group 1 final thesis report

ANALYSIS AND DESIGN

TA: ENG. OMAR, ENG

Amira Saleh 900100346

Fady Aziz 900114681

Fredy Vector 900114776

Haia Bediwy 900114810

Nada Abdellatif 900115019

CENG: 4980

SENIOR PROJECT 1

ANALYSIS AND DESIGN OF PEARL GARDENS HOTEL

SUPERVISED BY:

DR. EZZAT FAHMY

DR. SAFWAN KHEDR

DR. EZZELDIN SAYED-AHMED

DR. WAEL HASSAN

TA: ENG. OMAR, ENG ZAHRA, ENG. AHMED ABDELHAMID, ENG JASSER

1

PEARL GARDENS HOTEL

2

Abstract

The building that was chosen to be structurally designed was the Pearl Project. There are

different forms of high-rise buildings; all defined depending on their heights. A skyscraper is

used to describe buildings that are higher than 150m, such as that of the Pearl Project, which

reaches up to 187.67m in height. The objective of the work to be done is to accommodate

between design of the building due to gravity loads as well as lateral loading. In addition to that,

the design is to target the most economical solution as well as saving space by designing on the

smallest possible dimensions of structural elements.

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Table of Contents

Abstract ......................................................................................................................................................... 2

Table of Contents .......................................................................................................................................... 3

List of Figures ................................................................................................................................................ 5

Introduction .................................................................................................................................................. 8

Project Description........................................................................................................................................ 9

Sections ................................................................................................................................................... 11

Scope ........................................................................................................................................................... 12

Deliverables................................................................................................................................................. 13

Methodology ............................................................................................................................................... 14

Initial TimeLine .................................................................................................................................... 15

Challenges ................................................................................................................................................... 15

Preliminary Design ...................................................................................................................................... 16

Loads ....................................................................................................................................................... 16

Slabs ........................................................................................................................................................ 16

Benefits ............................................................................................................................................... 17

Columns .................................................................................................................................................. 19

Modelling of the building ............................................................................................................................ 21

Selection of the Gravitational Slab System ................................................................................................. 23

Elliptical Plan floors from 6th till 34th: ...................................................................................................... 23

ETABS Model: .............................................................................................................................................. 30

Seismic Analysis: ..................................................................................................................................... 30

Wind Analysis: ......................................................................................................................................... 36

System Selection: .................................................................................................................................... 37

Diaphragm Condition: ............................................................................................................................. 42

Remedial Measurements: ....................................................................................................................... 45

Modal Analysis: ....................................................................................................................................... 46

Swimming Pool System: .............................................................................................................................. 48

Shear Walls and Cores Analysis and Design: ............................................................................................... 49

4

Columns Design:...................................................................................................................................... 51

P-Δ effect: ............................................................................................................................................ 52

Torsion Check on Vertical Elements: .................................................................................................. 52

Stairs Design: ........................................................................................................................................... 53

Raft Design: ............................................................................................................................................. 54

Recommendations in Analysis of High Rise Buildings ................................................................................. 58

Aerodynamics Analysis ............................................................................................................................... 58

Differences in Etabs and GID .............................................................................................................. 62

Geotechnical Analysis, Constructions Stages and Foundation Design ....................................................... 63

Detailing ........................................................................................................................................................ 1

Columns .................................................................................................................................................... 1

Slab Reinforcement ................................................................................................................................... 2

Shear Walls ............................................................................................................................................... 7

Stairs: ........................................................................................................................................................ 7

References .................................................................................................................................................... 9

5

List of Figures

Figure 1 ......................................................................................................................................................... 9

Figure 2 ....................................................................................................................................................... 10

Figure 3 ....................................................................................................................................................... 11

Figure 4 ....................................................................................................................................................... 12

Figure 5 ....................................................................................................................................................... 16

Figure 6 ....................................................................................................................................................... 17

Figure 7 ....................................................................................................................................................... 19

Figure 8 ....................................................................................................................................................... 24

9 .................................................................................................................................................................. 24

10 ................................................................................................................................................................ 25

Figure 11 ..................................................................................................................................................... 26

Figure 12 ..................................................................................................................................................... 26

Figure 13 ..................................................................................................................................................... 27

Figure 14 ..................................................................................................................................................... 29

Figure 15 ..................................................................................................................................................... 30

Figure 16 ..................................................................................................................................................... 33

Figure 17 ..................................................................................................................................................... 33

Figure 18 ..................................................................................................................................................... 34

Figure 19 ..................................................................................................................................................... 38

Figure 20 ..................................................................................................................................................... 38

Figure 21 ..................................................................................................................................................... 39

Figure 22 ..................................................................................................................................................... 39

