Prestressed Slabs And Shells

Made Of Prefabricated Components

by Zenon A. Zielinski*

INTRODUCTION

The Industrial Buildings Re­search and Typical Design Office in Warsaw, Poland, since 1950 has been developing new kinds of pre­stressed and precast concrete struc­tural units. After tests and trial erec­tions, some of these structural units were standardized, published in cat­alogues, and are now being factory produced. As an example, for in­dustrial building roofs "economy girders" of 30 to 180 ft spans are in common use. These members were briefly presented in the Journal of the Prestressed Concrete Institute April1963. '

The aim of this paper is to pre­sent a new erection method for the surface structures (slabs, folded plates and different shells) which were also designed in the Research and Typical Design Office and have been in use since about 1956.

The idea of this new method is presented in Fig. 1. There are pre­fabricated components in the shape of panels (ribbed plates). The bor­der ribs of these panels have holes to conduct the post-tensioning ten­dons through. The separated com­ponents are located one ahead of the other; the joints between neighbor-

"Industrial Buildings, Research and Typical Design Office and Technical University in Warsaw. 1963-64, Visiting Associate Professor at North Carolina State of the Uni­versity of North Carolina at Raleigh, North Carolina

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ing ribs are filled with cement mor­tar. After this mortar hardens (the second day after casting) the tendons are prestressed and the system be­comes a surface structure (slab, shell).

Such a solution, in comparison with common beams or monolithic slabs, has some advantages:

a) It makes it possible to pro­duce in a mechanized and economical way, separated, simplified, and multi-use com­ponents;

b) It minimizes the labor con­sumption of component pro­duction as well as at the as­sembling of the whole struc­ture;

c) It minimizes materials con­sumption; the slab thickness of the components in some cases (roof shells, canopies) can be as thin as one inch;

d) It increases the speed of erec­tion;

e) It creates new possibilities in building shapes.

The erection of structures can be done on movable scaffolding or on movable shores. The tensioning work can be done in a short time after the casting of joints, while the joints are still at low strength (possibly the next day). This means that the movable shores are needed only for a short time, and erection of the structure can be accomplished quite quickly. Fig. 1 shows an example of the structure in the form of a long concave cylindrical shell with ribs on the top side and

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f 2 j 4 s B ~ lii A~

l f5o ! .,

Fig. 1-Method of creating the structure by use of precast panels, tied by means of prestressing tendons a) view b) cross section along the tendons. 1-tendons, 2-precast panel, 3-joint between panels filled with cement mortar, 4-border (rib).

the cables running in the corners of the side ribs. After post-tension­ing, these cables must be covered with a layer of mortar for protection against corrosion. The next step would be to cover the whole shell with (for example) lightweight con­crete precast slabs, bearing on the projecting ribs and with waterproof insulation. But similar structures could be made also in the reversed position-with ribs on the ceiling side. Tendons could also be con­ducted inside the ribs in which case it would be necessary to provide the ribs with holes and grout them with cement emulsion after post­tensioning, which is more compli­cated.

This method could be utilized for a one span simply supported beam or slab scheme as well as for the continuous multispan, one or multiple-way prestressed, slabs and

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shells. Also, if necessary, the ten­dons could be bent up (for shear or continuity purposes) by proper variable location of the tendon con­ducting holes. These ribs could also be strengthened and used for inter­mediate anchoring of the tendons.

Some erected structures illustrat­ing the versatility of this structural method are presented in this paper.

Slabs Fig. 2 illustrates a multistory in­

dustrial building made with two kinds of components-that of a pan­el and a column (structural design by S. Klimek). The depth of the panel is 20 in., and the slab thick­ness about 1.5 in. The column spac­ing in both directions is 19.7 ft. In one direction, plain reinforcement (existing in longer panel ribs) is used; in the other are the prestress­ing tendons. These tendons run

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Fig. 2-lnterior view of a precast panel structure before prestressing. Shown are steel beams and wooden shores support• ing precast panels. The prestressing ten· dons run freely in ribs between panels. After prestressing the beams and wooden shores will be removed to new position.

Fig. 3-lnterior view of a component mush· room precast and post-tensioned industrial structure. The components are: one-story column, cross block, octagonal panel and square panel.

