Tie rods spacing Form work 4

[bteljuice]

Hello,

I just graduated and have no field experience(few internships here and there).

i am currently bidding on a bridge and the abutment measurements are:

H=2.9m
W= 1.2m
L=13.4

I am using 3/4" plywood and 2x4 Lumber with 0.5m CtoC spacing and concrete is 30MPa.

My question is:
What type of tie rod should i use (diameter?) and what is the spacing CtoC between the rods that I should use.

Once i find the spacing of the rods and the size, i can estimate the amount of rods and cost.

Hope you can help me out, thanks.

 

[beton1]

Best to get some help from a formwork/accessory supplier. Or read up on ACI publications. Formwork for Concrete is a good place to start. You need to get educated on this prior to making decisions
like this.For example, 0.5m spacing of 2x4's won't work. You are looking for an answer, not guidance.

 

[vshep]

We use ties from Dayton Superior because it's what the local contractors use. They can tell you the tie breaking strength and you can figure the number of ties you need from there.

 

[bteljuice]

Beton1,

Thank you for the quick reply.

Would you mind explaining why 2x4 wont work? One of the estimators told me to use 2x4(since they will be widely available on site). I started doing calculations and deflection of plywood,weight,lateral pressure when my colleague looks at me and tells me that this is ESTIMATION and not design. If i do this to every concrete pouring, i won't be able to bid anything nor have the time and thus have to use common sense.

Having no experience, I honestly don't really have the skills to know all this information on top of my head.

Is there a rule of thumb i can follow or quick guide? I will start reading on Formwork for Concrete, hopefully I'll have time to do everything.

Regards,
B

 

[bteljuice]

@Vshep,

Dayton is one of the subs I am in contact with for this project.
I am just worried that they will underestimate my capabilities for asking such a preliminary question and would ask someone else from my company to deal with.

This is my first project and I want to literally try my best. To the extent that i didn't even ask my senior engineer for help, I wanted to find things on my own and with your help, thus being here on this forum.

 

[bteljuice]

The only way I could find the spacing of rods is by doing my calculations which will take a while (and was asked not to waste time doing so).

What I am mainly looking for is a Rule of Thumb. Like, one of the Rule of thumbs ive learned is, for every 1SF of 3/4" plywood, use 2BF of 2x4 Lumber. It's not entirely correct, but it's a quick way to estimate since lumber is cheap.

 

[vshep]

All tie specs are found online so I would just call the company and ask what type of tie they would use in this situation. They don't need to know your name or project specifics!

The tie spacing depends on the amount of concrete in the form, which subjects a pour pressure on the plywood/timber forms that increases with depth. Pour pressures are found in CSA A23.1-09 here in Canada. Read up on the codes!

Our contractors often use 4x4 lumber, but you can use two 2x4s with the tie sandwiched between them. Browse through some previous projects in your company to see what they used in the past.

 

[dik]

bteljuice... take a gander at the attached spreadsheet...

Dik

 

[dik]

You can use the spreadsheet as a guide to what is involved...

Dik

 

[bteljuice]

Gotta love this forum.
Thanks Vshep.

Dik, LOVE THE spreadsheet

 

[dik]

Also have one similar to it for slab formwork...

Dik

 

[dik]

vshep... ACI and CSA pour pressures are markedly different... I usually use the ACI and stipulate it for drawings...

Dik

 

[dhengr]

I understand what you are doing, and have done a bit of it over the years, but not off the top of my head, and I’ve got a lot more experience than you do at Structural Engineering. No one expects a freshly minted engineer or estimator to know everything, or even very much about some of this stuff. But, you are expected to pick it up pretty quickly, and should not have to ask the same question too many times. Work with your senior engineers and your boss, they know you won’t know all that they do, but they do have a vested interest in your being productive and successful and accurate in your work, most of them will be helpful. And, as a young estimator, there is no shame in asking for help, that is truly an experience based process. On your own time study catalogs, and books like the ACI publication “Formwork for Concrete,” that is how you will learn your trade. And, you have some obligation to put in that effort on your own if you want to be respected. Study Dik’s spreadsheet for what you can learn, you will be writing your own in no time based on the way your company and contractors do things, methods, available materials, type of work and forming, etc.

Come here for that additional view point or a different way of looking at things than just your company’s way of doing things, study and think about what you are told by some of these smart guys, and you might actually be able to offer a new, or better, or quicker way of doing things at your company from what you learn here. The thing I find interesting and valuable about E-Tips (and you will too) is the diversity of ideas, knowledge and engineering experience, different and sometimes better ways of thinking about a problem or doing things. When I talk about a problem in my own office, I have to remember that in many cases, I taught the other guys my way of doing things, so I may not be getting really new ideas, or a critique which looks at the problem from a different angle.

 

[bteljuice]

dhengr,

You are absolutely right and appreciate the wise words. I always appreciate comments from others who have more experience. I am always eager to learn and like to see other's point of view and ideas. As you said, a diversity of ideas.

Thanks again.

 

[bteljuice]

Dik,

Is it possible to also send me the one for slab formwork. Very helpful.

 

[msquared48]

My first consulting job 30 years ago was designing the formwork for a highway bridge pier in Denali, Alaska.

Taught me about the value of the ACI publication on formwork design. I suggest you get one and familiarize yourself with the tables, the same way i had to.

Mike McCann
MMC Engineering

 

[dik]

As requested...

Dik