Figure 23 ..................................................................................................................................................... 39

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Figure 24 ..................................................................................................................................................... 40

Figure 25 ..................................................................................................................................................... 40

Figure 26 ..................................................................................................................................................... 40

Figure 27 ..................................................................................................................................................... 41

Figure 28 ..................................................................................................................................................... 42

Figure 29 ..................................................................................................................................................... 42

Figure 30 ..................................................................................................................................................... 44

Figure 31 ..................................................................................................................................................... 44

Figure 32 ..................................................................................................................................................... 47

Figure 33 ..................................................................................................................................................... 48

Figure 34 ..................................................................................................................................................... 49

Figure 35 ..................................................................................................................................................... 49

Figure 36 ..................................................................................................................................................... 50

Figure 37 ..................................................................................................................................................... 50

Figure 38 ..................................................................................................................................................... 51

Figure 39 ..................................................................................................................................................... 54

Figure 40 ..................................................................................................................................................... 54

1 - Soil Parameters ...................................................................................................................................... 63

Table 1* ....................................................................................................................................................... 18

Table 2 ......................................................................................................................................................... 20

Table 3 ......................................................................................................................................................... 21

Table 4 ......................................................................................................................................................... 23

Table 5 ......................................................................................................................................................... 28

7

Table 6 ......................................................................................................................................................... 31

Table 7 ......................................................................................................................................................... 31

Table 8 ......................................................................................................................................................... 32

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Introduction

High-rise buildings started to emerge in the States during the last 19th century in urban

areas, due to the fact that an increase in land prices and great population densities created a large

demand for buildings that were rising vertically, rather than those spreading horizontally, and in

turn occupying lower areas of expensive land. High-rise buildings were made practicable by the

use of steel structural frames and glass exterior sheathing. By the mid-20th century, high-rise

buildings had become a standard feature of the architectural landscape in most countries in the

world.

High-rise buildings sometimes require foundations that can withstand and support very

heavy gravity loads. These foundation systems usually consist of concrete piers, piles or caissons

that are sunk into the ground. Beds of solid rock are the most desirable base, but ways have been

found to distribute loads evenly even on relatively soft ground. The most important factor in the

design of high-rise buildings, however, is the building’s need to withstand the lateral forces

imposed by winds and potential earthquakes. Most high-rises have frames made of steel or steel

and concrete. Their frames are constructed of columns and beams. Cross-bracing or shear walls

may be used to provide a structural frame with greater lateral rigidity in order to withstand wind

stresses. Even more stable frames use closely spaced columns at the building’s perimeter, or they

use the bundled-tube system, in which a number of framing tubes are bundled together to form

exceptionally rigid columns.

http://www.britannica.com/technology/steel

http://www.britannica.com/science/earthquake-geology

http://www.britannica.com/technology/order-architecture

http://www.britannica.com/technology/bundled-tube-system

Project Description

United Arab Emirates, Dubai

5 Star, Luxury Hotel

AL-KHAWAJAH Engineering Consultancy

United Arab Emirates, Dubai

KHAWAJAH Engineering Consultancy

Figure 1

9

10

Figure 2

11

Sections

Figure 3

12

Figure 4

Scope

● Propose a Structural System.

● Load Identification

● Identify Construction Method for excavation

● Structural Analysis due to gravity and lateral loads (Earthquake and Wind)

● Design of the superstructure components.

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● Analysis and design of the substructure and foundation.

● Producing drawings up to the design development stage.

Deliverables

● Valid Construction Method

● Adequate System for Lateral Loads

● Calculation Sheets

Load definition

Structural Analysis

Design Calculations for Superstructure and Substructure

● Design Development (up to 60%) drawings.

14

Methodology

● Gravity, wind and earthquake loads from ASCE 7-10.

● Preliminary sizing of structural members (slabs, beams, columns).

● Structural modelling and analysis using SAP2000, SAFE and ETABS 2015.

● Geotechnical and basement analysis using Geo5.

● Structural and Geotechnical design following ACI 318-14.

● Structural drawings and detailing using AutoCAD.

15

Initial TimeLine

Challenges

Designing the 4-storey basement.

Total of 19.58 m below the ground level

Considering uplift pressure of the water in the soil on depth of foundation

Large Spans & Restrictions due to deflection.

Swimming pool (mass irregularity).

Using new codes of practice.

Using new programs for analysis.

High likelihood for analytical torsion on top floors.

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Preliminary Design

Loads

Below is the table of load combinations as per the ACI

Figure 5

- Live Loads are reduced by around 30% in combinations with earthquakes.

