碳纤维布加固砌体填充墙抗近距离小当量炸药爆炸数值模拟研究

该文采用数值模拟方法对碳纤维布加固砌体填充墙抵抗近距离小当量炸药爆炸进行了研究。进行了1/2缩比的砌体填充墙爆炸实验,对文中墙体抗爆分析数值分析方法的有效性进行了检验。建立了实际墙体的有限元模型,采用LS-DYNA程序对单层和多层纤维布加固的砌体填充墙在爆炸荷载作用下的破坏形式进行了分析。研究表明:近距离小当量爆炸时,砌体填充墙的破坏主要表现为爆炸近区的砌块在爆炸荷载的驱动下,撕裂纤维布向后以较高的速度飞散运动;纤维布的破坏主要表现为横向拉伸应力超过强度极限而产生拉伸断裂,并由爆炸近区分别沿水平和垂直方向向周围发展;当纤维布层间粘结能力有限时,难以发挥纤维方向抗拉强度高的优点。     

无构造柱退层自建民居抗震加固试验研究

针对无构造柱退层砖砌体自建民居的破坏形式,设计了综合加固方案,即第一层退层处采用预应力钢筋、顶层粘贴碳纤维布进行加固。通过对加固后民居1/4模型的模拟振动台试验表明：（1）民居加固后能够承受加速度峰值为0.5g的地震作用,抗震性能较加固前有明显提升;（2）民居加固后的破坏形式为墙体开裂破坏、窗间墙破坏、墙角局部破坏等;第二层纵墙退层处开裂破坏严重,为整个结构的薄弱部位。此外,砌体结构的有限元模拟可采用整体连续模型。计算中砌体采用相同抗压强度的混凝土进行等效,通过调整混凝土的塑性应力-应变关系和损伤因子来实现材料的非线性,从而实现模型的非线性分析;加固采用的预应力可用分布压力简化加载,碳纤维布作用可采用壳单元模拟。通过与试验结果的对比,说明这种模拟方法是可行的。本文的研究成果,可用于我国村镇同类结构形式民居的加固与改造。     

FRP-砖界面粘结-滑移计算模型

近年来国内外对FRP加固砌体结构技术的应用和研究呈现出快速发展的趋势。FRP-砖的界面力学行为及剥离破坏是FRP加固砌体技术应用的关键基础问题,也是难点问题。该文主要进行了FRP-砖界面粘结性能有限元数值模拟,利用建立的计算模型成功模拟了加载端荷载-位移曲线、FRP-砖界面的滑移分布、粘结应力分布。分析了各影响因素对极限粘结荷载的影响,并与试验结果进行了对比。结果表明:吻合较好,该文采用FRP-砖界面粘结-滑移计算模型是可行的。     

冻融环境下砖砌体组合墙的抗震性能试验EI北大核心CSCD

为研究冻融大气环境下构造柱-圈梁约束砖砌体墙的抗震性能,利用气候模拟实验室对4片组合单墙片和4片组合双墙片试件进行了加速冻融试验,进而对其进行了拟静力加载试验。试验结果表明:试件在低周反复荷载作用下均表现为剪切破坏,冻融环境对砖砌体组合墙的破坏形态有一定影响;随着冻融循环次数的增加,试件的开裂荷载和极限荷载不断降低,刚度及耗能能力逐渐退化,而开裂位移和极限位移逐渐增加;冻融循环次数相同时,组合双墙片的承载能力、变形能力和耗能能力均高于组合单墙片,其滞回曲线更加饱满,延性系数约为组合单墙片的1.2倍,刚度退化速率明显降低,表明在冻融环境下设置多道构造柱可有效提高砖砌体组合墙的抗震性能。建立了考虑冻融循环作用次数的砖砌体组合墙受剪承载力公式,且计算结果与试验结果吻合较好。     

冻融环境下砖砌体组合墙的抗震性能试验

为研究冻融大气环境下构造柱-圈梁约束砖砌体墙的抗震性能,利用气候模拟实验室对4片组合单墙片和4片组合双墙片试件进行了加速冻融试验,进而对其进行了拟静力加载试验。试验结果表明:试件在低周反复荷载作用下均表现为剪切破坏,冻融环境对砖砌体组合墙的破坏形态有一定影响;随着冻融循环次数的增加,试件的开裂荷载和极限荷载不断降低,刚度及耗能能力逐渐退化,而开裂位移和极限位移逐渐增加;冻融循环次数相同时,组合双墙片的承载能力、变形能力和耗能能力均高于组合单墙片,其滞回曲线更加饱满,延性系数约为组合单墙片的1.2倍,刚度退化速率明显降低,表明在冻融环境下设置多道构造柱可有效提高砖砌体组合墙的抗震性能。建立了考虑冻融循环作用次数的砖砌体组合墙受剪承载力公式,且计算结果与试验结果吻合较好。     

