RC Lecture 4

RC Lecture 4 - TOPIC 5 PAD FOUNDATIONS LECTURE NOTES...

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CIVL2007 Theory and Design of Structures II RC Component (10 April 2007) page 77 TOPIC 5: PAD FOUNDATIONS - LECTURE NOTES - General A building is generally composed of a superstructure above the ground and a substructure which forms the foundations below ground. The foundations transfer and spread the loads from a structure’s columns and walls into the ground. The safe bearing capacity of the soil must not be exceeded, otherwise excessive settlement may occur, resulting in damage to the building and its service facilities (e.g. water or gas mains). It is important to ensure that settlement, either immediately after construction or during the intended life of the structure, will be uniform and acceptably small. Foundation failure can affect the overall stability of a structure causing it to slide, lift vertically or even overturn. The type of foundation selected depends on a number of factors, namely: c the depth of soil to a suitable bearing stratum, c the bearing capacity of the stratum, c the type of soil, c the proximity of existing structures and their foundations, and c an assessment of relative costs. Some typical foundations are shown in the following figures. In general the design of foundations requires an understanding of the principles of soil mechanics. In this course, we will deal only with the design of simple pad foundations (also known as spread footings or isolated footings ) for an individual column. Pile foundations will not be covered. Reference will be made to the Hong Kong Code of Practice for Foundations (2005) throughout this lecture. The Code is available for viewing at: http://www.bd.gov.hk/english/documents/index_crlist.html
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CIVL2007 Theory and Design of Structures II RC Component (10 April 2007) page 78 Figure 1. Types of Foundations
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CIVL2007 Theory and Design of Structures II RC Component (10 April 2007) page 79 Figure 2. Types of Foundations (Warner et al. 1998)
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CIVL2007 Theory and Design of Structures II RC Component (10 April 2007) page 80 Figure 3. Types of Foundations (Wang and Salmon 1998)
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CIVL2007 Theory and Design of Structures II RC Component (10 April 2007) page 81 A spread footing is a generally a shallow footing usually made of reinforced concrete. It transfers load from column(s) or wall(s) to the underlying soil or bedrock. The load is spread over a larger area of ground than simply bearing the columns and walls directly on ground. Their design is dictated by several factors but most importantly the bearing capacity of the soil. Such foundations consist of strips or pads or concrete (or other suitable materials) and are common in residential and commercial structures. Bearing pressure The actual distribution of soil pressure on the underside of a spread footing will vary depending on its flexibility, position of load application, and the type of soil. To simplify footing design in practice, it may be assumed that the pressure is uniformly distributed or linearly varying (depending on the applied load) throughout the area of the base. This assumption normally
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This note was uploaded on 10/24/2009 for the course BENG Civl2007 taught by Professor A.smith during the Spring '09 term at HKU.

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RC Lecture 4 - TOPIC 5 PAD FOUNDATIONS LECTURE NOTES...

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