Exposure C Open Terrain With Scattered Obstructions Engineering Essay

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Exposure D: Flat, unobstructed shorelines exposed to wind flowing over open water excluding shorelines in hurricane prone regions for a distance of at least 1 mile [1.61km]. Shorelines in Exposure D include inland waterways, lakes and non-hurricane coastal areas. Exposure D extends inland a distance of 660 ft [200 m] or ten times the height of the structure, whichever is greater. Smooth mud flats, salt flats and other similar terrain shall be considered as Exposure D.

In our case the exposure category our villa is considered to be exposure B.

Directionality Factor, (Kd)

The Directionality Factor is the reduced likelihood that the maximum wind speed occurs in a direction that is the most unfavorable for the building response. We can obtain the Directionality Factor from ASCE 7-05 standard Table 6-4 based on the type of the structure. In our case the directionality Factor will be 0.85.

Topographic Factor, (Kzt) (ASCE 7-05, 6.5.7)

The topographic factor is to account the wind speed-up effect due to the earth topography around the building. Since our villa in flat terrain, the value of Kzt equals to 1.

Gust Factor, (G, Gf) (ASCE 7-05, 6.5.8)

The Gust factor is a factor that describes the gutsiness and turbulence of the wind. It can be obtained based on the rigidity which can be specified by the natural period of the structure. According to the ASCE 7-05 the villa is considered as rigid if the natural period of the villa is less than one, where a constant value of G=0.85 is to be used. Otherwise, the villa is considered to be flexible. The following equation is used to calculate the Gust Factor of any structure:

Gust factor equation (ASCE 7-05, 6.5.8 1)

Where

gQ: Peak factor for background response = 3.4

gv: Peak factor for overall wind response = 3.4

gR: Peak factor for resonant response

gR= √(2 ln⁡ã€-(3600 n1)ã€- )+0.577/√(2 ln⁡ã€-(3600 n1)ã€- )

Where

n1: The building natural frequency

Internal Pressure Coefficient, (GCpi) (ASCE 7-05, 6.5.11.1)

According to the ASCE7-05 standards the Internal Pressure Coefficient can be determined from figure 6-5 based on the structure enclosure classification. Since our villa classified as closed villa the value of the Internal Pressure Coefficient is zero.

External Pressure Coefficient, (Cp) (ASCE 7-05, 6.5.11.2)

The external pressure coefficient can be determined from Figure 6-6 in the ASCE7-05 standards based on the classification of the external surface under consideration if its (windward wall, leeward wall or side wall). The Cp value determined for the windward is used when calculating the windward wall pressure. The value of Cp determined for leeward depends on L/B for the building and is used when calculating the leeward wall pressure.

L/B = (23/22) = 0.9 < 1

Windward Cp =0.8.

Leeward cp = 0.5

Wind Load Cases ASCE 7-05 6.5.12.3

According to the ASCE7-05 standard there are four load cases for wind load.

These cases reflect all possible wind directions and eccentricities from the center of the loaded surface of the building. It is important to mention that ETABS creates all these cases automatically.

Illustrated summary

The input parameters of wind load that matches our case are:

2.9 Load combination

The following combinations are used in the structural design as per ACI code.

2.9.1 Ultimate Limit State Combination

According to the ACI Standards, the following load combinations are the ultimate load combination originally used in the analysis and design of superstructure elements.

U=1.4(D+F)

U=1.2(D+F+T)+1.6(L+H)+0.5(Lr or S or R)

U+1.2D+1.6(Lr or S or R)+(1.0L or 0.8 W)

U=1.2D+1.6W+1.0L+0.5(Lr or S or R)

U=1.2D+1.0E+1.0L+0.2S

U=0.9D+1.6W+1.6H

U=0.9D+1.0E+1.6H

2.9.2 Working load combination:

The working load combination used in the analysis and design of foundation and serviceability checks:

U=D+F

U=D+H+F+ L + T

U=D+H+F+ (Lr or S or R)

U=D + H + F + 0.75(L + T) +0.75(Lr or S or R)

U=D+H+F+ (Wor 0.7E)

U=D + H + F + 0.75(W or 0.7E) +0.75L + 0.75(Lr or S or R)

U=0.6D+W+H

U=0.6D+ 0.7E+H

Where:

D: Dead load.

E: Combined effect of horizontal and vertical earthquake induced forces as defined in Section 12.4.2 of ASCE 7.

F: Load due to fluids with well-defined pressures and maximum heights.

Fa: Flood load in accordance with Chapter 5 of ASCE7.

H: Load due to lateral earth pressures, ground water pressure or pressure of bulk materials.

L: Live load, except roof live load, including any permitted live load reduction.

Lr: Roof live load including any permitted live load reduction.

R = Rain load.

S = Snow load.

T = Self-straining force arising from contraction or expansion resulting from temperature change, shrinkage, moisture change, creep in component

2.10 Structural system

The structural system refers to the members of the structure that they will act as a one integrated unit to counteract the subjected loads whether gravity or lateral loads.

It's really important to determine our structural system to withstand the loads illustrated above.

The structural system determined must be

Safe

Economical

Easy to construct

The structural system is composed of two main systems:

Super structure (slabs + beams + columns)

Sub structure (foundation)

2.11 Super structural system

The super structural system mainly focus on gravity loads which is composed of reinforced concrete slabs supported on reinforced concrete columns distributed on the plan according to the structural and architectural requirements.

2.11.1 Flooring system

The flooring system in general is a wide topic to discuss in which there are various types of flooring systems such as waffle slab, ripped slab and flat slab.

Figure 8 slab types (http://www.asandow.co.uk/Sheffield-Builder-Reports/Design-and-Technology/Design%20Technology%20and%20Materials%20Assignment%202%20task%203.html)

In this project we have narrowed our choices to use a flat slab as a flooring system. This decision was based on the advantages of this kind of slab such as:

1- It is the most commonly used in a villa construction.

2- Easy formwork.

3- Simple bar placement.

4- Convenient floor to floor height.

2.11.2 Flat slab

It is defined as a slab with no beams submerged in, loaded compatibly on a supporting system such as columns.

