Name: finding zero-force members in trusses
Uploaded: 2025-05-22T09:06:02.000Z
Duration: 1 min 30 s
Channel: JoVE

Pręt kratownicy, który nie doświadcza naprężeń w warunkach obciążenia, nazywany jest prętem o zerowej sile.
W przypadku połączenia kratownicowego z dwoma prętami niewspółliniowymi i bez obciążenia zewnętrznego lub reakcji podparcia, oba pręty muszą być prętami o zerowej sile.
Dla tego połączenia rysowany jest diagram swobodnego ciała. Suma sił wzdłuż kierunku pionowego jest równa zero, co sprawia, że siła wzdłuż BA wynosi zero. Użycie równania równowagi wzdłuż kierunku poziomego daje siłę wzdłuż BC równą zeru.
W przypadku połączenia z trzema prętami, w tym dwoma prętami współliniowymi, trzeci pręt jest prętem o zerowej sile, pod warunkiem, że w tym połączeniu nie jest stosowane żadne obciążenie zewnętrzne ani reakcja podporowa.
Ponownie, narysowanie wykresu swobodnego ciała i zastosowanie warunków równowagi statycznej dowodzi, że siła wzdłuż CA wynosi zero.
Rozważ kratownicę z podporą rolkowo-sworzniową i obciążeniem zewnętrznym na złączu E.
Identyfikowane są połączenia z trzema prętami, w tym dwoma prętami współliniowymi. Warunek zerowej siły na tych połączeniach oznacza, że FG, EH i FD są prętami o zerowej sile.
Jednak ED nie może być prętem o zerowej sile ze względu na obciążenie zewnętrzne.

<ol>
	<li>R. C., Hibbeler Inżynieria Mechanika Statyka, Pearson. str. 282</li>
</ol>

element o zerowej sile

Rozetka to konstrukcja składająca się z cienkich elementów połączonych na końcach stawami. Rozetki są powszechnie stosowane w inżynierii i architekturze do stabilizacji i wzmacniania konstrukcji, takich jak mosty, dachy i wieże. Elementy rozetki są projektowane tak, aby przenosiły obciążenia poprzez rozciąganie i ściskanie, co pozwala konstrukcji wytrzymać siły zewnętrzne.

Jednym z kluczowych pojęć w projektowaniu rozetek jest pojęcie elementów o zerowej sile. Odnosi się to do elementów rozetki, które nie przenoszą naprężeń podczas obciążania. Podczas analizy rozetki, pewne elementy mogą mieć zerową siłę, co oznacza, że nie przyczyniają się do ogólnej nośności konstrukcji. Identyfikowanie elementów o zerowej sile jest istotne dla optymalizacji projektowania struktur rozetkowych.

Istnieją dwie warunki dla istnienia elementów o zerowej sile. Po pierwsze, jeśli tylko dwa elementy niekolinearne tworzą łącze rozetki, i żadne obciążenie zewnętrzne lub reakcja podporowa nie jest stosowana do łącza, oba elementy muszą być elementami o zerowej sile. Po drugie, jeśli trzy elementy tworzą łącze rozetki, a dwa z nich są współliniowe, trzeci element jest elementem o zerowej sile, jeśli żadna siła zewnętrzna lub reakcja podporowa nie ma składowej działającej wzdłuż tego elementu.

<img alt="Figure 1" src="/files/ftp_upload/14284/14284_PT_Fig_1v2.svg" style="text-align: center; height: 350px;" />

Rozważmy rozetkę z podporą rolkową i sworzeń oraz obciążeniem zewnętrznym w łączu E. Tutaj łącza H i G są łączami trzy-członowymi z dwoma współliniowymi elementami. Zastosowanie drugiego warunku, elementy EH i FG są elementami o zerowej sile. Korzystając z warunku zerowej siły dla łącza F, DF jest elementem o zerowej sile. Jednak ze względu na obciążenie zewnętrzne, ED nie może być elementem o zerowej sile.

Elementy o zerowej sile są istotne dla utrzymania stabilności i równowagi rozetki, optymalizacji projektu konstrukcji oraz redukcji kosztów materiałowych i konstrukcyjnych.

Element o zerowej sile

Kratownica to rama, która składa się ze smukłych elementów połączonych na końcach przegubami. Kratownice są szeroko stosowane w inżynierii i architekturze do ...

