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.     

厚料层烧结技术的经济学解释

烧结料层透气性的Voice公式与经济学中的"柯-道生产函数"具有相似性,它们都是用来说明投入与产出之间的技术关系。用经济学中"规模效用递减"的基本法则和"边际分析"方法,引入到烧结生产中料层高度和抽风负压对烧结矿产出的分析中;作出了烧结生产的等成本曲线、等产出曲线;获得厚料层烧结生产条件下数量型增长和效益型增长的理论模型;首次从经济学角度解释了中国厚料层烧结生产机理和扩张路径,给出了烧结生产经济区的定义和确定方法;最后,提出厚料层烧结技术的发展方向不是单一或多个投入要素的提高,而是需要向提高全要素生产率的方向发展。     

Construction Production Planning

A new branch of optimization, Optimal Control Theory, is used as a computational method to formulate and solve construction production planning problems. An example of the literature, Griffis' application of queueing theory to determine the optimal number of trucks to perform an earthmoving job, is used. It is shown that under the presence of weather varying conditions, optimal production rates may be time varying. A feedback solution is found. The implications of such solution are discussed. A simulation is performed to compare the use of varying and constant production rates.     

Effects of Electroosmosis on Soil Temperature and Hydraulic Head. II: Numerical Simulation

A numerical model to simulate the distributions of the voltage, soil temperature, and hydraulic head during a field test of electroosmosis was developed. The two-dimensional governing equations for the distributions of the voltage, soil temperature, and hydraulic head within a cylindrical domain are derived based on the principles of charge, energy, and mass conservations, Darcy’s law, Ohm’s law, and Fourier’s law of heat conduction. We assumed that the voltage distribution was at steady state, whereas the soil temperature and hydraulic head were at transient states during the test. The simulated domain was segmented with a block-centered finite-difference scheme and the resulting equations were solved numerically with the successive overrelaxation method. The parameters (such as electrical, thermal, hydraulic, and electroosmotic properties of the soil, graphite, and sand) that were required by the model were measured either using core samples or slug tests. The model is able to predict the pattern as well as the magnitude of the voltage profiles observed. The simulated temperatures are similar in pattern and are within 3°C of the values observed in the four casings during 4 weeks of electroosmosis. The changes in the rates of temperature with an increase in energy input predicted by the model are in agreement with the observed changes. The output from the hydraulic head simulations showed that the model could predict patterns of hydraulic head changes in the vicinity of mesh and graphite electrodes. The model, however, underestimated the magnitude of the changes close to the anode. The simulated electroosmotic flow rate of 0.9 L/h is also consistent with the observation of 0.6–0.8 L/h.     

Linear Scheduling Model with Varying Production Rates

Activity production rates drive the development and accuracy of linear schedules. The nature of linear projects dictates an assortment of variables that affect each activity’s production rate. The purpose of this research was to expand the capabilities of linear scheduling to account for variance in production rates when and where the variance occurs and to enhance the visual capabilities of linear scheduling. This new linear scheduling model, a linear scheduling model with varying production rates (LSMVPR), has two objectives. The first is to outline a framework to apply changes in production rates when and where they occur along the horizontal alignment of the project. The second objective is to illustrate the difficulty or ease of construction through the time-location chart. This research showed that the changes in production rates because of time and location can be modeled for use in predicting future construction projects. Using the concept of working windows, LSMVPR allows the scheduler to develop schedule durations on the basis of minimal project information. The model also allows the scheduler to analyze the impact of various routes or start dates for construction and the corresponding impact on the schedule. The graphical format allows the construction team to visualize the obstacles in the project when and where they occur by using a new feature called the activity performance index (API). This index is used to shade the linear scheduling chart by time and location with the variation in color indicating the variance in predicted production rate from the desired production rate.     

