Bond Analysis of Titanium Rods Embedded in Masonry

Among the techniques utilized for strengthening masonry structures with advanced materials, the adoption of near-surface mounted (NSM) titanium rods stands out as a promising method for increasing the flexural and shear strength of masonry structures. This method is also known as Bed Joint Reinforcement. Ensuring an effective performance of this technique hinges on establishing a strong bond between the NSM reinforcement and the substrate masonry material. The primary objective of this project was to study the mechanics of this bond using NSM threaded and smooth titanium rods while scrutinizing the impact of key parameters on bond performance. Variables under investigation encompassed the rod type (smooth and threaded), bond length, and the material used to fill the groove (type of mortars). It was found that threaded rods outperformed all other types investigated, and pull-out strengths can be significantly improved through careful selection and optimization of the mortar type and bond length.

Ceramic Stress Sensor Based on Thick Film Piezo-Resistive Ink for Structural Applications

This paper presents a ceramic stress sensor with the dimension of a coin, able to measure the compressive force (stress) applied to its two round faces. The sensor is designed and engineered to be embedded inside concrete or masonry structures, like bridges or buildings. It provides good accuracy, robustness, and simplicity of use at potentially low cost for large-scale applications in civil structures. Moreover, it can be calibrated temperature compensated, and it is inherently hermetic, ensuring the protection of sensitive elements from the external environment. It is, therefore, suitable for operating in harsh and dirty environments like civil constructions. The sensor directly measures the internal stress of the structure, exploiting the piezo resistivity of thick film ink based on ruthenium oxide. It is insensitive with respect to the stiffness of the embedding material and the variation of the surrounding material properties like concrete hardening, shrinkage, and creep as it decouples the two components of stress.

Out-of-plane performance of structurally and energy retrofitted masonry walls: geopolymer versus cement-based textile-reinforced mortar combined with thermal insulation

This paper examines the out-of-plane performance of masonry walls (representative of infills in reinforced concrete frames) which have been upgraded with an outer skin of integrated structural and an energy retrofitting system. The benefits of such an integrated system are mainly cost-related. Nevertheless, before moving to full-scale applications, additional benefits to the structural performance need to be investigated. In this study, the examined configurations of this composite system comprised either thermal insulation boards bonded directly to the wall followed by layers of textile-reinforced mortar (TRM), or thermal insulation boards bonded in-between two TRM layers. Other than the retrofitting layers configuration, the following parameters were also investigated: a) the binder type (cement-based versus geopolymer-based mortars), and b) the textile type (open mesh glass fibre textile versus basalt fibre textile). The results of this experimental study are discussed in terms of failure modes, post-cracking stiffness and ultimate capacities. Overall, this study highlights the mechanical benefits of the TRM plus thermal insulation system while providing insights on the bond performance between the different materials selected. An important finding is that the integrated system is even more effective than a standard TRM application. Finally, the geopolymer mortar seems to be equivalent in terms of performance to the commercially available cement-based mortars.

Productivity Measurement through IMU-Based Detailed Activity Recognition Using Machine Learning: A Case Study of Masonry Work

Although measuring worker productivity is crucial, the measurement of the productivity of each worker is challenging due to their dispersion across various construction jobsites. This paper presents a framework for measuring productivity based on an inertial measurement unit (IMU) and activity classification. Two deep learning algorithms and three sensor combinations were utilized to identify and analyze the feasibility of the framework in masonry work. Using the proposed method, worker activity classification could be performed with a maximum accuracy of 96.70% using the convolutional neural network model with multiple sensors, and a minimum accuracy of 72.11% using the long short-term memory (LSTM) model with a single sensor. Productivity could be measured with an accuracy of up to 96.47%. The main contributions of this study are the proposal of a method for classifying detailed activities and an exploration of the effect of the number of IMU sensors used in measuring worker productivity.

Experimental Analysis of the Mechanical Response of Masonry Columns Partially Confined with PBO FRCM (Fabric Reinforced Cementitious Mortar) Composites

An experimental investigation on partially PBO (short of Polyparaphenylenebenzobisthiazole) FRCM (Fiber Reinforced Cementitious Mortar) confined clay brick masonry columns has been conducted. Ten small-scale specimens measuring 445 mm high with a square cross-section of the 250 mm side have been tested under monotonic axial loading until collapse. Two columns were unconfined, while the remaining ones were confined with single-layer PBO FRCM jackets varying the geometric configuration along their height. The vertical spacing ratio sf'/sf, being sf' and sf the center-to-center and the net spacings between two consecutive jackets, respectively, was considered as the key parameter of the confinement configuration. The failure modes, stress-strain curves and peak axial stress and strain values are reported. The experimental results have been compared to the predictions of models found in the Italian guidelines CNR DT 215/2018 and the American ACI 549-R20 standards. The main aspects analyzed involved (i) the evaluation of the effectiveness of partial confinement on the mechanical response of columns, (ii) the definition of the mechanical and geometrical parameters that influence the structural response of partially confined columns, and (iii) the development of appropriate analytical models for the prediction of the resisting capacity of masonry columns partially confined with PBO FRCM.

Description of Material Properties of Degraded and Damaged Segments of Multi-Leaf Masonry in Analyses of Large Three-Dimensional Structures

This article focuses on the description of material properties of segments of masonry structures in three-dimensional analyses. It mainly considers degraded and damaged multi-leaf masonry walls. In the beginning, the causes of degradation and damage to masonry are described with examples. It was reported that the analysis of such structures is difficult due to the adequate description of the mechanical properties in the individual segments of the structure and the amount of computational cost of large three-dimensional structures. Next, a method of describing large fragments of masonry structures by means of macro-elements was proposed. The formulation of such macro-elements in three-dimensional and two-dimensional problems was given by introducing limits of variation in material parameters and damage of structures expressed by the limits of integration of macro-elements with specified internal structures. Then, it was stated that such macro-elements can be used to build computational models by the finite element method, which allows the analysis of the deformation-stress state, and at the same time, reduce the number of unknowns in such issues. A strategy for performing analyses and examples of practical applications in masonry analyses were proposed. It was reported that the results of the analyses can be used to plan the repairs and strengthening of structures. Finally, the conducted considerations and proposals were summarised, as well as examples of practical applications.

