Friday, November 23, 2012

Effect of Settlement on the Structure - Foundations.

If the structure as a whole settles uniformly into the ground there will not be any detrimental effe on the structure as such. The only effect it can have is on the service lines, such as water an sanitary pipe connections, telephone and electric cables etc. which can break if the settlement  considerable. Such uniform settlement is possible only if the subsoil is homogeneous and the loa distribution is uniform. Buildings in Mexico City have undergone settlements as large as 2 m However, the differential settlement if it exceeds the permissible limits will have a devastatin effect on the structure.

According to experience, the differential settlement between parts of a structure may no exceed 75 percent of the normal absolute settlement. The various ways by which differentia settlements may occur in a structure are shown in Fig. 13.1. Table 13.1 gives the absolute an permissible differential settlements for various types of structures.

Foundation settlements must be estimated with great care for buildings, bridges, tower power plants and similar high cost structures. The settlements for structures such as fill earthdams, levees, etc. can be estimated with a greater margin of error.

Figure 13.1 Definitions of differential settlement for framed and load-bearing wall
structures (after Burland and Wroth, 1974)

 Table 13.1 a Maximum settlements and differential settlements of buildings in cm.
(After McDonald and Skempton, 1955)

Table 13.1b Permissible settlements (1955, U.S.S.R. Building Code)

Table 13.1c Permissible differential settlement (U.S.S.R Building Code, 1955)

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