Fig. 4-Erection view of a prestressed slab, assembled of precast equilateral triangular sections and the "knot" block. Shown are the prestressing tendons running freely be· tween triangular panels, over column heads and through bottom holes of the knot blocks.

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through the whole width of the building and after prestressing cre­ate a monolithic continuous slab us­ing panels and columns. The ten­dons are situated freely (between top borders of the panels) and con­ducted through the holes in the columns. The tendon anchorages are located in the exterior columns. Before post-tensioning the panels have been shored-by means of steel collars suspended from the columns and additionally by wood­en shores between columns, as is seen in Fig. 2. After post-tensioning, the empty channels through which the tendons run are filled with con­crete to protect the tendons against corrosion.

This is an example of an econom­ical ribbed and unit-made slab, with­out beams and branches on columns, designed for heavy loads (160, 220, and 320 lbs./sq. ft.). This structure has been used for many industrial buildings (such as drug and elec­trotechnical stores). Panels and col­umns have been produced in con­crete plants.

Figure 3 shows a multistory struc­ture made of four components: one story column, crossed head block, octagonal, and square plate (struc­tural design by W. Zalewski and I. Dragula). This is an example of an economically prefabricated mush­room structure, working as a mono­lithic one. In this case the tendons run through the ribs and the inserts in the slabs in two perpendicular directions.

The weight of each component is less than 6500 lbs. The column spacing in both directions is 19.7 ft. (6 meters). Live loading capacity is 320 lb. per sq. ft. This structure was used mostly for multistory com storages and warehouses.

Figure 4 illustrates a multistory

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building made of equilateral trian­gular panels (designed by the au­thor). In this case a slab structure had been created, prestressed in three directions by means of ten­dons running freely between panel ribs and through the holes in addi­tional knot blocks and over the tops of the columns. Knot blocks and columns of hexagonal cross section are of reinforced precast concrete. Figure 5 shows the erection of a drug production factory in Warsaw. This method has been used for a variety of buildings.

Folded Plates and Shells

Below are given brief descrip­tions of selected examples of shell structures erected on the same ba­sis, ie. as a unit made and tied to­gether by means of tendons.

Railroad Canopy in Sosnowiec

Arch. design by M. Borajkiewicz, structural-by author

Canopies have been designed in two different versions. One exam­ple is a thin walled cylindrical shell made of precast panels. The thick­ness of the panel slab which also determines the structural thickness of the shell is only 1.18 in. The span of the shell, which is equal to the column spacing, is 59 ft. The struc­ture was assembled on movable shores. These shores were moved to a new position after prestressing the .tendons (12 wires-0.196 in di­ameter). The tendons have been conducted through round holes in the border ribs of each shell com­ponent. The support-columns with corresponding branches and tie com­ponents-were prefabricated. The top view of this structure, during and after assembling, is shown in Figs. 6 and 7. In this case the trans­verse stiffness of the thin shell has

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Fig. 5-lnterior view of a triangle slab.

Fig. 6-The top view of the canopy in Sosnowiec. a) during assembly.

Fig. 7-b) after assembly.

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Fig, 8-Jnterior view of the struc­ture of Furniture Factory at Wysz­kov (in row stage).

been produced by the 5.90 in. deep ribs spaced at 4.8 ft.

The shell structure introduced here has very low material con­sumption data. The average con­sumption of materials used is as follows:

Concrete of 4250 psi in shell com­ponents-2.28 inches (as a thick­ness of horizontal layer)

Concrete of 3600 psi in joints. . . . . 0.27 inches

Total concrete con-sumption. . . . . . . 2.55 inches

Steel-high strength ... 0.31 lb/sq ft

Steel-mild (struc- 1 tural).......... 0.7 lb/sq ft

Total steel con- l sumption....... 1.01 lb/sq ft

The Furniture Factory at Wyszkow

Arch. W. Dzierzawski, Z. Pawelski; Struct. W. Zalewski, A. Wlodarz The factory roof is made of "but­

terfly" shells of a concave cross-sec­tion, (Fig. 8) and having a surface 19.7 ft. x 39.4 ft. or 19.7 ft. x 78.8 ft. At a greater span the shells are work­ing along with the columns as a frame system Because of the re-

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Fig. 9-Side view of the structure of Furniture Factory at Wyszkow during assembly of the 12th shell.

quired top lighting it was neces­sary to place the shells at two levels. The girders are composed of seg­ments which enable the roofing to be of various spans using the same components. The manufacturing of the elements took place in steel molds, in this case on the building site. The cantilevered shape of the shells (Fig. 9) allows an easy drain­age of rain water towards the col­umns.

