- Problem Definition
Beam girder is part of main structure that composed structural bridge frame and it is common structure for any toll road. They can be formed in precast concrete or steel both in single section or segmental sections. The challenge will be for the erection job and especially for the span crossing active toll road traffic flow. For this work, usually we have working window time when traffic is not busy [low traffic flow] and required intensive coordination with the Operator and traffic police. This is interesting blog topic concerning planning and scheduling.
Figure 1 Erection of Precast Bridge Girder
- Identify the Feasible Alternative
The main principle of this exercise is finding possibility target beam erection per bridge span during working window time with available unit cranes and plate set [one, two, three…etc].
- Development of the Outcome for Alternative
- Main data
I had developed the three options activities set for one beam erection as the basic time with my experienced superintendents combined with references &  present in Figure 2:
Figure 2 Activities Set for One Beam Erection
Others information or constraints present as follows:
- We didn’t consider girder transport time from casting yard which is variable depend on the distance of the location. This constraints will be part of final consideration for conforming our final plan
- Working window time is five hours at midnight time. Usual time provided by the Operator such as Jasa Marga is start from 11.00 PM until 5.00 AM. Off course there is penalty fee if we exceed this limit and we also have to pay for traffic blocking to them
- Since we have very limited time for working hours, then for exercise we picked pessimistic and mean activity time mode using Dephi technique
- We used one unit set crawler crane 100 ton [consist of 2 unit cranes] with one set plate erection as the basic unit for this exercise [the most common offered in the market since crane unit is the most expensive equipment for erection job]
- Activity Network Diagram
Present in Figure 3 activity network diagram for one and two beam erection with their activity paths & :
Figure 3 Activities Network Diagram for One and Two Beam Erection Time
- Selection Criteria
Using Figure 3 above we allocate the crane unit within window time to see if we have enough time to do one span complete erection consist several beams.
- Analysis and Comparison of the Alternative
My team has a conclusion using Figure 3 above that for additional one beam erection we need 62 minutes in mean time mode and 84 minutes in pessimistic time mode for one unit set crawler crane with one set plate erection. Based on this assumption then we plot the unit set crane in five hours window time present in Figure 4:
Figure 4 Allocating Crane Unit Set in Five Hours Window Time
It is easy to see from Figure 4 that for three beams per span we can finish the job in one night using one unit set crane in mean time mode. But we have to add.one set more if we want to finish this job in one night for five to nine beams per span. These numbers could go even higher if we use pessimistic time mode.
- Selection of the Preferred Alternative
Considering that any problems can occur in distance travelling using truck boogies if we order our precast girder to separate casting yard area then it we decide to go with pessimistic mean time mode. One important note must be given to casting yard operator that they have to provide us three unit boggie trucks minimum for precast delivery and two units for stand by just in case we have breakdown boggies.
- Performance Monitoring and the Post Evaluation of Result
Some options available for time reductions:
- Purchase or additional rent one set plate erection. This way we could reduce time by eliminate activity B* and shorten activity B for each two beams erection
- Additional rent one unit set crane if we want to finish the erection for one span consists six beams in one night [reduce cost for traffic compensation to toll road operator] or finish the job in two nights
- Consider to use mean time mode with additional rent one unit set crane to increase the probability for mean time mode [mean time mode is P50 probability-flip of a coin]
www.vsl.com. (2013). Bridge Construction Partner Brochure. Retrieved from http://www.vsl.com/brochures/all-brochures.html.
www.worksafe.vic.gov.au. (2004). Construction and Erection f Bridge Beams. Retrieved from http://www.worksafe.vic.gov.au/__data/assets/pdf_file/0007/13030/Bridge_Beams.pdf
Hillier, Frederick S., Lieberman, Gerald J., (2001), Introduction to Operations Research (7th Edition) (pp.468-492). New York, United States: McGraw Hill.
Humphreys, Gary C. (2011). Project Management Using Earned Value (2nd Edition) (pp. 163-173). California, United States: Humphreys & Associates.