Sharpening Part 4 – ‘Nando and the Sword Sharpener

And this is from my heart
Which is deep inside my body:
It’s better to look good
Than to feel good

Fernando

This post is a little longer and more roundabout than my previous posts, but I wanted to share with you some of Japan’s history, and examples of this country’s most fabulous art as produced by its blacksmiths and professional sharpeners. But before I get into that, I would like to share some relevant words of wisdom from Hollywood’s wisest man.

Billy Crystal in Fernando’s Hideaway

The handsome gentleman in the picture is Fernando. He is neither a blacksmith nor a sharpener of tools or weapons, but his insight into physical beauty and words of wisdom about happiness are pertinant to sharpening, as we shall see below. If you are not familiar with ‘Nando, I suggest you google him or view a video or two on Youtube.

So what does our dapper Latin Lover have to do with sharpening? And swords?

As ‘Nando taught the world, a wise person will not equate looking good with feeling good. Likewise, you would be wise to not confuse a blade’s appearance with its performance. Indeed, a blade that looks as sharp as the skinny end of nothing may not actually cut very well in some applications.  A good example is Japanese swords. Let me tell you a true story to illustrate my point.

When I was a University student in Japan, I was privileged to be entrusted with a number of swords that belonged at the time to the late Dr. Walter Compton, Chairman of Miles Laboratories and the inventor of Alka-Seltzer. He was a wealthy man who had a huge collection of swords obtained while an officer for the US military in Japan immediately after the war when Allied forces required the defeated Japanese people, on pain of death, to surrender all swords, civilian and military. Of course, many valuable and rare family heirlooms were surrendered or forcefully confiscated. Supposedly they all went to the bottom of Tokyo Bay in bunches, or were melted for scrap. But we know better, don’t we.

Towards the end of his life, Dr.Compton put a lot of money into having his better swords professionally sharpened, new shirasaya scabbards and furniture made, and formally evaluated in preparation for donating them to the Boston Museum of Art, where many of them reside today. Sadly, some were auctioned off without his permission. “The feckless sons of wealthy men” is the operative phrase in this case, I fear.

I assisted Dr. Compton’s representative by transporting over 70 of these swords to and from Japan and performing the necessary legwork to accomplish these goals inside Japan. During those years I held in my hands and feasted my eyes on rare and beautiful blades of great historical value several of which would have easily been designated National Treasures if they had been intended to remain in Japan (“National Treasures” may not leave Japan). 

During those years I spent a lot of time meeting, questioning, and requesting services of the best sword sharpeners in Japan, and learned a lot about swords, stones, and sharpening. Dr. Compton’s reputation was such, and his swords were of such rarity and high quality that I had no difficulty persuading the very best craftsmen to work on them or speak with me including Mr. Okisato Fujishiro.

Interestingly, in Japan such craftsmen are called “Togishi” (研師), an unambiguous word that can only be translated as “sharpener.” However, in the West these same Japanese craftsmen are called “ Sword Polishers.” In the post-war context, this actually may be more accurate than the Japanese term.

A very subtle, high quality sword tip brought to life by the arts of the Sword Sharpener. Notice the peaceful elegant hamon (wavy milky pattern at the cutting edge oriented towards the top of the photograph), the grain of the steel just below the hamon, and the burnished polish surrounding the fuller. Notice also the clean delineation where the blade tip, the “boshi,” begins. Very nice work.

Traditional Japanese society before the elimination of the caste system had 4 main divisions labeled  “Shi No Ko Sho,” meaning, in descending order, Warrior (samurai) Farmer, Craftsman, and Merchant at the bottom. The Emperor, Court Nobles, and Shoguns were above these strata, although only the Shogun possessed any actual power of the three. The man with the sword makes the rules, and those without weapons do what they are told or die. Such it has always been.

Blacksmiths and sword sharpeners were both in the craftsman caste, but the sword sharpener was above the swordsmith in rank. Depending on their support among the warrior caste, and with the generous application of yellow metallic lubricant, both swordsmiths and sword sharpeners occasionally obtained noble rank, an honor to which most other craftsmen, farmers, and merchants could not aspire My point is that sword sharpeners, while of low caste, often had a perceived rank higher than their craftsman position would suggest.

