Construction Of Solar Electric Generating System And Civic Infrastructure Essay.

Floor Cycle Time and Learning Curve

1). Part of the electrical power requirements for the HSR will be met from ‘renewable energy’ sources.  It is proposed to design and install a solar electric generating system (SEGS) - similar to what has recently being proposed for installation at Port Augusta in South Australia.

                                                     

A key component of a SEGS is the ‘Power Tower’ (as shown above), usually constructed in reinforced concrete that will incorporate a solar receiver system (SRS) that will be installed at the top of the reinforced concrete power tower.

A typical SRS can be seen in the papers referenced below.   The reinforced concrete power tower and the SRS are likely to be on the critical path for the project

a). Considerable research has been undertaken on the influence of ‘learning curves’ on multi-storey building construction and their impact on floor cycle times. Outline your understanding of what is meant by ‘floor cycle times’ as related to the construction of the ‘power tower’.  Study the section on ‘Learning Curves’ in Module 8, read the references (note there are also other references on the subject) and understand the Assumptions in Appendix 2 below.

From your reading and subsequent understanding, do you consider that there would be opportunities for saving construction time as construction of the power tower proceeds upwards? 

b) Craneage will play an important part in the construction of the power tower and SRS.  Outline the type and capacity of the crane/s that would be required for construction of the tower and lifting the SRS into position on top of the tower (Refer Appendix below for details).  Prepare a site analysis showing crane positions in plan and elevation for the construction of the power tower and for lifting the SRS into position.

c) Define what is meant by the phrase ‘long lead items’?How can a delay in delivery of ‘long lead items’ to the site impact construction schedule and what steps can be taken to try and ensure on program delivery of ‘long lead items’.

d) Estimate the construction time duration to build the reinforced concrete ‘power tower’ assuming that the structural foundations for the tower have already been completed (i.e. the area below ground level).

e) What do you perceive as the key risks and hazards involved in the construction of the power tower (from the ground upwards)?  

2). As part of the development of a regional city, a developer will be appointed to undertake the building of key civic infrastructure as follows:

a). Estimate the Client’s monthly payments to Contractors’ from the start to finish of the contract period (i.e. end of Stage 3) noting that intending contracting companies will require a 20% advanced payment on Stage 1 and 2 works and a 10% advanced payment on Stage 3. (HINT: READ THE MODULE ON ADVANCED PAYMENTS).  

Contractors’ will accept a 10% Retention on progress payments up to 5% maximum on all three stages.  

An S-curve for progress payments for projects with an 18-month and 14 month construction period can be used as a basis for payments in this exercise, the actual figures from this S-curve are reproduced below in Figure 1

b) Plot a graph of total monthly payments ($) vs. time. 

 Figure 1

Month	18 Month % Complete	14 Month % Complete
0	0	0
1	4	4
2	6	8
3	10	14
4	14	19
5	19	24
6	24	35
7	31	46
8	40	60
9	50	70
10	60	80
11	69	88
12	77	95
13	83	98
14	88	100
15	94
16	96
17	98
18	100

a). Floor cycle time and learning curve

In construction of high-rise buildings, floor cycle time is the time duration taken to complete operations or activities of constructing one floor of the building, from start to finish. It therefore means that the total time duration taken or needed to complete all the floors of the building is the aggregated floor cycle times (i.e. time taken or needed to complete one floor). In the context of this project, floor cycle time refers to the fastest repeatable time duration that will be required to complete a certain height of the power tower. Since the height of the power tower is 150 meters, the floor cycle time can be the time needed to complete constructing a section of 5 meters of the power tower (assuming that the power tower is divided into 30 sections of 5 meters long). Based on this assumption, the total duration needed to complete the power tower is the time duration that will be taken to complete one 5 meter long section multiplied with 30 sections (i.e. one floor cycle time multiplied with the number of floors or sections in this case). Therefore in this case, floor cycle time will be the time measured from the beginning of construction of a 5-meter section of the power tower to the beginning of construction of the subsequent 5-meter section of the power tower (Roser, 2015). Estimating and understanding floor cycle time is very important in this project as it will facilitate smooth flow of resources (including equipment, formwork, workers and materials) from one zone or section of the power tower to another. In other words, floor cycle time is very helpful in ensuring appropriate and efficient allocation and utilization of resources in construction projects (Leung & Tam, 2015).

