On the in-plane shear response of the high bond strength concrete masonry walls

Conventional unreinforced masonry walls subject to in-plane shear loading fail due to exceedance of shear and tensile bond strengths. This paper examines whether or not the in-plane shear capacity of masonry walls would increase with the increase in the bond strengths through experimental and numerical investigations. For these investigations, shear walls were built with high bond strength polymer cement mortar; they were applied in thin layers of 2 mm thickness each. Material tests were carried out to characterise the bond and the compressive strengths of the high bond strength thin layer mortared masonry; the bond strengths were found approximately double that of the conventional 10 mm thick cement mortars. The shear walls, however, exhibited significantly lower capacity (contrasting the expectation) and displayed base course sliding mode of failure. To ascertain the validity of the experimental results, a combined surface contact—interface element micro finite element (FE) modelling technique was formulated; the results adequately reproduced the experimental datasets. The validated FE model was then applied to examine the effect of the aspect ratios and pre-compression levels to the failure modes, deformation and strength of the high bond strength shear walls and is shown that once the pre-compression exceeds 15% of the masonry compressive strength, the base sliding failure mode changes to the diagonal cracking mode with corresponding increase in in-plane shear capacity. Therefore, it is concluded that the increase the bond strength without regard to pre-compression could adversely affect the safety of the high bond strength unreinforced masonry shear walls.     

Experimental study of dry stone masonry walls using digital reflection photoelasticity

Response of dry stack stone masonry walls under mechanical loading is complex and difficult to determine, mainly due to heterogeneous and discrete nature of the components of the stone wall. In this paper, reflection photoelasticity is used on scaled down models of stone masonry wall under uniaxial compression. Two walls are tested, and the methods to obtain near perfect dry stack masonry for reflection photoelastic studies are presented. Five-step phase-shifting methods are employed with TFP/RGB photoelasticity to quantitatively analyse the mechanical behaviour of the dry stack masonry walls. Isochromatics and isoclinic data are processed to obtain other whole field experimental stress data. Highly stressed zones are observed resulting in distinctive localised vertical failure in some of the stone units. In dry stack masonry construction, the failure mechanism is found to be dictated by the contact mechanics, which are governed by the non-uniformity of block geometry even in very regular dry stack masonry.     

The hygrometric behaviour of some artificial stone materials used as elements of masonry walls

The hygrometric behaviour of four artificial stone materials utilised in the building industry for thermal insulation has been investigated utilising analytical methods typical of the applied petrography. The experimental data on the water absorption both in the liquid and in the vapour phase are in agreement with the data obtained from the natural stone materials and point out the existence in each material of a strong correlation between the absorption mechanisms and the porosimetric characteristics.

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Résumé On a étudié, à l’aide de méthodes analytiques utilisées en pétrographie appliquée, le comportement hygrométrique de quatre matériaux pierreux artificiels utilisés dans l’industrie du batiment pour leurs propriétés d’isolants thermiques. Les données expérimentales sur l’absorption d’eau aussi bien à l’état liquide qu’à l’état de vapeur, sont en accord avec les données obtenues sur les matériaux pierreux naturels, c’est-à-dire que dans chaque matériel il y a de fortes corrélations entre les mécanismes d’absorption d’eau et les caractéristiques porosimétriques.

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Editorial Note The CNR (Consiglio Nazionale delle Ricerche) is a RILEM Titular Member. The University of Florence is a RILEM Associate Member.     

Shock-tube tests of concrete slabs

To investigate the high-speed dynamic behaviour of concrete structures on a scale that is realistic for this material, in tests of sufficient quality to yield quantitative results to validate codes, a slab testing procedure was developed at the LEA with the help of the concretes section of the LCPC. Special attention was paid to experimental control of the loading (use of the shock tube), conditions of support, instrumentation, and data acquisition. The test can be used to check and/or improve concretes and other structural materials intended to withstand shocks, impacts and explosions.     