Our villa is consisted of two stories + roof, so we have three different slabs to work with. But the major problem we will face is that the columns dislocations, it means that the columns normally they don't change their position from the base to the roof, but in our case the columns change their locations which will develop a massive punching shear force on our slab, to resist this kind of force we have increase our slab thickness. We have another problem, the supporting columns mostly located on the edge of the slab which also will create a punching force through the slab.

To check these assumptions we ran an analysis of the story 2 slab using CSI SAFE, because the slab thickness is adequate and the deflection was within the allowable range.

To check the punching shear, this picture demonstrates punching shear capacity / allowable reinforcement, if this ratio is larger than one it means that the column will punch the slab.

As noticed from the picture above the punching shear ratios are larger than one. At this point we have two solutions to overcome this matter.

The first solution is to impose drop panel on top of each columns, this solution will solve the punching shear problem but it will not give us the rigidity we are seeking. Therefore we will go to the second optimum solution, imposing beams at the perimeter of the slab.

In this case, the use of drop beams to carry the slab at the edges shall overcome many problems, such as high deflection, high bending moments in the system and punching shear in case of having the columns at the edges.

The third solution was avoided which was to increase the slab thickness to 50cm as it is not acceptable for a villa and doesn't meet with our cost plan.

So the final decision for the flooring system is to follow a flat slab with perimeter beams.

2.11.2.1 Slab layout

This figure demonstrated an elevation view of the case discussed above as we can see indicated how the column is located on the mid span of the beam, this is considered a high load for a beam to handle, so we increased the depth to 90 cm which increased the moment of inertia of the section and this will be a safe yet economical way.

2.11.3.2 Beams layout

Beams assignments

Table 3 Beams ID and Dimenstions

2.11.4 Supporting system

Supporting system indicates to the structural component that will support the flooring system and will withstand the lateral load of the wind. This system function is to transfer the loads from the villa to the foundation.

In our project the supporting system consists of rectangular and circular columns and a core wall.

2.11.5 Columns

A structural member subjected principally to compressive stresses. Concrete columns may be unreinforced, or they may be reinforced with longitudinal bars and ties (tied columns) or with longitudinal bars and spiral steel (spiral-reinforced columns). Sometimes the columns may be composite of structural steel of cast iron and concrete.

 

2.11.5.1 Columns lay out

2.11.5.2 Columns designation

In this project the column will be divided into two groups of naming:

Column ID

Naming each columns alone Based on the locations distinguished by column id as shown in figures (16a, 16b, 16c)

Design sections

Categorizing the columns based on uniform reinforcement and shape as shown in the table below (group designation).

Table of columns

Table 5 columns naming separately (Column ID and sections) (ETABS)

2.12 Sub structure

2.12.1 Foundation

The foundation is the structural element that will support the whole villa including the flooring and the supporting system and will transfer the load to the soil lying underneath it. The bearing capacity of the soil is in general much lower than the high stress intensities carried by the columns and beams in the superstructure. Hence the foundations can be considered as interface elements that spread the high-intensity.

Mainly there are two types of foundations;

Shallow foundation is, usually, embedded a meter or so into soil. One common type is the spread footing which consists of strips or pads of concrete which extend transfer the weight from walls and columns to the soil or bedrock. Another common type is the slab-on-grade foundation where the weight of the building is transferred to the soil through a concrete slab placed at the surface.

Deep foundation is used to transfer a load from a structure through an upper weak layer of soil to a stronger deeper layer of soil. There are different types of deep foundations including helical piles, impact driven piles, drilled shafts, caissons, piers, and earth stabilized columns. The naming conventions for different types of foundations vary between different engineers. Historically, piles were wood, later steel and reinforced concrete.

To determine whether to apply deep or shallow foundation we should take into consideration the soil laying the structure.

2.12.2 Soil

City of Abu Dhabi usually suffers from a low bearing capacity of soil; whereas the capacity of soil to support the loads applied to the ground in relatively lower than other places in UAE. Hence, loads coming from the building must be transferred to deeper and stronger stratum.

The soil in our site was found to be silty sand with these properties:

Due to our soil conditions the safest choice will be deep foundation and for this project the foundation system will be bored and cast in place with piles supporting a raft slab that will support the villa.

This system will score a high factor of safety against the loads applied on the structure and will provide the strength, rigidity, stability and durability that we are seeking.

2.12.3 Bored and Cast-in-Place Piles

Piles are structural members that are made of steel, concrete or timber. They are used to build pile foundations, which are deep and which cost more than shallow foundation. Despite the cost, the use of piles is often necessary to ensure structural safety.

Bored and cast-in-place piles, which are the type of piles we are going to use in our case, are one of the most convenient ways of foundation organization. Their diameter ranges between 0.5-1.5 m and their depth can reach up to 25 m. To increase the bearing capacity, bored piles can be produced with the widening in the lower part. Mostly they are used at heavy loading and deep foundations.

The construction of bored and cast-in-place piles involves a steel case to form a void in the soil which is then filled with concrete. The steel case is left in place to form a permanent casing and increase the reliability of the piles

There are several ways of bored and cast-in-place piles construction. The choice depends on geological conditions of the building site.

 

2.12.3 The advantages of this Piling technology:

1. High reliability provides the control of drilling process reaching the bearing layer.

2. It lets drill or takes out boulders.

3. Filling the bore hole is done through the pipe with the reinforced case thus excluding the formation of collars.

4. During the drilling process there is a direct control of engineering and geological conditions, which lets us avoid any errors and find the most suitable solution.

5. The possibility of making widening lets us use fully the bearing ability of piles.

6. Relatively cheap.

7. Easy to extend.

2.12.4 Raft /Mat foundation

Raft /Mat slab is a large slab located under the structure relatively high in depth; the area of this slab should cover the whole structure.

Such a slab is implemented because it spreads the load of the building across the ground. Think of it as a raft floating on the ground supporting a structure. Rafts may also be used to limit foundation movements over variable soils.

2.12.5 The advantages of using this slab:

It is considered to be less vulnerable to termite infestation because there are no hollow spaces or wood channels leading from the ground to the structure.

It forms a solid unit along with the piles that can resist high loads.

It is considered as power full load bearing which can resist weak bearing capacities of soil.

