Efficiency multipliers for construction productivity are often estimated on an ad-hoc basis, depending on the project characteristics. The purpose of the study is to define a structured approach allowing the determination of the appropriate empirical productivity relations and efficiency multipliers along with their respective values. The proposed method breaks down a given construction activity into distinct operational scenarios which represent unique combinations of key productivity variables, thus providing a perspective on construction productivity for both labor-intensive and equipment-intensive operations. In addition, this is the first study to explicitly describe the process and the theoretical prerequisites for the statistically valid derivation and comparative evaluation of new efficiency multipliers for a given construction activity. A case study of heavy-duty concrete paving activities over an eight month period is utilized as a testbed for the derivation of new efficiency multipliers. An excavation scenario with the use of published estimation formulae is also presented to demonstrate the approach's capability to corroborate the values of known efficiency multipliers. The results indicate that the proposed approach improves the accuracy of estimated multipliers stemming from past productivity studies and increases the estimation precision for the derivation of new multipliers related to future construction operations.
INTRODUCTIONConstruction productivity is one of the main drivers for completing projects within time and cost limitations (Moselhi and Khan, 2010) and as such its appropriate estimation is quite important for preparing construction schedules and budgets (Song and AbouRizk, 2008). To determine construction productivity one needs to estimate an average production rate (Kiziltas and Akinci, 2009;Song and AbouRizk 2008) and then adjust it to the specific operational conditions of the job, such as temperature, overall site organization, crew skill, on the job learning for repetitive work (Panas and Pantouvakis, 2014) etc by multiplying it by a set of "efficiency coefficients" or "efficieny multipliers" (AbouRizk et al., 2001).The average productivity is estimated using published formulae proposed either by manufacturers such as Caterpillar (Caterpillar, 2014) and Komatsu (Komatsu, 2009) or by widely acknowledged and accepted institutions such as the BML (1983). It should be noted that in some cases and for certain construction operations there are no published formulae in the literature (Panas and Pantouvakis, 2010). In these situations, one should determine the procedural framework allowing the incorporation of an initially unknown but defined later, during the process, set of operational factors (Pantouvakis and Panas, 2013).The average productivity is then multiplied by appropriate "efficiency multipliers" whose determination, however, is not trivial as the relationship between the affecting factors and productivity is not well understood (O'Connor and Huh 2006). Different methods may ...