Slabs

We need to choose a system for the slabs that will not be a problem to the architecture

design as it is a hotel building and architecture features is a major requirement. Choosing our

system to be a Flat Slab System for various reasons. It is one of the systems that provide the most

flexible arrangements for services distribution as services do not have to divert around structural

elements.

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Figure 6

Benefits

1) Construction

Construction of flat slabs is one of the quickest methods available. Lead times are very short

as this is one of the most common forms of construction. And this will be very efficient as a

critical activity to the project. Flat slabs are considered to be faster and more economic than

other forms of construction, as partition heads do not need to be cut around down stand beams or

ribs.

2) Procurement

Because this is one of the most common forms of construction, all CONSTRUCT members

and many other concrete frame contractors can undertake this work.

3) Cost, whole life cost, value

Flat slabs are particularly appropriate for areas where tops of partitions need to be sealed to

the slab soffit for acoustic or fire reasons.

http://www.construct.org.uk/

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Slab thickness came out to be 30 cm, according to the ACI states that slab thickness of

the slab is L/30* and since our largest span is 9 m. the slab thickness 30cm is taken from floors 6

to 34 only and not including the podium. Each slab is checked for deflection through SAP 2000

to check the accepted deflection.

Table 1*

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Figure 7

Columns

We started by taking the Architecture drawings and at each column suggested by the architect

we took the tributary areas and through excel equations to get the Ultimate the loads on each column.

According to the ACI the column dimensions should not be less than 30cm.

The ratio between the dimensions should be at least 0.4. The procedure of preliminary

sizing process is:

1- Locate column service area.

2- Multiply ultimate gravitational area loads by service area to get column’s axial load.

3- Assume As/Ag of 1%, determining column section area (Ag).

4- Multiply that area by 1.3 to account for lateral loads’ effect.

For Axial and account for eccentricity.

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Table 2

The table above is used in modelling of members to be cracked sections under flexure and axial

loads. In checking serviceability, factors are permitted to be multiplied by 1.4.

Initial table of the column sizes as per the tributary area (preliminary sizing of columns)

Modelling of the building

We will be modelling our project using SAP2000, ETABS & SAFE14. Each software

will result in special cases, the table below illustrates the differences and common features of the

software’s.

All the softwares will analysis our building and as well will give us the deformation of

the model, while only safe and etabs can give us the area steel required to cover the moment.

will be able to get the punching values at the columns by

Each software results in same and different results depending on the way it is modelled.

Software Specialties

SAP

2000

- Irregular Shapes

Regular Contouring

Control of mesh

Table 3

ling of the building




the model, while only safe and etabs can give us the area steel required to cover the moment.

will be able to get the punching values at the columns by modelling the project on SAFE.


Comparison

Irregular Shapes -

Regular Contouring -

Control of mesh

- Same +ve moments as

SAFE

- Different –ve Moment as

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the model, while only safe and etabs can give us the area steel required to cover the moment. We

the project on SAFE.


ve Moment as

22

- Locating Column as Point

hinges

- Manual Meshing

SAFE

SAFE 14 - Checking Punching to

Manual calculations

- Locating column as

section area

- Self Meshing

- Same +ve moments as

SAP

- Different –ve moment as

SAP; more accurate in

accounting for their

stiffness connection.

Due to discontinuity of nodes in

the shells

ETABS - 3D modelling, for transfer

floors modelling

- l3D modelling lateral

loads

- Self Meshing

-Accurate results for Lateral

Loads.

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Table 4

Selection of the Gravitational Slab System

Elliptical Plan floors from 6th till 34th:

- To maintain the view of the slab clear and to cover the large spans, a flat slab

acting as a rigid diaphragm is selected for the slab system. There are no edge

beams because slab edge is not ending at column faces, there are cantilever parts.

- By having the largest span of 9 meters and following ACI 318-14, the slab depth

is selected to be (hSlab = L/30 = 9000/30 = 300 mm). (i.e: the yielding tensile

stress of main reinforcing steel is 400 MPa which is approximately equivalent to

60,000 psi).

- To test the system’s capacity for flexure, immediate deflection and long-term

deflection, a model has been constructed on SAP2000 for typical floor from 6th to

13th.

24

9

Moments Results (M11):

Figure 8

25

10

- Slabs are also modeled using SAFE to account for columns stiffness giving more

accurate results for moments and deformation.

- Moments in M1-1 and M2-2 are obtained from analysis to choose an adequate

reinforcement mesh layer. Moment capacity with the chosen reinforcement mesh

is calculated to locate the areas that require additional bottom reinforcement for

positive moment and area that require additional top reinforcement for negative

moment.

- Punching Check is also check manually and through SAFE.

