CONCRETE STRUCTURES

The following is a review of the concrete related sections of
various  NCARB exams from previous years.

The sample questions are available at King Kopy
and are to be completed as Homework 10
Yes this is the last homework.

Try your best to complete the exam and turn it in
by Friday May 1, 1997

You may want to turn it in before,
to get propper feed back.

The exam is a good review for the final exam.

1.	The pair of gymnasiums designed for the Olympic Games in Tokyo in 1964 both had roofs 	suspended from immense cables hung from concrete masts.  The architect of the buildings was
	A.	Frei Otto
	B.	Ereo Saarinen
	C.	Tado Sato
	D.	Kenzo Tange

2.	The slope of a stress/strain diagram within the elastic range of a material indicates the 
	A. 	elastic limit
	B. 	modulus of elasticity
	C.	moment of inertia
	D. 	yield stress

3.	All structural materials deform under load.  If the deformation disappears when the load is 	removed, the material is said to be
	A.	plastic
	B.	elastic
	C.	brittle
	D.	deformable

4.	In which of the following diagrams of reinforced-concrete, cantilevered retaining walls is the 	major reinforcing shown properly?

5.	According to the ultimate-strength theory, which of the following statements about balanced 	reinforcement is a reinforced-concrete beam is correct?
	A.	It is the minimum tensile reinforcement stated in most building codes.
	B.	It exists when positive and negative bending moments are approximately equal.
	C.	It exists when the tension reinforcement reaches its specified strength fy as the 				compressive strain in the concrete reaches 0.003.
	D.	It refers to regularity of bar spacing.

6.	Which of the following men is generally considered to be the first to give architectural expression 	to the reinforced concrete frame?
	A.	Augusta Perret
	B.	Gustave Eiffel
	C.	Eugene Freyssinet
	D.	Eduardo Torroja

7.	Select the correct statement about the Pantheon.
	A.	Built-in iron chains were used to resist hoop tensile stresses in the dome.
	B.	Its dome was constructed of individual stones carefully fitted together.
	C.	It was destroyed in the great earthquake of 1847.
	D.	Its concrete dome, the largest of antiquity, still stands today.

8.	Which of the following men were important figures in the evolution of the skyscraper?
	I.	Elisha Graves Otis
	II.	Fazlur Khan
	III.	William LeBaron Jenney
	IV.  	Robert Maillart

	A.	I and III
	B.	II and IV
	C. 	I, II, III, and IV
	D.	I, II, and III

9.	The roof of the Dulles Airport terminal is supported by a series of monumental concrete piers.  	Why do these piers lean outward?
	A.	To express the concept of flight
	B.	To counteract the pull of the roof cables.
	C.	To counteract the thrust of the roof arches.
	D.	To provide greater resistance to lateral forces from wind or earthquake.

10.	The John Hancock building in Chicago, the Sears Tower, and the World Trade Center have what 		in common?
	I.	All three were designed by Skidmore, Owings, and Merrill.
	II.	They all employ tubular systems to resist lateral loads.
	III.	They all utilize reinforced concrete framing.

	A.	I only
	B.	II only
	C.	I and II
	D.	II and III

11.	Which of the following statements is true concerning the design of a reinforced concrete beam?
	A.	The ultimate load factors (U) for the beam design are less than those for the columns 			which support the beam.
	B.	The strength reduction factor (0) used in the design of the beam is smaller if a concrete 			strength (f'c) greater than 5000 psi is used.
	C.	The ultimate load factors (U) are different for the design of the reinforcing steel for 			bending than for the design of the stirrups for shear.
	D.	The ultimate load factors (U) are used to increase the actual loads to provide a factor of 			safety, and the strength reduction factor ()) is used to reduce the capacity of the beam to 			account for variations in the materials used in construction.

12.	You have specified a concrete compressive strength of f'c of 4000 psi.  At the age of 7 days, 	cylinder tests indicate a strength of 3000 psi.  What should you do?  
	A.	Nothing.
	B.	Revise the concrete mix design.
	C.	Order core tests.
	D.	Stop work on the project.

13.	What is temperature steel?
	A.	Reinforcing steel produced by hot rolling.
	B.	Reinforcing steel used in hot weather concreting.
	C.	Reinforcement provided for temperature stresses.
	D.	Reinforcement provided where the concrete will be subject to sub-freezing temperatures.

