A framework for the seismic assessment of existing masonry buildings accounting for different sources of uncertainty

The current formulation of Eurocode 8 Part 3 and the Italian building code for the seismic assessment of existing buildings accounts for epistemic (knowledge‐based) uncertainties by means of the identification of knowledge levels with associated values of the so‐called confidence factors, applied only as a reduction of material strengths. This formulation does not always produce consistent results and it does not explicitly account for other sources of uncertainty. The paper proposes a probabilistic methodology for the quantification of appropriately defined factors, allowing consideration of the different sources of uncertainty involved in the seismic assessment of masonry buildings by means of nonlinear static analyses. This simple approach, also including an alternative formulation of the confidence factors related with material properties, allows to obtain results which are consistent with the acquired level of knowledge and correctly account for the different sources of uncertainty without requiring to carry out any stochastic nonlinear analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Application of extended distinct element method with lattice model to collapse analysis of RC bridges

This paper proposes a simple lattice model for collapse analysis of RC bridges subjected to earthquakes by using the extended distinct element method (EDEM). In the model, a concrete element consists of lumped masses connected to one another by springs, and a reinforcement bar is represented by a discrete model or an integrated model. The proposed lattice model is simple but its parameters are reasonably defined. It has fewer element nodes and connecting springs, which will be of benefit by shortening the CPU time. The processes to determine the initial stiffness of concrete and steel springs, the parameters of the constitutive model and the fracture criteria for springs are described. A re‐contact spring model is also proposed to simulate the re‐contact of the concrete after fracture of springs; and a general grid searching method is used to decrease the CPU time for judging re‐contact after fracture. The lattice model is assessed by numerical simulations and experiments. As an application, a damaged single‐column pier subjected to the Kobe Earthquake in 1995 is analysed by EDEM with the proposed model. The simulation results indicate that the proposed model predicts well qualitatively the collapse process of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd.     

工业CT在增强硬质聚氨酯泡沫塑料无损检测中的应用

为提高作为结构材料使用时硬质聚氨酯泡沫塑料(RPUF)的力学性能,在基体材料中添加增强材料形成了增强RPUF(RRPUF),RRPUF内部的材料组成及结构特征影响其力学性能。本文应用微焦点锥束体式工业CT技术,进行了玻璃纤维RRPUF三维结构的工业CT检测,获得了高分辨率的RRPUF三维结构CT图像,并解析了RRPUF内部结构特征,包括玻璃纤维及泡孔的形状、位置、尺寸、体积含量以及分布状况等。研究表明微焦点VCT技术可有效地实现RRPUF内部结构特征的检测及分析,为进一步研究RRPUF的性能提供了重要方法。     

钢衬钢筋混凝土压力管道外包混凝土的裂缝控制研究

基于钢衬钢筋混凝土压力管道在设计荷载下外包混凝土将带裂缝工作的基本承载特性,以缓解开裂与限裂间的矛盾为指导思想,将减小坝后背管外包混凝土裂缝宽度和提高开裂管道的耐久性作为研究目的,结合模型试验和有限元法,研究了一些裂缝控制措施的应用效果,以及有效的计算内水压力下钢衬外包混凝土裂缝宽度的公式。结果表明：总用钢量相同时,减薄钢衬,加大钢筋用量,减小裂缝宽度效果明显;减薄钢衬外包混凝土厚度,也可减小裂缝宽度;性能可靠的防水涂料具备黏接性强和变形能力高的基本性质,可进一步研究其对提高管道耐久性的长期作用;采用П-780-83规范中的裂缝宽度公式,计算结果与模型试验结果较为符合。     

钢筋混凝土带暗支撑双功能剪力墙的力学计算模型

提出了钢筋混凝土带暗支撑双功能剪力墙结构。在试验研究基础上，建立了该体系的力学计算模型，计算结果与实测结果符合较好。     

Properties of geogrid-reinforced marine slope due to the groundwater level changes

Evaluation of slope stability, especially in the absence of a proper bed such as marine soils, is one of the most important issues in geotechnical engineering. Using geogrid layers to enhance the strength and stability of embankments is regarded as a commendable stabilization method. On the other hand, groundwater level erratically fluctuates in coastal areas. Therefore, the aim of this research is to study the effects of groundwater level changes on stability of a geogrid-reinforced slope on loose marine soils in Qeshm Island, Iran. At first, geotechnical properties of the site were obtained by comprehensive series of geotechnical laboratory and in situ tests. Then, by simultaneous changes of groundwater level and several parameters such as embankment slope, loading, geogrid length, geogrid number, and tensile strength of geogrid, different characteristics such as embankment safety factor (SF), vertical and horizontal displacements at embankment top and embankment base were studied. It was observed that groundwater level had significant effects on behavior of the embankment. For most of the observations, by decreasing the groundwater level, the displacements decreased and consequently safety factor increased. Increasing the length, number, and tensile strength of geogrid led to the reduction of displacements and an increase in the safety factor.     

沿海砼结构耐久性问题研究现状与对策

混凝土耐久性能不良引起的适用性、安全性问题以及由此引发的环境、能源、经济问题在全球范围内已引起广泛的关注.而沿海城市经济的飞速发展和大规模的开发海洋资源使得混凝土结构面临严峻的海洋环境的挑战.因此,了解沿海混凝土结构耐久性问题的研究现状与对策具有十分重要的现实意义.综合分析了沿海砼结构性能退化的原因及解决办法并在此基础上指出进一步研究的可能方向.     

隧洞衬砌中湿喷钢纤维混凝土的应用

基于湿喷钢纤维混凝土的性质，讨论了喷射混凝土的特点及其在暂时支护与永久支护中的应用。     

玻璃钢作地面沉降监测标体的可行性研究

玻璃钢具有质量轻、强度高、耐腐蚀等特性,可作为达到特定工程目的的成型材料。本文通过论证,认为在地面沉降监测工程中为了更准确灵敏地反映地下岩土的变形,选用轻质高强度的玻璃钢作引测标体是可行的。此外,由于玻璃钢成本低,因此,还可使中小城市开展地面沉降监测时减少基础性投入。     

Enriched finite element procedures for analyzing decoupled bolts installed in rock mass

Numerical procedures are developed to analyze interaction between fully grouted bolts and rock mass using ‘enriched finite element method (EFEM)’. A solid element intersected by a rock bolt along any arbitrary direction is termed as ‘enriched’ element. The nodes of an enriched element have additional degrees of freedom for determining displacements, stresses developed in the bolt rod. The stiffness of the enriched element is formulated based on properties of rock mass, bolt rod and grout, orientation of the bolt and borehole diameter. Decoupling at grout–bolt interface and elasto‐plastic behavior of rock mass have also been incorporated into the EFEM procedures. The results of this method are compared with analytical pull‐out test results presented by Li and Stillborg (Int. J. Rock Mech. Min. Sci. 1999; 36 :1013–1029). In addition, a numerical example of a bolted tunnel is provided to demonstrate the efficacy of the proposed method for practical applications. Copyright © 2010 John Wiley & Sons, Ltd.