Pile Construction Productivity Assessment

Bored piles are vital elements for highway bridge foundation. A large number of factors oversees productivity and cost estimation processes for piles, which creates many problems for the time and cost estimators of such process. Therefore, current study is designed to diagnose these problems and assess productivity, cycle time, and cost for pile construction using the artificial neural network (ANN). Data were collected for this study through designated questionnaires, site interviews, and telephone calls to experts in different construction companies. Many variables have been considered to manage the piling construction process. Three-layer, feed forward, and fully connected ANNs were trained with an architecture of seven input neurons, five output neurons, and different hidden layer neurons. The ANN models were validated and proved their robustness in output assessments. Three sets of charts have been developed to assess productivity, cycle time, and cost. This research is relevant to both industry practitioners and researchers. It provides sets of charts for practitioners’ usage to schedule and price out pile construction projects. In addition, it provides researchers with a methodology of applying ANN to pile construction process, its limitation, and future suggestions.     

基于普钢成本子系统的特钢ERP成本子系统及实现

成本子系统是江阴兴澄特种钢铁有限公司ERP系统的重要组成部分。为了争取在较短的时间内实现能适应公司特钢经营生产情况的成本子系统,在系统实现过程中少走弯路,经过充分的调研和论证,通过将成熟的普钢ERP成本子系统与特钢企业成本核算的特殊性进行有机结合,成功开发了特钢企业的ERP成本子系统。兴澄特钢成本子系统通过收集基本的投入、产出等信息,结合特钢核算方法,实现了特钢成本核算的信息化,做到了成本核算人为因素少和产品成本信息的真实可信,极大减少了成本核算人员的工作量,并贯穿产、供、销全过程,形成了以财务为中心的ERP系统,在实际运行中取得了很好的效果。     

Productivity Analysis of Construction Operations

An interactive system for analysis of construction operations is proposed. The analysis is carried out in the context of various work modules which address quantity development, resource definition, and production and cost analysis. The quantity work module generates quantities based on information available in the design documents. The resource definition module receives and stores data regarding the labor∕equipment combination to be used to execute work tasks. This module provides the user with a set of standard useful construction process models. For each construction operation to be analyzed, the terminal describes the standard models. The user makes input of a set of parameters for process keyname, quantity, work task durations, number of resources, production capacity of each unit, and cost per hour of each unit to the standard model to be used. Using input from the resource definition module, the productivity and cost analysis module generates production rates and unit costs based on process simulation using CYCLONE methodology.     

Elasticity of Space-Time: Basis of Newton’s 2nd Law of Motion

In this paper we derive Newton’s 2nd Law of Motion from the constitutive equation of elasticity of a space-time continuum in four dimensions. This we do by introducing a four-dimensional material continuum with a Minkowskian metric, in analogy with Einstein’s general theory of relativity. The four-continuum is deformable in both space and time. The physics of the deformation is embedded in a variational principle, which is a form-invariant extension of its classical mechanical counterpart in three dimensions, but with the acceleration term absent. General dynamic equations of elasticity in four dimensions are thereby derived. When the constraint of temporal inextensibility (universal time) is introduced, these equations yield readily the dynamic equations of elasticity in three dimensions. The presence of the inertia term in these equations, is a direct consequence of the temporal curvature induced by the deformation of the four-continuum. Newton’s law of motion for rigid bodies follows when the additional constraint of spatial inextensibility is introduced.     

Mathematical modelling of unsteady-state transport of metal ions through supported liquid membrane

In this study, a mathematical model for unsteady-state transport of metal ions from aqueous solution through supported liquid membrane containing carrier is presented. For a transport process using supported liquid membrane, the three resistances to consider are the membrane resistance and the aqueous boundary layer resistances at the side of feed and stripping phases. The transport of species in the feed, the membrane and the stripping phases is modelled by Fick's second law. Time-dependent boundary conditions for the feed, the membrane and the stripping phases are obtained by means of kinetics of chemical reaction in the feed–membrane and the membrane–stripping interface. Partial differential equations obtained for the feed, the membrane and the stripping phases are analytically solved by using Duhamel's Theorem. Concentration distribution within the aqueous film layers and membrane as a function of position and time was derived from models obtained. The obtained model is checked against experimental data corresponding to the transport of copper ions from aqueous solution through supported liquid membrane by LIX 984.     

