Lecture 5 Shallow Foundations PDF

Mousl university 2nd semester : Building Construction 2 Architecture department Date : xx / xx / xxxx Iraq CONCRETE FRAME STRUCTURES FOUNDATIONS Building Construction 2 Assistant Teacher. : Adil Khalil Definition Fou...

Mousl university 2nd semester : Building Construction 2 Architecture department Date : xx / xx / xxxx Iraq CONCRETE FRAME STRUCTURES FOUNDATIONS Building Construction 2 Assistant Teacher. : Adil Khalil Definition Foundation : The structure, that transmits the load of the building to the soil. Choosing a kind of foundation depends on: 1. the ground conditions 2. the groundwater conditions 3. the site, the environment (the buildings nearby) 4. the structure of our building Requirements: 1. structural requirements: safe, be able to carry the load of the building 2. constructional requirements: schedule, minimal resources, minimal cost The specialties: 1. it is expensive and difficult to repair 2. usually it is constructed under the ground, so it is out of sight 3. bad/ misapplied foundation could demolish the building The mistakes: 1. construction technology mistakes 3. planning mistakes: the type of foundation is not suitable for the ground layers / for the building Kinds of foundations in frame structure system( skeleton ) Solid raft foundations Beam and slab raft foundations Cellular (void) raft foundations  BALANCED foundations AND CANTILEVER foundations A balanced foundations which is also called as strap foundations consists of two separate footings connected by a strap beam. Balanced footing is required where the one of the footing has limited space for bearing, or if there is any restriction over the transfer of pressure from the footing to the ground. This case may arise where there is difference in soil bearing capacity. The loads in a balanced footing is transferred from one footing to the other by means of cantilever action, thus it is also called as a cantilever footing. Cantilever foundation Balance foundation Balanced footing is different from a combined footing in the sense that a combined footing has a single footing and a balanced or cantilever footing has two separate footings which are connected by a strap beam. The strap beam transfers the loads from external footing to the main footing by means of cantilever action. A balanced footing and cantilever footing is used under following conditions : 1.When the foundation does not have sufficient area to transfer the loads safely to the ground, such as in case of footing built on the property line( off center). It is also used when the soil supporting the foundation does not have enough bearing capacity to transfer the loads safely and area of the footing cannot be increased beyond the limit. 2. When the new structure is built near the existing building or structure, and the existing building cannot support the loads from new structure, then new column and footing has to be provided near the existing structure, but there will be limited space for footing. 3. the cantilever foundations are used when there is no possibility of digging near the foundations of nearby buildings due collapsed it. Combined footings can also be used for supporting two columns, but when the distance between the two columns is very large, it becomes uneconomical due to large bending moment to support two columns on a single footing, then a strap beam is used for connecting such footings.