What are the types of industrial steel strands?

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1. Unbonded Steel Strands

2. Bonded Steel Strands

3. Spiral Ribbed Steel Strands

4. Indented Steel Strands

5. Multistrand Steel Strands

6. Coated Steel Strands

7. Prestressed Steel Strands

Ever wondered how several construction designs for tower construction, such as long-span bridges and overhead crane beams, stay intact and secured? Industrial steel strands are an essential piece of hardware used in these concrete structures for reinforcement and security. 

This blog will explore the different types of industrial steel strands, each with unique characteristics and applications. Only the strongest, most long-lasting materials should be chosen because industrial strands must sustain thousands of pounds of concrete. Several distinct types of industrial strands are created for various applications, even though almost all of them are composed of steel.

What are the distinctions between these types, and which industrial steel strand is the best to use? Keep reading to find out!

Unbonded Steel Strands

Most uses for unbonded steel strands involve post-tensioning because they are adaptable steels. The steel strand in use can separate from the concrete thanks to anti-corrosion grease and polyethylene plastic, allowing the steel strand to move freely in the layer and making the construction more convenient. The friction between unbonded PC strand tendons is minimal and easily bendable into various curved shapes. 

Not to mention, they are made of high-strength steel wire coated in a corrosion-preventing substance. Due to its strong bonding properties, this steel strand is appropriate for unique structures such as cast-in-place concrete floors, heavy precast beam loads, massive concrete constructions like bridges, and high-rise buildings.

Bonded Steel Strands

High tensile strength, firm connection with concrete, stable construction and good combination with steel-reinforced concrete are all bonded PC Strand or bonded steel strand characteristics. It also saves material, reduces distortion and construction weight, and increases stiffness, abrasion, and water resistance. Precast concrete elements like beams and columns are normally built using bonded steel strands, sometimes called fully anchored steel strands. This steel strand is also used in large structures because of its strength, toughness, and great bonding properties.

Spiral Ribbed Steel Strands

One of the classic forms of steel strands is the spiral ribbed steel strand. Regarding strength and endurance, spiral ribbed steel strands are comparable to bonded steel strands and are utilized in precast concrete components. The steel wire&#;s surface features a spiral ribbed design, which makes a difference. This distinctive design has better adhesion to the concrete, making it an excellent option for construction under stress. Additionally, it is frequently used in water pipes, hollow slabs, and telegraph poles.

Indented Steel Strands

Indented steel strands resemble spiral ribbed steel strands in terms of surface texture. However, they are constructed from a single steel wire instead of numerous wires. Because of its high strength and longevity, this steel strand is frequently used to manufacture precast concrete parts like beams and columns. It has many uses in numerous industries, including construction, hollow slabs, and high-speed railway sleepers.

Multistrand Steel Strands

The tiny steel wires that make up multistrand steel strands are twisted together to create a single strand. Due to its strength and flexibility, this steel strand is perfect for precast concrete components like beams and columns. In contrast to other steel strands, Multistrand steel strands are reasonably simple to bend, making them an excellent option for use in curved or oddly shaped buildings.

Coated Steel Strands

In terms of elasticity, coated steel strands are comparable to unbonded steel strands, but they include a protective coating to fend off corrosion. This steel strand has better bonding qualities and weather resistance, making it perfect for post-tensioning applications.

Prestressed Steel Strands

In terms of strength and durability, pre-stressed steel strands are comparable to bonded steel strands; however, they are pre-stressed to increase the strength and stability of the concrete construction. This kind of steel strand is well known for its capacity to withstand high-stress levels and is frequently used in the building of precast concrete parts, such as beams and columns.

Key Takeaway

Industrial steel strands are essential to construction because they strengthen and stabilize concrete constructions. Steel strands come in various forms, each with particular properties and uses. It&#;s important for engineers and contractors to know the types of industrial steel strands so that they can choose the right ones for specific projects.

At Metal Exponents, one of the best steel manufacturers in the Philippines, we can provide you with industrial steel strands that can be galvanized or made out of high-carbon steel. This makes them more durable in large-scale structures such as bridges, high-rise buildings, railway lines, and the like.

Do you have questions in mind? Feel free to express your concerns or questions to us! Get in touch with Metal Exponents today.