It can score high factor of safety.

2.13 ETABS model

The completion of the analysis and the design of the villa was accomplished with the help of this program.So we will introduce ETABS and demonstrate how it can be handled.

To create this model we have to follow the following steps:

1. Define the grid lines and elevations

Figure 21 Define grid lines and elevation (ETABS)

2. Define the material properties

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3. Define our frame sections (beams and columns)

Figure 23 ETABS frame section (ETABS)

4. Define the wall and slab sections

Figure 24 ETABS slab and wall definition (ETABS)

5. Define diaphragms

Assigning a diaphragm to an area object provides a diaphragm constraint to all of the corner points of the area object and to any additional point objects that are enclosed within the boundaries of the area object. This includes any points (joints) that are created as a result of automatic area object meshing.

Figure 25 ETABS diaphragm's (ETABS)

6. Define static load cases

Figure 26 static load cases (ETABS)

7. Define load combination

ETABS also generates default load combination as per ACI code.

8. Drawing the project

The drawing tools are provided on the left screen of the ETABS to facilitate the drawing process, which starts drawing the columns , walls , beams and the slab for each story.

It is important once you click the drawing icon of lets say for example the beam and before start drawing the property of object your are about to draw is displayed , that way helps to lower the chance of confusion about the beam you were going to fix.

9. Assigning area mesh

Since the program uses the finite element method an area mesh (division) of the slabs is required, this option allows ETABS to understand the connection of the structure along with its geometry.

Also it can provide a great accuracy for the load distribution and load assignments.

ETABS automatically meshes (divides) area objects that are assigned deck properties or slab properties with membrane behavior only. Meshing helps distribute loads realistically.

Figure 29 Meshed model (ETABS)

10. Run analysis

11. Run concrete frame design

Figure 32 concrete design model (ETABS)

2. 13.2 ETABS output and results of the villa

Figure 33 Deformed shape under maximum load combination (DCON2) (ETABS)

Figure 34 Deformed shape under the effect of wind load (ETABS)

Figure 36 Frame maximum moment (ETABS)

2.13.3. Story drift

The lateral displacements due to lateral loads are obtained by finding the displacements at all levels caused by the load in one level, and then adding the effect of the loads of all levels. The procedure is carried out as follows:

As we can see that the structural system of the villa is rigid and stable because the drifts are very low in comparison with the allowable.

2.13.4 Wind load analytical graphs

Figure 40 lateral loads to diaphragm (ETABS)

Figure 41 lateral load to stories (ETABS)

Figure 42 Diaphragm displacement (ETABS)

Figure 43 Diaphragms drifts (ETABS)

Figure 44 Maximum story displacements (ETABS)

Figure 45 Maximum story drifts (ETABS)

Figure 46 Story shears (ETABS)

Figure 47 Story overturning moment (ETABS)

Chapter III

 

3.1 Design

The design period is the final period in processing this villa; it's an important phase as in this phase we will verify the following:

Slab thickness, stresses, deflection and reinforcement.

Beams dimensions, stresses and reinforcement.

Columns dimensions, stresses and reinforcement.

Pile length and diameter, capacity, reinforcement, number of piles required and the efficiency.

Raft thickness, stresses and reinforcement.

The Code followed to design these elements is ACI-318M with the help of ETABS for visualizing the villa and designing the columns and SAFE for designing the slabs and beams.

A manual design is also provided and compares to the results obtain from the program to show that the engineer should understand how these programs initiate their design as it is fair to say that these program can't substitute the engineering scene in the design, these programs only facilitates the engineers design.

Note that all the structural elements are designed based on the maximum load combination (DCON 2) which equals to (1.2 D + 1.6 L).

3.2 Slab design

To start the slab design first we have to determine the slab thickness, minimum slab thickness is determined as per ACI code TABLE 9.5(c) to limit deflection but in our case we didn't follow the minimum though the slab was safe against deflection because we had high punching shear due to columns dislocations in the middle of the slab so we increased the slab thickness.

In our case we should follow ln/33 as shown in table 8.

Slab thicknesses

Table 9 Our slab thicknesses

CSI SAFE design

CSI SAFE is the most integrated program to analyze and design slabs and foundations using finite element method. The software offers all about reinforcement, stresses, deformation, punching shear design and drawing detailing of the slab.

Importing the model

After finalizing the model in ETABS, the slab was exported from ETABS to SAFE with its dimensions, materials and loadings to carry out with the design process.

Roof slab deflection

We will start with the roof slab , the roof slab thickness was determined to be 20 cm as explained before , so first of all we need to check the deflection and whether its in the allowable limits, hence if the deflection is higher than the allowable an increment in the slab thickness will be required.

Figure 48 Deformed shape (DCON2) (SAFE)

As we can see , the program is accurate enough not only to show the maximum deflection but also it initiate a topographic drawing showing exactly where the deflection areas located so that we can determine the weakest point within the slab .

As per ACI code the Max allowable deflection = max span/480

= 6.66/480

= 0.0139 m (13.9 mm)

The max deflection obtained from SAFE = 4.8 mm< 13.9 mm

Therefore the slab is safe.

Punching shear check

As explained in chapter (2) the punching shear ratios obtained from SAFE must be less than one.

Figure 49 Punching shear ratios for roof slab (SAFE)

As noticed from figure 49 the punching shear for the middle columns is safe, on the other hand N/C (not calculated) is shown in the areas of the beams which indicates that no need for punching shear calculations in this area because its already safe.

Slab stresses

The following figures demonstrate the slab stresses such as:

Maximum moment under maximum load combination (DCON2)

Figure 50 Roof slab maximum moment (DCON2) (SAFE)

Maximum shear force under maximum load combination (Dcon2)

Figure 51 Roof slab maximum shear (DCON2) (SAFE)

Maximum normal force under maximum load combination (DCON2)

Figure 52 Roof slab maximum normal force (SAFE)

Slab reinforcement

CSI SAFE offers different approaches to design the reinforcement of the slab:

Strip method

This method can be accomplished by imposing design strips along the slab in x and y direction automatically or manually drawn and set the strips width as 1m.

