# Structural Design_2012_Strip_method (2).pdf - Chapter 2...

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11/21/2012 1 Chapter 2 – Strip Method for Slabs Dr.-Ing. Girma Zerayohannes Dr.-Ing. Adil Zekaria Eng. Misgun Samuel Chapter 2- Strip Method for Slabs 2.1 Introduction Different methods of analysis are allowed by EBCS-2 One of these is plastic methods Strip method is a plastic method of analysis 2 Dr.-Ing. Girma Zerayohannes Chapter 2- Strip Method for Slabs The upper bound theorem of the theory of plasticity is presented in chapter 1. The YL method of slab analysis is an upper bound approach to determining the capacity of the slab Disadvantages: An upper bound analysis if in error will be on the unsafe side. The actual carrying capacity will be less than, or at best equal to the capacity predicted, which is a cause for concern. 3 Dr.-Ing. Girma Zerayohannes Chapter 2- Strip Method for Slabs When applying this method it is necessary to assume that the distribution of reinforcement is known over the whole slab. a tool for review. Can be used for design only in an iterative sense, i.e., trail design until a satisfactory amount is found 4 Dr.-Ing. Girma Zerayohannes
11/21/2012 2 Chapter 2- Strip Method for Slabs These circumstances motivated Hillerborg (1956) to develop what is known as strip method for slab design In contrast to yield line analysis, the strip method is a lower bound approach, based on the satisfaction of equilibrium requirements every where in the slab 5 Dr.-Ing. Girma Zerayohannes Chapter 2- Strip Method for Slabs By the strip method, a moment field is first determined that fulfills equilibrium requirements, after which the reinforcements of the slab at each point is designed for this moment field 6 Dr.-Ing. Girma Zerayohannes Chapter 2- Strip Method for Slabs Lower Bound Theorem: If a distribution of moments can be found that satisfies both equilibrium and boundary conditions for a given external loading, and if the yield moment capacity of the slab is nowhere exceeded, then the given external loading will represent a lower bound of the true carrying capacity 7 Dr.-Ing. Girma Zerayohannes Chapter 2- Strip Method for Slabs Advantages: The strip method gives results on the safe side, which is certainly preferable in practice The strip method is a design method, by which the needed reinforcement can be calculated Simple to use, even for slabs with holes or irregular boundaries Economical, encourages use of strong band of steel where needed, such as around openings 8 Dr.-Ing. Girma Zerayohannes
11/21/2012 3 Chapter 2- Strip Method for Slabs 4.2 Basic Principles The governing equilibrium equation for a small slab element having sides dxand dyis: 9 Dr.-Ing. Girma Zerayohannes Chapter 2- Strip Method for Slabs 10 Dr.-Ing. Girma Zerayohannes Figure 1 Chapter 2- Strip Method for Slabs 11 Dr.-Ing. Girma Zerayohannes Figure 1 Chapter 2- Strip Method for Slabs 12 Dr.-Ing. Girma Zerayohannes wyxmymxmxyyx-=-+222222Summing moments about lines parallel to x and y axes and neglecting higher order terms gives,
11/21/2012 4 Chapter 2- Strip Method for Slabs Where w