Experimental Research On The Fire Resistance Behavior Of Unequal Limbs L-special-shaped Steel Reinforced Concrete Columns

Steel reinforced concrete special-shaped columns can play the advantages ofsteel and concrete respectively, section of high bearing capacity, good seismicperformance, to overcome the existing problems in use of the common reinforcedconcrete special-shaped columns, and has broad application prospects. At present,some research of the mechanical properties on steel reinforced concretespecial-shaped columns at ordinary temperature has been launched by someuniversities and research institutions, and studies on its fire resistance is lessinvolved.Steel reinforced concrete special-shaped columns has a larger surface areaaffected by fire, column limbs thin and the thickness of concrete cover minor, oncedestroyed in the fire, will result in partial or total collapse of the structure, causinghuge amounts of damage. Therefore, it has an important realistic meaning to researchthe fire resistance of steel reinforced concrete special-shaped columns.This paper mainly studied on the fire resistance performance of the unequallimbs L-special-shaped steel reinforced concrete column, which is very complicatedin a category of special shaped. Designing a total of10unequal limbsL-special-shaped steel reinforced concrete column specimens, conducted apreliminary analysis on the fire resistance performance of this type of crosssection of steel reinforced concrete special-shaped columns by experimental and finiteelement analysis methods. The major work and conclusions in this paper are asfollows:1, Carried out the fire experiment of9unequal limbs L-special-shaped steelreinforced concrete columns under standard heating process, got section temperaturefield, analyzed the influence of diverse eccentricity, load magnitude on the axial andlateral displacement of the special-shaped columns. The test results show that:(1) Measuring points temperature is inversely proportional to the distance from thefire, the closer, the higher the temperature, the greater temperature ranged.Conversely, the lower the temperature, more moderate temperature rises.(2) Due tothe presence of concrete cover, internal steel heats up smaller, the highesttemperature at about350℃. Visible, valid for internal steel framed, concrete played aresistance to fire, heat insulation effect.(3) Most of the measuring points having along or short platform in the vicinity of150℃，measuring points heat up slowly in this platform，when over this platform temperature rises faster.2, For1at room temperature and9after1hour by fire static load test ofspecial-shaped columns,analysed the law of the bearing capacity, deformation, strainand the change of bond slip etc. The study found:(1) After fire special-shapedcolumn’s injury is not serious, steel and concrete inner core less affected. Componentafter fire capacity about5.1%lower than that of component unaffect by fire, so itstill has a high bearing capacity.(2) Loading position and loading angle has animportant impact on the stress performance of the special-shaped columns. Comparedcolumn2with column5under0°loaded angel, when eccentricity increased200mmthe bearing capacity reduced59.1%; compared column9with column6under45°loaded angel, when eccentricity increased200mm the bearing capacity reduced70%.Compared45°loaded angel0°loaded angel，eccentricity of100,160,240, and300mm，the bearing capacity decreased by40.1%,55.3%,54.2%and56.1%.(3) Theplane section assumption is also suitable for the truss type unequal limbs L-special-shaped steel reinforced concrete columns.3, Using ABAQUS analysed the temperature field of unequal limbsL-special-shaped steel reinforced concrete columns under fire and assessed sectiondamage of special-shaped columns at different times by the fire. Analysis shows that:(1) The calculated results of temperature field are in accord with the experimentalresults overall.(2) On both sides exposed to fire conditions, temperature transferredfrom the fire surface to the internal of special-shaped columns, the temperature curveand special-shaped column shape similarity, each curve layered distribution, thedistribution graphics of the two limbs are basically the same.4, Using ABAQUS created the mechanical model for special-shaped columns,and considered the fire damage to calculate and analyze the mechanical propertiesof special-shaped columns after fire.The results show that:(1) Different loading anglehas a great impact on lateral displacements. Loading angle of0°, the maximumdisplacement of X direction is8.9mm and the maximum displacement of Y directionis9.1mm; loading angle of45°, the maximum displacement of X direction is7.8mmand the maximum displacement of Y direction is16.8mm.(2) According to the N-Mcurve movement can be judged big and small compression failure limit point,0°loaded angle limit of the eccentricity at about240mm,45°loaded angle limit near theeccentricity of100mm, which coincide with the test concludes.(3) The position of the neutral axis is closely related with the loading position, the loading position fartherfrom the section centre, position of neutral axis closer to the inner side section.