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结构机械制造工学模拟试题答桉
Chapter 3 (Chapter 7 in book)
Analysis of statically Determinate Truss
§1. Introduction
A truss is defined as a structure formed by a group of members which are assumed to be connected by pins and uniform in cross-section.
Trusses use material very efficiently and are consequent economical for spanning long distances. They are commonly used in bridges, towers and roof. Crane, etc.
A classic truss is shown in Fig.3-1
Fig.3-1
The truss is comprised by chords and webs .Chords can be divided into top and bottom, and web into vertical and diagonal.
The point at which web members connect to chord is called panel point (joint).
The length between two joints on the same chord is called panel.
The following assumptions are made in order to simplify the analysis of trusses:
Truss members are connected together at their ends by frictionless pins.
Fig.3-2
The centroidal axes of members are all straight lines .those meeting at a joint all intersect at a common point.
Fig.3-3
External loads and reactions are applied on the truss only at its joints.
Fig.3-4
According to above assumptions members of a truss are subjected to axial force only. In other words, the members in a truss are all two-force members.
It is customary to designate the tension as the positive axial force and compression as the negative.
Fig.3-5
§2. Classification of Trusses
Simple truss
A plane truss is formed by beginning triangle, and then units of two components are added on the triangle. Trusses formed in this way are called simple trusses.
Fig.3-6
Compound truss
Two or more trusses are connected according to two rigid pieces rule or three rigid pieces rule, the trusses formed in this way are termed compound trussed.
Fig.3-7
Complex truss
Trusses that cannot be classified as either simple trusses or compound are called.
Fig.3-8
§3. Method of Joints
In this method by a section passed completely around a joint, the joint is isolated from the rest of truss.
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