Concrete Flashcards
(15 cards)
most critical property in concrete
cement content per cubic meter of concrete and its ratio to water.
Basic assumptions for design for flexure of concrete member
- plane sections remain plane
- strain is proportional to distance from the neutral axis
- maximum steel stress does not exceed fy
- cracked section analysis
- ULS Mn is reached when crushing strain is 0.003
- concrete stress strain curve replaced by simplified shape
Standard regular stress block assumptions
force and moment remain equal (equilibrium)
how could we increase capacity of we have to keep the rebar and strength the same?
- increase section depth
- transform to T beam to increase the compression area of the concrete which increases the compression resistance.
You are analyzing a reinforced concrete beam and realise it doesn’t meet the tension
controlled requirement in NZS 3101. What are two modifications you can make to the
beam design so the tension control requirement will be met, without reducing the design
moment capacity of the beam?
- increase depth of section
- use a flanged beam
- reduce compression reinforcement
As a graduate engineer you have been asked to go to site to review the reinforcing cages
for a series of reinforced concrete beams that are to be poured tomorrow. Name four things
related to the design and detailing of beams that you would want to check off.
1) Check the cover (dist to steel cage has a minimum requirement)
2) Check steel grade being used
3) Check spacing between transverse stirrups
4) Check dimensions and alignments are correct e.g. spacing between the longitudinal reinforcement bars
NZS3604 has a number of requirements that must be met regarding the distribution of
bracing elements around the building. What is the purpose of having a minimum required
bracing unit capacity for all of the external walls, and a minimum bracing unit capacity for
each of the internal bracing lines?
We have bracing unit capacity to ensure that we exceed wind and EQ bracing demand.
The minimum required bracing in external walls ensures the building can resist lateral loads at the perimeter, while minimum bracing in internal bracing lines ensures load sharing and prevents torsional instability.
T =
As fy
C =
æ f’c b a
Ey =
fy / E
M =
T * jd or C * jd
jd =
d - a/2
Cmax =
0.75 Cb
amax=
b Cmax
d
is the effective depth taken from the extreme compression fibre to the centroid of the tension reinforcement.