As stated in the definition, it is important to note that floor cycle time is the fastest time, meaning that it does not include time losses and delays such as defects, breakdowns, etc. It is for this reason that learning curve comes in handy when estimating project schedule based on floor cycle time approach. One of the major benefits of learning curve is that it can help reduce the time and resources used to complete repetitive activities (Malyusz, 2016). Previously, the concept of learning curve was mainly applied in manufacturing industry that is associated with mass production (Jarkas & Horner, 2011); (Thomas, 2009). Since it is assumed the power tower in this project has been divided into 5-meter sections, zones or segments from down upwards, it means that constructing one section will simply mean repeating the same activities using the same resources and under the same conditions (Malyusz & Varga, 2017). This is expected to reduce floor cycle time considering the principles of learning curve (Panas & Pantouvakis, 2018); (Pellegrino, et al., 2012).  

Types and Capacities of Suggested Cranes for Construction

Learning curve plays a key role in reducing time and cost of construction projects (Srour, et al., 2015); (Sundaram, 2015). In this power tower project, learning curve can be used to create numerous opportunities of saving construction time during construction. Some of these opportunities include: developing and using a sophisticated planning, organization and management tools and techniques; use of s specialized equipment; applying a customized and advanced logistics system to ensure timely delivery of resources; hiring highly trained and specialized personnel; constant training of workers to increase productivity and efficiency; use of advanced concrete technology like rapid cycle concrete technology (how it is prepared, poured, vibrated, compacted and cured); use of high performance concrete; use of advanced and specialized formwork systems; use of intelligent software to operate the cranes; ensuring integration, collaboration, cooperation and cohesiveness of the whole project team; and use of advanced technological tools and software to monitor quality of materials and workmanship so as to avoid defects and losses.

b). Craneage

The types and capacity of suggested cranes for the construction of power tower and lifting the SRS into position include:

• Tower crane

This is a crane comprising of a vertical tower with a long horizontal jib fixed on it. One end of the horizontal jib has a counterweight while the other extends straight over the worksite. The jib has a trolley that travels along its length. The trolley holds the cable used for lifting loads. There is a cab at the intersection between the vertical tower and the jib from where the operator rides (Hazleton, 2017). The recommended tower crane is Favelle Favco M2480. This tower crane has a maximum load capacity of 275 tonnes at 12m, minimum boom length of 36m, tip load of 9 tonnes at 90m, and maximum boom length of 90m (Favelle Favco, 2018).  

• Crawler crane

This crane has the ability to maintain excellent maneuverability even when lifting very heavy loads. Despite its big size, the crane is easy to transport, assemble and disassemble. The recommended model of crawler crane for this project is Manitowoc lattice boom crawler crane – Manitowoc 16000. The crane has a maximum lifting capacity of 400 tonnes, a maximum boom length of 96m, a maximum jib length of 42.7m and a maximum luffing jib length of 84m. It features dual LCD color monitors and patented EPIC and CAN-Bus controls that ensure precise lifting and placement of loads.

• Mobile crane

The suggested mobile crane for this project is LTM 1750-9.1. This model of mobile crane is from the world’s leading crane manufacturer Liebherr. It has a maximum load capacity of 750 tonnes, maximum hoist height of 154m, telescopic boom of 52m, and maximum radius of 112m (Liebherr, 2018).

What are Long Lead Items and their Impact on Construction Schedule?

Site analysis

The position of crane on site is very important as it affects the effectiveness of the crane and safety of workers. There are several factors that influence location of crane o site, including: site constraints, layout of site, type of crane, crane configurations, quantity and type of needed materials or components, and shape and size of structure, among others (Abdelmegid, et al., 2015). The most suitable location of the cranes in this project should be determined using an optimization model. Generally, the crane should be located where it: does not interfere with access to other areas on site; allows adequate crane; enables easy storage; makes erection and dismantling easier and cost effective; does not interfere with the structure of the project or other related systems; allows maximum use of required working radius and hook height; etc. Depending on the size and layout of the site and the locations where different loads will have to be located, a suitable plan for various cranes have to be established from an optimization model.

Depending on how the crane should be positioned to enable efficient operations, the best position can either be inside or outside the project floor plan. Figure 1 below is an example of tower cranes plan

                                                       

                                                                                            Figure 2: Crane positioned with floor plan of the structure

                                                                                   Figure 3 below shows an example of details of crane position on site

                                                                      

As stated before, software simulations and optimization models should be used to determine zoning and anti-collision systems of the cranes.