14.	Reinforcing bars sometimes become coated with mud, oil, rust, or mill scale.  Which of the 	following coatings must be removed from the bars before placing concrete?
	A.	Mud
	B.	Mud or oil
	C.	Mud, oil, or rust
	D.	Mud, oil, rust, or mill scale

15.	Given the following reinforcing bar data:
	Bar Size			Area
	#4				0.20 in2
	#5				0.31 in2
	#6				0.44 in2
	#7				0.60 in2
	#8				0.79 in2
	#9				1.00 in2
	
	If the ultimate tensile capacity of 2-#6 grade 40 reinforcing bars is compared with that of 1-#8 	grade 60 reinforcing bar, 
	A.	the #6 bars have the greater capacity.
	B.	the #8 bar has the greater capacity.
	C.	the capacities of both sets of bars are identical.
	D.	the capacity cannot be determined without knowing the 28-day compressive strength (f'c) 		of the concrete in which the reinforcing bars are used.

16.	Three reinforced concrete members are shown above.  The minimum concrete coverages for 	reinforcement (a, b, and c) are, respectively, 
	A.	2", 1-1/2", 1"
	B.	2", 1", 3/4"
	C.	3", 2", 1-1/2'
	D.	3", 1-1/2", 3/4"

17.	Which of the wall constructions in the drawings below has the fastest erection time?

	A. CONCRETE BLOCK	
	B. REINFORCED BRICK	
	C. REINFORCED CONCRETE
	D. BONDED BRICK

18.	Which of the following retaining walls has the reinforcing steel INCORRECTLY placed?

19.	Concrete for footings is to be poured during cold weather, and it is discovered that the bottom of 	the footing excavation is frozen.  What is the best procedure to follow?
	A.	Place the concrete on the frozen ground.
	B.	Wait for warm weather to thaw the frozen ground.
	C.	Thaw the frozen ground by steaming.
	D.	Excavate the frozen ground.

20.	What is the maximum time period that mixed mortar can be used before hydration has a damaging 	effect on its final strength?
	A.	1/2 - 1-1/2 hours
	B.	2 - 3-1/2 hours
	C.	3-1/2 - 4-1/2 hours
	D.	4-1/2 - 6 hours

21.	Which of the following are acceptable methods for splicing reinforcing bars?
	I.	Lap and tie
	II.	Butt weld
	III.	Mechanical couplers
	IV.	End bearing
	V.	Lap weld

	A.	I, II, III, IV and V
	B.	I, II, and V
	C.	III, IV, and V
	D.	I, II, and IV

22.	Concrete is made of fine aggregate, coarse aggregate, cement, and water.  The maximum size of 	coarse aggregate specified in concrete is based on a number of factors.  In this regard, which of 	the following statements is INCORRECT?
	A.	The maximum size of coarse aggregate is limited by the dimension between forms.
	B.	The maximum size of coarse aggregate is less than the clear spacing between reinforcing 			bars.
	C.	For most building projects, it is not economical to specify aggregates larger than 2 or 
		2-1/2 inches.
	D.	The amount of water and cement required for concrete of a given 

23.	A building has been designed with 24-inch diameter reinforced concrete columns with 6-#9 	vertical reinforcing bars and #3 ties at 18 inch on center.  How may additional axial load capacity 	be obtained?
	A.	Use spiral reinforcement in place of the ties.
	B.	Use spiral reinforcement in addition to the ties.
	C.	Detail the columns to be pin-ended, so that they may be designed to resist no moment 			and thus have a greater axial load capacity.
	D.	Space the ties closer together.

24.	The temperature of a steel bar 20 feet long is increased from 70_ to 110_ F.  How much does it 	expand?  (The coefficient of thermal expansion of steel is 0.0000065.)
	A.	0.0143"	
	B.	0.0624"
	C.	0.0052"
	D.	0.1716"

25.	All of the following are advantages of using precast concrete sections, except
	A.	better quality control.
	B.	faster curing.
	C.	all-weather construction.
	D.	greater economy.

26.	"Saddles" and "chairs" are utilized in concrete construction to
	A.	support flexible pipes for pumping concrete
	B.	support reinforcing bars during concrete placement
	C.	facilitate the screening and floating of concrete
	D.	provide relief joints to prevent cracking form expansion and contraction

27.	The calculated deflection of a reinforced concrete beam is excessive, making it necessary to 	redesign the beam.  What is the most efficient way to reduce the calculated deflection, assuming 	that the load supported by the beam cannot be reduced?
	A.	Make the beam wider.
	B.	Add reinforcing steel.
	C.	Specify higher strength concrete.
	D.	Make the beam deeper.

