Higher productivity in organizations leads to national prosperity and better standard of living for the whole community. Improving productivity through time and motion study is used in the manufacturing sector and allied industries. Work study consists of two aspects method study and work measurement which when applied effectively results to higher productivity. This paper deals with the use of work measurement for rebar placement activity, studying the performance of workers and its analysis through statistics.

Puniavathi Puranam, M.E.Student
Prof. Pramila. R. Adavi, Civil Engg.Department MAEER’S MIT, Pune.

Introduction

Project cost and schedule performance depend largely on the quality of project planning, work area readiness preparation and the resulting productivity of the work process made possible in project execution. The construction industry sets in motion the process of economical growth in the country; investment in this sector contributes 6.5% of Gross Domestic Product (GDP) growth (Das, 2003). Every Rs.1 investment in the construction industry causes a Rs.0.80 increment in GDP as against Rs.0.20 and Rs.0.14 in the fields of agriculture and manufacturing industry, respectively. Statistics over the period have shown that compared to other sectors, this sector of economic activity generally creates 4.7 times increase in incomes and 7.76 times increase in employment generation potentiality. Statistics is defined as the scientific method for collecting organizing, summarizing, presenting and analyzing data as well as drawing valid conclusions and making reasonable decisions on the basis of such analysis. The three major functions where statistics can be found in major enterprise are:
  1. The planning of operations:- This relates to either special projects or to the recurring activities of a firm over a specified period of time.

  2. The setting up of standards:- Understanding the size of employment, volume of sales, fixation of quality norms for the manufactured product, norms of the daily output, and so forth.

  3. The function of control:- This involves comparison of actual production achieved against the norm or target set earlier. In case the production has fallen short of the target, it gives remedial measures so that such a deficiency does not occur again.
Work measurement techniques find the time required to do a job by a qualified operator working at a standard pace and using the standard method. The time in minutes or hours calculated is known as standard time. The commonly employed work measurement techniques are:
  • Stop Watch Procedure of Time Study

  • Predetermined Motion Time Systems

  • Synthesis-Synthesied Time Standards

  • Analytical Estimating

  • Work sampling
The study highlights the use of stop watch procedure of time study, work sampling for the rebar placement.

Time Study

Time study is a work measurement technique for recording the times and rates of working for the elements of a specified job carried out under specified conditions and for analyzing data so as to determine the time necessary for carrying out the job at a defined level of performance.

Essentials of Time Study

  • An accurate specification of where the job begins and where it ends, and the method by which it is carried out, including details of material, equipment.

  • A system of recording the observed times taken by workers to do the job while under observation.

Procedure of Time Study

  • Identifying the job to be timed and operations to be timed.

  • Obtaining an improved procedure from method study department.

  • Select worker for study

  • Collecting the equipment and arrange machinery required to conduct time study and ensure accuracy in recording time

  • Explaining to the worker the improved working procedure and use of tools and fixtures

  • Breaking the job into operations and operations into elements and writing them in a proper format

  • Conducting the observations and recording them on the time study form

  • Rating the performance of the worker

Applications of Time Study

  • For determining schedules and planning of work

  • For calculation of Standard costs and as an aid in preparing budgets

  • For determining machine effectiveness, the number of machines which one person can operate and also for construction activities.

Work Sampling

Work sampling is a work measurement technique in which a large number of instantaneous observations are made a random intervals over a specified period of time of group of workers machine and process of finding the percentage occurrence of a certain activity by statistical sampling.

Work sampling procedure can be divided in the following three phases:-

a) Preparing for work sampling
1) Statement of the main objective of the study, obtaining approval of the supervisor.
2) Establish quantitative measure of the activity, selection of training of personnel and making a detail plan for taking observations.

b) Performing work sampling
1) Describing and classifying the elements to be studied in details, designing the observation form and determining the number of days or shifts required for the study.
2) Developing properly randomized times of observations, observing activity and recording data, summarizing the data at the end of each day.

c) Evaluating and presenting results of work sampling.
1) Evaluate the validity and reliability of data, presenting, analyzing data and planning for future studies.

Uses of work sampling:-
1) determination of time standards and delay allowances
2) Aid in the measurement of overall performances
3) Job evaluation and manpower planning.
4) For appraisal of safety performance and organizational efficiency.

Case Study

Keeping the above technique in mind a residential project was taken up as a case study where data was collected from a G+7 apartment in Aurangabad, Maharashtra.

Work Sampling

Table1:- Workers Performance on rebar placement.

