Stairs

Stairs :

is a set of steps leading from one floor of a building to another, typically inside the building or   a series of steps or flights of steps for passing from one level to another.

An attractive stair  can enhance a location: fascinating, perfectly attuned to the architecture; a show piece. As a beautiful addition to your office, home or shop. Because there are so many options when it comes to style, materials and installation, staircase prices can vary tremendously. 

Stairs may be in a straight run, leading from one floor to another without a turn or change in direction. Stairs may change direction, commonly by two straight flights connected at a 90 degree angle landing. Stairs may also return onto themselves with 180 degree angle landings at each end of straight flights forming a vertical stairway commonly used in multistory and highrise buildings. Many variations of geometrical stairs may be formed of circular, elliptical and irregular constructions.

Step

Each step is composed of tread and riser.

Tread

The part of the stairway that is stepped on. It is constructed to the same specifications (thickness) as any other flooring. The tread "depth" is measured from the outer edge of the step to the vertical "riser" between steps. The "width" is measured from one side to the other.

Riser

The vertical portion between each tread on the stair. This may be missing for an "open" stair effect.

Nosing

An edge part of the tread that protrudes over the riser beneath. If it is present, this means that, measured horizontally, the total "run" length of the stairs is not simply the sum of the tread lengths, as the treads overlap each other.

Types of stairs :

• Straight Stairs.
• Straight Stair with central landing.
• L Shaped Stair.
• L Shaped Winder Stairs.
• Spiral Stairs.
• Curved Staircase.
• Library Ladder.

Geotechnical engineering

The first step to start any construction is the geotechnical investigation studies , these studies include type of soil , types of rock in the site and the it's topography .

Soil : 

There are many things that we have to know about the soil :
1- type of soil
2- physical properties
3- friction coeffecient angle
4- shear stresses
5- normal stresses
6- thermal resistivity

Any factor of these will affect on the excavation and foundation , for an example , for the weak soil may be we should use raft foundation or piles but for strong soil may be we use single footing . It doesn't affect just the type it's affect the thickness and other dimensions .

Rocks : 

The rocks are divided in three types :
1- Igneous rocks
2- sedimentary rocks
3- metamorphic rocks

Each one of these types differ from the others by physical properties , chemical properties , uses , textures and the procedure that resulted from .

Igneous rocks :

The igneous rocks is the result of magma or lava cools or hardens .

*magma is inside earth's interior 

*lava is outside earth crust

Igneous rocks are classified depending on : 

Texture size : texture mean how a rock looks and feels , and its based on the grain size .

Where the rock is made : rocks that cool slowly have larger crystals , but rocks that cools fast have smaller crystals .

Materials that the rock made from : the major silicate rock forming elements are : O , Si , Al , Fe , Mg ,K , Na , Ca . 

*When the silica percentage decrease the rock will become darker .

*Glassy texture means that the rock have no crystal grains .

In the next post we will talk about other types of rocks : sedimentary and metamorphic rocks .

Bridges engineering

Bridges is the structure element that carrying a road or a path , bridges consist from deck slab , abutment and piers .

Types of bridges :

1-slab bridge : the type of bridge that doesn't have beam , just slab on abutment and piers .

2-T-beam bridge : slab bridge subjected by T- beam consists from abutment , piers , deck slab and T-beam

3- prestressed bridge : type of bridges that have prestressed piers and slabs so the spans will be much longer and the slab is thinner .

4- Box girder bridge : is the bridge in which the main beams consist from hollow box , it may be done using prestressed concrete , steel structure or composite section from steel and reinforced concrete .

5- stayed-cable bridges : this type of bridges has towers to connect the cable with which carry the deck slab.

6-voided bridge : is a bridge that has voids inside the deck slab to reduce amount of concrete and reduce weight of structure , the voids usually circular made from galvanized steel .

steel structure

Today we will talk about steel structures in general and for the most important advantages and disadvantages:

The pros and cons of steel structure*

First the pros :-

1. beauty form.
2.  performance efficiency.
3.  low cost.
4.  lighting in all parts during the day.
5.  spaces and wide without prizes or columns, which provides good visibility extensive work, movement and space
6.  the possibility of a significant increase in the earth's load without additional costs
7. few dangerous incidents
8. possibility of vertically rise to the distances can not be accessed by any other material
9. Ease of installation and thus save time achievement
10. can be ceiling temporarily and then utilized unzip it and move it to another place
11. iron compliant borne vibration (such as winches in the laboratory)

Then the cons of steel structure:-

1. Deliver and store more heat and cold
2. iron needed for maintenance.
3. extensive glass areas increase the likelihood of maintenance, which means that maintenance costs are high.
4.  need for large land area for Sheds labs and spatial structures in which the roof is uncharted territory.

