不同温控措施对大尺寸混凝土结构物抗裂效果的影响

Influence of Different Temperature Control Measures on Crack Resistance of Large-size Concrete Structure

大跨桥梁下部结构如承台、桥墩的共同特点是3个维度尺寸大,混凝土内部绝热温度高。混凝土中心处最高温度甚至可达70℃以上,如果没有有效地控制好混凝土内部的最高温度、内外温差和表面与环境温差,往往可产生较大的温度应力,当温度应力大于混凝土的抗拉强度时,将导致混凝土结构表面开裂,影响桥墩的整体性和耐久性。已有的研究对大尺寸混凝土结构物的温控措施进行了大量的研究,均重点关注了降低最高温度、降低两类温差的方法和可采取的措施,未考虑这些方法或措施的实际效果。基于高速公路桥梁柔性墩实体段混凝土的工程实际,采用数值模拟的方法,研究分析了整体浇注、分层浇注和布置冷却水管等不同的施工方案及温控措施对桥墩混凝土抗裂效果的影响。结果表明,整体浇注混凝土时不论是否布置冷却水管,抗裂安全系数均不符合要求,仍然会产生温度裂缝;分两层浇注混凝土,抗裂安全系数较大,是合适的温控措施。对于混凝土桥墩而言,分层浇注时已能较好满足要求,尽管再布置两层冷却水管的效果更佳,但以施工便利和经济角度考虑,最合适的温控措施是分两层浇注混凝土并不布置冷却水管。

The common characteristics of substructure of long-span bridge, such as pile caps and piers, are that the large 3 D sizes and high internal insulation temperature of concrete. The maximum temperature of concrete center is up to 70 ℃. If the maximum internal temperature, the internal and external temperature difference and the temperature difference between surface and environment are not effectively controlled, the greater temperature stress could be produced. When the temperature stress is greater than the tensile strength of concrete, the cracks on the surface of concrete structure will induced and affect the integrity and durability of piers. The existing researches have done a lot of research on the temperature control measures of large-size concrete structures. The methods and measures for reducing the maximum temperature and 2 types of temperature difference are paid attention to, but the actual effects of these methods or measures are not considered. Based on the engineering practice of the concrete segments of the flexible piers of expressway bridge, the influence of different construction schemes and temperature control measures, such as integral pouring, layered pouring with cooling water pipes, on cracking resistance effect of concrete piers are analyzed by using numerical simulation method. The result shows that(1) If the concrete is poured in one time, whether or not there is cooling water pipe, crack safety factor does not meet the requirements and temperature cracks will still occur;(2) If pouring concrete in 2 layers, the safety factor of cracking resistance is larger, it is suitable temperature control measure. For concrete bridge piers, the layered pouring can meet the requirements well. Although the effect of the added 2-layer cooling water pipe is better, the most suitable temperature control measures are 2-layer concrete pouring without cooling water pipe considering construction convenience and economy.