Simulation-Based Decision Support System for Economical Supply Chain Management of Rebar

The economics of a materials management system is defined by the size of the shipments, the scheduling strategy that allows contractors to handle uncertainty and variability in the supply chain, and the timing of the shipments, which in turn depend on the environment in which the project is taking place. This study presents a simulation-based decision support system to assist contractors in selecting the most economical rebar management system prior to the start of construction by recommending lot sizes (large, small), a scheduling strategy (optimistic, neutral, pessimistic), and buffer sizes (large, medium, small) given the conditions of the project. This model is of benefit to contractors and researchers because it generates the probable cost of inventory of 18 alternative rebar management systems ranging from just in case (JIC) to just in time (JIT) and including different variations in between. It allows contractors to select the alternative with least cost of inventory at the planning stages of a project. The simulation model was tested by using actual data obtained from a trade center project in Istanbul, Turkey. As expected, the test indicated that JIC was the most economical rebar management system in a case study conducted in a developing country, as it generated a savings of 4.8% over JIT.     

基于供应链的企业库存成因及优化控制研究

基于企业全面库存管理思想,对库存成本、库存控制、库存系统优化等管理经验与前人研究成果进行分析,借鉴先进企业的库存管理理念和方法,以大型制造企业为核心研究对象,在集供应商、制造商、经销商为一体的供应链作为研究框架的基础上,运用供应链系统理论作为研究方法,分析了库存管理现状、影响因素及产生原因,从优化生产管理、整合企业内部供应链和跨企业供应链的角度提出库存控制的相应对策,以实现全面的库存优化,提高经营效益。     

基于供应链企业库存成因及优化控制研究

基于企业全面库存管理思想,对库存成本、库存控制、库存系统优化等管理经验与前人研究成果进行分析,借鉴先进企业的库存管理理念和方法,以大型制造企业为核心研究对象,在集供应商、制造商、经销商为一体的供应链作为研究框架的基础上,运用供应链系统理论作为研究方法,分析了库存管理现状、影响因素及产生原因,从优化生产管理、整合企业内部供应链和跨企业供应链的角度提出库存控制的相应对策,以实现全面的库存优化,提高经营效益。     

Strategic Positioning of Inventory to Match Demand in a Capital Projects Supply Chain

Industrial buyers of capital facilities have experienced and continue to experience pressure to reduce facility design and construction lead time. This pressure arises both internally (due to successes in manufacturing lead time reductions) and externally (due to competitive forces including narrowing product delivery windows). This paper presents a case study detailing one owner’s efforts to reduce the length and variability of delivery time for long-lead construction materials in order to improve overall project lead time. The owner adopted a long-term multiproject perspective, procuring material in advance of specific projects and holding it at a position in the supply chain selected to allow flexibility for customization. Reduction in lead time of 75% from order to delivery of the material resulted for individual projects within the owner’s capital plan. As a result, the material was available at the construction site well in advance of its need for erection. To study if holding material at alternative locations in the supply chain could provide a better match between delivery quantities and the demand for erection, the supply chain was simulated. In this case study, demand information was imprecise, allowing only the quantity of material delivered to be considered rather than matching specific items to specific locations. Nonetheless, the results demonstrate the utility of simulation in the capital projects supply chain and the value of improving demand forecasts.     

基于供应链的企业库存成因及优化控制研究

基于企业全面库存管理思想,对库存成本、库存控制、库存系统优化等管理经验与前人研究成果进行分析,借鉴先进企业的库存管理理念和方法,以大型制造企业为核心研究对象,在集供应商、制造商、经销商为一体的供应链作为研究框架的基础上,运用供应链系统理论作为研究方法,分析了库存管理现状、影响因素及产生原因,从优化生产管理、整合企业内部供应链和跨企业供应链的角度提出库存控制的相应对策,以实现全面的库存优化,提高经营效益.     

