Урок 4.10

Текст A

THE SEARS TOWER, CHICAGO, ILLINOIS, USA

Part II

Each column on the grid lines is supported by a caisson of about 7 to 10 ft (2.13 to 3.05 m) in diameter and 120 ft (36.58 m) length cored into rock. The tops of the caisson are tied together by a 5 ft (1.52 m) deep concrete mat which also serves to transfer a design horizontal wind force of 4500 tons (4080 tonnes) to a stratum of clay. For vertical transportation the building is divided into three zones, each 30 to 40 storeys high. Double deck lifts serve these ‘main’ floors from which ‘local’ lifts function, stopping at each floor in the zone The steelwork structure is clad with a black aluminium skin and has bronze-tinted glass.

Under wind loads, the structure works in a similar manner to a tube without openings cantilevering from ground level. The bundled tube system provides two internal web frames in each grid direction, in addition to those on the outside. The effect is to reduce shear lag on the flange frames, so there is a more uniform distribution of axial load among those columns on lines perpendicular to the wind force. An even distribution indicates good cantilever efficiency. The bundled tube system makes good use of the internal columns to increase the building's stiffness. The wind sway is about 0.3in (7.5 mm) per storey, the design wind pressure being 65 lb per sq ft (317 kg per sq m) at the top. The exterior columns were clad with 4in (100 mm) of insulation and had gravity circulation of inside air around them in order that at a design temperature of -20°F (-29°C) outside, the column was within 7°F(3.8°C) of the inside temperature of 75° F (24°C).

The steelwork was brought on to site as 'tree' sub-assemblies consisting of a two-storey column and half-length beams on either side. The 'trees' weigh 15 tons (13.84 tonnes) and are bolted together at beam mid-points, these connections being designed for shear only. The column connections above and below are welded and are mid-height between the floors. Almost all the welding necessary was done at the factory and this welding was extensively tested.

The bundled tube system is applied to very high buildings which can be split into tubes. The tubes may have different areas or shapes in plan. Of the completely regular ways of subdividing a plan shape into identical area modules, apart from the square, only hexagonal and triangular modules are possible.

Notes:

bundled tube system система пучка труб

even adj. равномерный

flange frame каркас с фланцем

hexagonal adj. гексагональный

shear lag n. поперечная инерция

sub-assembly n. монтажный блок

'tree' n. древовидная конструкция

web frame решётчатый каркас

sway n. колебание