An investigation into the influence of buildability factors on productivity of in situ reinforced concrete construction

摘要

Construction productivity is one of the most frequently researched topics due to its importance to the viability of the industry. It is regarded as a true reflection of the efficiency and economic success of the operations.Despite the plethora of research into construction productivity reported over the years, a thorough examination of the literature revealed a dearth of research into the influence of buildability factors, i.e.design variables, on the labour productivity of one of the most important materials in the construction industry; in situ reinforced concrete.According to the Construction Industry Research and Information Association (CIRIA), buildability is defined as "the extent to which the design of a building facilitates ease of construction, subject to the overall requirements for the completed building". Apart from the Singaporean Buildable Design Appraisal System (BOAS), which suffers from major shortcomings, to date, no comprehensive study was conducted to investigate and quantify the effects and relative influence of architectural and structural buildability factors on the labour productivity of in situ reinforced concrete buildings. In this project, the major buildability factors hypothesised to influence the labour productivity of the main trades, i.e. formwork, reinforcing steel fixing, concreting and finishing, included grid patterns of footings and columns, type of structural framing system, geometry and dimensions of elements,height of floors, the degree of design rationalisation, standardisation and repetition of elements, reinforcing steel quantity and diameters, location and congestion of reinforcement, volume and workability of concrete as well as surface finish.In addition, and due to its importance to the productivity of the construction industry, the effect of the learning curve theory has been the subject of several previous studies. However, a comprehensive investigation of the impact of the learning phenomenon on the major trades associated with in situ reinforced concrete buildings has not been carried out.The raw data were collected from thirty-nine different construction sites in the State of Kuwait, using specifically designed data collection forms for a total period of nineteen months. In order to triangulate the results, productivity data were collected and analysed at both levels; macro and micro. Since several sites were monitored simultaneously, the intermittent observation technique was selected to form the basis for the observation method.Several relevant buildability factors impact the labour productivity simultaneously. Therefore, to isolate the net effects and quantify the relative influence of these factors on labour productivity, linear regression was used for the statistical analysis throughout this research project. As a result, it was possible to quantify the relationship between labour productivity and the following buildability factors: a) footings and columns grid pattern; b) formwork area; c) variability of elements size; d) geometry of elements, i.e. circular versus rectangular columns, curved versus linear beams, non-rectangular versus rectangular slabs, and number of angles around the perimeter of slabs and walls; e) number of beams used to support the floor area; n number of beam intersections in the framing system; g) dimension of elements; h) reinforcing steel bar diameter; i) quantity of reinforcement fixed; j) location and congestion of reinforcement; k) volume and workability of concrete; I) height of floors above the ground level; and m) power- trowelled floor finish.The applicability of learning curve theory to formwork, reinforcing steel fixing and pumped concrete was investigated using the unit straight-line model. Due to the negative impact of height on pumped concrete productivity, the effect of learning on this trade could not be determined. On the other hand,the effect of the learning phenomenon on formwork and reinforcing steel fixing labour productivity was insignificant suggesting no potential context for the theory to be used as a useful tool to quantify the productivity improvement, allocate resources or schedule activity durations.This research project has quantified the relationship between the principal design characteristics of in situ reinforced concrete construction and labour productivity of the various trades involved. It can provide practical guidance to architects and structural designers who seek to optimise their designs.In addition, it can give a feedback on how well the designed building considers the requirements of the basic buildability principles and provides for tangible consequences of their design decisions on the construction labour productivity.