Quantification of Humidity and Salt Detection in Historical Building Materials via Broadband Radar Measurement

For the investigation of moisture and salt content in historic masonry, destructive drilling samples followed by a gravimetric investigation is still the preferred method. In order to prevent the destructive intrusion into the building substance and to enable a large-area measurement, a nondestructive and easy-to-use measuring principle is needed. Previous systems for moisture measurement usually fail due to a strong dependence on contained salts. In this work, a ground penetrating radar (GPR) system was used to determine the frequency-dependent complex permittivity in the range between 1 and 3 GHz on salt-loaded samples of historical building materials. By choosing this frequency range, it was possible to determine the moisture in the samples independently of the salt content. In addition, it was possible to make a quantitative statement about the salt level. The applied method demonstrates that with ground penetrating radar measurements in the frequency range selected here, a salt-independent moisture determination can be carried out.

Prediction of Mortar Compressive Strength Based on Modern Minor-Destructive Tests

The crucial task of the diagnosis of an existing masonry structure is to assess the current values of the mechanical parameters of the materials from which the structure was erected-usually bricks and mortar. The article presents the results of minor-destructive tests carried out on bed joints of three-brick-masonry prisms prepared in the laboratory. Three types of mortars used in the masonry were tested, which differ by the type and amount of binder. In order to determine mortar compression strength, three modern diagnostic methods were used: double punch test (DPT), standard penetrometric test (PT) and torque penetrometric test (TPT). Tests were carried out after 4, 12 and 90 weeks. The mortar strength determined in each of these tests was compared with the mortar reference strength determined on the beam specimen according to the methodology given in EN 1015-11. The results of the conducted tests confirmed the high usefulness of all three diagnostic methods. However, limitations in the application of the PT test were noticed-only lime mortars and weak cement-lime mortars can be tested with this method. In the case of mortars with an increased amount of cement binder, the impact energy is too low to estimate the compressive strength of the mortar in the brick wall joint. Technical limitations in the use of TPT and DPT tests were also indicated-weak lime mortars with low cohesion do not allow for obtaining reliable results. It was shown that DPT results strongly depend on two factors, specimen slenderness and mortar strength. Due to this fact, simple non-parameter conversion from mortar compressive strength according to the DPT test into mortar reference strength may lead to significant overestimation. As the results show, in newly built masonry, proper selection of diagnostic method is crucial due to the strong dependence of mortar curing dynamics on its location in the joint. This paper helps to match diagnostic techniques with the condition and type of mortar in the existing structure.

Numerical Modelling of the Constitutive Behaviour of FRCM Composites through the Use of Truss Elements

The modeling of the mechanical behavior of Fabric Reinforced Cementitious Matrix (FRCM) composites is a difficult task due to the complex mechanisms established at the fibre-matrix and composite-support interface level. Recently, several modeling approaches have been proposed to simulate the mechanical response of FRCM strengthening systems, however a simple and reliable procedure is still missing. In this paper, two simplified numerical models are proposed to simulate the tensile and shear bond behavior of FRCM composites. Both models take advantage of truss and non-linear spring elements to simulate the material components and the interface. The proposed approach enables us to deduce the global mechanical response in terms of stress-strain or stress-slip relations. The accuracy of the proposed models is validated against the experimental benchmarks available in the literature.

Compressive and Shear Behavior of Masonry Reinforced with Ultra-Rapid-Hardening Fiber-Reinforced Mortar (URH-FRM)

Masonry structures are very vulnerable to lateral forces such as earthquakes. In particular, for existing masonry buildings that have not been designed for earthquake resistance, appropriate seismic resistance retrofit is required. In this study, ultra-rapid-hardening fiber-reinforced mortar (URH-FRM), which has a high ductility, with an ultimate tensile strain of about 0.07, and is an economical and easy-to-construct seismic reinforcing material, was developed. Compressive strength and initial shear strength tests were performed on masonry prisms reinforced with the URH-FRM. As an experimental variable, the reinforcement thickness of the URH-FRM was varied from 10 to 30 mm and the structural performance was compared with specimens reinforced with general mortar and specimens without reinforcement. As a result, the beneficial effect of URH-FRM on the in-plane initial shear strength of horizontal bed joints in masonry prisms was confirmed. In addition, the thicker the URH-FRM reinforcement, the clearer the improvement in ductility through strain hardening.

Performance of Sustainable Insulated Wall Panels with Geopolymer Concrete

The increase in the population creates an increased demand for construction activities with eco-friendly, sustainable, and high-performance materials. Insulated concrete form (ICF) is an emerging technology that satisfies the sustainability demands of the construction sector. ICF is a composite material (a combination of expanded polystyrene (EPS) and geopolymer concrete (GPC)) that enhances the performance of concrete (such as thermal insulation and mechanical properties). To investigate the axial strength performance, five different types of prototypes were created and tested. Type I (without reinforcement): (a) hollow EPS without concrete, (b) alternative cells of EPS filled with concrete, (c) and all the cells of EPS filled with concrete; and Type II (with reinforcement): (d) alternative cells of EPS filled with concrete; (e) and all the cells of EPS filled with concrete. Amongst all the five prototypes, two grades of GPC were employed. M15 and M20 grades are used to examine the effectiveness in terms of cost. For comparing the test results, a reference masonry unit was constructed with conventional clay bricks. The main aim of the investigation is to examine the physical and mechanical performance of sandwich-type ICFs. The presence of polystyrene in ICF changes the failure pattern from brittle to ductile. The result from the study reveals that the Type II prototype, i.e., the specimen with all the cells of EPS filled with concrete and reinforcement, possesses a maximum load-carrying capacity greater than the reference masonry unit. Therefore, the proposed ICF is recommended to replace the conventional load-bearing system and non-load-bearing walls.