ECC面层加固受损砖砌体墙抗震性能试验研究

高延性纤维增强水泥基复合材料(ECC)具有高强度、高延性和受拉应变硬化等特性,在加固工程中具有广泛的应用前景。该文对4片采用ECC面层加固的受损砖墙进行了低周反复荷载试验,并与相关文献中4个试件进行比较,研究了ECC面层加固砖砌体墙的破坏机理、破坏形态、滞回特性和变形能力。结果表明:1) 采用ECC面层加固受损砖砌体墙,可显著提高砖墙的变形能力,改善加固后墙体的抗震性能;2) ECC面层对内部砖墙形成良好的约束作用,可显著改善砖墙的脆性破坏模式,是一种有效的砌体结构加固方法;3) 改善ECC面层与构造柱之间的粘结性能,保证ECC面层有效传递剪力,对提高加固后墙体的整体性能具有重要作用。该文的研究结果为砌体结构抗震加固提出了一种新方法,具有良好的推广和应用前景。     

基于装配式技术加固的砌体墙片的力学性能研究

基于装配式技术的砌体结构加固方案可以有效提高结构的抗震能力。采用预制钢筋混凝土墙板对原有的砌体墙片进行双面外贴加固,并用销键、灌浆、后浇带等连接方式保证砌体墙片与预制钢筋混凝土墙板的共同工作。该文通过非线性有限元模型分析了未加固砌体及加固砌体结构在循环往复加载下的力学行为,探讨混凝土墙板和砌体砖墙之间的传力途径,验证加固方法和三种连接措施的有效性。分析证明:采用预制钢筋混凝土贴墙墙板的加固方案可以显著提高砌体结构的抗震性能,强度提高3倍~4倍,刚度提高2倍~3倍,满足现行抗震规范的要求。三种连接方式中,后浇带最有效,在弹性阶段传递了70%的荷载,在后期传递了80%的荷载。     

组合材料加固砖砌体的有限元模拟方法

基于ABAQUS有限元软件,提出了组合材料加固砌体数值建模方法。该方法是在未加固砌体整体式模型的基础上,结合分离式思想建立组合材料加固砌体模型。通过对8片采用粘钢-聚合物砂浆组合材料加固的砖砌体墙体（其中,4片采用粘贴正交钢片,4片采用粘贴斜撑钢片）的拟静力试验结果进行了数值模拟对比分析,结果显示:模拟所得墙体滞回、骨架及刚度退化曲线与试验曲线基本吻合;仿真破坏形态与试验现象一致;计算所得荷载、位移、延性和耗能等全部指标中有81%的误差在20%以内。     

CFRP加固砌体结构的力学性能分析

在分析碳纤维加固的砖砌体在水平周期反复荷载作用下试验结果的基础上,研究了碳纤维加固砖砌体的约束及抗倒塌机理;建立了墙体侧向位移与碳纤维应变、碳纤维应变与墙体抗震剪切强度的关系;讨论了不同加固方式、碳纤维面积百分率等在墙体不同受力阶段对墙体抗剪承载能力和变形性能的作用与影响;提出了计算碳纤维加固墙体承载能力和变形的计算方法。计算方法考虑了不同粘贴碳纤维角度、碳纤维面积百分率等对墙体承载能力和变形性能的影响;推导了最优粘贴加固角;提出了改进的粘贴加固方法以提高加固效果。     

钢筋网高延性混凝土加固砖柱偏心受压性能试验及计算方法研究

通过27个钢筋网高延性混凝土(HDC)面层加固砖柱的偏心受压试验,研究了不同偏心距荷载作用下加固砖柱的破坏形态和受力性能,并对荷载-位移曲线、极限承载力以及砖柱截面应变进行了分析。结果表明:钢筋网HDC面层与砌体具有良好的协调工作能力,可大幅度提高砖柱的承载力和变形能力,改善了砖柱的脆性破坏特征,并且提高了砖柱的整体性;随偏心距增大,砖柱的承载力逐渐降低,但初始偏心距并未削弱钢筋网HDC面层的加固效果。考虑HDC的抗拉作用,并对加固层的应力进行计算简化,得到钢筋网HDC面层加固偏心受压砖柱的承载力计算公式,与试验结果吻合较好。分析了二次受力对砖柱承载力的影响,给出了不同初始偏心荷载作用下的HDC抗压强度利用系数,可供加固设计参考使用。     

