CONCRETE STRUCTURES

Question 1

Fig. 1 shows the cross-section of a concrete T-beam located inside a residential building. The beam is flexurally reinforced for a sagging moment with three D500N28 bars in the tension face and two D500N28 bars in the compression face, being D500N12 bars used for stirrups.

Fig. 1 – Cross-section (all dimensions in mm)

In the following questions assume a concrete cover of 25 mm whenever needed.

(1.75 marks) a) Determine the web shear reinforcement required to carry a design load of V* = 150 kN and sketch the layout of reinforcements.

(2 marks) b) If the design load V* was 350 kN, how would your design change?

Question 2

An 8-storey reinforced-concrete office building is to be constructed in Meckering, WA. All floors have the same layout based on the typical floor plan shown in the drawing below. This includes grid dimensions and typical beam, column and wall positions. The width of both primary and secondary beams is 400 mm. The specified office floor live load is 4 kPa, whereas the suspended ceilings represent a 0.15 kPa permanent loading. Concrete has a characteristic strength of 40 MPa in all members. N12 D500 reinforcement bars are to be used in all slabs and N28 D50 reinforcement bars in all beams and columns.

Fig. 2: Structural floor plan (dimensions in m).

Please refer to slab panel labelled A in Fig 2 for all questions below.

(2.5 marks) a) Calculate the minimum cover to satisfy durability and fire requirements according to Australian Standards. Note: the design Fire Resistance Levels (to satisfy the BCA) are 120/90/60.

(2.5 marks) b) Determine the combination factors for short-term and long-term loading effects, in accordance with AS 1170.

Note: In the following questions, assume that the suspended ceilings represent a 0.15kPa permanent loading. Consider the minimum cover is 20 mm, and Ψ_s = 0.7 and Ψ_l = 0.4 whenever needed.

(2.5 marks) c) Work out the minimum thickness for slab A using the deemed-to-comply approach in AS 3600 (do not forget to include its self-weight). Note: there is no compressive reinforcement.

Note: In the following questions, assume that the slab thickness is 160 mm.

(2.5 marks) d) Calculate the minimum longitudinal reinforcement required for slab A for moderate cracking and fully restrained situation.

(2.5 marks) e) Design the amount of longitudinal reinforcement in both directions for the ultimate limit state of flexure.

(2.5 marks) f) Check whether the slab requires shear reinforcement.

(1.25 marks) g) Finalise the layout of reinforcements using the deemed-to-comply approach in AS 3600.

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