论文部分内容阅读
在《部份预应力及其抗裂性探讨》一文中(刊于《公路设计资料》75年3期),我们曾讨论了预应力混凝土公路桥梁按部份预应力设计的可能性,合理性和某些情况下的必要性。这里介绍的是Leonhardt 在国际预应力协会——欧洲混凝土委员会(FIP—CEB)会议上(1974年5月纽约)所作的主要报告,他更尖锐地批评了全预应力,其主要论点可归结为:1.全预应力的概念是预应力诞生初期提出的。按全预应力设计用材多、造价高、因预压应力大而担更大风险、徐变也大而计及二次应力全预应力仍难免开裂。2.Finsterwalder 首先提出并在德国51年规范DIN 1227中采纳了“有限预应力”的概念。FID—CEB 在已有足够经验证明低预应力度优越性的基础上于70年规定了预应力度的等级。3.预应力度分成三级往往被误解为质量的分级,因而常错误地认为全预应力是质量最好的预应力结构,其实则往往相反。4.因此建议取消预应力分级,根据使用要求来确定预应力程度,对裂缝宽度而不是拉应力加以限制。5.建议在短载和经常的活载作用下不容许出现拉应力(相应没有裂缝),而全部荷载和温度影响下则限制裂缝宽度在0.1～0.2毫米。我国预应力混凝土公路桥梁设计规范正在编制中,如能反映预应力混凝土设计的新理论,不但可以节省大量高强度钢材,采用强度较低的钢材作预应力主筋,结构形式上也可更多样化,为我国公路桥梁上使用预应力混凝土创造更好的条件,而且它也反映了世界上先进的设计水平和动向。因此有必要大力破除预应力混凝土结构在使用荷载下不容许开裂(甚至不容许出现拉应力)的陈旧偏见,这也是我们翻译本文的目的。
In the article “Discussion of Partial Prestressing and Crack Resistance”, published in Road Design Materials, Issue 75, Issue 3, we discussed the possibility of partial prestressing of prestressed concrete highway bridges and rationality And the need in some cases. Presented here is Leonhardt’s key report at the International Prestress Association - New Concrete Council (FIP-CEB) meeting (New York, May 1974). He even more sharply criticized total prestress. The main argument can be attributed to : 1. The concept of total prestress is proposed in the early stage of prestressing. According to the full prestressed design materials, high cost, due to large preload stress to bear the greater risk of creep is also large and account for the secondary stress full prestress is still inevitable cracking. 2. Finsterwalder first proposed and adopted the concept of “finite prestress” in DIN 51 27, the German standard for 51 years. FID-CEB has pre-stressed the grade for 70 years on the basis of sufficient experience to prove the superiority of low prestress. 3. The division of prestressing force into three levels is often misunderstood as the grading of quality, and therefore often mistakenly believe that total prestressing is the best quality prestressed structure, but in fact it is often the opposite. 4. It is therefore suggested that the classification of prestress should be canceled, the degree of prestressing should be determined according to the requirements of use, and the width of crack rather than the tensile stress should be limited. 5. It is recommended that no tensile stresses (correspondingly no cracks) be tolerated under short-load and frequent live loads, and that the crack width should be limited to 0.1-0.2 mm under the full load and temperature effects. China’s prestressed concrete highway bridge design specifications are being prepared, if it can reflect the new theory of prestressed concrete design, not only can save a lot of high-strength steel, the use of lower strength steel prestressed tendons, the structure can also be more diverse It will create better conditions for the use of prestressed concrete on highway bridges in China, and it also reflects the advanced design level and trends in the world. Therefore, it is necessary to vigorously get rid of the prejudice that the prestressed concrete structure should not be allowed to crack under the service load (even the tensile stress is not allowed), which is also the purpose of our translation.