Class 1-WED,Jan31,2018/Materialsproperties Flashcards
In concrete (beams and columns ) we always have a minimum concrete cover for the steel of 4cm.
TRue
MInimum spacing between two bars of steel is greater or equal to 1 inch or to bar diameter.
TRue, however practically in real life we put every 10 cm 1 bar in order to allow concrete and aggregates to pass through w howwe mrta7.
Longest steel bar we can order from a factory is
12 m.
What is strain compatibility
Strain compatibility is when we have the strain in concrete is equal to that in steel at same fiber location implies a perfect bond between steel and concrete needed and we work on the site to ensure that bond.
Meaning I need the concrete to confine the bars.
Practically we use more bars of less diameter
TRue, we will have more safe structure if one of the bars failed.
Stress strain curve for concrete
Check Copybook
Notes on Curve:
+F’c is the Maximum compressive strength of the concrete.
+We assume concrete is elastic up to 0.7 f’c.
+Regardless of the strength, concrete reach their ultimate strength at a strain of about 0.002.
+Concrete fails (point of rupture) at strains from 0.003 to 0.004, but we assume it at 0.003.
+It is noticed that a concrete with higher maximum strength is more brittle than that of concrete with a lower compressive strength ( They will take less strains before they break.)
+Splitting tensile strength of concrete is about 10 % of f’c.
Modulus of elasticity of concrete Ec.
Ec= 33w^1.5rad(f’c in psi)
where :
* f’c is the modulus of elasticity of concrete in psi.
* w is the unit weight (meaning mass over volume not weight) of concrete in pcf (pound(mass) per cubic foot).
For normal weight concrete we can use the following formula:
Ec= 57000 rad(f’c in psi).
Normal unit weight of concrete.
- 145 poundpercubefeet
* 2500 kg/m3 (with steel , if without about 2300-2400).
Modulus of rupture
7.5rad(f’c) which is about 15 % of f’c.
When do we cure concrete
We cure concrete after 6 to 10 hrs according to the temperature, if it is too hot we cure after 6 hrs anf thus accordingly.
Note that in case if it is raining we isolate the concrete in order not to affect the water-cement ratio before curiing.
Steel material properties
*Check for the curve on the copybook
*Density of steel :490 pcf= 7850 kg/m3
*For grade 60 steel
fy(yield strength) : 60000psi=60ksi=4200 kg/cm2= 420 MPa
Steel bars diameter
#3 = 1 cm #4 = 1.3 cm #5 = 1.6 cm #6 = 1.9 cm #7= 2.2 cm #8= 2.5 cm #9= 2.9 cm #10= 3.2 cm #11= 3.6 cm #14= 4.3 cm #18= 5.7 cm
3
1 cm
4
1.3 cm
5
1.6 cm
