a) Differentiate between an under reinforced, over reinforced and balanced concrete
section (6 marks)
b) Explain why an over reinforced and balanced sections should be avoided in design and it
should always be ensured that an under reinforced section is designed. (3 marks)
c) A single span T beam of 6m effective span is fixed at its ends and carries a uniformly
distributed permanent load inclusive of self – weight of 15kN/m and a variable load of
6kN/m. the beam is 300mm wide × 600mm deep; Assuming grade 30 concrete, grade 460
steel, 20mm cover, 8mm links and 16mm diameter longitudinal bars;
| i) | Calculate the applied moment; | (2 marks) |
| ii) | Determine the effective depth of the beam; | (2 marks) |
| iii) | Determine its effective flange width; | (2 marks) |
| iv) | Calculate the area of tensile steel in the span; | (4 marks) |
| v) | Calculate the area of tensile steel in the support; | (6 marks) |
| QUESTION #02a) Using sketches, differentiate between one way and two way spanning slabs | (2 marks) |
b) Give the three functions of distribution steel in solid one way spanning reinforced
concrete slabs (3 marks)
c) The four span slab shown in the figure below is cats monolithically with the beams and
supports a variable load of 3.0kN/m2, plus floor finish and underside plaster of 1.0kN/m2.
The characteristic material strengths are fck = 25 kN/m2 and fyk = 250 kN/m2, assuming
an overall depth of 175mm, the unit weight of concrete is 24 kN/m3, 12mm diameter bars
and 20mm cover;
i) Determine the ultimate load in kN/m2; (2 marks)
ii) Using coefficients, draw shear force and bending moment diagrams; (6 marks)
iii) Determine the end span reinforcement; (3 marks)
iv) Check that the spacing of the end span reinforcement satisfies crack control
requirements; (2 marks)
v) Check that deflections are permissible; (7 marks)
QUESTION #03
a) Basing on the properties of materials, give three reasons why concrete should be
reinforced with steel bars (3 marks)
b) Name three fire resistance categories that are considered during a fire (3 marks)
c) Explain what is meant by creep of a concrete member and give two factor which affect
| creep | (3 marks) |
| d) Give one cause of shrinkage, one way how it can be controlled, on advantage of shrinkage |
| and one disadvantage of shrinkage | (4 marks) |
| e) A member contains 1.0% reinforcement and the free shrinkage strain of concrete is |
200 × 10-6. For steel the modulus of elasticity Es = 200N/mm2 and for concrete
Ecm = 25 N/mm2. Determine the stress in steel and concrete given that the member is
| restrained by reinforcement only; | (6 marks) |
| f) Give one advantage of mild steel bars over high yield bars | (1 mark) |
g) 12mm diameter reinforcement bars made of mild steel are used in a pad footing. The
anchorage bond length Lb is determined as the length from the column face. Determine
this anchorage bond length. (5 marks)
QUESTION #04
a) Give two advantages of maxspan (RC ribbed slabs with permanent blocks) slabs over solid
reinforced concrete slabs (2 marks)
| b) Explain why a steel fabric is provided in the topping of a maxspan slab | (2 marks) |
| c) Determine the depth of topping to be provided in a maxspan slab assuming 20mm cover, | |
| 12mm diameter bars over supports, 6mm mat (A142 BRC) also to serve as distribution |
| steel, 10mm spacers between the A142 BRC and the hollow blocks | (2 marks) |
| d) A ribbed hollow block slab continuous over three equal spans of 3m and is supported by |
walls carries a variable load of 2.0kN/m2, has a topping of 60mm, cement sand screed
floor finish of 25mm and underside plaster of 25mm. The hollow blocks (maxspans) are
300mm long, 125mm deep, 380mm wide at the top and 300mm wide at the bottom and
weigh 6kg. the cross – section of the RC hollow block slab is shown in the figure below. To
allow for passage of the porker vibrator, the ribs are 70mm at the top and 150mm at the
bottom. The materials are grade 30 concrete and grade 250 steel. Assuming 20mm cover,
12mm diameter bars, unit weight of concrete is 24kN/m3 and that of finishes and
underside plaster is 20 kN/m3;
(i) Determine the number of maxspans per square meter (3 marks)
(ii) Determine the ultimate load of the slab per square meter and per 0.45m strip
of slab (5 marks)
(iii) Using coefficients, draw shear and bending moment diagrams (5 marks)
| (iv) | Determine the reinforcement per rib in the first span | (3 marks) |
| (v) | Check the shear resistance of the slab | (3 marks) |
Question five
The footing is required to resist characteristic axial loads of 1100KN permanent and 450KN variable from a 400mm square column. The safe bearing pressure on the soil is 190KN / m2 and the characteristic material strengths are f ck 25 N / mm 2 and f yk 500N / mm 2 , assuming a footing weight of 130KN so that the total permanent load is 1230KN , a 600mm thick footing, an effective depth of 530mm , 16mm diameter bars.
| a) Determine the size of the base | ( 1 mark) |
| b) Determine ground pressure | ( 3 marks) |
| c) Check maximum shear resistance | ( 4 marks) |
| d) Determine bending reinforcement | ( 9 marks) |
| e) Check punching shear | ( 4 marks) |
| f) Check maximum shear | ( 4 marks |
