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SEV353 - Reinforced Concrete Structures
Individual Project A-Office
By: SILENGA MR BUSIKU
Student ID: 210037589
Table of Contents;
1. Introduction2. Scope and Assumptions
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3. Properties3.1 Material Properties3.2 Exposure Class & Cover
4. Loads & Load Combination Cases5. Floor Plans and Sections 6. Concrete Mix Design7. Beam Analysis
7.1 Loads & Load Summary Sketch7.2 Bending Moment Diagram7.3 Shear Force Diagram7.4 Torsion Diagram
8. Updates to Group Work9. Beam Design10. Slab Analysis11. Slab Design12. Reflection on Design Product 13. Appendix
Introduction
The aim of this project is to assume the role of a structural engineer and carry out a full reinforced concrete design for a selected continuous beam and slab panel on an assigned floor of a multi-storey office tower, this includes fixing the location, type and details of structural elements of the office floor.
Scope & Assumptions
The scope of this project includes the structural analysis and design of selected reinforced concrete beam and slab elements of an office floor of a multi-story building, particularly an extensive beam analysis and a concrete mix design that meet proposed project specifications(group report). This project also includes an analysis of an individually designed and detailed two-way reinforced concrete slab and continuous reinforced concrete beam elements (individual report).
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As the building is to be constructed in Australia, all structural analysis, design and material selection will be based on Australian design standards (AS Codes and SRIA design aids) and will be cross checked to ensure that all specifications are taken into account. We will also consider other factors such as safety, strength, ductility, cost and aesthetics. This scope will not include the consideration of the effect of environmental loads on our design. For our analysis we have chosen to use the office tower plan and have particularly made the assumption that the office space will be located on the 11th floor (surface of members not in contact with the ground). We have also provided detailed engineering drawings showing the dimensions of the floor, beam, column and wall placement with details of spacing’s, gridlines, and the selected beam(s) for simplistic analysis. Also we assume the construction location as Geelong (temperate climatic zone refer to figure 1) and a design life of 50 years (Buildings and other common structures).
Figure 1; Climatic classes
Properties
For General properties of concrete and reinforced steel refer to appendix 1.1
Based on 28 days of curing the material properties of our designed reinforced concrete specified according to the AS 3600 standards are summarised in table 3 and 4 below, noting also that the value of imposed floor actions namely uniformly distributed actions and concentrated actions is 3.0KPa and 2.7KN respectively (refer Table 3.1 AS/NZS
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1170.0,1:2002)and weight of concrete per cubic meter is 24KN/m3 [refer to table A1 AS/NZS 1170.1:2002 Unit weights of materials and construction]
Minimum Compressive
strength f’c (MPa)
25 MPa Based on A2 Exposure classification [Refer table 4.4 AS3600-2009 Minimum strength and curing requirements for concrete]
Mean in-situ compressive strength fc
mi(MPa)
28 MPa [refer to table 3.1.2 AS 3600-2009 Concrete properties at 28 days]
Modulus of Elasticity Ec(MPa)Ec=0.043wc
1.5√ f ' c
26700 MPa [refer to table 3.1.2 AS 3600-2009 Concrete properties at 28 days]
Flexural Tensile Strength f’ct.f
(MPa)f’ct.f=0.6√ f ' c
3.0 MPa [refer Table A.1 Design of Concrete Structure Design Aids]
Uniaxial Tensile Strength f’ct
(MPa)f’ct.f=0.36√ f ' c
1.8 MPa [refer Table A.1 Design of Concrete Structure Design Aids]
Coefficient of thermal expansion
10x10^(-6)/oc
Table 3[Properties of our standard grade concrete]
Note: f’c=25 (MPa) selected in the table is the minimum value, we will be able to nominate a greater grade value such as f’c =32MPa for our concrete mix design, taking into account strength considerations.
Note-D500N Deformed Bar is selected for reinforcement.
Min. Yield Strength fsy (MPa)
500 MPa [Refer Table 9.1 Notation for commonly-Available reinforcement-Reinforcement detailing handbook]
Shear Modulus(MPa) 77000MPaYoung’s Modulus(MPa) 200000MPa General for all
reinforcement steelsMin. Tensile Strength(MPa)
675 (MPa) AS4671:2001
Elongation at maximum force
5% AS4671:2001
Coefficient of thermal expansion
12 x 10^-6/oC.
Poisons ratio 0.3Table 4[Characteristic properties of our standard grade rebar.]
Cover and exposure class (minimum standards set by the AS 3600) are important in durability and fire resistance design. Cover is particularly important to ensure that the stresses in steel and concrete can be transferred to one another by bond [Reinforcement detailing handbook].In our design case, based on our assumed location we select an exposure classification of A2 (non-residential, temperate climate) [refer to table 4.3
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AS3600-2009-Exposure classifications].Based on the selected characteristic strength of our concrete(f’c) and exposure classification of A2 the required cover selected is 30mm [refer table 4.10.3.2 AS3600-2009 Required cover where standard formwork and compaction are used].