In-situ measurements of wall moisture in a historic building in response to the installation of an impermeable floor

When impermeable ground bearing slabs are installed in old buildings without a damp-proof course, it is a common belief of conservation practitioners that ground moisture will be 'driven' up adjacent walls by capillary action. However, there is limited evidence to test this hypothesis. An experiment was used to determine if the installation of a vapour-proof barrier above a flagstone floor in a historic building would increase moisture content levels in an adjacent stone rubble wall. This was achieved by undertaking measurements of wall, soil and atmospheric moisture content over a 3-year period. Measurements taken using timber dowels showed that the moisture content within the wall did not vary in response to wall evaporation rates and did not increase following the installation of a vapour-proof barrier above the floor. This indicates that the moisture levels in the rubble wall were not influenced by changes in the vapour-permeability of the floor.

Out-of-Plane Behavior of Masonry Prisms Retrofitted with Shape Memory Alloy Stripes: Numerical and Parametric Analysis

This paper provides a novel Finite Element (FE) simulation to estimate the out-of-plane response of masonry prisms retrofitted with Shape Memory Alloy (SMA) stripes. Empirical data were utilized to develop the computational analysis parameters (mechanical parameters for brick, mortar, and SMA materials) as well as the calibration of the computational FE-based models. For this purpose, a complete micro-modeling approach was applied, assuming perfect contact between mortar joints and brick units. A Concrete Damage Plasticity (CDP) model was developed to define the constitutive relation between brick and mortar. SMA stripes were mortar-installed on the surface of the prisms with a perfect connection. The masonry prism's verified computational model was utilized to generate parametric research to explore the effect of varying SMA stripe thicknesses and different SMA usage (Ni-Ti or Cu-Zn-Al). The FE study findings indicated that, independent of their material type or thickness, using SMA stripes greatly minimizes brick prism deterioration. SMA stripes greatly decreased residual displacement and plastic strains. Parametric tests, however, revealed that employing Ni-Ti SMA and increasing its thickness is more effective with respect to the masonry prism out-of-plane response than Cu-Zn-Al SMA.

Recycling of Mining Waste in the Production of Masonry Units

Masonry units made of clay or Autoclaved Aerated Concrete (AAC) are widely used in constructions from Romania and other countries. Masonry units with superior mechanical and thermal characteristics can improve the energy efficiency of buildings, especially when they are used as the main solutions for building envelope construction. Their production in recent years has increased vertiginously to meet the increased demand. Manufactured with diversified geometries, different mechanical and/or thermal characteristics have a high volume in the mass of the building and a major influence in their carbon footprint. Starting from the current context regarding the target imposed by the long-term strategy of built environment decarbonization, the aim of the paper is to analyze the potential of reusing mining waste in the production of masonry units. Mining waste represents the highest share of waste generated at national level and may represent a valuable resource for the construction industry, facilitating the creation of new jobs and support for economic development. This review presents the interest in integrating mining wastes in masonry unit production and the technical characteristics of the masonry units in which they have been used as raw materials in different percentages. Critical assessment framework using SWOT analysis highlights the key sustainability aspects (technical, environmental, social, economic) providing a comprehensive and systematic analysis of the advantages and disadvantages regarding the integration of mining waste as secondary raw materials into masonry units production.

Research and TLS (LiDAR) Construction Diagnostics of Clay Brick Masonry Arched Stairs

The study presents the terrestrial laser scanning (TLS) diagnostic of the clay brick masonry arched staircase in a historic building. Based on the measurements of the existing arched stair flights, 1:1 scale experimental models with and without stair treads were made. Strength tests of the models were carried out for different concentrated force locations in relation to the supporting structure. Force, deflections and reaction in the upper support of the run were measured during the tests. The influence of the masonry steps on the curved vault on the load capacity and stiffness of the run structure was analyzed. The conducted experimental investigations showed that the key element responsible for the actual load-bearing capacity and stiffness of this type of stair flights were the treads above the masonry arch.

Experimental Investigation of the TRM-to-Masonry Bond after Exposure to Elevated Temperatures: Cementitious and Alkali-Activated Matrices of Various Densities

Limited research has focused on the effect of high temperatures on the textile-reinforced mortar (TRM)-to-masonry bond. In this study, masonry prisms that were furnished with double-layered TRM strips were tested under shear bond conditions after their exposure to 200 °C and 400 °C for 1 h using the single-lap/single-prism setup. A total of four TRM systems were applied sharing the same type of textile -a dry AR glass fiber one- and different matrices: two cementitious matrices, namely a normal-weight (TRCNM) and a lightweight (TRCLM) one, and two counterpart alkali-activated matrices (TRAANM and TRAALM) based on metakaolin and fly ash. Specimens' exposure to elevated temperatures did not alter their failure mode which was due to the sleeve fibers' rupture along with core fibers' slippage from the mortar. The residual bond capacity of the TRM systems decreases almost linearly with increasing exposure temperature. The alkali-activated textile reinforced mortars outperformed their cement-based counterparts in terms of bond strength at every temperature. All systems retained close to 50% of their original shear bond strength after heating at 400 °C. Per the type of binder, lightweight matrices resulted in either comparable (cement-based systems) or better (alkali-activated systems) heat protection at the TRM/masonry interface.

Splitting test experimental dataset of hollow concrete blocks

Masonry structures are widely used nowadays for their advantages like low-cost workmanship, efficiency and fast construction techniques. The compressive strength of the materials that compose masonry (block and mortar) is very important to the behavior of the system, but the tensile strength is even more significant for the standards and building codes. In this work, a dataset for indirect tensile tests of hollow concrete blocks is obtained. Splitting tests as described in ASTM C-1006-13 are applied. Two sets of blocks were tested, one with medium compressive strength and the other with high compressive strength. The first set was tested in three directions named A, B, and C; the second one was tested in two directions, A and B. The data was collected with a servo-hydraulic machine. The data is presented in tables and can be used by material researchers, as well as in numerical modeling.

Bond Tests on Clay Bricks and Natural Stone Masonry Externally Bonded with FRP

Nowadays, the solution of durability problems of existing buildings has a key role in civil engineering, in which there is an ever-increasing need for building restorations. Over the past 50 years, there is a growing interest in a new composite material, fibre-reinforced polymer (FRP), suitable for increasing the resistance and the stability of existing buildings and, consequently, for extending their service life. In this context, the effectiveness of the strengthening system is related to the bond behaviour that is influenced by several parameters such as bond length, the stiffness of the reinforcement, the mechanical properties of the substrate, environmental conditions, etc. This paper aims to analyse the main experimental results from shear tests performed on two kinds of masonry substrates and different types of FRP reinforcements. The purpose is to highlight the role played by many parameters to the bond behaviour of these systems: the mechanical properties of substrates; the stiffness of reinforcements; the type of supports (i.e., unit or masonry unit). The obtained experimental results underlined that the specimens realised with masonry unit show an increase in debonding load and different stress transfer mechanisms along the bonded length with respect to the specimens with a unit substrate. The analysis of the data revealed that the presence of mortar joints cannot be neglected because it influences the interface global performance.

