Temperature gradient analysis of rectangular aqueduct transverse section under the effect of large temperature difference
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摘要: 渡槽在服役期间经历长期变温差循环作用,势必引起渡槽混凝土产生微裂纹等劣化,降低渡槽安全性。渡槽设计无专门规范,相关规范对渡槽是否考虑温度荷载也无明确指导意见。以新疆某矩形渡槽为例,通过有限元软件计算渡槽横截面温度场,分析其分布规律,探讨渡槽温度梯度及不同桥梁设计规范在渡槽设计中的适用性。研究表明:该渡槽通水时夏季横截面最大竖向正温差为35.8 ℃,不通水时为24.5 ℃;冬季通水时最大竖向负温差为−11.5 ℃,不通水时为−7.8 ℃。渡槽横向最大正温差为18.5 ℃,最大负温差为−8.4 ℃;较大的竖向与横向温度梯度会产生较大的温度应力,在设计中应给予考虑。实例竖向温度梯度与各种规范推荐的竖向温度梯度模式形式相似,但特征值存在较大差异,说明桥梁规范推荐值不宜直接应用于渡槽的温度应力分析,渡槽温度场宜根据槽身结构形式和运行工况计算确定。Abstract: During the operation period, the aqueduct experiences the cyclic fatigue effect of temperature variation for long term, which may cause the deterioration of the concrete of the aqueduct, such as micro-crack, and gradually reduce the safety degree of the aqueduct. There is no specific design-code for aqueduct design, and other relevant design-codes don’t provide clear guidance on whether to consider thermal effects for aqueduct. Taking a rectangle aqueduct in Xinjiang as an example and through the finite element software, the aqueduct temperature field is obtained and its distribution law is analyzed. Furthermore, the applicability of vertical temperature gradient pattern recommended by bridge codes in aqueduct design is discussed. The results show that the maximum vertical positive temperature difference in summer is 35.8 ℃ when the aqueduct is running, and 24.5 ℃ when the aqueduct is not running. In winter, the maximum vertical negative temperature difference is −15.1 ℃ when running water, and −7.8 ℃ when not running. The maximum transverse positive temperature difference of the aqueduct is 18.5 ℃ and the maximum transverse negative temperature difference is 11.2 ℃. Large vertical and transverse temperature gradient will produce large temperature stress, which should be taken into account in design. The vertical temperature gradient of the example is similar to the vertical temperature gradient modes recommended by various bridge codes, but there are large differences in the characteristic values, indicating that the recommended values of the bridge codes may not be directly applied to the temperature stress analysis of the aqueduct. The temperature field of aqueduct should be calculated and determined according to the structural form and operation conditions of the aqueduct.
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Key words:
- aqueduct /
- large temperature difference /
- temperature field /
- temperature gradient /
- design codes
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表 1 渡槽最大竖向正(负)温差
Table 1. Maximum vertical positive (negative) temperature difference of aqueduct
(单位:℃) 运行工况 渡槽形式 腹板位置 顶板 底板 夏季通水 有顶板渡槽 南侧腹板 30.5 15.2 北侧腹板 33.8 16.5 无顶板渡槽 南侧腹板 31.0 18.8 北侧腹板 35.8 18.7 夏季不通水 有顶板渡槽 南侧腹板 20.7 4.6 北侧腹板 24.5 5.5 无顶板渡槽 南侧腹板 16.1 4.9 北侧腹板 20.7 4.6 冬季通水 有顶板渡槽 南侧腹板 −9.0 −10.9 北侧腹板 −9.6 −11.5 无顶板渡槽 南侧腹板 −8.5 −7.7 北侧腹板 −8.6 −8.3 冬季不通水 有顶板渡槽 南侧腹板 −3.4 −5.7 北侧腹板 −4.9 −7.8 无顶板渡槽 南侧腹板 −3.8 −5.0 北侧腹板 −2.2 −7.6 表 2 渡槽横向最大正(负)温差
Table 2. Maximum transverse positive (negative) temperature difference of aqueduct
(单位:℃) 渡槽形式与位置 运行工况 顶板/底板位置 夏季最大正温差 冬季最大负温差 冬季最大正温差 有顶板渡槽顶板 通水 南侧端 12.6 −6.5 13.6 北侧端 7.9 −7.2 无 不通水 南侧端 4.7 −5.0 14.0 北侧端 1.0 −5.6 无 有顶板渡槽底板 通水 南侧端 18.5 −7.6 12.1 北侧端 11.7 −8.4 无 不通水 南侧端 9.7 −2.2 15.4 北侧端 3.4 −4.0 0.7 无顶板渡槽底板 通水 南侧端 17.7 −4.5 11.6 北侧端 12.0 −5.2 无 不通水 南侧端 1.6 无 15.2 北侧端 3.2 −2.1 4.4 表 3 温度梯度特征值与各规范推荐值比较
Table 3. Comparison of the characteristic values at the temperature gradient and the recommended values of each code
温度梯度类型 通水与否 规范 温度梯度模式 T1/℃ T2/℃ ΔH1/m ΔH3/m 规范推荐正温度梯度 中国公路[12] 双折线 25 不考虑 0.4 不考虑 中国铁路[21] 幂函数 20 不考虑 1.1 不考虑 AASHTO[22] 双折线 30 3 0.4 0.2 新西兰[23] 抛物线 32 1.5 0.8 0.2 渡槽正温度梯度 通水 有顶板 33.9 16.3 0.80 1.05 无顶板 35.8 18.4 0.95 1.10 不通水 有顶板 24.5 5.5 1.00 0.50 无顶板 16.1 1.6 0.30 0.05 规范推荐负温度梯度 中国公路[12] 双折线 −12.5 不考虑 0.4 不考虑 中国铁路[21] 幂函数 −10 不考虑 0.35 不考虑 AASHTO[22] 双折线 −15 −3 0.4 0.2 新西兰[23] 抛物线 不考虑 不考虑 不考虑 不考虑 渡槽负温度梯度 通水 有顶板 −9.6 −11.5 0.75 1.10 无顶板 −8.2 −8.5 0.85 1.05 不通水 有顶板 −5.0 −7.8 0.20 1.25 无顶板 −3.4 −5.7 0.15 0.65 -
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