Application of precast reinforced concrete products and structures for industrial construction in the USSR

UDC 693.56: 725.4 (47)

K. N. K A R T A S H O V

Director oj' the Central Research Itatitute of lnclustriul Bliildings atld Structures, Acuderr~y uf Building anrl Architecture ( USSR)

I N T R O D U C T I O N

The volume of industrial construction in the Soviet Union is constantly increasing. One of the main technical measures ensuring execution of the planned voluines of work is the progressive introduction of prefabrication of buildings and structures and the change-over froin conventional building operations to the assembly of structures inade of members prefabricated at specialized factories. The coefficient of prefabrication (ratio of cost of precast members to the total cost of the building) of industrial buildings is constantly increasing.

Precast reinforced concrete is the principal material used in the USSR for loadbearing and enclosing structures of mass-scale industrial buildings with Spans up to 30 m and overhead cranes of a lifting capacity up to 125 tons, as well as for almost all industrial struct ures (galleries, t unnels, tan ks, hoppers, cooling towers, etc.).

Every year the volume of precast reinforced concrete used for industrial construction increases. In some cases buildings and structures. including the foundations, are entirely precast.

The growth of the application of precast reinforced concrete structures is illustrated in Table I .

T A B L E 1

APPLlCATlON OF PRECAST REINFORCED CONCRETE IN THE USSR

( in ccihic nletres)

1958 1960 1965 (planned) - - - --

Total quantity of reinforced concrete for construction in the USSR 43,500,000 57,700,000 88,700,000

Including precast 18,500,000 30,400,000 58,000,000 Applicatiori of precast reinforced concrete

for industrial construction 8,300,000 1 3,700,000 30,700,000 lncluding for industrial buildings:

Ordinary precast structures 6,700,000 10,900,000 22,200,000 Prestressed concrete structures 250,000 1,500,000 5,600,000

Precast reinforced concrete units of industrial buildings and structures are manufactured at specialized factories producing all the required members completely. The number of such factories is constantly being increased in conformity with the plan for the development of the application of precast reinforced concrete.

Reduction of the costs of precast reinforced concrete structures may be achieved, first of all, by reduction of the number of manual operations required for manufacture and by raising the degree of mechanization of all processes at the factory. To this end the number of standard sizes of structures should be reduced and their mass production increased.

S T A N D A R D I Z A T I O N O F I N D U S T R I A L B U I L D I N G S A N D

S T R U C T U R E S

For several years, standardization of buildings and structures has been performed for various industries including all the niain branches (iron and steel, chemical, mining, machine- building, light, food, radio and electronics, instrument-making, pulp and paper, etc.) with a view to increasing the mass production of structures used in the USSR on the basis of a standard modular system. The main dimensions of buildings (spans, height, column spacing, etc.), loadbearing and enclosing structures, as well as some other parameters, such as values for loads acting on the structures (lifting capacity of cranes, service loads acting on the floors, etc.) and for climatic effects (snow and wind loads, minimuin and inaximum tem- peratures, etc.) have been standardized, this being of very great importance since the territory of the USSR stretches from the Arctic to subtropical regions.

The requirements of standardization are met to the greatest extent by one-storey multi- bay buildings with internal rain gutters. These buildings are applied most widely in the USSR.

One-storey buildings being constructed at present amount to as much as 80 per cent, while multi-storey buildings amount to 20 per cent of the total quantity (in area) of industrial buildings. In future the percentage of one-storey buildings will increase.

Technical and econoniic analysis of designs of erected buildings, as well as standard designs covering more than 70,000,000 m%f production area, made it possible to find the most widely used spans, column spacing, height and other dimensions of the buildings. This then made it possible to specify as obligatory for use in the large-scale construction of one- storey buildings :

Spans of 12, 18, 24, 30 and 36 m; Longitudinal column spacing of 12 m and, in some cases, for small buildings and for

external rows of columns, 6 m ; Height of columns up to the bottom of roof structures: 4.8, 6.0, 7.2, 8.4, 9.6, 10.8, 12.6,

14.4, 16.2 and 18.0 m. Up to 10.8 m the height of tlie columns changes every 1.2 m and for greater heights every

1.8 m. Tl-ie minimum column height for buildings equipped with overhead cranes is assumed

to be 8.4 m. For overhead cranes of 10, 15, 20 and 30-ton lifting capacities similar overall dimensions above the railhead and a similar height (1.2 m) are set for the crane girders at a column spacing of 6 and 12 m, the girders being reinforced concrete or steel.

All this has made it possible to standardize one-storey buildings very considerably, assuming only 10 heights for thern.

For multi-storey buildings erected on a mass basis the following parameters have been approved :

Spans of 6, 9 and 12 m; Longitudinal column spacing of 6 m with future use of 12 m; Storey height (measured from floor to floor) of 4.8, 6.0 and 7.2 m. The specification of the heights of buildings as multiples of a module of 0.6 m allowed

the use of wall panels 1.2 m, 1.8 m, and 2.4 m high. Such panels are properly joined with window panels, the height of which is also a multiple of the 0.6 m module.

