Concrete Block Wall Research Articles

Measurement of Attenuation by Building Structures in Cellular Network Bands

The power transmitted through obstacles is lower than the incident one due to reflection and absorption by them and this attenuation of electromagnetic waves reduces the radio coverage of any wireless communication system. This letter presents a study for the loss introduced by multiple building structures: brick, cavity and solid concrete block, and plasterboard walls; tile and slate roofs; and ten types of modern windows. The investigation is conducted in an anechoic chamber over the frequency range from 400 MHz to 2.7 GHz. Normal incidence is considered and both linear copolarizations (vertical–vertical and horizontal–horizontal) are tested. Strong frequency- and polarization-dependent attenuation is observed for the cavity concrete block wall and windows. The results demonstrate that the windows have the highest losses among the tested structures, which can reach up to 50 dB.

Performance of hollow concrete block masonry walls retrofitted with steel‐fiber and microsilica admixed plaster

The weakness of existing unreinforced masonry (URM) wall buildings in resisting lateral loads is a matter of concern, especially in locations exposed to seismic hazards. In order to address this shortcoming, considerable research effort has been dedicated in the last few years on the strengthening techniques of existing URM structures. This paper presents the test results of four hollow concrete block walls, one as control, one using high steel‐fiber reinforced mortar admixed with microsilica (SFR‐MS) mortar in joints and the other two walls plastered with 10 mm thick SFR‐MS mortar on one and both sides of the wall, respectively. The shear capacity, stiffness, cracking patterns and failure modes of the walls were investigated. In addition, a nonlinear finite element simulation of the walls in an ABAQUS environment is presented and results compared with those obtained from the experimental investigations conducted. Modified analytical equations for predicting the shear capacity of masonry walls with plaster is proposed and results compared with the experimental and finite element simulation results of the investigated walls.

Analysis of Thermal insulation performance of Aerated Concrete Block Wall in Solar Greenhouse

In recent years, the solid loam brick has gradually been forbidden. It made the construction of the solar greenhouse be confronted with a difficulty. In order to solve this problem, and satisfy the requests of the structural design and the heat preservation of solar greenhouse, aerated concrete, a new type of structural material, had been chosen to construct the north wall of solar greenhouse and replace the solid loam brick. The theoretical analysis and the actual tests all indicated that the aerated concrete brick was one of the appropriate structural materials for being used to construct the surrounding structure of the solar greenhouse. At the same time, economizing energy sources and protecting environment of this material would make it widely be used in the solar greenhouse.

Thermal Bridge Effect of Aerated Concrete Block Wall in Cold Regions

As a self-insulating building material which can meet the 65 percent energy-efficiency requirements in cold region of China, aerated concrete blocks often go moldy, frost heaving, or cause plaster layer hollowing at thermal bridge parts in the extremely cold regions due to the restrictions of environmental climate and construction technique. L-shaped part and T-shaped part of aerated concrete walls are the most easily influenced parts by thermal bridge effect. In this paper, a field test is performed to investigate the scope of the thermal bridge effect. Moreover, a heat transfer calculation model for L-shaped wall and T-shaped wall is developed. According to the simulation results, the temperature fields of the thermal bridge affected regions are simulated and analyzed. The research outputs can provide theoretical basis for the application of aerated concrete wall in extremely cold regions.

Seismic Performance of Reinforced Concrete Buildings with Masonry Infill

Unreinforced masonry Infills modify the behavior of framed structures under lateral loads; however, in practice, the infill stiffness is commonly ignored in frame analysis, resulting in an under-estimation of stiffness and natural frequency. The structural effect of hollow concrete block infill is generally not considered in the design of columns as well as other structural components of RC frame structures. The hollow concrete block walls have significant in-plane stiffness contributing to the stiffness of the frame against lateral load. The scope of present work was to study seismic performance of reinforced concrete buildings with masonry infill in medium rise building. The office medium rise building is analyzed for earthquake force by considering three type of structural system. i.e. Bare Frame system, partially-infilled and fully- Infilled frame system. Effectiveness of masonry wall has been studied with the help of five different models. Infills were modeled using the equivalent strut approach. Nonlinear static analyses for lateral loads were performed by using standard package ETABS, 2015 software. The comparison of these models for different earthquake response parameters like base shear vs roof displacement, Story displacement, Story shear and member forces are carried out. It is observed that the seismic demand in the bare frame is significantly large when infill stiffness is not considered, with larger displacements. This effect, however, is not found to be significant in the infilled frame systems. The results are described in detail in this paper.

