## 4 A Progressive Chronicle of Masonry Provisions in Turkish Earthquake Codes (1940-2018)
### Ring Beams (Hattl) and Confining Elements  
Earlier versions of the Turkish earthquake regulations at most briefly referenced \"belt courses\" or \"reinforced tie layers\", seldom explicitly designating them as ring beams (hattl) and providing little information on their integration into masonry walls. Between 1944 [47] and 1961 [50], the rules included only broad recommendations for additional horizontal supports in multi-story or corner-heavy structures, without specific requirements for rebar diameter or cross-sectional depths. The 1975 code [51] clearly identified ring beams as essential for preventing out-of-plane failure, but it mostly provided suggested guidance for their thickness and anchorage. Although the law acknowledged that residential expansions including additional floors should ideally use ring beams, it refrained from mandating local authorities to enforce this requirement in isolated regions.  
By 1997 [52], ring beams became firmly stated as a necessary component for multi-story URM. Yet, the code continued to allow single-story stone or adobe structures to bypass ring  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Type of Masonry** & **Minimum Thickness (mm)** &
\begin{tabular}{c} **Maximum** \\ **(Story Height/** \\ **Thickness)** \\ \end{tabular} \\ \hline URM (with natural or artificial stone) & 350 & 9 \\ URM (with other masonry units) & 240 & 12 \\ CM & 240 & 15 \\ RM & 240 & 15 \\ RAAC & 200 & 15 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of minimum and maximum thickness values of load-bearing walls according to TBEC 2018.  
beams if local officials deemed them safe. Occupant expansions frequently leveraged this oversight, adding rooms or entire upper floors without integrating horizontal beams. In a similar vein, although the 1997 [52] code did reference minimal ring beam cross-sectional areas, it did not stipulate anchorage details, stirrup spacing, or splicing lengths.  
The 2007 [54] code brought these confining elements to the forefront, requiring that any multi-story URM in moderate- or high-seismic-risk zones implement ring beams at every floor level. In addition, it proposed corner tie columns or vertical boundary members to confine the walls into box-like segments. This partial capacity design logic also meant ring beams had to meet some fundamental rebar continuity standards. Even occupant expansions that involved new floors in moderate-/high-risk areas technically needed ring beams retrofitted onto the older walls to ensure load path integrity. Notwithstanding these rules, code enforcement continued to be a weak link: occupant expansions often remained outside formal permissions, particularly in rural or semi-urban areas.  
The TBEC (2018) [13] refined these ring beams and confining element requirements further, mandating minimum cross-sectional heights and rebar coverage for ring beams in moderate-/high-risk zones, and calling for vertical boundary columns around large openings or corners. The code introduced more standardized approaches to confining masonry, especially when combined with improved mortar classes and more stringent analysis methods. However, occupant expansions still received no separate recognition in law, thus generally remaining unverified unless the homeowner voluntarily complied. Mandatory requirements related to ring beams are illustrated in Figure 16.  
Additionally, the TBEC (2018) [13] stipulates that the minimum cylindrical compressive strength of these ring beam (hatli) components should be no less than 25 MPa. The code stipulates that a minimum thickness of 10 cm for reinforced concrete slabs must include transverse reinforced horizontal beams to ensure that URM, RM, and CM structures achieve rigid diaphragm behavior. The vertical distance of the horizontal ring beams is limited to a maximum of 4 m.