Civil Engineering Online Review

The construction of a grouted rip rap is done as  follows. A 0.45m³ of rip rap can be constructed in one hour by a group of workers consisting of one foreman, one skilled laborer, and 5 unskilled laborer. The foreman is paid P50 per hour, the skilled laborer P40 per hour and the unskilled laborer is paid P35 per hour. The value of added tax is 10% of labor. A cubic meter of boulders cost P250. The materials needed for a cubic meter of rip rap are, 3 begs of cement at P130 per cu.m. The cost of administration, representation, insurance, etc. Is 30% of labor and materials.

1) Which of the following gives the cost of labor for 1m³ of riprap.

2) Which of the following gives the cost of material for 1 m³ of riprap.

3) Which of the following gives the total unit cost for 1m³ of riprap.

Solution:

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A reinforced concrete beam has a width of 300mm and an effective depth of 450mm. The beam is reinforced with 6-32mmØ bars at the bottom and 2-28mmØ bars at the top located 65mm from the maximum compression fiber. fc’ = 34.5 MPa, Fy = 345MPa. Assume that the contribution of the compression steel may not be neglected and that compression steel yields.

1) Which of the following gives the balanced steel ratio.

2) Which of the following gives the depth of the compression block.

3) Which of the following gives the nominal moment capacity of the beam.

Solution:

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Section 5.9.5.2.1 of the National Structural Code of the Philippines specifies the minimum thickness as shown on the table apply for one way construction not supporting or attached to partitions or other construction likely to be damaged by large deflections, unless computation of deflection indicates a lesser thickness can be used without adverse effects.

Minimum thickness of Non-Prestressed Beams or One Way Slabs Unless Deflection Are Computed.

For the continuous beam shown

1) Which of the following gives the minimum thickness of beam B-1.

2) Which of the following gives the minimum thickness of beam B-2.

3) Which of the following gives the minimum thickness of beam B-3.

Solution:

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The implementing rules and regulations of P.D. 1594 states that an unbalanced bid shall be defined as a bid containing one or more pay items that are 30% higher than the unit (AGE) Approved Gov’t Estimate with respect to major items whereas other pay items are priced lower than the unit AGE, major items being defined as pay items representing at least 20% ot the AAE or the first two items having the highest precentage of the AAE (Approved Agency Estimate) or those indicated or specified in the instruction to bidders. The quantities, AAE and contract prices for a project are as follows.

1) Which of the following gives the value of AAE.

2) Which of the following gives the cost for an item to be considered automatically as major items.

3) Which of the following are considered major items.

Solution:

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A cantilever prismatic beam is 8m. long and propped at one end. EI = 1750 N.m²

1) Which of the following gives the moment induced by a unit rotation at the propped end.

2) Which of the following gives the moment induced at the fixed end.

3) Which of the following gives the reaction at the propped support.

Solution:

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A rod is connected to a pin at A and a chord at B as shown. It holds a cylindrical drum which weighs 176N. The drum has a diameter of 1m.

1) Which of the following gives the force between the drum and the rod.

2) Which of the following gives the force in the chord BC.

3) Which of the following gives the reaction at the pin at A.

Solution:

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A 1800 kg car drives up an inclined of 8% from rest at uniform acceleration to a velocity of 60kph after traveling 75m. Its wheels are 3m. apart with its center of gravity midway of the wheels and 500mm. from the ground. If all frictional force is assumed to act at the rear wheels.

1) Which of the following gives the acceleration of the car

2) Which of the following gives the normal force on the front wheels.

3) Which of the following gives the minimum coefficient of friction needed so that motion is possible.

Solution:

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Section 4.5.1.4.5 of the National Structural Code of the Philippines states that for extreme fibers of flexural members not covered in sections 4.5.1.4.1, 4.5.1.4.2, 4.5.1.4.3 or 4.5.1.4.4, the allowable stresses are as follows.

1) Tensio:

F_b = 0.60Fy

2) Compression:

For member meeting the requirements of Sect. 4.9.1.2, having an axi of symmetry in, and loaded in, the plane of their web, and compression on extreme fibers of channels bent about their major axis:

The larger value computed by Formula (4.5-6a) or (4.5-6b) and (4.5-7), as applicable (unless a higher value can be justified on the basis of a more precise analysis), but not more than 0.60Fy.

Or, when the compression flange is solid and approximately rectangular in cross-section and its area is not less than that of the tension flange:

In the foregoing:

I = distance between cross sections braced against twist or lateral displacement of the compression flange, mm. For cantilevers braced against twist only at the support, I may conservatively be taken as the actual length.

r_t =  radius of gyration of a section comprising the compression flange plus 1/3  of the compression web area, taken about an axis in the plane of the web, mm.

A_f = area of the compression flange, mm³

C_b = 1.75 + 1.05(M_1/M₂) + 0.30(M_1/M₂)² but more than 2.3, where M₁ is the smaller and M₂ the larger bending moment at the ends of the unbraced length, taken about the strong axis of the members, and where M_1/M₂ the ratio of end moments, is positive when M₁ and M₂ have the same sign (reverse curvature bending) and negative when they are of opposite sighs (single curvature bending). When the bending moment at point within an unbraced length is larger than that at both ends of this length, the value of C_b may be computed by the formula given above for frames subject to joint translation, and it shall be taken as unity for frames braced against joint translation. C_b may conservatively be taken as unity for cantilever beams.