Compressive strength of masonry constructed with high strength concrete blocks

Abstract Although the use of high strength concrete blocks for the construction of tall buildings is becoming common in Brazil, their mechanical properties and behavior are not fully understood. The literature shows a gap in experimental studies with the use of high strength concrete blocks, i.e., those with compressive strength greater than 16 MPa. The work presented herein was conducted in order to study the behavior of high strength structural masonry. Therefore, the compressive strength and modulus of elasticity of concrete block walls tested under axial load were assessed. The specimens included grouted and ungrouted walls and walls with a mid-height bond beam; ungrouted walls were constructed with face-shell and full mortar bedding. The walls were built and tested in the laboratory of CESP and in the Structures Laboratory of the UNESP Civil Engineering Department in Ilha Solteira (NEPAE). Concrete blocks with nominal compressive strength of 16 (B1), 24 (B2) and 30 (B3) MPa were used. Ungrouted masonry walls had a height of 220 cm and a width of 120 cm while grouted masonry walls had a height of 220 cm and a width of 80 cm. Traditional Portland cement, sand and lime mortar was used. The testing program included 36 blocks, 18 prisms, 9 ungrouted walls (6 with face-shell mortar bedding and 3 with full mortar bedding), 9 grouted masonry walls, and 12 ungrouted walls with a bond beam at mid-height. The experimental results were used to determine the compressive strength ratio between masonry units, prisms and masonry walls. The analyses included assessing the cracking pattern, the mode of failure and the stress-strain curve of the masonry walls. Tests results indicate that the prism-to-unit strength ratio varies according to the block strength; that face-shell mortar bedding is suitable for high strength concrete masonry; and that 20% resistance decrease for face-shell mortar bedding when compared with full mortar bedding is a conservative consideration. The results also show that using a bond beam at the mid-height of the wall does not lead to a compressive strength decreased but it changes the failure mode and the shape of the stress-strain curve. In addition, the results show that estimating E = 800 fp is conservative for ungrouted masonry walls but reasonably accurate for grouted masonry walls and that there is no reason to limit the value of E to a maximum value of 16 GPa. Furthermore, the results show that, for design purposes, a wall-to-prism strength ratio value of 0.7 may be used for high strength concrete masonry.

Numerical and experimental analysis of the shear capacity of interconnected concrete block walls

Abstract Predicting the behavior of interconnected masonry walls is a challenging issue, given the influence of a wide range of factors, such as the mechanical properties of the materials (blocks and mortar) and the way the walls are connected to each other. In this paper, experimental results in H-shaped walls subjected to shear at the vertical interface are introduced with a numerical representation. Concrete blocks and two types of connections (running bond and U-steel anchors) were considered in the tests. Computational modelling was carried out using the Diana® FEM software to complete the study and understand the structural behavior of the masonry panels. The influence of the bonding pattern on the experimental and numerical response was studied and good agreement between the results was found. Moreover, the numerical analysis showed that the computer models of the interconnected walls adequately represented the behavior of the physical models regarding load capacity and cracking patterns.

Development of bio-based insulation materials for the improvement of thermal comfort of housing in Burkina Faso

Burkina Faso is located in the heart of Africa, where the average temperature during the dry season is about 40 °C. The 75% of the population is located in rural areas but, in the last years, there is a big migratory flow to the cities, in an irregular process of urban expansion where most of the houses are made with walls of concrete blocks and metal sheet roofs, generating a big lack of thermal comfort and habitability conditions. The main objective of this project is to develop a thermal insulation material, with low environmental impact, which could contribute to improve the living conditions in this new urban area of Burkina Faso. To this end, biomaterials locally available, in particular wastes or byproducts of agricultural industry have been used. Several formulations, based on peanut shells and sorghum canes and agglutinated with different kind of binders, have been investigated by evaluating properties as thermal conductivity, mechanical strength and fire reaction. The obtained insulation composites exhibited low thermal conductivity values and acceptable mechanical and fire reaction properties. Thus, according to the results, the material seems to be a promising renewable and locally manufactured product suitable for application in developing countries.

