Unreinforced Concrete Block Research Articles

Seismic Strengthening of Unreinforced Concrete Block Masonry Walls with High Ductile Fiber-Reinforced Concrete (HDC)

ABSTRACT Unreinforced concrete block masonry (URM) walls are seismic vulnerable. Thus, this study examined the responses of URM walls strengthened using high ductile fiber-reinforced concrete (HDC) to assess the effectiveness of the proposed retrofitting technique. A reference specimen and five retrofitted specimens were tested based on the cyclic loading program; the strengthening configurations included the HDC strips or layers. The experimental results validated the effectiveness of the retrofitting techniques for enhancing the seismic performance of URM walls. The paper proposed the formulas to calculate the bearing capacity of each specimen corresponding to different failure modes, which is informative for engineering design.

Seismic Retrofit or Rehabilitation of the Structures/Buildings - A Review

Abstract: This research programme provides solutions addressing the comparative absence of a national platform of knowledge and expertise associated with seismic retrofit or rehabilitation of the multi-storey buildings. This will be achieved through two research objectives that define retrofit solutions for building classes differentiated by:  Age and  Construction materials. The knowledge created in this proposal will be embodied in a Seismic Retrofit Manual titled “Assessment and Improvement of the Structural Performance of Buildings”. Dissemination of research findings will be achieved through “Seismic Retrofit Strategies and Solutions for Existing Buildings: Implementation of the retrofit manual within undergraduate and post-graduate structural engineering programs. Uptake of these solutions will provide national benefit through improved community resilience and greater readiness, as seismically retrofitted multi-storey buildings will be safer to occupy during and after a major earthquake. Economic benefit will primarily accrue through prevention of damage to multi-storey buildings and social benefit will result from lives saved. Rehabilitation is defined as the act or process of making possible a compatible use for a property through repair, alterations, and additions while preserving those portions or features which convey its historical, cultural, or architectural values. Keywords: Earthquake; Unreinforced Concrete Block Masonry; Retrofitting; Rehabilitation; Vulnerability assessment;

Seismic Assessment of Unreinforced Concrete Block Masonry Buildings Before and After Retrofitting: A Case Study

Abstract: This article presents the results of a case study on the performance of unreinforced concrete block masonry building system. The configuration and materials used for the single-story building are typical of those found in the northern areas of 2005 Kashmir earthquake. The retrofitting of the building was done using Ferro-cement overlay and cement based grout injection. Combined shear and flexure failure was observed during the test before retrofitting. The lateral load capacity of the retrofitted building was significantly improved and the damage mechanism was transformed from mixed compression-flexureshear to a more stable flexural rocking mode. Damage patterns and deformation behavior of the retrofitted structure are compared to the intact structure to quantify the benefits of retrofitting scheme, which is proposed as an efficient approach for the rehabilitation of the existing buildings. Study data were analyzed and presented in the form of force-deformation loops and envelope curves. Based on the measured data, different performance levels before and after retrofitting of the structure have been established. The results from this study are expected to guide future efforts on development of design recommendations and vulnerability assessment of buildings. Keywords: Earthquake; Unreinforced Concrete Block Masonry; Retrofitting; Quasi Static Test; Ferro-Cement Overlay; Rehabilitation; Vulnerability assessment;

Use of reclaimed water for unreinforced concrete block production for the self-construction of houses

AbstractExperiments were conducted to evaluate the possibilities of using treated wastewater for the production of unreinforced concrete blocks. Compressive strength, water absorption and morphology tests of concrete blocks, produced from different makeups of mixing water, drinking water, drinking water spiked with ammonium and phosphate, and the effluent of the city's wastewater treatment plant, were evaluated. Results showed that the compressive strength of blocks manufactured using treated wastewater was as high as of the blocks produced using drinking water. Ammonium, phosphate and chlorine were found not to have a negative effect on the strength of the blocks. Water absorption tests confirmed the results of the compressive strength, as lower humidity was found in cases of higher strength. In the process of cement hydration, crystals of calcium silicate and calcium hydroxide were observed by morphology tests. From the variability in the results, it could be concluded that the quality of the mixing water was not the only factor that influenced the strength of the unreinforced concrete blocks. The observed differences in strength could, for example, also be attributed to the manufacturing process.

Experimental behaviour of unreinforced and reinforced concrete block masonry walls under uniaxial compression

This paper presents the details of experimental investigations on the compressive strength of full scale hollow concrete block masonry walls. Comparison of load carrying capacity of unreinforced masonry walls with reinforced masonry walls have been studied as part of this study. The failure mechanism of reinforced hollow concrete block masonry (RHCBM) walls and unreinforced hollow concrete block masonry (URHCBM) walls have been studied. It is observed that the load carrying capacity of RHCBM walls are about 39.40% higher compared to URHCBM walls which is due to presence of marginal amount of reinforcement (about 0.12% of cross sectional area) and grout.