Predicting Airflow Rates in the Coarse Layer of Passive Dry Barriers

Laboratory experiments were conducted with steady wind velocities to measure pressure drops in pipes used to ventilate passive dry barriers. Two vent pipe diameters (100 and 150 mm) and several pipe end geometries were tested. Nondimensional ventilator equations were developed using the pressure drop data that, when combined with Darcy’s law, can be used to estimate airflow rates in passive dry barriers. A field experiment was conducted to verify the laboratory results. Comparisons were also made between flow rates predicted using the airflow rate equations and flow rates measured in two field-scale tests of dry barriers, one of which was constructed by the writers. Results of the laboratory tests indicate that a unique ventilator equation exists for each pipe end geometry, and that more than one equation may exist if the pipe end is not symmetrical (i.e., the pressure drop depends on wind direction relative to the pipe end). The field experiment indicated that the equations developed based on the laboratory data are in general agreement with average field conditions, but more scatter exists in the field due to varying wind velocities. Good correspondence exists between predicted flow rates and those measured in the field scale tests of passive dry barriers.     

Analysis of Techniques Leading to Radical Reduction in Project Cycle Time

Today’s construction business relies on first-to-market product strategies to gain competitive advantages and increase profit margins. This has created an increased demand for a high performance capital project delivery system that can achieve a dramatic reduction in project cycle time. Very few decision tools and guidelines exist to assist owners in choosing appropriate delivery systems and project strategies to radically reduce the project cycle time from the preplanning stage through start up. The research presented in this paper surveyed the construction owners and architectural/engineering/construction firms to identify projects that have achieved greater than 25% reduction in overall project cycle time when compared to current industry standards. The data collected were analyzed to determine the techniques that facilitate radical reduction in project cycle time. These techniques include, best practices and schedule reduction techniques as well as the various management techniques employed on the projects identified by the Construction Industry Institute (CII). This research also identified the barriers to radical schedule reduction. The research concludes that radical schedule reduction well in excess of 25% can be achieved through the selective employment of management techniques, schedule reduction techniques and CII best practices. Almost every construction manager can utilize this research to improve project performance whether for radical reduction or simply more effective execution.     

Probabilistic Duration Estimation Model for High-Rise Structural Work

The duration of a construction project is a key factor to consider before starting a new project, as it can determine project success or failure. Despite the high level of uncertainty and risk involved in construction, current construction planning relies on traditional deterministic scheduling methods that cannot clearly ascertain the level of uncertainty involved in a project. This, subsequently, can prolong a project’s duration, particularly when that project is high-rise structural work, which is not yet a common project type in Korea. Indeed, among construction processes, structural work is notable, as it is basically performed outdoors. Thus, no matter how precisely a schedule is developed, such projects can easily fail due to unexpected events that are beyond the planner’s control, such as changes in weather conditions. Therefore, in this study, to cope with the uncertainties involved in high-rise building projects, a probabilistic duration estimation model is developed in which both weather conditions and work cycle time for unit work are considered to predict structural work duration. According to the proposed estimation model, weather variables are divided into two types: weather conditions that result in nonworking days and weather conditions that result in work productivity rate (WPR) change. Obtained from actual previous data, the WPR is used with relevant nonworking day weather conditions to modify the actual number of working days per calendar days. Furthermore, on the basis of previous research results, the cycle time of the unit work area is assumed to follow the β probability distribution function. Thus, the probabilistic duration model is valid for 95% probability. Finally, a case study is conducted that confirms the model can be practically used to estimate more reliable and applicable probabilistic durations of structural work. Indeed, this model can assist schedulers and site workers by alerting them, at the beginning of a project, to project uncertainties that specifically pertain to structural work and the weather. Thus, the proposed model can enable personnel to easily amend, and increase the reliability of, the construction schedule at hand.     

