structures Flashcards
dead load and live load
dead load and live load
dead loads
are permanent static loads on a structure that remain relatively constant overtime.
example: weight of the structure itself, beams, walls.
love loads are produced by the occuoancy
cold form sections
sreel sheets.
They are of extremely thin profiles.
Probles
1.2mm, 2mm, 3mm.
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example
:
angle iron
c section
“Built up sections” are made up from two or more or hot rolled sections exclusively.
cold formed
They are made by means of connecting them.
lateral torsional buckling
lateral torsional buckling
This occurs when the load applied on the flexural member causes it to displace laterally and twist.
The displacement occurs due to the magnitude of the applied load and the twisting occurs if the
torsional Stiffness of the member section is insufficient applied. If the member u
In comparison to the load
Us more prone to lateral torsional buckling, it has a
smaller flexural capacity: the member will fail eavily. The member is prevented from developing is full
flexural strength.
cavity walls
A Two single leat walls built with a gap
in-between.
I act as one wall
m
There are Steel ties built into them, tying them together - Cavity ties.
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3. Cavity ties should be provided at Spacing go 900mm horizontally & 28450mm vertically
4* Each single leat wall can be of a different thickness
These walls have better thermal and acoustic insulation
faced walls
Faced wall
a faced wall is a wall built of two different material
It is structurally treated as abre same thickness wall
built with weaker material.
factors affecting the strength of a slender wall
All Factors pertaining to short walls (In the Same way)
2) Number and Sizes of Caps at the edges off Mostar joints. ↑ ↓
I
3) Lateral Load on wall (wind etc.) ↑ ↓
strength properties of timber
Tension Parallel to grain.
Bending Parallel to grain.
Compn // grain
Compn perpendicular grain
Shear // Grain
Modulus of Elasticity.
Perpendicular
factors affecting the strength properties of timber
Moisture in Timber
2) Growth characteristics.
3) Duration of Load
4) Size & Shape of Member
models of failure of solid timber flexural members
Splitting of Bottom Fibre
2) Lateral Torsional Buckling.
3) Shearing along Grain.
Members
4)Bearing at supports at concentrated loads
5)deflection
fiber saturation point
When Timber starts drying first the free moisture is evaporated Ones the total amounts of free moisture is evaporated, the timber has reached the Fiber Saturation Point
When timber dries further than “Fibre Sat point”,”
*Strength proporties will increase Incect or fungal attacks will decrease
at this point the moisture Content is about 25% - 30%
Only the bound moisture is present
timber will not have any reduction in vol
cellular walls
The stiffness of a cellular wall is greater since the overall thickness is more and slenderness is less
It has more strength for a Smaller amount of material
factors of affecting the load transfer capacity
nail joints
diameter of nail Penetration of head point
Penetration of point side
Strength class of timber
Number of nails.
*hammered into Joints
*Clean Shaft and point
screw joints
Should be inserted perpendicular
to grain
Point Side penetration -2x
Number of screw.
Strength Class of timber.
*transfer Shear load as well
as withdrawal loads.
* driven into joints.
Why is timber Considered as an hygroscopic and an isotropic material.
2020/
hygroscopic material - Possesing the ability to absorb and Shred water from a Environment
isotropic-
Proportis of timber material does depend on direction. Unlike steel which ever the direction you take strength properties remain the same
timber seasoning
Timber Seasoning
I brought downto equilibrium moisture contenter this process. is called timber seasoning.
Go air dried.
kiln.
* timber treatment is to make sure that it’ll not decay, not attacked by insects, fungi.
local timber -graded into a grades
method of treating timber
method of treatment.
1 Brush application / Sprayru 2) Open tank method
3) Hot & Cold Tank method. 9) Pressure Treatment
Wood Based Products.
Wood Based Products.
1 Particle Board -chip bearch.
a) Fibre Board (you can’t see particles in this
high
MDF, HDF.
(medium
-3) Ply wood
density fibre
t
Built-up Sections
3) Laminated Timber-
advantage of plywood
advantage of plywood
* you have grains running in both directions, good strength in both directions.
* Cost effective.
why masonary walls should not be subjected to bending moments, unless accomplained with a sufficient Compressive load.
Masonary is generally very good in resisting compression has good Compressive strength…
However it is weak
when subjecte to tensile strength.
If a masonary wall is axially loaded and there is a chance of it built buckling and falling, as it will be in both tension and compression
Since masonary is poor in bending and tension, the wall will crack (assuming that self weight is 2000)
axial Toad
If theres the wall was an elastic material & the Stress
distribution will be (draw)
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any element subjected to compression can buckle and it is one mode of faliure
Tension develops and then the wall.
fails
Tention develops on the inner curve of the “Column and Cashing develops so the wall fails due to buckling & Crushing.
effective thickness
its not the actual thickness of the wall its effective thickenss depebds on varius factors such as
Factors affecting effective thickness.