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Figure 11

Section Capacity Ratio for Punching Shear

Figure 12

- Punching is also check for all planted columns

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Figure 13

- Here is our excel sheet used for slabs’ flexure design:

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Table 5

- “True” means section is safe against flexure and “False” means the section still

needs additional reinforcement.

- Deformation is also checked on slabs.

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Figure 14

- In some case our limit for deflection was L/480 under immediate live loads as

slabs are connected to non-structural curtain walls.

- We also checked long term deformation by taking into consideration the creep

effect on concrete under dead and sustainable live loads; creep effect under dead

loads could be decreased using Cambering technique. The creep factor is

influenced by the time factor and compression steel in the section.

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ETABS Model:

Figure 15

- Dealing with structure dynamics and lateral loads on the structure, we have

modeled the structure on ETABS, performed seismic and wind analysis in

addition to selecting the adequate system.

Seismic Analysis:

- Special Reinforced Concrete Shear Walls system is adequate for SDC B and C for

no limit (NL) for the building height. The system is limited to buildings of height

160 ft (50m) for SDC D and it is not permitted to be used for SDC E and F. Our

building is more than 160 meters height using Special shear walls so SDC C is

acceptable at most.

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Table 6

Table 7

- In this case, SDS cannot exceed 0.5 and SD1 cannot exceed 0.2 to remain in SDC C.

- Here are the data input for Special Shear Walls: ASCE 7 and other model building codes

acknowledge that structures will be loaded beyond their elastic range during seismic

events. Damping and ductile yielding make it unnecessary to design for the full inelastic

design force, so the code divides the seismic response by the R-factor to get a lower

elastic design force or base shear. Higher R-factors represent more ductile systems and,

therefore, yield a lower seismic design force. Deflections are multiplied by the Deflection

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Amplification Factor (Cd) to obtain the expected inelastic deflections. Similarly, the

System Overstrength Factor (Ωo) is an amplification factor that is applied to the elastic

design forces to estimate the building can exist safely in Dubai, but we have assigned

seismic data for higher ground acceleration within the acceptable limit and SDC the

maximum expected force that will develop.

- The building can exist safely in Dubai, but we have assigned seismic data for higher

ground acceleration within the acceptable limit and SDC C to have seismic design.

- Here is the response spectrum for the selected seismic records to locate the acceleration

of the structure for each mode according to the mode’s period.

Table 8

- To maintain SDC C to maintain the adequacy of using Special Shear Walls system

maximum seismic record can be used is: Ss=0.31 and S1=0.14.

-

- Here is the Response Spectrum:

33

Figure 16

- Here is our ETABS data input following the response spectrum:

Figure 17

It is included that SDS and SD1 are within the limit of Seismic Design Category (C).

- Our project is residential and SDC is C so the importance factor is (1.0) which is case

2. For that, the allowable interstory drift is 0.025 following ASCE 7-10.

0

0.05

0.1

0.15

0.2

0.25

0.3

0 1 2 3 4 5 6 7

From (0) to (To)

From (To) to (Ts)

From (Ts) to (TL)

34

Figure 18

- Here is all seismic data input:

35

- Here is the seismic output with the base shear coefficient and the elastic base shear

acting on the structure. Load case (EQx) means 100% earthquake force on X-

direction and 30% in Y-direction; and vice versa with (EQy).

36

Wind Analysis:

- Following ASCE 7-10 specifically chapter 6, our project exists in urban area and is

satisfying surface roughness and exposure condition of B.

- Structure is considered to be flexible if the natural frequency is less than 1 Hz. In our

case, the fundamental period 6.233 second showing the natural frequency of (wn =

2π/6.233 = 1.008 Hz). So the natural frequency is just on the edge of being flexible to

rigid structure; as a result, wind gust factor is calculated twice; one for being flexible

and one for being rigid. As a result, the maximum gust effect factor is taken to be 1.

Four wind load cases are assigned; (X-direction), (Y-direction), -(X-direction), -(Y-

direction).

37

- Here is also our data input for topographic (Kzt) and directional (Kd) factors in

addition to the wind speed.

System Selection:

- After assigning the lateral loads on the structure, major problems appeared in the

system:

1- The top 3 floors are only supported laterally on 3 walls and almost supported

partially in Y-direction so they are very soft stories. Also, these walls are carrying

huge shear forces at these floors.

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Figure 19

2- The center of rigidity is very far from the center of mass which is inducing high

torsional stresses on these walls.

3- The drift is also deemed unsafe where it is more than the allowable. The drift was

0.015529*Deflection Amplificator (5) = 0.076145

Figure 20

39

Figure 22 Figure 21

- We have been thinking to replace some columns to be shear walls without any

violation for the architectural drawings. As a result, 10 columns are changed to be

shear walls and they are located within the center of mass so they are controlling drift

and reducing the distance between center of mass (CM) and center of rigidity (CR).

