Strengthening of Brick Masonry Arches with Externally Bonded Steel Reinforced Composites

The objective of this study is to investigate the efficiency of an innovative technique for strengthening masonry arches, based on the use of high strength steel cords embedded in either an epoxy (steel reinforced polymer) or mortar matrix (steel reinforced grout). Ten prototypes of brickwork arches strengthened by composite laminates were tested under a monotonic vertical load applied at the quarter-span. Load tests were performed to compare the behavior up to collapse of strengthened masonry arches; the influence of the types of reinforcement (steel and carbon fibers) and matrices (epoxy and cementitious), as well as location of the strengthening layer (intrados, extrados, and both) and the presence of anchorage systems has been investigated. The experimental results highlight the enhanced strength of the arches reinforced with steel cords, as well as the role of the mechanical anchoring with regard to the resulting final strength.     

Experimental Bond Behavior of FRP Sheets Glued on Brick Masonry

This paper deals with the experimental characterization of the mechanical tensile and shear bond behavior of fiber-reinforced polymer (FRP) sheets externally glued on masonry prisms, in terms of load capacity and stress distribution along the bonded length. The brick masonry adopted tries to replicate ancient brick masonry, by using handmade low-strength solids bricks and low-strength lime-based mortar. Key parameters relative to the FRP-masonry interface response, particularly bonded length, FRP materials, anchor scheme adopted, and shape of masonry substrate, were studied. Finally, an analytical bond stress-slip formulation was developed, allowing deducing local bond stress-slip curves directly from the experiments.     

Free Out-of-Plane Vibrations of Masonry Walls Strengthened with Composite Materials

The natural frequencies and the out-of-plane vibration modes of one-way masonry walls strengthened with composite materials are studied. Due to the inherent nonlinear behavior of the masonry wall, the dynamic characteristics depend on the level of out-of-plane load (mechanical load or forced out-of-plane deflections) and the resulting cracking, nonlinear behavior of the mortar material, and debonding of the composite system. In order to account for the nonlinearity and the accumulation of damage, a general nonlinear dynamic model of the strengthened wall is developed. The model is mathematically decomposed into a nonlinear static analysis phase, in which the static response and the corresponding residual mechanical properties are determined, and a free vibration analysis phase, in which the dynamic characteristics are determined. The governing nonlinear differential equations of the first phase, the linear differential eigenvalue problem corresponding to the second phase, and the solution strategies are derived. Two numerical examples that examine the capabilities of the model and study the dynamic properties of the strengthened wall are presented. The model is supported and verified through comparison with a step-by-step time integration analysis, and comparison with experimental results of a full-scale strengthened wall under impulse loading. The results show that the strengthening system significantly affects the natural frequencies of the wall, modifies its modes of vibration, and restrains the deterioration of the dynamic properties with the increase of load. The quantification of these effects contributes to the understanding of the performance of damaged strengthened walls under dynamic and seismic loads.     

Homogenization of Masonry Using Numerical Simulations

Homogenization is one of the most important steps in the numerical analysis of masonry structures where the continuum method is used. In the present study, equivalent elastic properties, strength envelope, and different failure patterns of masonry material are homogenized by numerically simulating responses of a representative volume element (RVE) under different stress conditions. The RVE is modeled with distinctive consideration of the material properties of mortar and brick. In the numerical simulation, various displacement boundaries are applied on the RVE surfaces to derive the stress-strain relation under different conditions. The equivalent overall material properties of the RVE are averaged by integrating the stresses and strains over the entire area. Failure of masonry is defined by three different modes, namely, tensile failure of mortar (Mode I), shear failure of mortar or combined shear failure of brick and mortar (Mode II), and compressive failure of brick (Mode III). The homogenized elastic properties and failure model can be used to analyze large-scale masonry structures.     

Experimental Behavior of FRP Strengthened Masonry Arches

This paper deals with the experimental behavior of solid clay brick masonry arches strengthened with glass fiber-reinforced polymer composites. Twelve half-scaled segmental masonry arches subjected to a load applied at the quarter span were tested under displacement control up to failure. The arches were built using handmade low strength bricks and a commercial lime-based mortar, trying to mimic ancient structures. Besides reference unreinforced arches, five different strengthening arrangements, including the use of spike anchors, were studied. The experimental results provide significant information for validation of advanced numerical models and analytical tools and for code drafting. The experimental results also show that (1) only continuous strengthening strategies are able to prevent typical local failure mechanisms of unreinforced arches; (2) strengthening at the intrados is the most effective option to increase strength; and (3) strengthening applied at the extrados provides the higher deformation capacity prior to failure, endowing arches with considerable ductility behavior.     

