A three-dimensional finite element program for thermal analysis of hydration heat in concrete structures with a plastic pipe cooling system is introduced in this paper. The program was applied to simulation of the tem...A three-dimensional finite element program for thermal analysis of hydration heat in concrete structures with a plastic pipe cooling system is introduced in this paper. The program was applied to simulation of the temperature and stress field of the Cao＇e Sluice during the construction period. From the calculated results, we can find that the temperaiure and stress of concrete cooled with plastic pipes are much lower than those of concrete without pipes. Moreover, plastic pipes could not be corroded by seawater. That is to say, a good effect of temperature control and cracking prevention can be achieved, which provides a useful reference for other similar nearshore concrete projects.展开更多
In order to optimize the current grinding procedure of the backup roll of 2050 continuously variable crown (CVC) mills, the behavior of rolling contact fatigue (RCF) cracking was investigated. Two RCF short cracks, in...In order to optimize the current grinding procedure of the backup roll of 2050 continuously variable crown (CVC) mills, the behavior of rolling contact fatigue (RCF) cracking was investigated. Two RCF short cracks, including vertical short crack and ratcheting short crack initiated from ratcheting, were observed. The behavior of both RCF cracks was analyzed in detail. Then a modified grinding procedure was proposed according to the behavior of RCF cracks and the preventive grinding strategy.展开更多
This study tries to highlight the role of magnetic and seismic data in the prevention of building cracking, which constitutes a geotechnical risk in Agadez City. This city is built on the faulted and fractured sandsto...This study tries to highlight the role of magnetic and seismic data in the prevention of building cracking, which constitutes a geotechnical risk in Agadez City. This city is built on the faulted and fractured sandstone formations of the “Agadez Sandstones Formations”, which were deposited in unconformity on the basement of the Aïr Mountain. This study focuses on the prevention of geotechnical damages related to building cracking in the Agadez region through geophysical methods, which are well known for investigating tectonic structures and their directions on the surface and subsurface. A methodological approach integrated the seismic and magnetic data interpretation combined with field measurement on the cracked building and its underlying substratum, represented by Agadez sandstones and basement. The extraction of seismic lineaments from the West African seismic map showed the seismic directions oriented NW-SE (N135˚ to N160˚), passing through the studied area. The structural interpretation of the magnetic map shows that the Agadez region is also affected by the subsurface lineaments mainly oriented in NW-SE (N135˚) directions, which are similar to the identified seismic lineaments in the same zone. A structural study carried out on the Agadez sandstones and the underlying basement showed that faults and fractures oriented N120˚ to N165˚ affect both the basement of the Aïr Mountains and the sandstone formations on which the city of Agadez is built. These observations showed that building cracking in the Agadez region has a higher propagation tendency according to the directions ranging from NW-SE (N135˚) to NNW-SSE (N165˚). Therefore, the building’s cracking has a stronger propagation component according to these mean directions that are not recommended for building. To prevent and reduce the risks related to building cracking in Agadez region, it is highly recommended to build in the minor directions of cracking propagation, which correspond to NE and SW directions.展开更多
为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用...为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用抗拉强度准则和裂缝尖端强度因子对衬砌结构破坏进行分析,提出合理的温控防裂措施。结果表明:1)衬砌温度场前期整体温度迅速上升,在第7天左右达到最大值,其中衬砌内壁温度可达到37℃,外壁温度可达到56℃。2)衬砌结构外墙环向应力可达到2.2 MPa,体现为拉应力状态;径向应力可达到2.7 MPa,呈现为压应力状态。3)衬砌结构强度的破坏主要受温度及结构本身稳定性2方面影响,可通过采用低热水泥、控制混凝土的入模温度以及严格监控施工过程来提高衬砌的稳定性。其中,采用低热水泥可降低衬砌结构的温升值,混凝土的最终水化热每降低50 k J/kg,衬砌结构内外壁的温差可降低1.85℃左右;适当提高入模温度可缩短水化热的放热周期及降低衬砌内外壁温差。展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 50779010)
文摘A three-dimensional finite element program for thermal analysis of hydration heat in concrete structures with a plastic pipe cooling system is introduced in this paper. The program was applied to simulation of the temperature and stress field of the Cao＇e Sluice during the construction period. From the calculated results, we can find that the temperaiure and stress of concrete cooled with plastic pipes are much lower than those of concrete without pipes. Moreover, plastic pipes could not be corroded by seawater. That is to say, a good effect of temperature control and cracking prevention can be achieved, which provides a useful reference for other similar nearshore concrete projects.
