homework problems

Give two examples each of ductile and brittle materials.

steel aluminum copper

Name two composite materials used in building construction.

reinforced concrete, plywood, metal, FRP

Name three important physical properties of materials.

density, SG, porosity, absorption capacity, moisture content.

A 25-in long member deforms to a length of 26 in when subjected to an axial force. What is

the strain

strain longitudinal = change in Length / Length initial = .04

define poissons ratio

ratio between lateral and longitudinal strain in axialy loaded members

A sample of aggregate has a moisture content of 10 percent. Its absorption capacity is 4

percent. What is the weight of free water in a 100-lb sample of this aggregate?

Surface moisture (free moisture) = MC - AC = 10% - 4% = 6% = 0.06

free wt of water = free moisture weight of aggregate = 0.06 100 lb = 6 lb

What is gap-graded aggregate?

Aggregate in which some intermediate sizes are missing

Using Sieves: No 4 (Full) No 8 (Full) No 16 (Full) No 30 (Full) No 50 (Full) No 100 (Full) If fineness modulus = 3, Find average size of sample.

Since each is a full sieve we count 3 sieves from smallest

No 30 sieve is average size or 0.0234 in / 600 um

A sample of fine aggregate with a specific gravity of 2.6 has a bulk density of 105 pcf. Find

the void content.

Void content = (SG w - beta) / (SG w) = (2.6 62.4 pcf - 105 pcf) / (SG w) = 0.35 = 35%

look at the hw solution

what are some considerations in mix design

workability , durability strength, economy

draw typical relationship between W/C ratio and ompressive strength

calculate weight of cement required to make 2 yd cubed of concrete of mix proportions: ( by part weight against cement): 2% air 1C ( cement): 2.5 FA ( fine aggregate) : 3.5 CA ( coarse aggregate): .5W ( Water)

what is the number of sacks of cement per cubic yard of concrete in 20

weight of concrete for 2 yd cubed is 1089lb. 1 yd cubed has weight of 544lb. 94 lbs per sack so 544/94 = 5.8 sacks or 6 sacks

in the mix design procedure, which property controlls the W / C ratio

compressive strength and durabilityin

mix design procedure, which property controls the amount of cement

W/ C which is controlled by strenght and durability

estimated water is slump and aggregate

what is curing and why is it done

maintaing adequate moisture while controlling temperature so that the concrete remains hydrated and can harden

find Ft given Fi = 4000 psi

use emperical relationship Ft = 6.7 square root of Fi = 424 psi

MOR = 12 square root of Fi = 759 psi

find E given Fi = 6000psi and gamma = 125pcf

E = gamma ^1.5 times (33) times square root of fi. gamma is equal to pcf and fi and E are equal to psi. 125^1.5 times 33 times sq root of 6k = 3.57 times 10 ^ 6

if the 28 day strength is 4000 psi what is the expected 7 day strength

70 - 80% of 28 day strength achieved in 7 days 2800-3200 psi

show position of steel reinforcement in a cantilever beam

what are 2 important pieces of information inscribed on surface of steel rebar

bar number, mill number, ASTM type, grade(strength)

explain purpose of adding fibers to concrete

control cracking, decrease shrinkage cracks, increase toughnessdes

describe the effects of creap and shrinkage

creep is deformation resultng from sustained loading, ussualy increase in deformation

shrinkage is volume decrease due to moisture loss in concrete.

these create cracking within concrete