Assessment of bonding stresses between FRP sheets and masonry pillars during delamination tests

Under the simplifying assumption of perfect adhesion, motivated by the wide adoption of highly resistant glues, delamination of FRP-reinforced masonry pillars turns out to be governed exclusively by the non-linear behavior of the quasi-brittle, heterogeneous support. However, at the structural level, the macroscopic delamination response can be described effectively by concentrating all the sources of dissipation and non-linearity at the masonry-FRP interface, and assuming the support to behave as a linear-elastic body. In this paper, a detailed and critical comparison between two different fully three-dimensional finite element models is developed: (i) a model in which only masonry (i.e. brick and mortar independently) is damageable whilst the FRP reinforcement adheres perfectly to the support (namely, exclusively bulk damage is accounted for), and an alternative model (ii) in which a cohesive, zero thickness interface between the FRP and the support is considered (i.e. interface damage), whilst masonry behaves as a heterogeneous linear elastic material. The overall response during delamination and local stress distributions at the interface are critically investigated, varying the FRP reinforcement width.     

A new shear-flexible FRP-reinforced concrete slab element

In this paper, a simple shear-flexible rectangular layered FRP-reinforced concrete slab element is developed based on Mindlin–Reissner plate theory and Timoshenko’s composite beam functions for nonlinear finite element analysis of FRP-reinforced concrete slabs. The Timoshenko’s composite beam functions are developed for FRP-reinforced concrete slabs based on those for composite laminates. The plane displacement interpolation functions of a quadrilateral isoparametric element with drilling degrees of freedom are employed to describe the membrane effects and the bending effects of the slab element are represented by the rotation functions of the slab element derived from Timoshenko’s composite beam functions. Both geometric nonlinearity and material nonlinearity of the materials are included in the new element. The efficiency of the element for nonlinear finite element analysis of FRP-reinforced concrete slabs is validated by comparing the computed results of two numerical examples with those obtained from lab tests.     

Compressive behaviour of a new reinforced masonry system

This paper presents the behaviour in compression of an innovative reinforced masonry system. The system is made of horizontally perforated units, having common steel bars or prefabricated trusses as horizontal reinforcement. At the wall edges or crossings, confining columns for vertical reinforcement are built with vertically perforated units. Experimental tests, aimed at obtaining basic mechanical characterisation of the construction system, were performed on single constitutive elements i.e., confining columns and masonry panels made of horizontally perforated units, and on completed reinforced masonry walls. Non-linear numerical models, interpreting stress and strain distributions, were developed on the basis of the results. In particular, this paper presents: (a) results of compression tests on columns, masonry panels, and complete reinforced masonry system; (b) comparison of walls built with two types of horizontal reinforcement; (c) outcome of numerical models; and (d) effectiveness of various design equations to evaluate the compressive strength of the system.     

Shear effect on seismic behaviour of masonry walls

Firstly, a finite element numerical model for nonlinear dynamic analysis of masonry walls is briefly presented. The model can simulate the main nonlinear effects of masonry and reinforced concrete. It is simple and intended to the engineering application. A macro model of masonry is adopted for simulation its behaviour in compression and for cracks modelling in tension. Two constitutive models are implemented to describe the shear resistance of the masonry wall: One that does not take the effect of the shear failure of masonry (Model 1), and second which takes into account shear failure of masonry (Model 2). By using the numerical model, the shear effect of masonry on the behaviour of two‐storey unreinforced and confined masonry walls exposed to harmonic base acceleration was investigated. The height to length ratio of the walls and the quality of masonry are varied. Analysis results for Model 1 and Model 2 are significantly different. Model 1 gives a significantly higher load bearing capacities of masonry. It was concluded that the shear effect of masonry significantly depends on the type of the masonry walls (unreinforced, confined), the quality of the masonry and height to length ratio of masonry walls.     

