## 4 Overview of Experimental Research in the Literature
### Stress-Strain Behaviour
Results from the study confirm that the compressive strength of wallette is more representative of full-scale wall panels since the strength results derived from the set of wallette tests were more conservative than those obtained from the prism tests. The authors noted that the proposed constitutive relationship was in good agreement with results obtained from the experiments since the model can be used to convert the prism strength to the equivalent wallette strength and incorporated into the design of real-world structural walls using the design standards. However, such a conversion is only applicable to solid blocks and bricks and thus cannot be further applied to other types of masonry walls. Hence, more laboratory experiments on URM walls--possibly on full scale--utilizing concrete block units and testing using different wall set-ups are needed to account for the discrepancies. Although several experimental works have focused on the compressive behaviour of URM wall structures, limited literature efforts are still available on the stress-strain behaviour of URM with openings under axial loads. In the case of walls with openings, for example, the strain response at the openings, which may encourage local stress concentrations and ultimately determine the load path of wall panels when under axial compressive load, should also be properly taken into account. In this regard, [PERSON] et al. [79] carried out an extensive experimental campaign to study the strain behaviour of full-scale brick URM walls--1700 mm \(\times\) 1700 mm, their nominal sizes--with different opening configurations under compressive loading. Lintel blocks were used at the top of the openings, and two different boundary conditions were assigned to test specimens: fully restrained (fixed end) at the bottom of the wall panels, while the top edges were either fixed end or left free. High localized strains were noticeable in close proximity at corners of openings, and these strains appeared to reduce with an increase in the distance of openings from the width direction. The authors also observed that the inclusion of openings in the wall panels enabled the transfer of the load path to the lintel support by an arching action formed at the top of the openings. However, the different types of boundary conditions assigned to the walls during the tests showed insignificant effects on the strain results, which was attributed to the small value in the slenderness ratio of the wall panels. Further detailed studies on the axial compressive stress-strain behaviour of URM walls utilizing full-scale specimens are strongly recommended. The elastic modulus of masonry is usually derived from the secant modulus of the linear portion of the stress-strain curve. The Eurocode 6 [24] recommends that this segment of the curve should typically be defined at service load conditions (i.e., at one-third of the peak stress), whereas the MSJC [40] recommends that the modulus be estimated at a stress level of 5 to 33% of the maximum compressive strength of the masonry. While the theoretical relationship between the elastic modulus and compressive strength may be considered irrelevant, it holds practical significance. Generally, the masonry's compressive strength and elastic modulus exhibit a linear correlation. According to MSJC [40], the elastic modulus can be estimated at 700 times the compressive strength of the masonry. The Eurocode 6 [24] and AS 3700 [26], on the other hand, both suggest the elastic modulus be estimated as 1000 times the masonry's compressive strength, while the Canadian standard [25] recommends a value of 850.