A Method to Calculate the Support Length of Beams Resting on Masonry Walls

Rehabilitation, strengthening, and retrofitting of existing masonry buildings represent an important challenge for the construction engineering field. Often, slab strengthening/retrofitting is performed by replacing existing timber and steel beams or by adding new beams to improve the slab load-carrying capacity. The computation of the stresses at the beam-masonry interface (i.e., the contact pressure) is crucial to properly design the beam support length, preventing local failure of masonry and beam. This paper presents a simple analytical procedure to compute the contact pressure at the beam-masonry interface. The analytical procedure is validated by comparison between analytical and corresponding numerical results obtained by finite element modeling. Different types of beam (solid and laminated timber beams and steel beams) were considered, as well as different support conditions (simply resting on the wall considering different support lengths or fully embedded). The results obtained show that the method proposed is simple and reliable, which makes it suitable for professional practice.

Effect of Wet-Dry Cycles on the Bond Behavior of Fiber-Reinforced Inorganic-Matrix Systems Bonded to Masonry Substrates

In recent years, inorganic-matrix reinforcement systems, such as fiber-reinforced cementitious matrix (FRCM), composite-reinforced mortars (CRM), and steel-reinforced grout (SRG), have been increasingly used to retrofit and strengthen existing masonry and concrete structures. Despite their good short-term properties, limited information is available on their long-term behavior. In this paper, the long-term bond behavior of some FRCM, CRM, and SRG systems bonded to masonry substrates is investigated. Namely, the results of single-lap direct shear tests of FRCM-, CRM-, and SRG-masonry joints subjected to wet-dry cycles are provided and discussed. First, FRCM composites comprising carbon, polyparaphenylene benzobisoxazole (PBO), and alkali-resistant (AR) glass textiles embedded within cement-based matrices, are considered. Then, CRM and SRG systems made of an AR glass composite grid embedded with natural hydraulic lime (NHL) and of unidirectional steel cords embedded within the same lime matrix, respectively, are studied. For each type of composite, six specimens are exposed to 50 wet–dry cycles prior to testing. The results are compared with those of nominally equal unconditioned specimens previously tested by the authors. This comparison shows a shifting of the failure mode for some composites from debonding at the matrix–fiber interface to debonding at the matrix-substrate interface. Furthermore, the average peak stress of all systems decreases except for the carbon FRCM and the CRM, for which it remains unaltered or increases.

Crack Detection in Images of Masonry Using CNNs

While there is a significant body of research on crack detection by computer vision methods in concrete and asphalt, less attention has been given to masonry. We train a convolutional neural network (CNN) on images of brick walls built in a laboratory environment and test its ability to detect cracks in images of brick-and-mortar structures both in the laboratory and on real-world images taken from the internet. We also compare the performance of the CNN to a variety of simpler classifiers operating on handcrafted features. We find that the CNN performed better on the domain adaptation from laboratory to real-world images than these simple models. However, we also find that performance is significantly better in performing the reverse domain adaptation task, where the simple classifiers are trained on real-world images and tested on the laboratory images. This work demonstrates the ability to detect cracks in images of masonry using a variety of machine learning methods and provides guidance for improving the reliability of such models when performing domain adaptation for crack detection in masonry.

Tensile Behaviour of FRCM Composites for Strengthening of Masonry Structures-An Experimental Investigation

This paper presents the results of direct tensile tests performed on six different FRCM (fabric reinforced cementitious matrix) strengthening systems used for masonry structures. The emphasis was placed on the determination of the mechanical parameters of each tested system and a comparison of their tensile behaviour in terms of first crack stress, ultimate stress, ultimate strain, cracking pattern, failure mode and idealised tensile stress-strain curve. In addition to the basic mechanical tensile parameters, accidental load eccentricities, matrix tensile strengths, and matrix modules of elasticity were estimated. The results of the tests showed that the tensile behaviour of FRCM composites strongly depends on the parameters of the constituent materials (matrix and fabric). In the tests, tensile failure of reinforcement and fibre slippage within the matrix were observed. The presented research showed that the accidental eccentricities did not substantially affect the obtained results and that the more slender the specimen used, the more consistent the obtained results. The analysis based on a rule of mixtures showed that the direct tensile to flexural tensile strength ratio of the matrixes used in the test was 0.2 to 0.4. Finally, the tensile stress–strain relationship for the tested FRCMs was idealised by a bi- or tri-linear curve.

Experimental Evaluation of Shear Behavior of Stone Masonry Wall

The evaluation of the shear behavior of masonry walls is a first fundamental step for the assessment of existing masonry structures in seismic zones. However, due to the complexity of modelling experimental behavior and the wide variety of masonry types characterizing historical structures, the definition of masonry’s mechanical behavior is still a critical issue. Since the possibility to perform in situ tests is very limited and often conflicting with the needs of preservation, the characterization of shear masonry behavior is generally based on reference values of mechanical properties provided in modern structural codes for recurrent masonry categories. In the paper, a combined test procedure for the experimental characterization of masonry mechanical parameters and the assessment of the shear behavior of masonry walls is presented together with the experimental results obtained on three stone masonry walls. The procedure consists of a combination of three different in situ tests to be performed on the investigated wall. First, a single flat jack test is executed to derive the normal compressive stress acting on the wall. Then a double flat jack test is carried out to estimate the elastic modulus. Finally, the proposed shear test is performed to derive the capacity curve and to estimate the shear modulus and the shear strength. The first results obtained in the experimental campaign carried out by the authors confirm the capability of the proposed methodology to assess the masonry mechanical parameters, reducing the uncertainty affecting the definition of capacity curves of walls and consequently the evaluation of seismic vulnerability of the investigated buildings.