Stress strain characteristics of reinforced hollow concrete block masonry melded with mesh reinforcement

Plain Masonry similar to unreinforced concrete, is resilient in compression and weak in tension. Masonry gains strength with age similar to concrete. Inspite of these resemblances, there exist numerous differences between masonry and concrete. The major difference is the regular pattern of horizontal joints(known as bed joints) at specific intervals along the height of walls introduce due to the method of construction of masonry. These bed joints make masonry a direction dependent material possessing orthotropic properties, unlike concrete which is usually regarded as isotropic atleast in the elastic range. Mechanical properties such as compressive strength, tensile strength, flexural strength are a pre-requisite as part of the design of masonry walls. The present study deals with the experimental study to evaluate the mechanical properties of hollow concrete block masonry specimens for varying cement mortar proportions melded with mesh reinforcement at bed joints. Parameters such as compressive strength, modulus of elasticity, failure pattern have been studied and compared for reinforced and unreinforced hollow concrete block prisms. The study showed higher compressive strength and improved elastic modulus for specimens with higher grade of mortar

In-plane cyclic loading tests of concrete hollow block masonry walls retrofitted with high ductile fiber-reinforced concrete

When subjected to horizontal loading induced by an earthquake, concrete block masonry walls generally exhibit vulnerability, particularly under high shear force. To improve the failure mode and lateral resistance of these walls, and to promote the application of concrete block units in multi-story masonry buildings, this study proposes techniques for retrofitting concrete hollow block masonry walls by installing coated high ductile fiber-reinforced concrete (HDC) layers. Six half-scale testing specimens, including three unreinforced concrete block masonry walls (URM) and three confined walls, were tested under in-plane cyclic loading to investigate their seismic performance before and after the upgrade. The test results indicate that these configurations significantly increased the lateral shear strength, stiffness, and energy dissipation capacity of the URM walls, and changed the brittle failure mode into a ductile mode. For the confined masonry walls, the lateral shear resistance and the stiffness were obviously enhanced, whereas the energy dissipation showed negligible improvement. The retrofitted walls showed higher residual strength and less damage, making them favorable for post-earthquake restoration. To estimate the ultimate shear strength of the tested specimens, relevant formulas developed in this study are presented.

In-plane seismic retrofitting of hollow concrete block masonry walls with RC layers

Results of numerical studies on the in-plane shear capacity of full-scale unreinforced concrete block masonry walls, externally retrofitted by reinforced concrete layers, are presented. Tests are first performed on small-scale masonry walls, results of which are used to develop and calibrate numerical micro models for full-scale walls. Nonlinear pushover analyses are conducted to investigate the effects of a number of problem variables on the performance of the retrofitted walls. Numerical results reveal that wall boundary conditions affect its response considerably. Also, a significant enhancement in wall capacity and ductility is observed due to the application of the reinforced concrete layers.

Seismic Capacity Assessment of Confined Brick Masonry Building: An Experimental Approach

Brick masonry is widely used for building construction throughout the world. However, unreinforced brick masonry buildings performed poorly in the 2005 Kashmir earthquake, in Pakistan, resulting in a decline in the use of brick masonry. In order to investigate and quantify the performance of brick masonry against the seismic forces by confining it through typical stiffer, line elements (column and beams), a full‐scaled room model of an area 3048 × 3658 mm (10 × 12 ft) and height of 3353 mm (11 ft) was constructed using confined brick masonry. The model was tested under quasistatic loading system. Crack pattern was noted at the end of each loading cycle. The response of the model was interpreted through a hysteresis curve, which was then idealized by a bilinear curve. A comparison of the results has been made with four different studies done on the similar model made of unreinforced brick masonry before and after retrofitting and unreinforced concrete block masonry before and after retrofitting previously tested at the same testing facility.

Seismic Behaviour Factor for Unreinforced Concrete Block Masonry Walls Retrofitted by RC Layers

This paper reports on experimental and numerical investigations of the seismic behaviour of unreinforced concrete block masonry (URCBM) structural walls, externally retrofitted on one, or both sides, by reinforced concrete (RC) layers. The behaviour factor (R) components are extracted from nonlinear static pushover analyses of full-scale masonry walls having different aspect ratios. It is found that R-value of masonry shear wall increases with an increase in the aspect ratio of the wall. Also, application of RC layers to the wall has a profound effect on the behaviour factor, as it directly affects both ductility and ultimate capacity of the wall. Finally, based on findings presented, R-values of 2.0, 2.5 and 3.0 are proposed for URCBM, one-sided and two-sided retrofitted concrete block masonry shear wall construction, respectively.

