钢筋混凝土柱的抗火性能

FIRE RESISTANCE OF REINFORCED CONCRETE COLUMNS

本文提供31根轴心荷载与6根偏心荷载钢筋混凝土柱抗火测试结果及分析资料。轴心荷载试件为长3.8m、截面边长或直径从203至914mm的方形、矩形与圆形柱。偏心荷载试件系3.8m长,截面边长305mm的方形柱,其中4根带牛腿。使用硅质、碳酸岩与轻质骨料浇注而成,保护层厚度为38mm,经适当养护后,柱件暴露在ASTME119标准火焰中,在轴心荷载或偏心荷载下进行抗火测试。试验结果证实按ACI318规范设计的混凝土柱,在最大容许轴向荷载下的抗火时数超过美国统一建筑规范(Uniform BuildingCodes)所要求的3小时下限。分析结果表明(1)荷载、骨料种类、截面尺寸是影响轴心荷载柱抗火性能的主要因素;(2)荷载、端点约束与骨料种类是影响偏心荷载柱抗火性能的主要因素;(3)在全使用荷载与柱件最大容许轴向荷载比值相同的条件下,偏心荷载混凝土柱的抗火性能比轴心荷载混凝土柱的抗火性能弱10～58％。

This paper presents test results including data analyses of 31 concentrically loaded columns and 6 eccentrically loaded ones subjected to the stantard ASTME-119 fire. The concentrically loaded columns measured 3.8m long, and hadsquare/rectangular/ circular cross section with their sides or diameters variedfrom 203 to 914 mm.The eccentrically loaded columns also measured 3.8m long,and had square cross sections of 305× 305 mm.Most columns had a concrete coverof 38 mm.Among the six eccentrically loaded columns, four were made withbrackets at both ends of the column. Concrete for casting specimens were madewith either siliceous, or carbonate, or lightweight aggregate.After a propercuring, each column specimen was subjected to a concentric load or eccentricload during the standard ASTM E-119 fire test.The test results showed thatcolumns designed in accordance with ACI 318 code requirements and subjectedto the maximum allowable load meets the minimum 3 hour fire resistance re-quired by the Uniform Buildi Codes.The data analyses revealed that(1 )load,aggregate type, and cross sectional geometry are the maior factors influencingthe fire resistance of the concentrically loaded coiumns; (2 ) load, end restra-int and aggregate type are the major factors affecting the performance ofeccentrically loaded columns exposed to fires; (3 )under the same full serviceload/the maximum allowable load ratios, the reduction of fire resistance ofeccentrically loaded columns range from 10 to 58% in comparision with thoseof concentrically loaded columns