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Planung und Konstruktion von Treppen
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gestemmte Wangentreppe eingeschobene Wangentreppe Wangentreppen aus Stahl verschiedene Stufenkonstruktionen bei Stahlwangentreppen
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Inset tongued-and-grooved string staircase Inset mortice-and-tenon string staircase Steel string staircases Various forms of tread construction with steel string staircases
Although building methods and styles have been subject to many changes over the centuries, the basic principles underlying staircases have remained the same. Formed of individual steps, they are a constructional element that allows differences of height to be overcome on foot. Staircases are subject to specific standards that can vary with the function of a building, and they can have different forms, depending on the geometry involved, the number of handrails, etc. (ill. 2). Climbing or descending stairs requires more energy than walking on a horizontal surface. For safety and comfort, the relationship of rise to going and the dimensions of the steps must remain constant. Twice the rise of a step plus the going should ideally be between 61 and 65 cm. (Further guidelines are G+R = 46 cm for safety with steeper stairs, and G-R = 12 cm for greater comfort.) The dimensions for minimum going and maximum rise are also defined (ill. 3, German standards). The same standards recommend an intermediate landing after a maximum of 18 steps (14 in places of assembly). These principles must also be applied to the length of intermediate landings: L = n x length of stride (63 cm) + 1 tread. Staircases should combine comfort and safety. This applies to sure footing, head height (at least 200 cm; see ill. 8), handrails and balustrades. Handrails may be omitted only when a stair flight has fewer than five steps and the height of fall is less than one metre. For staircases wider than 1.50 m, handrails are necessary on both sides; and for widths of 2.50 m or more, an additional free-standing handrail should be foreseen in the middle of the flight. Depending on the function of the building and the height of fall, there are certain minimum dimensions for balustrades (ill. 5), and a maximum spacing between the balusters of 12 cm. Where the presence of children is to be expected, it should not be possible to climb over balustrades. Whether a staircase can accommodate use by a number of people simultaneously will depend largely on the width of the flight and landings and on the dimensions of the starting and top step. As a design goal for multi-flight staircases, two flights running in counter-directions
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should ideally have a continuous line of deflection on the underside of the landing to ensure a well ordered soffit. In addition, a constant handrail height next to the stairs and landings is desirable. To achieve these goals, the positions of the starting step and top step may be offset and the landing thickness varied from that of the stair flight. If the starting step of the upper flight is set one tread width in front of the top step of the lower flight, the landings will be thinner, but the handrail height will be greater next to the landings (ill. 14). If the starting step of the upper flight is set one tread width behind the top step of the lower flight, the handrail height will be constant, but the landings will be particularly thick (ill. 15). Where starting and top steps are aligned, the line of deflection and the point of intersection of the handrails will be offset in the landing area, and the handrail to the landing will be higher than that next to the stair flight (ill. 16). Coordinating these various constraints is a complex matter. Structurally, one can differentiate between longitudinally and laterally spanned stair flights. In the former case, the flights and landings are spanned between the end walls like a 21 cranked beam (ill. 12a). Alternatively, the flights can be spanned between the two landings and separated from one or both end walls (ills. 12b and 12c). In the case of crossspanned flights, the parallel side walls serve as bearing elements (ills. 12d, 12e and 13). Although the basic forms of staircases have scarcely changed, their appearance differs according to the materials used, the type of construction and technical developments. Solid forms of construction are usually in reinforced concrete. The structure will correspond to a sloping slab spanned in a single direction. The landings can be constructed either as a single entity with the stair flight, or separately. Insitu concrete or precast elements are usual. Solid construction of this kind is the only form in which structural considerations, function and good fire resistance are united in one entity. As part of the overall structure, the stairs contribiute to the transmission of loads. Precast concrete stairs allow smaller tolerances than insitu concrete forms and have finer sur- 22
Alejandro Restrepo Montoya, Lehrstuhl für Nachhaltigkeit, Technische Studien und Experimente in der Architektur LEET, Fakultät für Architektur der Universität Pontificia Bolivariana UPB Medellín in Kolumbien, Doktorand an der Fakultät für Architektur der TU München. Alejandro Restrepo Montoya, Chair for Sustainability, Technical Studies and Experimental Work in Architecture LEET of the Faculty of Architecture of the Pontifical Bolivarian University (UPB), Medellin, Colombia, is a lecturer at the Faculty of Architecture of the University of Technology, Munich.