tp 020 - re-examining conventional wisdom in rebars detailing

8/11/2019 TP 020 - Re-examining Conventional Wisdom in Rebars Detailing

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Conventional Wisdom in Reinforcing Steel

Re‐examining Conventional Wisdom

By Amadeus L. Magpile,

President and CEO of Barlines Reinforcing Steel Co., Inc. (Phils)

Founder and President of Barlines Rebar Estimating & Detailing, Inc. (U.S.A.)

Change is not easy in a large organization. In an industry as a whole change may not be possible. There

is, predictably a strong reliance in any organization on conventional wisdom that had worked numerous

times before. But innovations make paradigm shifts. What was accepted wisdom years ago are one by

one falling apart as a misconception. The concrete reinforcing steel industry is no exception. What was

once a robust cut and bend practice at the jobsite in the Philippines is slowly giving way to offsite pre‐

fabricated supply and demand market. It cannot be helped. The economy is getting stronger , the

playing field is now global and climate change demands frugal use of resources. While I am not

advocating a complete change, I strongly urge the purveyor of rebar to re‐examine at least a few

conventional wisdom, that I find prevalent only in the Philippines.

Single Stock Length Vs. Multi Stock Lengths

While other countries revel on a one stock length; 60 feet in the US and 15 meter in Canada, Australia

and most of Europe ‐ the Philippines has several lengths of stock, 6.00m, 7.50m, 9.00m, 10.50m, and

12.00m. During the height of the cut and bend practice at the jobsite, multiple stock lengths was a

bright and useful innovation. The steel mill did construction a big favor by providing them. In so doing,

however, it seemed that they also benefited very handsomely on its drawback.

It was obvious, that the idea on multiple stock lengths stemmed from the absence of reinforcing steel

(commonly

called

rebar)

fabricators

with

equipment

to

properly

shear

and

bend

rebar

to

required

lengths as designed by structural engineers. The availability of multiple stock lengths, allowed

contractors to order rebar lengths as closed to what they need, to eliminate shearing at the jobsite and

save on materials. For example, when 5.50m long bars are required, they will order 6.00m long stocks.

Trimming it to length becomes a wasted labor. All 6.00m long bars will be placed in concrete and the

contractor feels delighted that he did not waste any material. Whatever he bought he used in its

entirety. Never mind that the required length needed is only 5.50m long.

In countries where one stock length prevails, this same contractor can buy exactly 5.50m long and pay

only for the exact length. However, the difference is that he is buying from a fabricator instead of the




steel mill. Obviously the fabricator added a certain premium for cutting the bars to length, which made

the cost a bit higher.

But wait. When a steel mill produces rebar, they produce them in one length only. After their

production and the subsequent shearing to different stock lengths, an added process, would not they

add a premium too? In fact, in this system – it seems to me the premium is there whether you buy the

post cut 6.00m or the production 12.00m length.

This is in essence is the simple advantage of buying rebar for use in construction from an offsite rebar

fabricator rather than a mill. The end user buys and pays only for the exact quantity, length and shape

that he needs from the rebar fabricator – no more and no less. While from the steel mill the end user

buys and pays for what he needs and then some – the remnants and scraps. Scraps and remnants are

best

left

in

the

steel

mill

–

after

all

they

are

the

ones

that

need

them

badly.

Rebars

are

produce

directly

from scrap metal.

The Philippines is not totally out of the cut and bend industry. It may be years before they totally

embrace offsite reinforcing steel fabrication. The multiple stock lengths, therefore still has a place in the

Philippines. What I want to see is more and more rebar fabricators to properly bend rebar against

hairline fractures, reduce waste and help make a jobsite a safe place to work. Exactly what Malaysia

and Singapore are aiming to do.

Shorter Class A Laps Saves Material than Longer Class B Laps

No one I know can argue this statement at face value. But of course – shorter laps are less material than

longer laps. This is inedibly stamped as a mindset among project engineers. Because the science of

rebar detailing was slow to come to the Philippines – this mindset was never held up close to scrutiny.

Sadly, the statement does not hold true in the design of seismic columns.

If you look at the construction skyline of the Philippines, you will see column vertical bars alternating

long and short, as if the bars are racing towards the sky. Traveling abroad, you will never find a similar

construction skyline. In San Francisco, the city that practically invented earthquakes, you see vertical

bars all cut at about the same height and column ties are all the way to the top of the vertical bars.

Same is true In Vancouver, Sydney, Dubai, Malaysia and Singapore.

Two factors made this happen in the Philippines. First ‐ the use of bundled bars, due again to the

absence of a rebar fabricator with shearing and bending equipment to handle large vertical bars.

Second ‐ the mindset of shorter laps against longer laps. The American Concrete Institute (ACI) code

requires that shorter laps and laps of bundled bars be staggered. Yet the same code allows longer laps

in single bars not staggered.




Because of the staggered laps, columns in the Philippines are prevented from being assembled into a

cage. That is why we do not see column ties in our skyline. What we see instead is our version of Cirque

Soleil ‐ironworkers

gingerly

climbing

swaying

vertical

bars

to

drop

multiple

ties

from

the

top,

while

other ironworkers are holding bars from swaying and relatives at the street level praying. It seems to

me – Corporate Social Responsibility (CSR) gone awry.

While bundling of bars is an acceptable practice, the diminished use will only come when more and

more rebar fabricators are around. In the case of the shorter class‐A lap versus the longer class B lap

mindset – re‐examining this wisdom is necessary.

Looking at the skyline of the Millenium Tower in San Francisco.