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Figure 53 SAFE design strips (SAFE)

Then after running the analysis of the model the program show the strip stresses such as maximum moment and shear to determine the maximum moment for design, CSI SAFE also can generate the reinforcement required for each strip.

Automatic design

The reinforcement required for the slab is automatically determined by CSI SAFE, but the problem with this method is that the rebar's determined by SAFE may not be available in the market, and also the reinforcement of the slab will not be uniform mesh, it will only provide reinforcement in the area required.

Finite element method

The reinforcement is determined by the designer and CSI SAFE will check the slab depending on the maximum load combination slab stresses, it is simply by selecting number of bars required with its spacing, then checking the slab area of steel still required besides the top mesh where extra is needed in this area.

If the top-bottom reinforcement chosen balances about 90% of the slab then the other 10% area needs extra reinforcement.

In this project we will follow the third method which is finite element based enveloping reinforcement.

Figure 54 SAFE finite element based enveloping reinforcement (SAFE)

Slab reinforcement design

The main mesh for the roof slab is determined to be T12 @ 200 mm spacing top bottom (both ways), but this selection might not balance the steel required which means extra steel required, usually extra steel is obvious at high moments locations, this means top extra steel must be provided at supports (columns/walls) because a high positive moment is located at supports, same situation apply for mid spans as high negative moment is located which requires extra bottom steel.

Extra top X-Direction

Figure 55 Additional steel to main mesh (TopX) (SAFE)

The program gives rebar intensity of the extra required steel, as we can see from figure 55 the selection of the main mesh as T12@200mm equalize more than 80% of the slab, hence the purple color indicates that there is no need for extra steel.

The required extra reinforcement is given expressed by mm2/m which means rebar intensity and extra steel will be determined for top-bottom (both ways).

Extra steel required: T12@150mm.

Extra top Y-Direction

Figure 56 Additional steel to main mesh (TopY) (SAFE)

Extra required: T12@150mm.

Extra bottom X-Direction

Figure 57 Additional steel to main mesh (BottomX) (SAFE)

Extra required: T12 @200mm.

Extra bottom Y-Direction

Figure 58 Additional steel to main mesh (BottomY) (SAFE)

Extra required: T12@200mm.

Roof slab design reinforcements

Slab main mesh Top X Top Y Bottom X Bottom Y

T 12 @ 200 mm T 12 @ 150 mm T 12 @ 150 mm T 12 @ 200 mm T 12 @ 200 mm

Slab drawing

All the drawings are generated using CSI detailer the following figures presents the reinforcement of the Roof floor slab.

Figure 59 Roof slab reinforcement (AUTOCAD)

The rest of the drawings are provided in the drawing book.

 

3.3Beam design

The beams design was carried out using CSI SAFE, SAFE was very helpful in designing the beams because it can display max controlling loads on the beams such as moments and shears, SAFE also display the area of steel required for each beam and the detailed bars with their overlaps.

Roof beams stresses

Maximum moment

Figure 60 Roof beams maximum moment (SAFE)

Maximum shear force

Figure 61 Roof beams maximum shear (SAFE)

Rest of the beams stresses are in Appendix (B).

Beam design using SAFE

SAFE generates a design of the beam based on ACI 318M code, the moment is the factor in determining the area of steel required, as we can see in figure 62 along with the reinforcement area displayed the moment diagram for each beam.

All the beams in the roof slab are 200 mm base and 700 mm width spanning at the perimeter of the slab with one beam at mid span.

One thing we should mention that the maximum moment is located at mid span which requires extra steel or it can be the controlling area of steel for the whole beam, and also above the support will require a higher area of steel because a high moment is located.

Figure 62 Roof beams area of steel (SAFE)

Manual design for nominated beam

The structural programs can always simplify and utilize the design process, but engineering sense must be present. That why it's important to understand how these programs calculate the design outputs to handle it better.

That's why we will select a beam from the villa and we will design it manually then we will compare the results with safe.

The selected beam is located at story 2 and the beams ID B53 as demonstrated in the following figure.

Figure 63 Nominated beam (B53) (ETABS)

The maximum moment B53 is obtained from ETABS which equals to 46.7 KN-m.

To determine the percentage of steel required ρ

ρ=(0.85*fc)/fy (1-√(1-(2 Rn)/(0.85*fc)) )

Where

Rn = Mu/(∅bd^2 ) = 46.7/(0.9*0.2*(0.6)^2 ) = 720.7

∴ ρ=0.0017

As required = ρ*b*d = 0.0017 * 0.2 * 0.6 = 2.08*10-4 m2 (208.1 mm)

Use 2 T 16  As provided = 398 mm2

Check the moment capacity of the beam

∅ Mn=∅*A_s*fy ( d-a/2 )

Where

a=(ã€-Asã€-_provided*fy)/(0.85*fc*b) = 0.025

∅ Mn=88.4 KN-m > Mu = 46.7 KN-m

The beam reinforcement is adequate

Check the strain

ε_t=(d-c)/c (0.003)

Where

c = a/0.85 = 0.03

ε_t= 0.059 > 0.005

The section is tension controlled.

Design of stirrups

Figure 64 shear design provissions (ACI 318-08-Table 8.1)

The maximum shear force from SAFE equals to 80 KN, we will use T10 bar with nominal area

(

The stirrups spacing will be at the maximum in the 1/3 middle of the beam because at mid span the shear equals to zero.

Figure 65 Stirrups distribution (AUTOCAD)

SAFE output of the selected beam

ACI 318-08 Concrete Beam Design

Geometric Properties

Combination = Overall Envelope

Beam Label = B53

Section Property = B20X70

Length = 4.54 m

Section Width = 200 mm

Section Depth = 700 mm

Distance to Top Rebar Center = 50 mm

Distance to Bot Rebar Center = 50 mm

Material Properties

Concrete Comp. Strength = 40 N/mm2

Concrete Modulus = 36050.00005 N/mm2

Longitudinal Rebar Yield = 420 N/mm2

Shear Rebar Yield = 420 N/mm2

Figure 66 B53

Figure 67 B53 maximum stresses (SAFE)

Figure 68 B53 maximum stresses (SAFE)

Manual design V.S SAFE

As noticed from the table the two values are very close, so we can say that SAFE is a perfect program to design slabs and beams.

