SPELMAN HALLS, PRINCETON UNIVERSITY, NEW JERSEY, USA

The development is made up of eight house units. Each house unit is an assembly of precast concrete elements and glazing, with further internal divisions made by thin but relatively heavy partition walls, generally 3⅜in (80 mm) thick. The precast concrete elements, that form the enclosure and structure for each unit, consist of wall and floor panels, stair flights and long precast beams. These 57 ft (17.4 m) long precast beams run along the south and east sides, the latter being a prestressed post-tensioned beam which cantilevers 22 ft (6.71 m) off an internal cross wall and, at the south-east corner, supports the former, which is simply supported at this end. Both beams are 8in (203 mm) wide at the top but 11in (279 mm) wide at the bottom, thus making a shelf to support the floor panels; the floor panels are attached with galvanised steel angles at 4 ft 10in (1.47 m) centres using a ¾in (19 mm) bolt that fixes to ferrules cast in a recess in the top of the slab and in the sides of the beam. Both beams are supported by the internal cross wall. These internal loadbearing walls are 11¼in (286 mm) thick. The other loadbearing wall panels, including those in the stair core and those supporting the far end of the beams, are 8in (203 mm) thick. All the wall panels rest on an upstand wall on a strip footing, both the latter being of cast-in-place concrete construction.

The floor panels are 8in (203 mm) thick but have different spans, the different slab strengths, thus required, being provided by post-tensioning. There is no concrete topping. Most floor panels are attached to the walls by galvanised steel angles at 4 ft 10in (1.47 m) centres using ¾ in (19 mm) bolts that fix to ferrules cast in the tops of the floor panels and the sides of the wall panels. For the joint between the floor panel and the 11¾ in (286mm) internal cross wall, these ferrules are cast both in the vertical edge of the floor panel, connecting to bars projecting from the wall panel below, as well as in the top of the floor panel, connecting by means of steel plates to the adjacent floor panel and by means of steel angles to the wall panel above. Both types of ferrule are placed at 4 ft 10in (1.47 m) centres.

There are two types of horizontal joint between the wall panel units. The 11¾ in (286 mm) internal cross wall, which supports floor panels on each side, also supports the wall panel above, initially by bars projecting from the centre of the lower panel, which are joined through a connector allowing adjustment for height. When in the required position, the gap between the floor and wall panels is filled with mortar or cast-in-place concrete. All the other walls support floor panels only on one side, with a ½in (13 mm) joint, on the other side, between it and the panel above. These panels bear onto steel plates with a locating pin using plastic shims for height adjustment.

The core walls are planned to provide support to the stairs and floor panels. The stair core is top lit by ¾in (19 mm) green-tinted toughened (tempered) glass. There were 61 different types of precast element for this house unit. At each typical floor, there are nine different types of floor panel; the other floors, or the roof, either repeat precisely or use largely the same floor types. All the panel types in the house unit considered are also used in other units.

The post-tensioned beam is stressed, from one end only, to a total prestress of about 160 tons (145 tonnes). Prestressing allows the load applied to be balanced, so that there is no deflection at the end of the cantilever.

Notes:

ferrule n. муфта

lit v. ( p.p. от light) освещённый

shim n. вкладыш

upstand wall подстенок (выступающий из фундамента)

Ответьте на вопросы к тексту

1. What kind of house are the units?

2. Which beams are post-tensioned?

3. How are the floor panels attached to the beams?

4. What do the wall panels rest on?

5. What is the thickness of the floor panels?

6. What is the distance between galvanised steel angles which connect floor panels to the walls?

7. What is the difference between the two types of horizontal joint connecting the wall panel units?

8. What are the core walls planned for?

9. How is the stair core lit?

10. Why is there no deflection at the end of the cantilever?