太钢新建4350 m~3高炉长寿炉缸炉底研究

以太钢新建4 350m3高炉为例,论述了为实现高炉炉缸炉底的长寿,从高炉的设计、选材和砌筑等方面采取的一系列措施。炉缸设计采用"传热法",炉底设计采用"隔热法",炉缸炉底整体设计采用了"扬冷避热梯度布砖法"。炉缸选材使用优质高导热系数的碳砖,为了克服冷却壁与碳砖之间捣打料带来较大热阻,砌筑过程中碳砖采用顶砌冷却壁方式,并且严格控制砖衬宽度;炉壳与冷却壁采用分段灌浆。通过建立炉缸炉底传热数学模型,进一步表明了该高炉炉缸炉底优良的性能,投产后1 150℃等温线位于炉缸砖衬热面附近,有利于渣铁壳的形成;同时碳砖内部温度普遍低于750℃,温度梯度较小,碳砖脆化及热应力对砖衬的破坏作用较轻,为日后实现长寿炉缸炉底创造了必要的条件。     

Prototype Robotic Masonry System

The introduction of robots and automation technology to construction operations will require considerable efforts to understand the mechanics of the many tasks better as they relate to building structures. To control arms, grippers, nozzles, and other production devices automatically, the mechanics of tools as they interact and work with the different construction materials requires extensive knowledge. One approach to learn about the behavior of all the components of an automated system for construction is to build scaled prototypes that are able to handle the actual material. This paper describes the design of an automated masonry system for prefabricating brick panels. It discusses the conditions that affect the bond strength of the masonry. It then describes the design and development of a Cartesian robot actuator and scaled‐down mortar spreader system built to test the bond strengths and accuracy of robotically placed bricks. The actual fabrication of the partially functional prototype helped the researchers to gain hands‐on familiarity with the many real‐world obstacles in using automation and robotics in construction. However, the learning experience also included an appreciation of the potentials offered by using advanced technologies in construction.     

Experimental In-Plane Behavior of Tuff Masonry Strengthened with Cementitious Matrix–Grid Composites

Tuff buildings are a significant part of the Mediterranean area and are to be preserved from a structural viewpoint especially in seismic areas. Over the past few decades, the interest in strengthening of historical tuff masonry structures has led to developing specific and noninvasive architectural and engineering strategies. In the present paper, a comprehensive experimental program on tuff masonry panels is presented; the results are intended as a contribution to the knowledge of in-plane behavior of tuff masonry strengthened with composite materials. Particularly, a cement based matrix-coated alkali resistant glass grid system (CMG) was used to strengthen tuff masonry walls; different CMG layouts were selected, and overall performances were compared with those of as-built ones. The characterization of base materials was carried out first, followed by uniaxial tests of masonry and shear tests on triplets. Finally, tuff masonry panels were subjected to diagonal compression loading under displacement control in order to measure their in-plane deformation and strength properties, including the postpeak softening regime in view of seismic applications.     

Homogenized Strategy toward Constitutive Identification of Masonry

The aim of this work is the study of masonry behavior by means of a homogenized model in several perturbative parameters. The difficulty in the mechanical modeling of masonry depends on its discrete character, as such, masonry is composed of blocks between which mortar is laid. Moreover, the building procedure leads to head and bed joint stiffnesses which may be different. Within the limits of the hypotheses of the model, the capacity of the homogenization method to grasp these features was investigated in this study. The homogenization model proposes a constitutive identification between the masonry and a standard continuum. Moreover, the introduction of two perturbative parameters enables one to grasp the influence of variations in the relative thickness of the joints with respect to the dimensions of the blocks, and of variations in the deformability of the latter on the constitutive homogenized functions. On a structural level, for a sample case, the capacity of the homogenized continuous model to describe the characteristic aspects of the behavior of masonry has been investigated by comparison with a discrete model.     

Bricks from Petroleum Effluent Treatment Plant Sludge: Properties and Environmental Characteristics

A voluminous and hazardous sludge containing a high amount of hydrocarbons and several trace metals is generated in petroleum oil field effluent treatment plants. The aim of this study was to utilize the sludge in preparing environmentally acceptable masonry bricks in a commercial brick plant. The effect of the sludge on the plasticity behavior of the brick raw mix was investigated. The addition of the sludge reduces the requirement of process water and fuel. The fired bricks meet all the requirements of the Indian Standard Specification. The bricks were subjected to toxicity characteristics leaching protocol leaching tests. Most of the toxic metals are fixed in the vitrification process and the leachates values meet the Environmental Protection Agency’s requirement for recycling of hazardous materials.     

