Design rationale for helicoidal stair slabs

Abstract

Owing to the architecturally fascinating appearance, helicoidal staircases as well as ramps arc increasingly being used in almost. every important building. The increasing architectural usc or helicoidal staircase has created the need for a simple but tho.rough and exact analysis of helicoids for the mOSI common casc of loading. A vigorous mathematical analysis ill t.erms general enough to include any unsymmetrical case of loading IS available, but the lrc-allllcn( IS abstract and becomes so elaborate lhal it is or lillie usc- 10 the design engineers. On the other hand some approxilllaic methods arc so approximalc and conservative that those fail 10 lake into consideration the beneficial structural behaviour of certain types 01' helical bC;lms thaI allows morc ambitious use. of this highly pleasing architcctural Irom. In the presellt Sl.udy. attempls havc beell made- to investigate the behaviour of helicoidal stair. eilher fixed or hinged at its ends, lindeI' uniformly distributed load. The classic;lI approach to analyse the behaviour of helicoidal staircases with bol.h ends fixed has bCC-ll eXlended further to deal with the hinged ended conditil)IL General equatiolls for delerminal.ion of redulldanls. moment and shear, at midspan of a uniformly [oade-d helicoidal girder eilher fixed or hinged at its ends have been derived. Tabulaled results for Ihese redundants have been presented for a wide range or design variables: selllicentral angJc. 011 projection, angle or slope, and cross-seclional dililensions. The clTects or these. variables on the redundant. have been discussed. A cOll1putc,r progralll for Ihe analysis and design or helicoidal staircase has bcen developed adopting thick shell finite clcmcnts of Ahmad. Thc cffcCls of varialions III IlOIl-dillH.',IlSional geomctrical parJIllCICrS 011 thc behaviour of helicoidal stairca:..;e have be,ell studied uSing IIH.: program. The relation bct wccn stress and stress-resultants has beell established for this spc-ciJI case of space heam having: skewed re,ctangular section. It is found that lhcse relation is coupled. To delcrmillc stresses. de-coupling or strcss-rcsullants is required firsl. The resulLs of' study of fixed ended helicoidal stair slabs with uniformly distributed load by using finite elcmcnt lCl"hniquc have becn presented in this thesis. Tile resulls or tile """lyses by Ihe two difrcrcnt methods, analytical and nUlllcrical, have been compared and good "agreements arc round. Based on the findings 0[' lhc IHCSC-Ill sl.udy. and distinctive rc..lIures or hclicoids, a new dcsign ralionale- 1l,IS hel'l! sll!:!~l'strd"