Efficiency of the prescriptive recommendations of the Iranian NBC-8 code for RC tie elements in confined masonry buildings

The Iranian national building code on masonry construction (NBC-8) provides fully prescriptive guidelines for design and construction of low-rise confined masonry (CM) buildings. These guidelines are too general, covering one to three storey buildings and all the seismic demand scenarios of the Iranian seismic code (Standard 2800). The guidelines are either adaptations from other codes, or based on observations made on the CM building performances in the past earthquakes. However, there has been no detailed scientific research aimed at verifying the efficiency and adequacy of these guidelines. In this study, the efficiency of some of the most important guidelines, regarding the RC tie system’s prescriptive detailing, strength of masonry walls and size and location of openings have been critically investigated. For this purpose, a number of most vulnerable (critical) plan layout and wall configuration scenarios for buildings of up to three storeys high, which are allowed by the NBC-8 code, have been identified and their base shear capacities have been evaluated numerically using the nonlinear pushover analysis method. The base shear capacities of the critical walls are then compared with a large number of seismic base shear demand scenarios of the Iranian seismic code (Standard 2800) for these walls. It is found that the general guidelines of the latest revision of the NBC-8 code (2019) on the RC tie detailing are too stringent for the single-storey CM buildings, unnecessarily increasing their construction cost. It is also noted that, for the two and three storey buildings, the NBC-8 recommended minimum compressive strength for masonry ( f′ _m = 2MPa) is too low for the masonry walls and piers to resist any of the seismic shear demand scenarios and that for these buildings it should be increased to at least 4MPa. Based on the results presented, separate detailing are recommended for the single-storey, two storey and three storey buildings situated in different seismic zones and subjected to different seismic demand scenarios.