The concrete consumption is 3.5 inches per layer, and the steel con­sumption 2.5 lbs/sq ft, including 0.55 lbs/sq ft of high-strength steel.

The Belchatow Type Shed Roofing

Arch. ]. Glowczewski, S. Sikorski; Struct. W. Zalewski, J. Koca

and author The Belchatow type shed roof­

ing, as used in Poland, is one of the more interesting examples of shell structures made of prefabricated ribbed plates. It is connected by 12 post-tensioning tendons 5 mm. in diameter (0.197 in.). This type of roofing developed in 1958, has been used on three buildings at Belcha­tow and Kalisz.

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Fig. 11-The view of one shed after con­ducting and prestressing of the cables.

Fig. 12-The precast components and as· sembled trusses produce a 98.4 ft. span. They carry the shells and create an air conditioning duct.

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Fig. 1 0-Cross-section of a cylindrical shed· shell of 93.5 ft. length (1 03.5 ft. at the support axis) applied at Belchatow and Kalisz.

1-ribbed plate I, 1.57 in. thick and 4.88 ft. wide (see section A·A) 2-ribbed Plate II 3-cover plate for the air-conditioning duct Ill 4-steel window cross bars 5-post·tensioning cables 12121 5 (0.197 in.) or 18121 5 (0.197 in.) steel strength 235 ksi 6-monolithic concrete made on scaffold­ings, connecting plates I and II 7-plate, 1.57 in. thick 8-glass wool, 2.0 in. thick layer 9-air stratum 10-2 layers of felt

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The characteristic feature of this roofing is the application of a shed in the form of a cylindrical conclave shell (to obtain volume reduction of the building, better light reflec­tion, good water drainage, and in­crease of the moment of inertia and strength), with a cross section as shown on Fig. 10. The structure consists of three prefabricated, 1.57 in. thick slabs with periphery ribs (Figs. 11 and 12). The ribs are provided with holes for external cable conduits. Base plates I and II are interconnected with mono­lithic concrete laid on movable scaf­folding (Fig. 12). Making a 96.3 ft. long and 25.3 ft. wide shed re­quires 19-4.92 ft. wide (at axis) slabs.

The Transverse joints between the slab ribs are filled with cement

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mortar. The stressing of the 12 ten­dons to 235 ksi takes place after the setting of the mortar in the joints and the hardening of the connecting concrete in the bottom connection.

Certain sheds are supported by double girders of a 98.4 ft. span (four sheds developed by one girder), which constitute at the same time the main air conditioning channels (Fig. 13). The girders are also com­posed of prefabricated segments connected by prestressing cables. 'The main segments of the girder­of triangular shape-serve at the same time as supports for lateral walls, which after being placed on slanted precast columns, present an interesting elevation effect to the factory building completed in Ka­lisz (Figs. 13 and 14).

Fig. 13-JIIustration of main girder com· ponents used for lateral wall structure.

Fig. 14-View of the wall made of com· ponents as in Fig. 13.

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Fig. IS-Interior view of the textile factory in Kalisz.

The described structure is of in­terest in view of the economical single-space interiors which were obtained with column spacing 98.4 ft. x 103.5 ft., which is advisable for modern textile industry facilities (Fig. 15).

The Belchatow type shed struc­ture is notable for its mechanical values (double insulation with an air space, good rain water evacuation, snow collection, etc.) as well as technical and economical values (prefabrication, low material con­sumption, reduced volume of the building, etc.). The indices for the shed structure are as follows:

Concrete consumption 4.4 in. layer of plan

Stressing steel consumption 0.75lbs/sq ft of plan

Column steel consumption 2.95lbs/sq ft of plan

Cotton Industry Complex Zdunska W ola

Arch. ]. Glowczewski, S. Sikorski, Struct. ]. Burzycki, Cz. Cywinski,

L. Szwedowski and author The whole complex is situated

under one common roof, built as

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a prefabricated prestressed struc­ture. Measurements of the main building are 800 ft. x 540 ft. (Fig. 16).