A simply supported beam having a span of 8m. is laterally unsupported is made up of A36 steel with Fy = 248 MPa with the following properties:

b_f = 0.210m                             r_t = 0.073m.

S_x = 0.002077m³*********t_f = 0.016m.

d = 0.533m.

1) Which of the following gives the slenderness ratio above which the beam would be considered long.

2) Which of the following gives the allowable bending stress.

3) Which of the following gives the maximum uniform load that can be carried by the beam.

Solution:

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From the given figure shows a shaft of 60mm diameter with value of G = 83000MPa.

1) Which of the following gives the reaction at the fixed end.

2) Which of the following gives the maximum torsional stress.

3) Which of the following gives the angle of twist of the shaft.

Solution:

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Allowable unit stresses in newtons per square mm of cross-sectional area of square or rectangular simple solid columns shall be determined by the following formulas, but such unit stresses shall not exceed values for compression, parallel to grain Fc as shown in the tables adjusted in accordance with the provision of sections of 3.4 of the National Structural Code.

1) Shortest columns (Le/d of 11 or less) Fc’ =Fc

2) Intermediate columns (Le/d greater than 11 but less than K)

3) Long columns (Le/d of K or greater)

A timber column of square cross section has a length of 3m. and a dimension of 140mm x 140mm. It is hinged at the ends so that K = 1.0. The relevant code on the compressive strength Fc is given on the specifications and also a table of timber with their corresponding working stresses for visually stress-graded unseasoned Apitong with 80% stress grade.

1) Is the column

a. Short column

b. Intermediate column

c. Long column

d. Not allowed by the code

2) Which of the following gives the allowable compressive stress.

3) Which of the following gives the allowable axial load.

Solution:

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A construction firm has the option of buying a truck which costs P1,000,000 with a salvage value of P300,000 at the end of its life of 4yrs and pay an annual maintenance cost of P125,000 per year or pay P1,000,000 for the cost of truck and an additional P200,000 for maintenance cost so that he will no longer pay maintenance cost every year. If money is worth 15% annually.

1) Which of the following gives the annual cost excluding maintenance cost.

2) Which of the following gives the annual maintenance cost.

3) Which of the following gives the total annual cost.

Solution:

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A 150 x 90 x 12mm. angular section is welded to a gusset plate as shown.

Area of angular section is 2736mm².

Fu = 550 MPa,              Fy = 250 MPa

Allowable shear            Fv = 0.30 Fu

Allowable tensile stress Ft = 0.60 Fy

1) Which of the following gives the design force P.

2) Which of the following gives the total length of weld using 12mm. fillet weld.

3) Which of the following gives the value of “b”

Solution:

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A composite beam is made up of a wide flange with two cover plates of 320mm x 12mm placed at the top and at the bottom. The beam has a simple span of 6m. and carries a total load of 360 kN/m.

Allowable bending stress Fb = 150 MPa

Allowable shear stress Fv = 100 MPa

Allowable deflection δ = L/360

Prop. of the wide flange section.

A = 0.02 m² t_w = 0.018 m.

d = 0.56 m.                    I =0.001568 m⁴.

E = 200,000 MPa.

1) Which of the following gives the section modulus of the section.

2) Which of the following gives the deflection of the beam.

3) Is the beam

a. Adequate

b. In adequate for flexure and shear

c. In adequate for flexure and deflection

d. In adequate for flexure, shear and deflection.

Solution:

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From the given frame point C is supported by a roller while A if hinged.

1) Which of the following gives the stress of BC due to actual loads only.

2) Which of the following gives the stress of BC due to a vertical unit load only.

3) Which of the following gives the vertical deflection at B using virtual work method.

Solution:

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A reinforced concrete beam has a width of 280mm, and an effective depth of 520mm. It is reinforced with 4-28mmØ bars at the bottom. If fc’ = 21MPa and fs = 140MPa, n =9.

1) Which of the following is the distance from neutral axis to the top of the beam.

2) Which of the following gives the beam description.

3) Which of the following gives the moment carried by the beam.

Solution:

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The first cost of a machine is P1,800,000 with a salvage value of P300,000 at the end of its of 5 years. Determine the book value after 3 years, using

1) Straight Line Method

2) Double Declining Balanced Method

3) Sum of Years Digit Method

Solution:

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A reinforced concrete tied column carries a dead axial load of 600 kN and a live axial load of 800kN. fc’ = 28MPa, fy = 400MPa

1) Which of the following gives the final factored load?

2) Using super position method, which of the following gives the smallest dimension of the column section if the steel ration is 2%.

3) Which of the following gives the no. of 20mmØ bars.

Solution:

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A wooden beam 150mm. wide by 300mm. deep is loaded as shown

1) Which of the following gives the max. moment capacity of the beam.

2) Which of the following gives the max. value of w if x = 2m.

3) Which of the following gives the max. value of P if x = 2m.

Solution:

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The resultant of the concurrent fores has a magnitude of 1000 kN and acts through the origin and points x = 2, y =3 and z = 4.

1) Which of the following gives the x-component of the resultant force.

2) Which of the following gives the y-component of the resultant force.

3) Which of the following gives the z-component of the resultant force.

Solution:

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From the given sets of parallel forces shown

1) Which of the following gives the resultant force.

2) Which of the following gives the location of the resultant force from the left support.

3) Which of the following gives the reaction at the left support.

Solution:

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