Work and delay lags in networks

[Sadeq]

Homework Statement

The attached page explain the work and delay lag
but actually i can't understand when he said for example that two bridges can't start together?why?
how he know that?
and in other graph he said the different directions of lag which is correct

actually i completely don't understand this part,so please explain it so i can understand the difference

what is work lag and what is delay lag and why in some circumstances there are not feasible

or please guide me to recourse to understand them

 

[jedishrfu]

you haven't provided the whole problem description. Is Bridge A and Bridge B on the same road? Is there some dependency that says bridge A must be done first otherwise trucks can't get to the excavation site...?

Delays come into play when one task is dependent on another task or they use common resources.

 

[Sadeq]

Sorry for that, I upload now another example, and my question is why he said that for splittable activity 6 day work is feasible while at not splittable 6 days work are not feasible,,please explain this form me

Also what if it was delay lag for both what happen

Basically i am confused in work and delay lag and maybe if you explain this to me i will be able to catch the idea


Thank you in advance

 

[jedishrfu]

It looks like you are working with a PERT chart which is used to design work schedules based on the idea that some tasks are dependent on one another while others can be done at the same time.

The dependency may be because one task lays a foundation for the next task or that only one person can do the task or simply that the task may require a set time for drying...

As an example, task A can be done while task B is being done but both A and B must be complete before task C can be started. The PERT idea is to study the tasks and figure out the proper order of tasks and the shortest time to complete given the times it takes to do a given task, the resources and other constraints.

Wikipedia has an article on it that may help:

http://en.wikipedia.org/wiki/Program_Evaluation_and_Review_Technique

Toward the end of the article is a chart that looks very similar to yours and may help you interpret it better.

I hope this helps.