LEGO PHILOSOPHY

I can make sure that every Civil Engineer have played LEGO when a child. So the question is: Could a building be constructed like playing LEGO?

Thanks to Zhang Yue, founder and chairman of Broad Sustainable Building, the answer is a big Yes.

After the video “A 30 story building in 15 days” he got famous as the responsible of this big achievement. In an interview, when asked by Lauren Hilgers, if he had decided to start a construction company, apart from his air condition business, Zhang Yue said: “It’s not a construction company. It’s a structural revolution.”

Versatile design

What LEGO does is to break a specific structure into typical pieces and some special ones, That is why design process is fundamental in LEGO Philosophy. Making as many typical pieces as they can provide us versatility, because it means: using the same pieces you can build several different structures.

But if pieces are typical, how do they acquire that versatility? The answer is because versatility of their connections. In LEGO you can either connect two pieces by extremes or by half large or one by extreme and the other by half large.

For example, I have taken just a couple of typical pieces and they can be connected in 4 different ways, as shown here:

Keeping in mind that the LEGO model I’m using for this experiment contains 65 pieces, as shown here:

A rough calculation to determine how many different shapes I can build would be:

# Shapes = (# ways of connecting two pieces) ^{# pieces of the model - 1}

So using our data:

# Shapes = 4^65-1 = 3.40 x 10³⁸

It means by using only this little LEGO model we could create 34000000000000000000000000000000000000000 different shapes, many of them even better than what is printed in the box.

Mass production

For getting as many typical pieces as possible, LEGO is specially designed to mass production. Perhaps some pieces left as non-typical, but they are only exceptions and won’t delay the delivery date.

As example, in our LEGO model we consider as special pieces all unique ones, so 7  out of 65 pieces are non-typical or unique in the set of pieces. You can identify the here, they are those that appear "1x" as quantity:

So we can comment that roughly the 89% of pieces are typical in a usual LEGO model

Easy Erection

A manual comes inside each LEGO box, in which you can see how assembly process should be and it is as easy that even a 10 years old child could finish the model.

Then speed in erection process depends on how well fast are connections.  For instance in my 65 pieces model I will suppose the same number of connections (65) and according to my tests I take almost 5 seconds to fix one typical connections, so my erection would be:

Erection Time = # Connections x time  per connection

Using our data:

Erection Time = 65 connections x 5 sec/connection = 325 sec = 5.42 min = 0.09 hours

So, finishing a model in just 5 minutes is a perfect example of how fast could we erect a building if we focus our endeavors on improving construction process, especially regarding to connections, at least in steel buildings.

Maybe our friends of LEGO were the only who didn’t get smashed while watching “A 30 story building in 15 days”, and even maybe they are asking: Why those Chinese took so long for just a 30 story building?

15 DAYS THAT CHANGED THE WORLD

 

After the video “A 30 story building in 15 days” he got famous as the responsible of this big achievement. In an interview, when asked by Lauren Hilgers, if he had decided to start a construction company, apart from his air condition business, Zhang Yue said: “It’s not a construction company. It’s a structural revolution.”

And I agree.

His success is based on redeveloping the three phases of constructing a building: Engineering, Manufacturing and Erection.

I could explain it as follows:
 

1- Engineering:  Design concerned about construction
 

Traditional structural design leads to use the minimum amount of materials, as well as the cheapest, because the owners always are looking for saving money. So, structural and facilities designers are not concerned for construction process, that is why they deliver only a basic engineering (drawings, schemes, etc.) enough to complete the analysis of the building but insufficient in order to carry it out. If during construction process an issue that involves design shows up, it is solved on the road and, depending on how important modifications are, a well performed building could turn into a behind of schedule project.

In regards to cost of materials, concrete has become the cheapest many decades ago. Concrete offers several advantages but is a very slow-placing material: before placing concrete you need to place steel rebars, to erect the formwork and, finally, to pour the concrete, which is usually limited to a certain volume for several reason but mainly geometry. In addition, it is mostly required to wait some more days, until it gets the design strength, to remove the formwork and to work on its surface. Precast concrete is more useful to construction process but has disadvantages too.

