## 4 A Progressive Chronicle of Masonry Provisions in Turkish Earthquake Codes (1940-2018)
### Material Eligibility and Standardization  
Which masonry compounds are allowed and how they should be standardized has been vital for URM structural integrity throughout variations in Turkish seismic laws. The 1940 code, which established modern legislation in this area, allowed the use of stone, adobe, and \"partially fired\" bricks without setting compressive strength or mortar composition standards, leaving rural builders to use traditional methods. The 1944 [47], 1949 [48], and 1953 [49] versions recommended \"better shaped stones\" or \"semi-industrial\" bricks but did not require thorough testing. Earthen mortar was accepted in single-story applications in these mid-century papers, showing indigenous materials' societal supremacy rather than scientific engineering. When revised in 1961 [50], the code initially advised against using clay mortar in multi-story structures but allowed it in single-story homes. This method acknowledged that occupant expansions or partial augmentations were not clearly defined. The 1975 [51] code mandated that \"units must be of sound manufacture\". This let communities adopt partly burnt bricks or better stone manufacturing methods without setting numerical compressive restrictions. To establish binding minimum compressive strength criteria (\(\geq\)5 MPa) for multi-story masonry, the 1997 [52] code initially used national standards (e.g., TS 705) for bricks. Therefore, tenant expansions that impacted load-bearing walls in moderate- or high-seismic-risk areas were implicitly assumed to follow these criteria, despite variable local enforcement. The 2007 [54] code established mortar classifications (M2.5, M5, and M10), penalized the use of earthen mortar in moderate- or high-risk areas unless heritage exemptions were applicable, and tightened HCT geometry and rebar anchorage specifications. The TBEC (2018) [13] allows four categories of masonry structures: URM, CM, RM, and RAAC. According to Table 4, these structures must be constructed with poor ductility at the allowable BYS values. If a URM building is under construction, the allowable BYS is 8, equating to a maximum total height of 7 m for DTS categories 1, 1a, 2, and 2a, and 10.5 m for DTS categories 3, 3a, 4, and 4a. Furthermore, the TBEC (2018) [13] mandated M5 mortar in moderate- and high-seismic-risk zones, TS EN 771-1 [55] HCT manufacturing requirements, and site-specific or \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Masonry Types** & **R** & **D** & **BYS** \\ \hline URM & 2.5 & 1.5 & 8 \\ CM & 3 & 2 & 8 \\ RM & 4 & 2 & \(\geq\)7 \\ RAAC & 4 & 2 & \(\geq\)7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Strength reduction factor (R), overstrength (D), and BYS correlations for masonry buildings. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Building Height** & \multicolumn{4}{c}{**Allowable Total Building Heights (m)**} \\
**DTS = 1, 1a, 2, 2a** & **DTS = 3, 3a** & **DTS = 4, 4a** \\ \hline BYS = 1 & H\({}_{\rm N}>\) 70 & H\({}_{\rm N}>\) 91 & H\({}_{\rm N}>\) 105 \\ BYS = 2 & 56 \(<\) H\({}_{\rm N}\leq\) 70 & 70 \(<\) H\({}_{\rm N}\leq\) 91 & 91 \(<\) H\({}_{\rm N}\leq\) 105 \\ BYS = 3 & 42 \(<\) H\({}_{\rm N}\leq\) 56 & 56 \(<\) H\({}_{\rm N}\leq\) 70 & 56 \(<\) H\({}_{\rm N}\leq\) 91 \\ BYS = 4 & 28 \(<\) H\({}_{\rm N}\leq\) 42 & 42 \(<\) H\({}_{\rm N}\leq\) 56 & 42 \(<\) H\({}_{\rm N}\leq\) 56 \\ BYS = 5 & 17.5 \(<\) H\({}_{\rm N}\leq\) 28 & 28 \(<\) H\({}_{\rm N}\leq\) 42 & 28 \(<\) H\({}_{\rm N}\leq\) 42 \\ BYS = 6 & 10.5 \(<\) H\({}_{\rm N}\leq\) 17.5 & 17.5 \(<\) H\({}_{\rm N}\leq\) 28 & \\ BYS = 7 & 7 \(<\) H\({}_{\rm N}\leq\) 10.5 & 10.5 \(<\) H\({}_{\rm N}\leq\) 17.5 & \\ BYS = 8 & H\({}_{\rm N}\leq\) 7 & H\({}_{\rm N}\leq\) 10.5 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Allowable total building heights related to the BYS and DTS (m). laboratory testing for multi-story or occupant additions.