## 5 Concluding Remarks  
Unreinforced masonry walls represent one of the most commonly used structural systems in low and medium-rise buildings worldwide. The compression behaviour of masonry walls is a key factor in the design of masonry structures for other actions, such as in-plane shear and out-of-plane flexural behaviour. Thus, an accurate assessment of the masonry performance when subjected to axial compressive loads is required for the appropriate design and analysis of masonry elements. Despite the importance of this subject area, experimental campaigns on the compressive performance of URM walls are still very limited in comparison to the extensive research related to their in-plane and \begin{table}
\begin{tabular}{l l l l} \hline \hline \multicolumn{1}{c}{**Reference**} & \multicolumn{1}{c}{**Masonry Type**} & \multicolumn{1}{c}{**E\({}^{\prime}\)m/f\({}^{\prime}\)\({}_{\mathbf{m}}\)**} & \multicolumn{1}{c}{**E\({}^{\prime}\)m/f\({}^{\prime}\)\({}_{\mathbf{k}}\)**} \\ \hline Eurocode 6 [24] & No division & - & 1000 \\ CSA 304 [25] & No division & 850 & - \\ MSJC [40] & No division & 700 & - \\ AS 3700 [26] & No division & 1000 & - \\ [PERSON] et al. [14] & High strength HCB & 650 & - \\ [PERSON] et al. [15] & Table moulded and wire-cut brick & 256–638 & - \\ [PERSON] et al. [72] & Clay brick & 391–843 & - \\ [PERSON] et al. [73] & Clay brick & 849–1928 & - \\ [PERSON] et al. [69] & Clay brick & 261 & - \\ [PERSON] et al. [75] & Clay brick & 477 & 575 \\  & Calcium silicate & 702 & 833 \\ [PERSON] et al. [76] & Fired-clay brick & - & 82–231 \\ [PERSON] and [PERSON] [81] & Clay brick & 563 & - \\ [PERSON] et al. [80] & HCB & 872 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: A summary of selected literature studies showing the relationship between the elastic modulus, _E\({}^{\prime}\)m_, and the characteristic compressive strength _f\({}^{\prime}\)k_, as well as the mean compressive strength of the masonry, _f\({}^{\prime}\)m_. Figure 13: Comparison between elastic modulus derived from the experimental literature and values predicted by the different masonry standards. out-of-plane behaviour. Nonetheless, experimental literature efforts have been increasing in recent years and are discussed in this present paper. The analysis of the experimental literature findings suggests a high degree of scatter in the geometric and mechanical properties of the units, which makes it challenging to compare results. While a relatively small number of wall specimens were tested squarely in axial compression in a large percentage of the tests, a majority of test specimens were constructed with clay brick units, few were built using hollow concrete block and far fewer with solid concrete block units. The strength distribution of URM walls showed a high variability due mostly to the heterogeneous composition of masonry elements, as well as the relatively small number of full-scale wall specimens tested. The effect of unit strength and mortar strength on the compressive strength of masonry walls were also observed in graphs constructed based on the reviewed dataset. In general, higher unit strength results in significant improvement in the compressive strength of URM walls. However, an increase in the compressive strength of URM walls is only marginal if a combination of high-strength mortar and lower unit strength are used. The studies reviewed in this present article also indicate that the type of the unit has a significant impact on the compressive strength of URM walls. The majority of the walls constructed with concrete units had compressive strength values ranging from 3.28 to 19.8 MPa (masony efficiency values ranging between 35 and 96%), which are typically higher than the compressive strength observed in walls built using clay units, which ranged from 1.1 to 13.9 MPa (masony efficiency ranging from 11 to 76%).