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Prestressing Jack Assembly

Prestressing Jack Assembly

Prestressing Jack Assembly

Can anyone guide me to a good source for Prestressing Jack assembly? I need to prestress some sample slabs with Steel, GFRP and CFRP, but I can not find a good place that explains how the bars can be gripped on the jack end. Would I simply use a wedge? If so how can I adapt it to a hollow jack? I see the enerpac and other jacks have a great system but we can't afford those since these are just test models. I've simply been looking at getting a 5 ton hollow jack, and pump for the first run. I have visited PTI and PCI with no results. Any help is greatly appreciated.

Thank you,

RE: Prestressing Jack Assembly

A hollow ram will work for stressing, either single-acting or double-acting, with electric or manually operated pumps. Make sure your hydraulic hoses are rated with bursting capacity significantly greater than working pressures.

Steel is typically 7-wire strand and gripped with re-useable barrel chucks that commonly use a 3-piece wedge. Precision-Surelock is a US based manufacturer of such components.

For CFRP and GFRP you may run into problems as wedge-based gripping devices can cause significant damage to the fibers. There are a few proprietary anchorage systems for FRP.

5 ton is a small capacity ram/jack. What is the jacking force you are proposing?

RE: Prestressing Jack Assembly

Actually it is not a 5 ton, I was reading the spec for the wrong jack. I am considering the Enerpac RCH 123 (http://cylinderjacks.com/hydraulic-cylinder/hydrau...),
Its a 12 Ton capacity with a 3" stroke. The slab samples will be 3'x10' simply supported slabs. I have .0305 strand available and I want to start my calculations with this strand in mind since I can get it local. The FRP I will have to order somewhere. The jacking force I expected to use was between 15kip to 20 kip, although I will confirm this when I finish designing the first slab. The slabs will be loaded 100psf and after observation loaded to failure.

My main concern is how to attach a grip to the enerpac hollow jack to grip the steel? I will certainly be using Surelock for the ends of the slab, but I'm concerned about the gripping of the jack to the strand for stressing. Have you ever seen any attachments to fit desired strand diameters added to these hollow jacks? The ordering of this equipment takes up to 2 weeks so I wanted to find something, order it and design during the waiting time of equipment to arrive.

The pumps I'm considering are the following, but I didn't find anything regarding the bursting capacity. I will definitely call and confirm before ordering any pump. Thank a lot for the reply and help.



RE: Prestressing Jack Assembly

I have the Powerteam SPX version of the same ram. A very very handy jack to have. Used it just yesterday to remove wedges from a failed PT tendon anchorage in a very tight space.

1. Go with the manual Enerpac ram not the Chinese copy.

2. Since this is a spring-return ram (one-way acting) you only need to purchase a single hydrailic hose - purchase a Enerpac one knowing it will be rated to bursting pressure for a max of 10,000 psi.

3. "0.0305 strand" - what is the diameter?, is it 7-wire strand?

4. For common 1/2" dia 7-wire strand, the stressing jack would use multi-use chucks like these: Link and the strand is inserted into the hollow centre of the ram and the chuck installed over the strand at the back of the ram. Use grease on the wedge to chuck barrel interface to make it easier to 'break-out' (remove) the wedges after stressing.

5. Is this a 'pretensioning' or 'post-tensioning' application? If pretensioned, your forms need to be designed for the jacking force or is there an external bulkhead?

6. Sounds like a fun project.

RE: Prestressing Jack Assembly

1. Go with the manual Enerpac ram not the Chinese copy
By this you mean the jack? So the jack i'm looking at there is actually an equivalent from china? Or did you mean the manual pump in comparing the enerpac and the zinko? Sorry for the confusion.

3. "0.0305 strand" - what is the diameter?, is it 7-wire strand?

Sorry I wrote the area. It is approximately .25" diameter wire. Its single wire strand. This is bonded pretensioning. For the anchoring of the forms I want to make a concrete pillar with a steel angle embedded that will hold the single strand prestress force. Then I would shore up with wood form to cast concrete for the slab. I will be breaking cylinders so as soon as I hit 80% of the 4ksi I will remove forms and the slab will be resting on the pillar at each end. After I reach 4ksi I will form around the slab with high walls that will hold an interior liner to allow us to load with water. I am looking forward to starting this, Ive never done it before.

I can't thank you enough for the help! It a relief to get some input on all of this. I realize i'm asking too much, but just in case, you wouldn't happen to have a picture of the chuck gripping the strand or anything similar? At this point my assumption is the chuck diamater is greater than the inside diameter of the jack therefore bearing behind it but the interior wedge holds the wire?

Thanks again for all the info!

RE: Prestressing Jack Assembly

1. Sorry, I should have said "pump". Go with the Enerpac pump!

2. That is small diameter wire (non-stranded)! You may be looking at custom grip chucks for such small diameter. PRECISION-SURELOCK have 0.25" multi-use chucks, but anyhting small and it will be custom. PRECISION have fabricated custom chucks for me - from very small to very large (2"). Contact Stan Landry at PRECISION and he will help you. I am assuming you are in the US.

3. The following photo is of the components that make up a small stressing set-up:

4. The following photo is how a multi-use chuck would grip a 7-wire strand on the back of a hollow centre ram:

You will need 2 multi-use chucks for each prestressing wire - one for each end. You will pre-cut your prestressing wire with one end say 2 or 3 feet longer for purposes of stressing each wire, so you need one additional multi-use chuck for stressing...BUT, stressing with a hollow centre ram you are going to require a 'nose' with a recess on the leading edge so that when you stress the wire chuck wedges can displace a small distance - if the wedges cannot 'slip' freely during stressing then you will not correctly stress the wire/s.

5. Your precast bed length is very short (10 feet), so the effective prestress force you obtain after accounting for losses is going to be significant. for example, if you 'seat' the chuck wedges for each wire and loose say 1/4" of seating loss you have lost a high % of total elongation over the 10 foot bed length. Also, you need to look at wire slippage and the 'development length' at the ends - these will effect your prestress force.

6. Stressing is a dangerous operation. I encourage you to obtain the services of an experienced person who understands all safety and operations of prestressing. Just

RE: Prestressing Jack Assembly

Ingenuity, thanks a lot for all of this. These picture are very helpful along with all your comments. You'de think we would have gone over this in grad school, but they show us the fancy expensive jacks and we assume those are the one and only to use. I remember going over the wedges and casings, but aside from that it was all calcs. I called Precision today but I didn't get a call back after I left a voicemail. I will call again tomorrow and ask for Stan. The slabs we are doing will be 2.5" , 3.5", and 4". So I have to design them and see which wire or strand size will work best. Since we are not ordering a whole lot I want to see if I can use just one size. I found the jack, pump and hose in Amazon and at a better price. I will be ordering them today. Below is an image of the risers we did a while back. You can see the wire they used on the first riser going up, that's the wire they have locally and are trying to sell us. After calcs we will see whether or not to purchase. Again thank you.

RE: Prestressing Jack Assembly


You are welcome.

I am interested in the specifications and supplier for the small wire/strand. If you have any details please share.

Look like an interesting project you have. Let us know how it turns out.

NOTE: Very important that you use a nose with a recess for the stressing chucks.

RE: Prestressing Jack Assembly

Is a compatible nose with recess available from Precision as well? Who would you recommend. I will get the supplier of wire on Monday as its when I'm meeting with the person selling me the small lengths I need. I will most definitely be posting updates. And thanks, I do find it very interesting although its a simple concept. Looking forward to comments on my progress.

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