Loads & Combinations Load Cases
Determination of loads on a structure can be a complex task. Loads are mostly classified into dead loads (Dead Loads=Self weight + imposed dead load) and live loads (Imposed Loads)
The bulk density of concrete and steel used for calculating self-weight of elements of structures and stored materials is 24KN/m3 and 77KN/m3
respectively[refer to table A1AS/NZS 1170.0, 1:2002 Unit Weight of Materials and construction].
Dead Loads= Self weight + imposed dead load (Ceilings [Portland cement plaster] + floors [Cinder-concrete filling]) (refer to table A2 Design Aids/Articles & tables-AS 1170.0,1:2002)
Dead Load(Gk) =24 + 0.29 + 0.43 =24.72 KN/m 2
The imposed (Live Loads) actions on Australian buildings as set by the Australian standards is a value of 3.0KPa for uniformly distributed actions on offices for general use and a value of 2.7KN for concentrated actions on offices for general use[refer Table 3.1 AS/NZS 1170.0,1:2002].
Load Combinations (Ultimate Limit State)
Dead load and live load, (1.2G + 1.5Q)- All spans loaded Dead load and wind load (1.2G + Wu ) Dead load, wind and live load, (1.2G + Wu + ψlQ)
Load Combinations (Serviceability)
Dead load and live load, ( G + Q)- All spans loaded Dead load, wind (G + Wu) Dead load, wind and live load, (G + Wu + ψlQ)
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Floor Plans & Sections
Key;
Beams
Columns
Concrete wall
Figure 2; Plans with dimensions shown
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Figure 3;Floor plan with columns shown.
Figure 4; Floor Plan with beams and dimensions shown.
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Figure 6;Floor plan with elements and selected panel shown
Concrete Mix Design: Volumetric Method
Concrete Mix design information;
Exposure classification; A2 Exposure classification (AS3600 – 2009 Table 4.3)
Concrete strength and cover; f’c=25 (MPa) selected in the table is the minimum value, we nominate a greater grade value of f’c =32MPa for our concrete mix design in order to meet design specifications, taking into account strength considerations. Required cover will then be 25mm for A2 exposure classification and nominated characteristic strength of 32MPa(Refer Table 4.10.3.2 AS3600-2009).
Mean in situ Compressive strength; 35MPa for the nominated concrete strength of 32MPa(Refer to AS3600-2009 Table 3.1.2)
Coarse aggregate-Gravel with crushed particles as coarse aggregate.
Standard deviation(s) of compressive strength of 2.4MPa is assumed (Enough samples so that no correction is needed)
Step 1; Strength Requirements
Required average compressive strength f’cr is determined as the larger value obtained from equations;
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f’cr = f’c + 1.34s = 35.22MPa f’cr = f’c + 2.33s – 3.45 = 34.14MPa
Therefore choosing the larger value; f’cr =35.22MPa
Step 2; Water-Cement Ratio Requirements
For our non-air-entrained concrete (strength above 31MPa) with compressive strength at 28days having a value of 35MPa, we select a water-cement ratio (w/c) by weight value of 0.48 (refer to table 7.1 Design of concrete structure design aids/tables & charts for concrete mix design).
Note: Table 7.1 is used to determine the water-cement ration because no historical records are present for use in our project.
Step 3; Coarse aggregate requirements
25mm < 1/5 (300mm) minimum dimensions
25 mm <3/4 (40 mm) rebar spacing
25 mm <3/4 (40mm) rebar cover
25mm aggregate size corresponds to a nominal maximum aggregate size of 19mm.
1/5*300 = 60 > 19 Acceptable
¾*40 = 30 > 19 Acceptable
¾*40 = 30 > 19 Acceptable
Sizes satisfy dimension requirements, however 25mm aggregate is more suitable as it provides a more suitable mix.
Assuming fineness modulus of 2.60 for the fine aggregate and the nominated nominal size of 19mm, the volume of coarse aggregate per unit volume of concrete is 0.64m3/m3 (refer to table 7.5 Design of concrete structure design aids/tables & charts for concrete mix design)
Therefore;
Dry unit weight of coarse aggregate = (1652) (0.64) = 1160 kg/ m 3
Coarse aggregate = 1057.28kg/ m 3
Step 4; Air content
Since we are analysing an office space on the 11th floor we expect moderate exposure, that is some freezing occurs, but concrete is not exposed to moisture or free water for long periods prior to freezing and concrete is not exposed to deicing salts.
Therefore using our nominal aggregate size of 19mm and moderate exposure ,our target air content will be 5% and our job range=4% to 7%
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base (Job specifications should be specified for moderate exposure).therefore we will design using 6%.
Step 5; Workability
Slump range is 25mm to 100mm (refer to table 7.7 Design of concrete structure design aids/tables & charts for concrete mix design).We will use 75mm in our design.