Physical-Mechanical Properties of Stone Masonry of Gjirokastër, Albania

In addition to reinforced concrete and steel buildings, a large part of the existing building stock in Europe is made of stone masonry. Prediction of the structural behavior requires the development of a systematic material characterization of the mechanical properties and structural details (units, arrangement, bonding, inter-connection). This study aims to analyze the mechanical and physical behavior of building stones in the historical city of Gjirokastër, Albania, known also as the Stone City. A thorough investigation of the regional stone quarries was performed, and the collected samples were cut into regular prismatic specimens for further analysis. The experimental campaign consisted of the determination of flexural strength and compressive strength, water absorption, porosity, specific gravity as well as structural analysis of the masonry material, using the MQI (Masonry Quality Index) method. The test results showed that there is a large scattering in the values of the mechanical and physical stone properties such as compressive strength varying from 20 to 115 MPa and flexural strength from 8 to 25 MPa. However, the analysis of the masonry material revealed a satisfactory structural performance, based on a frequent, systematic respect of the good construction practices (i.e., the rules of the art) in Gjirokastër.

New Composite Material for Masonry Repair: Mortar Formulations and Experimental Studies

The need for retrofitting existing masonry structures is progressively becoming more important due to their continuous deterioration or need to meet the current design requirements of Eurocodes. Textile-Reinforced Mortar (TRM) composite systems have emerged as a sustainable repair methodology suitable for structure retrofitting. Nevertheless, their mechanical performance is still far from being fully investigated. This paper presents an experimental study on the tensile and bond behaviors of a new mortar-based composite consisting of mineral additives, blended cement mortar, and stainless-steel grid. Three different mineral additives (silica fume, fly ash, and blast furnace slag), in binary and ternary systems were used. The experimental study included uniaxial tensile coupon testing on composite specimens and bond tests on composite material applied to clay-brick substrate. The results obtained with the different textile-reinforced cement-based mortars were compared and are discussed here. It was found that, for mortar formulations containing mineral additives-such as fly ash or blast-furnace slag-with high tensile and bond strengths, an adequate adherence between the constituents was obtained. The developed mortar presents mechanical performances equivalent to traditional mortars without additives. The study contributes to the existing knowledge regarding the structural behavior of TRM and promotes the development of a low impact carbon cementitious matrix.

FRP Confinement of Stone Samples after Real Fire Exposure

The mechanical properties of stone materials can be severely affected by exposure to high temperatures. The effect of fire on stone buildings could cause irreversible damage and make it necessary to retrofit the affected elements. Particularly, the strengthening of columns by confinement with composites has been widely improved during the last decades. Today, fiber reinforced polymer (FRP) confinement represents a very interesting alternative to traditional steel solutions. This work studied the behavior of cylindrical stone specimens subjected to real fire action and confined by means of CFRP or GFRP jackets, with the aim of assessing the effectiveness of these reinforcement systems applied to a material that has previously been seriously damaged by high temperature exposure. In general, the strengthened samples showed notable increases in strength and ductility. The response seemed to depend basically on the FRP properties and not on the degree of damage that the stone core may have suffered. Finally, the results obtained experimentally were compared with the confinement models proposed by the available design guides, in order to evaluate the accuracy that these models can offer under the different situations addressed in this research.

Experimental and Analytical Study of Masonry Subjected to Uniaxial Cyclic Compression

Structural evaluation of masonry against dynamic seismic actions invariably requires appropriate cyclic compression constitutive models. However, not many research studies have been dedicated to date to investigate the cyclic compression behaviour of masonry. Therefore, series of experimental investigation followed by analytical model verification were employed in this research to better understand the cyclic compression characteristics of masonry. Twelve masonry wallettes were experimentally tested under cyclic compression loading with different unit-to-mortar assemblies, which are commonly found in masonry structures. The experimental results indicated that the cyclic compression behaviour is greatly influenced by the masonry compressive strength and deformation properties. Thereafter, the ability of five literature analytical models to predict the masonry structural response under cyclic compression loading was investigated. The advantages and limitations of these models are presented and discussed, and the most appropriate analytical model to define the cyclic compression characteristics of masonry has been evaluated and reported. The suggested analytical model is shown to predict the cyclic compression characteristics of different masonry assemblies such as the envelop response, the stiffness degradation, the plastic strain history of the unloading and reloading stages.

An Orthotropic Elastic-Plastic Constitutive Model for Masonry Walls

The use of a continuum structural model for the analysis of masonry structures in the plane stress state is discussed in this paper. Attention is paid to orthotropic masonry at the material level and validation of the model after its implementation in a proprietary finite element method (FEM) system via user-supplied subroutine. The constitutive relations are established in the framework of the mathematical elastoplasticity theory of small displacements and deformations. Based on the orthotropic failure criterion that was originally proposed by Hoffman in the spatial stress state, the model includes a generalization of the criterion in the plane stress. As it is the case for isotropic quasi-brittle materials, different yield surfaces are considered for tension and compression, which are both of Hoffman type.

Finite Element Study on the Shear Capacity of Traditional Joints between Walls Made of AAC Masonry Units

This paper presents the development of a numerical model aimed at the simulation of nonlinear behaviour of traditional joints between walls made of autoclaved aerated concrete (AAC) masonry units. Nonlinear behaviour and cracking of AAC and mortar were simulated using the concrete damaged plasticity (CDP) model available in the ABAQUS finite element software. The paper also presents and discusses the results of an experimental campaign involving testing six T-shaped, monosymmetric samples with traditional joints between walls loaded in shear. The results were used to validate the numerical model. The validation confirmed that the model is capable of producing accurate results and predicting the structural behaviour with a reasonably good accuracy in elastic and post-elastic stages. Furthermore, a sensitivity study was conducted, in which the variation of elastic modulus, Poisson’s ratio, tensile strength, compression strength and fracture energy of AAC was investigated. Results showed that the variation of elastic modulus, tensile strength and fracture energy is most critical to the structural behaviour of the model, while variation of the remaining parameters has a negligible effect on the results.

