# Modeling of RC Moment Frame Retrofit with Mortar Walls Reinforced with Steel Wire Mesh
## 1 Introduction  
RC moment frames are a typical lateral load-resisting system widely used for decades. Modern codes allow the use of RC moment frames in high seismic regions as long as they implement special design detailing (for example, beam-column joint design) to achieve adequate lateral resistance during a seismic event [1]. Moreover, existing infrastructure was designed with previous codes that do not meet current design requirements. Existing structures that use RC moment frame systems are very flexible, so they tend to exceed current code drift limits. Furthermore, the structural response of these flexible structures is highly influenced by masonry division panels, which increase the overall lateral frame strength and may induce local failures [2]. On the other hand, RC shear walls perform better than RC moment frames [3, 4]. In a dual system (shear walls and moment frames), shear walls may prevent building damage, even though the frame elements are insufficient to support lateral loads [5]. Furthermore, shear walls reduce drifts and increase structural redundancy, but they must have sufficient strength, stiffness, and deformation capacity [6]. In addition to conventional shear walls, some variations of this system have been developed. For example, thin lightly reinforced concrete walls have been used in the last two decades to brace mid-to-high-rise buildings in some Latin American countries [7, 8, 9]. This alternative system uses walls between 80 to 100 mm thick with a single steel reinforcement layer of welded wire mesh. Similarly to the lightly reinforced concrete walls system, an approach has been used to retrofit moment frame structures by jacketing the masonry infill panels between the frames with thin mortar walls. Some studies of moment frame systems filled with confined masonry and retrofitted mortar walls have been carried out to characterize the performance of this approach [10; 11; 12; 13]. It has been observed that the jacketing of confined masonry with mortar walls reinforced with steel wire mesh is an effective technique for improving structural performance [10; 11]. For practical applications in structural design, the retrofit of existing structures requires predictions made with nonlinear structural models that must address the connectivity between existing and new elements. Moreover, mortar walls have different material properties than frame border elements made with concrete and reinforcing steel. The new transverse wall section of the border frame columns connected by a mortar wall web, will need to consider the new material properties to reach equilibrium. Therefore, calibrating the nonlinear computational model used in the structural analysis of moment frames retrofitted with mortar walls requires a verification of the connectivity and equilibrium of the system. This study proposes connectivity and constraint conditions for moment frame systems retrofitted with mortar walls and modeled with fiber elements with different material properties for existing and new elements. The connectivity and constraint conditions are calibrated based on benchmark capacity curves obtained by Bernoulli-Euler beam theory, moment-curvature analysis, and the plastic hinge model proposed by [PERSON] et al. [14]. The structural program SeismoStruct was used to develop fiber models [15], including wall aspect ratios (H/Lw) of 1, 2, and 3. The study found that using a single wall element to connect the top and bottom frame border elements with a rigid link constraint condition underestimates maximum strength, stiffness, and residual strength. A solution was proposed to improve the capacity prediction by including at least one intermediate connectivity node at the wall at mid-height, where the lateral columns are connected to the wall with rigid links. This approach improves the prediction of the capacity curve because it better represents the Bernoulli-Euler beam theory that plane sections must remain plain.