Structural Design And Analysis For Concrete Building - (3B+G+M+13) Tower

The Structural Design Criteria

GENERAL DESCRIPTION: This report represents the basic structural design criteria, design approach, and the properties of materials to be used in the design. This report incorporates structural design requirements and the design standards requirements to assure the safety, stability, durability, and economy of the project design.

The Structural Design Criteria.

PROJECT DESCRIPTION: The project covered and consider in this topic is F.B.H HOTEL 2,(3B+G+M+13) AT AL MIRQAB DISTRICT IN DOHA, with a total built-up area of 11674.67 m2.

DESIGN APPROACH: The 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, shear wall beams, and slabs.

The structural studies of the preferred structural systems yielded that the solid slabs with drop beams and flat slab system could be the preferred system as it is a straightforward structural system.

The requirements for lateral and gravity loads shall meet QCS. 2014 and IBC requirements (as well as British Standards, BS 6399 Part 2). The main characteristics of the design approach can be summarized as follows. The statically system is simple and capable of fulfilling the required architectural and structural functions.

Basic construction materials and techniques that are locally available shall be considered whenever possible. The system of foundation will be chosen according to the recommendations of the soil report and considering the type and value of acting loads.

DESIGN CONSIDERATIONS: In order to determine the optimum structural system of the buildings, the following design considerations are considered.

• Structural safety and serviceability.
• The functional layout of each building and area.
• Special requirements of the Client.
• Utility requirements and directions of main ducts.
• The method of construction and its effect on the construction duration and cost.
• The availability of materials in the local market.
• Natural and environmental conditions of the project site.
• Required durability and the expected lifetime of structures.
• Fire rating requirements, thermal and acoustic conducting of used materials.

DESIGN CONSIDERATIONS.

CODES AND STANDARDS

Unless otherwise specified herein, the following tables list the codes and manuals that shall be followed in design.

IBC 2012	International Building Code       ( FOR NATIONAL CALCULATIONS )
QCS 2014	Qatar Construction Specifications 2014
ACI 318-2011	Building Code Requirements for Structural Concrete
ASCE 7-2005	American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures
BS 8007	Design of Concrete Structures for Retaining Aqueous Liquids

 

OTHER REFERENCE: Mainly American Standards apply to this project. For items that are not covered by the above-mentioned standards, other international standards (BS, ASTM, DIN, etc.) may be used.

Other regulations and technical reports including the CIRIA guide to concrete construction in the gulf region shall be satisfied in the design. Most stringent specifications shall be applicable.

MATERIAL REQUIREMENTS AND STRENGTH

CONCRETE GRADES: The characteristic concrete cube compressive strength after 28 days in N/mm2shall be as follows.

• Cast‐in‐situ reinforced concrete (columns & shear walls and cores) 60 MPa.
• Cast‐in‐situ reinforced concrete (transfer slab at ground & Raft) 50MPa.
• Cast‐in‐situ reinforced concrete for (Slabs, beams, stairs, ramps & retaining walls …etc.) 40 MPa.
• Blinding/screed concrete  20 MPa. 

REINFORCING REBAR: Uncoated mild steel plain bars according to BS 4449 denoted “R" 20 MPa Minimum yield Stress 250 N/mm2.: Minimum elongation on gauge length, High tensile steel deformed bars according to BS 4449 denoted “T" 22%. 

Minimum yield Stress 500 N/mm2: Minimum elongation on gauge length 12%.

CODES AND STANDARDS.

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.

1. Condition 1: Concrete placed in forms and not to be exposed later to the weather, groundwater, freshwater, or to any combination of these.
2. Condition 2: Concrete placed in forms but later to be exposed to the weather, groundwater, freshwater, or to any combination of these.
3. Condition 3: Concrete placed directly in contact with the ground.
4. 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	-	-

  

LOADING

DEAD LOADS, UNIT WEIGHT OF MATERIALS.

