64. The region of the cross-section of a column M which compressive load may be applied without prodtking any tensile stress, is known as the core of the cross-section. In circular columns the radius of the core, is
A. one-half of the radius
B. one-third of the radius
C. one-quarter of the radius
D. one-fifth of the radius

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65.  In rectangular columns (cross-section b x h), the core is a
A. rectangle of lengths b/2 and h/2
B. square of length b/2
C. rhombus of length h/2
D. rhombus of diagonals b13 and h/3

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66.  A column is said to be of medium size if its slenderness ratio is between
A. 20 and 32
B. 32 and 120
C. 120 and 160
D. 160 and 180

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67. Columns of given length, cross-section and material have different values of buckling loads for different end conditions. The strongest column is one whose
A. one end is fixed and other end is hinged
B. both ends are hinged or pin jointed
C. one end is fixed and the other end entirely free
D. both the ends are fixed

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68. The length of a column, having a uniform circular cross-section of 7.5 cm diameter and whose ends are hinged, is 5 m. If the value of E for the material is 2100 tonnes/cm2, the permissible maximum crippling load will be
A. 1.288 tonnes
B.12.88
C. 128.8 tonnes
D.288

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69.  Rankine-Golden formula accounts for direct as well as buckling stress and is applicable to
A. very long columns
B. long columns
C. short columns
D. intermediate columns

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70. The equivalent length of a column fixed at both ends, is
A. 0.5 1
B. 0.7 1
C.1
D. 2 1

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