EXPERIMENTAL STUDY ON SHEAR PERFORMANCE OF STEEL-CONCRETE COMPOSITE BEAMS AFTER EXPERIENCING HIGH TEMPERATURES
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摘要: 为研究钢-混组合梁经历高温后的抗剪性能,以受热温度和冷却方式为试验参数,分别开展了普通混凝土、钢材高温后材料性能试验和钢-混组合梁高温后静力试验。对高温冷却后混凝土和钢材的基本力学性能进行了试验研究,并采用扫描电镜观察了高温后混凝土的微观结构;按“强弯弱剪”设计了7片钢-混组合梁,测定了升降温过程中截面温度场分布,开展了常温和经历高温冷却后组合梁加载破坏试验,对组合梁常温和高温后的极限承载力、跨中挠度和应变变化进行对比分析,研究了受热温度和冷却方式对组合梁受力性能的影响,并探讨了高温后组合梁极限抗剪承载力计算方法。结果表明:高温后混凝土内部水泥复合物疏松和水泥与骨料包裹界面出现裂纹是混凝土宏观力学性能劣化的主要原因;常温和高温冷却后钢-混组合梁的破坏形态均为混凝土板出现贯穿的斜裂缝;随着温度的升高,组合梁的承载力、刚度和延性均降低;低于400℃时冷却方式对承载力影响较小,600℃时喷水冷却后组合梁承载力大于自然冷却;与自然冷却试件相比,喷水冷却下试件的刚度较大,极限挠度较小;基于试验数据和回归分析建立了混凝土抗压强度、钢材屈服强度与受热温度之间的计算公式;修正后的AS/NZS 2327规范公式计算值与试验值吻合良好。Abstract: To study the shear behaviors of steel-concrete composite beams after experiencing high temperatures, Material performance tests on normal concrete and steel after high temperature and static load tests on steel-concrete composite beams after high temperatures were carried out involving experimental parameters of heating temperature and cooling regime. The mechanical properties of concrete and steel after high temperatures and two cooling regimes were studied, and the microstructure of concrete after high temperatures was observed by using the scanning electron microscope. Then, seven steel-concrete composite beams were designed according to 'strong bending and weak shear'. The distribution of the section temperature field during temperature rise and fall was measured. Loading failure tests on composite beams at room temperature and after experiencing high temperatures were carried out. The ultimate bearing capacity, mid-span deflection and strain of composite beams at room temperature and after high temperatures were compared and analyzed. Furthermore, the effects of heating temperature and cooling regime on mechanical performance of composite beams were analyzed, and the calculation method for ultimate shear capacity of composite beams after high temperatures was discussed. The results show that the loose cement compound in concrete and the crack at the wrapping interface between cement and aggregate are the main factors causing the deterioration of macro mechanical properties of concrete after experiencing high temperatures. The failure modes of steel-concrete composite beams at room temperature and after high temperatures are penetrating oblique cracks in concrete slab. The bearing capacity, stiffness and ductility of composite beams decrease with the increasing heating temperature. When the temperature is lower than 400 ℃, the cooling regime has little effect on the bearing capacity. When the temperature is 600 ℃, the bearing capacity of composite beams after water spray cooling is greater than that of natural cooling. Compared with the natural cooling specimens, the stiffness of the specimens after water spray cooling is large and the ultimate deflection is small. Based on the experimental data and regression analysis, the calculation formulas between concrete compressive strength, steel yield strength and heating temperature are established. The calculated values of the revised AS/NZS 2327 specification formula are in good agreement with the test values.
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表 1 混凝土力学性能
Table 1. Mechanical properties of concrete
温度/(℃) 抗压强度/MPa 抗折强度/MPa 自然冷却 喷水冷却 自然冷却 喷水冷却 20 61.72 61.72 4.51 4.51 200 55.14 54.52 3.88 4.43 400 56.78 49.06 2.95 1.44 600 41.35 36.41 1.68 0.89 表 2 Q345钢材力学性能
Table 2. Mechanical properties of Q345 steel
温度/(℃) 屈服强度/MPa 抗拉强度/MPa 弹性模量/GPa 伸长率/(%) 自然
冷却喷水
冷却自然
冷却喷水
冷却自然
冷却喷水
冷却自然
冷却喷水
冷却20 346.3 346.3 557 557 210.4 210.4 26.8 26.8 200 350.3 354.0 550 552 208.0 212.5 25.3 25.7 400 366.7 364.7 552 549 204.6 205.3 24.1 24.4 600 355.7 368.3 539 545 211.8 205.5 24.9 25.6 表 3 HRB400钢筋力学性能
Table 3. Mechanical properties of HRB400 rebars
温度/(℃) 屈服强度/MPa 抗拉强度/MPa 弹性模量/GPa 伸长率/(%) 自然
冷却喷水
冷却自然
冷却喷水
冷却自然
冷却喷水
冷却自然
冷却喷水
冷却20 452 452 533 533 200.3 200.3 13.6 13.6 200 426 477 536 549 202.3 201.1 13.9 14.6 400 426 464 514 545 209.3 201.2 15.0 13.9 600 441 451 522 508 204.1 192.9 14.6 14.0 表 4 组合梁参数
Table 4. Parameters of composite beams
试件分组 试件编号 受热温度/(℃) 冷却方式 1 B1 25 常温 2 B2 200 自然冷却 B3 400 自然冷却 B4 600 自然冷却 3 B5 200 喷水冷却 B6 400 喷水冷却 B7 600 喷水冷却 表 5 试件试验结果
Table 5. Test results of specimens
试件
编号极限
荷载/kN退化
系数初始刚度/
(kN/mm)退化
系数极限
挠度/mm退化
系数B1 512.8 1.00 344.50 1.00 7.60 1.00 B2 476.2 0.93 318.17 0.92 6.71 0.88 B3 439.1 0.86 189.74 0.55 6.54 0.86 B4 390.0 0.76 123.76 0.36 4.60 0.61 B5 479.5 0.94 397.39 1.15 6.20 0.82 B6 448.0 0.87 252.71 0.73 5.53 0.73 B7 407.9 0.80 147.66 0.43 4.40 0.58 表 6 抗剪承载力计算值与试验值比较
Table 6. Comparison between the calculated value and the test value of shear capacity
试件编号 剪力值Vexp/kN 计算值/kN GB 50017?2017[32] BS EN 1994-1-1: 2004[33] AS/NZS 2327: 2017[34] 修正公式 Vu1 Vu1/Vexp Vu2 Vu2/Vexp Vu3 Vu3/Vexp Vnew Vnew/Vexp B1 256.4 223.2 0.870 231.9 0.900 327.4 1.280 251.5 0.980 B2 238.1 222.3 0.930 231.1 0.970 322.6 1.350 239.4 1.010 B3 219.6 226.3 1.030 235.2 1.070 319.2 1.450 220.4 1.000 B4 195.0 221.1 1.130 229.8 1.180 301.3 1.550 193.3 0.990 B5 239.8 236.2 0.980 245.4 1.020 334.6 1.400 246.3 1.030 B6 224.0 220.8 0.990 229.5 1.020 309.5 1.380 213.1 0.950 B7 204.0 225.0 1.100 233.9 1.150 300.9 1.480 191.0 0.940 平均值 ? ? 1.004 ? 1.044 ? 1.413 0.986 方差 ? ? 0.007 ? 0.008 ? 0.007 0.001 变异系数 ? ? 0.091 ? 0.094 ? 0.063 0.033 -
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