Theoretical and experimental analysis of the influence of the height of vertical piers on the total stiffness of masonry stiffening wall.

Properly designed stiffening walls should reduce displacements (eccentricities) and safe transfer of horizontal shear forces to the foundation. The load may be caused by the action of wind on structures or the uneven subsidence of the ground. Although the stiffening elements ensure the geometric constancy of entire buildings, there is still no clear-cut regulation allowing the distribution of loads between the individual stiffening parts. In the literature, it is most often recommended to determine the values of shear forces and bending moments in proportion to the structure's stiffness - however, there are no clear guidelines for its determination. The total stiffness method (presented by the authors at the WMCAUS 2021 conference) estimates the stiffness of solid stiffening walls and walls with openings. The wall stiffness is calculated as the reciprocal of the total wall displacement under the action of a horizontal load. The equivalent stiffness is the sum of the stiffnesses of the masonry fragments. The necessity to divide the wall into components is most often due to the presence of window or door openings. There are horizontal lintel strips and vertical stiffening fragments in the plane of each wall. The shear wall can be calculated in two static schemes - fixed on both sides or cantilever. In calculations, the height of the vertical wall fragments is most often taken as the total height of the pillar based on the building geometry. Such an assumption would be valid only in the linear-elastic range of the building's behaviour. However, the cracking stresses in the masonry structure account for about 30% of the value of failure stresses. Cracks and damage to the wall, which may appear even at low stresses, cause a rapid decrease in the structure's stiffness. Experimental studies confirm that cracks and damages increase width before the building is destroyed under a horizontal load and cover an increasingly more extensive wall area. The actual height of the vertical pillars, and thus the total stiffness of the shear wall, is different than in the calculations that do not take into account the effect of the reduced stiffness. The paper proposes an experimental determination of the height of vertical inter-hole pillars in the stage before cracking the central part of the wall. Based on the author's research on a single walls and small building (low rise) with an uncomplicated shape, the actual height of the vertical fragments of the stiffening walls was analyzed. The test walls and building consisted of autoclaved aerated concrete (AAC) masonry units. The analyzes were devoted to monotonically loaded masonry structures. A hydraulic actuator applied the horizontal load at the level of the slab. The reduction of the height of vertical piers assumed in the calculations was based on the analysis of the walls cracking morphology and patterns. [ABSTRACT FROM AUTHOR]