Why was the Japanese sword sharpener of higher rank than the swordsmith? I haven’t seen documentation from back in the day confirming it, but I suspect it is because the sharpener turns the swordsmith’s plain steel blade into a thing of jewel-like sculptural beauty that almost seems alive. One only has to see a sword blade fresh from the blacksmith’s shop and compare it with the same sword after the sword sharpener’s ministrations to understand.

The Nikko Sukezane sword, a designated National Treasure of Japan
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This sword is known as the “Nikko Sukezane,” Nikko for the temple commemorating the Shogun Tokugawa Ieyasu (徳川家康, January 31, 1543 – June 1, 1616) where it is stored, and Sukezane (助真 meaning “Aid the Truth) for the name of the smith who forged it for the Kamakura Shogunate (1185~1333). The blade’s shape and crystalline pattern above the hamon are characteristic of Sukezane’s work. This sword’s brother was in my care for about 2 years while it was being polished and appraised in Tokyo.
大般若長光-画像2
This sword is another of Japan’s National Treasures. It was forged by a swordsmith name Nagamitsu (長光)during the same time period as the Sukezane above. The tang (nakago) is corroded by exposure to bare hands over a period of around 700 years. Multiple holes were drilled in the tang to accomodate different kinds of hilts during its lifetime. I also had a sword by this same smith and of very similar appearance in my care for about one year, although it was not owned by Dr. Compton.
A different Nagamitsu sword, also listed as a National Treasure. An unusually healthy example.

I have even witnessed a skilled sword sharpener create a beautiful hamon (a pattern formed on the edge of a sword by the steel’s crystalline structure) on a sword forged by a famous smith that had lost the crystalline structure necessary to form an actual hamon. While a deception of sorts, the intention was not to deceive for profit (the sword was donated to a museum), but to return an unusual and historically important sword to its former beautify, a glory that would have been lost but for this sword polisher’s exceptional skills.

A dramatic chouji midare hamon in a modern sword. The pattern exists because of the changing crystaline structure of the blade that results from the differential heat treatment process performed by the blacksmith, but it is only visible and beautiful because of the sword sharpener’s stones and his skill with them. Is the blade sharp? Don’t judge a blade’s performance by its polish.

If we liken the swordsmith with his forge and hammer to the quarry worker cutting marble from the mountain, then the sword sharpener is Michelangelo cutting the Pietà with his chisels and files. Both craftsmen work on the marble and blade respectively, and both are essential. The sculptor uses steel to bring stone to life, while the sword sharpener uses stone to bring steel to life.

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Another dramatic hamon in a modern sword.

But despite these artistic abilities, modern “Sword Polishers” have no interest in and make no effort to actually make a sword blade cut well. Indeed, in some cases, they actually intentionally dull the blade so it can’t cut, thereby making it safer. This intentional vandalism is called “habiki.”

A different style of hamon pattern on a blade with a different grain pattern. Notice the different colors and lines inside the hamon. All these tiny details have names, are categorized and studied intensely by aficionados. All things equal, this sort of pattern and color is considered to be more elegant and desirable than the two more dramatic hamon pictured above. An extremely deep rabbit hole, I assure you.

Here is the key point I want you to understand: Despite the long years of apprenticeship, advanced skills learned, and gallons of blood unintentionally leaked by sword sharpeners, the frank sword sharpeners I have spoken with all admitted that, of all the craftsmen in Japan that used edged tools, woodworkers like carpenters, cabinetmakers, and joiners routinely create sharper blades despite those blades not appearing as sharp as swords. This is consistent with my direct experience of handling over 70 swords before and after being worked on by sword sharpeners.

While there is great pleasure to be found in polishing a plane or chisel or knife blade to levels of great beauty, do not make the mistake of equating appearance with performance.