Shear effect on seismic behaviour of masonry walls

Firstly, a finite element numerical model for nonlinear dynamic analysis of masonry walls is briefly presented. The model can simulate the main nonlinear effects of masonry and reinforced concrete. It is simple and intended to the engineering application. A macro model of masonry is adopted for simulation its behaviour in compression and for cracks modelling in tension. Two constitutive models are implemented to describe the shear resistance of the masonry wall: One that does not take the effect of the shear failure of masonry (Model 1), and second which takes into account shear failure of masonry (Model 2). By using the numerical model, the shear effect of masonry on the behaviour of two‐storey unreinforced and confined masonry walls exposed to harmonic base acceleration was investigated. The height to length ratio of the walls and the quality of masonry are varied. Analysis results for Model 1 and Model 2 are significantly different. Model 1 gives a significantly higher load bearing capacities of masonry. It was concluded that the shear effect of masonry significantly depends on the type of the masonry walls (unreinforced, confined), the quality of the masonry and height to length ratio of masonry walls.     

Behavior and modeling of strengthened three-leaf stone masonry walls

The application of three different intervention techniques on three-leaf rubble stone masonry walls are discussed here. Injections, repointing, and the placing of ties connecting the two external whytes were considered, both singularly and in combination. Lime-based products were chosen for injection grouts and repair mortars, to ensure better compatibility with the original materials. The experimental tests, performed on seventeen large scale samples under compressive loads, showed that: (i) injections are very effective to improve the mechanical characteristics of the walls; (ii) the other techniques have less influence on the strength but can operate in avoiding ‘brittle’ failure modes (ties placing) and in improving the durability of the masonry (repointing); (iii) the combination of the techniques ensures the enhancement of the global behavior of the walls. The integration of the experimental results with data available in literature allowed the calibration of an analytical model able to predict the compressive strength of injected walls, based on parameters given by simple experimental tests.     

Strengthening of three-leaf stone masonry walls: an experimental research

The paper summarizes the results of an experimental research carried out on three-leaf masonry walls of typical granite stone constructions from the North of Portugal. The research aimed at studying the behaviour under compression of this wall typology, as well as the improvements introduced by common strengthening techniques applied for the structural rehabilitation of masonry heritage buildings. Ten masonry specimens were tested, plain or strengthened by transversal tying of the external leaves, with GFRP bars, or/and by injection of the inner leaf, with a lime-based grout. The results obtained showed that these strengthening techniques were successful in increasing the compressive strength of the walls and in improving their behaviour under compressive loads.     

Full-scale field tests of concrete slabs subjected to blast loads

This paper describes full-scale field explosion tests on protected and unprotected concrete slabs. The experiments were performed by the Protective Technologies Research & Development Center of the Faculty of Engineering Sciences of the Ben-Gurion University of the Negev (BGU-PTR&DC) under a contract with the Israeli Ministry of Defense (MoD) and the supervision of the IDF Steering Committee for R&D of Protective Structures. The aims of the tests were to: (1) extract data on the dynamic response of an elementary concrete structure to blast loads in order to verify and validate (V&V) our corresponding computer codes; and (2) check the ability of aluminum foams to mitigate blast wave loads. Time-dependent measurements of the response of the concrete slabs to the blast wave loads were successfully recorded using a variety of measurement devices. The obtained data have been used to verify and validate our computer codes.     

Determination of partial resistance factors for unreinforced masonry shear walls

Partial safety factors for resistance applied in the design equation of semi‐probabilistic formats can be obtained from the evaluation of a test database. These partial safety factors are influenced by two factors, the material uncertainty and the model uncertainty. This topic is covered in a former publication [1]. It includes the determination of a partial factor for the model uncertainty of unreinforced masonry shear walls. In this study the authors examine the next step, and calculate the partial factor of resistance applying the same method, as recommended i n EN 1990 – Annex D. In addition to the Coefficient of Variation (COV) for the model uncertainty, the calculation of the resistance partial factor considers deviations in geometry, as well as loading and material properties. The influence of the material uncertainty on structural performance is considered in the calculation by means of a weighted average of all COV values for various types of material properties, based on the number of relevant failure modes in the test database. In the last step, the resistance partial factors for models defined in DIN EN 1996‐1‐1/NA and DIN EN 1996‐1‐1/NA – Annex K are calculated by applying the probabilistic methods recommended in EN 1990 – Annex D and the model bias.     

