Fire-resistant Steel Research Articles

Experimental Study on Fire Resistance of Fire-Resistant Steel Beams.

This paper is to verify the fire resistance of beams made from fire-resistant(FR) structural steel by means of a full-scale loaded heat test. Because of the elements contained, FR Steel has higher strength than conventional structural steel at elevated temperatures. Its 0.2% proof stress at 600°C is equal to or greater than two-thirds the value specified at room temperature. Rockwool, ceramic fire protection, and foaming-type intumescent coating were used as fire-protection materials. The results showed that the fire-protection thickness can be reduced below what is required for conventional steel beams and that 1-h fire resistance can be obtained by intumescent coating with a lower insulation property.

Mechanical Properties of Weld Metal for Fire-Resistant Steel with Large Heat Input Submerged Arc Welding.

Large heat-input welding is increasingly employed because of its high productivity. For this welding, titanium and boron (Ti-B) bearing welding materials are suitable in acquiring high toughness at low temperatures. However, their properties at high temperatures have not been known. Preferable ductility at high temperatures is required when they are applied to the welding of fire-resistant steels. The present study examines the mechanical properties of Ti-B bearing welding materials for fire-resistant steels in large heat-input welding.Submerged arc welding with two electrodes in tandem was conducted with the heat-input of 13 kJ/mm. The mechanical and metallurgical investigation were v-notch Charpy tests, weld metal tensile tests, chemical analyses, and metallographic observation on ruptured surfaces.It was found that the addition of titanium and/or boron lowers the high temperature elongation. This reduction was caused by grain boundary fracture at the prior-austenite grain boundaries of the weld metal with titanium and boron. However, the high temperature properties were recovered in the weld metal with titanium as low as 30 ppm and nil boron, and this weld metal fractured in an intragranular mode with enough toughness.

Fire-safe design of modern steel buildings in Japan

This paper presents fire-safe design of buildings using fire-resistant (FR) steel. Because of the elements contained, FR steel retains strength at high temperatures compared with conventional structural steels for buildings. Through the use of FR steel and fire-safe design calculating fire intensity, steel temperature and deformation of a frame at high temperature, FR steel can reduce thickness of fire protection materials compared with conventional structural steels and also can be used in steel buildings without any protection in cases where the steel temperature would not exceed 600°C. In this paper, the fire-safe design of Yokohama Sogo warehouse and Tobihata Building are presented together with the mechanical properties of FR steel and the design method of buildings using FR steel. Yokohama Sogo warehouse employs FR steel for its interior columns and beams by reducing the thickness of sprayed ceramic-cement protection according to required fire resistance in hours. In the Tobihata building, unprotected FR steel was used for its external frames since it was confirmed that the temperature of the frame heated by projecting flame would not exceed 600°C.

AP-FIM study on the effect of Mo addition on microstructure in Ti-Nb steel

AP-FIM technique was applied successfully to analyze the strengthening mechanism of a newly developed Ti-Nb-Mo-bearing fire-resistant steel, which maintained high yield strength at elevated temperatures. FIM observations of Ti-Nb-Mo and Ti-Nb steels before and after aging at 873 K for 0.9 ks made it clear that Nb(C, N) precipitated in ferrite matrix of Ti-Nb-Mo steel during aging was finer in size (2.3 nm) and greater in number than that of Ti-Nb steel. In the as-hot-rolled condition, corresponding to the situation before aging of those steels, a similar tendency was recognized with Nb(C, N), being coarse in size and small in number. These facts suggest that precipitation hardening of Nb(C, N) at 873 K and room temperature in Ti-Nb-Mo steel is higher than that in Ti-Nb steel. AP analyses of Mo-bearing steels, Ti-Mo steel and Ti-Nb-Mo steel, before and after aging, clearly yielded us two important facts. One was that almost all Mo atoms were in solution in ferrite matrix of both of the Mo-bearing steels, which suggested Mo solid-solution hardening was equal for both of the Mo-bearing steels. The other was that Mo atoms strongly segregated at the Nb(C, N)/ferrite matrix interface in Ti-Nb-Mo steel, which probably suppressed the diffusion of Nb atoms into Nb(C, N) from ferrite matrix. This directly results in fine precipitates in Ti-Nb-Mo steel.

