ELEMENTS OF ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN DR. ANNE NICHOLS SPRING 2019 letue eighteen steel onstution: olumn design Co-Ten Steel Sulptue By Rihad Sea Museum of Moden At Fot Woth, TX (AISC - Steel Stutues of the Eveyday) Steel Columns 1
Stutual Steel standad olled shapes (W, C, L, T) tubing pipe built-up Steel Columns 2
Design Methods (evisited) know loads o lengths selet setion o load adequate fo stength and no bukling Steel Columns 3
Allowable Stess Design (ASD) AICS 9 th ed F slendeness atio a fo kl/ C f itial F. S. Kl 12 23 2 E Kl 2 = 126.1 with F y = 36 ksi = 107.0 with F y = 50 ksi Steel Columns 4
C and Eule s Fomula Kl/ < C shot and stubby paaboli tansition Kl/ > C Eule s elationship < 200 pefeed C 2 2 E F y Steel Columns 5
C and Eule s Fomula Steel Columns 6
Shot / Intemediate L e / < C whee F a F. S. 5 3 Kl 1 2C 2 3 2 F y F. S. Kl Kl 8C 8C 3 3 Steel Columns 7
Unified Design limit states fo failue 0. 90 P n F A g P a P u P n P n 1. yielding 2. bukling KL KL E 4. 71 o Fe Fy E 4. 71 o Fe F F e elasti bukling stess (Eule) y 0. 44F 0. 44F y y Steel Columns 8
Unified Design P n = F A g fo fo whee KL KL 4. 71 Fy E Fe F 0. 658 Fy 4. 71 E F 0. 877F F F e y 2 E KL 2 e F y Steel Columns 9
Poedue fo Analysis 1. alulate KL/ biggest of KL/ with espet to x axes and y axis 2. find F (see Note) fom appopiate equation tables ae available 3. ompute P n = F A g 4. is P a P n /? o is P u P n? yes: ok Note: text uses F and old = 0.85 no: insuffiient apaity and no good Steel Columns 10
Poedue fo Design 1. guess a size (pik a setion) 2. alulate KL/ biggest of KL/ with espet to x axes and y axis 3. find F a o F (see Note) fom appopiate equations o find a hat 4. ompute P n = F A g Note: text uses F and old = 0.85 Steel Columns 11
Poedue fo Design (ont d) 5. is P a P n /? o is P u P n? yes: ok no: pik a bigge setion and go bak to step 2. 6. hek design effiieny peentage of stess = if between 90-100%: good P 100% P if < 90%: pik a smalle setion and go bak to step 2. Steel Columns 12
Column Chats, F Steel Columns 13
Column Chats Steel Columns 14
Beam-Column Design moment magnifiation (P-) M m 1 fatoed B1 u B M u max C m modifiation fato fo end onditions = 0.6 0.4(M 1 /M 2 o 0.85 estained, 1.00 unestained P e1 Eule bukling stength P e 1-1.00 (LRFD), 1.60(ASD) Kl 2 C 1 ( P / P ) 2 EA e1 Steel Columns 15
Beam-Column Design LRFD (Unified) Steel fo P Pu 8 0. 2 : P P 9 n M bm ux nx M M b ux nx 1. 0 fo P P 0. 2 : Pu 2 P P is equied, P is apaity n M bm M M esistane fato fo ompession = 0.9 esistane fato fo bending = 0.9 ux nx b ux nx 1. 0 Steel Columns 16
Design Steps Knowing Loads (evisited) 1. assume limiting stess bukling, axial stess, ombined stess 2. solve fo, A o S 3. pik tial setion 4. analyze stesses 5. setion ok? 6. stop when setion is ok Steel Columns 17
Rigid Fame Design (evisited) olumns in fames ends an be flexible stiffness affeted by beams and olumn = EI/L G fo the joint EI EI l is the olumn length of eah olumn l b is the beam length of eah beam measued ente to ente l l b Steel Columns 18
Rigid Fame Design (evisited) olumn effetive length, k A B Steel Columns 19