Integrated Use of Measurements for the Structural Diagnosis in Historical Vaulted Buildings

The process of the structural diagnosis of historical buildings is analyzed. The correlation of different data is a fundamental issue, related to the multidisciplinary nature of the study of built heritage. Quantitative data are collected by sensors, these being environmental data (temperature and humidity) or cracks (displacements). Another important source being qualitative data, derived from historic investigation, diagnostic investigations, etc. However sometimes the results may be difficult to correlate due to the different nature of the data, being quantitative and qualitative, as well as spread over the long life of the construction. In particular, the here proposed methodology suggests the use of light detection and ranging (LiDAR) scanning for the geometric and structural deformation survey, damage survey, historic evolution, monitoring of the crack pattern and environmental data. The integrated use of the collected data with digital and finite element models is investigated in two case studies. The combined use of the set of collected data is shown to be fundamental to the interpretation of the active damage mechanisms in the system, and for making appropriate decisions related to their safety. Finally, a guideline is proposed to allow for a more general use of the herein proposed structural diagnosis procedure.

Study on Retrofitted Masonry Elements under Shear Using Digital Image Correlation

Architectural heritage is usually built with masonry structures, which present problems under lateral in-plane loading conditions, such as wind pressure or earthquakes. In order to improve the shear behavior of masonry, the use of a fabric-reinforced cementitious matrix (FRCM) has become an interesting solution because of its synergy of mechanical properties and compatibility with masonry substrates. For a proper structural evaluation, the mechanical behavior of reinforced masonry and the FRCM itself needs to be characterized. Hence, a numerical model to evaluate the FRCM reinforcement requires some mechanical parameters that may be difficult to obtain. In this sense, the shear behavior of masonry can be evaluated by means of diagonal tension tests on small specimens (71 × 71 cm). In this work, a digital image correlation (DIC) monitoring system was used to control displacements and cracking patterns of masonry specimens under shear stress (induced by diagonal tension with FRCM layers) applied to one or two sides. In addition, the mechanical behavior of FRCM coupons under uniaxial tensile tests was also registered with DIC. The displacement measurements obtained by DIC were validated with the measurements registered with LVDT. Unlike LVDT-based techniques, DIC monitoring allowed us to measure deformations in masonry during the full test, detecting crack initiation even before it was visible to the eye.

Fundamental Properties and Thermal Transferability of Masonry Built by Autoclaved Aerated Concrete Self-Insulation Blocks

This paper performed a detailed study on the fundamental properties and thermal conductivity of autoclaved aerated concrete (AAC) self-insulation block, and the mechanical properties and heat transfer resistance of the AAC self-insulation block masonry. Different kinds of joints and the plastering surface were used to build the masonry specimens. The distinctive feature of the blocks and mortars is the lower thermal conductivity with expected strength. Compared to those with larger thickness of insulation mortar joints, the masonry with thin-layer mortar joints had better compressive performance and lower shear strength. The compressive strength of masonry was related with the block and mortar strengths, the shear strength of masonry along mortar joints was related with the mortar strength. The stress–strain relationship of masonry in compression could be predicted by the similar expression of conventional block masonry. The tested heat transfer coefficient of AAC self-insulation block masonry with thickness of 250 mm without plastering surfaces was (0.558 ± 0.003) W/(m²·K). With the plastering surfaces, the heat transfer coefficient reduced by 4.4% to 8.9%. Good agreements in values of heat transfer coefficient existed by using the test, theoretical computation and ANSYS (ANSYS Inc. Canonsburg, PA, USA) analytical methods. Based on the extensibility analyses, the heat transfer coefficients of AAC self-insultation block masonry with different thickness are proposed. The best thickness is proposed for the outer walls of residential buildings in different cold zone to meet the design requirement of energy conservation.

Effect of hollow bit local exhaust ventilation on respirable quartz dust concentrations during concrete drilling

Drilling large holes (e.g., 10-20 mm diameter) into concrete for structural upgrades to buildings, highways, bridges, and airport runways can produce concentrations of respirable silica dust well above the ACGIH^® Threshold Limit Value (TLV^® = 0.025 mg/m³). The aim of this study was to evaluate a new method of local exhaust ventilation, hollow bit dust extraction, and compare it to a standard shroud local exhaust ventilation and to no local exhaust ventilation. A test bench system was used to drill 19 mm diameter x 100 mm depth holes every minute for one hour under three test conditions: no local exhaust ventilation, shroud local exhaust ventilation, and hollow bit local exhaust ventilation. There were two trials for each condition. Respirable dust sampling equipment was placed on a "sampling" mannequin fixed behind the drill and analysis followed ISO and NIOSH methods. Without local exhaust ventilation, mean respirable dust concentration was 3.32 (± 0.65) mg/m³ with a quartz concentration of 16.8% by weight and respirable quartz dust concentration was 0.55 (± 0.05) mg/m³; 22 times the ACGIH TLV. For both LEV conditions, respirable dust concentrations were below the limits of detection. Applying the 16.8% quartz value, respirable quartz concentrations for both local exhaust ventilation conditions were below 0.007 mg/m³. There was no difference in respirable quartz dust concentrations between the hollow bit and the shroud local exhaust ventilation systems; both were below the limits of detection and well below the ACGIH TLV. Contractors should consider using either local exhaust ventilation method for controlling respirable silica dust while drilling into concrete.

Some of the Latest Active Strengthening Techniques for Masonry Buildings: A Critical Analysis

The present paper deals with the retrofitting of unreinforced masonry (URM) buildings, subjected to in-plane shear and out of-plane loading when struck by an earthquake. After an introductive comparison between some of the latest punctual and continuous active retrofitting methods, the authors focused on the two most effective active continuous techniques, the CAM (Active Confinement of Masonry) system and the Φ system, which also improve the box-type behavior of buildings. These two retrofitting systems allow increasing both the static and dynamic load-bearing capacity of masonry buildings. Nevertheless, information on how they actually modify the stress field in static conditions is lacking and sometimes questionable in the literature. Therefore, the authors performed a static analysis in the plane of Mohr/Coulomb, with the dual intent to clarify which of the two is preferable under static conditions and whether the models currently used to design the retrofitting systems are fully adequate.

