The Concrete Building Structural Analysis And Design
1. Overall description.
The project covered and consider in this topic is Masjid and Imam Quarter in the -------- area, for the client. Ministry Of Endowments And Islamic Affairs, with project manager; Public Works Authority that consists of the following buildings.
- Masjid (ground floor + roof area) with a total-built up area of 1323.66 m2.
2. Structural system
The structural design of buildings shall meet applicable town planning, and building regulations in effect at the time of construction. The building shall be of in-situ reinforced concrete framework and the structural system shall include reinforced concrete columns, beams, and slabs.
The structural studies of the preferred structural systems yielded that the solid slabs with drop beams and hollow block slabs with hidden beams system could be the preferred system as it is a straightforward structural system. Solid slabs with a thickness of 150mm and Drop beams with general depths from 300 to 700 mm will be used, hollow block slabs with 300, and 350 mm thicknesses, and hidden beams with the same thicknesses.
The requirements for lateral and gravity loads shall meet QCS. 2014 and IBC requirements (as well as British Standards, BS 6399 Part 2). The effects of thermal movement shall be incorporated into the design.
3. Foundations and Soil Conditions
The design of foundations shall be made according to soil report no. S15000105 was submitted by the Arab Center for engineering studies by date October 2015, and it is the contractor’s responsibility to verify it during construction.
The Foundation system shall be a shallow foundation, with isolated footings supported on the soil as per the building’s requirement and soil report recommendations.
The design of the foundation shall consider both structural requirements and the following soil report recommendations as per soil report no. S15000107 date October 2015:
- Bearing capacity at the foundation level is 400 KN/m2.
- modulus of Sub-grade reaction 12 MPA (assumed).
- Foundation level is (-1.0) m from the natural ground level.
- Ground water table level is -2.0 m from the natural ground level.
- Cement type is ordinary Portland cement (OPC).
4. Material Requirements
4.1 Concrete Grades
The characteristic concrete cube compressive strength after 28 days in N/mm2 shall be as follows:
· Cast-in-situ reinforced concrete 30 N/mm2
· Cast-in-situ reinforced concrete for slab-on-grade 30 N/mm2
· Blinding concrete 20 N/mm2
4.2 Reinforcing Rebar
Uncoated mild steel plain bars according to BS 4449 denoted “R"
· Minimum yield Stress 250 N/mm2
High tensile steel deformed bars according to BS 4449 denoted “Y"
· Minimum yield Stress 500 N/mm2
Steel wire fabric mesh according to BS 4483
· Minimum yield Stress 500 N/mm2
4.3 Concrete Cover
The cover shall not be less than as given below, according to the type of structural member and the placing and exposure conditions as follows.
· Condition 1: Concrete placed in forms and not to be exposed later to the weather, groundwater, freshwater, or to any combination of these.
· Condition 2: Concrete placed in forms but later to be exposed to the weather, groundwater, freshwater, or to any combination of these.
· Condition 3: Concrete placed directly in contact with the ground.
· Condition 4: Concrete to be exposed to corrosive vapors, corrosive groundwater, seawater, or sea spray. Sufficient protection to the reinforcement shall be provided by: adopting the minimum cover for exposure condition 3 and applying a protective coating or membrane on the concrete surface. The method of protection shall be in accordance with the provisions of the specification and to the approval of the Engineer.
Structural Member | Minimum Cover (mm) for Placing of Reinforcement for Exposure Condition | ||
Condition 1 | Condition 2 | Condition 3 | |
Pad footings and Pile Caps | - | 65 | 75 |
Strip footings | - | 50 | 65 |
Bored or Cast Piles | - | 50 | 75 |
Columns of all types | 30 | 40 | 75 |
Walls, including retaining walls | 25 | 30 | 75 |
Beams | 30 | 40 | 65 |
Slabs, including concrete joist and hollow block construction | 25 | 30 | 65 |
Cover to embedded pipes | 25 | 30 | 65 |
Reinforcement adjacent to blocks in hollow block slab construction which are integral with the structure | 10 | - | - |
5. Design Codes
Unless otherwise specified herein, the following tables list the codes and manuals that shall be followed in design.
BS 6399 - 1: 1996 | Loading for buildings - Part 1. Code of Practice for Dead and Imposed Loads |
BS 6399 - 2: 1997 | Loading for buildings - Part 2: Code of practice for wind loads. |
IBC 2012 | Earthquake loads |
BS 6399 - 3: 1988 | Loading for buildings - Part 3: Code of Practice for Imposed Roof Loads |
QCS 2014 | Qatar Construction Specifications |
BS 8110 - 1: 1997 | Structural use of concrete Part 1: Code of Practice for Design and Construction |
BS 8110 - 2: 1985 | Structural use of concrete Part 2: Code of Practice for Special Circumstances |
BS 8110 - 3: 1985 | Structural use of concrete Part 3: Design Charts for Singly Reinforced Beams, Doubly Reinforced Beams and Rectangular Columns |
BS 8004: 1986 | Code of Practice for Foundations |
BS 5950: Part1 | Code of practice for steel structures |
|
|
6. Design Loads
6.1 Dead Loads
6.1.1 Unit Weight of Materials
· Unit weight of reinforced concrete 24.0 kN/m3
· Unit weight of plain concrete 22.0 kN/m3
· Unit weight of block walls 20 cm*20cm*40cm (including plaster) 3.30 kN/m2
· Unit weight of block walls 15 cm*20cm*40cm (including plaster) 2.80 kN/m2
· Unit weight of block walls 10 cm*20cm*40cm (including plaster) 2.20 kN/m2
· Unit weight of structural steel 78.5 kN/m3
6.1.2 Minimum Super Imposed Dead Loads
· Stairs flooring cover 2.00 kN/m2
· Horizontal concrete roof flooring cover 4.00 kN/m2
· False ceiling and services 0.50 kN/m2
6.2 Live Loads
6.2.1 Minimum Live Loads
Load Description | Uniformly distributed load kN/m2 |
- Domestic & residential areas | 2.00 |
- Stairs, Corridors & balconies | 4.00 |
- Mosques and Prayer Areas | 5.00 |
- Water tank area | As per its height |
-Roofs not accessible except for normal maintenance and repair. | 0.60 |
- Accessible roof. | 2.0 |
- Mechanical (HVAC) Rooms | 7.50 |
-Storage Areas | 2.4 for each meter of storage height |
6.3 Design Wind Pressures
Design wind pressures shall be applied according to Qatar Construction
Specifications (QCS 2014), wind speed (mean hourly wind speed) is 25m/s.
