Space frame type dry coal shed

1.Project Overview Construction of space frame dry coal shed in a power plant is divided into phase one and phase two. The project's first phase is 104 meters in length, 75 meters in span, 37.5 meters in height, with an expanded area of 12,253 square meters and a projected area of 7,800 meters. Phase II: 113.4 meters in length, 75 meters in span, 37.5 meters in vector height, 13,360 square meters in unfolded area and 8,505 square meters in projected area. The dry coal shed is a semi-circular double layer lattice structure. The space frame is in the form of quad-pyramid structure, and the joints are welded bolt balls. The space frame dry coal shed constructed in two phases of the power plant is shown in Figure 1.1.

 

FIG. 1.1 Space frame dry coal shed of a power plant

 

Figure 1.2 Space frame model

2. space frame structure form
1) Space frame structure
The space frame structure of the dry coal shed is a combination of forward-releasing and evacuated quad-cones. The two ends of the space frame are put in a square cone structure and the middle part is evacuated square cone structure. The plane expansion of the space frame of the second phase dry coal shed is shown in Figure 2.1. The net frame structure composed of quadrangle cone, its basic unit is composed of 4 chords, 4 inclined bars of the positive quadrangle cone, namely pentahedron. Cones can be either anteriorupside down. When these four pyramidal structures are arranged to form a space frame, the adjacent cones are connected with an upper chord or a lower chord. According to the combination of the cone and the direction of the chord connecting the cone top, these four cones can form different space structures. Composition is put four pyramid space frames of the four cone bottom edge is parallel to the boundary or vertical, pyramid spread throughout the space frame plane, bottom chord node on the space frame is suitable (down) at the apex of the pyramid, can also be used as the Angle of the inverted pyramid, making tongfang upward, lower chord plane projection for just two sets of parallel lines, each half of the space frame spacing. If the translation value of the upper and lower strings is changed, or the upper and lower strings are rotated relative to each other, and some corresponding strings are taken out appropriately, various forms of quadrangle truss can be obtained. The upper and lower nodes of the square pyramid space frame are respectively connected with 8 rods, and the structure of the nodes is relatively uniform.

 

 

FIG. 2.1 Expansion diagram of phase II space frame dry coal shed

The four ventral rods and the corresponding four lower chord rods of the cone are drawn by jumping on the basis of the four ventral rods of the cone. Make the size of the lower chord mesh twice that of the upper chord mesh. Generally speaking, the number of rods of this kind of space frame is small, and the total number of belly rods is about 3/4 of the total number of belly rods of the four-angle cone space frame, and the lower chord rod is reduced by about 1/2, so the structure is simple and the production cost is low. No change in the upper chord, no evacuation, easy to lay the roof.

1) Roof

A glass fiber reinforced composite wall panel (GRC panel) is arranged on the double layer space frame of dry coal shed. The GRC plate is the abbreviation of the English name Glass Fiber Reinforced Cement. It is a new wall material made of low alkalinity sulphoaluminate cement as cementing material, perlite as light aggregate, fly ash, sand, and so on. It has the characteristics of lightweight, fire resistance and sound insulation, sawing and planing in construction, and convenient and fast installation. Each GRC board is 4m×4m and weighs 1.5 tons.

 

FIG. 2.2 Space frame structure of quad pyramid system

2) Bar
The rods of the space frame is made of seamless steel tubes, whose elastic modulus E=20600Mpa and density ρ=7800kN/m2. The space frame rod is symmetrical, and there are 9 kinds of rod sections. Rod specifications: φ 60×3.5, φ 76×3.8, φ 89×4, φ 114×4, 133×6, φ 140×8, φ 159×12, φ 159×20, φ 219×20.

3) Node

 

FIG. 2.3 Bolt-ball node

The dry coal shed network frame is connected by bolt balls. The shape and structure of bolt balls are shown in Figure 2.3. The bolted ball is a solid ball with bolt holes made in advance. The installation process is as follows: Will be high strength bolt after the initial screw bolts into the ball, the box spanner pull (sleeve, sleeve rotates, via the pin to bolt ball screw drive the high-strength bolts, as a result of the movement of high strength bolt, the fixed on the sleeve pin is relative to the tank after moving gradually, to readjust the place so far, the role of this deep groove is envoys points is not easy to lose. According to the different forces of the rod, the force transmission route and the role of the parts are also different. When the rod is pulled, the force transmission route is tension - steel tube - cone head or sealing plate - bolt - ball, then, the sleeve is not stressed. When the rod is pressed, the force transmission route is pressure - steel tube - cone head or sealing plate - sleeve - steel ball. When the net frame bears the load, for the pull rod, the internal force is transmitted through the bolt, and the sleeve is gradually unloaded with the increase of internal force, for the pressure rod, the internal force is transmitted through the sleeve, with the increase of internal force, the bolt is gradually unloaded. A pin or fastening screw is used only during installation. Check that the bolt is inserted into the ball to see if it is in place. After installation, its use is terminated.

The advantages of the bolt-ball joints are that the manufacturing accuracy is guaranteed by the factory, the site assembly is fast, and the construction period is short, which is conducive to the shortening of the building cycle. The fabrication cost is higher than welding hollow ball joint, but the assembling cost is lower. Its disadvantage is that there are many parts of the node, which increases the manufacturing cost. The slotting on the high-strength bolt is unfavorable to its force, and it is not easy to check whether it is tightened when installing. When installing, special attention should be paid to the sealing anti-corrosion treatment of the joint surface, especially in the southern region with higher humidity, more attention should be paid to anti-corrosion measures.

The dry coal shed space frame used bolt ball has 7 specifications, for φ 100, φ 130, φ 150, φ 180, φ 220, φ 280, φ 330.
5) Support
The second phase of the dry coal shed network frame is supported by two chord nodes at the bottom of the longitudinal side, and each longitudinal side has 15 bearing nodes. The lower part of the space frame adopts the concrete beam with larger stiffness. The bearing node of the space frame structure is supported on the concrete beam so that the overall space frame is subjected to uniform force and is convenient for direct and effective transmission of vertical load. The bearing node is the use of a diameter 220mm bolt ball cut off about a quarter, and then the support plate around the welding, the bolt ball is fixed on the bottom plate, each support with 4 ribs to strengthen. The bottom plate is connected to the lower concrete pier. The lateral thrust is generally borne by the weld and the rib between the bolt ball and the bottom plate.