Carbon rods are the next thing in strengthening buildings
Carbon rods: the next thing in strengthening buildings?
Interview with Eng Avi Cohen
The main headline in the "Davar Hayom" newspaper on July 11, 1927 was dramatic: "Yesterday at exactly three past seven, the complacent residents of Jerusalem were surprised by a terrible earthquake, the likes of which had not been felt in Jerusalem for many years." This earthquake, the last devastating tremor felt in Israel, claimed the lives of 285 people and injured nearly 1,000.
Considering that the average frequency of earthquakes of this magnitude in the Land of Israel is once every 80 years, the next earthquake is only a matter of time, and not even a long time. Are we, like the residents of Israel in 1927, "complacent"?
We talked about earthquakes, building reinforcements and the ability of sheets and carbon rods to help, with Eng. Avi Cohen from the firm of Yaron Ofir Engineers, and we received direct answers, a little disturbing, but also with an optimistic outlook.
Eng. Avi Cohen: "We are called the 'Doctor House' of building upgrades"
Avi Cohen knew he wanted to be an engineer already when he was a child in Mexico. While other children toyed with dreams of being police officers or firefighters "when they grow up", my father was interested in buildings and how they were designed. He completed his engineering studies in Mexico, and immigrated to Israel about ten years ago. After a short military service, he joined the engineering office of Yaron Ophir and became one of the experts in seismic strengthening of buildings.
Avi, why did you choose to focus specifically on the field of strengthening existing buildings?
Because building reinforcement is a more challenging field than building design. Our office is called the "Doctor House" of building upgrades, because in every project one must diagnose in depth, investigate, dig into studies, think creatively. In this field there is no template planning that repeats itself, but a continuous cracking of challenges and constant innovation.
Constant innovation? Engineers are considered conservative, aren't they?
Engineers are indeed conservative. The office where I chose to work sees it differently. We don't do what everyone else does, and are always looking for innovative solutions. Of course, we back them up with complementary local and international standards, conduct experiments when necessary, but are not afraid of innovation. By the way, this is the trend today in the largest offices in the world.
How indifferent is the Israeli economy to strengthening against earthquakes?
In the public sector there is awareness, and we strengthen public buildings such as hospitals and schools. In the private sector it is a different story. There are more and more businesses that understand the need to strengthen their structure in preparation for earthquakes, and especially the business-economic aspect of such strengthening, but many small businesses - still not.
What is meant by the "business-economic aspect" of strengthening against earthquakes?
The damage of an earthquake is not limited to whether the structure has collapsed or not. The damage is peripheral: what did the earthquake do to the equipment in the office or factory, how long will the work stop due to the need to repair damages, etc. This is why we talk about "functional design" - a planning and strengthening method that we invented that deals with the question of how to ensure the building's continued functionality after an earthquake, and how to strengthen the building so that we can control plastic sections and focus on energy waste that will cause minimal damage to the ongoing activity, while ensuring accurate strengthening in the right places.
And Israeli businesses, of which the "it will be fine" method characterizes some of them, dedicate a budget to this?
There are more and more of them, yes. The business perspective on restoring a business in the event of a disaster permeates quite a few businesses in Israel, and don't forget that international companies with international standards also operate in Israel. On top of that, some of the reinforcements for earthquakes are sometimes the result of building zoning changes that businesses want to make, and the work is absorbed there.
"The Israelis of this generation have not experienced a significant earthquake, hence the indifference"
After all, what score would you give Israel in preparing for earthquakes?
Awareness is rising, but the situation in Israel is not good. It starts with the fact that Israelis in this generation have not experienced first hand what a significant earthquake feels like. As a child in Mexico, earthquakes were a part of our lives, as they were felt at least once a year. In Mexico, they learn to design engineering for earthquakes before planning in concrete. That's how it is, there are countries that learn to live in the shadow of earthquakes, and there are countries that learn to live in the shadow of missiles.