Linear Elastic and Viscoelastic Deformation Behavior of Ice

The dependence of overall elastic and viscoelastic behavior of polycrystals on properties of hexagonal single crystals of ice is predicted using established methods of micromechanical analysis. The self-consistent and bounding methods are used first to relate elastic behavior of S2 columnar and granular ice to single crystal properties. The results for S2 ice are then extended to viscoelastic behavior in order to relate overall creep behavior, as well as other time and rate-dependent behavior, to crystal parameters. Good agreement with experimental results is shown. Emphasis in this paper is on linear viscoelastic behavior of S2 ice due only to intragranular creep. The effect of this creep and grain boundary sliding on microcracking is considered briefly in the concluding remarks.     

Directionally Constrained Viscoplasticity for Metal Matrix Composites

A theoretical framework along with an experimental comparison and numerical simulation is presented, for the modeling of the viscoplastic behavior of metal matrix composites (MMCs). MMCs are finding increasing applications in aerospace structures. MMCs have strong directional properties that directly influence the evolution of the internal variables, namely, the backstress and viscoplastic strain. The model is developed within a micromechanical framework for MMCs using the equilibrium surface approach. The directional properties of MMCs are incorporated by proposing a constrained equilibrium surface, which is based on the constrained stress terms proposed. The micromechanical framework combines the viscoplastic properties of the matrix with the elastic properties of the fiber. Model-generated experimental comparisons and simulations are also presented.     

Three-Dimensional Micromechanical Finite-Element Network Model for Elastic Damage Behavior of Idealized Stone-Based Composite Materials

This paper presents a three-dimensional (3D) micromechanical finite-element (FE) network model for predicting elastic damage behavior of the idealized stone-based materials. Stone-based composite materials have multiphase structures: an aggregate (or stone) skeleton, a binding medium, fillers, and air voids. Numerical simulation of the micromechanical behavior of the idealized stone-based materials was accomplished by using a microframe element network model that incorporated the mechanical load transfer between adjacent particles. The elastic stiffness matrix of this special element was obtained from an approximate elastic stress-strain analysis of straight cement between particle pairs. A damage-coupled microframe element was then formulated with bilinear damage laws, including elastic and softening behavior based on the equivalent fracture release energy. Indirect tension and compression simulations were conducted with developed FE models on the idealized digital samples of the stone-based materials. These simulations predicted the internal microdamage distribution and global fracture behavior of these samples, which qualitatively agree with the laboratory observations. The results indicate that the developed FE models have the capability to predict the typical loading-related damage behavior observed from the stone-based materials.     

Temperature Dependence of Elastic–Plastic Properties of Fine-Pitch SAC 0307 Solder Joint Using Nanoindentation Approach

This paper highlights the advantages of using the nanoindentation approach over the conventional method for the mechanical characterization of components used in electronic packaging. The limitation of the conventional method has become more critical with the miniaturization of electronic packages, giving inadequate information regarding the mechanical properties of metallurgical interconnections. The load–displacement approach via nanoindentation was used in this study to determine the micromechanical properties of a fine-pitch solder joint subjected to aging for 1000 hours. This approach is more advantageous than tensile testing, as it focuses on the elastic behavior unlike that in conventional mechanical testing. The nanoindentation analysis results showed that the elastic–plastic behavior before failure can be assessed in a wide range of temperatures and thus help study the temperature dependence on the mechanical properties of fine-pitch solder joints. The characterization was done beyond the elastic range beforehand of conventional method. The modulus and hardness of the fine-pitch SAC 0307 solder joint decreased while its plastic and elastic behaviors became pronounced at higher aging temperatures. This implies that solder joints become weaker and less resilient with increasing temperature, at least for a duration of 1000 hours.     

Elastoplastic Damage Behavior of a Mortar Subjected to Compression and Desiccation

This paper deals with experimental investigation and numerical modeling of drying effects on the mechanical behavior of cement-based materials. First, the main results from an experimental study on the mechanical behavior (failure strength, induced damage, and plastic deformation) of a mortar subjected to the desiccation process are presented. Then, a coupled elastoplastic damage model is proposed to describe the mechanical behavior of cement-based materials subjected to tensile and compressive stresses. A particular emphasis is put on the pressure sensitivity of plastic flow and damage evolution. Capillary effects on mechanical behavior due to desiccation have been taken into account in the framework of partially saturated porous media. Finally, numerical simulations and experimental data are compared in order to verify the capacity of the model to reproduce the basic characteristics of the mortar in saturated and unsaturated conditions.     