Day-1
 Workers:-
Visit No.12345678
10:45IWIWIWIWIWIWIWIW
10:55IWIWIWIWIWIWIWIW
11:05IWIWIWIWIWIWIWIW
11:20SWSWSWSWSWSWSWSW
11:25SWSWSWSWSWSWSWSW
11:32SWSWSWSWSWSWSWSW
11:40SWSWSWSWSWSWSWSW
11:48SWSWSWSWSWSWSWSW
12:05SWSWSWSWSWSWSWSW
12:15SWSWSWSWSWSWSWSW
12:30SWSWSWSWSWSWSWSW
12:45SWSWSWSWSWSWSWSW
2:45IWIWIWIWIWIWIWIW
2:55IWIWIWIWIWIWIWIW
3:12IWIWIWIWIWIWIWIW
3:27SWSWSWSWSWSWSWSW
3:40SWSWSWSWSWSWSWSW
4:00SWSWSWSWSWSWSWSW
4:12SWSWSWSWSWSWSWSW
4:25SWSWSWSWSWSWSWSW
4:40SWSWSWSWSWSWSWSW

6 days required for the placing of beams in proper location for 6th floor wing c. No. of workers on the working area:-8. Workers: - 1-5 are fitters, 6-8 are helpers. Table here shows the sample of 2 days of work sampling procedure.

Day-2
No. of workers on the working area:-10. Workers: - 1-5 are fitters, 6-10 are helpers.
 Workers:-
Visit no.12345678910
10:00DWDWDWDWDWDWDWDWDWDW
10:17DWDWDWDWDWDWDWDWDWDW
10:22DWDWDWDWDWDWDWDWDWDW
10:35DWDWDWDWDWDWDWDWDWDW
10:40DWDWDWDWDWDWDWDWDWDW
10:45SWIWDWDWIWSWSWDWDWSW
10:55SWIWDWDWIWSWSWDWDWSW
11:05SWIWDWDWIWSWSWDWDWSW
11:20DWDWDWDWDWDWDWDWDWDW
11:25DWDWDWDWDWDWDWDWDWDW
11:32DWDWDWDWDWDWDWDWDWDW
11:40DWDWDWDWDWDWDWDWDWDW
11:48DWDWDWDWIWDWDWDWDWIW
12:05DWDWSWSWIWSWSWSWSWIW
12:15IWIWSWSWSWSWSWSWSWSW
12:30IWIWIWIWIWIWIWIWIWIW
12:45IWIWIWIWIWIWIWIWIWIW
2:45SWSWSWSWSWSWSWSWSWSW
2:55SWSWSWSWSWSWSWSWSWSW
3:12SWSWSWSWSWSWSWSWSWSW
3:27DWDWDWDWDWDWDWDWDWDW
3:40DWDWDWDWDWDWDWDWDWDW
4:00DWDWDWDWDWDWDWDWDWDW
4:12DWDWDWDWDWDWDWDWDWDW
4:25DWDWDWDWDWDWDWDWDWDW
4:35DWIWIWDWDWDWDWDWDWDW
4:55DWDWDWDWDWDWDWDWDWDW
5:10DWDWDWDWDWDWDWDWDWDW
5:20DWDWDWDWDWDWDWDWDWDW
5:35DWDWDWDWDWDWDWDWDWDW
5:45DWDWDWDWDWDWDWIWDWDW

CategoryStudy Number
 1234567
Direct work60.02%

71.27%

61.75%71.22%68%70.53%70.08%
Essential contributory work.20.98%17.10%18.82%15.51%17.7%14.00%15.48%
Ineffective work19.0%11.63%19.43%13.27%14.3%15.47%14.44%

The Table depicts work sampling used for measuring the performance of workers on rebar placement: - It consists of studies taken from 6th floor wing c, 7th floor wing a, b, c Roof level wing a, b, c.

Categories are further subdivided into narrowly defined categories of activity as follows:
  • Direct or Effective Work:-

    1.Direct work—Place, align, force, and tie into position plus those Elements which contribute directly to completing the unit of work.

  • Essential Contributory Work :-

    2. Obtain or transport tools and materials within immediate vicinity of work area including torch, sledge, wire cutters, rigging, reinforcement tie wire, etc. Also includes searching for materials. The immediate vicinity is defined as the existing concrete mat. The staging area is excluded.

    3. Obtain or transport tools and materials outside of immediate vicinity of work area including all tool and material movement not in close proximity to the work location. Activities in the staging area are included.

    4. Includes activities associated with crane deliveries until such time as the lift actually begins.

    5. Receive/give instructions and read drawings involving instructions communicated to or by supervisors and among crew members. Casual talking is not considered instructions. Also included is the studying of drawings and planning work. Foreman in staging area looking for materials is considered as planning work.

    6. Minor contributory work measuring or marking bar location, holding a bar to prevent movement, cutting w/torch, moving scaffolding, etc.

  • Ineffective Work:-

    7. Travel empty-handed to and from the work area and within the work area, either on foot or in a vehicle.

    8. Idle, unexplained waiting that cannot be accounted for. Distinction between idle and waiting for prerequisite activity or craft is if worker is in a position to assist, he is waiting for prerequisite work, otherwise, unexplained. Includes personal time while in the immediate vicinity of the work location.

    9. Waiting for tools, materials, instructions, crane deliveries, prerequisite work, other crafts, etc. Workers should be in position to continue work when the delay ends.

    10. No contact—failure to observe worker who is assigned to a specific work location. Includes early quit, late start, and time away from the immediate work location.

Conclusion

The optimum number of personnel for rebar placement is 10 - 12 on the work location. The optimum number of human resources assigned for construction activities leads to economy, reduction in time and quality work is obtained.

