Im­por­tance of Cold-Formed Steel in Seis­mic-Re­sis­tant De­sign of Struc­tures

NBM&CW - - CONTENTS - N Mu­niru­drappa

Cold Formed Steel is a prod­uct made by rolling steel or press­ing steel in to semi-fin­ished or fin­ished goods at rel­a­tively low tem­per­a­tures. Man­u­fac­tur­ing of Cold Formed Steel (CFS) oc­curs at room tem­per­a­ture. In present sce­nario the use of CFS sys­tem is sig­nif­i­cantly in­creas­ing in coun­tries where tra­di­tional struc­tural so­lu­tions have al­ways dom­i­nated the con­struc­tion sec­tor. This is mainly due to the de­vel­op­ing and in­creas­ing tech­ni­cal, struc­tural and eco­nomic com­pet­i­tive­ness of such sys­tems. The ad­van­tages with CFS are light­ness of sys­tems, high qual­ity of end prod­ucts, flex­i­bil­ity due to wide va­ri­ety of shapes and sec­tion di­men­sions, short ex­e­cu­tion time due to dry con­struc­tions and min­i­miza­tion of en­vi­ron­men­tal im­pacts due to the pos­si­bil­ity to re­use the el­e­ments at the end of the life cy­cle. This pa­per presents the im­por­tance of CFS in var­i­ous struc­tural el­e­ments to mit­i­gate the dam­age cost to these el­e­ments dur­ing earth­quakes. These el­e­ments are in­ves­ti­gated for seis­mic re­sis­tance in multi storey mo­ment frames, fac­tors like pre­ma­ture lo­cal buck­ling and low out of plain stiff­en­ers known as the main struc­tural de­fi­cien­cies of CFS with thin walled el­e­ments hence in struc­tures with CFS as the main load bear­ing com­po­nents there is less en­ergy dis­si­pa­tion due the above men­tion de­fi­cien­cies. There­fore in or­der to im­prove the en­ergy dis­si­pa­tion of CFS, an in­no­va­tive CFS beam with curved flange was de­vel­oped. The main aim of beam was to pro­duce plas­tic mo­ment due to large width thick­ness ra­tios of thin walled el­e­ments of CFS sec­tion; de­vel­op­ment of plas­tic mo­ment was avoided. To over­come these lim­i­ta­tions, the CFS el­e­ments were in­tro­duced with flange bends in C sec­tion lead­ing to a curved flange sec­tion. Also mod­i­fi­ca­tion like flange lips, in­tro­duc­ing intermediate flange stiff­en­ers and in­creas­ing the num­ber of flange bends re­sults in in­crease in mo­ment re­sis­tance, duc­til­ity ca­pac­ity and ini­tial stiff­ness. Steel sheeted CFS us­ing gyp­sum board claddings with dif­fer­ent con­fig­u­ra­tion on shear walls and par­ti­tion walls on ei­ther or both sides re­sulted in in­creased of lat­eral stiff­en­ers; shear strength and en­ergy dis­si­pa­tion ca­pac­ity. Use of MLC (Mod­u­lar Light weight Cold Form beams) are de­signed to pre­vent early buck­ling phe­nom­ena that could af­fect the struc­tural be­hav­iour when thin sheets are used also pro­vide high re­sis­tance to tor­sional flex­u­ral buck­ling.

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