The buildings shall be designed for wind loads calculated in accordance with BS 6399,
Part 2, using the standard method.
· Basic wind speed (mean hourly wind speed) 25 m/sec
· Altitude factor Sa = 1.0
· Direction factor Sd = 1.0
· Seasonal factor Ss = 1.0
· Probability factor Sp = 1.0
6.4 Earthquake Loads
The seismic design shall be based on IBC. Code with factors as shown in the Etabs model.
7. Load combinations
Structures, buildings, and foundations shall be designed to have design strengths at least equal to the required strength calculated for the various load combinations developed and utilized for design based on recognized international standards.
BS 8110-97 | |
SN | Ultimate load combinations |
1 | 1.4 D + 1.6 L |
2 | 1.0 D + 1.4 Wx |
3 | 1.0 D - 1.4 Wx |
4 | 1.0 D + 1.4 Wy |
5 | 1.0 D - 1.4 Wy |
6 | 1.4 D + 1.4 Wx |
7 | 1.4 D - 1.4 Wx |
8 | 1.4 D + 1.4 Wy |
9 | 1.4 D - 1.4 Wy |
10 | 1.2 D + 1.2 L + 1.2 Wx |
11 | 1.2 D + 1.2 L - 1.2 Wx |
12 | 1.2 D + 1.2 L + 1.2 Wy |
13 | 1.2 D + 1.2 L - 1.2 Wy |
| Earthquake load combinations According to IBC. code |
14 | 0.9 D - Qx |
15 | 0.9 D - Qy |
16 | 0.9 D + Qx |
17 | 0.9 D + Qy |
18 | 1.2 D + L - Qx |
19 | 1.2 D + L - Qy |
20 | 1.2 D + L + Qx |
21 | 1.2 D + L + Qy |
BS 8110-97 | |
SN | Service load combinations |
1 | D |
2 | D + L |
3 | D + WX |
4 | D - WX |
5 | D + WY |
6 | D - WY |
7 | D + L + WX |
8 | D + L - WX |
9 | D + L +WY |
10 | D + L - WY |
| Earthquake load combinations According to IBC. code |
11 | D - 0.70 Qx |
12 | D - 0.70 Qy |
13 | D + 0.70 Qx |
14 | D + 0.70 Qy |
15 | D + 0.75 L - 0.525 Qx |
16 | D + 0.75 L - 0.525 Qy |
17 | D + 0.75 L + 0.525 Qx |
18 | D + 0.75 L + 0.525 Qy |
Where
D (SELF + WALLS + FLOOR COVER+CEILING)
L (Live)
SELF (Indicating self-weight of the structural elements)
WALLS (Indicating Internal Partitions Load)
COVER (Indicating Flooring Cover Load)
LIVE (Indicating Live Loads)
Wx (Indicating Wind Loads in X-Direction)
Wy (Indicating Wind Loads in Y-Direction)
Qx (Indicating earthquake Loads in X-Direction)
Qy (Indicating earthquake Loads in Y-Direction)
8. Serviceability and Durability
Serviceability limits shall be based on required international standards with regard to short-term and long-term deflections & crack width limitations. Creep and shrinkage of concrete shall also be considered. All structural elements shall be designed For a 2-hours fire rate. Concrete cubic strength is 30 N/mm2 and the reinforcement strength is 500 N/mm2.
8.1 Deflection of Concrete
To avoid excessive deflections and damage to non-structural elements, the residual deflection after the initial camber shall be limited to the following values:
L/250 Total deflection.
L/500 Or 20 mm (whichever is lesser) for the part of deflection after the construction of brittle materials.
L/350 Or 20 mm (whichever is lesser) for the part of deflection after construction of non-brittle partitions or finishes.
For beams (L<= 10 m), it will generally be satisfactory to use the span/effective depth ratios given in BS8110-Part 1 table 3.9, clause 3.4.6.3 for reinforced concrete.
Where L is the span of the beam or slab or in the case of a cantilever its length.
8. Constructability
Consideration shall be given to ease and economics of construction when choosing structural systems, elements, and materials.
9. Design software
Elastic finite element analysis of all structural elements shall be made. The structural analysis design shall be performed using the following software.
ETABS; Three-Dimensional Static Building Analysis and Design – Version 15.0.0 BS 8110 design excel sheets.