1. Unit weight of reinforced concrete 24.0 kN/m3
2. Unit weight of plain concrete 22.0 kN/m3
3. Unit weight of block walls
4. (Hollow Block walls only for bathrooms and main kitchen) 18.0kN/m3
5. Unit weight of block walls (Lightweight Block walls ) 6.0kN/m3
6. Unit weight of structural steel 78.5 kN/m3

MINIMUM SUPERIMPOSED DEAD LOADS.

1. Stairs flooring 3.00 kN/m2
2. Horizontal concrete roof flooring 3.50 kN/m2
3. 100 mm floor finishing 2.00 kN/m2
4. False ceiling and services 0.50 kN/m2

LIVE LOADS, MINIMUM LIVE LOADS: The live load of storage areas or mechanical rooms shall be taken either the actual weight of stored material or mechanical equipment or the above-mentioned values whichever is greater.

Load Description	Uniformly distributed load kN/m2
‐ Domestic & residential areas (Rooms)	2.00
‐ Offices, meeting rooms	3.00
‐ Stairs, Corridor	4.00
‐ Gym, cafes and restaurants.	5.00
‐ Kitchen, laundry	7.20
‐ Mosques and Prayer Areas	5.00
‐ Car parking areas (not exceeding 2500 kg gross mass),aisle ways and ramps	3.0
‐Roofs not accessible except for normal maintenance and repair.	0.60
‐ Horizontal accessible roof with parapets	Same as typical floors.
‐ Mechanical (HVAC) Rooms	7.50
‐Storage Areas	5.0

 

EQUIPMENT LOAD: Load of mechanical equipment to be specified in the calculation as per the manufacturer specifications and data sheets. In case this information is not available, a constant value of 7.50 kN/m2 shall be used.

SEISMIC LOAD: Occupancy Category II (Table 1.5‐1, ASCE 7‐10). Seismic importance factor, I=1.0 (Table 1.5‐2, ASCE 7‐10). Site class is considered class‐C. Mapped spectral response accelerations, Ss and S1:(5% Critical Damping), Ss = 0.15g. 

Mapped MCE spectral response acceleration at a period of 1 sec (5% Critical Damping) S1 = 0.065g. Spectral response coefficients, SDs and SD1, The design spectral response acceleration at short periods (0.2 sec), SDs = 2/3 *SMs=0.10g

The design spectral response acceleration at a period 1 sec, SD1 = 2/3 * SM1=0.0433g
basic seismic‐force‐resisting system (shear wall‐frame interactive system with reinforced concrete moment frames and ordinary reinforced concrete shear walls).

1. Seismic Design Category (B) as per (Table 11.6‐1 & Table 11.6‐2, ASCE 7‐10).
2. Response modification factor, R=4.50 (Table 12.2‐1, ASCE 7‐10).
3. Deflection Amplification factor Cd=4.0 (Table 12.2‐1, ASCE 7‐10).
4. System Over strength Factor Ωo = 2.5 (Table 12.2‐1, ASCE 7‐10).

WIND LOADS: The following information related to wind loads needs to be used, regardless of whether wind loads govern the design of the lateral‐force‐resisting system of the building.

• Basic wind speed, 38 m/s (Return Period: 50yrs, Averaging Time: 3sec.).
• Exposure Category = B (ASCE 7‐05 ,6.5.6.3).
• Wind Directionality Factor (Kd) = 0.85; (Table 6‐4, ASCE 7‐05).
• Gust factor = 0.85.
• Topographical factor (Kzt) = 1.0.
• Occupancy Category II, (Table 1‐1, ASCE 7‐05).
• Wind importance factor, I= 1.0 (Table 6‐1 ,ASCE 7‐05).
• Structure Type MWFRS (Main Wind Force Resisting System.