In the main parts of the building there are factory halls built as shed structures. All of the sheds have cross-sections as shown in Fig. 17, formed of prefabricated ribbed plates I, II, and III and connected by means of 12 and 18-5 mm. (0.197 in.) post-tensioning tendons. The view of the finished plates, which were made on the site, and assem­bling work is presented in Fig. 18. From these plates, sheds are made using freely supported beams on 80 ft. spans and also into continu­ous beams of 80-100-80 ft. spans.

The characteristic feature of the shed structure is the application of straight-line tendons, laid in groups through enlarged holes in the ribs, and anchored gradually in these ribs according to the moment dia­gram (Figs. 17 and 19).

The sheds were mounted, simi­larly as in Kalisz, on movable scaf­foldings (Fig. 18). All of the sheds are supported by grillage beams of a

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Fig. 16-View of the model of the cotton industry complex in Zdunska Wola.

a) r··--·-----·-·----~--

1---·:_

I

~

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c) 5

'"fl-.,., ./~

J)(:f 1 1 1 1 1 14 r 1 1 'Jtj r 1 1 1 1 1 1 1 1 1 1 l.llljjl 1 1 11 1111 1 !\JI 'll .(_ 2-150 - t . :?t!So" j . ..:.tlf.RJ -----4-

Fig. 17-Scheme of shed-shell applied at the Cotton Works Zdunska Wola: a) cross-sec­tion of the shell, b) scheme of an intermediate cable anchorage, c) scheme of a continuous three bay shell, prestressed with cables of different lengths.

1-ribbed plate I 2-window ribbed plate II 3-cover plate for the air conditioning duct 4-window ribs S-cabies 12 or 18 flJ 5 (0.197 in.) 6-perimeter plate ribs 7-prestressing jack 8-hardware of the ribs holes edges 9-98.4 ft. long girders composed of pre­cast segments connected by prestressing

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Fig. 18-Precast components and assembly

98.4 ft. span, composed also of pre- has been employed in the buildings fabricated segments connected by of the Sporting Center at Rzeszow 18-5 mm. ( 0.197 in.) cables and The sporting hall with suspended supplied with transverse holes shell roofing, as well as the entrance through which the cables of the hall roofed by cylindrical shells and shells are passed. This type of con- the covered swimming pool, are struction has also been used on a completed here in prestressed con-number of other buildings. crete. Only the main swimming

A resembling but quite different pool hall is briefly described below. structural system had been applied The triangular spatial beams at on the finishing work and storage the roof of the swimming pool hall building, where the roofing is in constitute a double covering of a 78.6 the form of 39.4-39.4-39.4 ft. long ft. span and at the same time blow-folded plates and is made of pre- ing ducts for heated air (Fig. 20). fabricated 4.92 ft. wide ribbed In this way condensation of water plates connected by post-tensioning vapors in the moist air of the swim-tendons laid through ribs at the ming pool is avoided. In this case, plate corners. two kinds of precast components in

As in the case of the sheds, the the form of ribbed panels were plates are placed with the ribs up- used. These panels are connected ward, obtaining in this way a multi- together in each corner by means layer roofing with an air gap and of a poured in place joint (Fig. 21). a smooth inside surface which is es- The girders were assembled at pecially recommended for textile ground level and then hoisted by industry halls. On the ribs are means of common winches along placed foam concrete insulating the columns without the use of plates. Sporting Center at Rzeszow cranes (Fig. 21). The swimming

A h A M S S K Pool itself represents a monolithic rc . . artens; truct. t. us, ]. Sieczkowski, A. Zorawski 8 em. thick prestressed concrete

A similar method of construction shell structure.

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Fig. 19-The top view of assembled shed with groups of cables at the bottom (middle of span in the front of the picture)

Fig. 20-Assembly of the unit made thin girders of the swimming pool roof in Rzeszow

Fig. 21-Hoisting of the assembled girders by means of winches

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