Experimental Study on Lateral Strength Evaluation of Unreinforced Masonry-Infilled RC Frame

In this study, RC frames with unreinforced masonry (URM) infill for typical school buildings in Korea are experimentally investigated to evaluate their seismic performance. For this purpose, one-bay, one-fourth scale specimens, with unreinforced concrete block (CB) infill having different boundary conditions due to beam rigidity, are tested under in-plane cyclic loading, using a distinctive measurement scheme consisting of three-axis strain gauges attached to all CB units. In this paper, the diagonal strut mechanism of CB infill including its main strut angle, average compressive strain, and equivalent strut width is discussed using principal compressive strains on CB units. The lateral strength carried by CB infill and RC frame from the overall response of the specimens is also explained, based on the compressive stress acting on the infill and the curvature distribution along RC members during the test.

지진피해를 입은 무보강 조적채움벽체를 갖는 RC 골조의 손상도 및 잔존내진성능의 평가

After an earthquake, the major concerns to damaged buildings are their safety/risk to aftershocks, quantitative damage assessment to evaluate their residual seismic capacity and to identify necessary actions on the damaged buildings. Few investigations on unreinforced masonry infill walls, however, have been made to quantitatively identify their damage level and criteria to judge necessary actions for their continued use, repair and rehabilitation although their damage has been often found in the past damaging earthquake. In this study, reinforced concrete (RC) frames with unreinforced concrete block (CB) walls for school buildings in Korea were tested under cyclic loadings to propose the evaluation method of their residual seismic capacity. In this paper, the relationships between the damage class represented by residual crack widths and the seismic capacity reduction factor corresponding to residual seismic capacity for columns and CB walls were estimated analytically and experimentally, and the factor corresponding to each damage class of RC frame with CB wall was proposed. Futhermore, the damage descriptions and crack widths corresponding to damage classes for CB walls was defined.

Seismic Capacity Assessment of Unreinforced Concrete Block Masonry Buildings in Pakistan Before and After Retrofitting

This article presents the results of an experimental study on the performance of a full-scale unreinforced concrete block masonry (URCBM) building system tested under quasi-static loading. The configuration and materials used for the single-story URCBM building are typical of those found in the northern areas of Pakistan affected by the 2005 Kashmir earthquake. The retrofitting of the building was done using ferro-cement overlay and cement based grout injection. Combined shear and flexure failure was observed during the test before retrofitting. The lateral load capacity of the retrofitted building was significantly improved (more than 200% of the original strength) and the damage mechanism was transformed from mixed compression-flexure-shear to a more stable flexural rocking mode. Damage patterns and force-deformation behavior of the retrofitted structure are compared with those of the intact structure to quantify the beneficial effects of retrofitting scheme, which is proposed as an efficient approach for the rehabilitation of the existing buildings. Experimental data were analyzed and presented in the form of force-deformation hysteresis loops and envelope curves. Based on the measured data, different performance levels before and after retrofitting of the structure have been established. Response modification (R), displacement ductility (μD), and displacement amplification (Cd) factors were also derived. The results from this study are expected to guide future efforts on development of design recommendations and vulnerability assessment of buildings in Pakistan.

Explosive Demolition of Buried Unreinforced Concrete Block

Explosive Demolition of Buried Unreinforced Concrete Block

Time-Response Analysis of Arching Unreinforced Concrete Block Walls Subjected to Blast Loads

The new ASCE59-11 standards currently limit the use of unreinforced masonry (URM) walls in blast-resistant construction, regardless of the wall boundary conditions. This is attributable in part to the lack of experimental and analytical studies focusing on evaluating the response of URM walls under blast when the walls are forced to arch between the surrounding frame members. In this paper, the out-of-plane displacement response and structural stability of one-way vertical arching URM walls subjected to blast loads are investigated. A simple bilinear moment-rotation relationship is developed to simulate the arching wall responses. The model takes into account the masonry material strength, thrust forces, and wall geometry. Time-response analyses were performed using both single-degree-of-freedom (SDOF) and two-degrees-of-freedom (2DOF) models. Both models take into account the rocking phenomenon and second-order effects. Responses generated by both models were validated using experimental data reported previously. For preliminary design, performance charts were developed to correlate the effects of the wall slenderness ratio, masonry strength, and block size to the wall response under different levels of blast loads. The developed model and charts can be used as simple and quick calculation tools to estimate the required thickness, height, and strength of the wall under an expected blast threat when hardening of URM walls is necessary, with arching being considered as one of the alternatives.

