» Method of Sections

Method of Sections

1850
Truss bridge model analysis in civil engineering workspace using Method of Sections.

A technique used in statics to determine the internal forces in specific members of a truss structure. The method involves making an imaginary cut through the members of interest, isolating a portion of the truss. By applying the three static equilibrium equations ([latex]\Sigma F_x=0[/latex], [latex]\Sigma F_y=0[/latex], [latex]\Sigma M_A=0[/latex]) to the isolated section, the unknown member forces can be solved directly.

The power of the 方法 of Sections lies in its ability to find forces in members located in the middle of a complex truss without first having to solve for the forces in all the preceding members, as required by the Method of Joints. The key is to choose a section cut that passes through no more than three members whose forces are unknown. This is because there are only three independent static equilibrium equations available for a 2D rigid body.

Once the section is cut, one of the two resulting pieces of the truss is chosen for analysis. All external forces (loads and support reactions) acting on that piece are shown, along with the unknown internal forces of the cut members. These internal forces are typically assumed to be in tension (pulling on the joint). A negative result in the calculation simply indicates that the member is actually in compression (pushing on the joint). The moment equilibrium equation, [latex]\Sigma M_A=0[/latex], is particularly powerful. By summing moments about a point where two of the three unknown forces intersect, the third unknown force can often be solved for with a single equation.

UNESCO Nomenclature: 3305
– Civil engineering

类型

抽象系统

中断

实质性

使用方法

广泛使用

前体

  • 牛顿运动定律
  • concept of static equilibrium
  • free-body diagrams
  • understanding of trusses as assemblies of two-force members
  • Varignon’s theorem for calculating moments

应用

  • manual analysis of bridge trusses
  • design of roof trusses for buildings
  • analysis of crane structures
  • educational tool for teaching statics and equilibrium
  • quick 确认 of forces in specific members from a computer analysis

专利:

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Related to: method of sections, truss analysis, statics, equilibrium, structural analysis, civil engineering, internal forces, Ritter’s method, bridge design, frame structures.

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