Appearance aside, and looking strictly at cutting performance, will a chisel or plane or knife blade skillfully sharpened on a 15,000 grit stone cut better and longer than if sharpened on an 8,000 grit stone? In the case of woodworking blades and kitchen knives, no it won’t. In fact, due to higher levels of friction in the cut, it will certainly not cut wood as well. More on this subject later.

Hidarino Ichihiro Oiirenomi. The hazy silver of the hard steel hagane lamination and the cloudy grey of the softer iron jigane lamination, combined with the shape and upward curvature of the corners of the lamination are indicative of unexcelled craftsmanship by the blacksmith, superior skills of the sharpener, and excellent stones. Such details are considered sublimely beautiful to tool connoisseurs. But will the edge cut well? We can’t tell from this photo.

Keep in mind that the stones used to apply the beautiful polish and accentuate the hamon on Japanese swords are different from those used to sharpen woodworking tools. For instance, the uchigumori stones sword polishers use are small slices of very soft stone glued to paper using urushi lacquer, and are only 3,000~5,000 grit. These small slips of stone are rubbed on the sword blade using thumb and fingertips.

Here is a link to a blog showing Mr. Fujishiro, son of one of the sword sharpeners I employed back in the day, making and using these thin slices of stone.

Tools are designed to perform specific tasks. Although it could do the job, more or less, you wouldn’t use a crescent wrench to stir spaghetti sauce on the stovetop would you? A longish spoon just might work better. Does a sword’s edge need to be extremely sharp to cut the enemy effectively? No, it doesn’t because the sword’s speed, impact force, and swordman’s technique influence its cutting effectiveness much more than sharpness. So sword sharpeners have always been more focused on edge durability, resistance to chipping, and appearance than absolute sharpness. In modern times, when swords are almost never used to cut living flesh outside of Saudi Arabia, the blade’s appearance may be critical, but sharpness is not a practical concern.

Another example is food preparation knives. A chef’s knife looks terribly sharp, and as it slices tomatoes and fillets fish we can see that it cuts well. But how sharp is it really? In comparison with a joiner’s plane blade, not really that sharp. But both tools are exactly suited to the job assigned them.

柳刃包丁(刺身包丁)
The sashimi knife is made long to facilitate long draw-strokes that cut the fish cleanly. The chef applies little downward pressure which would rupture the cells ruining the flavor of the tuna sashimi. Yes, a properly sharpened knife and expert technique make a difference in flavor, just another reason why the Japanese are obsessed with sharp things.

The chef’s knife is most effectively used in slicing or drawing motions, much as expert swordsmen use their weapons against enemies. In this style of cut, a smooth and uniform cutting edge does not perform as well as a more ragged, serrated edge as seen at the microscopic level. Therefore, there is little if any practical benefit (assuming beauty is not practical) to be obtained by sharpening a kitchen knife beyond 1,000 or 2,000 grit. In fact, at least in Japan, these are the upper-limit of stones in daily use by professional chefs of all varieties. Yes, and that includes sushi chefs.

But don’t misunderstand my point: In the case of both swords and yanagiba hocho knives, the bevel angle must be correct for both the blade being used and the material being cut, and the microscopic edge must be a clean intersection of planes. If you get these two factors wrong, a crescent wrench might work just as well.

The other point I want to make is that, while I enjoy using high-level skills to create a very sharp blade with a beautiful appearance, such a blade will not perform better than an identical blade of equal sharpness but with a less polished appearance, and the extra time and money spent on improving outward appearance is wasted on bread and butter work. 

Since Hollywood celebrities have the answers to all the world’s problems (at the cost of other people’s money, labor and freedom, of course) perhaps our quest for the sharp edge can benefit from the wisdom of the famous Latin lover ‘Nando, Tinseltown’s most elegant star. ‘Nando once shared his father’s advice that it is “better to look good than to feel good.” Accordingly, perhaps we should all go crazy nuts and polish our blades like beautiful but dull museum swords and wear waistcoats and cravats as we cut sliding dovetails and plane door stiles. After all, one must be ready for every photo op. In this way, our woodworking blades may be worthy of ‘Nando’s highest praise: “You, dahling, you look mahvelous, absolutely mahvelous.”

