Block Masonry Buildings Research Articles

Analytical prediction of the seismic resistance of masonry buildings retrofitted by Steel Fiber Reinforced Mortar coatings

An extensive experimental program has been performed in the last years at the University of Brescia to show the effectiveness of the in-plane seismic strengthening or repairing of existing masonry buildings by Steel Fiber Reinforced Mortar (SFRM) coatings. In particular, the tests on a full-scale hollow clay block masonry building showed the applicability of the retrofitting technique on the external surface of the structure only.An analytical model already developed and validated is briefly presented in this article and applied to the building experimentally tested. Particular attention is paid to the simplified schematization of the masonry piers based on the fracture lines expected before and after retrofitting. The effectiveness of the analytical model in predicting the seismic resistance of the building is assessed by comparing the analytical results with those obtained from the experimental test.Finally, the analytical model is applied to a real two-story residential building made of concrete hollow units to perform the seismic verification of the structure. The analytical prediction of the global seismic resistance of the building is compared with that obtained from a non-linear static analysis carried out with the finite element program Midas FEA. The results of the comparison will further prove the reliability of the proposed analytical model.

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;

Confined hollow concrete block masonry buildings: An experimental approach for vulnerability assessment

This paper presents experimental study on the response of a sustainable structure 3.65 x3.05x3.35 m, made with confined hollow concrete block masonry (CHCBM). The model was tested under quasi-static cyclic test to assess the response against seismic load and to determine the potential vulnerability. Based on test data, envelope curves and bilinear idealized curves were drawn according to both Magenes–Calvi and Elnashai methods. Different performance levels i.e. Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP) were evaluated based on both methods. Damage pattern and force-deformation behavior of CHCBM building was compared with models of the similar configuration and loading conditions. Similarly values of Response modification factor (R), Displacement Ductility (µD) and Displacement amplification factor (Cd) were calculated and compared with the previously tested models and it confirmed that CHCBM building was ductile and structurally integrated under earthquake loading.

Geometrically modified auxetic polyurethane foams and their potential application in impact mitigation of masonry structures

Hollow block masonry buildings constructed alongside busy roads are vulnerable to vehicular impacts resulting in damage to property and harm to the building and vehicle occupants. This paper presents a method for the design and insertion of various forms of geometrically modified auxetic foam structures inside the hollow cores of block masonry walls for mitigating the adverse effects of such impacts. Due to the low tensile strength of masonry, the insertion material should possess high energy absorption characteristics and high strength for impact damage mitigation which can be achieved through auxetic foams with negative Poisson’s ratio. To this end, finite element models of geometrically modified auxetic foams (GMAFs) are developed by inserting thin polyester sheets and hollow acrylonitrile butadiene styrene (ABS) tubes of various geometries into conventional polyurethane foams. The proposed geometrical configurations of inserted tubes and sheets result in auxetic behaviour of the conventional foam with a maximum negative Poisson’s ratio of about −12. These foam models are validated analytically and then employed to model masonry walls with auxetic foam insertions in the hollow cores of blocks. These masonry wall models are then analysed under high-velocity lateral impacts. Results show the beneficial change in the failure mechanism of the masonry walls which altered from severe damage of wall face to the rebound of the impactor without penetration by reducing the displacement by four times, due to the presence of the auxetic foam insertions. This phenomenon occurred due to the significant energy dissipation caused by the combined effects of the re-entrant shaped hollow tubes and thin polyester sheet arrangements in the GMAF. Outcomes of this study will contribute towards safer masonry buildings along busy road fronts.

Shaking table experiment of a recycled concrete block masonry building structure with a ‘self-contained’ structural system

This paper proposed a ‘self-contained’ structural system for structural columns and ring beams and used recycled concrete blocks (RCBs) as wall materials. Based on this design concept, a full-scale model of a new masonry building structure was established. The Castaic wave, the Taft wave, and an artificial wave were sequentially input to the shaking table, and the effects of different ground motions on the structural model were simulated. The changes in the natural frequency and damping ratio of the test model and the acceleration, displacement, and strain responses of the structure were studied under different seismic wave excitations. Finally, the overall seismic resistance of the model was determined. The results showed that the ‘self-contained’ structure system exhibited excellent cooperative performance. Moreover, the test model can fully meet the degree-7 seismic fortification requirements, in which the damage sustained from small earthquakes is not substantial, the damage sustained from moderate earthquakes can be repaired, and the damage sustained from large earthquakes does not cause structural failure. The results showed that RCBs can replace ordinary concrete blocks in practical engineering projects. However, the construction measures for the door and window openings should be strengthened in actual projects.

Repair of Block Masonry Panels with CFRP Sheets.

In the 1980s, block masonry started to be widely used for new constructions in Italy’s earthquake prone areas. However, recent seismic events demonstrated that block masonry buildings may need to be repaired after earthquakes due to cracking. Construction defects are the main cause for cracking of block work masonry. Carbon fiber reinforced polymer (CFRP) sheets have been used as a local repair method for non-defective and defective wall panels. An experimental program was formulated to investigate the shear behavior of block masonry walls repaired with CFRP sheets. A total of six wall panels were constructed in the laboratory and tested in shear (in-plane lateral loading). It was found that, although the control (non-defective) wall panels had a high ultimate load capacity, the use of CFRPs reduces the effects of construction defects and restores the lateral load capacity in non-defective walls. Overall, this research suggests that the use of epoxy-bonded CFRP sheets could be used for local repair of cracked wall panels.

