Triaxial elastoplastic damage constitutive model of unreinforced clay brick masonry wall

Due to differences in the properties of composition materials and construction techniques,unreinforced masonry is characterized by low strength,anisotropy,nonuniformity,and low ductility.In order to accurately simulate the mechanical behavior of unreinforced brick masonry walls under static and dynamic loads,a new elastoplastic damage constitutive model was proposed and the corresponding subroutine was developed based on the concrete material constitutive model.In the proposed constitutive model,the Rankine strength theory and the Drucker-Prager strength theory were used to define the tensile and compressive yield surface function of materials,respectively.Moreover,the stress updating algorithm was modified to consider the tensile plastic permanent deformation of masonry materials.To verify the accuracy of the proposed constitutive model,numerical simulations of the brick masonry under monotonic and cyclic uniaxial tension and compression loads were carried out.Comparisons among the numerical and theoretical and experimental results show that the proposed model can properly reflect the masonry material mechanical properties.Furthermore,the numerical models of four pieces of masonry walls with different mortar strengths were established.Low cyclic loadings were applied and the results show that the proposed constitutive model can properly simulate the wall shear failure characteristics,and the force-displacement hysteretic curves obtained by numerical simulation are in good agreement with the tests.Overall,the proposed elastic-plastic damage constitutive model can simulate the nonlinear behavior of unreinforced brick masonry walls very well,and can be used to predict the structural response of masonry walls.

Blast response of clay brick masonry unit walls unreinforced and reinforced with polyurea elastomer

Clay brick masonry unit(CBMU) walls are widely used in building structures,and its damage and protection under explosion loads have been a matter of concern in the field of engineering protection.In this paper,a series of full-scale experiments of the response characteristics of 24 cm CMBU walls unreinforced and reinforced with polyurea elastomer subjected to blast loading were carried out.Through setting 5.0 kg TNT charges at different stand-off distances,the damage characteristics of masonry walls at different scaled distances were obtained.The reinforcement effect of different polyurea coating thicknesses and methods on the blast resistance performance of masonry walls under single and repeated loads were also explored.Five failure grades were summarized according to the dynamic response features of masonry walls.Based on the stress wave propagation pattern in multi-media composite structures,the internal stress distribution of masonry walls were analyzed,and the division basis of the masonry walls’ failure grades was then quantified.Combined with Scanning Electron Microscope(SEM)images,the deformation characteristics of soft and hard segments of polyurea and effects of detonation products on microstructures were revealed respectively,which provides an important reference for the design and application of polyurea in the blast resistance of clay brick masonry walls.

A 3-D DDA damage analysis of brick masonry buildings under the impact of boulders in mountainous areas

In mountainous areas, geological disasters carrying large boulders can cause severe damage to the widely used masonry buildings due to the high impact forces. To better understand the damage of brick masonry buildings under the impact of boulders, a "block-joint" model is developed using threedimensional discontinuous deformation analysis(3-D DDA) to simulate the behaviour of the "brick-mortar" structure. The "block-joint" model is used to capture not only the large displacement and deformation of individual bricks but also the large-scale sliding and opening along the mortar between the bricks. The linear elastic constitutive model is applied to account for the non-plastic deformation behaviour of brick materials. Furthermore, the mechanical characteristics of the mortar are represented using the Mohr-Coulomb and Drucker-Prager criteria. To propose safe structural design schemes and effective reinforcement for brick masonry buildings, seven construction techniques are considered, includingdifferent grades of brick and mortar, effective shear areas and reinforced members. The proposed 3-D DDA model is used to analyse the velocity distribution and the key point displacements of the brick masonry building under the impact of boulders. The results show that upgrading the brick and mortar, increasing the wall thickness, making full use of the wall thickness, and adding a circular beam and structural column are very effective approaches for improving the impact resistance of brick masonry buildings.