FRP로 보강된 신형 소파블록의 정적 성능 실험

In this study the mechanical performance of the new wave dissipating block is evaluated through experiment and numerical analysis. Also, by selecting adequate reinforcement, the improvement of the structural performance is examined. The reinforcement is designed by predicting the amount of tensile force and the location where the tensile stress develops in the new wave dissipating block through numerical analysis. The new wave dissipating block is reinforced with the ordinary steel bars and the fiber reinforced plastic(FRP) bars which have advantages in ocean environment in terms of corrosion and fatigue. The test result shows that the fracture resistance of the un-reinforced concrete block is 350 kN which is about 6.2 times that of the weight of the block. All the test blocks which are reinforced by either steel of FRP bars show strength capacity of over 900 kN which is the maximum load of the test equipment. Although the single reinforcement with larger-diameter bars has advantage in terms of construction convenience, it is recommended to use multiple number of smaller-diameter bars in order to reduce the crack width.

Earthquake Disaster Mitigation through Retrofitting of Unreinforced Concrete Block Masonry Buildings

This paper presents an experimental study on the improvement of unreinforced block masonry buildings against earthquake disasters. Unreinforced concrete block masonry piers have been tested for lateral strength before and after retrofitting. Welded mesh and injection of cement grout techniques have been used for piers retrofitting. The analysis of experimental results demonstrates that proper retrofitting can decrease the risk to concrete block masonry buildings in future scenario earthquakes. Retrofitting increases not only the overall strength of unreinforced masonry piers but also the ductility.

In-Plane Shake-Table Testing of GFRP-Strengthened Concrete Masonry Walls

In-plane shake-table tests were performed on eight full-scale unreinforced concrete block walls. Three of the walls were left as plain unreinforced masonry and five were strengthened using glass-fiber-reinforced plastic (GFRP) strips in four different configurations. All walls were first subjected to design-level earthquake records to determine the improvement obtained from the addition of the GFRP. The walls were then subjected to extreme-level earthquake records to examine the ultimate failure modes and the effects of the various GFRP configurations on the response of the walls. It was observed that all strengthened specimens performed well during the design-level shaking, and three of the four GFRP configurations also performed well during the extreme-level shaking. The tests showed that the use of vertical GFRP strips alone is able to improve the in-plane performance of URM walls. The strips were also able to control the failure modes, and prevent collapse after severe damage, improving significantly the life safety performance of URM walls.

Optimum strength ratio of hysteretic damper

An accurate and practical testing technique to study seismic performance of multi-storey infilled frames is formulated. This technique is based on the pseudo-dynamic method which can provide an acceptable approximation of the dynamic performance of structures under the influence of earthquake excitation. The pseudo-dynamic experimental technique is outlined and applied for testing a two-bay, twc-storey gravity load designed steel frame infilled with unreinforced concrete block masonry walls. From the discussion of the results, the dynamic performance of the tested structure is assessed.

Response of infilled frames using pseudo-dynamic experimentation

SUMMARY An accurate and practical testing technique to study seismic performance of multi-storey infilled frames is formulated. This technique is based on the pseudo-dynamic method which can provide an acceptable approximation of the dynamic performance of structures under the influence of earthquake excitation. The pseudo-dynamic experimental technique is outlined and applied for testing a two-bay, two-storey gravity load designed steel frame infilled with unreinforced concrete block masonry walls. From the discussion of the results, the dynamic performance of the tested structure is assessed. ( 1998 John Wiley & Sons, Ltd. Pseudo-dynamic experimentation is a testing procedure in which the dynamic response of the structure is calculated and the obtained displacements are statically applied to the structure in an on-line procedure. This technique is essentially identical to traditional time domain analysis but rather than idealizing the non-linear sti⁄ness characteristics of the structure, the static restoring forces are directly measured from the specimen as the experiment proceeds. Computation of displacements is based on numerical integration of the governing second-order di⁄erential equations of motion of a system with assumed mass and damping properties and with a forcing function corresponding to a selected dynamic loading. During the test, actual displacements and restoring forces are measured using equipment normally used for static experiments. These measured quantitites are utilized in subsequent calculations. In this way, both dynamic e⁄ects and progressive damage of the specimen are included in the imposed displacements, and the procedure allows for an in-depth monitoring of the performance of the structure for the entire duration of realistic earthquake excitation. Infilled frames have been investigated experimentally by many researchers, most often with monotonic (see e.g. Reference 1) or quasi-static cyclic loading (see e.g. Reference 2), and in a few cases with actual dynamic