The rest of the outputs about beams reinforcement are provided in APPENDIX B.

3.4 Design of Columns

ETABS program was used to perform the structural design the columns and a comparison between ETABS values against hand calculation was provided in the next paragraphs.

ETABS design criteria

The design process is set to follow the ACI 318M design code. After defining the columns cross-sections and running the analysis, the user has to select "Design => Concrete Frame Design => Start Design/Check of Structure" from the main menu to start the columns design process. ETABS displays the area of steel required as shown in the figure below.

Figure 69 Frames (columns and beams) area of steel (ETABS)

Two column was selected as an example to be designed manually and then comparing the results with ETABS.

Figure 70 Nominated columns (C14, C2) (ETABS)

These marked columns are the nominated columns to be designed, they are selected from story-1; the first column C2 is located at the edge while the other one C14is located in the middle of the slab.

ETABS design for the nominated columns

ETABS automatically design the column's reinforcements without considering the minimum area of steel. Because of that if reinforcement is reported by ETABS as zero, minimum reinforcement is to be used instead. Moreover, ETABS displayed the safe columns with green color and its degrees, while the unsafe columns shown with red colors.

For further details of any columns a right click on the required column will bring "concrete column design information" menu which display the capacity ratio, the design parameters and the overwrites option as shown later on.

C2 output data

Figure 71 C2 design output (ETABS)

Column loads

Figure 72 C2 design summery (ETABS)

The picture illustrates the column design criteria as it displays the design load like ultimate normal force, ultimate moment and the shear force.

Area of steel

The area of steel required for this column is 1200mm2.

At last we can obtain a summery table from ETABS for all columns displaying the design loads and area of steel required which described in details in APPENDIX (C).

C14 output data

Figure 73 C14 design output (ETABS)

Column loads

Figure 74 C14 design summery

Area of steel

The area of steel required is 1600 mm2.

3.4.1 Manual design of the columns

ACI Code provisions

The ACI code specifies some limitations on the reinforcing and lateral restraint such as:

The percentage of longitudinal reinforcement may not be less than 1% of the gross sectional area of the column (ACI Code 10.9.1). if the percentage of steel is less than 1% there will be a distinct possibility of a sudden non ductile failure. The 1% minimum steel value will also limit the effect of creep and shrinkage and provide some bending strength for the column.

The maximum percentage of steel may not be greater than 8% of the cross sectional area of the column (ACI Code 10.9.1) to prevent too much crowding of rebar's, practically it's difficult to fit more than 4% to 5% into the shuttering forms and cast concrete around the bars , this will increase the chances of honeycomb in the concrete.

The maximum numbers of longitudinal bars permissible for compression members are as follows; 4 bars for rectangular sections, 3 for triangular sections and 6 for circular sections.

Design formula

Minimum eccentricities are not specified, but the same objective is accomplished by requiring that theoretical axial load capacities be multiplied by a factor which equals to 0.85 for tied columns and 0.8 for tied columns.

For tied columns (ACI equation 10-2)

∅pn=0.8 ∅ [ 0.85*fc (A_g- A_st )+ fy* A_st]

This equation presented here is applicable only for situations where the moment is sufficiently small so that e is less than 0.1h for tied columns or less than 0.05h for spiral columns.

In our case we will consider this equation since the moment values are relatively small and the eccentricity is less than 0.1h as demonstrated in the following table.

It is important to mention that these criteria will consider that the column is loaded axially due to low values of moments, if the values of moments are higher we should consider different approach using the interaction diagram of the column to determine the percentage of steel required.

Percentage of steel

The percentage of steel used to design the columns is used as 1% of the gross area.

To determine this percentage a simple study of the loads applied on the columns against the load capacity of the column is conducted, the load capacity of the column depends on the area of steel. To best alternative should be safe and economical and that why we used this approach.

Depending on the sections only the following table will reflect the section strength.

6 1735.552

Comparing the load capacity (Pn) of the column with the table of loads applied on the columns obtained from ETABS (this table is shown in APPENDIX C), we found that following 1% Ag as a percentage of steel is safe, economic and adequate.

ETABS also considered this percentage as the optimum percentage for designing the columns.

Area of steel

3.4.2 ETABS area of steel vs. manual

We can easily notice that the data obtained from ETABS are exactly similar to the data obtained from the manual design, ETABS automatically analyzed the loads and the eccentricities then used 0.01% Ag of steel 1200mm2 for C1 and 1600mm2 for C14.

3.5 Design of ties

According to the ACI 318-05 Code all longitudinal bars shall be enclosed by lateral ties. For longitudinal bars No. 32 or smaller the recommended tie is bar size No. 10, and at least No. 13 ties for longitudinal bars No. 36, No. 43 and No. 57. For this project all the columns were reinforced with bars size No. 19, No. 22 or No. 25. So the ties chosen for these columns will be bar of size No. 10. Moreover, the ACI-318-05 specifies the vertical spacing between the ties to be the smallest of the following three values:

16 longitudinal bar diameter,

48 tie bar diameter,

Least dimension of the compression member.

Figure 75 explains the requirements for the tie reinforcement in columns depending on the clear distance between longitudinal bars.

Figure 75 Ties shapes (Design of einforced concrete - Eighth edition - ACI 318-08)

The nominal bar selected for our ties will be T10.

Tie spacing selected for the selected columns

 

3.6 Foundation design

The foundation system for our villa is consisted of mat slab supported by 56 piles, the slab thickness and reinforcement is determined in the following pages. Also number of piles and the piles reinforcement will be determined.

There are different approaches to design these elements. The approach followed to design the raft is similar to design a flat slab as for the piles it's designed as a short spiral column.

3.6.1 Pile design

As mentioned in chapter 2 the piles considered for our project is circular bored and cast in place piles.

Length and Diameter of the Piles:

To find the diameter and the length of the piles needed to be able to carry the load coming from the building, we need at the beginning to study the soil that our tower will be constructed on. That is why we take the boreholes tests and get the SPT "N value."

The piles ability to carry the load comes from the friction it makes with the sand around it and the bearing capacity that acts on it from the soil. So, we have to find Qs (Skin Friction Load) and Qp (Base Resistance).

