Урок 4.9

Текст A

THE SEARS TOWER, CHICAGO, ILLINOIS, USA

Part I

This office block is important not for its extreme height but for the original and simple method by which it resists the huge wind loads on it. The building is 1450 ft (442 m) high, with 109 storeys above ground, and has a gross floor area of 4.4 million sq ft (408 760 sq m).

The building was designed to have maximum repetition of elements and building methods and this was a major factor in successfully achieving the required cost and speed of construction.

From street level up to level 50, the building is made up of nine 75 ft (22.86 m) square area modules which combine to form a larger square with sides having an overall dimension of 225 ft (68.58 m). Below, occupying a larger plan area than the office tower, are three basement floors formed inside 2 ft 6in (750 mm) thick concrete walls in a nearly square shape; these walls support the basement floors and are braced by them. At level 50 the building is stepped back, two of the corner area modules being omitted. The other two corner area modules are omitted at level 66, leaving five area modules in a cruciform plan shape, and another three area modules - at level 90, leaving only two going to the full height. The framed tube of each module consists of deep built-up columns at 15 ft (4.57 m) centres welded to deep built-up beams at the floor to floor distances, typically 12 ft 10in (3.91 m). Typical column and beam depths were 3 ft 3in (1.00 m) and 3 ft 6in (1.06 m) respectively. Major columns, those on grid line intersections, have flanges varying in area from 24 x 4in (600 x 19 mm) at the top to 24 x 4in (600 x 100 mm) in the box sections at the bottom; beam flanges vary from 10 x 1in (250 x 25 mm) to 16 x 2.7in (400 x 69 mm). Two adjacent framed tubes share one set of beams and columns.

Two-level high belt trusses are provided on grid lines below levels 66 and 90, which are set-back levels; four-level belt trusses are provided below level 33 and at the very top of the building. The trusses serve to spread out the concentrations of gravity force that occur in members at set-back levels, to reduce the effect of differential column shortening under the wind and gravity loads and to increase the overall lateral stiffness of the building by some 15%. The floor is made composite with the truss by shear studs. Every six floors the span direction of the trusses is altered by 90 degrees to equalize loading on the columns.

Notes:

cruci­form adj. крестообразный

gravity force сила тяжести

repetition n. повторение