RESEARCH ARTICLE Experimental and parametric investigation of effects of built-in staircases on the dynamics of RC buildings Faizan Ul Haq Mir | Durgesh C. Rai Department of Civil Engineering, Indian Institute of Technology, Kanpur, India Correspondence Durgesh C. Rai, Department of Civil Engineering, Indian Institute of Technology, Kanpur 208016, India. Email: dcrai@iitk.ac.in Summary Past earthquakes, in many instances, have demonstrated poor performance of commonly used built-in staircase configurations. Codal provisions in India per- taining to staircases present a rather simple approach wherein the effects of built-in staircases on the overall dynamic properties or on the local behavior of structures are not addressed explicitly. Studies in the past have highlighted the scale of such effects, but most of them have relied completely on analytical models of buildings. This study analyzes the adequacy of the codal provisions by investigating two finite element (FE) models calibrated using ambient and forced vibration measurements. The effects of variations in building height, layout of staircase in plan, and presence of masonry infill walls in stairwells are also examined. The codal guidelines regarding empirical estimation of period and provision of enclosure walls around built-in staircases are found to be adequate. However, for the case of built-in staircases without enclosure walls, the force and displacement demands on landing beams are found to be considerably high. Drift-based approaches to estimate these demands are proposed. KEYWORDS built-in staircases, dynamic characterization, finite element modeling, landing beams, pushover analysis 1 | INTRODUCTION Staircases serve as the primary means of egress in most buildings and are critical for exit in emergency situations partic- ularly earthquakes. For satisfactory performance, a staircase should remain fit for use even after severe or moderate shaking. Past earthquakes, however, have demonstrated otherwise. Damage has occurred in structures because of inter- action with staircases and in staircases because of inadequate design. 1-5 On one hand, staircases can introduce undesir- able torsional eccentricities in buildings that may lead to the failure of primary structural elements, while on the other hand, owing to their inherently high lateral stiffness, they can attract large seismic forces leading to the failure of local elements like landing beams or supporting columns. 6 The codal provisions in India pertaining to staircases present a rather simple approach wherein three types of staircase construction systems are identified—separated staircases, built- in staircases, and staircases with sliding joints. 7 Owing to ease of construction, built-in staircases tend to be more com- mon. The effects of such staircases on the overall or local behavior of structures are not addressed explicitly in the code. The code recommends providing enclosure walls around such staircases, thus entailing application of provisions that are actually meant for infilled frames to such staircase configurations. Even though studies in the past have focused Received: 19 June 2018 Revised: 15 December 2019 Accepted: 20 December 2019 DOI: 10.1002/eqe.3251 Earthquake Engng Struct Dyn. 2020;1–16. wileyonlinelibrary.com/journal/eqe © 2020 John Wiley & Sons, Ltd. 1