BURJ KHALIFA DESIGN BRIEF

The present article provides ready reference structural information about the world’s tallest structure Burj Khalifa. The main objective of article is to provide bench mark quantities for structural information for tall building.

	Project Type	:	Mixed Use Project ( Five Star Hotel, Office, Retail and Residential)
	Total Floor area	:	439,935m2
	Site Area	:	104,210m2
	Height	:	828m ( Concrete 606m Plus Steel  222m)
	Gross Floor area above Grade	:	312,400m2
	Floor Plate Size at Grade Level	:	3,065m2
	Floor Plate Size at Upper top	:	380 m2
	Floor Plate Size at Basement	:	35,300m2
	Structural Consultant	:	SOM
	Wind Engineering Consultant	:	RWDI Wind Tunnel Analysis Rigid Model Force Balance Tests Full Multi Degree of Freedom Aero-elastic Model
	Floor Geometry in Plan	:	Y Shaped (to reduce the wind forces on the tower, as well as to keep the structure Simple and foster constructability)
	Structural System	:	“Buttressed” Six Sided Central Core, Each wing, with its own high performance concrete core and perimeter columns, buttresses the others via a six-sided central core, or hexagonal hub
	Foundation	:	Pile Supported Raft
	Number of piles under tower	:	194
	Pile Diameter	:	1.5m
	Length of pile	:	43.0m
	Concrete Cube Strength for Pile	:	60MPa SCC ( Self Compacting Concrete)( Triple Blend 25% Fly Ash + 7% Micro silica + Portland Cement, Water Cement ratio 0.32)
	Pile Load Test	:	6000 t
	Working Design Capacity	:	3000 t
	Raft Thickness	:	3.7m
	Reinforcement Spacing	:	300 mm c/c­­­­
	Concrete Cube Strength for Raft	:	C50 Self Consolidating Concrete
	Super Structure
	Number of Outrigger Levels	:	5
	Concrete cube strength for Vertical Element (Reinforced Concrete Wall/column)	:	C80 ( at Base checked at 90 Days instead of 28 Days) – C60 (at Upper Level)
	Composition of Concrete for Vertical Elements	:	Portland Cement + Fly Ash
	Analysis Software and Model Size	:	ETABS (Version 8.4) , 73,500 Shells and 75,000 Nodes
	Reinforced Concrete Design Code	:	ACI 318-02
	Free Vibration Analysis Result 1st Mode, Lateral Side sway 2nd Mode, Lateral Side sway 5th Mode, Torsion Mode	: : :	11.3 sec 10.2 sec 4.3 sec
	Top Steel Portion ( Spire)	:	Diagonally braced lateral system
	Steel Design Code	:	AISC LRFD 1999
	Seismic Zone	:	Zone 2A ( Z = 0.15) as per UBC97
	Modulus of Elasticity of Concrete (Ec)for Core and Outrigger at Lower Portion at 90 Day	:	43,800MPa
	Walls and Columns optimized	:	Virtual Work Method
	Effect of Column Shortening	:	Perimeter columns were sized such that the self-weight gravity stress on the perimeter columns matched the stress on the interior corridor walls.
	Weight of Empty Building	:	500,000MT
	Quantity
	Concrete	:	330,000 m3
	Reinforcement Steel	:	39,000MT
	Glass used for Façade	:	103,000 m2
	Stainless Steel used for Cladding	:	15,500 m2
	Structural Steel for Top Spire	:	Approximately 4000MT

                                    

UBC97 and IBC/ASCE Seismic Load Comparision

Structural Dynamics - Interview Questions - Structural Engineers

Calculate natural frequency ( or fundamental time period) 

for following problems

UBC97 - Seismic Base Shear Calculation Procedure

UBC 97 Seismic Base Shear Calculation Steps are as follows

1. Seismic Zone Factor (Z)

Civil Engineering Softwares

3D Frame ( Steel and Concrete) General Purpose Software

1. SAP2000
2. STAAD Pro
3. ROBOT Structural Analysis
4. OASYS
5. ETABS ( 3D Building Analysis and Design Software)

Building Floor System

1. RC Slabs - SAFE
2. Post Tension Slabs - ADAPT PT, RAPT, RAM Concept
3. Metal Deck Composite FLoor - TATA Comflor
4. RoofDeck Analysis Software from TEDS