The new designers are involved in construction process too. They are aware that any failure in alignment of holes for bolts would delay the erection process, this is avoided when engineering has got a high detailed level, and fortunately that precision could be achieved nowadays by using 3D Design Systems or BIM which allow them to make drawings ready to manufacturing and 3D models if required in complex cases. With these new methods, designers apart from checking the structural performance of the building, are able to run a simulation of the erection process, making sure this way there won’t be any interference or defect that can paralyze the construction. You can see it on this video:
 

 

On the other hand steel is more expensive than concrete but offers many advantages over, specially when thinking about a fast erection. Steel pieces can be mass produced, easily connected whether by welding or by bolts during the erection process and start to work immediately after fixed.

Zhang’s building was mainly made from steel, a little of wood but not any concrete, and

In sum, while traditional design is made to save money by reducing materials, on the other hand this new engineering is leading to save money by reducing manufacturing and erection times.

I bet on the second one.

 

2- Manufacturing: Mass production
 

The most efficient way of production continues to be the assembly line invented by Henry Ford almost 100 years ago. In this industrial process, materials and consumables are carried by conveyor belts through several work stations until obtaining the final product. Physically we could describe this as a Horizontal Production Process.

On the other hand a building is constructed from the basement or first level up to the top, it means if you haven’t finished the first floor you can’t start the second one or if you haven’t finished the second level you can’t start the third one and so forth. Physically we could describe this as a Vertical Production Process.

It is easy to realize that Horizontal Production Process is more efficient than Vertical Production Process because it doesn’t have constrains involved in the last one.

Zhang Yue has realized this perfectly and performs Horizontal Production Process in manufacturing of buildings pieces, and keeps Vertical Production Process only when it can’t be avoided, it means during erecting process. Comparing with traditional way of construction, we could say he builds 90% of the building in assembly line and keeps the 10% left over to be erected as usual.

Charles Chaplin realized better than anyone, and his film Modern Times shows comically how fast assembly line works.

 

Well played again.

3- Erection: Continuous process
 

Actually changes in Engineering and Manufacturing come from redeveloping Erection process, in order to make it a continuous process.

Only a perfect design can leads us to a non-interruptions erection process. On these times, times of 3D models and BIM, good is not enough, it is required to be perfect. The proof is there, his design was as perfect that they didn’t have any interruption during those revolutionary 15 days.

Planning is important too, because while in an usual building the most of the stores is typical and are divided into sectors, which run in parallel up to the last level; he has divided the stores into pieces, it means finished blocks which only have to be placed and well connected to get the building. Organizing day-night shifts, hiring suitable equipments, coordinating transport from factory to site and keeping safety and quality high patterns were important as well.

In sum, when Engineering and Manufacturing have been made under Zhang’s philosophy, Erection process is the easiest thing in the world, don´t waste your time on that, no more than 15 days.

For example these Indians took only 48 hours in a 10 story building.

 

Thanks Zhang it doesn’t sound impossible, not any longer.

 

 

 

NEW COMPRESSION SCHEDULE TECHNIQUE: BREAKING

The most used Schedule compression techniques are Crashing and Fast track, which are very effective in order to reduce activities time and shorten Project duration. This Paper consider a new technique called “Breaking” which makes up an additional way for compressing schedules.

Introduction

-          Crashing.- This technique reduces duration of critical path by allocating more resources to involved activities, see Sketch 01.

Sketch 01: Crashing

-          Fast track.- This technique reduces duration of critical path by overlaping (either total or partially) involved activities which were planned one next to another, see Sketch 02.

Sketch 02: Fast track

Breaking

This new method for Schedule compression proposses to shorten Project duration by either eliminating or modifying relations among activities on critical path. It is compounded by three stages:

-          Dependency determination

-          Dependencies and overcosts analysis

-          Displaying options

Dependency determinación

First step is to group dependencies among activities according to PMI’s reccomendations, it means:

-          Mandatory dependencies.- They are relations that can not be changed. For instance Formwork -> Concrete Pouring is a mandatory dependency because isn’t possible concrete pouring without fixing formwork before.

-          Discretionary dependencies.- They are relations that can be changed but were chosen from a group of alternatives because represented the cheapest path to complete the Project.