Tests of Fire‐Resistant Bolts and Joints

This paper reports on the results of experimental studies on the high‐temperature mechanical properties of high‐strength fire‐resistant (FR) bolts for fire‐resistant steel (FR steel), and the shear strength of the friction joints using FR bolts at high temperatures. Since the FR bolts have been adopted for joints made of FR steels to be used at temperatures as high as 600°C, this study placed emphasis on the shear strength after slip occurs in addition to the conventional slip load. The results led to the following conclusions. The tensile strength of FR bolts at high temperatures is superior to that of conventional high‐strength bolts. The slip load of the joints can be roughly estimated on the basis of the results of relaxation tests for bolt materials. The slip load of the joints using FR bolts decreases rapidly in temperatures over 400°C, and the shear strength is still greater than allowable shear force at temperatures up to 650°C.

建築構造用耐火鋼材の開発

建築構造用耐火鋼材の開発

High‐Temperature Properties of Fire‐Resistant Steel for Buildings

This paper presents properties of fire‐resistant (FR) steel for structural use. Because of the elements contained and its rolling process, FR steel retains strength at high temperatures compared with conventional structural steels for buildings. Through mechanical‐properties tests at high temperatures and full‐scale fire tests of load‐bearing members, it is confirmed that FR steel can bear a load corresponding to the allowable stress for structural steel under permanent loading (which is two‐thirds of the room temperature yield point) at 600° C. Also, applications of FR steel to buildings are presented. Through these tests and applications, it is confirmed that FR steel can reduce fire protection compared with conventional structural steels and can also be used in steel buildings without any protection in cases where the steel temperature would not exceed 600° C.

建築構造用耐火鋼柱の耐火性能に関する実験的研究

This paper presents experimental results of a full-scale fire test with loading by Fire Resistant steel (FR steel) columns and their numerical analysis. Because of the elements it contains, FR steel excels, compared to conventional structural steels, in strength at elevated temperatures. Sprayed rockwool and an intumescent coating are used in providing FR steel's fire protection. Experimental results show that FR steel columns can bear a load corresponding to two-thirds of their room temperature yield point at 600℃, reduce the thickness of rockwool compared to conventional steel columns, and provide one hour of fire resistance with an intumescent coating. Also, a numerical analysis shows that it is possible to simulate fire, resistance time and deformation behavior by the numerical properties of FR steel and an elasto-plastic creep thermal deformation analysis.

耐火鋼用高力ボルトの高温強度特性に関する実験的研究

This paper reports on the results of experimental studies of the high temperature properties of the high strength FR bolts for fire resistant steel, and the strength of the friction joints using the FR bolts at high temperatures. The results have shown that the tensile strength of the FR bolts at high temperatures is superior to that of the conventional high strength bolts and that the friction joints using FR bolts have a high maximum strength, although they produce some slipping at high temperatures.

建築構造用耐火鋼材の高温強度特性

This paper presents properties of newly developed fire resistant steel (FR steel) for building structural use. Because of the elements contained, FR steel excels, compared to conventional structural steels, in strength at elevated temperatures. Elevated temperature tensile tests were carried out and their results were expressed in numerical values. Full scale column fire tests with loading were also carried out and it was confirmed that FR steel loadbearing members can display the elevated temperature characteristics of FR steel itself. Also actual examples of building using FR steel, where a reduction and elimination of fire protection materials, were presented.

Load capacity and deflection of fire-resistant steel beams

The methodology of defining safety of constructions in fire has not yet been sufficiently verified and agreed upon. This paper includes calculation results for steel beams, which prove that the ultimate load-bearing capacity predicted by plastic design theory, which is valid in engineering calculations, is not sufficient for determining the critical temperature. The reason is that this temperature tends to be limited in some cases by large deflections of beams in fire.