AERATED CONCRETE MICROWAVE REFLECTION AND TRANSMISSION PROPERTIES IN A WET ENVIRONMENT

Excess water content within the building material could greatly alter the interaction of the microwave with the material. In this study aerated concrete (AEROC) block walls (60x60cm) were investigated for their microwave (2.4 GHz) properties under wetting conditions. The spray wetting of the wall was conducted to simulate the environmental processes such as raining or water damage. 50ml/m² water dosage was applied on the surface of the concrete 21 times in 1 min intervals. The results show a noticeable decrease in microwave penetration power through the material after the sample gets enriched with water. As the water content on the surface of the material rises, so does the transmission loss. During the different water content of the aerated concrete, the reflection loss varied from -15.04 dB (dry wall) to -5.03 dB (wet wall’s surface). The transmission loss continues to rise during the entire length of the experiment, from -4.5 dB as a dry sample to -8.3 dB after 441 ml (1035 ml/m² during 23 min) of sprayed water. The variation of reflected microwave power was approximately ten times, which is quite a significant indicator of alteration of microwave propagation. The results demonstrate wetting process as an considerable factor in assessing microwave propagation in near the sources, such as mobile phone base station antennas, industrial microwave heaters and ovens etc.

Modeling thermal performance of exterior walls retrofitted from insulation and modified laterite based bricks materials

Uninsulated concrete block walls commonly found in tropical region have to be retrofitted to save energy. The thickness of insulation layer used can be reduced with the help of modified laterite based bricks layer (with the considerably lower thermal conductivity than that of concrete block layer) during the retrofit building fabrics. The aim of this study is to determine the optimum location and distribution of different materials. The investigation is carried out under steady periodic conditions under the climatic conditions of Garoua in Cameroon using a Simulink model constructed from H-Tools (the library of Simulink models). Results showed that for the continuous air-conditioned space, the best wall configuration from the maximum time lag, minimum decrement factor and peak cooling transmission load perspective, is dividing the insulation layer into two layers and placing one at the exterior surface and the other layer between the two different massive layers with the modified laterite based bricks layer at the interior surface. For intermittent cooling space, the best wall configuration from the minimum energy consumption depends on total insulation thickness. For the total insulation thickness less than 8 cm approximately, the best wall configuration is placing the half layer of insulation material at the interior surface and the other half between the two different massive layers with the modified earthen material at the exterior surface. Results also showed that, the optimum insulation thickness calculated from the yearly cooling transmission (estimated only during the occupied period) and some economic considerations slightly depends on the location of that insulation.

Experimental Assessment of the System-Level Seismic Performance of an Asymmetrical Reinforced Concrete Block–Wall Building with Boundary Elements

AbstractUsing boundary elements in reinforced masonry (RM) walls allows closed ties to be used and multiple layers of vertical bars to be accommodated, thus providing a confining reinforcement cage...

Perspectives of Safe Work Practices: Improving Personal Electrical Safety of Low-Voltage Systems from Electrical Hazards

A person’s understanding of a safety hazard has a dramatic effect on his or her behavior. An in-depth understanding of a hazard usually results in a healthy respect for what can happen. People who know the most about a specific hazard tend to rely more heavily on procedures and plans to guide their actions. Personal protective equipment selection and use are influenced by increased understanding of a hazard. Training and training programs are influenced by the depth of knowledge held by all members of the line organization. Recent work has focused attention on the thermal effects of arc flashes. However, when electrical energy is converted into thermal energy in an arcing fault, still another energy conversion is taking place. Applications are on record that suggest that a considerable amount of force is created during an arcing fault. Concrete block walls can be destroyed by the increased pressure that is created during an arcing fault. This study is present about preventing injuries to people. We will study about injuries and then develop some understanding about electrical hazards. Also, we will present about safe work practices, responsible, and then about what makes us act as we do.