The pile diameter is 0.5 m with penetration depth of 10m.

Calculation of Qs:

D = 0.5 m and H = 10 m

φ= 40 (angle of friction)

Ks/Ko = 0.85 (according to the installation method which is bored and cast in place piles)

Ko = 1 - sin φ = 0.34

Ks = 0.34 * 0.85 = 0.29 coefficient of soil stress

Ƴsat = 15 KN/m3

q = 15 * 10 = 150 /m2

Qs = (q/2) * (0.29) * (tan 40) * (Ï€ D H ) = 303 KN

To find Qp:

Qp = Nq * q * Ab

Ab = (Ï€ * (0.5)^2) / 4 = 0.2

Nq = 64.2 (bearing capacity factor)

So: Qp = 1926 KN

Pile capacity

After finding the Qs and Qp values, the allowable load of the pile, which takes into consideration the safety factor, is found to complete the design on it.

Qtotal = Qp +Qs = 2229 KN

Qallowable = Qtotal / 3 = 743 KN which is equal to ~ 75 tons

Pile reinforcement

Piles reinforcement is designed as the reinforcement of short columns. It may seem that piles with such length are supposed to be designed as long column but it is actually the opposite since of the presence of soil around the pile helps in carrying the load with it.

Assume that approximately 1% longitudinal steel using fc'=40 MPA and fy=420 MPA. So, from equation 10-1 from the ACI Code:

∅Pn = ∅ (0.85) {0.85 fc' (Ag-Ast) + fy Ast}

Where:

Pn: axial load applied on the pile

Ag: gross concrete area

Ast: total cross-sectional area of longitudinal reinforcement

The Ast found was equivalent to 1600, so the reinforcement needed is 8 T 16.

Check

∅Pn = 392 tons > 75 tons ok

Design Spiral:

The ACI Code (7.10.4) states that spiral may not have diameter less than 10mm and that the clear spacing may not be less than 25 mm.

Ag = π (0.5)2 / 4 = 0.196m

Ac= π (0.4)2 / 4 = 0.126m

fs = 0.45 (Ag/Ac- 1) (f'c/fy) = 0.024

Figure 78 spiral (Principles of Foundation Engineering, 2nd edition by Braja M Das.)

use T 10 mm spiral , as = 3.14*10-4m

fs = 4as (Dc - db) / s * Dc2  s = 0.147m

Use Spitch =150mm.

Pile Settlement:

s = total pile settlement = s1 + s2 +s3

s1 = settlement of pile shaft

S2 = settlement of pile caused by the load at end bearing

S3 = settlement of pile caused by the load transmitted along the pile shaft

Source: Principles of Foundation Engineering, 2nd edition by Braja M Das.

To find the settlement of pile shaft:

S1 = ((Qp+ᶓ Qs)* L)/(Ap*Ep)

Where:

Qp : load carried by end bearing under working load combination

Qs: Load carried by shaft friction under working load condition

Ap: area of pile cross section

L: length of the pile from cut-off level

Ep: Young's modulus of the pile material

ᶓ : 0.67 for triangular load distribution

S1 = 9.6*10-4 (0.96 mm)

To find settlement of pile caused by the load at end bearing:

S2 = (qwp*D)/Es ( 1 - µ) 2 Iwp

Where:

D: Diameter of Pile

qwp: point load per unit area at the pile point = Qp/ A p

Es: Young's modulus of silty sand

Iwp: influence factor(0.85)

Figure 79 Values of modulus of elasticity of soil (Principles of Foundation Engineering, 2nd edition by Braja M Das.)

µ = Poisson's Ratio

Iwp: Influence Factor = 0.85

S2 = 0.0176 m (17.6mm)

To find settlement of pile caused by the load transmitted along the pile shaft:

S3 = (Qs*D)/(P*Le E) (1- µ)2 Iws

Where:

P: Perimeter of the pile

Le: embedded length of pile

Iws: influence Factor (Iws = 2 + 0.35 √(L/D) = 3.56)

S3 = 7.25*10-5 m (0.07 mm)

So the total settlement was found to be:

S tot = 0.96 + 17.6 + 0.07 = 18.63 mm < 25 mm (Acceptable and Safe)

Pile drawing

Figure 80 Pile reinforcement layout (AUTOCAD)

Estimating the Number of Piles

The approximate number of piles can be estimated by the following equations:

N~MF ((P total)/(Pile capacity))

Where

N: Number of Piles.

Ptotal : Total gravitational load of the building as due to load combination (D+L).

Pile Capacity: Allowable load resistance per pile.

MF: A factor bigger than one to account for the additional number of piles due to extra loads from lateral loads on the building, usually (1.2 => 1.5).

The total load of the villa is obtained from ETABS under the maximum load combination.

Design load = 3500 tons.

N = 1.2 (3500/75) = 56 piles.

Calculation the Spring Stiffness of Piles

Typically piles are modeled in SAFE program as springs Kv and Kh in the vertical and lateral directions, respectively. Modeling the piles as a spring helps simulate the actual pile situations better than using a fixed support.

The stiffness of the vertical spring is estimated as follows:

Kv = load/deformation = (pile capacity)/(allawable sttlement (0.01 D)) = 150 KN/m

Where

Kv: Stiffness of the vertical spring of the pile

D: Diameter of pile

The horizontal pile stiffness (Kh) is approximately taken as 10% of the vertical value (Kv).

Kh = 15 KN/m.

Figure 81 springs supporting Raft foundation (SAFE)

3.6.2 Raft/Mat slab

The raft is imported from ETABS to safe to complete the design procedures, ETABS include importing the raft along with the loads from above, it means that when the raft is imported from ETABS to SAFE the loads is already designed with their positions as noticed from figure 81 as the villa loads is demonstrated in blue color. This option helps designing the raft based on the actual situations and loadings (punching shear) so we can say that SAFE sets a perfect modeling data of the raft with their loadings that is supported by piles which demonstrated by springs.

Soil pressure

The soil pressure is a very important factor to consider, but the soil behavior is hard to predict even some engineers neglect the soil lying underneath in design or change the whole site soil in some cases.

