【正文】 凝土內(nèi)外溫度差及混凝土表面梯度，防止表面裂縫?；炷梁弯摻罨炷两Y(jié)構(gòu)的表面常常會(huì)發(fā)生細(xì)而淺的裂縫，其中大多數(shù)屬于干縮裂縫。要想根據(jù)已知的溫度準(zhǔn)確分析出溫度應(yīng)力的分布、大小是一項(xiàng)比較復(fù)雜的工作。在鋼筋混凝土中，拉應(yīng)力主要是由鋼筋承擔(dān)，混凝土只是承受壓應(yīng)力。 Measures to improve the constraints are: (1) a reasonable subblock joints。 (2) basis to avoid too much ups and downs。在素混凝土內(nèi)或鋼筋混凝上的邊緣部位如果結(jié)構(gòu)內(nèi)出現(xiàn)了拉應(yīng)力，則 須依靠混凝土自身承擔(dān)。在大多數(shù)情況下，需要依靠模型試驗(yàn)或數(shù)值計(jì)算。雖然這種裂縫一般都較淺，但它對(duì)結(jié)構(gòu)的強(qiáng)度和耐久性仍有一定的影響。 2）防止混凝土超冷，應(yīng)該盡量設(shè)法使混凝土的施工期最低溫度不低于混凝土使用期的穩(wěn)定溫度。 從理論上分析，新澆混凝土中所含水分完全可以滿足水泥水化的要求而有余。 4）減水防裂劑可以改善水泥漿的稠度，減少混凝土泌水，減少沉縮變形。新澆筑早期拆模，在表面引起很大的拉應(yīng)力，出現(xiàn) “ 溫度沖擊 ” 現(xiàn)象。由 第 113 頁 于彈性模量的變化，這一時(shí)期在混 凝土內(nèi)形成殘余應(yīng)力。由于遇到的主要是施工中的溫度裂縫，因此下面僅對(duì)施工中混凝土裂縫的成因 和處理措施做一探討。2) In the operation process, the temperature changes have influence on stress state of structure which cannot be ignored. Since temperature crack caused in the construction is mainly met , the causes of cracks and Processing measures in the construction is explored in this paper. causes of the cracks Cracks in concrete are a variety of reasons, mainly temperature and humidity changes, brittle and uneven concrete, as well as the structure is irrational, failure of raw materials (such as alkaliaggregate reaction), template deformation, and so on the basis of differential settlement. The concrete to harden off a large number of cement during the hydration heat, the internal temperature rising on the surface caused by tensile stress. Late in the cooling process, due to coagulation on the basis of or be bound by the old, will emerge in the concrete tensile stress. Lower temperatures in the concrete surface will be a lot of tensile stress. When the tensile stress beyond the capacity of concrete crack, the cracks will appear. A number of concrete changes in the internal humidity or changes very little slow, but possible changes in surface humidity or more dramatic changes. Such as conservation, failed to keep dry when wet, surface shrinkage deformation of concrete subject to internal constraints, but also often leads to cracks. Shortterm loading at the time of ultimate tensile deformation only ( ~ ) 104, the limit of longterm loading spaces when the only stretch deformation ( ~ ) 104. Unevenly as a result of raw materials, watercement ratio of instability, and transportation and pouring in the process of segregation phenomena, in the same piece of concrete in the tensile strength is uneven, there are many low tensile capacity, easy to fracture in a weak position. In reinforced concrete, the tensile stress is mainly borne 第 107 頁 by the steel, concrete is subject to pressive stress. In plain concrete or reinforced coagulation on the edge of the site if the structure of the tensile stress appears to be relying on its own concrete mitment. 2. thermal stress analysis According to the formation of thermal stress can be divided into the following three stages: (1) early: Since the beginning of pouring concrete to cement the end of exothermic basic general about 30 days. Two characteristics of this stage, first, to release a large number of cement hydration heat, and the other is the elastic modulus of coagulation dramatic changes. Modulus of elasticity as a result of changes within this period in the formation of residual stress in the concrete. (2) mediumterm: from the basic role of cement heat until the end of the stable temperature of the concrete cooling time, during this period, the temperature stress was mainly due to cooling and the outside concrete caused by temperature changes, stress and early formation of these residual stress superposition phase, during which the coagulation of the elastic modulus changed little. (3) late: concrete pletely cooling period after the operation. Thermal stress is mainly caused by external temperature changes, the stress and the first twophase s