Coupled heat and moisture transfer in hollow concrete block wall filled with compressed straw bricks

Coupled heat and moisture transfer has a severe influence on building envelop durability. This phenomenon has more concerns as the rapid development of new moisture buffering materials. In this paper, a detailed description of hollow concrete block filled with compressed straw bricks is presented. In order to reveal heat and moisture coupling mechanism of the multilayer energy-saving wall, a series of tests were developed based on our designed controllable coupled heat and moisture test. The experiments were divided into 3 groups according to directions of heat and moisture transfer and the variations of boundary conditions. The temperature and humidity profiles within the wall thickness through two different directions are monitored during the test. The experimental results highlight the important influence of temperature and relative humidity gradient on the hygrothermal properties of the multilayer wall. It also illustrates that filling compressed straw bricks into hollow concrete block can hinder heat transfer and improve moisture buffering performance of multilayer wall. Based on our developed model, a piece of software (HMCT 1.0) to simulate the hygrothermal performance in multilayer wall was proposed for deep understanding of the experimental results. A good agreement was found between simulation results and tested values.

Experimental evaluation of the interaction between strength concrete block walls under vertical loads

Abstract This paper aims to evaluate the interaction between structural masonry walls made of high performance concrete blocks, under vertical loads. Two H-shaped flanged wall series, all full scale and using direct bond, have been analyzed experimentally. In one series, three flanged-walls were built with the central wall (web) supported and, in the other one, three specimens were built without any support at the central web. The load was applied on the central wall and vertical displacements were measured by means of displacement transducers located at eighteen points in the wall-assemblages. The results showed that the estimated load values for the flanges were close to those supported by the walls without central support, where 100% of the load transfer to the flanges occur. The average transfer load rate calculated based on the deformation ratio in the upper and lower section of the flanged-walls, with the central web support, were 37.65% and 77.30%, respectively, showing that there is load transfer from the central wall (web) toward the flanges, particularly in the lower part of the flanged walls. Thus, there is indication that the distribution of vertical loads may be considered for projects of buildings for service load, such as in the method of isolated walls group. For estimation of the failure load, the method that considers the walls acting independently showed better results, due to the fact that failure started at the top of the central wall, where there is no effect of load distribution from the adjacent walls.

Numerical strategies for damage assessment of reinforced concrete block walls subjected to blast risk

Computational tools and numerical strategies for the determination of the response of masonry walls under blast overpressure often rely on oversimplifying and conservative assumptions, which, although justifiable for design purposes, are not as warranted when fragility analysis and risk assessment are the objectives. In addition, due to the composite nature of reinforced masonry construction, the evaluation of multivariate fragility functions may likely require significant computational effort, owing to the multiplicity of variables describing the constituent materials and their associated uncertainty. The problem is further compounded by the effects of the high strain rates typically induced by blast loading, which make the understanding of masonry behaviour even more challenging; although efforts are being made in order to account for strain rate effects at the macro-scale, no well established models are available for reinforced masonry walls. Therefore, in order to perform accurate yet expedient fragility analyses that can effectively capture rate dependent phenomena, a dynamic model based on single-degree-of-freedom (SDOF) approach is developed. The SDOF model accounts for the nonlinear stress–strain behaviour obtained from standard prism tests and integrates strain rate dependent formulations provided in the open literature. The model predictions are corroborated using data—including pressure and displacement histories—from field testing of six scaled concrete block walls subjected to the detonation of live explosives. Within the scope of the current study, the proposed model is found to be a reasonable trade-off between computational efficiency and numerical accuracy and is an improvement upon a basic SDOF approach, which is typically based on the fixed dynamic increase factors recommended by modern design standards and technical manuals for blast protection. The results presented in this study are expected to contribute to the ongoing development of a comprehensive framework for the probabilistic risk assessment of structures subjected to explosive loading.

In situ assessment of the fabric and energy performance of five conventional and non-conventional wall systems using comparative coheating tests

Comparative coheating tests have been carried out in five test buildings with walls constructed of Concrete Block Masonry and timber framed Hemp-lime composite, Polyisocyanurate (PIR), Wood Fibre and Mineral Wool. Five different methods of determining heat loss coefficient (HLC) were applied during the data analysis. While some variability in HLC values was observed between the different forms of construction, the hierarchy of HLC values among the test buildings were consistent, with the Concrete Block Masonry exhibiting the highest and Wood Fibre test building exhibiting the lowest HLC values. Except for the Concrete Block Masonry, there was good agreement between the calculated HLC values and those derived by applying the method 5 where the analysis incorporated both the effects of solar radiation and thermal mass. The in-situ U-value for the Concrete Block wall, determined by the average method, was 32.8% higher than its design value, whilst the other wall systems showed marginally lower U-values than their corresponding design U-values.