Unified Theory for Flexural Strengthening of Masonry with Composites

Recent calamitous events have shown the fragility of the existing masonry buildings. Many of them are heritage structures, such as churches and monumental buildings. Therefore, optimized strengthening strategies are necessary. Experimental studies performed on masonry elements strengthened with composite systems have shown the performance of these materials. However, further development is necessary to optimize the intervention strategies. In fact, due to the lack of general validity models, the design is usually based on prescriptive approaches according to manufacturers' broad instructions, often producing systems with low efficiency and overestimations of the amount of reinforcement. In this paper a generalized approach is proposed to assess the flexural behavior of masonry sections strengthened with composites. The proposed theory has allowed performance of a sensitivity analysis assessing the impact both of the mechanical parameters of masonry and of the strengthening system. In particular, the impact of several constitutive relationships of composites (linear, bilinear, or trilinear) have been evaluated in terms of ultimate behavior of the strengthened masonry. For strengthening systems more compatible with the masonry substrate, the form of the stress⁻strain relationship becomes a key aspect. For such cases, the modeling of the reinforcement plays a fundamental role and the form of the relationship is strongly correlated to the type of reinforcement selected, e.g., organic versus inorganic matrix.

Investigation of the Behavior of Hardening Masonry Exposed to Variable Stresses

This paper analyzes the behavior of masonry under variable loads during execution (construction stage). It specifies the creep coefficient for calcium silicate brick masonry, presenting the research data of masonry deformation under variable and constant long-term loads. The interaction of separate layers of composite material in masonry is introduced and the formulae for determining long-term deformations are offered. The research results of masonry’s compressive strength and deformation properties under variable and constant long-term loads are presented. These are then compared to calculated ones. According to the presented comparison, the calculated long-term deformations coincide quite well with those determined experimentally.

Flexible Adhesive in Composite-to-Brick Strengthening-Experimental and Numerical Study

This paper investigates composite-to-brick strengthening systems with flexible adhesive made of polyurethane (Carbon Fibre Reinforced Polyurethane (CFRPU) and Steel Reinforced Polyurethane (SRPU)) and epoxy resin (Carbon Fibre Reinforced Polymer (CFRP) and Steel Reinforced Polymer (SRP). The specimens were tested in a single lap shear test (SLST). LVDT displacement transducers (LVDT ⁻ Linear Variable Differential Transformer) and digital image correlation method (DIC) based measurement systems were used to measure displacements and strains. The obtained results were applied in a numerical analysis of the 3D model of the SLST specimen, with flexible adhesives modeled as a hyper-elastic model. The DIC and LVDT based systems demonstrated a good correlation. Experimental and numerical analysis confirmed that composite-to-brick strengthening systems with flexible adhesives are more effective on brittle substrates than stiff ones, as they are able to reduce stress concentrations and more evenly distribute stress along the entire bonded length, thus having a higher load carrying capacity.

Numerical Investigation of Masonry Strengthened with Composites

In this work, two main fiber strengthening systems typically applied in masonry structures have been investigated: composites made of basalt and hemp fibers, coupled with inorganic matrix. Starting from the experimental results on composites, the out-of-plane behavior of the strengthened masonry was assessed according to several numerical analyses. In a first step, the ultimate behavior was assessed in terms of P (axial load)-M (bending moment) domain (i.e., failure surface), changing several mechanical parameters. In order to assess the ductility capacity of the strengthened masonry elements, the P-M domain was estimated starting from the bending moment-curvature diagrams. Key information about the impact of several mechanical parameters on both the capacity and the ductility was considered. Furthermore, the numerical analyses allow the assessment of the efficiency of the strengthening system, changing the main mechanical properties. Basalt fibers had lower efficiency when applied to weak masonry. In this case, the elastic properties of the masonry did not influence the structural behavior under a no tension assumption for the masonry. Conversely, their impact became non-negligible, especially for higher values of the compressive strength of the masonry. The stress-strain curve used to model the composite impacted the flexural strength. Natural fibers provided similar outcomes, but a first difference regards the higher mechanical compatibility of the strengthening system with the substrate. In this case, the ultimate condition is due to the failure mode of the composite. The stress-strain curves used to model the strengthening system are crucial in the ductility estimation of the strengthened masonry. However, the behavior of the composite strongly influences the curvature ductility in the case of higher compressive strength for masonry. The numerical results discussed in this paper provide the base to develop normalized capacity models able to provide important information on the out-of-plane behavior of masonry elements strengthened with inorganic matrix and several kinds of fibers, both synthetic and natural.

Fifty Years of Burn Care at Shriners Hospitals for Children, Galveston

More than 50 years ago, Shriners Hospitals for Children expanded their philanthropy to include care for burned children. In so doing, the effects of their work weightily expanded from rehabilitation and quality of life outcomes to include survival proper. As the first facility dedicated to the care of burned children, originally designated the Shriners Burn Institute, the Galveston hospital remains the cornerstone of this endeavor. Shriners maintains charitable pediatric hospitals, provide care irrespective of the patient's or the family's ability to pay, and promote research. The sole criterion for admission at Shriners Hospitals for Children is the determination by a surgeon at a Shriners hospital that "the child's trouble may be corrected or improved." This philanthropic effort to provide medical care for children is one expression of the human commonality recognized by Shriners. In this article, we provide some background information on how this hospital came into existence as well as a global summary of its interventions toward greater survival and more complete rehabilitation of burned children. Based on the findings presented herein, we assert that there is less suffering and less loss of life due to childhood burns today than in previous years. We attribute much of this improvement to the simple voluntary collective decision by Shriners to provide alms for burned children.

The role of frictional contact of constituent blocks on the stability of masonry domes

The observation of old construction works confirms that masonry domes can withstand tensile hoop stresses, at least up to a certain level. Here, such tensile resistance, rather than a priori assumed as a property of the bulk material, is attributed to the contact forces that are developed at the interfaces between interlocked blocks under normal pressure, specified by Coulomb's friction law. According to this rationale, the aspect ratio of the blocks, as well as the bond pattern, becomes of fundamental importance. To investigate the complex assembly of blocks, supposed rigid, we present a non-smooth contact dynamic analysis, implemented in a custom software based on the Project Chrono C++ framework and complemented with parametric-design interfaces for pre- and post-processing complex geometries. Through this advanced tool, we investigate the role of frictional forces resisting hoop stresses in the stability of domes, either circular or oval, under static and dynamic loading, focusing, in particular, on the structural role played by the underlying drum and the surmounting tiburium.

