Drivers for Cost Estimating in Early Design: Case Study of Residential Construction

This paper proposes the use of a series of independent variables for an early estimation of the building construction cost of residential buildings. Based on 70 German residential properties, these variables serve as the cost drivers of a project, and the regression model, tested against the 70 properties, has a mean absolute percentage error of 9.6%. When applied to predict the cost of five more properties that were excluded from the 70 in the regression model, the percentage error ranges between–12 and 13%. The identified cost drivers are: compactness of the building, number of elevators, size of the project, expected duration of construction, proportion of openings in external walls, and region.     

Production System Loading–Cycle Time Relationship in Residential Construction

Production home building possesses characteristics similar to manufacturing processes, such as the construction of more or less similar houses repeatedly and a growing demand for mass customization of homes. As a result of these similarities, larger homebuilders often attempt to view their production system as an assembly line process. However, the management tools generally utilized by these home builders are those used in other sectors of the construction industry, such as critical path method scheduling, cost estimating, and earned value analysis. These management tools do not provide an explanation or control/prediction tools for many undesirable situations that arise during home building, such as increasing cycle time which slows delivery of product to consumers and increases project capital costs, and increasing amounts of work in process that increases capital investment and thereby decreases company financial performance. In order to bring better management tools to the residential construction industry, this study examines relationships between cycle time, work in process, system throughput, new construction starts, and the capacity of the production system using building permit data for new single family homes in Chandler, Ariz. The applicability of Little’s law, a basic equation used in factory production management models, to a residential production system is examined. This study shows a definite, predictable relationship between cycle time, work in process, and production system throughput. It provides a pathway for further study of production system characteristics that have historically not been included in construction management models, with the expectation of developing new construction management tools that will account for more of the characteristics of construction production systems that affect project performance and company financial performance.     

Lean Management Model for Construction of High-Rise Apartment Buildings

Execution of the finishing works in high-rise apartment buildings is made complex by the need to customize apartments to the varying requirements and designs of individual clients. The conventional construction planning practice of progressing upward from floor to floor breaks down in the face of the arbitrary sequence in which clients finalize their decisions. The results are long cycle times for delivery of completed apartments and corollary high levels of work in progress, budget and schedule overruns, and general dissatisfaction with the process on the part of the developer, contractor, subcontractors, and the clients. Application of lean construction principles to this problem has led to development of a management model that adopts pull scheduling, reduced batch sizes, and a degree of multiskilling. The main benefits expected are an enhanced ability to provide customized apartments, improved cash flow, and reduced apartment delivery cycle times. The model was first formulated in theory, then tested using a management simulation game and computer simulation, and subsequently, developed for practical application. This paper presents an analysis of conventional practice, the theoretical background to the lean approach, and the specific management changes proposed.     

Development of Lean Model for House Construction Using Value Stream Mapping

Lean construction has recently attracted considerable attention in the home building industry. Lengthy delivery time and significant waste in the construction process have caused many home builders to seek a more effective production model that will increase process reliability, reduce total lead time, and improve quality. However, although housing construction provides the closest analogy to manufacturing, a high level of variability prevents the direct transplantation of lean paradigm and techniques. In collaboration with a local home builder, a systematic approach based on value stream mapping technique is developed in this research to analyze the current process and to formulate a lean production model. The model has four main features: synchronized first-in, first-out lane-based flow, production leveling at pacemaker, work restructuring, and improved operation reliability. A simulation template is built to verify the model and to assist in the development of interim implementation models. This paper presents data collection and value stream selection, current practice analysis, and specific changes proposed for the lean production model.     

Integrating Neurofuzzy System with Conceptual Cost Estimation to Discover Cost-Related Knowledge from Residential Construction Projects

Cost estimation during early stage of a building construction project plays an important role for feasibility analysis in the planning and design phase. Traditional knowledge-based approaches suffer an essential difficulty due to resource price fluctuation in the market. This paper presents a hybrid method that integrates the principal items ratio estimation method with the adaptive neurofuzzy inference system for mining of cost estimation data. The proposed method provides exceptional capability for mining estimation knowledge that is difficult to be discovered by traditional knowledge-based approaches. A case study of residential building projects in China is conducted to demonstrate the proposed method. The testing results show that the proposed method does not only achieve high estimation accuracy, but also provide desirable features for estimators, such as explicit fuzzy decision rules and graphical presentations.     

Assessing the Environmental Impacts of a Lean Supply System: Case Study of High-Rise Condominium Construction in Korea

Prefabrication and just-in-time (JIT) delivery are important components of a lean supply system. Past research focuses on how much lead time is reduced and how much costs are saved, but few have studied the environmental impacts. While most of those studies on environmental impacts have focused on select life cycle phases or specific building materials and components, the impacts of different construction methods or supply strategies from the construction phase were ignored or simply approximated. This paper presents the results of a case on the environmental impacts of prefabrication and JIT delivery strategy of rebar supply on a high-rise condominium project in Korea.     