Spatial and Temporal Variation of Manning’s Roughness Coefficient in Furrow Irrigation

Manning’s roughness coefficient is one of the input parameters in many surface irrigation simulation models. It affects the velocity of flow and thereby its variation with time and distance along the field length influence water application. In this study, variation of Manning’s roughness coefficient was studied for a furrow plot consisting of three 40 m long free drained furrows of parabolic shape and having a top width of 0.30 m, a depth of 0.15 m and a slope of 0.5%. The irrigation experiments were carried out with the inflow rates of 0.2, 0.3, 0.4, and 0.5?L?s1; and 0.3, 0.4, 0.5, 0.6, and 0.7?L?s?1 under bare; and cropped field conditions, respectively. Furrow cross-section data were collected before each irrigation event at 0.5, 13, 26 and 39.5 m from the head end along the center furrow using a profilometer. During the irrigation event, water depth and velocity of flow were measured at these locations at an interval of 15 min using point gauge and color dye, respectively. The furrow cross-section data were fitted into a second-degree polynomial equation to determine the furrow shape parameters that were used along with the flow depth data for determining the wetted area and wetted perimeter. The wetted area, wetted perimeter, and the velocity data were used to estimate Manning’s roughness coefficient spatially and temporally. It is found that for both bare and cropped field conditions, Manning’s roughness coefficient was more at second and last quarter of the furrow due to soil erosion at these locations. Manning’s roughness coefficient at these locations varied from 0.019 to 0.022 and 0.015 to 0.018 for bare field whereas from 0.02 to 0.024, and 0.019 to 0.022 for cropped field, respectively. The temporal variation of Manning’s roughness coefficient for both bare and cropped furrow conditions decreased with the elapsed time. However, these decreasing trends were observed more for lower inflow rates. Further, the average Manning’s roughness coefficient for the subsequent irrigations was varied from 0.018 to 0.02 and from 0.019 to 0.0245 for bare and cropped conditions, respectively. Thus, the values of Manning’s roughness coefficients were more for cropped furrow conditions than for bare furrow.     

Productivity Aspects of Urban Freeway Rehabilitation with Accelerated Construction

Over the last 5?years the California Department of Transportation (Caltrans) has completed three experimental long-life urban freeway rehabilitation projects by utilizing a fast-track (accelerated) construction approach of around-the-clock operations under extended closure. This paper presents the fast-track rehabilitation approaches and the as-built production rates of major rehabilitation operations monitored at the three experimental projects. The monitoring results show that the contractor’s production rates varied considerably depending upon the construction logistics, material delivery and hauling methods, lane-closure tactics, and/or pavement designs being implemented. A higher production rate and a noticeable “learning-curve effect” were observed when full-width rehabilitation was compared with partial-width rehabilitation, when continuous lane reconstruction was compared with random slab replacements, and when full roadbed closures were compared with partial lane closures. Findings in this study suggest that Caltrans should evaluate project-specific conditions and constraints, which might restrict use of a preferred rehabilitation scheme, by taking production rate variances into account when establishing schedule baselines of construction staging plans and incentive/disincentive contracts for urban freeway rehabilitation projects.     

Graduate Education in Construction Management

Construction management has become a vital aspect of the construction process over the years. This paper reviews the Master’s programs in construction engineering and management (CEM) offered by departments of civil engineering in the United States. The findings indicate that only 20% of the American educational institutions, which offer accredited civil engineering programs, offer Master’s programs in CEM. Most of the Master’s programs in CEM constitute an effort to convey information to students on mainly six categories, namely, contract administration, project management, scheduling, equipment management, construction technology, and CEM research. It seems that the Master’s programs in CEM do not differ much from program to program in terms of content. When the trends in course offerings are compared in 1982, 1996, and 2008, there seems to be minimal change except for the number of courses in project management that went up significantly while the number of courses in cost estimating went down. The trends in the remaining courses have been stable. Even though contents and trends in CEM programs appear to be relatively stable, there seems to be some variability in the concentration of the course offerings. Some CEM programs concentrate on some of the categories at the expense of other categories. A close relationship and a sound dialogue between construction educators and the industry are likely to lead to Master’s programs that are in sync with the expectations of the industry.     

