Strain field investigation of limestone specimen under uniaxial compression loads using particle image velocimetry

The particle image velocimetry (PIV) method was used to investigate the full-field displacements and strains of the limestone specimen under external loads from the video images captured during the laboratory tests. The original colorful video images and experimental data were obtained from the uniaxial compression test of a limestone. To eliminate perspective errors and lens distortion, the camera was placed normal to the rock specimen exposure. After converted into a readable format of frame images, these videos were transformed into the responding grayscale images, and the frame images were then extracted. The full-field displacement field was obtained by using the PIV technique, and interpolated in the sub-pixel locations. The displacement was measured in the plane of the image and inferred from two consecutive images. The local displacement vectors were calculated for small sub-windows of the images by means of cross-correlation. The video images were interrogated in a multi-pass way, starting off with 64×64 images, ending with 16×16 images after 6 iterations, and using 75% overlap of the sub-windows. In order to remove spurious vectors, the displacements were filtered using four filters: signal-to-noise ratio filter, peak height filter, global filter and local filter. The cubic interpolation was utilized if the displacements without a number were encountered. The full-field strain was then obtained using the local least square method from the discrete displacements. The strain change with time at different locations was also investigated. It is found that the normal strains are dependant on the locations and the crack distributions. Between 1.0 and 5.0 s prior to the specimen failure, normal strains increase rapidly at many locations, while a stable status appears at some locations. When the specimen is in a failure status, a large rotation occurs and it increases in the inverse direction. The strain concentration bands do not completely develop into the large cracks, and meso-cracks are not visible in some bands. The techniques presented here may improve the traditional measurement of the strain field, and may provide a lot of valuable information in investigating the deformation/failure mechanism of rock materials.     

超高层建筑地下室顶板施工荷载设计与施工研究

某超高层建筑位于CBD(中央商务区)核心区,由于区域内建筑密度高、施工场地狭小,无法满足施工要求,只能考虑以地下室顶板施工荷载设计及作为施工场地。鉴于此,介绍了地下室顶板施工荷载设计及施工时梁、板、洞口、后浇带位置的具体处理方法。该方法既不影响原设计的使用功能,又可满足现场施工需要,同时也避免了地下室顶板大量的后加固措施,工程应用取得了良好的经济效益。     

超高层动臂塔机内爬升施工模拟分析与应用

以超高层项目动臂塔机在核心筒内爬升施工为案例,介绍了动臂塔机的支撑梁、牛腿及埋件的设计与安装方式,分析了塔机在工作和非工作状态下,标准节上下支撑梁在0°、45°、90°、135°、180°共5个方向的荷载工况,运用有限元数据模拟方法复核了各工况下支撑梁系统和剪力墙的受力状态,结果表明支撑钢梁和牛腿的应力比、剪力墙的受力状态均满足设计要求。对超高层项目塔机的选择和支撑系统的设计提供了一种精确、可靠的计算方法。     

合肥恒大中心钢板组合楼板施工技术

通过对合肥恒大中心518m超高层钢板组合楼板施工技术的介绍,详细论述钢板组合楼板施工工艺、过程问题的处理措施、施工中重难点的控制。