Is it just a matter of public awareness or is there a regulatory matter here?
There is also a regulatory issue. Standards in Israel, for example, are not sufficiently developed. We do not have a functional standard. More than once we use advanced international standards, and sometimes we have to carry out experiments ourselves in order to meet the Israeli standards. Seismic engineering is a field that has a lot of innovation, and regulation is having trouble keeping up.
If we are talking about smart solutions, how do the carbon sheets fit into the seismic reinforcement?
Working with composite materials such as carbon sheets and carbon rods has become an integral part of seismic strengthening. This technology allows us to strengthen existing concrete components and increase ductility, increase their ability to waste energy, and thus reach an optimal solution in planning and execution. There are places where you have to use the conventional methods of strengthening with the help of iron and concrete additions, and there are places where the desired solution is carbon sheets or carbon rods and in many cases the customer is the one who requests the use of sheets to reduce costs and shorten work times.
In which cases is the required use of carbon sheets?
Carbon sheets have special properties compared to steel and concrete. They provide strength on the one hand, similar to iron and concrete, but also traction on the other. The combination of carbon fiber with epoxy creates a strong and rigid matrix and its use in concrete elements allows to prevent unwanted failures to maximize the performance of that element. In addition, there are elements that, due to their shape, such as columns or beams for reinforcement, can be strengthened with carbon sheets since they can be wrapped around the column or beam without harming the aesthetics.
In the past, the solution of carbon sheets was considered an exception, to what extent is it in the design standard today?
We are currently in a situation where almost everyone who plans to strengthen a structure will want to know what the cost of conventional strengthening will be compared to the cost of using carbon sheets. A business perspective requires this: using carbon sheets is not only more aesthetic, it also saves the volume of iron and concrete use and its application is also faster and cleaner - and all of these have economic and business consequences. In many cases, the solution of carbon sheets looks expensive on paper, but from a broad business perspective, it is actually the cheapest and profitable, and even shortens execution times.
Carbon rods: the new kid in the composite materials neighborhood
As Avi pointed out, the field of strengthening buildings against earthquakes is a rapidly developing field. Alongside the use of carbon fiber sheets, which has already become a desirable off-the-shelf solution, new technologies are coming into use. One of these technologies is carbon rods.
Avi, you are currently the only one in Israel who plans reinforcement work with carbon rods. what is it Anyway?
The material is the same material, a composite material, which is based on carbon fiber and an epoxy material. The difference from carbon sheets is that the rods come as a rigid rod from the factory. The application is different than with carbon sheets: instead of wrapping the concrete, the concrete is cut and the rod is threaded inside. The rod comes to replace the ferrule inside the component that is being strengthened.
So what are the benefits of using it compared to using iron?
Conventional steel rods cannot be threaded using the method of carbon rods. The interface between the carbon and the epoxy is stronger than that of the steel and the concrete, which allows the installation of the rods in a minimal groove at the limit of the thickness of the cover, without damaging the existing zion. Using iron requires deep exposure of the concrete and damage to the existing grout. On top of that, CFRP material does not rust so there is no need for standard cover thicknesses. In the application of carbon rods, compared to steel rods, it is a minimal groove of half an inch, and a rod diameter of only a quarter to half an inch.
And what are the advantages of carbon rods versus using carbon sheets?
The application of carbon sheets requires some preliminary work. The concrete surface should be well sanded, dust cleaned, prepared for gluing, applied precisely. A carbon rod that is anchored in a slot requires less work that we call "wet", therefore it is also faster and involves fewer processes.
So in which cases do you recommend strengthening with carbon rods and in which cases with carbon sheets?
Usually it is a combination. There are places, such as strengthening beams and columns, where the carbon sheets are the required solution, since
The interview ends with a mixed feeling. On the one hand, the situation in Israel is far from good. On the other hand, awareness is rising and the solutions for strengthening seismic buildings are becoming more innovative. Let's all hope that the earthquake will not catch us "complacent" like in 1927.
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