Education

JoVE Core

Mechanical Engineering

Inżynieria mechaniczna

Unit 1

Jednostka 1

Structural Analysis

Analiza strukturalna

KEY TERMS AND CONCEPTS

Kluczowe terminy i pojęcia

Zero-Force Member

finding zero-force members in trusses

Trusses are frameworks made of slender members that connect at their ends by joints. Engineers and architects use them to stabilize and strengthen structures such as bridges, roofs, and towers. Truss members carry loads through tension and compression so the structure can handle external forces.

A key part of truss analysis is spotting zero-force members. A zero-force member is a truss member that carries no stress under loading conditions. During analysis, some members may show zero force, which means they do not add to the load-bearing capacity of the structure. Finding these members helps improve the design of truss structures.

There are two common conditions for zero-force members. If only two non-collinear members meet at a joint, and no external load or support reaction acts on that joint, both members are zero-force members. If three members meet at a joint and two are collinear, the third member is a zero-force member, as long as no external force or support reaction has a component along that member.

A truss with a roller and pin support and an external load at joint E shows how these rules work. Joints H and G each have three members with two collinear members, so EH and FG are zero-force members. At joint F, the same idea makes DF a zero-force member. ED is not a zero-force member because the external load affects it.

Zero-force members are important for truss stability and equilibrium. They also help optimize structural design. In many cases, identifying them can reduce material use and construction cost.

Finding Zero-Force Members in Trusses

introduction to structures

Structure Types and Force Paths

Structures are systems of interconnected members that support or transfer forces and handle the loads placed on them. Engineers can find the internal forces in a structure by breaking it apart and drawing free-body diagrams for individual members or groups of members. This helps show how structural elements behave and how the whole system stays stable under load. There are three main categories of structures: trusses, frames, and machines. Trusses are stationary structures that stay rigid when...

simple trusses

Simple Trusses and Triangular Frames

Simple trusses are planar trusses built from slender members joined at points in one flat plane. They are designed to carry external loads while using less material and keeping weight low. A truss is a structural framework, and the simple truss is one of its most basic forms. The most basic simple truss uses three members arranged in a triangle. That triangular shape is naturally stable and rigid because of its geometry. It gives students a clear starting point for understanding how larger...

method of joints

Truss Forces Using the Method of Joints

The method of joints is used to find the forces in structural trusses. It relies on equilibrium, which means the forces at a joint must balance. In this model, the truss members are connected by frictionless pins. For a plane truss, the members lie in the same plane. That means each joint has a coplanar and concurrent force system. The analysis begins by identifying and labeling all the joints in the truss. Next, each joint is isolated and shown in a free-body diagram. This diagram includes...

method of joints: problem solving i

Truss Joint Force Analysis by Equilibrium

The method of joints uses equilibrium to find forces in structural trusses. It treats the truss members as being joined by frictionless pins. For each joint, the forces acting there must balance. That balance makes it possible to solve for the member forces one joint at a time. Here, a truss has 20 N acting at joint C and 10 N acting at joint D. The method of joints is used to find FCB, FDC, FDB, and FAD. The analysis starts with a free-body diagram of joint C. Free-body diagram means drawing...

method of joints: problem solving ii

Truss Force Analysis at Joints A to E

Truss force analysis at joints A to E uses the method of joints to find the force in each member. The truss has frictionless joints, a wall support, and a roller support. A 150 N force is applied at joint A, and the member forces are solved from joint to joint. First, the angle between members AC and AB is found using the inverse tangent of the ratio of BC to AB. This gives an angle of 67.38°. A free-body diagram of joint A is then drawn, and each unknown force is split into vertical and...

zero-force member

Trusses are frameworks made of slender members that connect at their ends by joints. Engineers and architects use them to stabilize and strengthen structures such as bridges, roofs, and towers. Truss members carry loads through tension and compression so the structure can handle external forces. A key part of truss analysis is spotting zero-force members. A zero-force member is a truss member that carries no stress under loading conditions. During analysis, some members may show zero force,...

method of sections

Truss Member Force Analysis by Sections

Truss member force analysis by sections finds the force in selected members of a truss. In this problem, forces F1 and F2 act at joints B and D. The goal is to determine the forces in members EF, DC, and DF. The method uses the idea that a truss in equilibrium also has each of its sections in equilibrium. A free-body diagram of the whole truss is drawn first. The moment equation about joint A is then used to estimate the support reaction at point E. Next, a cut is made along a sectional plane...