Role of Inventory Buffers in Construction Labor Performance

Buffers of material stockpile (inventory) are formed at the work level in construction to help manage production. The size of material stockpiles often has an important bearing on construction project performance. In construction projects, where conditions are often uncertain and variable, some have suggested that buffers be sized and located according to the conditions. New management thinking like lean construction and theory of constraints suggests that the size of buffers needs to be managed carefully, because when oversized, buffers are wasteful, impede workflow, and hinder performance. Research has shown that project variability can be affected with the careful deployment of buffers but has not really evaluated the impact on construction labor performance. This paper reports an exploratory analysis of the relationship between inventory (buffers) and construction labor performance with data collected from three commercial projects in Brazil. In this study, the size of the buffer between rebar fabrication and installation in the construction of a structural system is compared to the labor performance of the fabrication and installation crews. The results show that some buffer helps achieve the best labor performance in the construction operations studied.     

Stochastic Time-Cost-Resource Utilization Optimization Using Nondominated Sorting Genetic Algorithm and Discrete Fuzzy Sets

In a construction project, the cost and duration of activities could change due to different uncertain variables such as weather, resource availability, etc. Resource leveling and allocation strategies also influence total time and costs of projects. In this paper, two concepts of time-cost trade-off and resource leveling and allocation have been embedded in a stochastic multiobjective optimization model which minimizes the total project time, cost, and resource moments. In the proposed time-cost-resource utilization optimization (TCRO) model, time and cost variables are considered to be fuzzy, to increase the flexibility for decision makers when using the model outputs. Application of fuzzy set theory in this study helps managers/planners to take these uncertainties into account and provide an optimal balance of time, cost, and resource utilization during the project execution. The fuzzy variables are discretized to represent different options for each activity. Nondominated sorting genetic algorithm (NSGA-II) has been used to solve the optimization problem. Results of the TCRO model for two different case studies of construction projects are presented in the paper. Total time and costs of the two case studies in the Pareto front solutions of the TCRO model cover more than 85% of the ranges of total time and costs of solutions of the biobjective time-cost optimization (TCO) model. The results show that adding the resource leveling capability to the previously developed TCO models provides more practical solutions in terms of resource allocation and utilization, which makes this research relevant to both industry practitioners and researchers.     

Optimizing Material Procurement and Storage on Construction Sites

Efficient planning of materials procurement and storage on construction sites can lead to significant improvements in construction productivity and project profitability. Existing research studies focus on material procurement and storage layout as two separate planning tasks without considering their critical and mutual interdependencies. This paper presents the development of a new optimization model for construction logistics planning that is capable of simultaneously integrating and optimizing the critical planning decisions of material procurement and material storage on construction sites. The model utilizes genetic algorithms to minimize construction logistics costs that cover material ordering, financing, stock-out, and layout costs. The model incorporates newly developed algorithms to estimate the impact of potential material shortages on-site because of late delivery on project delays and stock-out costs. An application example is analyzed to demonstrate the capabilities of the construction logistics planning model in simultaneously optimizing material procurement decisions and storage layout plans.     

Time-Cost-Quality Trade-Off Analysis for Highway Construction

Many departments of transportation have recently started to utilize innovative contracting methods that provide new incentives for improving construction quality. These emerging contracts place an increasing pressure on decision makers in the construction industry to search for an optimal resource utilization plan that minimizes construction cost and time while maximizing its quality. This paper presents a multiobjective optimization model that supports decision makers in performing this challenging task. The model is designed to transform the traditional two-dimensional time-cost tradeoff analysis to an advanced three-dimensional time-cost-quality trade-off analysis. The model is developed as a multiobjective genetic algorithm to provide the capability of quantifying and considering quality in construction optimization. An application example is analyzed to illustrate the use of the model and demonstrate its capabilities in generating and visualizing optimal tradeoffs among construction time, cost, and quality.     