This may be a shock to construction engineers, just like the first time I showed them coiled rebar stocks

in our fabricating shop.

THERE IS ONLY ONE WAY TO SAVE ON REBAR MATERIALS – AND THAT IS OPTIMUM SHEARING.

This is not a trade secret. Everyone in the rebar industry outside the Philippines knows this. Optimum

Shearing is sorting all the required lengths and combining them to fit a stock length to reduce waste. If

an engineer is given the task of scheduling the shearing of rebar from a long list of bars of different

lengths such that the outcome will produce the least amount of scrap and remnants – he may come

close but not against a computer. Why? There is no known formula. His calculations will require him to

iterate over and over again. You need to do a number of what ifs before you can come close to an

optimum result. Then even if he succeed, he will not find anyone that can maintain and follow his

schedule.

The

shearman

will

always

grab

the

most

convenient

stock

to

shear

against

his

schedule.

Meanwhile, a properly tooled rebar fabricating shop has a software that can provide an optimized

shearing schedule in nano‐seconds and an automatic shearline that can process such a schedule. Not a

portable shearing equipment but a long shearline like as shown below.

A fully automatic shearline capable of processing optimum shearing schedule. Loaded and sorted at one

end and segregated by length at the other end after shearing.




Now, let me show you a typical seismic column in the Philippines. Both are reinforced with 32M vertical

bars. One column lap spliced with a shorter class‐A lap staggered and the other lap spliced with a longer

class‐B

lap

but

not

staggered.

Typically

vertical

bars

such

as

these

columns

are

fabricated

from

a 9.00m

stock.

The final results after fabricating from a 9.00m stock are as follows:

The class‐A lap generated a vertical bar 8.38m long and a 0.62m scrap (remnants shorter than 10% of

the stock length is considered scrap), while the class B lap generated a vertical bar 8.79m long and a

0.21m scrap. At 8.79m long, I will not even bother to cut the 9.00m stock to save labor. Even If you do

not add the advantage of cage assembly and lifting in place by the tower crane, thus avoiding




ironworkers climbing bars – Class‐B lap is the only logical choice. Anyone would conclude that since

they will throw away scraps, wouldn’t it make sense to use them instead?

ACI overwhelmingly recognized this that in their Detailing Manual they did not even mention class A in

drawing a Typical seismic‐resistant details of columns. See Fig. 6, from ACI below.




Closed Stirrups vs Open/Capped Stirrups

The ACI Fig 6 brings me to the next subtle difference in construction in the Philippines ‐ that is puzzling

to me. Open stirrups are seldom found in any jobsite in the Philippines. Even though the majority of

floor framing designs are beams and slabs variety. Very few are flat plate designs, which are very

common in most high‐rise building projects in the world.

Construction does not seem to allow open and capped stirrups in assembling girders and beams. If

someone decided that open and capped stirrups require more materials than closed stirrups –again I

will say this is a misplaced decision. Once again, to save materials you need optimum shearing, period.

When beams and girders are crossing each other, the only way to build them with closed stirrups is to

temporarily assemble them above floor, and slowly lower them after they are all tied together. Beams

framing into girders will require that the girder be raised also. Girders framing into columns will require

that a number of ties be displaced. I see ironworkers having an easier time on single span beams and

girders but a horrendous time on multiple spans.

Consider Fig. 6 from ACI Detailing Manual. The ties that need to be out of the way for the girders

assembly are the critical ties within the Joints and above the joints. These critical bars are usually

multiple and are closely spaced. How are they displaced? They are gathered within the girder assembly

and slowly put in place as the girder is lowered. This is, of course, easier said than done – when you are

dealing with not one but multiple ties within the columns, spaced too close to each other. What really

happens when

ties,

stirrups

and

girder

bars

are

in

each

other

way

and

the

inspectors

are

not

around?

The ironworkers bring out their only tool in getting out of tight spot – an acetylene torch. Either the ties

or stirrups get torched or worse the girder or column bars get torched. There is a brand new building in

Las Vegas – the Harmon Hotel, scheduled for demolition by the owners, whose structural engineers are

claiming a lot of rebar are missing in the column and beam joints.

We suspected that the detailing was outsourced out of the United States to a group who is unfamiliar

with standard practice in the United States. In the installed rebar market in the United States all stirrups

are detailed open and capped per ACI code, notwithstanding how they are shown in the contract

drawings.

Once

again,

the

American

Concrete

Institute

overwhelmingly

acknowledged

this

practice,

by

showing alternate open capped stirrups in their detailing manual. See Fig. 5 on the next page.

When stirrups are open and capped, bars can be dropped and tied in place inside the forms. Main bars

are threaded into girders and columns and no ties are displaced whatsoever. It makes for a cleaner

assembly. Inspectors are able to see inside the beam cage before cap ties are tied in place. Leaving a

few cap ties open allow for concrete hose and vibrators to reach critical joints. And lastly it speeds up

the work tenfold. Ever wonder how construction in the U.S. can rise every three or four day cycle?




Open and

capped

stirrups

simplify

placement

of

girders

and

beams,

without

displacing

other

bars.

Finally, if change is necessary, where does the first line of change need to occur? I suspect, maybe, at

the drafting department of a structural engineers office. Could it be that it is high time to sort through

old boiler‐plate typical details and get rid of some that has seen its usefulness? Rebar detailers, such as I

are sometimes, without thinking, detail exactly according to what is shown on contract drawings – true

to what we learned from rebar detailing 101.

tp 020 - re-examining conventional wisdom in rebars detailing

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