In our case we will consider the soil partially in the raft design using a factor of safety equals to 3.

To assign the soil pressure using SAFE a sub grade modulus value (KN/m3) must be determined.

Figure 82 Subgrade modulus (SAFE)

k = 40 x FOS x Qa

Where

FOS: factor of safety considered in Bearing pressure calculation and

Qa: allowable bearing capacity.

 k = 40 * 3 * 200 = 24000 KN/m3.

Raft thickness

Our main object as engineers is to produce an economical outcome yet safe, the option of selecting the raft is not that economical but it's safe, so we minimized the raft slab as possible.

To determine the raft thickness a major indicator must be taken into consideration, the punching shear forces and settlements.

The raft slab was chosen to be 50 cm which is the minimum safe thickness.

Raft punching shears

As we mentioned the punching shear safety is what we are seeking, not only the punching columns loaded on the slab but also the punching piles supporting the slab should be taken into consideration.

After running the analysis of the raft in SAFE the punching shear ratios is shown below to check whether it's in the safe zone or not, hence if the punching shear ratios is bigger than one we have to raise the thickness of the raft to overcome this matter.

Figure 83 Raft slab punching shear ratios (SAFE)

As obtained from figure 83all the punching shear ratios are less than one which indicates that the raft thickness is adequate, at this point we can say that the slab is 75% safe the other 25% left depends on the settlement.

Raft settlement

The maximum allowable settlement in sandy soils from Terzaghi and peck is found to be 25mm on the other hand the maximum allowable differential settlement is 3/8 *25 = 9mm.

Figure 84 Raft deformed shape (DCON2) (SAFE)

Using SAFE the maximum settlement in our raft equals to 3 mm which is less than 25 mm.

The slab is safe and ready for reinforcement design.

Raft reinforcement

The numerical design of raft slab has different approaches; in our project we will design it using SAFE and it will be similar to a flat slab design.

In rafts it's noticeable that the reinforcement intensity increases in the bottom mesh especially in the columns and walls locations because of high punching shear force produced while the top reinforcement might not require such high rebar intensity.

The main mesh of our raft is T16@150mm.

Extra top

As mentioned, no extra top reinforcement required in both ways (X-Y).

Extra bottom reinforcement X-direction

Figure 87 Additional steel (BottomX) (SAFE)

Extra required: T16@150mm spanning along X-Direction.

Extra Bottom reinforcement Y-Direction

Figure 88 Additional steel (BottomY) (SAFE)

Extra required: T16@150 mm spanning along Y-Direction.

Raft drawing

Figure 89 Raft layout (AUTOCAD)

Chapter IV

 

4.1 Cost

Cost estimating is one of the most important steps in project management. A cost estimate establishes the base line of the project cost at different stages of development. Actually the first step in preparing a detailed cost estimate is calculating the quantities or it can be called the quantity surveying, it is done by breaking down the project in to small segments in order to be priced, and then prepare quotations of these segments. The main sources of the quantity take off are the contract documents, drawings and specifications. There are several rules and guidelines an estimator can follow while estimating the quantities. The first step is estimating the preliminaries. The section of preliminaries of a bill of quantities is the section that provides a description of the project, the contractor's general obligations, general facilities, Management and Staff salaries, tools, machines, setup and running costs. After that the cost engineer starts to calculate the Civil work cost, in this step many factors must be calculated accurately, these factors are Earth work, Substructures work, super structure work, Block work, Finishing and External work. Then we calculate the subcontractor's work of Mechanical or electrical work.

Chapter V

 

5.1 Conclusion

The construction industry has an important role in the economical development of any nation which is the case in the UAE during the last decade. The world has witnessed a substantial increase in the economic progress in the UAE, especially in Emirate of Abu Dhabi.

This project presents the structural analysis and design of a reinforced concrete residential villa located in Abu Dhabi city. The main objective of the project is to provide safe and economical design according to the ASCE7-05 and ACI318-08 codes. Since there are different possible materials and structural systems that may be used in such projects, our aim was to seek safe, economic and workable system. This was followed by selecting of the suitable construction material in order to achieve the required design objectives and specifications.

There is no doubt that, the optimum structural design is strongly built on a perfect, extensive and comprehensive analysis. Therefore, one of the main goals of the preliminary design is to show clearly the basis and results of the structural analysis of the residential villa in order to perform all the design tasks and report the deliverables in the design phase. This was accomplished by firstly determining the different applied loads, gravity and lateral, and secondly by studying the structural behavior of the different structural elements after the application of the load.

Due of the complexity of the design, two programs, ETABS and SAFE, have been used during both the analysis and design phases of the structure. The programs were chosen because of their capabilities of providing fast and accurate results which help in comparing several design alternatives. Apart from the software, manual calculations were performed to verify the validity and acceptability of software output.

As a summary, the structural design of the floor slab, beams, columns and foundation have been performed and reported on appropriate structural drawings. The structural drawings, which are produced using AutoCAD, show the geometrical dimensions of the different elements, the distribution of the steel reinforcement, and the portions that require extra steel reinforcement; if needed.

5.2 Entrepreneurship Concept and Definition

"Entrepreneurship is the process of creating something new with value by devoting the necessary time and effort, assuming the accompanying financial, psychic, and social risks, and receiving the resulting rewards of monetary and personal satisfaction of independence."… Robert Hisrich

"Entrepreneurship is an act of initiative, drive, commitment, diligence, perseverance, organized effort, and achievement outlook, to undertake some specific functions of performing productive activities and the capacity to bear and associated with the investment".

Economic Policy Paper on Entrepreneurship Development through Educational Reform-Bangladesh

5.2.1Value Proposition:

A value proposition is the basic reasoning for why people should consider your product or service.

In our project our value proposition is developing a sustainable structure using composite materials instead of the basic materials such as reinforced concrete. This proposition will save time and money.

