RCA Flashcards
Steps in WORKING STRESS DESIGN METHOD
STEP 1: Convert the steel area into an equivalent concrete area
STEP 2: Determine π by the by moment of area
STEP 3: Compute the allowable moment corresponding to the stress limit for concrete
STEP 4: Compute the allowable moment corresponding to the stress limit for steel
STEP 5: The smaller value of π(πππππ€) will govern
Modular elasticity/ratio formula
π=πΈπ /πΈπ
STEP 2 formula (Determine π by the by moment of area)
ππ₯ (π₯/2) =ππ΄π (πβπ₯)
Allowable moment corresponding to the stress limit for concrete
ππππππ€ = πΆ (πβ1/3 π₯)
where: πΆ= 1/2 ππ₯(0.45πβ²π)
Allowable moment corresponding to the stress limit for steel
ππππππ€ = π (πβ1/3 π₯)
where: π = ππ π΄π
_______ is accurate only for elastic materials and is considered an obsolete design philosophy for RC.
WSD (Working Stress Design)
USD (Ultimate Stress Design) is also called
Strength Design
WSD (Working Stress Design)
Alternate Design Method
NSCP 2015 emphasizes the use of _____
USD
Based on the empirical evidence the stress-strain relationship of both concrete and steel is _______________
inelastic
USD Basic assumptions (for concrete)
Concrete on the tension side is assumed to be cracked at ultimate strength. Strain at the extreme concrete fiber is 0.003 at ultimate strength.
Strain at the extreme concrete fiber is ____ at ultimate strength.
0.003
USD Basic assumptions (for steel)
Steel stress is ππ=π¬πππ when the strain is less than the yield strain.
Steel stress is ππ=ππ when the strain is greater than the yield strain.
Capacity point is reached when the strain in the farthest concrete fiber reaches 0.003. At such point, the stress in the equivalent uniform concrete stress block can be assumed to be ____ of the concrete compressive strength from tests
85%
In LRFD, load effects are enlarged by _________; while resistance or capacity is reduced by ___________. The separate set of factors for load effects and capacity recognizes the differing statistical nature of each.
-load factors
-strength factors
In ASD, the primary design parameter is the ______________.
maximum stress
In ASD, The applied stress is compared to nominal strength divided by a safety factor greater than ____. The safety factor varies depending on the member designed and other conditions.
1
______ is the newer and more empirically accurate philosophy
LRFD
____ usually results in a more conservative (but less economical) design than _____
- ASD
- LRFD
Inputs in structural analysis
E
I
other member properties
loads
constraints
Outputs in structural analysis
Reactions
Member Forces (Mu, Vu, etc.)
Node Displacements
Members deformations
Main components of Structural analysis
Modelling
Loading
Calculation
loads due to the weight of the permanent components
Dead Loads
loads due to the weight of temporary or moving components
Live Loads
loads due to pressure and vibration caused by wind
Wind Loads
loads induced forces due to ground motion
EQ loads
loads due to soil pressure
Soil Lateral Loads
loads due to the accumulation of water from rain
Rain Loads
hydrostatic and hydrodynamic loads due to surface runoff
Flood Loads
The designer should first consider the ____________ according to the intended use of the area.
actual loading conditions
In NSCP 2001, the strength reduction factor for axial and moment is simply ____.
0.90
In NSCP 2001, compression-controlled design is simply disallowed by requiring a steel ratio of not exceeding ____ the balanced steel ratio
75%
Starting NSCP 2010, compression-controlled design was permitted but with a more conservative strength reduction factor of _____.
0.65
in first-order analysis, the structural analysis assuming P-delta effects are _________
negligible
In second-order analysis, the structural analysis assuming P-delta effects are _______
significant
the phenomenon of force and displacement magnification due to the change of geometry of the member
P-delta effect
The code usually refers to P-delta effects as _______________
βslenderness effectsβ
effects are caused by lateral forces
P delta (π·ββ)
effects are caused by geometric imperfections of the member
P sigma (π·βπΉ)
Examples of RC frames βbraced against sideswayβ
Diagonal Bracing
Shear Wall
If bracing resisting lateral movement of a story have a total stiffness of at least 12 times the gross lateral stiffness of the columns in the direction considered, it shall be permitted to consider columns within the story to be _______________
braced against sidesway
formula of r (radius of gyration)
r = sqrt (Ig/Ag)
0.30 times the dimension in the direction stability is being considered for rectangular columns
0.25 times the diameter of circular columns
The primary design aid to estimate the effective length factor k is the
Jackson and Moreland Alignment Charts
Effective Length is
k
provide a graphical determination of k for a column of constant cross section in a multi-bay frame
Jackson and Moreland Alignment Charts
If slenderness effects are not permitted to be neglected, it is required to perform
a) Moment magnification method after first-order analysis OR
b) P-delta analysis (Second order analysis)
Steps in Moment Magnification Method (Non-sway frames):
1) Calculate ππ (6.6.4.4.2)
2) Determine πΆπ (6.6.4.5.3)
3) Calculate πΏ (6.6.4.5.2)
4) Apply πΏ to π2 (6.6.4.5.1)
Steps in Moment Magnification Method (Sway frames):
1) Calculate π and ππ (6.6.4.4)
2) Calculate πΏπ (6.6.4.6.2)
3) Apply πΏπ to π1 and π2 (6.6.4.6.1)
In Second-order (P-delta) analysis, P-delta analysis requires _____________
iterative geometric updating
Steps in Second-order (P-delta) analysis
Start > Modelling of structure and loads > Perform a first-order analysis > Geometry is altered due to deformation. Remodel the structure