ENVIRONMENTAL DAMAGE FROM WALL TECHNOLOGIES FOR RESIDENTIAL BUILDINGS IN ISRAEL

Four wall technologies used for residential building in Israel (concrete, lightweight concrete block, autoclaved aerated block, and concrete block) were evaluated for their total environmental damage. The production and construction (P&C) and operational energy (OE) stages were considered. Influences of the climate (the four climate zones of Israel), building type (regular and low-energy), and primary fuel source [natural gas and photovoltaic (PV) for energy production] on the selection of the best wall technology were analyzed. EnergyPlus software was used to evaluate building heating and cooling needs for the OE stage. The ReCiPe method was used for both the P&C and OE stages to evaluate environmental damage via human health, ecosystem quality and resource depletion damage categories. It was determined that both concrete block walls and concrete walls were the best choices when natural gas was used, while the concrete block and autoclaved aerated block walls were the best choices when PV was used. The following two conclusions were reached: wall technologies with high thermal mass are environmentally preferred when natural gas is used, whereas wall technologies with reduced cement quantity are environmentally preferred when PV is used.

Behavior and Design Aspects of FRP-Strengthened URM Walls under Out-of-Plane Loading

AbstractThe use of externally bonded fiber-reinforced polymer (FRP) composites for upgrading the out-of-plane flexural resistance of unreinforced masonry (URM) walls is experimentally and analytically investigated in this study. A total of six hollow concrete block walls were tested to failure using an airbag and a reaction frame to obtain a uniform load on the wall. The masonry walls were placed horizontally and tested as one-way slabs with span direction perpendicular to the bed joints. The first wall was left unstrengthened to be used as control specimen; the other five walls were strengthened using different schemes of externally attached glass-fiber-reinforced polymer (GFRP) sheets. The main parameters studied experimentally were FRP reinforcement ratio and stiffness. In addition to the experimental program, an analytical model was developed to predict the ultimate moment capacity of the URM walls. The procedure outlined in standard guidelines was also utilized to compute the flexural capacity of wal...

Blast response of polymer-retrofitted masonry unit walls

Abstract This paper presents recent efforts that used polyurea to reinforce clay brick masonry unit walls in dynamic event. In order to investigate the peak pressure of damage, failure modes and failure mechanisms of spray-on polyurea reinforced clay brick masonry unit walls subjected to blast, six tests were performed. The results of tests suggest that the polyurea layer can have a significant effect on the damage pressure of the clay brick masonry unit wall and aerated concrete block wall. The primary damage of the clay brick masonry unit wall are the fracture of the brick and the mortar crack that extended from top to bottom at the center of the wall. The deformation of clay brick wall is minimal. The failure modes of the aerated concrete block wall are the most mortar crack and dominant entire deformation. The polyurea layer can significantly improve blast resistance, and turn the collapse of unreinforced wall into local mortar joint separation and the development of flexure in the walls. The presence of polyurea coat approach offers the potential advantage of more-efficiently absorbing strain energy of host structure. The masonry unit wall test results clearly indicate that the blast resistance of clay brick masonry far exceeds that of aerated concrete block wall. The polyurea layer can effectively prevent the collapse and structural failure of the wall, and minimize producing deadly fragments of the reinforced walls.

Ener-Habitat: An online numerical tool to evaluate the thermal performance of homogeneous and non-homogeneous envelope walls/roofs

The online numerical tool Ener-Habitat, designed to evaluate the thermal performance of homogeneous and non-homogeneous walls or roofs of the building envelope using a time-dependent heat transfer model, is presented. This tool is useful in evaluating constructive systems composed by up to seven homogeneous layers and also constructive systems composed by one non-homogeneous layer plus up to six homogeneous layers. The non-homogeneous layer can be either filled or hollow block type. Ener-Habitat solves the time-dependent heat transfer equation with convective boundary conditions on both sides, in one-dimension for homogeneous constructive systems and in two-dimensions for constructive systems containing one non-homogeneous layer. It takes into consideration that the constructive system is either in a non air-conditioned room or in an air-conditioned one. The one-dimensional model for homogeneous multilayered constructive systems is validated by comparison with EnergyPlus results. The two-dimensional model is validated by calculating the heat transfer through a concrete hollow block wall in steady-state and the comparison with experimental results. Ener-Habitat is proved to be a reliable tool.