👉Allowable settlement (part one)
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▶️The allowable settlement is defined as the acceptable amount of settlement of the structure and it usually includes a factor of safety.
The allowable settlement depends on many factors, including the following:
*The Type of Construction – For example, wood-frame.
buildings with wood siding would be much more tolerant than unreinforced brick buildings.
*The Use of the Structure – Even small cracks in a house might be considered unacceptable, whereas much larger cracks in an industrial building might not even be noticed.
*The Presence of Sensitive Finishes – Tile or other sensitive finishes are much less tolerant of movements.
*The Rigidity of the Structure – If a footing beneath part of a very rigid structure settles more than the others,the structure will transfer some of the load away from the footing.
However, footings beneath flexible structures must settle much more before any significant load transfer occurs.
Therefore, a rigid structure will have less differential
settlement than a flexible one.
*Aesthetic and Serviceability Requirements – The allowable settlement for most structures, especially buildings, will be governed by aesthetic and serviceability requirements, not
structural requirements.
Unsightly cracks, jamming doors and windows, and other similar problems will develop long before the integrity of the structure is in danger.
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Bent up bars: Are the main reinforcements bent at a suitable angle to act as shear reinforcements.
Reinforcements are bent up to the supports/ends where greater compressive force occurs.

Bars Are Bend Near At Support To:

1- To resist shear force .
2-To resist (NBM) adjacent at supports.
3- To increment the strenth of RCC in  slab.
4- Bent Up bar can abate the amount of steel.
5- Bent up bars in slab is more strong form normal slab.
6- Bent up bars sufficiently increase the deformation capacityof slabs as compared to those not having bars bent.
7- By extending bars up to supports, we can also lower the risk of brittle failure due to higher compressive stresses causing the structure to collapse.

SETTLEMENT OF FOUNDATIONS (part two)
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The vertical downward movement of the base of a structure is calied settlement and its effect upon the structure depends on
its magnitude, its uniformity, the length of the time over which it takes place, and the nature of the structure itself.
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Foundation settlement may be caused by some or a combination of the following reasons:
1. Elastic compression of the foundation and the underlying soil.
2. Inelastic (or plastic) compression of the undertying soils, which is much larger tban the elastic compression. The
inelastic compression can be predicted by the theory of consolidation.
3. Ground waser lowering. Repeated lowering and raising of water level in loose granular soil tends to compact the soil and cause settlement of the ground surface. Lowering of water level in fine grained soils cause consolidation settlement.
4. Vibrations due to pile driving, blasting and oscillating machineries may cause settlement in deposits of granular soils.
5. Seasonal swelling and shrinkage of expansive clays.
6. Ground movement on earth slopes , such as surface
erosion, slow creep or landslide.
7. Other causes such as adjacent excavation, mining
subsidence, underground erosion, etc.
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A certain amount of elastic and inelastic settlement of foundations is unavoidable,and it should be taken into account in design.
Provided the settlement is uniform over the whole area of the building and is not excessive, it does little damage. If, however, the amount of settlement varies at different points under the building, giving rise to what is known as relative or differential settlement, stresses will be set up in the structure.
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These may be relived in the case of brick structure, for example, by the setting up of a large number of cracks at the joints, but in more rigid structures, overstressing of some structural members might occur. It is suggesed that the allowable pressure should be selected such that the maximum settlement of any individual foundation is 2.5 cm.
It has also been suggested that the differential settlement of uniformly loaded continuous foundation and of equally loaded spread foundations of approximately the same size, is unlikely to exceed half the maximum settlement, and that normal structures such as office buildings and flats can satisfactorily withstand differential settlements of about 18 mm between adjacent columns spaced 6 to 8 m apart.
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▶️ Doubly reinforced beam
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👉beams with tension reinforcement only( reinforcement to assist concrete carry tension) are called singly reinforced beams

👉 due to different reasons, it isn't always possible to use singly reinforced beam and it becomes necessary to assist concrete to carry compression too. And beams with both tension and compression reinforcement are called doubly reinforced beams.

▶️ doubly reinforced beams are advantageous over singly reinforced beams for the following reasons :

*Reduces sustained deflection( long term deflection)

* Increases ductility

* Enhances tension mode of failure

* Decreased depth of section, leading to astetics
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