Estimation of Construction Duration

c). Long lead items

Long lead items are materials, equipment, products or systems that have to be identified as early as possible so as to ensure on time delivery for the project to be completed within the stipulated time. The reasons for identifying these items at the earliest stage possible is because they take a long time to procure, create, process, implement or acquire. The process of getting these items should start before they are needed. This project will have numerous long lead items considering its tight schedule, bureaucratic processes, sophisticated construction methods and complex components that have to be engineered, tested and certified before installation. A delay in delivery of long lead items to the site will result to an extension of construction schedule. This is because long lead items affect the critical path of the project hence if they are not delivered on site then it means that the main project activities will have to stop until these items are delivered. For this reason, long lead items should always be delivered on time.

Some of the steps that can be taken to ensure on program delivery of long lead items include: identifying the long lead items at the earliest stage of the project (during design stage); prioritizing acquisition of these items in the project schedule (WorkPack, 2017); placing an order of the long lead items as soon as they are identified (before they are needed on site); fast tracking the procurement process of these items; monitoring processing progress of the items; and constantly communicating with all stakeholders involved in acquiring these items so as to understand the progress, challenges, etc. (WorkPack, 2018).

d). Construction time duration

Through benchmarking of similar projects that have been completed before and use of learning curve, construction of the reinforced concrete power tower is likely to take six months. But for this to be achieve, there should be a proper schedule plan and all necessary resources (including materials, equipment/machines and workforce) must be provided on time and whenever needed.    

e). Key risks and hazards

Key risks and hazards in the construction of the power tower include:

1. Working at height

The power tower is 150m high meaning that tradesmen will be working at height most of the time. There is always mobility restriction and added access for people working at height, which exposes them to risks. Small mistakes by people working at height can also be disastrous.

2. Moving objects

The construction site is expected to get quite hectic considering the number moving vehicles, machines, equipment (such as lifting equipment, dumper tracks, supply vehicles, etc.) and tradespeople that will be working on site.

3. Slips, trips and falls

Key Risks and Hazards Involved in Construction

Since there will be a diverse range of activities being undertaken on the site at any given time, they are likely to cause slips, trips and falls. The site will be full of holes on the ground, stored equipment and materials, scaffolding, etc. Workers at height may also fall when scaffolds are not properly erected or used.

4. Noise

The heavy machines and equipment that will be used on site and the lifting and hitting of different components of the power tower will produce significant level of noise.

5. Falling objects

There will be a lot of lifting on site using cranes and other equipment. This will expose workers to hazards of being struck by overhead loads or caught within the swing radius of the crane. The cranes should be inspected properly before every use.  

6. Material and manual handing

Workers on the site will be involved in constant lifting and moving of materials and equipment from one point to another, either by use of lifting machines or manually. This will expose them to some degree of risks (Alcumus Group, 2014).

To prevent or reduce these risks, appropriate safety policies should be followed. The company should also develop a suitable safety program that will constantly provide safety information and reminders to workers. Additionally, equipment should be routinely maintained, operated by qualified personnel, protected and stored properly and all workers on site must always be in appropriate personal protective equipment. The risks of these hazards can be reduced significantly through proper training of workers (Collier, 2017).

 2).

Assumptions:

• All the three stages of the project will start simultaneously
• Advance payment will only be made once (at the start of the project)
• Advance payment will be deducted at a rate of 20% (for stage 1 and 2) and 10% (for stage 3) of progress payment starting from the first month of thee stage until it is fully repaid.

Question 2 a: Client’s monthly payments to contractors

 

