Upload
laura-hernandez
View
227
Download
0
Embed Size (px)
Citation preview
7/27/2019 Foundation design.ppt
1/34
7/27/2019 Foundation design.ppt
2/34
Introduction The primary function of all structural elements is to
transfer the applied dead and imposed loading, fromwhichever source, to the foundations and
subsequently to the ground. The type of foundation required in any particular
circumstance is dependent on a number of factorssuch as: the magnitude and type of applied loading,
the pressure which the ground can safely support,
the acceptable levels of settlement,
the location and proximity of adjacent structures.
7/27/2019 Foundation design.ppt
3/34
Types of foundation1. Pad foundation
2. Combined foundation
3. Strip footing
4. Raft Foundation
5. Piled Foundation
7/27/2019 Foundation design.ppt
4/34
Pad foundation
7/27/2019 Foundation design.ppt
5/34
Combined foundation
7/27/2019 Foundation design.ppt
6/34
Strip footing
7/27/2019 Foundation design.ppt
7/34
Raft Foundation
7/27/2019 Foundation design.ppt
8/34
Piled Foundation
7/27/2019 Foundation design.ppt
9/34
Loading The loading effects which occur in foundations, are
generally one or more of the following three types:
horizontal forces due to lateral loading such as wind
on the supported structure or friction between theunderside of the base and the ground horizontalforces are not usually of sufficient magnitude to affectthe size of foundations,
vertical forces due to columns and/or walls and thebearing pressure from the ground underneath the base,
moments due to loading from columns and/or wallsetc. which are eccentric to the centroid of the base.
7/27/2019 Foundation design.ppt
10/34
Base Pressures The magnitude of the pressure in each
case is determined using elastic
analysis. Case 1: Uniform Pressure (compression
throughout)
7/27/2019 Foundation design.ppt
11/34
Base Pressures Case 2: Varying Pressure (compression
throughout)
7/27/2019 Foundation design.ppt
12/34
Base Pressures Case 3:Varying Pressure
(compression over part of the base)
7/27/2019 Foundation design.ppt
13/34
Pad Foundation Design1. Calculate the plan size of the foundation using
the permissible bearing pressure and the criticalloading arrangement for the serviceability limitstate.
2. Calculate the bearing pressure associated withthe critical loading arrangement at the ultimate
limit state.3. Assume a suitable value of thickness (h) and
determine the effective depth (d).
7/27/2019 Foundation design.ppt
14/34
Pad Foundation Design4. Determine the reinforcement required to resist
bending.
5. Check that the shear stress at the column face isless than 5 N/mm2 or 0.8 cu f,whichever is thesmaller.
6. Check that the direct shear stress at a section
1.0dfrom the column face is less than vc fromTable 3.8.
7. Check that the punching shear stress on aperimeter 1.5dfrom the column face is less than
vc from Table 3.8.
7/27/2019 Foundation design.ppt
15/34
7/27/2019 Foundation design.ppt
16/34
Design Data:
Characteristic dead load on column 800 kN
Characteristic imposed load on column 300 kN
Characteristic concrete strength fcu = 40 N/mm2
Characteristic of reinforcement fy = 460 N/mm2
Net permissible ground bearing pressure pg = 200kN/m2
Column dimensions 375 mm 375 mm
Exposure condition severe
7/27/2019 Foundation design.ppt
17/34
Solution
7/27/2019 Foundation design.ppt
18/34
Solution
7/27/2019 Foundation design.ppt
19/34
Solution
7/27/2019 Foundation design.ppt
20/34
Solution
7/27/2019 Foundation design.ppt
21/34
Solution
7/27/2019 Foundation design.ppt
22/34
7/27/2019 Foundation design.ppt
23/34
Solution
7/27/2019 Foundation design.ppt
24/34
Solution
7/27/2019 Foundation design.ppt
25/34
Solution
7/27/2019 Foundation design.ppt
26/34
Combined Foundation
Designed when there are 2 columneither when they are relatively close
together or when one of the columns isadjacent to an existing structure.
The shape can be rectangular,
trapezoidal or T-shape.
7/27/2019 Foundation design.ppt
27/34
Example 5.33:Combined Foundation An inverted T-beam combined foundation is required
to support two square columns transferring axialloads as shown in Figure 5.125. Using the dataprovided, design suitable reinforcement for the base.
Design Data: Characteristic dead load on column A 450 kN Characteristic imposed load on column A 450 kN Characteristic dead load on column B 750 kN Characteristic imposed load on column B 750 kN
7/27/2019 Foundation design.ppt
28/34
Characteristic concrete strength fcu = 40 N/mm2Characteristic of reinforcement fy = 460 N/mm2
Net permissible ground bearing pressure pg = 175 kN/m2Nominal cover to centre of main reinforcement 40 mmColumn A dimensions 350 mm 350 mmColumn B dimensions 350 mm 350 mm
7/27/2019 Foundation design.ppt
29/34
7/27/2019 Foundation design.ppt
30/34
7/27/2019 Foundation design.ppt
31/34
7/27/2019 Foundation design.ppt
32/34
7/27/2019 Foundation design.ppt
33/34
7/27/2019 Foundation design.ppt
34/34