Analysis of metal structures and pile foundations of exhaust pipe

The projected structure of the exhaust tower is designed to support the process equipment - high-rise exhaust pipe.

13.07.2023
Analysis of metal structures and pile foundations of exhaust pipe

Author of the design model: "Promstroy engineering" LLC

Description of construction

The projected structure of the exhaust tower is designed to support the process equipment - high-rise exhaust pipe.

The designed structure of the extraction tower is square in plan, with dimensions in axes 12,0x12,0 m with a supporting metal frame. The height of the structure frame is 94,0 m. The top mark of the exhaust pipe is +98.0 m.

The frame of the extraction tower is a spatial jointed bar lattice tetrahedral metal structure of variable cross-section in plan. From +0,500 to +64,300 the height dimension of the pyramidal part of the tower changes from 12,0x12,0m to 5,0x5,0m, from +64,300 to +94,000 the height dimension of the prismatic part is 5,0x5,0m.

Inside the tower in the center of the tower there is a gas discharge barrel with an internal diameter of 2800. The jointing of the gas discharge barrel elements is carried out through socket joints, so that the effects of expansion or contraction of the barrel due to temperature differences are not transmitted to the steel structures of the tower. Interceptors are used as aerodynamic oscillation dampers - three spiral ribs from 58,800 to +98,000. To support the load-bearing steel frame of the gas discharge barrel and transfer horizontal loads, horizontal tower diaphragms are provided at 9,500, +15,700, +21,700, +31,200, +39,700, 47,900, +56,100, +64,300, +72,500, +80,700, +88,900, +94,000, which are at the same time transition platforms and maintenance platforms (including for regular maintenance of the gas discharge barrel joints).

Vertical chords (columns) of the tower, braces, brace beams, vertical and horizontal joints are made of steel welded longitudinal and seamless hot-formed pipes according to GOST 10704-91, GOST 20295-85, GOST 8732-78. Beams, elements and horizontal connections of platforms are provided from I-beams according to GOST R 57837-2017, channels with parallel edges of flanges according to GOST 8240-97, angles according to GOST 8509-93, round pipes according to GOST 10704-91. Vertical and horizontal connections, braces, beams to columns and between each other are hinged. Connection of chords of variable cross-section between each other (assembly joints) - rigid.

The spatial and geometric invariability of the exhaust tower frame is ensured by systems of vertical and horizontal connections and braces, rigid disks of service areas (diaphragms), as well as rigid joints between the tower columns and the foundation.

The foundation of the extraction tower is a complex of 2 pile pedestals connected in pairs by strip foundations (braces). Vertical breakaway forces are transmitted by foundation bolts, horizontal forces are transmitted by spurs made of channels welded on the sides of the base plates.

The foundation is supported by 8 bored piles with 620 mm outside diameter. The depth of the footings of the piles is provided below the frost depth at the mark - 3,000 m from the surface of the planning ground (absolute mark 28,000 m). The depth of pile sinking from the the bottom of the foundation footings is 6.15 m.

Brief description of the design scheme and analysis methodology

The structure analysis was performed using the licensed certified software - LIRA-SAPR 2019.

A spatial finite element model (FEM) is assumed for the analysis. The finite element model is a complex spatial system consisting of finite elements such as "universal spatial bar FE" - finite element type No. 10, "universal rectangular shell FE" - finite element type No. 41, "universal triangular shell FE" - finite element type No. 42, "universal quadrilateral shell FE".

The analysis is based on the finite element method with the use of displacements and rotations of the nodes of the design model as the main unknowns. In this regard, the idealization of the structure is made in a form adapted to the use of this method, namely: the system is represented as a set of bodies of a standard type, called finite elements, attached to the nodes.

The foundation analysis was carried out taking into account the stiffness above the foundation structure and the perception of loads (forces) directly through the lower support section of the tower columns.

Two design situations were considered in the analysis of the designed pile foundation:

Option No. 1: Pile foundation operation with regard to the contact of the footings (consideration of forces in the walls and the foundation slab during ground support);
Option No. 2: Pile foundation operation with consideration of force transfer to the piles without contact between the foot of the pile and the ground (maximum pile loads).

Both options were analyzed in a special METEOR module for the combined design combinations of forces. The reinforcement was also selected taking into account the combination of the two variants.

The stiffnesses of the soil base were calculated in the specialized module LIRA SOIL taking into account the characteristics of the soils presented in the geological surveys.