method of sections: problem solving i

Truss Member Force Calculation by Sections

Truss member forces can be found with the method of sections in a symmetrical roof truss. The structure here includes vertical, diagonal, and horizontal members. Each horizontal member is 4 m long. The vertical members FB and HD are 4 m long, and member GC is 6 m long. The roof truss carries loads at several joints. Joints F, G, and H each have a 2 kN load. Joints A and E each have a 1 kN load. To start the analysis, moment equilibrium is used at point A. The force and distance values are...

method of sections: problem solving ii

Truss member force analysis by sections finds the forces in selected members of a wall-mounted truss. The structure here includes diagonal, vertical, and horizontal members. The known loads and member lengths are used to solve for the forces in CB, GB, and GH. A cut is made through members CB, GB, and GH. The right side of the truss is then isolated as a free-body diagram. Next, the moment equilibrium equation is taken about point G. This step gives the force in member CB as 4 kN, and the...

space trusses

Space Truss Forces and Stability

A space truss is a three-dimensional truss made from members joined at their ends. It is the 3D version of a planar truss. These frameworks often use ball-and-socket joints, which help the structure stay stable and flexible under load. Space trusses are used in many construction projects because they can adapt to complex forces. Their basic building block is the tetrahedron. A tetrahedron has six members and four triangular faces. Engineers can build larger space trusses by adding one joint...

space trusses: problem solving

3D Truss Force Analysis with Joint Equilibrium

A space truss is a three-dimensional truss structure made of members connected at their ends. It often uses ball-and-socket joints to form a stable and versatile framework. Because it can handle complex loads, this type of structure is used in many construction projects. The example begins with a tripod made from a tetrahedral space truss. A ball-and-socket joint is located at C. The height and the lengths of the horizontal and vertical members are known. A tensile force is applied at joint D.

frames

Frame Analysis in Structural Systems

Frames are important parts of many mechanical and structural systems used every day. They are valued for stability and for their ability to bear heavy loads. A frame is built from two-force members and multi-force members, and the parts are connected with pin joints. Trusses are different because they are made entirely of two-force members. Frames appear in many practical settings. They can support beams and columns in buildings. They are also used in automobile chassis construction. In the...

frames: problem solving i

Jib Crane Reaction Forces in Frames

Jib crane reaction forces in frames are found by analyzing the pin joints, the cable tension, and the load carried by the pulley. The structure in this problem has an external load suspended from the pulley, and the member sizes are shown in the figure. Because the pulleys are frictionless, the force balance can be worked out step by step. The frame has two main parts. Member BD is a two-force member, which means it is a straight part loaded only at its two ends, D and B. Those end forces are...

frames: problem solving ii

Hydraulic Hoist Force Analysis

Hydraulic hoist force analysis shows how to find the forces in key members of a simple frame. The load is 1 kN, and the structure is represented with known member dimensions. In this setup, BF and BD act as two-force members. EFG and EDC are multi-force members, so each one is analyzed with a free-body diagram. The first step is to study member EFG. The inclined force in BF is split into vertical and horizontal parts. Then the moment equilibrium condition is applied at joint E. Using this...

machines

Cutting Pliers as a Force-Multiplying Machine

Cutting pliers are a machine that helps transmit force through movable, pin-connected members. In this example, the handles and cutting edges work together to cut wire by turning an input force into a larger output force at the jaws. When equal and opposite forces are applied to the handles, the cutting edges move toward each other. They then apply equal and opposite reaction forces to the wire. These reaction forces are greater than the forces applied to the handles, which is why the wire can...

machines: problem solving i

Toggle Clamp Force Analysis

A toggle clamp can be analyzed to find its clamping force from a known handle force. In this example, a 200 N force is applied at the handle. The clamp is used in holding and clamping tasks in woodworking, metalworking, and assembly operations. The toggle clamp is a machine structure made of movable, pin-connected multi-force members. These members form a stabilized system that transmits force. Member CD is a two-force member, which means the forces at its ends are equal in magnitude and...

machines: problem solving ii

Lifting Tong Force Analysis

Lifting tong force analysis shows how forces move through a pin-connected machine. The structure uses movable sections DAF and CBG with member AB linking them together. Because these parts work as connected members, the load can be studied with equilibrium methods. The example starts with a 100 kg load at point E. The load weight is found by multiplying mass by gravity, which gives 981 N. The cable tension acts upward and balances that weight. Since the structure is symmetrical at E, the...

key terms and concepts

Learn how to identify zero-force members in trusses using joint rules, with a worked example that shows how they affect design and cost.

Finding Zero-Force Members in Trusses | JoVE K12

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

Finding Zero-Force Members in Trusses

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