Before Adjustments After Adjustments

- The limitation in increasing the stiffness, the period decreases which matches higher

ground acceleration since we are in “displacement sensitive” zone in response

spectrum.

- After these adjustments, the top 3 floors are no longer soft and drift is safe.

Figure 23

40

Figure 26 Figure 25

- Drift = 0.004235*Deflection Amplificator = 0.0212.

Lateral Loads on the structure:

- Lateral Wind Loads on stories diaphragms from X-direction in step number 2:

Figure 24

Story Shear from Seismic Loads on the Structure

EQx EQy

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Drift due to Earthquake (EQx):

Figure 27

Drift = 0.004235*Deflection Amplificator = 0.0212

Earthquake Drift Criticality = 0.0212/0.025 = 0.848

- Drift due to Wind (Windx):

42

Figure 28

Wind’s Drift Criticality = 0.000747/0.0025= 0.3

Earthquake is governing as its drift is more critical than wind.

Diaphragm Condition:

Figure 29

- Slab Diaphragm is considered to be rigid if (Max/Avg) diaphragm drift is less than 2

or if the void area is 50% greater than the total area. Rigid diaphragm is not likely to

43

get deformed and it is capable of transferring stresses to its vertical support. Flexible

diaphragm is considered to be simply supported on its vertical elements.

- In our model, we have assumed rigid diaphragm to be checked after running the

model.

- From the analysis results, our assumption is valid.

- Seismic Moments on slabs from ETABS are very small as slabs are modeled as rigid

diaphragms. So slabs are exported from ETABS to SAFE with all loads cases to

account for moments acting on the slabs from seismic loads.

44

Figure 30

Moment M1-1 from ETABS for EQx

Story 12th

Figure 31

M1-1 from SAFE for EQx in accounting for cumulative deformation and seismic

moments on Slabs

Story 12th

- To check the match between ETABS and SAFE in transferring loads cases, moments

and stresses on the slabs from vertical loads are checked to be similar in both

softwares.

45

Remedial Measurements:

- In case of structure irregularities, ASCE 7-10 is permitting remedial actions to

account for irregularities based on Seismic Design Category. Types of irregularities

are:

1- Torsional Irregularities that took place in upper 3 floors(Horizontal Irregularity)

2- Mass Irregularity due to swimming pool (Vertical Irregularity)

3- Stiffness Irregularity between podium and basement floors (Vertical Irregularity)

Example for types of Torsional Irregularity

- The remedial actions depend on the type of irregularity and the SDC of the structure.

- List of Remedial Measurements:

46

Modal Analysis:

- Modal Analysis has been performed to get the modal shapes of the structure under

free vibration; there is a specific period for each modal shape. Under each mode, the

building undergoes specific ground acceleration and modes are combined together

using (CQC); not Square Root of Summation of Squares (SRSS) since the difference

between the participation in most cases is less than 10%. The target is to reach 90%

of modal participation so we have performed analysis for 90 modes.

47

Figure 32

- 69 modes are enough to be used in the analysis after reaching 90% percent

participation.

- Ritz Modal analysis is used over Eigen analysis as Ritz-vector analysis seeks to find

modes that are excited by a particular loading. Ritz vectors can provide a better basis

than do Eigenvectors when used for response analysis that are based on modal

superposition. Eigen Modal is not really efficient for High Rise Buildings due to the

huge number of DOFs which requires much more modal shapes to reach participation

of 90%.

- 2nd and 3rd modal shapes are torsional which may lead to critical condition in case of

structure free vibration. As a result, the structure system is adjusted to minimize this

problem especially the torsional stresses in free vibration.

48

Swimming Pool System:

- A large swimming pool exists in the 4th floor in the podium with an average depth of

2 meters inducing area loads of 15kN/m2 over the pool’s area. In addition, there is the

problem of large span of 16 meters; as a result, flexure and deflection are very

critical. That area in the 3rd floor is “Plant and Equipment Room”, so our goal is to

make it functional for the equipment; not to be open for the people comfort. We

thought of Planted Columns to support the swimming pool system.

Figure 33

- The Criteria of placing the columns and their orientation was:

1- Span of 5 meters to maintain the space for equipment

2- Minimizing the unbalanced moments transferred to columns to reduce the

likelihood of Punching Shear.

3- Considering the load path to efficiently locate the columns orientation.

4- Controlling one-way slab shear to be fully controlled and resisted by concrete.