Dependencies and overcosts analysis

The next step is to find the Project critical path.

We will use Turbine – Generator Erection Project as example to clarify each step. This Project will last 425 days, the deadline is on June 20^th 2014 and the red activities form the critical path, according to Chart 01.

Chart 01: Project critical path

 

Then it is required to sort dependencies in two groups: mandatory dependencies and discretionary dependencies as explained before.

Filtering critical path activities would be very advisable, see Chart 02, as well as to make a difference between both types of dependencies, for exambpe by painting green all the mandatory dependencies and, in contrast, painting orange all discretionary dependencies.

Chart 02: Sorting dependencies

Then it is possible to address each discretionary dependency (orange colored) looking for either eliminate them (first option) or modify them (second option) until there is no discretionary dependency on critical path or, at least, we have optimized those left in order to shorten Project duration.

On the example, successors of activity ID14: Bridge Crane Installation belong the same construction process: first we install Bridge Crane and next we use it to install Draft Tube (successor ID15), Spiral Case (successor ID16), Turbine (successor ID17) and Generator (ID18). It is supposed this installation was chosen for being the least expensive option, because you can take the chance of using a Project Bridge Crane to lift and install other components. Neverthless we can eliminate this dependency if considering to hire a Crane which help us to install these other components, at least before Project Bridge Crane is finished up and working. There would be US$ 1 500 000.00 as additional costs for hiring this Crane.

If this decision is made, Decision 1, Draft Tube, Spiral Case, Turbine and Generator wouldn’t depend on Bridge Crane, so we could eliminate these dependencies from ID14: Bridge Crane Installation successors activities, as shown in Chart 03.

Chart 03: Eliminating ID14: Bridge Crane Installation successors

In Chart 03 there is a new critical path, 18^th April 2014 is new deadline and 380 days is new Project duration, which means this decision would shorten Project schedule in 45 days (425 - 380 = 45 days)

Now the process is repeated again on the new critical path.
 

As above, critical path activities are filtered and painted green (mandatory dependencies) and orange (discretionary dependencies) as shown in Chart 04.

Chart 04: New critical path

There is only one discretionary dependency (orange color) we can address to, it is located in successor activities of ID17: Turbine Erection and corresponds to the usual installation process that considers first placing Turbine into the pit and after that installing Generator which is located above. Precasting the Generator and placing Turbine can be made at the same time, so once Turbine is finished, Generator could be just lifted en connected in its final location. This decision involves U$ 200 000.00 as additional costs for moving more people and equipment to site, in order to work in parallel both activities.

If this decision is made, Decision 2, we can turn the link involved into a start-start dependency now because Turbine and Generator would be parallel activities, as shown in Chart 05.

Chart 05: Eliminating ID17: Turbine Erection successor

As well in Chart 05 it is shown a new critical path, 13^th December 2013 as new deadline and 290 days as new Project duration, which means this decision would shorten Project schedule in 90 more days (380 – 290 = 90 days), keeping in mind 380 days as current duration.
Again the process is repeated on the new critical path.

As above, critical path activities are filtered and painted green (mandatory dependencies) and blue (optimized discretionary dependencies) as shown in Chart 06.

Chart 06: New critical path

On new critical path, there is only mandatory dependencies (green dependencies) or optimized discretionary dependencies (blue dependencies), and there is no simple discretionary dependencies (orange dependencies), so it is not possible shorten project duration any longer, Breaking process has finished.

Displaying options

It is very useful to elaborate a decisions tree for displaying options.

Number of branches in decisions tree depends on how many decisions are possible, according the next formula:

Number of branches = 2ⁿ

Where:

n = Number of decisions we can make

For better understanding see Graphic 01.

