When the floor of my home/office in Quezon city vibrated and then swirled around a bit early this week, I didn’t panic at all because I trusted the design, engineering, and construction of the building would withstand what i suspected was a pretty strong earthquake.
Although I survived the strong quake to make nervous jokes about it, my “faith” in the science and workmanship that went into the penthouse unit where I was was shaken after reading an email.
The email was sent by a friend around forty eight hours after the April 22 earthquake which emanated from Porac, Pampanga.
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I’ve known this friend of mine for years now and not once has my friend sent me a bum steer. So I gave the two documents emailed to me a thorough read and knowing a little about steel, I realized the dire implications of what the documents were saying.
Before showing you what the document says, let me first say that I believe engineers, builders, and land developers here in the Philippines would not knowingly endanger the lives of millions of Filipinos.
Moreover, they may be well aware of certain practices of construction material suppliers and have accounted for it using a variety of means. Although I do not know it for a fact, but I assume that they have their own ways of testing the materials they use in constructing high rise buildings and have executed their designs knowing exactly the sorts of stresses that their materials can withstand.
Now, on to content of the email…
It basically argues that government regulators have been using a standard for steel used in the construction of high rise buildings that other countries around the Pacific Ring of Fire have junked in favor of standards that they claim are superior.
Here is an excerpt from the email which makes reference to a senate hearing last year:
The hearing tackled the issue on the mislabeling of the quality grade of the steels that are locally produced. Quench tempered (QT) steels are made with softer cores, and the outside coating is hardened during the temping process; this is done by spraying water on the heat-
tempered steel to toughen the coating. But unfortunately, the standards of testing steel in the Philippines are not as thorough, and a product that is made with grade 40 steel could pass as grade 60 because of the quench tempered coating.
The second hearing, dated September 11, 2018, pressed more on the issue of the mislabeling, plus emphasis on the discussion of the effects of the use of QT bars in the construction of high-rise buildings.
The hearing also touched on Engr. Morales’ findings on the effects of the QT steel used in high-rise construction. Some 10 years ago, Pagasa Steel (name not quoted in hearing notes) questioned Steel Asia’s use of the new method of quench tempering steel; at the time, micro alloyed steel bars were prominently produced and used. They wanted to give the new process a bad taste in the mouth, and urged Morales to do research on the situation.
Backed with funding from Pagasa, Morales penned a research piece “A Clear and Present Danger – The Use of QT or TMT Rebars in Seismic Zone 4”, it states that there is a danger with the use of the bars in question in areas surrounding the Pacific Ring, and where earthquakes can go up high in magnitude numbers.
As mentioned above, steel rebars in the Philippines are only tested for tensile strength, which is not an accurate measure of durability and toughness when faced in high magnitude conditions. A cyclic loading test can provide a much more accurate account, which puts the steel under multiple cycles of pressure to determine withstanding strength, but unfortunately is not a practice used in the Philippines.
Moreover, out of 195 countries, 5 have banned/discontinued the use of quench tempering high-grade steel. These countries are Japan, Taiwan, New Zealand, Canada and the US. Most of these countries are near the Pacific Ring / seismic faults.
If you are like me and wondering what steel rebar is, this page from Design Buildings Wiki may be sufficient for getting some idea:
Rebar, also known as reinforcement steel and reinforcing steel, is a steel bar or mesh of steel wires used in reinforced concrete and masonry structures to strengthen and hold the concrete in tension. To improve the quality of the bond with the concrete, the surface of rebar is often patterned.
Rebar is necessary to compensate for the fact that whilst concrete is strong in compression, it is relatively weak in tension. By casting rebar into concrete, it is able to carry tensile loads and so increase overall strength.
Different uses of rebar include:
- Primary reinforcement: Used to provide resistance to support design loads.
- Secondary reinforcement: Used for durability and aesthetic purposes by providing localised resistance to limit cracking and temperature-induced stresses.
- Provide resistance to concentrated loads, spreading it through a wider area.
- Assist other steel bars in accommodating their loads by holding them in the correct position.
- External steel tie bars to constrain and reinforce masonry structures, sometimes as a means of building conservation.
- Reinforced masonry: Some masonry blocks and bricks include voids to accommodate rebar to carry tensile loads. The rebar is secured in place using grout.
The email goes on to say that the problem is not Quench Tempering itself, but alleges that the steel from PISI (an association of Steel companies for high rise infrastructures) has grade 40 core material which can pass grade 60 after QT.
Although not completely grade 60, it is alleged that they are sold as grade 60. It also claims that 50% of steel in PH comes from company that practices mislabeling and conjectures that 50 percent of buildings in the country are at risk.
Assuming that this is true or even partly true, shouldn’t the government find out if buildings have this mislabeled steel and if so, determine the measures that must be undertaken to reduce the risk of a catastrophic collapse of these structures WHEN the next earthquake hits.