System for Slabs Large Spans:

49

- All Podium floors except the second floor are having a areas of large spans of 16

meters; having one slab of thickness 30 cm is deemed unsafe against deflection, and

having one slab of 60 cm is deemed uneconomic for the other areas. As a result, it is

decided to design a slab of thickness 60 cm only for the area that needs it. The thick

slab’s borders are targeted to have minimal stresses on them, so a model has been

made to locate the inflection points.

Figure 34

- Moving with the line of inflection points, the cutting line has been located.

Figure 35

Shear Walls and Cores Analysis and Design:

- Checking the nominal shear and torsion are less than the maximum allowable

specified by ACI.

- Checking the maximum acting axial load from “Envelope” load combination to locate

the plastic centriod and getting the dimensions of Boundary Element.

50

- Determining the type of boundary element (Special, Ordinary, no ties)

- Interaction Diagram has been developed to first estimate the reinforcement needed.

Figure 36

- Exporting results from all load combinations from ETABS to CSICOL to check steel

reinforcement and capacity ratio.

Figure 37

Example for One Core Wall in CSICOL

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

-5000 0 5000 10000 15000 20000 25000

Mue 1%

Mue 2%

Mue 3%

Mue 4%

51

- Confining ties for the boundary elements are checked.

- Transverse Horizontal reinforcement is calculated and checked to be above minimum.

Columns Design:

- Following the same procedure of walls regarding:

1- Nominal Shear and Torsion Check.

2- Using interaction diagram to estimate the required reinforcement.

3- CSICOL Modeling to check the selected reinforcement for flexure under all load

combinations.

4- Design for Shear.

Figure 38

Column Analysis using CSICOL

52

P-Δ effect:

- Slenderness or “P-delta” effect is considered in designing vertical elements as it

induces higher moment values.

Torsion Check on Vertical Elements:

- Even after adjusting the lateral structure system, the center of mass and the center of

rigidity for the diaphragm slab are still not close adequately. So, it is important to

check torsion on vertical elements. Torsion is taking place due to accidental torsion

with eccentricity of 0.05 in addition to analytical torsion due to the distance between

center of mass and center of rigidity.

53

All units in lb and in

- If the nominal torsional torque is less than quarter the cracking torsion, no torsion

reinforcement needed for the section.

Stairs Design:

- The project contained two different types of stairs; Slab Stairs and Helical Stairs. For

more accurate and economic analysis, stairs are first modeled using SAP 2000 on

hinges boundary condition, and then we could identify the load reaction for each

hinge for load cases and ultimate combination. Moving to ETABS, we could identify

the deformation at the locations of supports for the same load case. Moving back to

SAP 2000 Model, springs are assigned for the slab’s boundary conditions where the

stiffness used is the reaction force divided by the deformation for the same load case.

Iterations have been made in order to reach same deformation under the same load

case so the stair and the support are acting dependently as one unit.

54

Figure 39

Helical Stairs Modeling using SAP2000

Figure 40

Slab Stairs Modeling using SAP2000

Raft Design:

- All loads in the base are exported from ETABS to SAFE to model the raft. The area

of raft is limited with the boundaries of diaphragm walls. However, the raft is not

fixed to the diaphragms to avoid structure collapse in case of Raft’s settlement so they

have to behave independently.

55

- In modeling, soil properties (Modulus of Sub grade) have been assigned according to

the soil report.

- For Raft, settlement is more critical than soil bearing capacity and the maximum

allowable settlement is 50 mm under working loads condition.

- After Multiple iterations to adjust settlement, bearing capacity and avoid tension on

edges, the final thickness of the raft is 2.5 meters.

Settlement under working Loads

56

Soil Pressure Table in kN/m2

- Balanced-Failure reinforcement percentage has been calculated.

- The reinforcement percentage is limited between the minimum (0.2%) and balanced

reinforcement percentage.

- For flexure resistance for “Envelope” load case, we are using 3 layers top and 3 layers

bottom each of reinforcement web 10φ25/m. However, this reinforcement is not

enough for some areas requiring additional steel.

- For the blue shaded parts, additional of 10φ25/m.

57

- Shrinkage reinforcement is needed to be 5 layers of 10φ12/m. Although Raft is not

exposed to temperature frequently, but concrete pouring takes place in stages to

minimize the strain of concrete.

- Punching Check gives positive results where there is no likelihood for columns

punching the raft.

58

Recommendations in Analysis of High Rise Buildings

- Slabs are not preferred to be modeled independently using 2D model using hinges as

elastic shortening of columns shall be considered especially for the top floors.

- Slabs are not preferred to be designed under gravitation loads only as seismic loads

induce additional moments on the slab. Further, the system might get changed after

assigned lateral loads.

- Using Ritz Modal Analysis rather than Eigen Modal Analysis since the latter requires

much more modal shapes to achieve 90% modal participation factor due to the huge

number of degrees of freedom.