Graphic 01: Decisions tree

In our example, there are 2 possible decisions, therefore:

            Number of branches = 2ⁿ = 2² = 4

Taking apart each decision:

-          Decision 1

Additional costs by Decision 1 = $ 1 500 000.00 (see above-mentioned)

Cut days by Decision 1 = 45 days (see above-mentioned)

Project Duration by making only Decision 1 = Project duration - Cut days by Decision 1 = 425 – 45 = 380 days

-          Decision 2

Additional costs by Decision 2 = $ 200 000.00 (see above mentioned)

Cut days by Decision 2 = 90 days (see above mentioned)

Project Duration by making only Decision 2 = Project duration - Cut days by Decision 2 = 425 – 90 = 335 days

Combined effect:

-          Decision 1 + Decision 2

Additional costs by Decision 1 + Decision 2 = Additional costs by Decision 1 + Additional costs by Decision 2 = 1 500 000.00 + 200 000.00 = $ 1 700 000.00

Cut days by Decision 1 + Decision 2 = Cut days by Decision 1 + Cut days by Decision 2 = 45 + 90 = 135 days (check this, it is not always arithmetic addition, but it happens that way in our example)

Project Duration by making Decision 1 + Decision 2 = Project duration - Cut days by Decision 1 + Decision 2 = 425 – 135 = 290 days

Finally our decision tree would be like Graphic 02:

Graphic 02: Displaying options in decisions tree

Conclusions
 

-        If “Crashing” is not applicable because physical limitations, as usual in construction business, and “Fast track” turns into a very risky alternative keeping in mind quality and other features affected by; we can use “Breaking” in order to shorten Project duration.

-        While “Crashing” deals with resources and “Fast track” deals with leads and lags; “Breaking” is looking for eliminating or modifying construction processes, which means “Breaking” deals with innovation and could give us important advantages over competence. (In following posts I will show you how Chinese builders applied “Breaking” on traditional build construction process to get “30 story building in 15 days”.)

Reccomendations
 

-        Comparing additional costs related to Breaking with economic benefits by finishing before deadline, would complete the analysis and help us to make best decisions.

-        Applying Breaking does not exclude neither Crashing nor Fast track, so these techniques could be perfectly combined.

-        Breaking would be easier if Planning softwares (MS Project, Primavera, etc.) have an option to sort dependencies: mandatory dependencies (green in our example), non optimized discretionary dependencies (orange in our example) and optimized discretionary dependencies (blue in our example), so far they don’t have one.

LET'S KILL GANTT

A few months ago Profesor Gui Ponce de León from University of Michigan came to Perú and gave us a speech called “Gantt Chart rest in peace”, of course I was there.

In that speech he introduced us a new tool called GPM to represent and review the schedule of a Project, pointing out its advantages over Gantt. I´m not going to describe here what’s GPM because I haven’t used it yet, but those who are willing to know more about could try on this link http://pmatechnologies.com/ , here you could get more information regarding GPM from creator’s mouth.

In fact, just as Gui, I belong to the “Let´s kill Gantt Club”. Neverthless I confess that I have tried several times to kill Gantt and it is not only that I haven´t got  it, but Gantt emerged more powerful after each attack. That’s why I think Gantt continues as the best way to represent time of a Project.

For instance this was my last try:

Issue

In Construction, generally, manpower is grouped in crews which go from one work station to another and so on through Project’s life. Knowing how the crews move would be very useful for planning a Construction Project but it is no possible in Gantt chart, let’s check why.

Henry Gantt invented his famous chart in 1915, for automobile industry and during Ford age, it means assembly line was already operating. One of the biggest differences between automobile industry and construction industry is that while in the first one manpower is static, materials goes towards them by using conveyor belts,  in the second one manpower is moving all the time in search of  work to complete.

So, how can we check crew rotation?. I didn’t have to go any further, the answer is in the same Gantt chart.

Analysis

Gantt chart has two dimensions: the first one is the timeline located in horizontal axis and the second one is the work breakdown structure located in vertical axis (See Chart 01)

Chart 01: Gantt’s structure

We would need a third dimension to show crew rotation up; and there is only one moment in which Gantt chart acquires a third dimension, it is when we identify critical activities and non critical activities by using colors. Therefore it is possible to get this third dimension calling for colors.

In order to get an easy way to visualize this crew rotation, it would be very useful to make a structure which shows a timeline in the horizontal axis and a list of work stations where crews are moving through in the vertical axis (See Chart 02).

