Modeling Building Construction Durations in Nigeria
Chapter One
Aim of the research
To develop a multivariate construction time predicting model for Nigeria.
Objectives
The objectives through which the above stated aim was achieved were as follows:
- To evaluate the project scope factors influencing construction time of building projects.
- To assess the qualitative factors influencing durations of building
- To develop the model
- To test the model
CHAPTER TWO
LITERATURE REVIEW
Construction Time Estimating Methods in Practice
According to Telford (1994) there are two common methods of estimating project completion time in practice. They include; (1) time constraints of the client e.g. occupancy need or, (2) through a detailed analysis of work to be done and resources available, using estimates of the time requirements for each specific activity. Nkado (1995) corroborated the above assertion by Telford (1994) as he noted that construction time can be deduced from the client’s brief or derived by the construction planner from available project information.
Two major shortcomings have however been identified with these methods. The first method can lead to unrealistic construction time estimates caused by external factors, mostly in the form of a fixed date of occupancy (Hoffman, 2007). The second method on the other hand, could be very tedious and often impractical in view of the time limitations imposed on contractors at the tendering stage (Ng et al., 2001).
Both shortcomings point to the fact that; 1) these methods are highly dependent on opinions or feelings, rather than on facts or evidence and 2) they cannot be used when construction time estimates need to be made as quickly as possible. Attempts to develop a means by which construction durations can be accurately predicted in a quick, quantitative and objective manner has however, long become a problem of concern and interest to both researchers and practitioners in the construction industry as can be seen in the several efforts been made to model construction time.
Modelling Construction Time
Efforts to model construction time commenced largely with the use of project scope factors. This can clearly be seen in; the time-cost model originally developed by Bromilow (1969); the validation of the Bromilow (1969) model by other researchers as well as in; attempts to modify the Bromilow (1969)’s time-cost model.
The Bromilow (1969) time-cost model
The first model of construction time was developed by Bromilow (1969), following his pioneering investigation of the time performance of 309 building projects completed in Australia between the year 1964 and 1967. The model, often referred to as the Bromilow’s time-cost (BTC) model, enables construction time to be predicted in the form of the formula:
Where T is the duration of the construction period from date of site possession to practical completion, in working days; C is the final cost of the building in millions of Australian dollars, adjusted to constant labour and material prices; K is a constant describing the general level of time performance for a $1 million project and; B is a constant describing how the time performance is affected by project size, as measured by cost.
Bromilow (1969) considered cost to be the best indicator of project duration on the basis that; it provides not only a measure of the physical size of the project, but also reflected the complexity and quality of the work completed. Bromilow (1969) was able to establish the above relationship between construction duration and cost, through the use of regression analysis in which he obtained the values of K and B to be 313 and 0.3 respectively. The resulting model was non-linear and can be expressed as:
T = 313���0.3
In order to make the model linear and thus, obtain a more significant time-cost relationship, Bromilow (1969) transformed his data set using the logarithmic transformation. The non-linear model in the form of a power equation thus, became linear after the logarithmic transformation was applied to the data set. The resulting linear model took the form:
ln (T) = ln (KCB) = ln (K) + Bln(C)
The Bromilow’s (1969) time-cost model provided a quick and objective means of predicting construction duration. It however had a limited applicability due to the fact that each construction industry as well as project type has its own unique characteristics and therefore different parameter estimates of K and B in the Bromilow’s time-cost relationship may exist for different project types as well as for different construction industries. This limitation basically provided the need for the research work conducted by Bromilow et al. (1980) which was essentially a revised version of the Bromilow (1969) time-cost model.
In Bromilow et al. (1980), the time-cost data for a total of 419 building projects completed in Australia between 1970 and 1976 were investigated. However, unlike in Bromilow (1969) where the sample data was considered wholly (despite containing significant variability in project type), in Bromilow et al. (1980) the sample data was partitioned in order to account for differences in project characteristics. It was partitioned into government projects and private sector projects completed prior to 1974 and government projects and private projects completed after 1974. This resulted into four different models which all confirmed the initial Bromilow (1969) time-cost relationship and also, illustrated that significantly different parameter values could be used to model construction durations across a range of differing project characteristics. The models and their corresponding K and B values were as shown below:
CHAPTER THREE
RESEARCH METHODS
Research Approach
In order to achieve the research objectives set out in chapter one and thus, realise the aim of the research, a quantitative research approach involving the use of a self-administered questionnaire survey was adopted for the research. As defined by Hughes (2006), quantitative research is concerned with the collection and analysis of data in numeric form. The self-administered questionnaire survey yielded the required numeric data which was then used for the model development and testing.