Prestressed concrete

Prestressed concrete is the type of concrete that has a tensioned steel inside the concrete as strands , the basic concept of this concrete is to transform the section from tension - compression section to compression -compression section .
This can be happened when the steel is tension until we reach a certain limit then we cut the steel so the force that will applied from steel to the section is compression force .

And we can reduce the stress by introducing moment from the steel by make a eccentricity from the centroid (M=P*e) and the stress will equal (stress=My/I )

The profile of the steel is called tendon and there are many shapes of it :
1- linear profile : we can called this type constant eccentricity .
2- parabolic profile : we can called this type variable eccentricity .
3- linear - parabolic profile

Method of prestressed concrete :
1- pre-tensioning : the steel is tensioned then the concrete will be cast then the steel is cut.
2- post-tensioning : the concrete is cast then the steel is tensioned and cut .

Benefits of prestressed concrete :
Allows longer span , thinner slab and fewer beams .
Lower building height.
Prevent cracking because the cracking is introducing by tension .

There are two main methods to design prestressed concrete members :
1-allowable stress method : in this method we have to check that the actual stresses is equal or less than the allowable stress .
2- load balancing method : in this method we design prestressing steel to carry a percentage of dead load .

There are many things that can be affect on the design such as :
1- type of tendon : bonded or unbonded tendon
2-type of steel : low or normal relaxation
3-the strength of concrete

In the prestressing process the total force doesn't remain constant , there is a drop in force due to losses  :
1-short term losses : it is immediate losses occur during prestressed of tendons .
a-elastic shortening of concrete
b-slip at anchorage
c-friction

2-long term losses : it's time dependent losses
a-creep and shrinkage .
b-relaxation of prestressed steel .

Columns

The second structural element is column (compression member) ,this element which provide construction elevation and connects the footing with beams and slabs to transfer the loads .

types of columns according to braces :

1-braced column; this system prevent the side sway because of connection columns with beams , most of braced columns is made from steel , and this is one of it's good features and the other one is to carry lateral load like wind load and seismic load.

2-unbraced column; this types of column didn't prevent side sway and can't carry any of lateral loads .

types of columns according to column cross sectional shape :

1-Circular columns 

2-Rectangular columns

3-Square columns 

4-Hexagonal columns

types of columns according to column's length :

1-long columns : when the ratio of length to least cross sectional dimension is more than 12
2-short columns : when the ratio of length to least cross sectional dimensions is less than 12 and more than 3 

Buckling in columns 

The short columns will fail in compression before it reach buckling , but the long columns will fail firstly in buckling and this depends on many factors :

1-length of columns

2-cross section dimensions 

3-the fixity of column's end

4-slenderness ratio

ties in columns :

types of ties in columns :

1-rectangular ties

2-spiral tieds

we use ties in columns to :

1- bind and hold longitudinal bars .

2-prevent concrete from splitting outwards

3-resisting horizontal force (shear )

4-spiral ties are carrying 10% of the axial load on the column .

       columns reinforcement 

Foundation

Foundation is on of the structural element , the function of the foundation is to connect the structure with the ground .

Types of foundation : 

1- shallow foundation : 

a) single footing ( isolated ) : the type of footing that is support one column .

b) combined footing : the footing that support two column . And we use this type when the two columns are near from each other .

c) strap footing : type of footing connect two single footing together, we use this type when the column is near to the property line son the column will be at a corner of footing so we use the strap to avoid large moment .
d) raft foundation : this type is used when the load is high and the footing will cover more than 60% of the building area .
e) strip footing : this type of dooting to support wall .

2- Deep foundation :

 this type of foundation is used to transfer the loads to the deep ground's layer .

a) piles foundation
b) shaft foundation
c) caissons
d) cylinders

civil engineering

civil engineers can be subdivided into five types :

1- Structural engineers : design and analysis of structures like buildings .

2- Geotechnical engineers : the engineer who study the ground situation ( rocks and soil )

3-Environmental engineers : find a solutions for the environment issues and problems.

4- Water resources engineer : seeks to improve the quantity and quality of water resources.

5- Transportation engineer : the engineer who responsible for design highway, bridges and airport .