Fernando Lamas in “The Merry Widow.” The crease in his pant leg could slice bacon.

No, on second thought, while there is much one can learn from Fernando’s elegant philosophy, his standards of beauty and suffering are too high for me. I would rather be a simple joiner or cabinetmaker in stained work clothes that has the ability to make a blade exceptionally beautiful but chooses not to expend the time and cost required to do so most of the time, rather than someone who doesn’t because they can’t.

Although Fernando has a pressing appointment for a tango lesson he must give (discretion prevents me from naming the young lady he is pressing) and won’t be providing further insight, our adventures in sharpening Japanese woodworking tools will continue in Part 5 of this series.

Let’s meet at Tsukiji for sushi afterwards.

YMHOS

© 2019 Stanley Covington All Rights Reserved

Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the question form located immediately below.

Sharpening Part 3 – Philosophy

A wild boar was sharpening his tusks upon the trunk of a tree in the forest when a fox came by and asked, Why are you doing that, pray? The huntsmen are not out today and there are no other dangers at hand that I can see. True, my friend, replied the Boar, but the instant my life is in danger, I shall need to use my tusks. There will be no time to sharpen them then.”

Aesop (621~565 BC)
Always ready for battle

It’s nice to have a philosophy on a subject because it helps one distill random thoughts down to the essentials.

Allow me to explain my philosophy about sharpening woodworking tools, not because it is charming and unique, and not because you should emulate it, but because it will provide insight into the things I have written and will write about sharpening on this blog and elsewhere. Use it to calibrate your BS meter. It is often neck-deep when people talk about sharpening stuff.

My philosophy regarding sharpening was shaped by my experience as a carpenter, contractor, commercial cabinetmaker, and joiner working under pressure, against a clock, sometimes with a boss watching with eagle eye, and often in front of customers, not as a hobbyist fiddling around in a garage workshop. Married young with a growing family to support, I quickly discovered that children eat constantly and in ever-increasing quantities, so efficiency was and is important to me. 

Efficiency was also important to the Clients who hired me. Sharpening and maintaining tools was indeed part of the job, but from the Client’s viewpoint, it was wasted time, so it was important to minimize time spent fiddling with tools during the work day. I followed the example of craftsmen I respected and started the day with sharp tools in good working order, and kept spare planes and chisels sharpened and ready to go as backup.

Self-employment hammered into me the monetary value of time. It also taught me quality sharpening stones and tools are expensive and wear out, and that to feed wife and babies every day I had to work efficiently to minimize time and money expended on maintaining tools, while maximizing the amount of work I accomplished between sharpening sessions. 

I developed a strong dislike, nay hatred, for blades that fail, dull quickly, or take too much time and effort to sharpen. I loathe them not just because they are irritating, but because they waste my time and money. Even considering the higher initial cash outlay, the cost-effectiveness of handmade, professional-grade tools in helping my mind and hands feed the family became as obvious as a road flare in a candlestand.

You, Gentle Reader, may not feel the time and financial pressures that professionals do, but learning how to sharpen your tools more efficiently will make woodworking less frustrating, more profitable, and more enjoyable.

What is your philosophy?

Sharpening a chisel at the jobsite, then back to work, jiggety-jog.

The journey will continue in Part 4 with wisdom from a celebrity and pictures of pretty swords.

YMHOS

© 2019 Stanley Covington All Rights Reserved

Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the question form located immediately below.

Sharpening Part 2 – The Journey

You don’t have a soul, Doctor. You are a soul. You have a body, temporarily.” 

Walter M. Miller Jr., A Canticle for Leibowitz
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Life is not a race. It’s a hard journey along many paths all leading to a single gateway.

What matters in this journey are the friends and family that travel with us, the kind deeds we do, the joy we share, the things we learn along the way, and the quality of our souls at the journey’s end. It’s no coincidence that these are all that will remain with us after we pass through the gateway.

