现浇钢筋混凝土建筑生产率英文文献和翻译(3)
The coordination level among plant operators, assistants, commonly referred to as guides, and crew members, moreover, becomes increasingly important as the height of concreted elements above ground level increases. As the height increases, the functional flexibility of mobile cranes and concrete pumps is substantially reduced, and the effectiveness of communication among the various parties involved becomes significantly low, which necessitates closer vigilance and heedfulness on their part.
In view of the preceding discussion, it can be hypothesized that the following factors can be significant in their influence on the labor productivity of pumped and skipped placement methods, and thus the efficiency of the concreting operation: (1) concrete workability, (2) reinforcing steel congestion, (3) volume of pours, and (4) height of concreted elements relative to ground level.
Research Method
Because numerous factors, other than buildability, influence labor productivity on sites (Horner et al. 1989; Jarkas 2005), which may mask or overshadow the effect of buildability on the concreting operation, the focus was on selecting construction projects that shared common features such as, contract procurement method, geographical locations, and to a reasonable extent, construction methods and site management level, yet differed in types and magnitudes, so that the impacts of the explored buildability factors could be unraveled; similar sites, largely share similar characteristics of buildability factors; therefore, their influence may not be best revealed. Consequently, sites observed included residential and office buildings, commercial centers, industrial facilities and warehouses, which ranged from one to eight floors in height, 700 to 7,500 m 2 in built-up areas, and US$ 0.80 to 3.50 million in construction cost.
The parameters of pumped and skipped concreting labor productivity indices, i.e., volume of concrete placed ( m 3 ) per man-hour (mh), which were part of a larger research project, were collected over a period of 19 months from 39 different construction sites located in the State of Kuwait, where in situ reinforced concrete is the prevailing type of construction.
The differences in management procedures applied across the sites monitored, at the project level, have little effect at the activity level of observation, whereas the possible impacts of other interfering factors such as, supervision quality, restricted site accessibility, crew size and composition, skill, experience and motivation of operatives, can be reasonably moderated by collecting a large volume of labor productivity data (Jarkas 2005).
To minimize the negative influence of interruptions and disruptions on labor productivity, which may further mask the influence of buildability on the concreting operation, major encountered delays, e.g., inclement weather, delay in truck-mixers arrivals, plants break-down, accidents, were recorded and discounted from the related labor inputs. Only productive inputs were used to quantify the labor productivity indices of the operation.
Because the shutters of vertical elements, i.e., columns and walls, are susceptible to lateral pressure during the placement process, especially when traditional formwork is used, in almost all sites observed, skipped concrete was the prevailing placement method for vertical members, whereas pumped concrete was used for all horizontal members. Because of the difference between elements concreted by the two different placement methods, i.e., shape factor, a meaningful comparison between pumped and skipped concreting was not possible (Anson and Wang 1998). Therefore, it became necessary to conduct two separate analyses to quantify the effects of the buildability factors explored on both, pumped and skipped concreting labor productivity.
Concrete workability is measured on site by the “Slump Test” (Thomas 1980). According to the slump values specified by the American Concrete Institute (ACI 1975), and on the basis of the researcher's site experience, a workable concrete mix design usually has a slump value ranging from 80 to 120 mm. To classify the concrete workability into a consistent scheme, however, the researcher further elicited the professional opinion of 78 and 117 experienced foremen and crew members, respectively. All personnel interviewed possessed a minimum field experience of 15 years in the concreting operation. An almost unanimous feedback categorizing the workability of concrete into three classifications (high, medium, and low) was obtained. Therefore, the workability classification scheme shown in Table 1 was used throughout this investigation.
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