ne {\text{j}}} {{\text{r}}_{{\text{ij}}}^2 } } + \sum {\sum\limits_{{\text{i}} \ne {\text{j}}} {\alpha_{{\text{ij}}}^2 } } }}$$
(2)

Here rij stands for simple correlation coefficient and a2ij.1,2,3,…k stands for partial correlation coefficient. When the KMO is greater than 0.9, it indicates that the correlation between variables is very appropriate, and 0.8 to 0.9 indicates that the correlation between variables is very appropriate.

As can be seen from the rubble chart (Fig. 2), the broken line gradually flattens after 5, while it shows a sharp decline before that, indicating that it is more appropriate to extract 4 common factors from 34 indicators.

3.6 Structural Validity Test

According to the rotated component matrix. The factor load value of each variable is greater than 0.4, so these 34 variables are useful.

The validity analysis proves that the data analysis is effective. The observed values are consistent with the actual situation, and the internal stability of the questionnaire has been guaranteed to a certain extent. The content of the questionnaire is well-targeted and relatively comprehensive, and the indicators have independent significance, which indicates the reliability and credibility of the questionnaire.

Fig. 2.
figure 2

Lithotriptic plan

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3.7 Correlation Test

On this basis, through the design factors, production factors, transportation factors, installation factors and other external factors and the correlation between the cost control effect of prefabricated buildings [10], and then the cost control effect of these factors on prefabricated buildings is deeply studied. These results are shown in Table 3.

Table 3. Correlation test
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4 Conclusion

By analyzing the relevant test results of the survey samples, the following conclusions can be drawn:

  • (1) the influence coefficient of design factors, manufacturing factors, transportation factors, installation factors and other external factors on the assembly construction cost is below 0.05, indicating good significance, and the five factors have a very important role in the control of the assembly construction cost.

  • (2) design factors, manufacturing factors, transportation factors, installation factors and other external factors will have a positive impact on the control of combined construction costs.

  • (3) the importance of the combined construction cost is sorted as follows: design cost > Construction cost > Manufacturing cost > Transportation cost > Other external costs.