| An experimental program was designed and conducted to investigate the strain gradient effect on the capacity, behaviour, constitutive relationship and effective flexural rigidity of masonry prisms. Twenty-one large scale masonry prisms including both grouted and hollow specimens were tested under different loading conditions. Ultimate loads and corresponding applied moments, lateral deflections at critical cross-sections and vertical deformations on tension and compression faces of specimens were obtained and presented in either table or graph format. Linear elastic analysis was used to calculate the compressive stresses at the extreme fibre and moment vs. curvature curves were used to determine the effective flexural rigidities, (EI) eff, at the time of failure for each specimen. Experimental results showed that for both grouted and hollow specimens under compressive loading only, the ultimate loads decreased as the eccentricity increased. This decrease was more significant for grouted specimens than for hollow specimens. At eccentricity vs. thickness ratio, e/t, of 0, 1/6 and 1/4, the grouted specimens attained higher ultimate loads than those of hollow specimens. However, for e/t of 1/3, the hollow specimen failed at a higher load than the grouted specimen. As the end eccentricity ratio, e1/e2, changed from 1 representing single curvature bending to -1 representing double curvature bending, the ultimate load increased. For specimens under combined axial and lateral loading, the effect of axial load on the transverse strength of the prism is associated with the failure modes.; The compressive stresses of grouted specimens subjected to combined axial and single curvature bending were on average 1.5 times that of specimens under concentric loading with specimens under the combined axial and lateral loading showing the highest compressive stresses. In the case of hollow specimens, the ratio was determined to be 1.1. This indicates that strain gradient has more effect on grouted masonry than hollow masonry. It is also observed that the eccentric vs. concentric stress ratio increased with an increase in eccentricity. A comparison of compressive stresses obtained from single curvature bending and double curvature bending showed that strain gradient effect was more significant in double curvature bending case. The variation of the stress-strain relationship as a result of strain gradient was only noted at high stress levels.; An evaluation of rectangular stress block theory and (EI) eff values currently used in the Canadian masonry design code S304.1-04 indicates that code, in general, tends to underestimate the resistance and effective flexural rigidity of plain masonry compression members and thus leads to a conservative design over a range of parameters. This underestimation is most significant for compression-controlled failure within an e/t region of 0 to 0.25. In the regions of tension-controlled failure, the code appears to agree reasonably well with the available data. A value of (EI)eff equal to 0.7 (EI)o is justified in the e/t region of 0 to 0.25. |