28.	All of the following statements about reinforced concrete beams are true, EXCEPT
	A.	when shear cracks occur, they extend from the bottom face of the beam in a diagonal 			direction toward the center of the span.
	B.	stirrups are reinforcing bars used to resist shear stress in excess of that resisted by the 			concrete.
	C.	if the allowable shear stress in the concrete is exceeded, the beam must be made wider 			and/or deeper.
	D.	the maximum shear is computed at a distance d from the face of the support.

29.	Which of the following statements concerning the flat plate floor system are generally correct?
	I.	The construction depth is shallow.
	II.	Shear stresses near the columns are high.
	III. 	The system is inherently very stiff.
	IV. 	Beams between the columns are required in both directions.
	V.	The system is economical for live loads of 100 psf or more and for spans of 
		about 30 feet.
	A.	I and II only		
	B.	II, III, and V
	C.	I, IV, and V
	D.	I, II, and V

30.	Which of the following statements concerning the water-cement ratio of a concrete mix is
	not true?
	A.	It is common to express the amount of water in any mix as a ratio of the volume, not 			weight, of the cement present.
	B.	A low water-cement ratio reduces the shrinkage of concrete and increases its durability.
	C.	The strength of concrete remains the same for a give water-cement ratio of the paste 			irrespective of the amount of aggregate embedded in the paste.
	D.	Provided there is sufficient water to hydrate the cement and to avoid air being trapped 			because the mix is too stiff to compact thoroughly, the strength of concrete increases as 			the water-cement ratio increases.

31.	The actual punching shear stress in a reinforced concrete pile cap is determined by which of the 		following?
	A.	The type of soil in which the piles are founded.
	B.	The square root of the 28-day compressive strength of the concrete used in the cap.
	C.	The number of piles supporting the pile cap.
	D.	The location of the piles supporting the pile cap relative to the location of the column 			supported by the pile cap.

32.	Select the correct statements.
	I.	The principal factors affecting the strength of concrete are the water-cement ratio and the 		extent of the hydration.
	II.	Air-entrained concrete is more resistant to freezing and thawing than non-air-entrained 			concrete.
	III.	Concrete having a low water-cement ratio is stronger and more resistant to freezing and 			thawing than concrete with a high water-cement ratio.
	IV.	The length of time during which concrete is moist-cured affects its strength and 				watertightness.
	V.	Excessive bleeding tends to make the surface of concrete weak.

	A.	I, III, V
	B.	I, II, IV
	C.  	II, IV, V
	D.  	I, II, III, IV, V

33.	A steel bar 1-1/2 inches in diameter and 25 feet long stretches 0.18" when subject to a load.  
	If the modulus of elasticity E is equal to 29,000,000 psi what is the unit stress in the bar?
	A.	20,880 psi	
	B.	17,400 psi
	C.	 36,000 psi
	D. 	10,191 psi

34. 	A composite floor deck is 

	A.	a steel deck and the concrete slab above it, which act together as a single structural 			element.
	B.	a floor deck made of two different grades of steel.
	C.	a steel deck which incorporates electrical raceways.
	D.	a concrete slab poured over precast concrete planks.


ANSWER QUESTIONS:
AO	Accelerating agent
A1	Air entraining agent
A2	Construction joints
A3	Control joints
A4	Expansion joints
A5	Hardening agent
A6	Isolation joints
A7	Retarding agent
A8	Waterproofing agent
A9	Workability agent

Among the terms listed above, select the ones that best answer questions 35 and 36.

35.	If you are pouring a large concrete slab and wish to avoid the random cracks caused by shrinkage, 	what kind of protection should you provide?

36.	When pouring concrete in hot weather, what precaution would be appropriate?

37.	The purpose of a concrete slump test is to
	A.	determine the plasticity of the mix.
	B.	measure the consistency and workability of the mix.
	C.	test the compression of the mix.
	D.	define the compression strength of the mix.

38.	Which of the following qualities are normally associated with light-weight concrete?
	I.	Good thermal insulation
	II.	Great compressive strength
	III. 	Excellent fire resistance
	IV.	Low cost
	V.	Difficulty of handling

	A.	I and II
	B.	II and III
	C.	I, III, V
	D.	II, IV, V

39.	Which of the following governs the amount of sand in a concrete mix?
	A.	The moisture content of the sand
	B.	The water-cement ratio.
	C.	The weight of the cement
	D.	The volume of coarse aggregate

40.	In curing concrete slabs, which of the following procedures is rarely used?
	A.	Overlay with plastic membrane
	B.	Spray with moisture
	C.	Blow with fans
	D.	Cover with sand

41.	An architect supervising a concrete pour notices that the entire concrete load has been deposited 	from a 6-foot height at the middle of a 40-foot long form. 
	For question 41, indicate if the following would be appropriate or inappropriate by marking 
	A or I.
	The architect should direct the contractor to immediately spread the wet concrete throughout the 	length of the form, in order to avoid segregation of the mixture.
	A
	I

42.	The steel in reinforced concrete
	A.	furnishes rigidity.
	B.	provides tensile strength.
	C.	increases bond strength.
	D.	adds ductility and durability.

