Howard H. Bashford

CEPM 3: process mapping of residential foundation slab construction processes

With the purpose of mapping residential foundation slab construction processes, the authors collected the necessary process mapping information. After the completion of the process mapping for several common residential foundation slab construction processes, the team then used the process maps to identify potential process improvements and documented these in new, revised process maps. The residential foundation slab construction process mapping effort coupled with process simulation demonstrated the existence of opportunities for residential foundation slab construction process improvements. This has motivated the homebuilder partners to further pursue the issue by developing a residential foundation slab construction process to a stage where several prototype foundation slabs can be built. This report provides information on all steps accomplished and all issues involving the process mapping effort.

Special purpose simulation template for workflow analysis in construction

Workflow analysis is an important component in the simulation of construction operations. It involves creating a specific number of work requests for a crew every time period, computing outputs such as work arrival rate for a downstream crew and plotting work in process (WIP). These outputs are not directly provided in many construction simulation software tools. Determining these outputs is generally considered a time consuming and tedious undertaking. Developing modeling constructs that automate the computation of these workflow outputs will be useful for construction modelers. This paper presents a special purpose simulation (SPS) template developed for workflow analysis. The SPS template consists of four modeling constructs that implement the workflow analysis functionalities mentioned above. The SPS template logic was verified using two simulation experiments. Use of this SPS template for analyzing different workflow based issues as well as to test the production management principles in construction is also highlighted.

A Discrete Event Simulation Model to Analyze the Residential Construction Inspection Process

Inspections performed by code enforcement officials (building inspectors of a code enforcing jurisdiction) to confirm building code compliance are an important part of the home building production process. In 2003, an estimated 10 to 15 million code compliance inspections for residential construction were performed in various jurisdictions around the nation. The inspection process and its outcome have a significant impact on all the stakeholders, including city building departments, homebuilders, and trade contractors. This paper focuses on the inspection process in production homebuilding and provides critical analysis via a discrete event simulation model. The design of the simulation model is at the subdivision level and provides a mechanism through which a critical analysis of the process can be performed and waste due to inefficiencies can be identified. The simulation model has been developed in SLAM-II. Input data for the simulation model was obtained from municipal jurisdictions within the Phoenix metropolitan area. Key output parameters include inspection failure rates, impact of failure rates on the production cycle time, and impact of inspection failure on resources provided by individual stakeholders. Even though the model is developed at a subdivision level its results can be extrapolated at the city level and broad conclusions can be drawn.

RESIDENTIAL CONSTRUCTION AND THE INFLUENCE OF INSPECTIONS ON CYCLE TIME

A key component of the homebuilding process is inspection of construction by the building permitting agency within the jurisdiction where the work is performed. Several inspections are made throughout the construction process, but four of the inspections, pre-slab, framing, drywall, and final, lie on the work schedule critical path. This research focuses upon these particular inspections to determine if the inspection failures influence construction cycle time. Inspections of production homes are examined to determine how often these critical path inspections do not pass the first time, and how many reinspections are required. The number of days utilized to pass those inspections and reinspections is also measured and reported. The research finds that, on average, 12 days are required, to pass these critical path inspections, thus adding 8 days to the construction cycle time. When these inspections do not pass the first time the inspection is made, rework and reinspections must be completed before construction can proceed. The results show that this process may occur within the same day as the original inspection, and the subsequent inspection takes place the next day. More research is necessary to determine precisely wh y these inspection failures occur, what cost is incurred because of such failures, and in turn, what opportunities are lost.

Relationships Between System Loading and Cycle Time in a Residential Construction Production System

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). Home builders generally utilize critical path method scheduling, cost estimating, and earned value analysis management tools to manage their production process. However, these tools are not responsive to many undesirable situations that arise during the production process, such as increasing cycle time and increasing amounts of work in process, both of which increase capital investment, decrease company financial performance, and slow product delivery to customers. This study examines relationships between cycle time, work in process, system throughput, new construction starts, and production system capacity using building permit data for new single family homes in Chandler, Arizona. The applicability of Little’s Law, a basic equation used in factory production system design, to a residential production system is examined. This study shows a definite, predictable relationship between cycle time, work in process, and production system throughput. This study provides for further study of production system characteristics that have historically not been considered in construction management models, with the expectation of developing a new construction management system that will account for more of the characteristics of construction production systems that affect project performance and company financial performance.

CARBON EMISSIONS OF ON-SITE EQUIPMENT USE IN POST- TENSIONED SLAB FOUNDATION CONSTRUCTION

This paper quantifies carbon emissions due to on-site equipment use in the post-tensioned slab foundation construction process of production homes in Phoenix Arizona. The construction activities performed during post-tensioned slab foundation construction, trades/sub-trades/vendors and the list of construction equipment used for every activity are identified. Data collection involved field visits to several subdivisions, interviews with trades, quantification of use time and the fuel use rate for each equipment as well as the fuel type used for every construction activity. Emissions from fuel consumption were quantified using the guidelines provided by the U.S. Environmental Protection Agency. Analysis of emissions indicates that the concreting trade, the plumbing trade and the grading sub-trade are the three most significant trade components. Activities ‘set floor’, ‘plumbing’, ‘pour floor’ and ‘backfill and grading’ are the four most significant construction activities. Emissions of on-site equipment use are in the range of 4 to 15% of emissions due to transportation. This study is useful for home builders, trade contractors and vendors involved in production home building construction to measure emissions of on-site construction processes, identify significant construction activities and trade components and plan for improvement.