Woodworking is both something we learn and a source of joy during this journey. For many it is a way to keep body and soul connected.

Travelers on the path to becoming excellent woodworkers learn early that dull tools will not and cannot make excellent wooden products regardless of the skill of the hand and eye that manipulates them.

Indeed, dull tools are not simply inefficient; I believe they are an impediment to good work because, being an extension of the user’s mind and hands, a dull tool will often darken the mind and leaden the hand of even an accomplished woodworker.

It is no coincidence that for millennia the first thing apprentices were taught once they were permitted to handle valuable tools was how to sharpen them properly. It has always been the first and most important woodworking skill.

Anyone who aspires to become an accomplished woodworker and more than an artisan or machinist must obtain minimal sharpening skills. All other woodworking accomplishments flow from this bedrock skill. This attitude has thousands of years of history behind it.

In our time the prevalence of machinery with built-in precision and blades driven by motors and sharpened by others has made it possible for those lacking even basic sharpening skills to represent themselves as craftsmen. Although they may be skilled artisans, I believe such individuals are less craftsmen and more machinery operators.

I believe, perhaps because the men I learned from and respected also believed, that free-hand sharpening is the way a skilled craftsman maintains his tools. My experience and observations over many years support the validity of this belief and the efficiency of the results. It is consistent with my work-driven philosophy about sharpening I will explain in more detail in the next post in this series.

Sharpening a blade free-hand is a zen-like activity. It requires observation. It requires muscle memory. It requires consistency. It requries composure. It requires meditative focus. And at the pinnacle, it requires one to feel with hands and hear with ears a place that cannot be seen, a place where destruction creates order. A place where nothing becomes something.

Some will disagree with my beliefs about free-hand sharpening, especially the machinist-types, those disinclined to remove their “training wheels,” the scribblers and gurus promising instant results in a few hours for the price of a book, DVD, or class, and the purveyors of sharpening jigs, of course. No mystery there.

When accomplished woodworkers gather in the presence of edged tools, they will always be curious about the quality of other men’s tools. In Japan, it is considered rude to pick up another man’s tools and examine the edges, or even to look at them too hard, but the desire is always there nonetheless because it is human nature to compare oneself to one’s peers. 

Indeed, much can be learned about a man’s quality standards and skill from his blades. Perhaps the condition of his tools can give a tiny glimpse into his character. Who can say?

What do your tools say about you? They are terrible gossips, you know. (ツ)

The journey will continue in Part 3 with wisdom from a celebrity and pictures of pretty swords.

Tianmen Gate, China. 999 steps in the stairway.

YMHOS

© 2019 Stanley Covington All Rights Reserved

Please share your insights and comments with everyone in the comments section below. If you have questions or would like to learn more about our tools, please use the questions form below.

Sharpening Japanese Woodworking Tools Part 1

It is well with me only when I have a chisel in my hand

Michelangelo 1475-1564
Hidari no Ichihiro Oiirenomi

This is the first in a series of posts that will describe the sharpening procedures I use and recommend for Japanese plane and chisel blades.  

This long series of posts is not comprehensive, but I hope it will at least remove some of the confusing fog that seems to swirl around the process of sharpening Japanese woodworking blades.

I didn’t learn the techniques outlined in this document from books, magazines, DVDs, tool retailers/importers/distributors, the internet, or even woodworking classes. They are the result of hard experience working with, and lessons learned from, professional craftsmen in Japan over a period of some 30 years, sometimes working as a professional woodworker, and other times working as an employee of two of Japan’s largest “super” general contractors.

This series of posts has 4 objectives: To save you (1) time, and (2) money, and to make your Japanese blades (3) sharper, and (4) cut longer. These benefits are worth obtaining if you are serious about woodworking, but the requisite attention to detail and manual skills may not come easy to some. 

Indeed, you may need to unlearn bad habits, and develop new habits, skills and muscle memory in order to achieve these objectives. This is not a 90 minute process but will take months, maybe years. It certainly took me years to unlearn my bad habits and develop the necessary skills. These tips should make the process more efficient for you.