7 Types of Industrial Steel Strands

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Pre-stressing Strand as Mild Reinforcement

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Pre-stressing Strand as Mild Reinforcement

Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

16 Dec 11 10:50

I have a strong recollection that there are limitations on using pre-stressing strands as mild reinforcement (not prestressed), but I can't find it anywhere in ACI 318.  Am I way off base, or just looking in the wrong location?

Replies continue below

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RE: Pre-stressing Strand as Mild Reinforcement

slickdeals

(Structural)

16 Dec 11 11:11
thread507-: Unstressed Strands as Reinforcing
 

Some discussion in this thread

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

16 Dec 11 12:36

Thanks, slick.  

It looks as though the limiting factor for this is the ability to develop the breaking strength before the concrete crushes.  

I can see how that's a problem in typical members, but if you have a very deep member, you can easily develop the breaking strain in the strand before the concrete reaches a strain of 0.003.

rapt, are you around?  Does that sound about right to you or am I missing something?

RE: Pre-stressing Strand as Mild Reinforcement

rapt

(Structural)

16 Dec 11 16:46

Lion06,

I do not see how the depth of the member affects this. It is related more to the amount of tension force being developed comapred to the depth.

But this all comes out in the calculations if you do not make the assumption of yield, instead do the calculations by strain compatability and you will know what stress is developed in the strand. To ensure a balanced design you will have to limit the neutral axis depth much more severley than the default limits in codes.

The biggest problem still is how much stress can be developed based on bond and developemnt lengths. In the tests I mentioned in the previous discussion on this, they show, as expected, that it is not possible to develop full yield stress if the strand is not prestressed.
In areas where stress/strain changes gradually along the strand (positive moment areas with UDL loading), you might be able to develop up to -MPa.
In areas where the stress/strain rate of change is more severe (negative moment areas, changes in section, point loads, etc) only 800-900MPa might be able to be developed.

So, no you cannot simply use strand without stressing it and assume full yield strength.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

16 Dec 11 16:53

The neutral axis depth is always the same for a given tensile force.  If you have a very large d (say 40'), then the strain in the steel at crushing of the conrete will be high enough to fail the cable, no?  

RE: Pre-stressing Strand as Mild Reinforcement

rapt

(Structural)

18 Dec 11 17:59

Yes, but that happens with low ductility steel or FRP also if you do the calculations properly.  Even Class N steel in Australia and europe (Normal Ductility 5% peak strain) theoretically has this problem for lightly reinforced sections. For normal reinforcing steel calculations most designers simply ignore this check and do not cfalculate steel strain, as the codes do not specifically limit reinforcing tensile strain, though logically they should. In normal situations it does not have a significant effect on ultimate member capacity and is not easy to calculate without computers so codes have ignored it.

The correct solution is to limit the concrete strain to less than .003/. to reduce the steel strain to less than the peak strain. This will result in a deeper neutral axis depth which is the only thing codes really limit, for ductility (this does not mean codes are correct, just lazy).

RAPT gives the designer the option to do this in a design if desired.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

For more PC Strand Bondedinformation, please contact us. We will provide professional answers.

(OP)

21 Dec 11 07:45

ACI assumes concrete crushes at 0.003 - well, that's the usable strain that we're allowed to assume.

Just humor me here for a minute.  Looking at this from only a strain and subsequent force standpoint for unstressed prestressing strand - say you have a 20' deep member (let's say it's 100' long so we're not concerned about bond length) with two 1/2" diameter, 270ksi strands.  The member is 10" wide with 5ksi concrete.  The neutral axis depth is assumed at ((2*0.153*270)/(0.85*5*10))/0.8 = 2.43".  With the depth of the strands at say 19' = 228", the strain in the strands when the concrete reaches 0.003 is 0.278.  This is much higher than the strain needed to reach 270ksi, which would be 270/ = 0..

Is that all there is to it, other than the bond length, of course?

Do you happen to have any literature on the subject?  My searches have turned up little.  

RE: Pre-stressing Strand as Mild Reinforcement

RWW

(Structural)

21 Dec 11 10:14

• http://files.engineering.com/getfile.aspx?folder=b3a-68e1--97d2-cb

What about serviceability issues? Regardless of bond, if grade 270 steel is sized to have the same moment capacity of a section with mild steel, the curvature at service-load moment would be significantly greater than that for mild steel (due to less steel in the cross section). Attached is a sketch of some moment-curvature diagragms of the same section with grade 60 and 270 steel. If high strength steel is used, deflection would govern designs and effectively eliminate the advantages of having high-strength steel.

