Strengthening of an existing reinforced concrete structure
2.1 Analysis background:
Perhaps the most important and most difficult task faced by the structural designer is the accurate estimation of the loads that may be applied to the structure during its life. After loads are estimated, the next problem is to decide the worst possible combinations of these loads that might occur at one time.
The loads that will be used in this project are dead and live loads.
Dead loads are loads of constant magnitude that remain in one position. They include the weight of the structure under consideration, as well as any fixtures that are permanently attached to it. For reinforced concrete building, some dead are the frames, walls, floors, ceiling, stairs, roofs and plumping.
Reasonable estimates of structure weights may be obtained by referring to similar structures or to various tables available in the most civil engineering handbooks.
Live loads are loads that can change in magnitude and position. They include occupancy loads, warehouse materials, construction loads, overhead service cranes, equipment operating loads and many others. In general they are induced by gravity. These loads, which are taken from table 4-1 in ASCE 7-95, act downward and are distributed uniformly over entire floor.
Load factors:
The ACI code (9.2) states that the required ultimate load carrying ability of the member U provided to resist the dead load D and the live load L must at least equal
U = 1.4D + 1.7L
The Loads carried by the structure are transferred from one structural element another until it reaches it final destination to the supporting ground. The loads that come from slabs to beams can be estimated according to the slabs design system and the geometry of these slabs. In one direction slabs the beam is carrying half of the slab as a rectangular or square shape but in two way slabs the each beam around the slab is carrying triangle or trapezoidal shape of the slab.