Chart 02: Crew movement structure

We can notice timeline matches with Gantt’s, but list of work stations doesn’t with work breakdown structure necessarily. So the only one condition, not so hard to achieve, is that items on list of work stations and activities of Gantt work breakdown structure must be the same.

Finally, the most recommended for an easy visualizing is to set work stations on the last detail level as above and in the previous level we should place disciplines or types of crews, therefore it would be as follows:

Level 1: Project name

Level 2: Disciplines

Level 3: Work stations

Instructions

1-      Creating Project name.- In our example we will try a Hydropower plant (See Chart 03).

Chart 03: Detail level 1, Project name

2-    Creating Disciplines.- Work crews in a Powerhouse construction can be divided into four disciplines: Tests, Excavations, Civil Works and Mechanical – Electrical (See Chart 04).

Chart 04: Detail level 2, Crew disciplines

3-    Creating Work Stations.- In our example we create the tasks, but keeping in mind they must be work stations too (See Chart 05).

Chart 05: Detail level 3, Work stations

4-    Calculating durations and linking activities.- Generally crews into a discipline have the same amount of people, in others words they have the same performance too, therefore each duration is established by dividing quantity of work in each task over a performance rate of the corresponding discipline’s crew. In addition, we must link activities too, according to planned construction process. See Chart 06.

Chart 06: Durations and links assigning

5-    Identifying some possible paths for crews. For example between tasks ID16: CONCRETE ON POWERHOUSE (1^ST STAGE) and ID17: CONCRETE ON POWERHOUSE (2^ND STAGE) there is a 39 days gap, which can be filled by a non-linked task like ID27: CABLES TUNNEL with 40 days for duration. So we take advantage of these "non-linked" activities in order to get a continue work for the crew going through. We assign a color to identify each specific crew running through its activities or work stations. We have chosen green for this crew (See Chart 07).

 

Chart 07: Crew rotation planning

6-    In the same way, we can move some tasks or connect each other ones just being careful on keeping deadline date. In our example we can visualize crews rotation, for instance green crew of CIVIL WORKS discipline runs through the following path: ID16: CONCRETE ON POWERHOUSE (1^ST STAGE) -> ID27: CABLES TUNNEL -> ID17: CONCRETE ON POWERHOUSE (2^ND STAGE) -> ID19: CONNECTION TUNNEL -> ID23: DISCHARGE TUNNEL (1^ST STAGE) -> ID28: OUTSIDE INSTALLATIONS -> ID18 CONCRETE ON POWERHOUSE (3^RD STAGE) -> ID24: DISCHARGE TUNNEL (2^ND STAGE) and then green crew leaves the Project, as shown in Chart 08.
 

Chart 08: Project planning using colors to identify crews rotation

Advantages

-       It doesn't only offers advantages of Gantt chart, but also describes perfectly crew movement through Project execution. If any changes happen during Project, planner can visualize exactly which will be the impact on manpower force planning, in case of added scope it is easy include these new works according to crew releasing and in case of reduction on scope it is also possible determine when the involved crew will be in stand by and to reassign them to another work station.

-       It is not necessary make a resource assignment in each activity if working on a planning software (MS Project, Primavera, etc.) to get the manpower’s curve.

For example if we change Chart 08 in order to have only crew life in the Project, not showing work stations, something like Chart 09 would result:

Chart 09: Crew life through Project

And if we drop down each bar on the horizontal axis as in Chart 10, manpower’s curve will show up immediately. For example, in Chart 10  we see the are two peaks in manpower’s curve, the highest is located just on the first quarter of 2011 and it is perhaps  the most crowded time of Project, because in this peak we have Light blue crew, Light gray crew, Green crew, Pink crew, Sky blue crew, Light red crew and Cherry crew working at the same time. 

Chart 10: Manpower's curve

Conclusions

-        Sorry, I couldn’t kill Gantt this time, but I’ll be back. I swear.

Reccomendations

-       The most recommended softwares to carry this out are those that offer several layouts for setting colors, for instance Primavera Project Planner, because we can use a first color layout to identify critical path, as usual; a second color layout to identify crews rotation; and a third color layout to visualize rotation of a critical resource we need to focus in, aside manpower.