300736 Concrete Structures

Part: 2 Analysis and design

Design Information and Requirements:

• Concrete compressive strength, f’c = 32 MPa

• Modulus of Elasticity of concrete, Ec = 30,000 MPa

• Yield strength of longitudinal reinforcing steel, fsy = 500 MPa (Use N class bar)

• Yield strength of transverse reinforcing steel, fsy.f = 400 MPa

• Modulus of Elasticity of steel, Es = 200,000 MPa

• Concrete density = 25 kN/m3

• εcs = 600 με; ψs = 0.7 and ψl = 0.4

• Superimposed dead load = 3.0 kPa

• Consider self-weight

• Slab live load = 3.0 kPa across the floor

• Columns are 400 mm x 400 mm

• Beam widths are fixed at 400 mm

• Slab depth is 200 mm

• Concrete slabs are supposed to be built monolithically with the supporting beams; therefore, the beams must be designed as L or T-beams.

Calculation and data collection:

Standard load combinations – AS1170.0 (section 4.2.2) by considering strength criteria

The combinations below are used to design office building structure and achieve M*, V* and N*.

As1170.0 (4.2.2)

There are other loads as well such as wind load, earthquake imposed load etc. but it neglected as it was not used in the design specification

Serviceability limit state

According to AS/NZS1170.0:2002, Section 4: Combinations of actions, table 4.1, page 17, shown in figure 3 below:

Figure 3: Short-Term, Long-Term and Combination factors, as shown in Table 4.1 in AS/NZS1170.0:2002

Short-Term effect also referred to as “immediate deflection” will be:

G+ sQ

Long-Term effect, which is the part of deflection that occurs due to shrinkage of concrete and due to creep:
G+ lQ

Both load combinations are used to find M*, V* and N* for deflection.

Load calculation

Structural Analysis:

Dead loads:

The following diagram consider for calculating beams self-weight and square area 400 x 400 mm

Assuming, bef=1200

Depth of section = 1000 mm

Density x Cross sectional area of the beam = force per m of the beam.

P x A = F/m

24 kN/m3 x (0.4m x 0.8m) = 7.68 kN/m

Slab self-weight:

By considering internal beams, the uniform distributed load has doubled the external beam uniformly distributed load which demonstrates as following by considering internal beam should doubled.

Density x width x thickness = force per m of the beam.

p x b x t = F/m

Critical slab load section for external beams:

24 kNm3 x 3.5m x 0.2m = 16.8 kN/m

Superimposed Dead load:

The super imposed load will be = 1 kPa x 3.5 = 3.5 kNm

Imposed load considered total dead load = dead load + self-weight

Live Loads

Floor Slab Live Load

Using the AS1170.1 T3.1 B and given that the criteria mentioned was for building construction for a general load value of 3kPa to obtain the live load. 3kPa was applied to each floor of the structure.

The live load on each floor, transferred to each internal beam to give:

3kPa x 3.5m = 10.5 kN/m.

The live load on the floor slabs transferred to the External Beams will be:

3kPa x 3.5m2 = 5.25 kN/m

Roof Slab Live Load

Table 3.1 of AS1170.1 was used to obtain the live load of the roof slab, using this table, the live load was determined using the equation below.

Q (kPa) = greater of (1.8A + 0.12) or 0.25

Plan A projects the supported surface area of the roof of each member in square meters.

A (the area supported by the beam)

A = 3.5m x 15m (quarter of slab) = 52.5m2

1.852.5+0.12 = 0.154

Q = greater of: 0.168 or 0.25, Therefore Q = 0.25 kPa

Peak live load on the roof slab will be:

0.25 kPa x 3.5m = 0.875 kN/m

Design Actions

First load combination

Strength Load Combination

Load Combination 1.35G (KN)

Second load combination

Load Combination 1.2G + 1.5Q (KN) :

Third load combination

Fourth load combination

Fifth load combination

Bending moment and shear force diagrams :

The following is provided maximum bending moment and shear force daigram for the building members. The daigram obtained by the different strength and serviceabilty loads respectively. These are located on the 3rd floor.

Outcome

From the obtained value at different condition, the design assessment can completed by ensuring the beam, columns and slab suitability by considering force magnitude . The effective load combination is as 1.2G + 1.5Q and obtained parameter as following i.e. M*,V*,N*

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