43.	The size of coarse aggregate in a concrete mix is governed by the
	I.	Type of cement used.
	II.	strength of concrete desired.
	III.	thickness of concrete section.
	IV.	water-cement ratio.
	V.	space between reinforcing bars.
	A.	V only.
	B.	I and IV
	C.	II and III
	D.	III and V

44.	In general, the most economical reinforced concrete framing system is one in which 
	A.	the amount of reinforcing steel is kept to a minimum by increasing the sizes of the 			members.
	B.	the vertical loads are resisted by bearing walls and the lateral wind or earthquake loads 			by rigid frames.
	C.	the areas in which the concrete is in tension are replaced with voids, as in a waffle slab, 			thus reducing the weight of the system.
	D.	the forming is uniform and repetitive and the reinforcing layout is simple and repetitive.

45.	Select the correct statements concerning the reinforced concrete floor framing systems.
	I.	In a pan joist floor system, shear stress near the support is often a controlling factor.
    	II.	A reinforce concrete slab 10 feet by 25 feet in plan is usually assumed to span in the 10 			foot direction only.
    	III.	The concrete floor framing system requiring the simplest formwork is the flat plate floor.
     	IV.	Slab band construction requires more beam reinforcement than a conventional beam used 		for the same span and loading conditions.
	A.	All of the above
	B.	II and IV
	C.	I and II
	D.	I, II, and III

46.	In the latter half of the nineteenth century, buildings with longer spans and greater heights were 	made possible by the development of steel construction.  Which of the following buildings did 	NOT utilize a metal frame?
	A.	Crystal Palace
	B.	Home Insurance Co. Building
	C.	Reliance Building
	D.	Marshall Field  Wholesale Store

47.	Reinforcing bars used in the construction of parking decks in cold climates can be epoxy coated in 	order to
	A.	facilitate sorting by size
	B.	reduce corrosion resulting from contact with concrete mix
	C.	eliminate bonding between bars and concrete
	D.	control rust due to moisture penetration of the cured concrete

48.	The nominal diameter and yield strength of the bar shown on the following page are as follows:  
	A.	Diameter = 0.40 inch, yield strength = 60 ksi
	B.	Diameter = 12 inch, yield strength = 60 ksi
	C.	Diameter = 0.60 inch, yield strength = 40 ksi
	D.	The markings shown designate only the producer of the bar and the chemical content.

49.	Which of the following is the appropriate waterproofing to use on the exposed interior side of a 	foundation wall?
	A.	Membrane
	B.	Hydrolytic
	C.	Acrylic sealer
	D.	Sheet metal

50. The terrazzo construction element labeled A in the figure below is
	A.	a double-bead divider strip
	B.	a monolithic divider strip
	C.	an expansion strip
	D.	a floor anchor

51.	The purpose of masonry expansion control joints is to 
	A.	provide positive bonding
	B.	allow for differential movement
	C.	act as a firestop
	D.	provide cavity drainage

52.	Which of the following statements about prestressed concrete construction is NOT true?
	A.	Precast, prestressed members are usually posttensioned.
	B.	Prestressed members utilize their cross-section more efficiently than conventional 			reinforced concrete members.
	C.	Pretensioned members require no end anchorages.
	D.	Creep and shrinkage cause losses of prestress which must be considered.

53.	Given the following reinforced concrete beam:

54.	What is the required area of reinforcing steel if grade 60 steel is used?
	A.	3.09 in2	
	B.	0.27 in2	
	C.	3.29 in2
	D.	2.96 in2

20.	Which of the following statements concerning the dome of the Florence Cathedral is NOT 	correct?
	A.	It was designed by the great Renaissance architect Brunelleschi.
	B.	It consists of a thick inner dome connected to a thinner outer dome.
	C.	The construction of the dome required the largest temporary structure ever used up to 			that time for shoring.
	D.	A series of built-in iron chains act to resist tensile forces and prevent the dome from 			cracking or collapsing.