## 4 Overview of Experimental Research in the Literature
### Effect of Slenderness Ratio and Eccentricity  
The current design of masonry structures compensates for the eccentric gravity loads and wall slenderness by the introduction of the capacity reduction factor to the compressive strength of the masonry. In conventional masonry construction, the load-bearing wall structure is usually thick; therefore, the influence of slenderness could be neglected if the height-to-thickness (h/t) ratio is less than 10 [71]. The DIN 1053 [92] allows for a slenderness ratio of masonry walls up to 20, and just two better quality grades between 10 and 20 are permitted. Within this permissible range, only light loads are allowed on the masonry with slenderness greater than 14, and the strength of the material may be reduced by a factor (25-h/t)/15, whereas the Eurocode [24] permits a slenderness ratio of up to 27. Within this constraint, [PERSON] and [PERSON] [20] investigated the influence of slenderness ratio and load eccentricities on the compressive strength of the URM wall and compared the results with the capacity reduction factors prescribed in the British code [93]. Tests were conducted on twenty-five brick walls using different slenderness ratios (i.e., 6, 12, 18, and 25), with various support conditions (hinged, RC slab, and flat end) and loading eccentricities (0, t/3, and t/6). Observations from the test results indicated a decrease in wall strengths of specimens tested with flat-end conditions with an increase in slenderness ratio, with the exception of specimens with a slenderness ratio of 12. The authors observed that in wall specimens tested with hinged support conditions and eccentrically loaded 0, the capacity reduction factor permitted in the British code is almost 10% less, with the exception of specimens having a slenderness ratio of 25, whereas in wall specimens tested with eccentricity t/3, the capacity reduction factor was about 25% greater than that permitted in the British code. However, in wall specimens with eccentricity t/6, the capacity reduction factor yielded almost identical value as that found in the British code. It is worth highlighting that while the maximum value of wall slenderness used in [20] is 25.0 and the values in [93] provide up to 46.1 slenderness ratio, the British code is now obsolete and is superseded by the Eurocode [24]. In the opinion of the authors, tests on masonry wall panels with a slenderness ratio higher than 30 are more a matter of academic rather than practical interest since the results obtained by the authors for wall panels loaded with zero eccentric loads were about 18% lower than that reported by [PERSON] [94]. On the contrary, for wall panels loaded with t/6 eccentricities, the results obtained in [94] were higher than those obtained in [20]. [PERSON] and [PERSON] [21] investigated the influence of different slenderness ratios (12.4, 22.8, 32 and 42.5 and eccentricities (0, t/6 and t/3) on the load capacity of full-scale brick URM wall panels constructed with low-strength and high-bond mortar. In the case of wall specimens having a slenderness ratio of 22.8 and loaded with eccentricity t/6, the strength of the walls built using high-bond mortar was 25% higher than the compressive strength of the same wall panels constructed using normal-strength mortar. Similarly, for wall specimens loaded with eccentricity t/3, the compressive strength of walls constructed using high-bond mortar was 33% higher than the resistance of the same wall panels constructed using lower-strength mortar. A similar finding was also reported by [PERSON] and [PERSON] [22]. The authors investigated the effect of different slenderness ratios (5.6, 11.1, 18.8, and 27.7) on the strength of URM walls constructed using different heights (0.63 m, 1.25 m, 2.12 m, and 3.12 m) and different concrete blocks. Results from the study showed a reduction in load capacity in all tested wall panels with the increase in slenderness ratio (e.g., see Figure 10).