|By: Richard Mowat||POSTED: 10/13/11 8:33 PM
FILED AS: Articles, Demand, Steel
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Standardized seismic design standards were first implemented in China in the 1920s after major earthquakes in NanAo and Haiyuan. Seismic engineering increased markedly in the mid 1950s, when experts from the former Soviet Union helped Chinese scientists prepare “An Illustration of Seismicity of China,” which combined information from 15,000 seismic events over a 3,000 year period. The text presented seismic maps that allowed engineers and architects to assess earthquake risks, and in 1956 the Soviet Seismic Zone Construction Regulation was translated into Chinese.
Two years later, the country began using dynamic response theory to improve structural seismic resistance. New design standard building codes included criteria for buildings, roads, and utility infrastructure. They presented construction requirements for buildings based on four different classes of foundations and used four different dynamic response ideas. Additional requirements for retrofitting pre-existing structures were put into place after the Heibei -Tangshan Earthquake in 1976 that killed 240,000 people.
In 1989, the “Design Code for the Seismic Construction GBJ11-89” was published. New construction methods were created, new materials were developed, and new civil engineering standards were put into place. Another series of devastating earthquakes struck the region in the 1990s. The Japanese Kobe Earthquake in 1995, the Yunnan-Leejiang Earthquake in 1996, and the Taiwan Juju and Turkey Izmit Earthquakes in 1999 led to the development of GB50011-2001, which was an update of the previous GBJ11-89 document.
In May of 2008, the Wenchuan Earthquake struck in eastern Sichuan province and resulted in more than 12,000 deaths. Eight schools were destroyed, and hundreds of students were buried at the Juyuan Middle School in Dujiangyan. After this event, a re-examination of seismic building codes revealed that the codes were appropriate, but that code enforcement was lacking in rural areas. Since that tragic event, construction code enforcement has been pursued more rigorously.
Chinese construction currently accounts for about 45 percent of all global steel demand, but the country has historically used low percentages of vanadium when compared to other steel-producing nations. With a renewed focus on seismic building code, vanadium steel demand has increased markedly. Japan has always been a consumer of vanadium steel, but massive reconstruction efforts following the March 2011 earthquake and tsunami have dramatically increased demand in that country also.
Both countries have building codes that require the use of high-strength rebar in construction projects. It is typically formed through a process known as Quench and Self Temper, or QST. In QST, low carbon-manganese steel alloys are rapidly quenched as the material leaves the rolling mill. The process produces a very hard martensitic crystalline outer layer in the rods, but the interior core is unchanged and retains austenite crystalline properties. The manganese does make it harder than ordinary low carbon reinforcing bars. The resulting rods exhibit a low tensile strength to yield strength ratio.
Microalloy rebars have a uniform cross section. Vanadium steel is tremendously strong because stable vanadium-carbides and vanadium-nitrides are formed uniformly throughout the material. This creates vanadium rebar that is more suited to the stresses encountered during an earthquake event. Seismic grade steel is strong but not brittle. It is designed to deform under stress without completely failing. Ordinary rebar strengthens and stabilizes reinforced concrete structures effectively, but the benefit is lost if the rebar fails under seismic vibrations. Vanadium microalloy high strength seismic grade reinforcement bars absorb seismic energy without breaking, and the strengthening and stabilization effects in the reinforced concrete are maintained.
China’s demand for vanadium rebar is expected to remain strong for at least the next 10 years. It is estimated that the demand for the alloy in seismic reinforcing will soon approach 30 percent of the current worldwide vanadium supply. That supply is already being taxed by the growing demand for vanadium-lithium batteries.
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