محمدصالح دشتي رحمت ابادي

Construction projects affect daily lives as they provide all physical spaces and systems for home, work, and travel. On-time completion is a crucial success factor in managing and eva‎luating the performance of a construction project. Thus, effective scheduling is vital to plan and control various processes and time-oriented events in a construction project. Several scheduling techniques are developed in the last decades, including bar charts, Gantt charts, network-based methods such as the Critical Path Method (CPM), and simulation-based scheduling techniques. Resources are included in the scheduling of construction projects to represent their actual conditions better. Space is also a constrained resource in construction projects. The total available site space is limitedly shared among the required spaces of the building elements under construction, temporary facilities, laborers, materials, and machinery. However, space is usually neglected in planning construction activities. The traditional network-based scheduling techniques, such as those based on the CPM, only consider the activities' temporal interferences. Creating construction schedules considering space availability is challenging due to the complexity of modeling spatiotemporal relationships among activities. Space management in construction projects deals with three areas of knowledge including Site Layout Planning (SLP), time-space conflict management and mobile resources' motion planning. Site layout planning involves coordinating limited site space to accommodate the temporary facilities, as they can function efficiently. This efficiency is essential due to its impact on project productivity, safety, and total time and cost. Dynamic Layout Planning of Temporary Facilities (DLPTF) is defined as creating facilities layouts that change during the project according to the dynamic variations in the site space's availability. Time-space conflict management in construction projects deals with identifying the time-space conflicts in the entire project duration, eva‎luating the detected conflicts, and consequently resolving them to prevent their negative impacts. Paying attention to the facilities layout's dynamic nature sheds light on its mutual interactions with the project schedule and mobile resources' motion plan. Most previous studies have investigated these areas of knowledge independently, without considering their interactions. Considering these mutual interactions increases the efficiency of site space usage and safety level, which leads to a more realistic temporary facilities layout and schedule in construction projects. Furthermore, little attention is paid to propose an automated, integrated system for managing potential time-space conflicts, considering the site space system's dynamic nature. Therefore, this study contributes to the body of knowledge by proposing an integrated simulation- based scheduling approach for dynamic site layout planning in construction projects. The system is based on a hybrid approach based on the following concepts: Lean Construction, Building Information Modeling (BIM), Discrete Event Simulation (DES), Genetic Algorithm (GA) method for optimization and Rapidly-exploring Random Tree (RRT) path planning algorithm. The proposed approach can consider the deep interactions between DLPTF, scheduling, and mobile resources' motion planning. The system dynamically generates diverse temporary facilities layouts during the project by considering possible site space's availability changes. It can test a vast number of "What-If" simulation-optimization scenarios for minimizing the project duration under dynamic changes in the layout of the temporary facilities. The proposed approach considers the dynamic changes in space requirements of the process- level activities and their entire interactions using a simulation-based scheduling engine. It considers all the possible temporal conflicts between all types of site spaces (e.g., the spaces of the building elements, activities, machinery, temporary facilities). The system automatically generates the required site spaces using the BIM model for time-space planning. It can automatically detect, eva‎luate, and resolve the time-space conflicts and modify the project's schedule. The motions of the mobile resources during the construction process are also simulated. The developed system is implemented and eva‎luated in a real underpass construction project under critical time and space constraints. A software is developed in the .Net framework as an add-on in Autodesk Navisworks Manage environment for implementing the approach. The results of implementing the proposed integrated system in the case study demonstrate its capabilities in considering the dynamic nature of temporary facilities layout planning and its deep mutual interactions with project's scheduling and motion planning of the mobile resources. The system minimized the duration of the project by determining the near-optimum value of a wide range of parameters such as the exact start and finish time of the process level activities, the exact set-point positions of the temporary facilities, the exact setup and dismantle time of the temporary facilities, the travel distances and travel frequencies of the mobile resources, and finally utilization and productivity of the resources. Implementing the proposed system illustrates its capabilities in automatic management of the time- space conflict during the entire project duration. It realistically takes into account the impacts of space limitations on the estimation of the project duration. A three-step algorithm based on using various bounding volumes (i.e., Bounding Spheres (BS), Axis-Aligned Bounding Boxes (AABB), and Oriented Bounding Boxes (OBB)) is used to accelerate detection of the time-space conflicts during the project simulation. Once the time-space conflicts are detected, the system automatically takes a suitable decision for resolving them based on the conflict percentage and some predefined if-then rules. Combining simulation-based scheduling (which can consider the process-level activities) and RRT* informed path planning method enables the proposed system to plan and trace the site's mobile resources' motions. The proposed approach's simulation-based scheduling engine also allows practitioners to track project resource utilization and construction processes' productivity rate. The system also generates a post-simulation D digital model based on enriching the project's BIM model with all the required time-space management data. The results indicate that the proposed system increases site space utilization efficiency, which leads to a more realistic temporary facilities layout and project schedule, particularly in those congested construction projects under time and space constraints. It can considerably prevent the negative impacts of the time-space conflicts on productivity and safety, especially in congested construction sites. The proposed system's capabilities can be better understood in cyclic construction and infrastructure projects under critical time and space constraints. It is so difficult for the site engineers of these projects to manually or mentally have a reliable estimate of the parameters in dynamic layout planning of temporary facilities, scheduling, and mobile resources motion planning. This is because of the deep interactions between these parameters and the project operations' multiple interacting cycles. On the other hand, the network-based scheduling methods such as CPM cannot consider the dynamic complexities in cyclic projects. Therefore, the practitioners can use the proposed system as an efficient decision support system for complicated processes of space management, scheduling, budgeting, and supply chain management of the mentioned projects.

زمان‌بندي , مديريت فضا , برنامه‌ريزي پوياي چيدمان كارگاه , تداخلات فضايي-زماني , مدلسازي اطلاعات ساخت , شبيه سازي گسسته پيشامد , بهينه سازي

scheduling , space management , Dynamic Site Layout Planning , Time-Space Conflict , Building information modeling (BIM) , Discrete Event Simulation (DES) , Optimization

Mohammad Saleh dashti

Dr. Khanzadi