Month	Stage 1 ($Million)				Stage 2 ($Million)				Stage 3 ($Million)				Developer Monthly Payment ($Million)
	Prog. Pay	Adv. Pay	Ret.	Total Pay	Prog. Pay	Adv. Pay	Ret.	Total Pay	Prog. Pay	Adv. Pay	Ret.	Total Pay
0	0	23	0	23	0	20	-0	20	0	3	0	3	46
1	4.6	-0.92	-0.46	3.22	4	-0.8	-0.4	2.8	1.2	-0.12	-0.12	0.96	6.98
2	2.3	-0.46	-0.23	1.61	2	-0.4	-0.2	1.4	1.2	-0.12	-0.12	0.96	3.97
3	4.6	-0.92	-0.46	3.22	4	-0.8	-0.4	2.8	1.8	-0.18	-0.18	1.44	7.46
4	4.6	-0.92	-0.46	3.22	4	-0.8	-0.4	2.8	1.5	-0.15	-0.15	1.2	7.22
5	5.75	-1.15	-0.575	4.025	5	-1	-0.5	3.5	1.5	-0.15	0.15	1.2	8.725
6	5.75	-1.15	-0.575	4.025	5	-1	-0.5	3.5	3.3	-0.33	0.33	2.64	10.165
7	8.05	-1.61	-0.805	5.635	7	-1.4	-0.7	4.9	3.3	-0.33	0.33	2.64	13.175
8	10.35	-2.07	1.035	7.245	9	-1.8	-0.9	6.3	4.2	-0.42	0.42	3.36	16.905
9	11.5	-2.3	-1.15	8.05	10	-2	1	7	3	-0.3	0	2.7	17.75
10	11.5	-2.3	0	9.2	10	-2	0	8	3	-0.3	0	2.7	19.9
11	10.35	-2.07	0	8.28	9	-1.8	0	7.2	2.4	-0.24	0	2.16	17.64
12	9.2	-1.84	0	7.36	8	-1.6	0	6.4	2.1	-0.21	0	1.89	15.65
13	6.9	-1.38	0	5.52	6	-1.2	0	4.8	0.9	-0.09	0	0.81	11.13
14	5.75	-1.15	0	4.6	5	-1	0	4	0.6	-0.06	0	0.54	9.14
15	6.9	-1.38	0	5.52	6	-1.2	0	4.8				-	10.32
16	2.3	-0.46	0	1.84	2	-0.4	0	1.6				-	3.44
17	2.3	-0.46	0	1.84	2	-0.4	0	1.6				-	3.44
18	2.3	-0.46	0	1.84	2	-0.4	0	1.6				-	3.44

b). Graph of total monthly payments vs. time

The graph of total monthly payments vs. time is as shown below

                                                                                  

                                                           

References:

Abdelmegid, M., Shawki, K. & Abdel-Khalek, H., 2015. GA optimization model for solving tower crane location problem in construction sites. Alexandria Engineering Journal, 54(3), pp. 519-526.

Alcumus Group, 2014. Top Ten Health and Safety Risks in Construction. [Online]
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[Accessed 23 May 2018].

Collier, E., 2017. Construction Site Hazards. [Online]
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[Accessed 23 May 2018].

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[Accessed 24 May 2018].

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[Accessed 22 May 2018].

Jarkas, A. & Horner, M., 2011. Revisiting the applicability of learning curve theory to formwork labour productivity. Construction Management and Economics, 29(5), pp. 483-493.

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Liebherr, 2018. LTM 1750-9.1. [Online]
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[Accessed 24 May 2018].

Malyusz, L., 2016. Learning Curve Effect on Project Scheduling. Procedia Engineering, Volume 164, pp. 90-97.

Malyusz, L. & Varga, A., 2017. An Estimation of the Learning Effect on Project Cost Scheduling. Procedia Engineering, Volume 196, pp. 723-729.

Panas, A. & Pantouvakis, J., 2018. On the use of learning curves for the estimation of construction productivity. International Journal of Construction Management, 18(4), pp. 301-309.

Pellegrino, R., Costantino, N., Pietroforte, R. & Sancilio, S., 2012. Construction of multi-storey concrete structures in Italy: patterns of productivity and learning curves. Construction Management and Economics, 30(2), pp. 103-115.

Roser, C., 2015. How to Measure Cycle Times - Part 1. [Online]
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[Accessed 22 May 2018].

Srour, F., Kiomjian, D. & Srour, I., 2015. Learning Curves in Construction: A Critical Review and New Model. Journal of Construction Engineering and Management, 142(4).

Sundaram, R., 2015. Applying Learning Curve Theory in Construction Cost Estimating. [Online]
Available at: https://www.fgould.com/americas/articles/applying-learning-curve-theory-construction-cost/
[Accessed 22 May 2018].

Thomas, H., 2009. Construction Learning Curves. Practice Periodical on Structural Design and Construction, 14(1).

WorkPack, 2017. Beginner's guide to managing long lead items for solar projects. [Online]
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[Accessed 23 May 2018].

WorkPack, 2018. How WorkPack can help with procurement of long lead items for construction projects. [Online]
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