Aerodynamics Analysis

Using the GID software, which will analysis the pressure, exposed to the Slab edge of our

project.

What is GID? GID is a universal, adaptive and user-friendly pre and postprocessor for

numerical simulations in science and engineering. It has been designed to cover all the common

needs in the numerical simulations field from pre to post-processing: geometrical modelling,

effective definition of analysis data, meshing, data transfer to analysis software, as well as the

visualization of numerical results.

The main idea behind the analysis is to find weather the shape of the building is suitable

for the wind in the area of the project.

Analysis:

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- Evaluate the wind action over structure

- Wind forces and pressures acting on a building structure

Importance, determination of airflow patterns around the building for interference effect among

adjacent building may alter the velocity filed in the surrounding.

Wind @ x direction velocity Streamline

Presssure @ x direction Pressure stream line

Kn/m

Pressure

n velocity Streamline

Pressure stream line Ranging Pressure 656 Kn/m to

Suction

Suction

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Ranging Pressure 656 Kn/m to -585

The drag force wind in the x direction is per meter height in order to get the force for the floor

with a height of 3.5m = 12.25 *3.5

Rotated the building in the other direction to see the effect of the wind in the other

surface.

Wind @ Y direction Velocity


with a height of 3.5m = 12.25 *3.5


Velocity streamline

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Pressure @ Y direction

Pressure stream line

Ranging Pressure 1310 Kn/m to

Differences in Etabs and GID

In the comparison of the drag forces between the GID and etabs we found

slight differences between the force. In the GID software, we import the slab edge without any

Ranging Pressure 1310 Kn/m to -3400 Kn/m

In the comparison of the drag forces between the GID and etabs we found

differences between the force. In the GID software, we import the slab edge without any

62

In the comparison of the drag forces between the GID and etabs we found out, we have

differences between the force. In the GID software, we import the slab edge without any

63

41 - Soil Parameters

voids, columns or shear walls while in etabs the slab is modelled with Structure Interaction and the

Direction Factors, and the structure system.

Geotechnical Analysis, Constructions Stages and Foundation Design

We started off by analyzing and assessing the soil report in details to be able to determine the

type of soil we have and hence come up with initial proposals for our foundation and

construction stages.

Our soil type was general weak rock and since it was more convenient, we used the conversion

of rock parameters to soil parameters to perform our analysis and design. The following table

shows the soil profile with its shear parameters:

64

We first started off by determining the maximum depth to which the excavation can be carried out

without bracing/support. This was done by obtaining the active lateral earth pressure acting on the

soil profile as shown:

It is estimated that only about depths 3 to 6 m would be stable, while the rest of the soil would

fail. This would be inapplicable to having an open-cut excavation. Since we also have a

basement depth of 19.5 m under the ground we settled for an installation of a reinforced concrete

diaphragm wall that will support the soil as we excavate deep in the soil for more than 20 m. The

diaphragm wall will also be of advantage because it will act as the basement wall at the same

time. Stresses on the diaphragm as a basement wall were also taken into consideration using the

ETABS program. A raft foundation was chosen to be the most suitable foundation type for our

soil because of it being a weak rock and because we already have a deep basement. We have a

ground water table at 13m under the ground which we’ll have to dewater or place a jet plug to

decrease it to at least 22 m under the ground. We initially settled for the use of a jet plug to avoid

any settlement in the soil that will affect the surrounding building foundations.

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Our initial step was to be able to settle for proper construction stages. Many trials were

performed on the Geo5 program (sheeting check) to be able to determine an initial proposal of

construction stages and hence we verify each construction stage. Our initial Proposal was as

follows:

- Diaphragm wall of 2m thickness and 26 m depth.

- Excavation of 22m depth.

- Decreasing water level from 13 m to 21 m under the ground

We later on edited this initial proposal to a thickness of 1 m since a 2 m thick diaphragm wall

would be hard to construct in weak rock with a high chance of caving in. Excavation depth was

increased to 25 m deep underground to account for any increase in the raft depth. Also, depth of

the diaphragm wall was increased to 33 m to try to overcome any uplift pressure that will result

from decreasing the water level from 13 m to 25 m underground. Four Anchors will be placed at

different stages of the construction stages to limit the displacement of the diaphragm wall to less

than 2 cm to avoid any effect it may have on the superstructure of the high rise building. The

anchor specifications were obtained from Strand Anchor Systems with a cross sectional area of

12880 mm^2, placed at an angle of 15 degrees to the horizontal line, has a length of 10.5m and

anchor spacing of 4m:

- First Anchor at 8 m deep

- Second Anchor at 10 m deep

- Third Anchor at 18 m deep

- Fourth Anchor at 20 m deep

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Then we came up with the following ten final construction stages and checked the stability of the

diaphragm wall at each stage, the maximum moment, shear and displacement at each stage, the

internal stability of each anchor at each stage and finally the overall slope stability at each stage:

1st Stage: 8 m deep excavation

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2nd Stage: 1st Anchor

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3rd Stage: 10 m deep excavation

71

4th Stage: 2nd anchor

72

5th Stage: Placement of Jet Plug

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6th Stage: 18m deep Excavation

76

7th Stage: 3rd anchor

78

8th Stage: 20 m deep excavation

80

9th

Stage: 4th anchor

82

10th Stage: 25 m deep excavation

84

As seen previously, each stage is stable in terms of internal anchor stability and overall slope

stability. Also the maximum stresses and displacement the diaphragm wall is subjected to are:

- Maximum Moment of 763 KNm/m

- Maximum Shear Force of 531 KN/m

- Maximum Displacement of 1.34 cm

Since we initially settled for an installation of a jet plug at 25 m depth under the ground, we had

to calculate the uplift pressure resulting from this decrease. The uplift pressure was calculated

manually by drawing a flow net and obtaining the uplift pressure at the most critical point at the

end of the diaphragm wall and then checking how much of the soil can overcome the uplift

pressure and final determining the depth of jet plug we need to help overcome it. This is a picture

of the flow net hand drawn along with the calculations performed:

Hence these calculations allowed us to settle for a jet plug thickness of 1.5 m deep.

This depth was to our advantage because we were able to then maximize the depth of

our raft as we please but while keeping our bearing capacity and settlement limits. We

choose a raft depth of 2.5 m and performed the allowable bearing capacity

calculations for rock to determine the allowable bearing capacity for the raft

foundation. Nevertheless, we were more concerned with settlement issues than

bearing capacity issues since rafts undergo local shear failure and our analysis

obtained a settlement of 48 mm which is less than the allowable of 50 mm. The

following page shows the calculations performed to determine the bearing capacity of

the raft foundation:

Detailing

Columns

The reinforcement of the columns was determined according to design calculations.

Some of the columns were safe with little reinforcement, however the

was increased to satisfy the minimum code limitations (

required steel in each of the columns, the bars were arranged in the columns

maintaining the symmetrical requirement, and ensuring that the spacing between bar

and stirrups do not exceed 150 and 300 mm respectively, by placing stirrups every

two bars (ensuring that the maximum spacing between each bar is less than 150 mm).


Some of the columns were safe with little reinforcement, however the reinforcement

was increased to satisfy the minimum code limitations ( = 0.01). Upon finding the


maintaining the symmetrical requirement, and ensuring that the spacing between bar



1


reinforcement

= 0.01). Upon finding the


maintaining the symmetrical requirement, and ensuring that the spacing between bars



2

Elevation for a Typical C38 Column

Slab Reinforcement

Reinforcement for the slabs was determined through the moment analysis done by

SAFE. For each floor two plans were drawn, one to show the top reinforcement, and

one to show the bottom reinforcement of the slab. Each of these plans showed the

moments coming from both directions on each slab (M11 and M22). A mesh was

unified across the entire slabs for each the top and bottom, and additional steel was

added in areas that required more reinforcement where the additional steel

reinforcement varied from slab to slab, depending on the moments acting on it.

3

First Floor Bottom Mesh

Unified Mesh for Entire Slab

4

First Floor Top Mesh

M11 Reinforcement

M22 Reinforcement

5

14th to 24th Typical Plan Top Mesh

Areas showing additional moment, requiring extra reinforcement

6

32nd Floor Bottom Mesh

32nd Floor Top Mesh

7

Shear Walls

This is the detailing of one of the shear walls based on NIST for reference, showing

special boundary element, which are used in areas that have high compression from

both moment and axial.

Shear Wall Reinforcement

Stairs:

Since this is a slab type staircase, the main reinforcement is placed at the bottom, and

the secondary reinforcement is placed parallel on top of it. The stirrups are placed

perpendicularly over the two layers, holding then together in place.

8

Stairs Reinforcement

9

References - Codes Used: - American Concrete Institute 315-99 - American Concrete Institute 318-14 - American Society of Civil Engineers 7-10 - National Institute of Standards and Technology

- Articles/Books Used: - Strand Anchor Systems for Permanent and Temporary Rock and Soil Anchors.

(2011, February). Retrieved April, 2016, from http://www.contechsystems.com/cts-cd/Strand/Catalogue.pdf

- Taranath, B. (n.d.). Structural analysis and design of tall buildings.

http://www.contechsystems.com/cts-cd/Strand/Catalogue.pdf

group 1 final thesis report

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