Abstract—Reinforced concrete stair slabs with mid landings i.e. Dog-legged shaped are conventionally designed as per specifications of standard codes of practices which guide about the effective span according to the varying support conditions. Presently, the behavior of such slabs has been investigated using Finite Element method. A single flight stair slab with landings on both sides and supported at ends on wall, and a multi flight stair slab with landings and six different support arrangements have been analyzed. The results obtained for stresses, strains and deflections are used to describe the behavior of such stair slabs, including locations of critical moments and deflections. Values of critical moments obtained by F.E. analysis have also have been compared with that obtained from conventional analysis. Analytical results show that the moments are also critical near the kinks i.e. junction of mid-landing and inclined waist slab. This change in the behavior of dog-legged stair slab may be due to continuity of the material in transverse direction in two landings adjoining the waist slab, hence additional stiffness achieved. This change in the behavior is generally not taken care of in conventional method of design. Keywords—Dog-legged, Stair slab, F.E. Analysis, Landing, Reinforced concrete. I. INTRODUCTION N low and medium rise buildings, stair slab are provided for vertical movements. These stairs are connected at floor level directly or through beam-column arrangement. Dog-legged stair slabs, commonly used for easy movements, are supported at landing levels on walls or beams provided along and/or at right angles to the direction of flight. These supports provide significant rigidity in the stair slab and hence a redistribution of moments is possible along the span of the flight. This phenomenon is normally ignored when designers consider the stair slab as simple beam supported at the ends and the span of the stair slab is taken as the distance between the end supports. Even the American code of practice [1] does not provide any recommendation regarding the restraining effect in the slab due to inherent support conditions. British code [2], however, considers the above fact and a reduction in the effective span of the stair slab are suggested which results in some saving in the design as compared to the conventional design. For stair slabs with landings supported parallel to the direction of flight, Indian code of practice for plain and reinforced concrete [3] Abdul Baqi is Professor in the Department of Civil Engineering, Aligarh Muslim University, Aligarh, India, (phone: +91-9897818122; fax: +91-571- 2721328; e-mail: baqiamu@rediffmail.com). Zaid Mohammed, is M.Tech. student in the Department of Civil Engineering, Aligarh Muslim University, Aligarh, India, (e-mail: zaidzhcet@gmail.com). suggests a reduced span of the stair slabs i.e. equal to the going of the stairs (the horizontal projection of the inclined portion) plus at each end either half the width of landing or 1m, whichever is smaller. An experimental study conducted in Bangladesh [4] also claimed a considerably high ultimate load (about 133%) achieved in the stair slab designed as per specifications of the British Code [2]. A similar study by Ahmad et. al. [5] proved that the landings supporting the stair slab derive considerable restraining effect both at inner and outer edges of the flight. Consequently, a reduction in span of 30% and 20% of the going respectively in dog-legged and open-well stair slabs of selected size was suggested. Aslam [6], based his analytical study on the behavior of dog-legged stair slab, reported that the maximum sagging moment obtained as per provisions of Indian code [3] are on conservative side. Further, the study revealed that considerable hogging and twisting moments are developed at different locations in stair slab and the landings for which no care had been suggested by Indian code. Yahya [7] has studied the effect of evacuation time, in case of emergency, on the stair slab with and without intermediate landing Since the complex behavior of stair slab is still not well understood, a comprehensive test study is therefore needed to establish the behavior of dog-legged stair slabs with different support arrangements. II. METHOD OF ANALYSIS The conventional method of design and analysis of stair slab is mostly based on the recommendation of the codes of practices which specify the effective span according to the support conditions and the critical values of moments are calculated for given loads. However, most of these codes do not take into account the effect of kinks (i.e. the junction of waist slab and landing) and restraining effect on inner or outer edges of waist slab with the presence of landings. For example, as per the Indian code of practice (IS 456:2000), the effective span and hence the critical moments for given loads for a single fight stair slab attached with landing on one or both the sides and simply supported at the ends shall be same as that of a similar double flight stair slab. A. Present Study Firstly, the behavior of a single flight stair slab attached with horizontal landings on both sides and supported at ends has been compared with a similar double flight stair slab attached with landings. The geometry and height of a single Effect of U-Turn in Reinforced Concrete Dog-Legged Stair Slabs Abdul Baqi and Zaid Mohammad I World Academy of Science, Engineering and Technology Vol:7 2013-06-21 1060 International Science Index Vol:7, No:6, 2013 waset.org/Publication/3289