Abstract：Based on the literature comparison and experimental verification, it is found that the I-shaped mechanical unit commonly exists in grouted masonry. In this paper, a compressive stress-strain constitutive relationship based on concrete softened theory is proposed, which is applicable to the grouted masonry with I-shaped internal structure. In the expression, hollow ratio of masonry, strength ratio of block and grouted concrete, softening coefficient are taken into account. Calculation results show that the peak point is very close to that in documentary records and verification test results. The degradation of tangent modulus agrees well with the three stages in the process of failure, and the calculated curve is in good accordance with the measured one. The test phenomenon shows that the crack development and failure characteristics of specimens with I-shaped mechanical unit are similar to those recorded in the literature, i.e. three stage failure process during the test. I-shaped mechanical unit is reasonable and the prediction result is in good agreement with the literature and experimental data. Therefore, the theory has high applicability to the grouted masonry with I-shaped internal structure.