钢铁厂流程结构优化与高炉大型化

高炉是钢厂生产流程中物质、能量最为密集的工艺装置,对钢厂的物质流网络和能量流网络的构建与合理化运行有着重大影响。高炉的功能不仅是通过还原反应过程获得优质的铁水,而且伴随大量的能量转换和信息的输入/输出过程,应当在整个钢铁生产流程结构优化的前提下,综合思考高炉的合理座数、合理容积和合理位置。通过分析国际高炉的发展趋势和首钢京唐钢厂5 576m3高炉与迁安钢厂4 080m3高炉的比较,建设2×5 576m3高炉和3×4 080m3高炉可以得到相近的产量,但前者在节省投资、能源节约和信息控制等方面具有明显优势。由此可以看出,为了优化钢厂生产流程,提高市场竞争力,高炉大型化是一种明显的趋势。但是,并不是追求单座高炉越大越好,更不应盲目追求"最大"。应该在产品结构、物质流结构、能量流结构优化和动态运行优化前提下实施高炉大型化。一般的趋势是一个高效益、低成本生产的钢厂应以2～3座高炉为宜,并由此得到高炉大型化的合理容积、合理座数及其合理位置。这种发展趋势不仅适合于生产薄板的大型联合企业,而且也适合于生产建筑用棒/线材的中、小型钢厂。     

Contextual Information Requirements of Cost Estimators from Past Construction Projects

Past project data sources provide key information for construction cost estimators. Previous research studies show that relying only on one’s own experience during estimation results in estimators’ bias. Having and referring to historical databases, containing objective information on what happened in past projects, are essential for reducing estimators’ biases. The first step toward development of useful project history databases is to understand what information estimators require from past projects. The research described in this paper targets estimators’ information needs identified through interviews, brainstorming sessions, task analyses, and card games conducted with estimators with different experience levels and specialized in heavy/civil and commercial construction projects, and exploration of historical and standard databases available in companies to determine what is being currently represented. Findings show that estimators need contextual information, depicting the conditions under which specific production rates were achieved, so that they can identify which production rate would be more realistic to use during the production rate estimation of an activity in a new bid. Comparison of the contextual information needs identified in this research with information items available in historical data sources (such as company cost reports, RSMeans, previous studies) highlighted some gaps and important opportunities for improvements in those sources. The identified contextual information items are significant for practitioners in developing ways to augment their existing project history databases to make them more beneficial for estimators.     

Determination of Most Economical Scrapers Fleet

Scrapers are valuable construction equipment for large earthmoving operations. Their production rates vary widely as they depend on the equipment performance, operation’s travel time, and haul-road conditions. Determining the most economical selection of the size, model, and number of scrapers is a rather tedious process that involves repetitive calculations. A spreadsheet application was created in order to facilitate such calculations and select the most economical scraper from the list of available equipment for the job under consideration. The application is made of seven spreadsheets containing a scrapers’ database, performance charts, soil properties, and other supporting worksheets. The application provides a user interface to solicit all data entries specific to a project. Once the user enters the required data the system compares the production rate, time required for the job, determines the estimated unit cost for each scraper in the database, and recommends the most economical selection.     

Premium-Rating Model for Workers’ Compensation Insurance in Construction

Providing adequate workers’ compensation insurance (WCI) is mandatory by legislation in most countries for employers to hire workers. It is enforced to safeguard the interests of occupational injury victims while eliminating their employers’ financial burden of compensation. WCI’s significance in construction is immeasurable because the construction industry appears to be recording higher injury and fatality rates globally. On the other hand, insurance companies must be meticulous in deciding premiums for WCIs for construction projects. Traditionally, insurers have been adopting the experience modification rating technique for premium-rating of WCI. However, this technique has been proven ineffective for construction applications due to the unique characteristics of construction projects. Hence, a new premium-rating model for construction was developed and tested in the Singapore general insurance industry. The proposed model streamlines structured analyses of project hazards, contractors’ safety management systems, market conditions, and insurers’ internal factors to decide optimal premiums. Moreover, it infuses the partnering notion in WCI for construction. The implementation of the proposed model in the insurance industry would facilitate accident control in the construction industry and thereby loss minimization for insurers.