Of course these are not the only viable solutions available. Many woodworkers are self-taught nowadays and learn how to sharpen from books, magazines, videos, and classes, and have developed methods that work well for them. I am not minimizing those successes, merely proposing methods to further advance their skills.

However, be aware that several of the techniques described herein may directly contradict methods taught by the gurus that make a living scribbling, making videos, and teaching classes about woodworking tools. These guys achieve popularity and financial success by helping amateurs get better results very quickly after reading only a few pages in their $29.99 book, or attending their 2-hour class. To maintain their popularity and income, the techniques some (but not all) of them promote must be dumb-as-dirt simple, and are often shortcuts and gimmicks yielding “instantaneous gratification,” without the need to actually develop real skills. 

Unlike amateurs satisfied with superficial results, professionals need real skills that yield consistent long-term results. 

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Don’t be shocked, but I am not offering 90 minute gratification in exchange for your money.  I have no “click goals, ” or “SEO strategy” to deploy; I don’t care if you “like” me, “subscribe” to my YouTube channel” (I don’t have one), or buy access to my online tutorials (don’t do those either). The advice I offer is free, but if you prefer gimmicks to skills, the techniques described here are not for you. 

Do I have a profit motive? Nope, this information is free. I am not a sneaky corporate shill trying to sell books, magazines, videos, advertising space, banners, sharpening stones, or heaven forfend, powertools with laser sights. I have never been lent or given a tool in exchange for a nice review, or been wined, dined, laid or paid to write good things about crappy tools. 

Over the years, my professional needs and curiosity have lead me to purchase literally hundreds of planes and chisels made by many blacksmiths and companies. The keyword here is purchase. With my own money. Not a single one was ever given or loaned to me. Some I later sold, the good ones I kept. The two points I want to make are that I put my money where my mouth is; and that I have no financial conflict of interest.

I have several motivations for writing and sharing this information. One is simple convenience. Over the years, people have asked me how to sharpen Japanese tools, and I have explained the process in letters, emails, and in person many times. This document is a collection of my scribblings on the subject over several decades, and is intended to make it easier to explain the process.

Another motivation is to ensure that the people who buy the small number of hand-forged tools I sell know how to properly sharpen them, so that those tools will provide them long, productive, high-performance service. Tools have feelings too.

But my primary motivation is to fulfill a promise I made to freely share the techniques I learned from the many carpenters, woodworkers, blacksmiths, tool makers and professional sharpeners in Japan who taught me. In exchange for this free advice all I ask of you, Gentle Reader, is an open mind, and eager hands. Please, don’t cut either of them.

This adventure will continue in Part 2. But be forewarned, the price of admission may double.

YMHOS

© 2019 Stanley Covington All Rights Reserved

Please share your insight, questions or comments in the comments section below. If you would like to learn more about our tools, please use the contact form located immediately below.


Seismic Damping

The more one gardens, the more one learns; And the more one learns, the more one realizes how little one knows.

Vita Sackville-West

This post is definitely different from my previous ones. It will deal with buildings and earthquakes. It has nothing to do with wood or woodworking tools.

Image result for toranomon hills business tower
Toranomon Hills Business Tower (foreground)

In my day job I am an executive with a large international Real Estate and Construction Project Management company in Tokyo, Japan. Without going into details that might violate non-disclosure agreements, my job involves managing all aspects of real estate acquisition and leasing, as well as the design, procurement, and construction of commercial and industrial projects. Mostly for non-Japanese Clients.

The photo above is one project I am involved in on behalf of a Client.

Tokyo is an expensive place to set up operations, and the real estate and construction processes are especially confusing for foreign companies. Ergo, the need for me and my teams.

My educational background is structural engineering, focused on seismic-resistant design. All of my Clients are very concerned about the earthquakes Tokyo experiences almost daily. There will be several magnitude 4~5 quakes here each year. This tends to keep people focused.