Step 6; Water Content
Based on our project specifications, 19mm aggregate with air entrainment and 75 mm slump, water= 184kg/m3 for angular aggregates. Since we have gravel with crushed particles, we reduce water by 21 kg/m3. Therefore required water = 184-21=163kg/m 3 .
Step 7; Cementing Materials Content
We assume
Water cement ratio=0.48, Water=163kg/m3, Cement=Water/water-cement ratio Cement= 163/0.48 = 340kg/m 3 <320kg/m 3 (therefore design is OK)(minimum requirements of cementing materials, table 7.9 Design of concrete structure design aids/tables & charts for concrete mix design).
Step 8; Admixture requirements
No admixture is required for this design.
STEP 9; Fine Aggregates Requirements
V fine aggregate= 1- V water - V cement - V coarse aggregate -
V air
Therefore;
V water =163/ (1 x 1000) = 0.163 m3/m3 (Water specific gravity=1)
V cement= 340/ (3.15 x 10000) = 0.108 m3/m3 (Water specific gravity=3.15)
V coarse aggregate=1057.28/ (2.63 x 1000) = 0.402m3/m3
V air = 6% =0.06m3/m3
Subtotal volume = 0.733m3/m3
V fine aggregate=1-0.733 = 0.267m3/m3
Fine aggregate dry weight = 0.267 x 2.572 x 1000 = 686.724Kg/m3
Step 10; Moisture Corrections
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Coarse aggregate: Need 1057.28kg/m3 in dry condition, therefore we increase
by 1.5% for moisture content.
Moist coarse aggregate =1057.28 x 1.015 =1073.14kg/m3
Fine aggregate needed is 686.724kg/m3 in dry condition, therefore we increase
by 4% for moisture content
Moist fine aggregate = 686.72 x 1.04 = 714.19kg/m3
Water: Reduce for free water on aggregates =163 – 1057.28 (0.015-0.004) -
686.72(0.04-0.008) =130Kg/m3
Summary
Batch Ingredients Required (1m3 PCC)
Water 130Kg
Cement 340Kg
Fine aggregate 714.19Kg
Coarse aggregate 1073.14Kg
Admixture N/A
Appendix;
1.1 General properties of concrete
Construction material choice is almost entirely governed by the properties of the material. The properties of concrete which govern the design of a concrete mix include its strength, durability, workability and economy. Some of concrete’s most important properties include its strength and durability. It has the ability to gain strength over time; its structure is not weakened due to moisture or mould and if properly designed it has the ability to withstand natural disasters like earthquakes. Another important property of concrete is its versatility, being able to be used for nearly any type of construction work possible, for example buildings, bridges etc. Perhaps one of its most important properties is its affordability and easy accessibility. In an age where environmental sustainability plays a vital role in the construction industry concrete is a choice material because of its low life-cycle CO2 emissions, 80% of buildings CO2 emissions are generated not by the production of the materials used in its construction, but in the electric utilities of the building over its life-cycle [1.world business council for sustainable development]. Another key property of concrete is the fact that it is low maintenance and does not lose its
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key properties over time. Concrete is fire resistant, this is an effective barrier in the spread of fire in buildings and finally the thermal mass property of concrete slows passage of heat moving through, reducing the need for heating or air conditioning [1.world business council for sustainable development].The following table gives a general summary of concrete’s material strength properties [2.engineering toolbox].
Density 2240 - 2400 kg/m3
Compressive Strength 20 - 40 MPaFlexural Strength 3 - 5 MPaTensile Strength 2 - 5 MPaModulus of elasticity 14000 - 41000 MPaPermeability 1 x 10-10 cm/secCoefficient of thermal expansion 10-5 oC-1 (5.5 x 10-6 oF-1)Drying Shrinkage 4 - 8 x 10-4
Drying shrinkage of reinforced concrete 2 - 3 x 10-4
Poisson’s ratio 0.20 - 0.21Shear Strength 6 - 17 MPa
Specific Heat Capacity 0.75 kJ/kgTable 1[Typical properties of normal strength Portland cement concrete]
description value unit
Density 7,850 kg / m3
Unit Weight 77 kN / m3
Modulus of elasticity 200,000 MPa
Shear Modulus 77,000 MPa
Thermal Coefficient 11.7 x 10-6 / oC
Poisson Ratio 0.3
Table 1[Typical properties of Steel]
Property Concrete Steel
strength in tension poor good
strength in compression good good, but slender bars buckle
strength shear fair good
durability good corrodes if unprotected.
fire resistance good poor - rapid loss of strength at high temperatures when unprotected.
Table 2[Comparison of properties between concrete and reinforcing steel]
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1. www.bom.gov.au/climate/environ/other/kpn.all.shtml
2. http://www.wbcsdcement.org/index.php/key-issues/sustainability-with-concrete/properties-of- concrete
3. http://www.engineeringtoolbox.com/concrete-properties-d_1223.html
4. http://www.sria.com.au/expertise/aus.html
http://www.webcivil.com/cbfea.aspx