Showing posts with label STRUCTURE ANALYSIS. Show all posts
Showing posts with label STRUCTURE ANALYSIS. Show all posts
Friday 19 February 2016
BAR BENDING SCHEDULE IMP
Civil Engineering Competitive Exams Books :
Wednesday 1 July 2015
Characteristic strength of concrete
Characteristic strength of concrete is one of the important properties of concrete which indeed unanimously by design engineeror any other person involved in the construction sector.
The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested at 28 days (fck)- as per Indian Standards (ACI standards use cylinder of diameter 150 mm and height 300 mm). The characteristic strength is defined as the strength of the concrete below which not more than 5% of the test results are expected to fall.
This concept assumes a normal distribution of the strengths of the samples of concrete.
Normal Distribution curve on test specimens for determining compressive strength
The above sketch shows an idealized distribution of the values of compressive strength for a certain number of test specimens. The horizontal axis represents the values of compressive strength in MPa. The vertical axis represents the number of test samples for a
particular compressive strength. This is also termed as frequency.
The average of the values of compressive strength (mean strength) from the graph is 40 MPa. The characteristic strength (fck) is the value in the x-axis below which 5% of the total area under the curve falls. From the graph we can clearly say that 30 MPa is the characteristic strength of the given concrete mix. The value of fck is lower than fcm (40 MPa- mean strength) by 1.64σ, where σ is the standard deviation of the normal distribution.
So we can say the given concrete mix has a characteristic strength of 30 MPa or it is a M30 grade mix.
M- Mix
* Note: For a 95% confidence level k=1.64 , hence k value varies on the confidence level of the experiment
Definition:
Characteristic strength of concrete is the strength of concrete specimens casted and tested as per given code of practice and cured for a period of 28 days; 95% of tested cubes should not have a value less than this value.
About piles
End Bearing Piles ::-
1:-In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock.
2:- The load of the building is transferred through the pile onto the strong layer.
3:-In a sense, this pile acts like a column.
4:-The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.
Friction Piles ::-
1:-Friction piles work on a different principle.
2:- The pile transfers the load of the building to the soil across the full height of the pile, by friction.
3:-In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil.
NOTE: In practice, however, each pile resists load by a combination of end bearing and friction
Thursday 23 October 2014
10 Tallest Bridges In The World== >
1. Millau Viaduct, France – 343 metres (1,125 ft) tall. Opened in 2004, this 4 lanesbridge is a cable-stayed bridge that spans the valley of the River Tarn near Millau in southern France. The bridge has 7 piers of different heights. The second one is the tallest with a height of 244.96 m (803 ft 8 in) – making it the tallest structure in France, taller than the Eiffel Tower!
3. Sutong Bridge, China – 306 metres (1,004 ft) tall. Opened in 2008, this bridge spans the Yangtze River between Nantong and Changshu
8. Great Belt East Bridge, Denmark – 254 metres (833 ft) tall. Opened in 1998, this bridgeruns between the Danish islands of Zealand and Funen. It is the third tallest bridge in Europe
2. Russky Bridge, Russia – 320.9 metres (1,053 ft) tall. Located in Vladivostok, the bridge was completed in 2012. It connects the mainland part of the city with Russky Island
4. Akashi-Kaikyo Bridge, Japan – 298.3 metres (979 ft) tall. This beautiful suspension bridge was opened in 1998. It links the city of Kobe on the mainland of Honshu to Iwaya on Awaji Island. It is the tallest suspension bridge in the world
5. Stonecutters Bridge, Hong Kong – 298 metres (978 ft) tall. A high level cable-stayed bridge which spans the Rambler Channel in Hong Kong, connecting Nam Wan Kok, Tsing Yi island and Stonecutters Island. The bridge deck was completed and opened to the public in 2009
6. Yi Sun-sin Bridge, South Korea – 270 metres (890 ft) tall. Except of being the 6th tallest bridge in the world, it’s also the second tallest suspension bridge in the world and the fourth longest suspension bridge in the world
7. Jingyue Bridge, China – 265 metres (869 ft) tall. This cable-stayed bridge in Jianli County was opened in 2010 and crosses the Yangtze River
8. Great Belt East Bridge, Denmark – 254 metres (833 ft) tall. Opened in 1998, this bridgeruns between the Danish islands of Zealand and Funen. It is the third tallest bridge in Europe
9. Zhongxian Huyu Expressway Bridge, China – 247.5 metres (812 ft) tall. Completed in 2010, this bridge crosses the Yangtze River in Zhong County
10. Jiujiang Fuyin Expressway Bridge, China – 244.3 metres (802 ft) tall. A Cable-stayed bridge under construction and should be completed by the end of 2013. With a main span of 818 m (2,684 ft) it will become one of the longest cable-stayed bridges in the world upon its completion
Friday 18 October 2013
Overview of arches
Overview of arches
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Arches
An arch is an opening spanned by a collection of wedge shaped pieces (voussoirs)
which stay in position by pressing in on one another. The joints
between the pieces appear to radiate from some central point lying
within the opening, and sometimes from points which lie outside, so
every type of arch has a characteristic curvature. The simplest and
visually most natural shape for an arch is the semicircle but many other
designs have been used.
How an Arch "Works"
The central voussoir (keystone)
is traditionally the last to be set into position to "lock" the whole
thing into a strong and stable structure. A keystone is not always
necessary, however; there may be a joint at the apex instead, as is
common in Gothic arches. Gravity tries to pull the keystone
downwards, but the thrust is carried on either side by the voussoirs
immediately flanking it. These in turn have their total thrust carried
through the whole semicircle of pieces in a sideways direction until it
reaches the vertical part of the wall and can descend directly to the
foundation. In short, an arch works because vertical weight is deflected
into sideways thrust and transferred to the walls.
The graphic at right shows the principal parts of a conventional
semicircular arch. Most arches of this type are made slightly taller
than true semicircles -- thespring line is above the impost line --
simply because it looks "normal." The smaller inset drawing shows how
an arch converts the downward pressing weight of the wall above it into
outward thrust.
Limitations of the Arch
Because of the sideways thrust the arch is not a stable structure in
itself, because that thrust tries to make the bottom of of the structure
spread out on either side. To stop this happening there must be enough
solid material at the side to act as flanking buttresses. For
this reason an arch is more naturally placed within the body of a wall
rather than at either end. Series of arches are suitable for bridge
building or aqueducts because the river banks or valley sides make
excellent buttresses. Similarly, long colonnades consisting of repeated
arches, such as the ancient Roman aqueducts, need sizeable lengths of
unperforated wall at each end to beat the combined thrust of the entire
series, though intervening posts or piers can themselves be quite
slender.
Solid flanks are unnecessary where colonnades are completely circular,
for their entire weight becomes a single, unified downward thrust. The
best example of such a construction is the Colosseum at Rome, consisting
of three stories of circular arch colonnades surmounted by a visually
solid fourth-story wall. The inherent stability of the arch is also
testified to by the Colosseum; built between 70 and 82 A.D., the
structure is still standing and is still structurally sound.