Coefficient of stiffness (K)
thickness of wall (t).
gap between Piers from center to center (SP)
(4 breadth of pier (bp).
Thickness of wall with Pier (tp)
How effective thickness varies with thos factors
(K) increases (+) EFincreases ↑
(SP) increases. EF (bp) increases t
(TP) increases
BASICALY WHEN ALL THIESE INCREASE ET INCRESE
Why 2 different PFOS is applied for love load and dead load
Pfos dead load= 1.4
PFOS live load= 1.6
Live loads create uncertainty due to its variance therefor it requires higher PFOS comp dead load which certain and can be calculated accurately
Slenderness ratio
When slenderness ratio increases the tendency to buckleup increases
Factors effecting the strength of slenderwalls
1.Slenderness ratio of the walls
2.Gaps in the edges of the wall
Due to shrinkage and workmanship motabed dsnt continue right throughout the bed
Lateral loads (wind load) acting on the load increases the weaker the wall
Glu laminated timber
Glu large number of thin planks which is horizontal or vertical laminated, glu planks in the grain directing the longitudinal direction
Adv laminated timber
Larger cross sections are possible by stacking on top of each other
Larger longer members by gluing and by vertical joints shouldn’t coincide
Better quality timber
By removing deflect and gluing the planks again
Efficient sections
By the top and bottom most plank has a strong variety of timber middle weaker timber where the stresses are low. Aka selective layering
Weaved members are possible
Grains to the longitude axis there for stronger
Easy cheap to treat
Why masonry walls should not be subjected to bending moments unless accompanied by sufficient compressive loads
Masonry good atresistong compression not at tension/tensile strength
If axialy loaded it may buckleup and fail in both tension and compression
Since it’s poor at bending and tension it will Crack
Under compression ot will buckleup
Tension develops on the inner curve the column crushing develop and the walls fail.
Modes of failure of solid timber flexual members
Splitting of bottom fibers
Tensile strength affected over the allowable stress the bottom fibers splits
Lateral torsional buckling
Bottom fibers stays straight while the top fibers buckle causing the timber to twist
Sjear along the grain
Timber is weak in the horizontal shear.
Timber is strong g on the horntal shear
Deflection (draw)
Bearing at supports at co centrated loads
Moisture content
%of water contained in timber
Moisture cont= weight if water in timber sample/ weight of water in dry timber sample × 100
moisture will! The strength of the timber and will decay
As it’s subjected to seasoning
Fiber saturation point
When timber starts drying first free moisture evaporated (water inbetween the cells draw)
When evaporated ot reaches its first evaporated point. The moisture content is 25-30%
Only bind moisture remains( moisture inside the cell)
Timber will not have any reduction in volume, strength proposes increases. Insect and fungi attacks will decrease.
Equilibrium moisture content
When u further dry timber than bond moisture will start to evaporate then timber cell tubes will contract and the volume of the timber will reduce.
Below fiber saturation point it will reach the moisture content. This os where we use are timber structuraly
Moisture content is 8-20%
Factor effecting the strength properties of timber
Moisture in timer
Growth characteristics of timber- slope of grains , knots and waves
Duration of loads
Size and shape of timber
Hudroscopic
Possessing the ability to absorb and shed water from env to the env
Composite slabs
Precast + insitu cast
AdV
Insitu conc= pured to obtain the thickness to woth hold the load
Lighter oannels easy to transport and cheaper
Form work not needed pre cast pannel act as a deck
Series of simply supported pannels
Pre stressed concrete advantage
Small ant of construction material
Longer soan and length can be achieved
Few joints needed than traditional RC there low maintenance
Reduce the formwork as multiple uses of formwork is possible
Rapid construction with better quality
Requires small amt of construction materials
DISADVANTAGES OF PRE STRESSED CONCETE
REQUIRE HIGHER strength concrete amd higher Tensile strength
Requires additional special equipment like Jackson and Anchorage
Concrete pretending requires skilled technology and high skill workers
Higher construction cost than RCC
Role of reinforcement on a concrete beam
Reinforcement are designed to carry transverse external loads,
Loads cause bending shear and tortion across their lenth
Concrete stronger in compression not jn tension
Steel reinforcement is to take Tensile stress of the reinforce concrete
Safe bearing capacity of soil
Dense soil has high bearing capacity
Loose clay has low bearing capacity
Peat has no bearing capacity
Normal soil has a about 100m
Geotypicak surveys are dine to find the soil properties msucj a s the bearing capacity.
Most typical foundation is pad footing provided separately for each column
And the column are categorized into shallow and deep foundation
