Spectral analysis of surface wave response of multi-layer thin cement mortar slab structures with finite thickness

The method of spectral analysis of surface waves (SASW), a nondestructive testing method, has mainly been developed and used for many years in the fields of geotechnical engineering and highway engineering, such as for examining the material properties of pavement systems and soil media under an infinite half-space condition. Extensive research in this area has been focused on understanding the applicability and limitations of the SASW method in recent decades. This method consists of generation, measurement, and processing of dispersive surface waves. During an SASW test, the surface of the medium under investigation is subject to an impact to generate surface wave energy at various frequencies. Two vertical accelerometer receivers are set up near the impact source to detect the energy transmitted through the testing media. By recording signals in digitized form using a data acquisition system and processing them, surface wave velocities can be obtained by constructing a dispersion curve. Through forward modeling, the shear wave velocities can also be found, which can be related to various material properties. This paper presents the relationship between the theoretical and experimental compact dispersion curves when the SASW method is applied to multi-layer thin cement mortar slab systems with a finite thickness. The test results of surface wave velocity obtained from the experimental compact dispersion curve are found to have higher values than the results obtained from the theoretical dispersion curve due to different boundary conditions and reflections from the boundaries. An experimental study was conducted to examine if the dispersive characteristics of a Rayleigh wave exist in the multi-layer cement mortar slab systems. This study can be utilized in examining structural elements of general concrete structures and can be applied in the integrity analysis of concrete structures with a finite thickness.     

金刚石组锯绳技术综述

与金刚石砂锯相比,用金刚石组锯绳锯切花岗岩大板具有锯切石材利用率高、对环境友好、板材表面质量好、生产效率高及综合成本低等特点。文章对比了组锯机各主要部件作用及特点,提出了目前国内组锯设备应解决各绳恒张力控制及制造精度等关键问题,组锯绳应解决钢丝绳强度低,串珠配方和结构设计及制造质量稳定等关键问题。     

闭口型压型钢板-混凝土组合板数值模态分析研究

目前,压型钢板-混凝土组合板结构在工业厂房和电厂中得到广泛应用,其组合板振动特性也日渐为业主和设计人员所关注。利用ANSYS有限元分析程序对闭口型压型钢板-混凝土组合板进行数值模态分析,得到组合板各阶自振频率及振型。对模态分析过程中所涉及到的材料模型定义、单元划分以及建模技术等问题进行了详细介绍,数值模拟结果与组合板模态试验结果比较吻合,表明所采用的有限元模态分析方法能较准确模拟组合板的振动特征。进一步运用ANSYS程序对一系列不同跨度和边界条件下的组合板进行数值模态分析,得到不同跨度和边界条件下组合板的振型和自振频率,为组合板的振动设计提供有益的参考和依据。     

减少无委托板坯的措施及实践

由于无委托板坯影响企业的资源利用率和合同的完成,使其的管理日益受到重视。宝钢第二炼钢厂无委托板坯源于合同原因、质量原因和规格原因,其中主要是合同和质量的原因。为减少无委托板坯,从无委托板坯产生的源头、操作过程和质量管理等方面采取了措施,使无委托板坯下降50%以上。     

预应力混凝土空心叠合板试验研究

针对现有的一般预应力空心叠合板楼盖板厚较大,自重较大等缺点,提出了一种新形式的预应力混凝土空心叠合板,通过对3块简支板,3块简支叠合板和1块两跨连续叠合板进行静力荷载试验,分析了这种板在静力荷载作用下的裂缝、承载力、挠度等特点,研究了其开裂荷载和极限承载力较高的原因。试验结果表明这种预应力空心叠合板具有良好的抗裂性能和较高的极限承载能力,建立了开裂弯矩、极限承载力、挠度的计算方法,为这种叠合板的设计和工程应用提供了依据。     

现代建筑的新型楼盖结构体系

总结了现代建筑的多种钢筋混凝土和预应力混凝土结构楼盖体系的技术性能、施工特点、设计计算方法的要点。重点介绍了在跨度(或柱网)为6～12m的多层与高层建筑中应用的三种新型的预应力混凝土楼盖结构体系:密肋板、空心板和夹层板,及如何合理地选择这些楼盖体系。对8.4m×8.4m柱网的多种轻型楼板组成的楼盖结构体系与常规的梁板和实心板进行了技术经济比较,提出了控制结构层高度、结构层折算厚度和结构自重的建议。     

无粘结预应力现浇空心板楼盖在高层建筑中的应用

着重介绍无粘结预应力现浇空心板在高层建筑中的应用。对现浇空心板的截面选择、内力计算、预应力钢筋和非预应力钢筋的确定进行了详细分析。对于解决高层建筑中的大跨度结构和降低层高等问题进行了有益的探索     

Analysis of lateral load transfer by internal slab-column joints

The results of an analytical study examining the behavior and load transfer mechanism of 16 interior flat slab-column joint models, transferring lateral load, are presented. Predictions of the connection response were calculated using a professional finite element computer program, utilizing three-dimensional, elasto-plastic, concrete elements.

Currently, various analytical methods are suggested for calculating the load transfer. The assume that the slab sections carry the external unbalanced moment by developing a bending moment on the front and back faces, and a torsional moment on the side faces. Several studies have tried to determine the relative contribution of the bending and torsional moments. Slots or cutting through the slab, made along the respective column faces, were introduced in an attempt to isolate the components that resist the external moment.

According to the present analysis, the various types of connections have a minor effect on the response. They display very similar deformations and stress distributions in the slab, except for very local stress concentrations, almost ignoring the slots and cuttings. As a result of this analysis, the attempts to isolate appear to be unsuitable since the slab's bending and torsional mechanisms are highly coupled.     

混凝土单向板的受拉薄膜效应计算

为有效地计算混凝土单向板在大变形下的极限承载力,基于屈服线理论提出了考虑受拉薄膜效应的板块平衡法。该方法在建立板块平衡方程时计入了大变形下塑性铰线截面处逐渐显著的钢筋合力的竖向分量,即受拉薄膜效应。进行了3种不同边界条件的6块钢筋混凝土单向板的大变形静力加载试验,获得了荷载-挠度曲线、极限承载力和破坏时的裂缝形态等。将改进后的板块平衡法的计算值与试验结果进行了对比,吻合较好,适于工程设计应用。     

无机胶粘贴碳纤维布加固板防火涂层厚度取值

为确保火灾下用无机胶粘贴的碳纤维布能正常发挥加固作用,保证结构安全,需要选用一定厚度的厚型防火涂料作为碳纤维布的防火保护层.基于对加固板高温变形限制的考虑,采用ABAQUS对其高温变形进行试算,提出以板底温度415℃作为控制温度计算涂料厚度的原则.采用ABAQUS对加固板温度场进行分析,表明涂料厚度、导热系数以及受火时间是影响板底温度的主要因素,因而决定涂料保护层厚度的关键因素为导热系数和受火时间.在此基础上,按耐火时间和涂料导热系数的不同,分涂料品种并考虑相应构造要求的基础上,给出基于温度控制的防火涂料保护层厚度取值建议.