- PROBLEM DEFINITION
Further to Week 5 blog on the construction of trench RC barrier for SPJ – 12B project and the effects of Learning curve on production, it was determined that the Contractors expected productions gains due to increased familiarities and repetition cannot be solely relied on to achieve required weekly production output and meet target schedule dates.
Subcontractor must now look at other alternatives to increase production. Based on current projections, we can expect a 30 day delay in works if we solely reply on productivity gains from learning curve effect.
Works scope / details areoutlined are as follows
We will now assess alternatives to increase production
2. FEASIBLE ALTERNATIVES
The following alternatives were considered under Week 5 blog. alternative 1 was determined to be unacceptable. we will now consider items 2 & 3 i.e. changes to manpower quantity and working times;
- Do nothing. Barrier can be completed by the specified dates
- Increasing manpower in current crews (current planned – 10 men)
- Increasing overtime / hours worked each day
3. DEVELOPMENT OF OUTCOMES
Do Nothing. Production of crews will achieved necessary production and dates
This was determined to be unacceptable with a likely delay of 30 days to result due to average manhours / unit unlikely to drop sufficiently enough to be covered by the Subcontractors current manpower planning.
Extending Manpower in current crews
Subcontractor plans to use a 10 man crew to erect formwork, install cast in items, cast concrete and then strip.
Firstly we will assess current productivities for the crews;
Using data obtained from site from the 4th to the 9th September, crews were able to construct a 35m length of wall plus a further 35m of 75m high kicker (base for wall).
By measuring manpower and output we have determined basic productivities for the main elements of the wall construction. this is outlined in Figure 1 below. Total manhours for the week based on the 6 man crew have also bee determined to assist in calculating a utilisation factor. Refet to Figure 2.
Using this information, and assuming that the actual productivities determined with the smaller crew reflect the unit rate work requirements, an estimate of the total manhours required to construct 100Lm of barrier wall each week is outlined under figure 3.
Based on the required weekly work quantities and current productivities, a total of 17 men is now required to meet the target production of 90Lm per wee
Increasing Overtime / hours worked each day
As can be seen in the figures above, a total man hour requirement of some 1020 hrs must be invested into the work each week to satisfy the quantities demanded by the production schedule, this cannot be satisfied with working overtime alone using a 6 or even 10 man crew
Whilst the productivities above were computed using a 70 hour working week for the crews, these figures have been taken from a single week where the previous working week included extended public holidays and crew working hours were considered low.i.e. productivities are not impacted by fatigue.
In a scenario where by effort is sustained over consecutive weeks, production losses due to fatigue are likely to affect, particularly given the use of heavy steel formwork and minimal plant to assist in shifting formwork.
To reflect this effect we will assume a 10% loss going from a 58 hour work week to 70 hour i.e. each man is only 90% effective then the required man hour input is as follows;
Under this scenario, a minimum of 16 men would be required to satisfy schedule and production requirements.
4. SELECTION CRITERIA
Satisfy man hour requirements based on observed production levels and weekly quantity targets (90Lm) using least number of men.
5. ANALYSIS OF THE ALTERNATIVES
Based on the above, an increase in the above manpower to 16 men is considered most appropriate given this will result in the least amount of men however having “a few extra” is never a bad idea for critical works.
In the next blog, an analysis of programme impact potential will be considered to determine if target production figures are excessive / unnecessary.
6. Performance Monitoring
During last week, the crews managed to cast 2no. 16.5m sections of wall using a 6 man crew. These were effectively the 5 and 6th Cycle of casting.
The total hours expended to achieve the 33Lm of wall was 420 hours.
This equates to a total of 250mhrs / 20m section of wall.
Based on the learning curve analysis conducted under week 5, by the sixth cycle, the expected man hours required to construct every 20Lm of wall using a predicted gain of 20% i.e. 80% learning curve with an initial effort of 447 mnhrs was 334 hrs.
However the above results indicate crews are operating closer to a 70% learning curve. This may result in the further reduction in average manhour / unit from 177 hrs/unit to only 100 hrs/unit. refer to attached graph below
Further monitoring to be conducted on both overall production as well as individual productivities to assess both learning curve gains and fatigue impact where working hours include excessive overtime.
- Sullivan, G. W., Wicks, M. E., & Koelling, C. P.(2014). Engineering economy 16th Edition. Chapter 3 – Learning and Improvement., pp.110-112.
- Chapter 11.5 Managing Project Data Basis – Guild of project controls compendium and reference (CaR) | Project Controls – planning, scheduling, cost management and forensic analysis (Planning Planet). Retrieved from http://www.planningplanet.com
- Chapter 9.5 Project Performance Forecasting – Guild of project controls compendium and reference (CaR) | Project Controls – planning, scheduling, cost management and forensic analysis (Planning Planet). Retrieved from http://www.planningplanet.com