Nonlinear finite element analyses of FRP-reinforced concrete slabs using a new layered composite plate element

A simple and shear-flexible rectangular composite layered plate element and nonlinear finite element analysis procedures are developed in this paper for nonlinear analysis of fiber reinforced plastic (FRP)-reinforced concrete slabs. The composite layered plate element is constructed based on Mindlin–Reissner plate theory and Timoshenko’s composite beam functions, and transverse shear effects and membrane-bending coupling effects are accounted for. Both geometric nonlinearity and material nonlinearity of the materials, which incorporates tension, compression, tension stiffening and cracking of the concrete, are included in the new model. The developed element and the nonlinear finite element analysis procedures are validated by comparing the computed numerical results of numerical examples with those obtained from experimental investigations and from the commercial finite element analysis package ABAQUS. The element is then employed to investigate the nonlinear structural behavior and the cracking progress of a clamped two-way FRP-reinforced concrete slab. The influences of reinforcement with different materials, ratio and layout in tension or compressive regions on structural behavior of the clamped slabs are investigated by parametric studies.     

MIXED INTEGER PROGRAMMING FOR THE OPTIMAL (LEAST COST) DESIGN OF ECCENTRICALLY LOADED MASONRY BEARING WALLS:Part II. High Eccentricities

A mixed integer approach for the least cost design of structural masonry walls with high eccentricities is developed. The integer variables in the approach are used to select the optimum values from a range of discrete block sizes, discrete grouting conditions, and discrete reinforcement levels. The structural constraints in the model are based upon the requirements of the Transformed Section type of analysis for masonry walls. The non-linear functions representing the relationships for determining the resisting capacities of the masonry element are approximated by linear functions which come very close in form and results to the original curves. Application of the model to an example problem demonstrates that in spite of the integer requirements, the approach is easily and efficiently solved using a standard software package.     

Model validation and parametric study on the blast response of unreinforced brick masonry walls

Numerical simulations are carried out to estimate the response and damage of unreinforced brick masonry walls subjected to explosive blast loading based on the transient dynamic finite element program LS-DYNA. A previously developed dynamic plastic damage model was used for brick and mortar. A new model for strain rate effects of bricks and mortar is included in the numerical analysis. The results obtained from the numerical models are compared with field test data and good agreement can be found. Parametric studies are conducted to evaluate the effect of material strength, boundary conditions, and thickness of the wall on the blast response of unreinforced brick masonry walls. It was found that boundary conditions and wall thickness significantly affect the blast response, while the effect of material strength is relatively small.     

CMYK与RGB颜色空间数字水印 在印刷品中的应用比较

为提高水印抗印刷/扫描攻击的鲁棒性,比较了在CMYK与RGB颜色空间嵌入的水印经印刷/扫描后提取的效果.采用离散小波变换域傅里叶全息数字水印算法生成水印图像,经印刷/扫描后,可以提取到水印;然而,由于印刷/扫描过程中颜色空间的转换,使得原本嵌入某一颜色通道的水印转移到其他通道,降低了单通道提取的水印质量;且相对于RGB颜色空间,在CMYK颜色空间嵌入水印生成的水印图像经历印刷/扫描后提取到的水印质量普遍较高,说明CMYK→RGB→CMYK颜色空间的转换相对于RGB→CMYK→RGB颜色空间的转换,对水印图像的改变较小.为减小印刷/扫描攻击的影响,考虑下一步研究工作主要集中在CMYK颜色空间嵌入水印.     

Nonlinear finite element analysis of masonry wall strengthened with CFRP strips

In many experimental studies, it has been proved that unreinforced masonry (URM) brick walls have high strength against lateral forces acting in plane. However, out-of-plane strength of URM brick walls against lateral forces has found to be quite low. According to the experiences that were obtained from the major earthquakes, the low out-of-plane performance of URM brick walls resulted in excessive loss of human lives during an earthquake, hence the strengthening of URM brick walls with CFRP strips has been appeared to be a very important subject. However, very limited literature has been found. Especially, the data obtained from experimental studies must be increased for the true understanding of the behavior of strengthened brick walls under out-of-plane lateral forces. However, in most cases, this procedure required large number of expensive experiments. At this stage, numerical analysis can be an appropriate choice, thus in this paper a finite element model is presented for modeling URM brick walls that are strengthened with CFRP strips. The numerical results are compared with the experimental ones and consistent results are obtained from the finite element model. General purpose finite element analysis software ANSYS is used throughout this study. Contact elements are used along the masonry wall–CFRP strip interfaces for the investigation of the stress distribution and load – strain behavior.