anranr Truss structure (Truss structure) refers to the anranr Truss was the red Truss beam's, is a lattice of beam type structure. anranr truss structure is often used in the large span plant, the exhibition hall, the stadium and other public buildings and Bridges. Since most used in construction of roof structure, anranr truss usually is also called the roof. anranr truss type a, according to anranr truss appearance is divided into: two, to anranr truss geometric composition means cent: 3, according to by the horizontal thrust points: anranr truss internal force characteristics Each stem a stress are on a one-way pull, pressure is given priority to, through the XiaXian stem and web members on the reasonable decorate, can adapt to the internal structure of the moment and shear distribution.
Due to the level of the direction of pull, pressure realized their own internal balance, the whole structure not produce thrust bearing level. The structure arrangement flexible, application range is very wide. anranr truss beam and real abdomen beam (that is, we generally see beam) than in bending aspect, as will the tensile and pressed on both ends up and down in cross section layout, and increases the behavior and the inside, make to the same materials dosage, achieve greater bending strength. In the shear, through the reasonable layout of abdominal stem, able to transfer to support the shear gradually.
So whether bending or shear, anranr truss structure can make material strength into full play, so as to apply to various span building roof structure. The more important significance is that it will turn the under the action of abdominal beam of internal complex stress state into anranr truss rod in a simple and compressive stress state, so that we can understand the directly force distribution and transfer, facilitate the change of the structure of and combination. Only by external load node and the ideal hinge and whose system say anranr truss structure. It is by some stem axis given over to a bit of engineering structure abstract and a simplified. anranr truss bridge and roof built in the first been practical.
The ancient Romans build across the Danube anranr truss with the features of the LeiJiangQiao upper structure (found in Rome relief sculpture, the Renaissance, Italian architect (pola dior Palladio) began to use wooden anranr truss bridge appear lang type, ShangShi, house type anranr truss. The earliest metal anranr truss is completed in 1845, suitable for ShangShi wood anranr truss similar anranr lattice truss, and in the second year of the triangular warren type anranr truss. anranr truss according to the characteristics of the different classification. A, according to the shape of anranr truss is divided into:
1. Parallel string anranr truss (easy to decorate double structure; to standardized production, but stem force distribution is not enough even);
2. Fold the string anranr truss (such as parabolic anranr truss beam, appearance with uniformly distributed load of simply supported beam under bending moment figure, stem force distribution uniformity, the use of economic material, structure is more complex);
3. The triangle anranr truss (stem force distribution uneven, structural layout more difficult, but cant meet roof drainage need).
Second, to anranr truss geometric composition way points:
1. Simple anranr truss (by a basic hinge and in turn increase two yuan triangle body composition);
2. The united anranr truss (by some simple anranr truss according to the same system composed of simple geometric rules together);
3. Complex anranr truss (different from the former two other static DingAn Rachel's truss).
According to three, by horizontal thrust points:
1. No thrust, LiangShiAn red truss (and the corresponding real beam structure comparison, empty, XiaXian rod on the rate of bending, abdominal shear stress, rod are reasonable, timber economy);
2. Have thrust GongShiAn Rachel's truss (arch ring and arch structure in the eqm good entirety, facilitating construction, cross, and a strong ability to save steel materials). Mechanical characteristics is structural internal force only axial force, and no bending moment and shear. The mechanical characteristics reflect the actual structure of the main factors, the axial forces say anranr truss Lord internal force. The actual structure (such as reinforced concrete roof, riveting (bolt) meet or welding steel truss bridge anranr) because of the nodes in the ideal hinge "wait for a reason, also exist small bending moment and shear, the axial force also have very small effect (for rigid and anranr truss stem node cross-sectional area of inertia and the size of the ratio of different, generally is reduced by 5% ~ 0.1%), called time internal force.
Consider the balance of each node anranr truss, node bear HuiJiao forces interracted, successive establishment of each node projection balance equation, can work out all the unknown stem force, this kind of method says node method, the most suitable for simple anranr truss.
According to the characteristics of solving inappropriate judge first zero bar and, if possible, to avoid solution simultaneous equations. Sometimes only a few stem a demand for internal force or joint anranr truss and complex anranr truss, node method can't work, need to use section method. Selectively truncation stem a (usually less than three pole) to anranr truss for balance of local object, can be obtained by the balance equation for stem a axial force.
For some anranr truss (such as K type anranr truss), combined application of the node method and section method is more effective. For many of the complex anranr pole pieces or space truss anranr truss, the best choice is computer methods.