RE: Pre-stressing Strand as Mild Reinforcement

Dinosaur

(Structural)

21 Dec 11 12:56

I have not designed a concrete member in quite some time but I seemt to recall there was a maximum YP allowed for mild steel, which was something around 75ksi.  Is this still in the code or has it really been that long?

RE: Pre-stressing Strand as Mild Reinforcement

yakpol

(Structural)

21 Dec 11 13:19

Lion06,

In your example, the strand will yield at strain 0.9(270)/ = 0. and will rupture at strain = 0.05 well before concrete compressive concrete strain reaches 0.003. As rapt said, prestressing strands perform poor if not prestressed.

 

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

21 Dec 11 14:41

yakpol-

How do you figure that the concrete is reaching a strain of 0.003 before the cable yields or ruptures?  As I noted above, the strain in the strand when the concrete reaches a strain of 0.003 is 0.278.  This is well above the two strains you just listed, which means that teh steel is straining before teh concrete crushes.


RW002- Point well taken.

RE: Pre-stressing Strand as Mild Reinforcement

yakpol

(Structural)

21 Dec 11 18:57

Lion06,
The strand will rupture first. According to your calcs the strand tensile strain 0.278 at the time concrete compressive strain is 0.003.
The ultimate strain is near 0.05 for prestressing steel and 0.12 for A706 mild steel (both less than 0.278). The 20-foot deep section is grossly underreinforced, so steel yields and ruptures before strain in concrete reaches 0.003.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

21 Dec 11 20:20

yakpol-

That's exactly what you want to have happen to develop the strength of the cable.  If the concrete crushed before the breaking strain was reached, THEN you wouldn't get the full strength of the cable.  I'm not following the point you're making.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

21 Dec 11 20:25

yakpol-

For a typical RC member, you simply check the strain of the steel when the concrete is at 0.003 and if the steel strain is above yield, then you use the yield strength of the bars in the calcs.  Why would (from an purely analytical standpoint) this condition be the exact opposite?

RE: Pre-stressing Strand as Mild Reinforcement

rapt

(Structural)

27 Dec 11 15:30

Lion06,

But what if the strain is above fracture?

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

27 Dec 11 18:05

Why is that not what you want?  You don't need the concrete to reach 0.003, that's just the max that the code allows you to use.  If the steel reaches yield BEFORE the concrete reaches 0.003, then all is good, right?

RE: Pre-stressing Strand as Mild Reinforcement

yakpol

(Structural)

27 Dec 11 23:23

FRACTURE - not yield.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

28 Dec 11 05:57

Who cares? The required moment is reached before then. The required moment capacity is reached b
BEFORE anything fractures.  The only thing the strain diagram is telling you is that the concrete doesn't crush first.  I've never seen any requirement to check steel strain against fracture.

The point I'm trying to make is that the steel will not see the strain associated with fracture, because the moment capacity (moment associated with steel strain reaching fpu) is achieved long before that.  

Your point is well taken, but I'm really only concerned with understanding if it's possible to develop the full breaking strength of a non-prestressed prestressing cable.  The use is chord reinforcement in a diaphragm.  It's common in precast construction to use very little steel (far below code minimums for flexural members) for chord reinforcement.  I've always seen mild steel, but I have a guy who wants to use non-prestressed cable.  I just want to make sure he's using the right cstrength for his calculation - i.e. 100% of fpu, not like 25% of fpu.

RE: Pre-stressing Strand as Mild Reinforcement

RFreund

(Structural)

28 Dec 11 07:59
I don't understand the counter-argument. Is it that the steel is not ductile and will fracture instead of yielding therefore making this a 'brittle' failure state similar to the crushing of the concrete?   

Lion's point IMO is well made if the steel yields before the concrete crushes then the design is ductile. You then limit the capacity of the member to the yield strength of the steel (and verify that the steel yields first).I don't understand the counter-argument. Is it that the steel is not ductile and will fracture instead of yielding therefore making this a 'brittle' failure state similar to the crushing of the concrete?

EIT

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

28 Dec 11 09:12

Another way of verbalizing my point is that at some point before the concrete crushes (just at some point, I don't really care when) the steel will reach its full fpu.  Then in the nominal moment capacity I can use the full breaking strength.   