激发剂对赤泥-黄金尾矿-碱矿渣体系性能的影响

为提高危险固体废弃物的综合利用水平,依据赤泥、黄金尾矿及矿渣三种固体废弃物的特性,研究NaOH、KOH和Na₂SiO₃三种激发剂对赤泥-黄金尾矿碱矿渣体系性能的影响。并在此基础上通过XRD、FT-IR、TGA/DSC和SEM等表征手段明晰其微观反应机理。结果表明,当Na₂SiO₃为激发剂时,复合胶凝材料体系的激发效果最好,标养3天的胶砂抗折强度和抗压强度分别达到5.5和23.5 MPa;标养28天的胶砂试件抗折强度和抗压强度分别为8.8和43.21 MPa,可达到P·I42.5水泥强度指标。通过微观分析得知,试件的主要强度来源物质为钙矾石和水化硅铝酸钙凝胶,力学性能高的材料其微观结构更为密实,碱激发水化产物数量更多。     

In-Plane Shear Behavior of Masonry Panels Strengthened with NSM CFRP Strips. I: Experimental Investigation

An experimental investigation was conducted to study the in-plane shear behavior of masonry panels strengthened with near-surface mounted (NSM) carbon fiber-reinforced polymer strips (CFRP). As part of the study four unreinforced masonry panels and seven strengthened panels were tested in diagonal tension/shear. Different reinforcement orientations were used including vertical, horizontal, and a combination of both. The effect of nonsymmetric reinforcement was also studied. The results of these tests are presented in this paper, and include the load-displacement behaviors, crack patterns, failure modes, and FRP strains. The results showed that the vertically aligned reinforcement was the most effective, with significant increases in strength and ductility observed. The dowel strength of the vertical reinforcement did not likely contribute significantly to the shear resistance of the masonry. Instead, it was likely that the vertical reinforcement acted in tension to restrain shear induced dilation and restrain sliding. In some panels cracking adjacent to the FRP strip, through the panel thickness was observed. This type of cracking reduced the bond between one side of the FRP strip and the masonry, and led to premature debonding. A comparison of the test results with the results of other tests from the literature is also presented in this paper.     

Assessment of Mortar and Brick Strength in Earthquake-Affected Structures in Peru Using a Schmidt Hammer

This study describes results of surveys with Schmidt hammer conducted after the earthquake of August 15, 2007 in coastal cities of Ica, Pisco, and Chincha, Peru. Statistical analysis included comparison of data on compressive strength collected from various types of buildings in damaged and intact walls and bricks. Results of statistical analysis suggest that architecture and nonstructural building design considerations in masonry structures may be more important determinants of seismic resistance than construction material strength. Comparison of mortar samples with respect to structure ownership revealed that strength of mortar at test locations in privately owned buildings was significantly greater than in public buildings.     

Curved Sandwich Panels Subjected to Temperature Gradient and Mechanical Loads

The results of a detailed study of the nonlinear response of curved sandwich panels with composite face sheets, subjected to a temperature gradient through the thickness combined with mechanical loadings, are presented. The analysis is based on a first-order shear-deformation Sanders-Budiansky-type theory, including the effects of large displacements, moderate rotations, transverse shear deformation, and laminated anisotropic material behavior. A mixed formulation is used with the fundamental unknowns consisting of the generalized displacements and the stress resultants of the panel. The nonlinear displacements, strain energy, principal strains, transverse shear stresses, transverse shear strain energy density, and their hierarchical sensitivity coefficients are evaluated. The hierarchical sensitivity coefficients measure the sensitivity of the nonlinear response to variations in the panel parameters, the effective properties of the face sheet layers and the core, and the micromechanical parameters. Numerical results are presented for cylindrical panels subjected to combined pressure loading, edge shortening or extension, edge shear, and a temperature gradient through the thickness. The results show the effects of variations in the loading and the panel aspect ratio, on the nonlinear response, and its sensitivity to changes in the various panel, effective layer, and micromechanical parameters.     

FRP Confinement of Square Masonry Columns

The problem of masonry columns subjected to structural deficiency under axial load was studied and reported in this paper. The results of an extensive experimental campaign are presented in order to show the behavior of columns built with clay or with calcareous blocks, commonly found in southern Italy, especially in historical buildings. Rectangular masonry columns were tested for a total of 33 specimens; uniaxial compression tests were conducted on columns taking into account the influence of several variables: different strengthening schemes (internal and/or external confinement), curvature radius of the corners, amount of fiber-reinforced polymer (FRP) reinforcement, cross-section aspect ratio, and material of masonry blocks. Materials characterization was preliminarily carried out including a mechanical test on plain masonry. For all cases the experimental results evidenced a significant increase in load carrying capacity and ductility after FRP strengthening, which identified the columns as ductile elements despite the brittle nature of the unconfined masonry. Differences in mechanical behavior, due to the geometry of the columns, to the nature of different materials, to different strengthening schemes, and to the amount of reinforcement, are presented and discussed in the paper. The calibration of design equations recently developed by Italian National Research Council, CNR was conducted to compare analytical prediction and experimental results. The same procedure was applied to calibrate an analytical model recently published, in which the existing coefficients are related only to clay. Here the model is applied to limestone for the first time. Thus, new important information is furnished to researchers and practitioners involved in structural assessment and strengthening of compressed elements in historical buildings.