## 4 Overview of Experimental Research in the Literature
### Effect of Slenderness Ratio and Eccentricity
Consequently, it can be inferred that URM walls exhibit maximum load-carrying capacity when their aspect ratio (i.e., \(l/h\)) is equal to 1. [PERSON] and [PERSON] [71] also gave evidence of a decrease in load-bearing capacity in HCB URM walls with the increase in eccentric loads, which was mostly accompanied by greater shattering at failure in tested specimens. To complement previous experimental findings, [PERSON] et al. [78] conducted an extensive analysis to study the axial performance of a large number of scale brick URM wall panels constructed using various combinations of slenderness ratio and eccentric loads. As expected--and in accordance with previous findings [21; 22]--an increase in slenderness ratio and eccentric load significantly affected the strength of tested walls. Observations from the study indicated that the decrease in load-bearing capacity of wall panels having a slenderness ratio of 6.8 could vary between 25% and 40% and between 55% and 70% for  
Figure 10: Influence of slenderness ratio and eccentricity on the load capacity of axially loaded URM wall panels as derived from several literature sources for (**a**) e = 0 [20; 21; 22; 71; 78], (**b**) e = t/3 [20; 22; 71; 78], and (**c**) e = t/6 [20; 71; 78]. walls with a slenderness ratio of 25.6 if eccentrically loaded at t/6 in comparison with walls loaded with zero eccentricity. Similarly, the reduction in load capacity for wall panels with a slenderness ratio of 6.8 could be between 60% and 75% and between 80% and 90% for walls constructed with a slenderness ratio of 5.6, if eccentrically loaded at t/3, in comparison with walls loaded with zero eccentric loads. The study findings emphasize the fact that the maximum load capacity of the URM wall reduces significantly with an increase in the slenderness ratio and eccentric loading. For the sake of clarity, Figure 10a-c presents a comparison among experimental literature results. The comparisons are made in terms of \(f_{\text{m}}/f_{\text{b}}\), where \(f^{\prime}_{\text{m}}\) is the maximum compressive stress of the URM walls and \(f_{\text{b}}\) is the compressive strength of the unit used in the individual experimental campaign. The comparisons are made only between experimental tests having identical support conditions (i.e., hinge supports at both the top and bottom of walls) and eccentric loadings (e = 0, e = t/6, and e = t/3). Remarkably--and despite the different materials and geometry employed in the various experimental campaigns--similar trends can be seen between the slenderness ratios and normalized compressive strength in the majority of experimental results considered. A common feature of these studies is that a decrease in wall slenderness will cause an increment in its compressive strength, which is duly recognized. Accordingly, this holds true if the URM walls are constructed using different thicknesses of units and tested with hinged support conditions under axial compression and eccentric loads. This phenomenon may not be true if the lateral and rotational restraint conditions are considered, for which limited experimental studies indicate an increment in thickness of URM walls built using various types of units did not cause a corresponding increase in the wall compressive strengths despite the reduction in slenderness ratio [16; 17]. In addition, observations in [23] indicate that the strength of the masonry is dependent on the height of the wall rather than its slenderness since experimental tests on two walls (270 cm high, 25 cm and 38 cm thick) constructed with bricks (25 \(\times\) 12 \(\times\) 6\(\cdot\)5 cm) resulted in the same axial compressive strength despite the difference of wall slenderness ratios [23]. [PERSON] et al. [17] noted that the capacity reduction factor prescribed in the various masonry standards underestimates the strength of URM walls. The authors conducted tests on nine full-scale walls, which were constructed using different slenderness ratios and tested under axial and eccentric loads.