What is a ladder type grantt chart??

Hi Jamesh - Welcome to Planning Planet.

It is where a series of tasks with a similar duration are linked both SS and FF with equal lags.

The result looks a bit like a leaning ladder.

It is mostly used in manufacturing to contro assembly linel production.

It has limited use in construction.

Use the search facility to see earlier debates on this topic.

Best regards

Mike Testro

Hi,

Ladder is similar to Stair.

The Bars are viewed with similar looks like what you can see at Great Wall of China!

Cheers.

Thanks mike and Laza.

Mike is only half right – ladders use a combination of both SS and FF links between the activities but the durations don’t need to be the same.  If the software supports ‘Ladders’ there is some form of progressive feed that allows the shorter activities to stretch and balance the longer activities.  The technique originated on Main Frame ADM scheduling packages and has only been used effectively on a few PC based systems such as Micro Planner.  Others like Microsoft Project completely ignore the concept.

For more on how the calculations work see: Links, Lags & Ladders http://www.mosaicprojects.com.au/PDF/Links_Lags_Ladders.pdf

Hi Patrick

If you read my text a bit closer you will find I did not say the "same" duration but "similar".

But thank you for explaining why Ladder planning has no place in construction.

Best regards

Mike Testro

Mr. Mike Testro,

Waiting for your comments on my thread “DRAG of Critical Path” posted in Planning, Scheduling & Programming Discussionon Sun, 2012-01-15 08:50.

Cheers & Thanx

Ladder activities occur everyday in construction projects. One example would be formwork and reinforcing steel when there is a circular relationship within activities progress.

Let say elevated slabs are of the beam-slab type. First you install beam bottoms and cannot continue without installing beam rebar. After beam rebar is installed beam sides and slab formwork continues and then you install slab rebar.

If you stop formwork installation rebar installation must be stopped, if you stop beam rebar installation then form sides must be stopped.

The SS and FF relationships might have different lag values but the links are strict links.

Another example would be CMU installation and tie beams and columns on a high CMU wall as stopping either will stop the other.

You might graphically mimic how the ladders look and by manually adjusting the durations they will seem equivalent but I doubt float values will be the same. I used Micro Planner before, I used the ladder activities in my construction schedules and loved the functionality. It was long ago so I do not recall all details.

In the following example if you model the circular relationship between formwork A and rebar A if you slow the installation of rebar A then formwork A will be slowed, activity rebar A shall have no free float or total float in such model. In many real life models such circular relationship exists.

Hi Tanveer

You are getting all the advice you need from Steve and Rafael.

My advice is don't use it in construction programming.

Best regards

Mike Testro

Hi Rafael

You already know my philosophy on the use of SS FF links in construction programmes.

Particularly with Lead Lags - they should never be used.

Best regards

Mike Testro