# Research on an Assembly Building Buffer Zone Based on Gray Critical Chain
###### Abstract  
The complexity of construction in prefabricated buildings makes it vulnerable to uncertainty in project timelines, and traditional project timeline management is insufficient to control project timelines for prefabricated buildings. Therefore, research on project timeline management for prefabricated buildings is needed in order to optimize project timelines and improve project execution rates. This study proposed an improved method of setting prefabricated building buffer zones through the use of improved grey critical chain technology. Five major factors affecting project timelines in actual prefabricated construction projects were selected: personnel experience, degree of prefabrication, technical complexity, reasonableness of construction plans, and degree of construction space availability. The OPA technique was introduced and combined with the entropy weight method to improve the comprehensive weight coefficient of the grey critical chain calculation of the factors affecting the timeline. Other influencing coefficients were determined, and a new calculation method for the size of prefabricated building buffer zones was proposed. Monte Carlo simulations were conducted in Matlab on actual construction projects to ensure the scientific rationality of the improved method. The results showed that compared with the classical buffer calculation methods (cut-and-paste method, C&PM and square root standard deviation method, RSEM), the project timeline was reduced by 14.3% and 11.7%, respectively, using the improved method. The improved method not only reduces project uncertainties, but also achieves the goal of optimizing project timelines, and it is reasonable and effective. The results of the study provide a direction for the project timeline management of prefabricated building critical chains, and this method can be applied to the planning and management of prefabricated building buffer zones. s +
Footnote †: journal: Applied sciences  
have become a common occurrence. Therefore, the establishment of a schedule management system specifically tailored for assembly construction projects holds significant practical importance. [PERSON] [12] combined the Theory of Constraints (TOC) with project management to form Critical Chain Project Management (CCPM), which sets buffers to absorb the impact of uncertainties while satisfying the constraint conditions. CCPM has been applied in various fields [13; 14; 15; 16; 17] since it was proposed by [PERSON], and has shown great effectiveness. It has been proven that CCPM is a powerful tool for managing project schedules in the presence of uncertainties. CCPM extracts safety time from the processes to form a buffer, which is inserted at the end of the critical chain as a Project Buffer (PB) to absorb the impact of uncertainties. At the intersection of the critical chain and non-critical chains, a Feeding Buffer (FB) is inserted to prevent delays in non-critical chain processes from affecting the critical chain [18]. Therefore, setting the buffer is the most crucial part of CCPM, and the size of the buffer directly determines the project completion time. Classic methods for determining buffer size include the Cut-and-Paste Method (C&PM) [12] and the Root-Square Error Method (RSEM) [19]. However, subsequent research has found limitations in these two methods, so scholars from both domestic and international sources have proposed improvements by considering project uncertainties in buffer size determination. [PERSON] et al. [20] proposed two solution methods, resource tightness and network complexity, which effectively reduce buffer size. [PERSON] et al. [21] and [PERSON] [22] consider factors such as resource availability, network complexity, and activity slack, and propose methods for setting resource buffers in multi-project management. [PERSON] et al. [23] propose a buffer size determination method that takes into account the comprehensive impact of information and resources, effectively shortening project duration.