Research On Two-stage Scheduling Of Prefabricated Building Component Parts

"Complex spatio-temporal operation" is one of the basic characteristics of the prefabricated construction,which is different from traditional construction methods.To enjoy the prefabricated building,it is necessary to carry out the ordered coordination of the various stages of time and space.A crucial issue in prefabricated construction is the scheduling of components in the production,transport and assembly process,which means how to ensure accurate and orderly flow of component parts at different stages.Inefficient scheduling of component parts will directly lead to the advance or delay in production and supply.Early supply and insufficient stacking space on construction sites will put pressure on site storage and yard layout planning,leading to additional costs such as storage and secondary handling.Supply delays can cause workers to slow down and wait for materials on the construction site,thus affecting the construction progress and cost.The production and supply of prefabricated component parts and the layout of the stacking yard are the key links to connect manufacturing and construction.There is not only the inherent order and restraining relationship between them,but also a coordinated and unified purpose.The above problem is considered as a two-stage scheduling problem.Weather conditions,construction environments and other factors affecting project progress lead to changes in the demand for component parts.Changes in production and supply capacity affect the production and supply decision-making of component parts.The problem of the production schedule in an uncertain supply-demand environment is considered to be the first stage.Due to the limited and dynamic space of construction sites,the problems of stacking,storage and transportation management of component parts site are significant.Therefore,the second stage is to solve the on-site scheduling problem of component parts.The key to solving the two-stage scheduling problem is how to effectively deal with the relationship between multiple spaces for different jobs.In order to deeply describe the whole scheduling process and the relationship among spatio-temporal stages,the crucial factors of scheduling activities are analyzed,and the major characteristics of two-stage scheduling are pointed out.Then a two-stage scheduling model framework is established by using the object process methodology.It also analyzes the internal relationship between the two-stage sub-models,and clarifies the implementation path of the model.The first stage scheduling is to consider the "several to one" supply relationship between the factory and the construction site from the perspective of the construction site,focusing on the production and supply decision-making of component parts.Uncertain supply and demand factors are taken into account,and the changes in production capacity and construction demand are estimated respectively.Using the feedback information of the second stage scheduling,the impact of site space availability is considered at this stage.According to the above constraints,the stochastic programming method is used to minimize the total scheduling cost.The production scheduling model of component parts in the environment of uncertain supply and demand is established to determine the optimal production and supply scheme.The results of application case show that the scheduling model can minimize sum of holding and delay costs,and improve early or delayed supply.It is conducive to achieving the objective of "forward planning,precise control,efficient allocation and complete process link".The second stage of scheduling is the research into the scheduling of component parts on construction sites.It mainly takes the stacking yard layout planning as the core,and associates the initial production and supply with the back-end storage and transport,storage and consumption.By analyzing the non-centralized and dynamic storage demand,the overall framework of the on-site scheduling model is proposed.Firstly,according to the results of the first stage scheduling,the building information model is integrated to obtain the supply information of component parts;Secondly,using site surveillance videos,the image recognition method is applied to obtain the state information of the given stacking area;Finally,the dynamic programming model of stacking yard layout is established based on the information of the above two parts.On the premise of meeting the construction requirements and spatio-temporal constraints,the secondary handling is reduced and the total cost of on-site handling and centralized storage is minimized.The result indicates that this method effectively reduces the project cost,and improves the construction efficiency.This also provides a more practical process and method for the storage and stacking of component parts on site,reflecting the scheduling idea of "front-end link".