Finite Analysis Software (having Macro/command line and advance elements)

1. NISA
2. GT-Strudl
3. ANSYS
4. ADYNA

Bridge Analysis Software

1. SAP2000-Bridge
2. Sofistik
3. RM Bridge

Foundation Engineering Question

1. Broadly describe classification of piles 
2. Calculate Structural compression capacity of 1500mm diameter concerete (C40 Grade) pile
3. What % of Piles to be tested for Static Test, Dynamic Test, Integrity Test and Sonic Test
4. Describe initial load test of piles
5. Draw bending moment diagram for free and fixed head pile along length of pile under lateral load
6. Provide approximate relationship between safe bearing capacity and N ( standard penetration test N Value).
7. Provide approximate relationship between safe bearing capacity and undrained shear strength 
8. What is minimum c/c distance between piles for Driven Piles, Bored Piles and Mini piles
9. What is relationship between safe vertical load capacity and displacement and lateral capacity of pile
10. Write Terzaghi's soil bearing capacity formula
11. Classification of Granular (Non-cohesive) soil and Cohesive soil

Earthquake Resistant Design Interview Questions

Questions are taken from book - "Seismic Design of Building structures" By Michael Lindeburg and Majid Baradar

1. What is difference between stiffness and rigidity as used in seismic design?
2. What is difference between ductility and flexibility as used in seismic consideration?
3. What is ductility and ductility factor?
4. What is the natural period of a building? Describe Method A and Method B to compute natural time period described in UBC97?
5. What does the term redundancy means as it is used in the context of modern high rise buildings
6. What causes torsional shear?
7. What is negative torsional shear?
8. What is response spectrum?
9. Describe how base shear is calculated according to the UBC97 / IS 1893/IBC equation
10. What is the P - Delta effect?
11. What possible values can R take on for a moment resisting frame?
12. Describe different Vertical and plan irregularity in Building
13. Describe principle of seismic detailing in beam and column in moment frame?
14. Describe three principles of design of special moment frame
15.  Draw vertical distribution of seismic force along height of building 

Cocnrete Technology - Interview Questions

Concrete Questions
Following questions are taken from Concrete Book by Mehta and Monterio

1. Compared to steel , what are the engineering benefits of using concrete for structures?
2. Describe in brief High Strength Concrete and High Performance Concrete
3. What is the difference between strength and toughness? Why is the 28 - Days compressive strength of concrete generally specified?
4. Discuss the significance of drying shrinkage, thermal shrinkage and creep in concrete
5. which is common test performed for Durability of Concrete?
6. explain how water cement ratio influence the strength of the cement paste matrix and the interfacial zone in concrete
7. In general, how are the compressive and tensile strength of concrete related? which tests are used to find tensile strength of concrete?
8. Draw a typical stress-strain curve for concrete. What is relationship between young's modulus of concrete and cube strength of concrete?
9. which factors affect creep of concrete only and why?
10. Describe five different type of Portland Cement and blended Portland cement based on BS EN 197
11. briefly describe the measures that should be considered for the control of corrosion of embedded steel in concrete.
12. What is the alkali-aggregate reaction? List some of the rock types that are vulnerable to attack by alkaline solutions. Discuss the effect of aggregate size on the phenomenon.
13. what is minimum grade of concrete for water retaining structure based on BS 8007?

Engineer Hemant Gor, GorHemant@GMail.com

Interview Questions - Prestressed Concrete and Bridge Engineering

1. Describe through sketch/figure hyperstatic stresses in case of Prestressed concrete strcutres.
2. Explain Kern Distances and procedure to compute for given cross section
3. Describe Pre stress losses and procedure to compute these losses
4. Draw influence line diagram for Reaction at Support A, Bending Moment at Support B and Shear force at Support C for continuous three span girder shown below

Three Span Continuous Girder, Draw Influence Line Diagram 

5. For Single cell box girder prestressed simply supported box girder shown below for Highway bridge, Provide approximate range for Span/D, dimension l1/dimension l2 and Angle of Web with horizontal