Impact of Using an E-Marketplace in the Construction Supply Process: Lessons from a Case Study

The procurement process is critical for construction companies. To improve it, many are resorting to e-marketplaces although they usually do not know exactly how much they can gain by doing so. This paper describes a study that measured the benefits of using an e-marketplace to support the procurement process of a construction company. The study included three marketplaces currently operating in Chile. However, in this paper, we focus on Iconstruye, the most important one. 70 executives and professionals from 25 construction companies randomly selected from the 89 that used this marketplace, were interviewed and asked to fill out a questionnaire. This data was validated using data from Iconstruye and from 33 suppliers. The results show that the adoption of an e-marketplace reduces turnaround time, errors, urgent orders, and irregular purchases. A more reliable procurement process directly contributes to a leaner construction process by reducing upstream variability, procurement cycle times, and the need for large inventories on site. Users also perceive an improvement in certain global indicators when using an e-marketplace.     

LEAPCON: Simulation of Lean Construction of High-Rise Apartment Buildings

A lean model has been proposed for the construction management of high-rise apartment buildings with customized apartment designs. It incorporates a number of changes to traditional management practice, including single-piece flow with pull scheduling, work restructuring, and multiskilling. A simulated construction process scenario was devised for experimental evaluation of the model. The simulation was first implemented as a live management game, in which participants played the roles of the clients, general contractor, and subcontractors. Eleven runs with different teams indicated that the lean model increased throughput, improved cash flow, and reduced apartment delivery cycle time. However, the limitations of the live simulation led the writers to implement a discrete event computer simulation of the same process. The computer simulation reinforced the findings of the live simulation and emphasized the specific beneficial effect of single-piece flow under pull scheduling. The lean model may be of immediate interest to construction planners and managers because it enables full customization with minimal waste and no additional resources. The demonstrative clarity of the lean model simulation, both live and computerized, makes it a powerful tool for education and research.     

Residential Construction Lot Grading Approval Process Optimization: Case Study of City of Edmonton

Rapid growth of residential construction in the city of Edmonton, Alberta, Canada has led to an increased demand for lot grading (LG) inspectors. The traditional inspection process has contributed to inspection delays, backlog, and decreased customer satisfaction. The aim of the research presented in this paper is to study, evaluate, and optimize the existing LG approval process. Data from past years were collected and analyzed to establish a baseline performance level. Flowcharts were developed to visualize the process and a survey was conducted to determine potential areas of improvement from the perspectives of different shareholders. Lean thinking principles were applied to identify and reduce the nonvalue added activities and improve performance. The final phase of the research involved the simulation of the process to evaluate the impact of the implementation of various recommendations. Based on the simulation results, final recommendations were made and later implemented with the help from the city’s Information technology department. These modifications to the existing process produced significant gains in quality and productivity, as predicted by the simulation model.     

Impact of Inspected Buffers on Production Parameters of Construction Processes

This paper examines the production implications of quality control inspections conducted on the buffer between processes in a construction project by modeling the linkage between these processes. Inspection of partially completed work at the end of one activity but before the beginning of work by the next activity is fairly common. Work that is deemed to be of sufficient quality is then made available for the next activity. Work that is deemed insufficient requires rework, typically by the trade appropriate to the activity that fed into the buffer, to bring the work into compliance. This has implications for workload management for that trade, of course, as well as for the reliability of work flow to the successor or downstream processes. While such situations are common in all construction sectors, an example from the residential construction sector was examined via a simulation model augmented by field data collected from residential construction projects. The impacts of the work flow into the predecessor process, the inspection pass rate, and resource availability were examined. The inspection pass rate was found to dramatically affect the reliability of work flow, unless resources are unlimited. Furthermore, the inspection pass rate was found to be functionally related to the production parameters of the process.     

RH生产超低碳钢的关键控制技术研究

目前钢铁行业采用中薄板坯连铸机生产超低碳深冲钢有很多控制难点,针对济钢RH—ASP工艺路线生产超低碳深冲钢的技术难题逐一进行了分析研究。对钢水可浇铸性,碳、氧、氮的控制,提出了生产超低碳铝镇静钢时要减少RH处理氧气吹人量,造还原渣,保证纯脱气时间和对夹杂物改质来提高钢水的可浇注性,及保证超低的碳含量、合适的环流气体量、钢水中尽可能低的氧和硫等建议。     

Study of Passive Deck-Flaps Flutter Control System on Full Bridge Model. II: Results

Using the analytical format set forth in the first of these two companion papers, numerical simulations of a passive aerodynamic control method for suppression of the wind-induced instabilities of a very long span bridge are presented in this paper. At first, the aerodynamic stability of the uncontrolled system is discussed using a sectional model and full bridge model, respectively. Next, the efficiency of the proposed asymmetric and symmetric cable connection control systems is studied. Both systems offer similar maximum improvements in critical wind speed. The asymmetric cable connection system turns out to be very sensitive to horizontal motions, which strongly degrade its effectiveness. On the contrary, the symmetric cable connection system is not sensitive to horizontal motions, but its efficiency is limited by divergence.     

Study of Passive Deck-Flaps Flutter Control System on Full Bridge Model. I: Theory

A passive aerodynamic control method for suppression of the wind-induced instabilities of a very long span bridge is presented in this paper. The control system consists of additional control flaps attached to the edges of the bridge deck. Control flap rotations are governed by prestressed springs and additional cables spanned between the control flaps and an auxiliary transverse beam supported by the main cables of the bridge. The rotational movement of the flaps is used to modify the aerodynamic forces acting on the deck and provides aerodynamic forces on the flaps used to stabilize the bridge. A time-domain formulation of self-excited forces for the whole three-dimensional suspension bridge model is obtained through a rational function approximation of the generalized Theodorsen function and implemented in the FEM formulation. This paper lays the theoretical groundwork for the one that follows.