5.2.2 Customer Segmentation:

Is a way of dividing a customer database into segments in a special orientation which is relevant to marketing, age, gender, habits, and nationality. Customer segmentation allows a company to target specific groups of customers effectively and allocate marketing resources to best effect. According to an article by Jill Griffin for Cisco Systems, traditional segmentation focuses on identifying customer groups based on demographics and attributes such as attitude and psychological profiles. Value-based segmentation, on the other hand, looks at groups of customers in terms of the revenue they generate and the costs of establishing and maintaining relationships with them. "Customer segmentation procedures include: deciding what data will be collected and how it will be gathered; collecting data and integrating data from various sources; developing methods of data analysis for segmentation; establishing effective communication among relevant business units (such as marketing and customer service) about the segmentation; and implementing applications to effectively deal with the data and respond to the information it provides"(techtarget.com). Our idea should be shown to the city hall to be approved by the customers who later will let us implement the design with its benefits and advantages.

5.2.3 Competitor's Matrix:

Is a way of identifying how good is your product and how efficient is your product. This matrix allows the customers to give their opinions and comments on the product from all directions and aspects, such as, price, safety, and quality. A simple matrix can be a simple chart, containing the structures and benefits of the company's product or service on one side and the names of similar villas or products on the top row. Then fill the chart with appropriate information about each competitor in regards to your products or service.

5.2.4 Positioning Strategy:

There is always competition between companies and there are always ways to be ahead of other companies. In this project you may ask why would someone use us and not use other companies. What we are offering is a new idea in construction in which if it is proved to be successful people might actually start to use it because we offer it with much quicker finishing time and much cheaper and it also depends on the marketing of the idea.

5.2.5 SWOT Analysis:

SWOT is known to stand for Strengths, Weaknesses, Opportunities and Threats

A SWOT analysis generates information that is helpful in matching an organization or group's goals, programs, and capacities to the social environment in which it operates.

It is an instrument within strategic planning.

When combined with dialogue it is a participatory process

Factors internal to the program usually can be classified as strengths (S) or weaknesses (W), and those external to the firm can be classified as opportunities (O) or threats (T).

Strengths and Weaknesses are known to be internal factors, of which a company has total control, while opportunities and threats are external factors that a company cannot control in any way.

 

5.2.6 SWOT: Internal Factors

Strengths

Positive tangible and intangible attributes, internal to an organization.

They are within the organization's control.

5.3 Strengths:

What do you do particularly well?

What do you do that is unique in the "marketplace?"

What do your customers/clients/patrons ask for you to do over and over again?

What do you have the right tools/resources to accomplish?

5.4 SWOT: External Factors

5.4.1 Opportunities

External attractive factors that represent the reason for an organization to exist and develop.

What opportunities exist in the environment, which will propel the organization?

Identify them by their "time frames"

The vast amount of building in the UAE, which means more market for our product.

The new rules that have been applied in the UAE, stating that everything should be sustainable, composite and Eco-friendly.

5.4.2 Threats:

Huge and old firms that have already established their projects and reputation.

Lack of financial support

5.4.3 Key Activities:

Methods that are performed in order to maintain a good and a competitive business. In addition, it maintains the clients trust and keeps the business flowing in a perfect track. We are using the best composite materials available such as glass, wood, and carbon fiber in the structure.

Four points to be discussed:

Value Proposition: a promise of product made that will meet the customers' satisfaction and expectations.

Channels: is a way of delivering the value proposition such as, channels or mediums. We want to deliver this villa or product in a modern way such as international green exhibitions that care about the environment and the future. Also, submitting this design to big companies in the UAE such as, Estidama, that will rate out structure according to specific requirements and rules. Moreover, we are going to present this idea after its approved by the city hall by hiring representatives to visit construction companies and explain this idea and what it can improve in the construction Segments. Another way we can use to present this idea is to put Advertisements in Malls and in places where people can see and gain knowledge about.

Customer Relationship: type of interaction between the customer and the company we are working with.

Revenue Streams: the method that the company makes income and profit from contractors and consultants. In addition, we could use this idea as a Patent to gain revenue in which anyone that wants to apply our idea should pay for it.

5.4.4 Key Resources:

Physical Resources: the equipment we are using as well as the building materials.

Intellectual Resources: the resources which we came up with from our experience and ideas we want to achieve.

5.4.5 Pricing Strategy:

Cost-Based Pricing: a pricing method in which a fixed amount of the total cost is added to the cost of the product or the villa to appear in the customers' price.

Competitive-Based Pricing: includes the setting of prices based on what competitors are charging.

Value-Based Pricing: a business strategy which sets the prices mainly, on the rate, exact or estimated, to the customer expectations other than the real cost of the product.

5.4.6 Cost Structure:

Cost of Equipments.

Cost of the composite materials & concrete.

Cost of advertisements and presentations.

5.4.7 Revenue Streams:

We could use this idea as a Patent to gain revenue in which anyone that wants to apply our idea should pay for it.

5.4.8 How will you make profit?

Charge a low rate at the beginning to let your product be known in the market. Later on, price can be raised. The product has to be known in the market and between the competitors. Also, marketing the product perfectly gives us a huge amount of profit if it is displayed and marketed properly. Try to keep the overhead low, such as working from home or sharing offices space.

6.1 References:

http://searchcrm.techtarget.com/definition/customer-segmentation

Benito CA. (2001) S.W.O.T. Analysis PPT cited 23 March 2009 at: www.sonoma.edu/users/b/benito/swot.ppt

Drouin, C. (2007) Strategic Planning SWOT. Cited Feb 15th 2009 at http://www.planonline.org/

http://en.wikipedia.org/wiki/Structural_load

http://www.engg.uaeu.ac.ae/departments/units/gra/presentation/nd_03_04/male/cem_2_1/G.P.21/BackgroundTheory.html

http://text.lsuagcenter.com/en/family_home/home/la_house/my_house/Hazard+Resistant/Whats+a+Wind+Load.htm

http://www.accessscience.com/search.aspx?rootID=794349

Foundation (Engineering)-Frederic P. Miller, Agnes F. Vandome, McBrewster John- VDM Publishing, 2010.

http://www.estel-company.com/razdel/67/

Design of reinforced concrete - Eighth edition - ACI 318-08 code - jack c. mccormic and russel h.brown

Principles of Foundation Engineering, 2nd edition by Braja M Das

ACI code 318-05

ASCE code 7-05

IBC code

Doctor notes

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