## 3 Observed Damage Mechanisms in Eastern T\(\ddot{\text{u}}\)rkiye's Masonry Buildings
### Observed Structural Failures Attributed to Occupant Expansions  
Analytical evaluation of post-earthquake reconnaissance reports following significant seismic occurrences in eastern T\(\ddot{\text{u}}\)rkiye, such as the 2011 Van earthquake, the 2020 Elazig-Sivrice event, and the 2023 Kahramanmaras earthquakes, reveals a recurring theme: unregulated alterations and expansions by occupants significantly contribute to the structural weaknesses of URM homes. These modifications, often implemented without professional engineering guidance or proper municipal regulation, result in sudden variations in mass distribution, structural stiffness, and the efficiency of lateral load transfer mechanisms [3; 11; 41; 44]. In instances of vertical expansions, where an additional story is constructed on top of an existing structure, failures predominantly originate at the junction where the original walls meet the newly added upper level. These expansions frequently lack the necessary structural reinforcements, such as ring beams or adequate mechanical anchoring, at the wall-to-roof interface. Further weakening structural integrity is the new masonry, which is usually created with HCT units or partly heated bricks connected with weak, friction-based mortar. Figure 15 shows a relevant example from the February 2023 earthquakes showing  
Figure 14: Observed failures at corners and orthogonal wall intersections. a situation where a second-story extension constructed using HCTs suffered total collapse, whereas the underlying story, made of rubble stone masonry, survived with minor damage. The root cause of failure was identified at the interface of the expansion, where continuity of the ring beam and vertical confinement were absent. Horizontal expansions, including additions such as kitchens, living areas, or storage spaces, have been identified as contributing factors to structural instability. These modifications usually necessitate the creation of new openings in existing load-bearing walls to facilitate connections between the new and existing structures, resulting in a significant reduction of the in-plane shear capacity. Empirical observations, particularly after the seismic events in Elazis in 2020 and Van in 2011, showed that expansion walls built with ungraded stone or adobe were often just set against pre-existing walls without suitable integration techniques including toothing, tie columns, or ring beams. A lack of interlocking and structural confinement caused the development of vertical planes prone to failure. These damaged interfaces were focal areas for crack initiation during seismic events, with diagonal or vertical cracks running through the expansion joints, therefore compromising the integrity and stability of the newly added sections. It is essential to note that the failures attributable to structural expansions were not confined to a single seismic event. The analysis of four distinct earthquakes, including the 2020 Sivrice earthquake, revealed a consistent pattern: reconnaissance teams observed instances of collapsed or significantly compromised expansions, whereas the original masonry cores remained intact. Certain extensions raised building height over the story-height-to-thickness ratios approved by the TBEC (2018) [13]. In other cases, these changes  
Figure 15: Representative examples of severe structural damage in single-story masonry dwellings caused by occupant-driven expansions and inadequate seismic detailing. resulted in the removal of vital shear piers and the installation of extended unsupported wall sections, all in an attempt to generate more internal space. Furthermore, in most instances, the expansion operations were carried out without the supervision of official licenses, inspections, or seismic design assessments, which highlights the widespread lack of visibility for these changes within the current regulatory framework.