## 4 Overview of Experimental Research in the Literature
### Effect of Strength of Components and Loading Orientation  
In real-world situations, the majority of masonry buildings are typically stressed in compression. As a result, it is of significant importance to assess masonry's compressive strength for which challenging problems exist to test full-scale wall specimens. In recent decades, several experimental campaigns have been conducted to assess the compressive strength of small-scale specimens, i.e., masonry prisms, for which comprehensive reviews have been published (see ref. [36]). However, the strength values of these types of specimens may not be representative of the actual performance of full-scale walls. It is for this reason that several scholars have conducted a significant number of experimental campaigns to study the axial load response of URM walls. Results from past studies indicate that the load-bearing capacity and deformation behaviour of URM walls are closely related to the relative strength of the individual masonry element, production and test procedure, as well as the geometry of the test walls. Recent research generally confirms the widely accepted fact that higher unit strength results in improved compressive strength for URM walls constructed using different types of units. The studies reviewed in this present article indicate that the type and strength of the unit have a significant impact on the compressive strength of URM walls. As depicted in Figure 5a, the majority of the walls constructed with concrete units had compressive strength values ranging from 3.28 to 19.8 MPa, which are typically higher than the compressive strength observed in walls built using clay units, which ranged from 1.1 to 13.9 MPa. Additionally, the majority of the walls constructed using concrete units exhibited a masonry efficiency--defined as the ratio between masonry compressive strength and compressive strength of unit (\(f^{\prime}_{\rm m}/f_{\rm b}\))--ranging between 35 and 96%. In contrast, the masonry walls built using brick units demonstrated \(f^{\prime}_{\rm m}/f_{\rm b}\) values ranging from 11 to 76%. \begin{table}
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Table 1: _Cont._For example, [PERSON] and [PERSON] [16] carried out axial compression tests on fourteen full-scale URM wall panels made up of table-mounded bricks (\(f_{\text{b}}\) = 5.85 MPa), solid concrete blocks (\(f_{\text{b}}\) = 4.57 MPa), and HCB (\(f_{\text{b}}\) = 6.08 MPa) available in South India. All walls were constructed using the same mortar strength (\(f_{\text{m}}\) = 9.42 MPa). Observations from the study generally indicated that the HCB walls have better performance in load-carrying capacity among all three different types of blocks in the set of experiments. The compressive strength of the wall panels made with concrete blocks (hollow/solid) was found to be in the range of 3.05 and 4.2 MPa, while the strength of the wall panels made with bricks was found to be between 1.28 and 1.72 MPa, indicating the better performance in load capacity of concrete block walls in comparison to wall panels made with bricks. Similar findings are also observed in [17; 19]. In the study by [PERSON] et al. [17], in particular, the entire experimental campaign focused on cellular concrete blocks (CCB) and HCB URM walls. The test results--nine specimens in total--gave evidence of better performance in the load capacity of wall panels built with HCB in comparison to that of brick walls tested in previous experiments [15; 16].