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20th Annual Conference of the International Group for Lean Construction - San Diego, California, USA - 2012

Relationship of Time Lag Buffer to Material Stockpile Buffer Levels

Elias Espino¹, Consuelo Aranda², Kenneth Walsh³, Tara Hutchinson⁴, Jose Restrepo⁵, Matthew Hoehler⁶ & Robert Bachman⁷

¹Graduate Research Assistant, Department of Civil, Construction, and Environmental Engineering, San Diego State University, San Diego, CA, USA, 92182-1324
²Graduate Research Assistant, Department of Civil, Construction, and Environmental Engineering, San Diego State University, San Diego, CA, USA, 92182-1324
³AGC-Paul S. Roel Chair in Construction Engineering and Management, Department of Civil, Construction, and Environmental Engineering, San Diego State University, San Diego, CA, USA, 92182-1324, Phone +1(619)-594-0911, [email protected]
⁴Professor, Department of Structural Engineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0085, La Jolla, CA, USA 92093
⁵Professor, Department of Structural Engineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0085, La Jolla, CA, USA 92093
⁶Research Director, Hilti Corporation, Corporate Research and Technology, Feldkircherstrasse 100, Schaan, 9494, Liechtenstein
⁷Principal, RE Bachman Consulting Structural Engineers, Laguna Niguel, CA, USA 92677

Abstract

This paper presents observations of buffer implementation and usage during the construction of a five-story, full-scale, reinforced concrete, earthquake test structure. Over 40 private industry partners performed a majority of the construction work inkind, each covering a different scope of work. Activity durations were often longer than expected, particularly because research interests often resulted in changes in scopes of work for partners, sometimes requiring design work. Due to the fluctuation between the initial baseline construction lookahead schedule developed early in the project, and the pace of actual construction, inventory often sat in the laydown area or in the workface area for lengthy periods of time. This was true even though a pull approach was used to coordinate activities. A simulation experiment was used to determine the impact on inventory levels of activity durations exceeding planned durations. Because material lead times were on the order of the planning horizon, orders for upcoming activities were often made without knowledge of delays in intermediate activities, resulting in additional inventory time on the site. The simulation experiment exhibited a similar behavior, and showed that excess inventory levels increase rapidly with the degree to which actual durations extend beyond planned durations.

Keywords

Buffers, production control, inventory control.

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