Twin lintel belt in steel for seismic strengthening of brick masonry buildings

A single-room,single-storey full-scale brick masonry building with precast RC roofing system was tested thrice under displacement controlled lateral cyclic loading,to assess the effectiveness of the basic repair and seismic strengthening techniques.Initially,the virgin building specimen was loaded laterally to f^tilure.In the second stage,the damaged building was repaired by stitching across the cracks,and tested under the same lateral loading.In the third stage,the twice-damaged structure was repaired once more by stitching and strengthened by twin lintel belt in steel and vertical comer reinforcement, and re-tested.The building strengthened by twin lintel belt in steel showed about 28% higher strength under lateral loading than the virgin building.

Dynamic Analysis of Historical Brick Masonry House

Brick masonry constructions are very common in many areas in the world and their failure in earthquakes has been the cause of many deaths. Since human safety is main issue of disaster management, people are more concerned about the structural assessment and strengthening of those constructions. One historical brick masonry house located in Kathmandu world heritage site is modeled by FEM （finite element method） and analyzed in E1 Centro earthquake ground motions. Bricks are modeled as solid elements and the interfaces between the brick units are modeled as zero thickness joint elements. Then, non-linear analyses of the house are applied satisfying the famous Mohr-Coulomb failure criterion. The result shows that the house is very weak and sustains large deformation in El Centro 1940 Earthquake. A strengthening solution modifying the connections of existing elements and adding wooden frame inside the house can reduce the deformations significantly.

Investigations of Physical and Chemical Characteristics of Masonry Stones and Bricks during Building Cleaning： Part 1. Physical Testing

This series of study focused on analysing and assessing the changes of the physical and chemical characteristics of the surfaces of the masonrystones and bricks during the sandblasting cleaning process by conducting various physical and chemical tests. Seven masonry stones and bricks were adopted, including yellow sandstone, red sandstone, limestone, marble, granite, white clay brick and yellow clay brick. The physical testing included evaluating the cleaning degree, determining the Vickers hardness, and detecting the water absorption. Using a digital imaging analysis method, the greyscale and cleanness were introduced to quantitatively assess the effectiveness of masonry building cleaning and confirmed to be useful and appropriate. The cleanness analysis, together with the hardness and water absorption tests showed that a masonry stone or a brick with a higher cleaning degree corresponded to a brighter and harder stone surface. In general, the physical properties were found to vary largely during the building cleaning.

Investigations of Physical and Chemical Characteristics of Masonry Stones and Bricks during Building Cleaning： Part 2. Chemical Testing

This series of study focused on analysing and assessing the Changes of the physical and chemical characteristics of the stone surfaces during the sandblasting cleaning process by conducting various physical and chemical tests. Seven masonry stones and bricks were adopted, including yellow sandstone, red sandstone, limestone, marble, granite, white clay brick and yellow clay brick. The chemical investigations included the micrographing of the stone facade and the analysis of the chemical elements and compounds on four of the seven stones and bricks before and after the cleaning using the Scanning Electron Microscope （SEM） and Energy-Dispersive X-ray Spectroscopy （EDX） techniques. In general, the chemical properties were found to vary largely during the building cleaning. The chemical tests showed that the chemical elements and compounds on the stone facade significantly varied after long term exposures to the atmosphere, mainly due to the soiling on the building fagade caused by environmental erosion and weathering.

Infilled Reinforced Concrete Beams for Sustainable Construction

This paper presents a study carried out on infilled reinforced concrete beams for sustainable construction. In reinforced concrete beams, less stressed concrete below neutral axis can be replaced by some light weight material to reduce the weight of the structure and also achieve the economy. The used infilled material is brick. Sustainability can be achieved by replacing the partially used concrete. By saving concrete, the authors save cement, which reduces the green house gases emissions. So it is considered as environment friendly. Since infilled beam acts like a layered member, there needs a theory to analyze it. Method of initial functions is used for the analysis of the infilled RC （reinforced concrete） beams. This method is successfully applied on infilled beam. Results show that physical conditions are verified for infilled beam.