Table 2:- TIME STUDY PROCEDURE USED FOR BEAMS.
Continuous time study: - 6th Floor WingC
Time required (secs)Work locationCrew activity
612.82B117Align, position, marking of stirrups.
271.11B117Placing of stirrups
556.23B117Tying of stirrups to top bars
1160.63B117Placing of bottom bars and tying
482.1B47,B48Align, position, marking of stirrups
309.11B47,B48Placing of stirrups
1339.26B47,B48Tying of stirrups to top bars
1852.63B47,B48Placing of bottom bars and tying
500.13B123Align, position, marking of stirrups
198.74B123Placing of stirrups
759.56B123Tying of stirrups to top bars
1076.27B123Placing of bottom bars and tying
733.62B38Align, position, marking of stirrups
465.36B38Placing of stirrups
653.26B38Tying of stirrups to top bars
446.64B38Placing of bottom bars and tying
441.36B84Align, position, marking of stirrups
192.68B84Placing of stirrups
563.65B84Tying of stirrups to top bars
802.16B84Placing of bottom bars and tying
553.23B72,73Align, position, marking of stirrups
513.43B72,73Placing of stirrups
753.26B72,73Tying of stirrups to top bars
922.1B72,73Placing of bottom bars and tying
620.32B119Align, position, marking of stirrups
491.25B119Placing of stirrups
685.36B119Tying of stirrups to top bars
870.18B119Placing of bottom bars and tying

Time study and work sampling applied for rebar placement show us that there was a lot of physical stress and strain for the essential contributory work, i.e. workers working manually. The stress and strain can be reduced by using the material handing lift on site for stirrups and cover blocks which reduces time, and effective time can be used for direct work. Bar cutting and bar bending machine on site helps in improvement of labour productivity.

The normal distribution, normal curve with respect to beams shows that the area under the curve for one standard deviation from the mean covers more than 68.27% area and area under the curve from mean for 2ó, 3ó covers 95.45%, 99.73%. The reasons for the above results is due to the alteration in the drawings, delay in payment and also change in the gang working on the work location from slab to slab.

The results of the statistical analysis for the time study:-
Statictics using EXCEL SheetsActivity aActivity bActivity cActivity d
Mean 566.99366.41740.36976.67
Standard Error33.0050048.7005589.77151147.79122
Mode 0.000.000.000.00
Median 572.80387.24669.31896.14
StandardDeviation 93.352137.75253.93 418.02
Sample Variance 8714.61897464481174738
Kurtosis -0.6248-1.71642.14860.6224
Skewness 0.3744-0.17821.8667 1.0420
Range 292.26320.75783.031405.99
Minimum 441.36192.68556.23446.64
Maximum 733.62513.431339.31852.6
Sum4535.92931.25922.87813.4
Count8888
Correlation Coefficient
r 120.6419-----------------
r 13-0.3570-------------
r 14-0.5541-------------
r 23-0.0762-------------
r 24-0.4071-------------
r 340.8243-------------
Partial correlation coefficients
r12.340.5220---------------
r13.24-0.0869----------------
r14.23-0.1493--------------

The onsite training programs for the operators and personnel should be conducted. Motivation and job evaluation through questionnaires can be used in finding the best way for performing the activities. Checklist for different construction activities reduces time and improves the efficiency of workers.

Time and Motion Study, Analysis Through Statistics
Rebar placement and installation

Work Study and study of ergonomics can be used for developing better incentive schemes and safety measures. The study on occupational and health safety and working conditions is a must. Use of statistics through softwares reduces time, the samples of different construction activities can be evaluated and graphs interpretated in an efficient manner, thus improving the quality of construction as well as improving the working conditions of the workers on site. The factors which effect the labour productivity are material shortages, delay in inspection, payment delay, alteration in drawings and specification during execution, tool / equipment shortages etc.

References

  1. H. Randolph Thomas (1991) Labor Productivity and work sampling the bottom line, J.Cons. Eng. Management., p.p-423-444.
  2. Md. Salim and Leonhard E. Bernold, (1993) Effects of design-Integrated process Planning on productivity in rebar placement. J. Constr. Eng. Management p.p-720-738.
  3. Fwu-Shiun Liou1 and John P. Borcherding (1986) Work sampling can predict Unit Rate of productivity, J.Constr. Eng. Management p.p 90-103.
  4. H. Randolph Thomas, Jeffrey Daily, (1983) Crew performace measurement via Activity sampling J. Cons. Engg. Management p.p 309-320.
  5. Adnan Enshassi, Sherif Mohamed, Ziad Abu Mustafa1 and Peter Eduard Mayer (2007) Factors affecting labour productivity in building projects in the Gaza strip. J. of Civil Engg and Management .p245-254
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  9. G.C.Beri Business Statistics Tata Mc Graw Hill.
  10. Murray R.Spiegel, Larry J Stephens, Adapted by Narinder Kumar Schaum’s outlines Statictics. Tata McGraw Hill Publication.

NBMCW May 2012