Box Girder, Half symmetric cross section

6. Describe load path for following Bowstring Girder bridge

Bow String Girder Bridge

7. Describe various construction technology for large span bridge superstructure with sketches

8.  Describe two structural design criteria for Cables in cable stayed bridge shown below

9. Describe critical Imposed Load ( Uniformly distributed Load) position for Cable marked "A" and "B" below

Two span symmetrical cable stayed bridge

10. Describe structural design criteria for Cables in Extradosed bridge shown below

Engineer Hemant Gor, GorHemant@GMail.com

 

Structural Engineering Interview Question

1. For following two cases ( A and B) Shear Force Diagram and Bending Moment Diagram will remain same ( True/False)

2. Calculate approximate member forces for members marked "A" and "B" in following truss, P = 100kN and L=50m, Depth of trusss 5m

3. Calculate approximate member forces for members marked "A" and "B" in following cantilever truss

4. For following Vierendeel girder find out bending moment in Member marked A, P = 100kN

5. Calculate torsional stress in square hollow section of 200mmx200mmx10mm (thickness) under torsional moment of 100kNm.

Structural Engineer Interview Questions (Reinforced Concrete, Prestressed Concerete, Steel and Seismic)

1. Why permissible shear stress in Steel is 0.4fy while bending tensile stress is 0.67fy in ASD( Allowable Strength Design)?
2. Describe any three material failure criteria. Which failure criteria is used in Steel design?
3. List and Describe tests performed on fresh and hardened concrete.
4. List and describe non-destructive tests performed on welded connections
5. Draw simple shear connection and moment connections
6. Describe different lateral load resisting systems for tall buildings
7. Describe design criteria for serviceability in tall buildings
8. Describe principle of Tuned mass Dampers in tall buildings
9. Describe application/principle of seismic base isolation
10. Define Centre of rigidity in Building and Negative Torsional Shear
11. Define Hyperstatic stresses in prestressed concrete members
12. Define creep of Concrete and measures to reduce creep deformation
13. Describe different irregularities in building with respect to Seismic actions
14. Describe ductility and how it is achieved in reinforced concrete stuctures
15. Describe Method A and Method B to compute time period of Buildings in UBC 97
16. What is relation between elastic and inelastic deformation of building for earthquake action?
17. Describe principle of capacity based design
18. Describe reinforcement design in shear wall
19. How cracked section property of beam and column is accounted in 3D computer analysis of Buildings?
20. Explain parameters affecting long term deflection of concrete beams
21. Which are possible substitute materials for cement in concrete?
22. Describe High Performance Concrete and how it is different from High Strength Concrete?
23. Describe principle of concrete design in water retaining structures

Structural Design (Interview Question for Design RCC / Steel Building)

3C for Durable Concrete : Cover, Compaction and Curing

4S for Structural Design : Strength, Serviceability, Stability and Simplicity (Shortest Load Path)

Cover for Reinforcement - Fire Protection, Durability

Floor Systems in Reinforced Concrete cast-in situ

1. One Way slab with downstand beam
2. Two way slab with downstand beam
3. Flat Slab ; with/without Column Head; with/without Drop Panel
4. One way ribbed slab
5. Waffle slabs

Floor Systems in Precast Concrete

1. Hollow core slab and cast-in situ topping 
2. Semi Precast slab ( Filigree slab)
3. T Girder and cast-in situ topping
4. Hourdi Blocks - Ribbed slab

Floor Systems in Composite ( Steel and Concrete)

1. Metal Deck sheet and cast-in situ concrete (CF60/CF80 etc.)
2. Deep metal deck and cast-in situ concrete ( Slimflor / Slimdek)

Shoring work options (provide support to the sides of deep excavations)

1. Soldier system (single type)
2. Soldier system ( Double type)
3. Contiguous piles
4. Secant piles
5. Diaphragm wall
6. Sheet pile
7. Open excavation with (sloping and benching system)

Options in Steel Building Floors

1. Composite steel beam
2. Asymmetric steel beam (ASB) (Bottom half from UC and top half from UB)(Slimdek)
3. Slimflor ( UC section with Bottom steel plate welded)
4. Castellated Beams 
5. Cellular Beams
6. Trussed Girder
7. Haunched Plate girder