m7l37

m7l37 - Module 7 Influence Lines Version 2 CE IIT Kharagpur...

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Module 7 Influence Lines Version 2 CE IIT, Kharagpur
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Lesson 37 Moving Load and Its Effects on Structural Members Version 2 CE IIT, Kharagpur
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Instructional Objectives: The objectives of this lesson are as follows: Understand the moving load effect in simpler term Study various definitions of influence line Introduce to simple procedures for construction of influence lines 37.1 Introduction In earlier lessons, you were introduced to statically determinate and statically indeterminate structural analysis under non-moving load (dead load or fixed loads). In this lecture, you will be introduced to determination of maximum internal actions at cross-sections of members of statically determinate structured under the effects of moving loads (live loads). Common sense tells us that when a load moves over a structure, the deflected shape of the structural will vary. In the process, we can arrive at simple conclusion that due to moving load position on the structure, reactions value at the support also will vary. From the designer’s point of view, it is essential to have safe structure, which doesn’t exceed the limits of deformations and also the limits of load carrying capacity of the structure. 37.2 Definitions of influence line In the literature, researchers have defined influence line in many ways. Some of the definitions of influence line are given below. An influence line is a diagram whose ordinates, which are plotted as a function of distance along the span, give the value of an internal force, a reaction, or a displacement at a particular point in a structure as a unit load move across the structure. An influence line is a curve the ordinate to which at any point equals the value of some particular function due to unit load acting at that point. An influence line represents the variation of either the reaction, shear, moment, or deflection at a specific point in a member as a unit concentrated force moves over the member. 37.3 Construction of Influence Lines In this section, we will discuss about the construction of influence lines. Using any one of the two approaches (Figure 37.1), one can construct the influence line at a specific point P in a member for any parameter (Reaction, Shear or Version 2 CE IIT, Kharagpur
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Moment). In the present approaches it is assumed that the moving load is having dimensionless magnitude of unity. Classification of the approaches for construction of influence lines is given in Figure 37.1. Construction of Influence Lines Tabulate Values Influence Line-Equation 37.3.1 Tabulate Values Apply a unit load at different locations along the member, say at x . And these locations, apply statics to compute the value of parameter (reaction, shear, or moment) at the specified point. The best way to use this approach is to prepare a table, listing unit load at x versus the corresponding value of the parameter calculated at the specific point (i.e. Reaction R, Shear V or moment M) and plot the tabulated values so that influence line segments can be constructed.
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This note was uploaded on 06/30/2009 for the course CE 358 taught by Professor Trifunac during the Fall '07 term at USC.

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m7l37 - Module 7 Influence Lines Version 2 CE IIT Kharagpur...

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