RE: Pre-stressing Strand as Mild Reinforcement

yakpol

(Structural)

28 Dec 11 10:11

Lion6,
Assuming that you check against fracture strain, the cracking of concrete in tensile zone still remains a issue. Typically steel stress associated with allowble crack width is below 36 ksi.
Also, search the papers and make sure the bond between strand and concrete at high stress level is still there. The codes do not cover this stress range.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

28 Dec 11 10:26

Yakpol- I'm still not seeing the need to check the fracture strain.  The very instant the steel reaches fpu (provided the concrete doesn't crush before then) I'm done.  That's my nominal moment strength.

As far as the bond strength at this stress range; this is done every day with bonded, prestressed construction - double tees, hollow core plank, etc.  Granted, these shallower members aren't getting up to 270 ksi in the steel, but they're pretty close.

RE: Pre-stressing Strand as Mild Reinforcement

yakpol

(Structural)

28 Dec 11 11:43

Lion06,
Note:
1. Not fpu, but fpy=0.9fpu
2. The concrete stress will be of triangular shape if strain is less than 0.003. You will need to run strain compatibility analysis to determine flexural capacity rather than simplified approach based on rectangular compression block.
3. Release stress 0.8(270)ksi is taken by concrete in compression. In the case of non-prestressed strand, concrete around the strand will be in tension and badly cracked. You really need a test proof. You may end up with unbonded, non-prestressed steel.
4. Serviceability?  

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

28 Dec 11 12:24

1. I don't have my PCI Design manual in front of me, but I think you can take pretty close to fpu if the strain compatibility analysis shows that you develop that strain in the cable.

2. This technically correct, but at the level of strain I'm talking about with two cables in a 20' deep member, whether rectangular or triangular, the steel strain will be well above where it needs to be.  This is a non-issue in my mind.  

3. Point taken.

4. Point taken here, too, but again, I started this thread with the sole purpose of finding out if you can develop the breaking strength of a prestressing cable that isn't prestressed.  I definitely appreciate and welcome the other comments and thoughts, but they're outside the direct scope of the question.

RE: Pre-stressing Strand as Mild Reinforcement

rapt

(Structural)

28 Dec 11 17:01

Lion06,

All of this still relies on being able to develop the bond between the concrete and the strand, and the tests I have been involved with show that you cannot develop sufficient bond to develop the yield stress in the strand. The amount you can develop depends on the strain/stress profile along the member and varies from about 900MPa to -MPa depending on the situation.

Anchorage at the end would also be important in a tie situation!

RE: Pre-stressing Strand as Mild Reinforcement

TXStructural

(Structural)

28 Dec 11 17:20

ACI 318 does not recognize the use of PT strand as non-PT reinforcement.  ACI 318 section 9.4 specifically prohibits the design of members using deformed reinforcement over 80 ksi, with the commentary clearly indicating that the reference to "prestressing steel" means "prestressed reinforcement."

Using strand in place of mild steel will not allow the use of ACI 318 load and resistance factors, development lengths (obviously), formulas or computational methods.  These all assume certain behavior of materials which are not approximate by kludging the code for use of strand.  The behavior of a member with properly bonded reinforcement will be different from one which does not bond in a similar way.  Doing as you suggest does not meet the standard of care required unless you fully evaluate not just the tension and strain compatibility, but also the assumptions underlying the code used for design.  Although strand would not meet the definition of deformed reinforcement, that is the use you propose.

RE: Pre-stressing Strand as Mild Reinforcement

Lion06

(Structural)

(OP)

29 Dec 11 07:47

TX-
That's kind of what I'm looking for - if it's explicitly not allowed or if it's just buried somewhere.

This is not my design.  This is being suggested by a PC supplier and he claims they do this all the time.  I've asked for some literature on the subject from him, but he has yet to provide any.

RE: Pre-stressing Strand as Mild Reinforcement

slickdeals

(Structural)

4 Jan 12 07:08
Also, see below in the Structural Engineer Magazine on strength of reinforcing

http://www.gostructural.com/magazine-article-gostructural.com-12--restrictions_on_the_strength_of_reinforcement_in_aci_318_08-.html

@Lion,Also, see below in the Structural Engineer Magazine on strength of reinforcing

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