Seismic strengthening of clay block masonry buildings with composites: an experimental study of a full scale three-storey building model

The efficiency of strengthening of unreinforced hollow clay block masonry buildings with fibre reinforced mortar coatings has been investigated. A full scale three-storey building model and a series of accompanying walls have been built and tested. Reference unstrengthened, and strengthened specimens of each type have been tested by subjecting them to cyclic shear at constant compressive load. First, the three-storey model was tested in its original state until the maximum resistance was attained and major, but still repairable damage, developed in the walls. Then, the damaged model was strengthened with fabric reinforced cementitious mortar coating and re-tested up to near collapse limit state. Typical storey mechanism was observed in original and strengthened state, with the majority of damage concentrated in the walls of the bottom storey. Diagonally oriented shear cracks prevailed in the elements in the direction of loading. The behaviour of single walls in cyclic shear tests was similar to that observed in the piers of the building models. The analysis of test results indicated that the resistance and displacement capacity of unreinforced masonry structures of the particular type tested can be significantly improved if delamination and separation of coating is prevented. Finally, a calculation model for the assessment of seismic resistance of reference and strengthened building model is presented and the comparison between calculated and experimental results discussed.

High‐rise concrete and clay block masonry building in Brazil

AbstractBrazilian structural concrete and clay block masonry construction shares many common features with construction all over the world: blocks of a similar shape are bedded in mortar, vertical and horizontal reinforcement is placed in grouted cells, engineering analysis and design follows universal principles and local design codes mimic those adopted elsewhere. However, loadbearing masonry construction in Brazil has become one of the most preferred high‐rise building systems due to its cost‐effectiveness and ease of construction compared to normal reinforced concrete solutions. This paper provides an overview of loadbearing masonry building in Brazil, including case studies on notable high‐rise masonry structures, with an overview of how Brazilian materials, codes and practices differ from the rest of the world. Finally, the paper explains how the use of high‐strength units assists the growing demand for taller and taller buildings and provides insight into why owners and general contractors often prefer to use structural masonry.

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.

Observed damages in Pakistan due to 16 April 2013 Iran earthquake

This paper presents the record of damages which were observed in Pakistan due to a strong earthquake on 16 April 2013 in Iran. Mashkel was the nearest town in Pakistan close to the epicentre of earthquake. The damages were documented by a survey team during the visit of Mashkel. The intensity of earthquake in most of the visited areas was found to be VIII on the Modified Mercalli Intensity scale. The infrastructure facilities were undamaged and were operating satisfactorily. On the other hand, heavy damage to adobe buildings was caused by the earthquake. Most of the building failure was resulted by the out-of-plane wall collapse; nearly 40 % adobe buildings were collapsed due to ground shaking in some of the affected areas. Reinforced concrete and cement concrete block masonry buildings performed better than adobe buildings. Using the data of building damage and earthquake intensity fragility curves for adobe buildings in Mashkel were developed.

Shaking Table Study of Two Reduced-Scale Single-Storey HCSE Block Masonry Building Models

The seismic resistance characteristics of two building models constructed by Hollow Compressed Stabilized Earth Block from locally available soil that represents normal single room building was examined via the experimental studies in the shake table. One model was constructed with earthquake-resistant features (EQRF) having sill band, lintel band and vertical bands to control the building vibration, and another one was without EQRF. The model with EQRF provides superior seismic resistance as compared with that model without EQRF. To examine the seismic capacity, the models were subjected to harmonic acceleration with gradually increasing amplitude, and specimens were shaken repeatedly until its failure. The test results from Hi-end Data Acquisition system show that model with EQRF behaves better than without EQRF. This modified masonry model with new material combined with band system is used to improve the behavior of masonry building.

Research on recycled concrete and its utilization in building structures in China

Large quantities of construction and demolition (C&D) building waste are being generated as a result of rapid urbanization and natural disasters in China. An increasing awareness of environmental protection is escalating C&D waste disposal concerns. This paper presents a brief introduction to current shaking table test research in China on structures built with recycled aggregate concrete (RAC). Test structures include a cast-in situ frame model, a precast frame model and a block masonry building. The test results prove that it is feasible to use RAC as a structural material in seismic areas, with recommended modifications and proper design, especially in low-rise structures. This paper also presents several successful applications of RAC in civil and structural engineering projects in China, which will serve to promote RAC as a global ecological structural material.

Shaking Table Tests on a Recycled Concrete Block Masonry Building

A full scale model of a block masonry building with the tie column + ring beam + cast-in-place slab system, which was made of recycled aggregate concrete (RAC), was tested on the MTS shaking table at the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China. The design and production of the test model, the design of the testing program and the experimental phenomenon were described in detail. The natural frequency, equivalent stiffness of the structure, the structural damping ratio, the acceleration response, the seismic force response, the displacement response, the base shear response and the structural fragility etc. were analyzed and discussed. The test results demonstrate that the RAC block masonry structure confined by the ‘tie column + ring beam’ system is a good solution to withstand earthquakes. The storey drift ratio and the overall behavior meet the requirements of Chinese design code. Generally, the RAC block masonry structure bounded by the ‘tie column + ring beam’ system with proper design exhibits good seismic behavior and can resist the earthquake attacks under different seismic levels in this study.

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.

Optimum Soil Grading for the Soil-Cement Blocks

Large numbers of soil-cement block masonry buildings exist in India and many other countries. The paper deals with an experimental study on the influence of soil grading on the characteristics of soil-cement blocks and shear-bond strength of soil-cement block masonry triplets. Influence of clay content of the soil-cement block on strength, absorption and durability characteristics, and interfacial mortar-block bond strength has been examined. Some of the major conclusions of the study are: (1) optimum clay content leading to maximum strength is in the range of 14–16%; (2) saturated water content of the blocks increases with increase in clay content of the block; (3) initial rate of absorption decreases with increase in clay content of the block; (4) weight loss after ASTM wire scratch test is minimum when the clay content of the block is about 16%; and (5) optimum clay content for the highest modulus for the blocks and for highest shear-bond strength is about 16%.