连铸-热轧集成生产库存优化模型

从实际问题从发,研究连铸和热轧两阶段集成生产的库存与生产计划优化问题。根据顾客对板坯和钢卷的订货情况,考虑连铸机和热轧机的生产能力约束及板坯库和热轧卷库的库容约束,针对板坯的外卖量和作为热轧机原料量之间的协调及板坯与热轧卷之间的匹配情况,同时考虑板坯库和热轧卷库的库存成本以及对板坯和钢卷的订货需求可以延迟满足,但需支付惩罚费用等特点,以利润最大为目标函数,建立了相应的线性规划模型。通过大量的数值测试,验证了模型的有效性。     

Constructability and Economics of FRP Reinforcement Cages for Concrete Beams

This paper presents a quantitative economic analysis and a qualitative constructability analysis of three-dimensional fiber-reinforced plastic (FRP) reinforcement cages for concrete beams. Material, labor, and life-cycle costs are provided, and construction practice aspects are discussed. The results of the analyses indicate that prefabricated FRP cages can offer benefits to the construction industry. Although the initial costs of the FRP materials are likely to be higher than those of steel rebar, there is a significant potential for cost savings due to reduced maintenance and labor costs, as a result of the corrosion resistance of the FRP and the increased construction productivity. When direct life-cycle costs are considered, FRP reinforcements already constitute, in many cases, an economically competitive alternative to conventional steel reinforcement in adverse environments. If, in addition, the indirect cost savings as well as quality and safety issues are considered, the FRP reinforcement may be even more competitive.     

Minimizing Construction-Related Security Risks during Airport Expansion Projects

Airport expansion projects often require the presence of construction personnel, material, and equipment near airport secure areas/facilities, leading to an increase in the level of risk to airport security. Construction planners and airport operators need to carefully study this challenge and implement active measures in order to minimize construction-related security breaches and comply with all relevant Federal Aviation Administration guidelines. This paper presents the development of an advanced multiobjective optimization model for planning airport construction site layouts that is capable of minimizing construction-related security breaches while simultaneously minimizing site layout costs. The model incorporates newly developed criteria and performance metrics that enable evaluating and maximizing the construction-related security level in operating airports. The model is developed using a multiobjective genetic algorithm, and an application example is analyzed to demonstrate the use of the model and its unique capability of generating a wide spectrum of optimal trade-offs between construction-related airport security and site layout costs.     

Risk-Based Framework for Safety Investment in Construction Organizations

The costs of construction injuries can have a substantial impact on the financial success of construction organizations and increase the overall costs of construction up to 15%. Following the Occupational Safety and Health Act of 1970, construction firms began to implement a variety of management techniques to reduce the frequency of injuries. Although these strategies decrease the cost of injuries, they consume time and other significant resources. Thus, it is imperative for construction organizations to objectively evaluate the cost-benefit of investments in injury prevention through formal and robust processes. This paper presents a risk-based framework that can be used to evaluate the incremental return on investment of a series of investments in highly effective injury prevention strategies. The framework was developed using foundational risk quantification and analysis techniques and is illustrated using a hypothetical case study that is based on archival data published by United States government agencies. The conclusion of this study is that the optimal investment strategy can be identified through a formal analysis and that optimization depends on the frequency and cost of injuries, the sequence in which the specific injury prevention techniques are implemented, the risk mitigated by each strategy, and the organization’s attitude toward acceptable risk.     

Economic Evaluation of Reinforced Concrete Structures with Columns Reinforced with Prefabricated Cage System

A new reinforcement system termed the prefabricated cage system (PCS) that can be used as an alternative to the rebar reinforcement cage is economically evaluated. PCS is a prefabricated reinforcement that enables easier, faster, and more reliable construction. Use of PCS shortens the construction schedule time and lowers total construction cost. This is important to both owners and construction contractors. The engineering economics methods presented in this paper would also be of interest to researchers. Reinforced concrete structures with PCS reinforced columns have been considered in this research, as it is one of the major applications of PCS. Various parameters affecting the economics of PCS are reviewed and a case study structure is analyzed comparing the costs of the structure with rebar reinforced columns to costs of the structure with PCS reinforced columns. The investigation shows that using PCS results in a 33.3% time savings and a 7.1% cost savings over rebar for each column. This results in an average of 3.6% savings on total project cost; an average of 22.2% savings on total column costs; 20.4% savings on total project time period, and 33.3% savings on columns construction time period. The cost savings are estimated based on production of small quantities of PCS reinforcement. Mass production of PCS reinforcement would result in even higher cost savings.     