The Quantitative Research Approach
Quantitative research approaches seek to gather factual data and to study relationships between facts and how such facts and relationships accord with theories and findings of any research executed previously (in literature) (Fellows and Liu, 1999).
It is usually driven by the researcher’s concerns and deals with measurable and quantifiable aspects of phenomena under study. It focuses on the questions; to what extent? By how much? What relationship exists between factors? What causes particular processes or situations? It is concerned with phenomena amenable to measurement of quantity and amount (Eboh, 2009). In quantitative research approaches, scientific techniques are used to obtain measurements (quantified data) e.g. social surveys such as; self-administered questionnaires, interview surveys, telephone surveys, computer assisted surveys, as well as web based survey.
As stated earlier, the quantitative research approach was adopted in this study in order to achieve the research objectives and thus realise the overall research aim. In line with previous researches (outlined in chapter 2), a self-administered questionnaire survey was the technique used to obtain measurements (quantified data).
CHAPTER FOUR
DATA PRESENTATION, ANALYSIS AND DISCUSSION
Data Received from the Survey
Table 6: Percentage of Questionnaires Returned and Not Returned.
CHAPTER FIVE
SUMMARY, CONCLUSION AND RECOMMENDATION
Summary of findings
The findings of the study following the presentation, analysis and discussion of results carried out in chapter four, were as follows:
- Ten(10), out of the several key qualitative factors influencing building construction time in Nigeria are uncorrelated principal components which can be used to summarize the entire qualitative factors influencing construction time in Nigeria without much loss of information. The ten factors are; delay in progress payment by owner, change order by owner during construction, delay in delivering the site to the contractor by the owner, complexity of project design, lateness in revising and approving design document by owner, lateness in selection of finishing materials, poor site management and supervision by contractors, unclear and inadequate drawings, rain effect on construction activities, and insufficient data collection and survey before
- The predictive ability of multivariate construction time predicting models in Nigeria is determined by the accuracy of the classification considered for the model; broad based classifications which aggregate groups of projects into a single category are poor classifications, while specific classifications which separate projects into their exact type are better
- Cost alone can only account for less than 50% of the total variation in the duration of building construction projects in Nigeria. The more greater percentage (over 50%) is accounted for by other project scope factors and qualitative/managerial factors which influence construction time in Nigeria, namely; GFA (m2), delay in progress payment by owner, lateness in revising and approving design document by owner, delay in delivering the site to the contractor by the owner, change order by owner during construction, complexity of project design, poor site management and supervision by contractors, as well as rain effect on construction
- Quantitative (project scope related) factors and qualitative (management related) factors can be combined to predict the duration of public sector projects and private sector projects in Nigeria, in the forms shownbelow:
Public sector projects:
Where:
Y = duration in days,
C = estimated final cost in millions of Naira, G = GFA in m2
Q1 = dummy variable for delay in progress payment by owner
Q2 = dummy variable for lateness in revising and approving design document by owner
Q3 = dummy variable for delay in delivering the site to the owner by the contractor
Q4 = change order by the owner during construction
Private sector projects:
Where:
Y = duration in days
C = estimated final cost in millions of Naira
Q1 = dummy variable for complexity of project design
Q2 = dummy variable for poor site management and supervision by contractors Q3 = dummy variable for rain effect on construction activities
Each of the forms/models stated above have been tested and validated in the study. In both forms/models, three (3) instead of one (1) is to be used for the dummy variables. This is because; a likert scale which ranged from zero to five was used in the study’s survey questionnaire and as log transformation can only be applied to numbers above zero, it was therefore necessary to add a constant number (3 in the case of this study) to each number in the study’s data set, in order to eliminate all zeros obtained in the data set (as a result of the 0 to 5 likert scale used), before the log transformation was applied. For this reason, it is considered that using 3 instead of 1 (for the dummy variables), will reflect the original scale used.
Conclusions
Based on the foregoing, the study thus, concludes that the duration of building constructions in Nigeria can be predicted through a combination of project scope factors and several other qualitative/managerial factors which influence construction time in Nigeria, namely; Cost, GFA (m2), delay in progress payment by owner, lateness in revising and approving design document by owner, delay in delivering the site to the contractor by the owner, change order by owner during construction, complexity of project design, poor site management and supervision by contractors, as well as rain effect on construction activities. However, care must be taken to ensure that proper classifications are made when developing models that can incorporate both factors to predict construction time.
Recommendations
- This study considered building construction projects, but found that more specific classifications (public and private sector projects) produced models with better predictive abilities. It thus, recommends further studies to be conducted using other specific classification of building construction projects e.g. residential construction projects, educational projects,
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