My point is that earthquakes are a constant threat taken seriously and for good reason. Accordingly, to one degree or another as building codes and Owners require, all buildings incorporate aseismic design features.

I have worked on buildings with expensive full-blown base isolation using rubber bridge bearings and hydraulic dampers similar to giant automotive shock absorbers, and other systems designed to dissipate damaging earthquake forces, but what I would like to show you today is a “slip-joint brace damper” just installed at a building near my office located in Marunouchi near the Imperial Palace (not the building in the perspective rendering above).

Notice how deep the beams are, and how thick the steel is. Although they don’t show up well in the photo, the columns too are massive. Much heavier than is typical in Western structures. I love Japanese structural steel!

Slip-joint Brace Dampers (white), Tokyo

I am not involved in this high-rise building, but a contractor I have used in the past named Obayashi Corporation 大林組 is the General Contractor. I was able to snap this picture of Obayashi’s jobsite while walking to my office from the subway station last week during a rare moment when the front gate was open and nothing was in the way.

The white columns and diagonal braces are the key to this seismic damping system.

The white paint is a fire-resistant intumescent coating designed to protect the steel from heat during a fire. Structural steel is very weak when exposed to fire, much more so than wood or concrete, so this sort of protection, while expensive, is necessary. The rest of the structural steel will be sprayed with a thicker, less-expensive and less-durable fire-resistant coating of one variety or another.

The diagonal braces in the photo are basically two steel plates bolted together face to face. The bolt holes are slotted to allow the bolts and plates to slip past each other when subjected to a certain amount of force.

The plates and bolts are contained in a steel pipe filled with high-friction oil to prevent the brace from buckling, prevent corrosion, and ensure the coefficient of friction between the plates/bolts remains constant for many decades in the future.

As the ground moves during an earthquake, the building moves with it, and the structural steel sways. The rectangular opening framed by connected beams and columns changes shape, becoming longer or shorter in the diagonal directions. Braces resist this “racking” movement.

As the plates and bolts in these dampers slip past each other, a great deal of friction is created converting the earthquake’s energy to heat, slowing down the racking motion, and controlling the harmonic vibration of the entire building.

Image result for racking forces

Although fixed-length braces are common in lighter, shorter structural frames, they are not usually a good thing in large structural steel frames because they tend to behave erratically and fail suddenly. This can be inconvenient.

The steel frame must be made strong enough without fixed-length bracing to absorb these forces without failing anyway to make a reliable structure. But if the frequency of the building’s movement back and forth and side to side begins to match that of the ground, then something called “resonance” can occur potentially doubling the forces acting on the building, forces powerful enough to suddenly and violently bend, break and topple the building. This can be inconvenient.

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The center image employs the damping braces as in the 2nd photo above.

An alternative to this sort of damping brace system is the more expensive “Base Isolation System”

So why would anyone use an expensive system like base isolation?

Base isolation allows the entire building, from its base up, to move opposite the ground motion in the horizontal direction, reducing the induced sway, racking, and damage to its interior and systems and equipment stored inside. This level of protection is necessary if the building must continue to function uninterrupted immediately after a large earthquake. Hospitals, R&D centers, Data Centers and other sensitive buildings with lots of expensive equipment that must be kept running no matter what are often worth the cost of base isolation systems.

But in the case of an office building like the one in the photo, the owner decided some interior damage, and the business interruption repairs would entail after the earthquake, would be acceptable.

The photos below show two components of the typical base-isolation system.

Base isolation bearings being tested. Very stiff in the vertical direction, but flexible in the horizontal direction. Two bearings are being tested in this photo, but they are never stacked like this in actual installations
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Hydraulic damper combined with base isolation bearings in the background to form a base-isolation system. The building’s entire weight is supported on these bearings. The dampers keep the building’s movement from getting out-of-hand, like shock absorbers on an automobile.

I hope you found this post interesting. Let me know if you want to see more stuff like this.

YMHOS

© 2019 Stanley Covington All Rights Reserved

Please share your insight, questions or comments in the comments section below. If you would like to learn more about our tools, please use the contact form located immediately below.