钢铁企业轧制计划与能源调度协同优化

钢铁企业物质流网络与能量流网络的协同优化是实现钢铁行业高层次系统节能的关键。钢铁企业在不同工况下煤气的富余量以及蒸汽和电力需求量不同,轧制工序(含加热炉)作为电力和煤气消耗大户,轧制计划的改变会影响能量流网络中能源介质的分配和调度。提出了钢铁流程物质流与能量流协同优化方法,在分时电价的条件下,利用启发式规则调度方法对一天内的轧制单元进行合理的排程,然后用线性规划方法以系统运行能源成本最小为目标函数,建立钢铁企业煤气 蒸汽 电力系统不同工况下的耦合优化调度模型。通过LINGO求解出模型的最优解,得到了轧制单元的最优排程以及不同工况下煤气、蒸汽、电力的最优实时生产调度方案,用于指导实际生产。利用S钢厂实际数据进行实例分析,得出的调度方案可实现煤气 蒸汽 电力系统的最优化分配,系统运行的能源成本降低8.54%,验证了模型的有效性。     

Trade-off between Safety and Cost in Planning Construction Site Layouts

Planning construction site layouts involves identifying the positions of temporary facilities on site, and accordingly it has a significant impact on the safety and efficiency of construction operations. Although available models are capable of minimizing the travel cost of resources on site, they do not consider safety as an important and separate objective in the optimization of site layouts. This paper presents the development of an expanded site layout planning model that is capable of maximizing construction safety and minimizing the travel cost of resources on site, simultaneously. The model incorporates newly developed concepts and performance criteria that enable the quantification of construction safety and travel cost of resources on site. The present model is developed in three main phases: (1) formulating decision variables and optimization objectives in this site layout planning problem; (2) identifying and satisfying all practical constraints in this optimization problem; and (3) implementing the model as a multiobjective genetic algorithm. An application example is analyzed to illustrate the use of the model and demonstrate its capabilities in optimizing construction site layouts and generating optimal trade-offs between safety and travel cost of resources on site.     

Reducing the Economic Risk of LNG Tank Construction under Conditions of Fluctuating Resource Prices

Fluctuating resource prices affect the costs of the materials used in the construction of LNG (liquid natural gas) tanks. In this paper, methods based on the field experience of the writers for the reduction of the cost of LNG tanks in general and in-ground LNG tanks in particular are discussed. Of the various components of the construction cost, the price of steel materials is a significant contributor. Using a newly defined cost impact index, the costs of construction of different types of LNG tanks are compared. Further, by considering actual examples of the construction of in-ground tanks, important issues relating to the use of steel materials are identified and, by using a cost reduction index, recommendations are made for the reduction of the cost risk during fluctuations in resource prices.     

Optimal Planning and Scheduling for Repetitive Construction Projects

This paper presents a multiobjective optimization model for the planning and scheduling of repetitive construction projects. The model enables construction planners to generate and evaluate optimal construction plans that minimize project duration and maximize crew work continuity, simultaneously. The computations in the present model are organized in three major modules: scheduling, optimization, and ranking modules. First, the scheduling module uses a resource-driven scheduling algorithm to develop practical schedules for repetitive construction projects. Second, the optimization module utilizes multiobjective genetic algorithms to search for and identify feasible construction plans that establish optimal tradeoffs between project duration and crew work continuity. Third, the ranking module uses multiattribute utility theory to rank the generated plans in order to facilitate the selection and execution of the best overall plan for the project being considered. An application example is analyzed to illustrate the use of the model demonstrate its new capabilities in optimizing the planning and scheduling of repetitive construction projects.