COLUMN Flashcards
1
Q
Column Design Steps
A
1) Design Actions
2) Load Combinations
3) Column Moments
4) Section Design
5) Code Checks
6) Transverse Reinforcement
7) Lapping
2
Q
1) Design actions
A
- Dead Load, Ng
- Live Load, Nq (apply area reduction factor)
- Earthquake Induced, Neo (resultant of beam overstrength shears either side of joint)
3
Q
2) Load Combinations
A
critical load combinations: max. compression; min. tension
1) N* = Ng + Nq + Neo (max compression)
2) N* = Ng - Neo (min tension)
3) N* = 1.2Ng + 1.5Nq (typically never governs)
4
Q
3) Column Moments
A
- determine overstrength factor
- magnify moments obtained by dynamic modification factor
- since moment gradient of column unknown, assume 60% of critical shear to act concurrently with design moment
5
Q
overstrength factor
A
phi0 = sum(Mo) / sum(Me)
- scales up column moments from analysis to ensure stronger than the overstrength moment of beams
- this is to: 1) avoid “soft storey” mechanism 2) have “weak beam” mechanism
- because a) column sections less ductile than beams b) ductile detailing for column hinges more elaborate
6
Q
dynamic modification factor
A
- factor allows for higher modes
- static analysis considers only the first mode
7
Q
4) Section Design
A
- use design charts or appropriate software to determine required long. reinforcement
- design charts underdesign by about 7%
8
Q
5) Code Checks
A
- determine max. bar size to avoid bond failure
- check min and max reinforcement ratios
- determine practical bar layout (must be symmetrical and satisfy code spacing)
9
Q
6) Transverse reinforcement
A
- determine PPHZ where ductile detailing required
- size of PPHZ dependent on axial load f(N / Agf’c)
- transverse steel area requirements for confinement, anti-buckling and shear
- check stirrup spacing against code
10
Q
7) Lapping
A
- below level 2 all lapping should be at mid-height of column (cannot lap at PPHZ due to likely loss of bond as columns elongate)
- above level 2 can lap just above joint (easier to construct and safer)