文摘In order to optimize the current grinding procedure of the backup roll of 2050 continuously variable crown (CVC) mills, the behavior of rolling contact fatigue (RCF) cracking was investigated. Two RCF short cracks, including vertical short crack and ratcheting short crack initiated from ratcheting, were observed. The behavior of both RCF cracks was analyzed in detail. Then a modified grinding procedure was proposed according to the behavior of RCF cracks and the preventive grinding strategy.
文摘This study tries to highlight the role of magnetic and seismic data in the prevention of building cracking, which constitutes a geotechnical risk in Agadez City. This city is built on the faulted and fractured sandstone formations of the “Agadez Sandstones Formations”, which were deposited in unconformity on the basement of the Aïr Mountain. This study focuses on the prevention of geotechnical damages related to building cracking in the Agadez region through geophysical methods, which are well known for investigating tectonic structures and their directions on the surface and subsurface. A methodological approach integrated the seismic and magnetic data interpretation combined with field measurement on the cracked building and its underlying substratum, represented by Agadez sandstones and basement. The extraction of seismic lineaments from the West African seismic map showed the seismic directions oriented NW-SE (N135˚ to N160˚), passing through the studied area. The structural interpretation of the magnetic map shows that the Agadez region is also affected by the subsurface lineaments mainly oriented in NW-SE (N135˚) directions, which are similar to the identified seismic lineaments in the same zone. A structural study carried out on the Agadez sandstones and the underlying basement showed that faults and fractures oriented N120˚ to N165˚ affect both the basement of the Aïr Mountains and the sandstone formations on which the city of Agadez is built. These observations showed that building cracking in the Agadez region has a higher propagation tendency according to the directions ranging from NW-SE (N135˚) to NNW-SSE (N165˚). Therefore, the building’s cracking has a stronger propagation component according to these mean directions that are not recommended for building. To prevent and reduce the risks related to building cracking in Agadez region, it is highly recommended to build in the minor directions of cracking propagation, which correspond to NE and SW directions.
文摘为分析高地温水工隧洞衬砌结构温度应力特性,基于拉普拉斯变换推导出衬砌结构瞬态温度场的解析解,并借助弹性抗力法推导出衬砌结构的弹性温度应力分量。依托新疆布伦口水电站监测数据对衬砌结构瞬态温度场及应力场进行计算分析,并采用抗拉强度准则和裂缝尖端强度因子对衬砌结构破坏进行分析,提出合理的温控防裂措施。结果表明:1)衬砌温度场前期整体温度迅速上升,在第7天左右达到最大值,其中衬砌内壁温度可达到37℃,外壁温度可达到56℃。2)衬砌结构外墙环向应力可达到2.2 MPa,体现为拉应力状态;径向应力可达到2.7 MPa,呈现为压应力状态。3)衬砌结构强度的破坏主要受温度及结构本身稳定性2方面影响,可通过采用低热水泥、控制混凝土的入模温度以及严格监控施工过程来提高衬砌的稳定性。其中,采用低热水泥可降低衬砌结构的温升值,混凝土的最终水化热每降低50 k J/kg,衬砌结构内外壁的温差可降低1.85℃左右;适当提高入模温度可缩短水化热的放热周期及降低衬砌内外壁温差。