EARTH PRESSURES: Retaining walls and tank walls that are restrained at the top with relatively rigid stiffness or restrained through cross walls shall be designed to resist at Rest earth pressure based on factor Ko according to Geotechnical investigation report recommendations.

Retaining walls, trench walls, and tank walls that are free at top shall be designed to resist Active earth pressure based on factor Ka according to Geotechnical investigation report recommendations.

Retaining walls or part of retaining structures that are subjected to the movement against soil shall be designed to resist Passive earth pressure Kp according to Geotechnical investigation report recommendations. The Internal friction angle of soil and unit weight shall be in accordance with the soil investigation report. Retaining walls shall satisfy the following minimum safety factors.

1. Factor of safety against sliding at SLS=1.50.
2. Factor of safety against overturning at SLS=1.50.
3. Factor of safety against uplift at SLS (including overburden)=1.30.
4. Factor of safety against uplift at SLS (construction phase)=1.20.

The effect of groundwater level on the structures shall be considered based on the following weights: Unit Weight of Soil 18.0 kN/m3, Unit Weight of Water 10.0 kN/m3.

NOTIONAL HORIZONTAL LOAD

The structures shall be capable of resisting a notional design horizontal load applies at each floor Fx = 0.01 Wx in accordance with IBC-2012 Where. Fx = the design lateral force applied at story x. Wx = the portion of the total dead load of the structure located or assigned to level x.

LOAD COMBINATIONS

LOAD COMBINATIONS FOR STRENGTH DESIGN ASCE-7, IBC12, AND ACI 318M-11.

1. 1.4D.
2. 1.2D + 1.6L + 0.5 Lr.
3. 1.2D + 1.6(Lr) ± 0.8 W.
4. 1.2D ± 1.6 W + L + 0.5(Lr ).
5. 1.2D ± 1.0E + L.
6. 0.9D ± 1.60W  0.9D ± 1.0E.

SERVICEABILITY LIMITS STATE LOAD COMBINATIONS.

1. D.
2. D + L.
3. D + (Lr).
4. D + 0.75L + 0.75(Lr).
5. D ± ( W or 0.7E).
6. D + 0.75L ± 0.75(W) + 0.75(Lr).
7. D + 0.75L ± 0.75(0.7E).
8. 0.6D ± W.
9. 0.6D ± 0.7E.

Where.

• D (SELF + WALLS + COVER + false ceiling).
• L (Live load).
• Lr (Roof live loads).
• SELF (Indicating self‐weight of the structural elements).
• WALLS (Indicating Internal & External wall Load).
• COVER (Indicating Flooring Cover Load).
• W (Indicating Wind Loads in X & Y‐Directions).
• E (Indicating Seismic Loads in X & Y Directions).

FIRE RESISTANCE

All structural elements shall be designed to withstand the fire rate requirements according to the type and usage of the building. For concrete elements: concrete cover and a minimum dimension of elements shall be adopted to achieve the required fire rate.

SERVICEABILITY LIMITS STATES

DEFLECTION OF CONCRETE ELEMENTS: According to ACI 318‐11/TABLE 9.5(b), the deflection of structural elements shall be limited to the following values:.

LIMITATION OF LATERAL DRIFT: Wind lateral drift, The lateral wind drift (calculated based on the service loads) should not exceed the following values: Story height / 400. Overall building height / 400‐600.

Lateral seismic drift, The deflections of any floor level at its center of mass should not exceed 0.02 x story height below this considered level (as per Table 12.12‐1 ASCE7‐10). This deflection shall be calculated using eq. 12.8‐15 ASCE7‐10.

LIMITATION OF CRACK WIDTH: Excessive cracking and wide cracks affect both durability (corrosion of steel in aggressive environments) and appearance (for members that are visible).

According to BS 8110 and BS 8007, the calculated maximum crack width shall not exceed the following values: Visible elements and elements in an aggressive environment = 0.3 mm. Retaining aqueous liquids structures and retaining walls = 0.2 mm.