Shear design of reinforced concrete beams, slabs and walls

The paper presents the background to the shear design provisions for reinforced concrete beams and slabs used in the Australian practice. Correlation of design equations with experimental results are given. The design provisions are illustrated by examples. The importance of shear strength in the design of structural walls is discussed. A new expression to calculate the shear strength of walls is presented.     

Shear resistance of masonry walls and Eurocode 6: shear versus tensile strength of masonry

In the case of masonry structures subjected to seismic loads, shear failure mechanism of walls, characterised by the formation of diagonal cracks, by far predominates the sliding shear failure mechanism. However, as assumed by Eurocode 6, the latter represents the critical mechanism for the assessment of the shear resistance of structural walls. The results of a series of laboratory tests are analysed to show that in the case of the diagonal tension shear failure the results of the Eurocode 6 based calculations are not in agreement with the actual resistance of masonry walls. The results of calculations, where the diagonal tension shear mechanism and tensile strength of masonry are considered as the critical parameters, are more realistic. Since the results of seismic resistance verification, based on the Eurocode 6 assumed sliding shear mechanism, are not in favour of structural safety, it is proposed that in addition to sliding shear, the diagonal tension shear mechanism be also considered. Besides, in order to avoid misleading distribution of seismic actions on the resisting shear walls, the deformability characteristics of masonry at shear should be determined on the basis of experiments and not by taking into account the Eurocode 6 recommended G/E ratio.     

Structural behaviour of basalt fibre reinforced glass concrete slabs

Small-scale slab tests at ambient and elevated temperatures, conducted on horizontally unrestrained simply supported slabs, are presented in this paper. The aim of this research is to investigate the structural behaviour of concrete produced from different percentages of glass sand (20, 40, and 60 % by weight) and reinforced with different volume fractions of basalt fibre (0, 0.1, 0.3, and 0.5 % by total mix volume), when subjected to large vertical displacement. The results were also compared against similar structural members with concrete that did not contain glass or fibres. The results showed that the fracture of the reinforcement was the mode of failure for all the slabs and the load carrying capacity was enhanced above the theoretical yield-line load. For the slabs tested at elevated temperatures, the enhancement due to membrane action was at least twice as high as that recorded in the ambient temperature tests. The slabs with higher glass sand and basalt fibre content also exhibited greater enhancement and failed at higher displacement. The results also showed that the enhancement in the concrete with glass aggregate and basalt fibre was greater than that in concrete that contained no glass or fibre by up to 26 and 31 % at ambient temperature and in fire respectively.     

Flexural behaviour of small steel fibre reinforced concrete slabs

Influence of length and volumetric percentage of steel fibres on energy absorption of concrete slabs with various concrete strengths is investigated by testing 28 small steel fibre reinforced concrete (SFRC) slabs under flexure. Variables included; fibre length, volumetric percentage of fibres and concrete strength. Test results indicate that generally longer fibres and higher fibre content provide higher energy absorption. The results are compared with a theoretical prediction based on random distribution of fibres. The theoretical method resulted in higher energy absorption than that obtained in experiment. A design method according to allowable deflection is proposed for SFRC slabs within the range of fibre volumetric percentages used in the study. The method predicts resisting moment–deflection curve satisfactorily.     

Flexural behaviour of concrete slabs reinforced with steel sheet

This is a report on tests carried out on concrete slabs reinforced with bonded steel sheet, where flexural stiffness and ultimate capacity were improved versus conventional r. c. slabs. In the case of sheet metal, which has biaxial strength properties, the steel is far better utilized than in that of the uniaxial reinforcing bars, hence the slab structure is more economical. Fire- and corrosion protection is provided by a 10 mm coating of fire-shield plaster (or some other insulating agent).