Image Analysis Technique for Material Behavior Evaluation in Civil Structures

The article presents a hybrid monitoring technique for the measurement of the deformation field. The goal is to obtain information about crack propagation in existing structures, for the purpose of monitoring their state of health. The measurement technique is based on the capture and analysis of a digital image set. Special markers were used on the surface of the structures that can be removed without damaging existing structures as the historical masonry. The digital image analysis was done using software specifically designed in Matlab to follow the tracking of the markers and determine the evolution of the deformation state. The method can be used in any type of structure but is particularly suitable when it is necessary not to damage the surface of structures. A series of experiments carried out on masonry walls of the Oliverian Museum (Pesaro, Italy) and Palazzo Silvi (Perugia, Italy) have allowed the validation of the procedure elaborated by comparing the results with those derived from traditional measuring techniques.

The Effects of Bit Wear on Respirable Silica Dust, Noise and Productivity: A Hammer Drill Bench Study

Objectives

Hammer drills are used extensively in commercial construction for drilling into concrete for tasks including rebar installation for structural upgrades and anchor bolt installation. This drilling task can expose workers to respirable silica dust and noise. The aim of this pilot study was to evaluate the effects of bit wear on respirable silica dust, noise, and drilling productivity.

Method

Test bits were worn to three states by drilling consecutive holes to different cumulative drilling depths: 0, 780, and 1560 cm. Each state of bit wear was evaluated by three trials (nine trials total). For each trial, an automated laboratory test bench system drilled 41 holes 1.3 cm diameter, and 10 cm deep into concrete block at a rate of one hole per minute using a commercially available hammer drill and masonry bits. During each trial, dust was continuously captured by two respirable and one inhalable sampling trains and noise was sampled with a noise dosimeter. The room was thoroughly cleaned between trials.

Results

When comparing results for the sharp (0 cm) versus dull bit (1560 cm), the mean respirable silica increased from 0.41 to 0.74 mg m-3 in sampler 1 (P = 0.012) and from 0.41 to 0.89 mg m-3 in sampler 2 (P = 0.024); levels above the NIOSH recommended exposure limit of 0.05 mg m-3. Likewise, mean noise levels increased from 112.8 to 114.4 dBA (P < 0.00001). Drilling productivity declined with increasing wear from 10.16 to 7.76 mm s-1 (P < 0.00001).

Discussion

Increasing bit wear was associated with increasing respirable silica dust and noise and reduced drilling productivity. The levels of dust and noise produced by these experimental conditions would require dust capture, hearing protection, and possibly respiratory protection. The findings support the adoption of a bit replacement program by construction contractors.

Fiber Reinforced Polymer Strengthening of Structures by Near-Surface Mounting Method

This paper provides a critical review of recent studies on strengthening of reinforced concrete and unreinforced masonry (URM) structures by fiber reinforced polymers (FRP) through near-surface mounting (NSM) method. The use of NSM-FRP has been on the rise, mainly due to composite materials' high strength and stiffness, non-corrosive nature and ease of installation. Experimental investigations presented in this review have confirmed the benefits associated with NSM-FRP for flexural and shear strengthening of RC and URM structures. The use of prestressing and anchorage systems to further improve NSM-FRP strain utilization and changes in failure modes has also been presented. Bond behavior of NSM-FRP-concrete or masonry interface, which is a key factor in increasing the load capacity of RC and URM structures has been briefly explored. Presented studies related to the effect of temperature on the bond performance of NSM-FRP strengthened systems with various insulations and adhesive types, show better performance than externally bonded reinforcement (EBR) FRP retrofitting. In summary, the presented literature review provides an insight into the ongoing research on the use of NSM-FRP for strengthening of structural members and the trends for future research in this area.

Stress State Analysis and Failure Mechanisms of Masonry Columns Reinforced with FRP under Concentric Compressive Load

The strengthening and stabilization of damaged compressed masonry columns with composites based on fabrics of high-strength fibers and epoxy resin, or polymer-modified cement mixtures, belongs to novel, partially non-invasive and reversible progressive methods. The stabilizing and reinforcing effect of these fabrics significantly applies to masonry structures under concentric compressive loading whose failure mechanism is characterized by the appearance and development of vertical tensile cracks accompanied by an increase in horizontal masonry strain. During the appearance of micro and hairline cracks (10⁻³ to 10⁻¹ mm), the effect of non-pre-stressed wrapping composite is very small. The favorable effect of passive wrapping is only intensively manifested after the appearance of cracks (10⁻¹ mm and bigger) at higher loading levels. In the case of “optimum” reinforcement of a masonry column, the experimental research showed an increase in vertical displacements δ_y (up to 247%), horizontal displacements δ_x (up to 742%) and ultimate load-bearing capacity (up to 136%) compared to the values reached in unreinforced masonry columns. In the case of masonry structures in which no intensive “bed joint filler–masonry unit” interaction occurs, e.g., in regular coursed masonry with little differences in the mechanical characteristics of masonry units and the binder, the reinforcing effect of the fabric applies only partially.

Bond Behavior of Historical Clay Bricks Strengthened with Steel Reinforced Polymers (SRP)

In the strengthening interventions of past and historical masonry constructions, the non-standardized manufacture processes, the ageing and the damage of masonry units, could significantly affect the properties of the surfaces where strengthening materials are applied. This aspect requires particular care in evaluating the performance of externally bonded strengthening layers, especially with reference to the detachment mechanism. The bond response of old masonries could be very different from that occurring in new masonry units which are the ones generally considered in most of the bond tests available in technical literature. The aim of the present paper is the study of the bond behavior of historical clay bricks strengthened with steel reinforced polymers (SRP) materials. In particular, the results of an experimental study concerning new manufactured clay bricks and old bricks extracted from different historical masonry buildings are presented. The obtained results, particularly in terms of bond resistance, detachment mechanism and strain distributions, are discussed for the purpose of analyzing the peculiarities of the historical bricks in comparison with new manufactured ones. Some considerations on the efficacy of the theoretical formulations of the recent Italian code are also carried out.