软土地基钢筋混凝土板整体基础的小桥涵

湖州市自1984年以来,在软土地基采用钢筋混凝土板整体基础建造小桥涵几十座。使用结果,不但结构可靠、施工方便,而且可降低造价、缩短工期。文章介绍钢筋混凝土板整体基础小桥涵设计采用有限元计算模型进行计算分析;还介绍了4个实例,可供设计人员参考。     

流态混凝土梁板构件裂缝成因及控制

流态混凝土 ,特别是在高强度、大流动性条件下 ,具有水泥用量多 ,用水量大 ,砂率高 3个主要特点 ,所以产生裂缝的潜在危险大 ,在工程实践中梁板构件出现裂缝的情况比较多 ,对此必须引起足够的重视 总结了流态混凝土梁板构件非结构性裂缝产生的规律 ,将裂缝分成混凝土塑性收缩裂缝、干燥收缩裂缝、骨料塑性沉落裂缝、温度应力裂缝几类 ,系统地分析了以上几类裂缝的形成原因以及相关因素 提出从优化混凝土设计、提高混凝土生产质量、加强混凝土施工管理 3个方面对裂缝进行有效控制     

减少连铸坯表面振痕的方法研究

分析了结晶器振动产生连铸坯表面振痕的生成机理,论述了振痕对连铸坯质量的影响,研究和探讨了减少铸坯表面振痕的途径,提出了减少连铸坯表面振痕,提高连铸坯表面质量的有效措施。     

Efficient Strengthening Technique to Increase the Flexural Resistance of Existing RC Slabs

Composite materials are being used with notable effectiveness to increase and upgrade the flexural load carrying capacity of reinforced concrete (RC) members. Near-surface mounted (NSM) is one of the most promising strengthening techniques, based on the use of carbon fiber-reinforced polymer (CFRP) laminates. According to NSM, the laminates are fixed with epoxy based adhesive into slits opened into the concrete cover on the tension face of the elements to strength. Laboratory tests have shown that the NSM technique is an adequate strengthening strategy to increase the flexural resistance of RC slabs. However, in RC slabs of low concrete strength, the increase of the flexural resistance that NSM can provide is limited by the maximum allowable compressive strain in the compressed part of the slab, in order to avoid concrete crushing. This restriction reduces the effectiveness of the strengthening, thus limiting the use of the NSM technique. A new thin layer of concrete bonded to the existing concrete at the compressed region is suitable to overcome this limitation. Volumetric contraction due to shrinkage and thermal effects can induce uncontrolled cracking in the concrete of this thin layer. Adding steel fibers to concrete [steel fiber-reinforced concrete (SFRC)], the postcracking residual stress can be increased in order to prevent the formation of uncontrolled crack patterns. In the present work, the combined strengthening strategy, a SFRC overlay and NSM CFRP laminates, was applied to significantly increase the flexural resistance of existing RC slabs. Experimental results of four-point bending tests, carried out in unstrengthened and strengthened concrete slab strips, are presented and analyzed.     

Failure Resistance of the Historic Stone Bridge Structure of Charles Bridge. I: Susceptibility to Nonstress Effects

The monitoring of deformations of the stone structure of Charles Bridge in Prague proved the gravity and relevance of nonstress effects (temperature, moisture content) on cyclic deformations and permanent strain accompanied by a gradual disintegration of its stone masonry, growing tilt of the breast walls, and development of cracks in the masonry of the stone bridge structure. Each deformation cycle is accompanied by a gradual growth in permanent deformations. The “unmanifested” primary deformation due to, e.g., a temperature change causes a mechanical state of tension, and it is mainly the tensile stresses thus arising that contribute to the development of tensile cracks in the stone masonry.     

连铸板坯表面温度控制器的设计

以某钢厂引进的连铸板坯二冷动态控制系统为研究对象,提出了基于改进粒子群BP算法的板坯二冷区表面温度神经网络控制器.以实际生产现场的设备、工艺参数为基础进行了仿真研究,结果表明表面温度神经网络控制器的输出结果与实际生产参数的误差小于2%,研究结果对引进的同类连铸板坯二冷控制系统的升级改造具有指导意义.     

连铸板坯表面横裂纹成因分析

本文通过对铸坯裂纹产生机理的分析,指出了连铸板坯表面横裂纹产生的原因,讨论了影响连铸板坯表面横裂纹产生的因素。     

The behaviour of asymmetric slim floor steel beams in fire

Computer software has been developed to predict the structural response of asymmetric slim floor steel beams, used with composite concrete floor slabs consisting of deep profiled steel decking. Comparisons between predicted behaviour and that recorded in standard fire tests, showed that the software is very accurate. By including the rotational stiffness of the beam-to-column connections, the fire resistance of the beam is significantly enhanced. This is mainly due to the connections retaining most of their strength during a fire, since they are fully encased in concrete as a consequence of this type of construction. The analyses presented in this paper indicate that it may be possible to increase the fire resistance of the steel beams from 60 to 90 minutes, by including the connection behaviour. The software has also been used to aid the design of a future large-scale fire test on the asymmetric slim floor system. Predictions of the structural response have been presented. These will enable the fire load and ventilation conditions in the test to be designed. In addition the software has been used to identify the minimum amount of fire protection that is required for the supporting columns.     

FRP加固钢筋混凝土板的分析与设计

分析了用纤维增强复合材料(FRP)加固钢筋混凝土板的特点,指出了上海市颁布的《纤维增强复合材料加固混凝土结构技术规程》(DG/TJ08—012—2002)和中国工程建设标准化协会颁布的《碳纤维片材加固混凝土结构技术规程》(CECS146)在对钢筋混凝土板的加固要求上存在一些不足之处,提出了一种简单可行的设计方法,并通过例题比较了该方法与上述规程的差别。     

Effect of temperature field and cooling rate along casting direction on surface transverse cracks of microalloyed steel

The temperature field and cooling rate especially for surface center and corner, which located at 0-5mm under the slab surface were calculated along the casting direction based on the two- dimensional heat transfer and solidification model of slab continuous casting, combined with the actual casting process conditions. The results show that the temperature of slab drops rapidly from liquidus temperature to 1200-900?? in the mold, and then drops slowly in the secondary cooling zone with the corner 200?? about lower than the surface center. As to the cooling rate, for 0-5mm layer under surface, it is up to 40??/s in the mold with the average cooling rate about 10??/s. For the secondary cooling zone, it is about 3-6??/s in the foot zone, and then drops to a steady value about 0. 1-0. 5??/s. The results can be used to optimize the continuous casting process and provide the basis for the control of the surface and corner transverse cracking of continuous casting slabs based on the solidification and phase transformation principles.