The standardization of industrial engineering structures in the USSR has been developed to a lesser extent than that of buildings. At present standard designs are available only for some kinds of structures, although a large amount of work is being performed on the stan- dardization of all main kinds of structures, determining for each of them a small number of optimum capacities, dimensions, etc., depending on the application of the structure.

This work leads, in particular, to widening the field of use of precast and composite reinforced concrete structures. We shall examine the possibility of erecting one type of

structure of precast members (foundations, columns, girders, slabs, etc.) designed to be used for other kinds of structures as well.

In spite of the fact tliat in some cases this step may involve an insignificant increase in material consuniption, on the whole this results in a saving of construction costs since the reduction of the number of standard dimensions of precast members simplifies their man- ufacture at factories.

S T A N D A R D P R E C A S T R E I N F O R C E D C O N C R E T E S T R U C T U R E S

F O R I N D U S ' T R I A L B U I L D I N G S

On the basis of various building Parameters it became possible to work out standard load- bearing and enclosing precast reinforced concrete structures, reducing the number of stan- dard sizes to a minimum, which is particularly important for their manufacture at factories. These structures are included in the catalogue of precast reinforced concrete structures for industrial construction, the use of which is obligatory throughout the USSR.

Tlie catalogue includes structures with various kinds of reinforcement, manufactured by various production methods. This allows local organizations to choose those structures which correspond to the equipment of the enterprises they have.

As structures of higher efficiency are created, the quality of the materials and the flow processes at factories have to be improved, and, with a view to introducing new methods of transportation and erection of precast reinforced concrete, the catalogue is supplemented periodically with niore modern structures, while the out-of-date structures are deleted.

The worlc done in the field of standardization of buildings and structures has enabled the creation of standard designs and sizes of buildings suitable for workshops for various branches of industry and, as a result, the design and erection of similar buildings for different branches of industry, which considerably siniplifies the provision of buildings with the required building units.

A most eficient system of precast reinforced concrete structures for one-storey industrial buildings is one consisting of columns rigidly connected with the foundations, main load- bearing roof structures in the form of girders or trusses hinged with the columns, and large- sized roof slabs spanning the space between the girders or trusses. This system is econom- ically advantageous. It ensures the interchangeability of structural members and the simplic- ity of their manufacture and erection. It is rational to have a substantial Part of the precast structures prestressed. Table 1 shows that in 1960 prestressed concrete structures in industrial construction already amounted to 14 per cent, while in 1965 their number is expected to be as high as 25 per cent. At present all rafters and trusses spanning 12 m and over are prestressed. Crane girders, roof slabs of a 12 m length and others are also prestressed.

Experience has shown that it is advisable to manufacture short prestressed concrete members (6 m and even up to 12 m long) on vibrating tables with the prestressing forces carried by the forms and pallets. Menibers of a length of 12 m and over are manufactured on linear beds 100-150 n~ long with the prestressing forces carried by end abutments.

A very simple and cheap method of electrothermal tensioning of reinforcement with the prestressing forces carried by the steel forms has been widely used in the USSR during the last few years.

The manufacture of prestressed concrete structures using the method of continuous re- inforcing performed by special self-propelled machines has proved to be a highly efficient method. At present such machines are used only for manufacturing large-sized roof slabs, sleepers and other coniparatively small members. Now a method has been developed for manufacturing large-sized members (up to 30 m long) with continuous reinforcing. The combination of this method with self-propelled concreting macliines and compacting ma- chines allows a change-over to completely mechanized manufacture of all kinds of precast structures. Automatie control of such machines, operating according to a predetermined

Programme, ensures the complete industrialization of the manufacture of precast reinforced concrete with a minimum of manual operations.

Prestressed concrete roof slabs of 3 Y 6 m and 1.5 X 6 m are being used in construction on a mass scale.

For buildings with 12-m column spacing, the cheapest solution is obtained by spacing triisses at 12 m, the slabs having a size of 3 X 12 in.

For the roofs of heated buildings being erected in regions with severe climates, 1.5 s 6.0 m gas-concrete slabs 25 cm thick are beginning to be used instead of ribbed reinforced concrete slabs with a heat-insulating layer. A bottom layer of 3.5-4.0 cm heavy concrete in such slabs allows thein to be pre-tensioned. Tlie comparatively small width of gas-concrete slabs is explained by the fact that in the USSR inost of the autoclaves used for autoclaving slabs have a diameter of 2.2 m.

For the main loadbearing structures it is most rational to use girders for spans up to 18 m, while for spans of 24 m and over preference should be given to trusses with a pre- stressed lower chord. Segment trusses with a light lattice, which are not stressed under uniform loads, are also widely used.

Fig. I . Building with 24-1-11 standard trusses.

The height of standard trussed rafters is assumed to be not more than 3.6 m, taking into account the conditions of their transportation by railway and over city streets.

Depending on the equipment available, various t russ designs have been approved. Du ring the last years trusses consisting of two halves are being widely used. The chords of thece halves are connected at the mid-span by welding steel inserts embedded in the concrete. The bottoin chords of the trusses are prestressed with tendons, consisting of bundles of wires or large-diameter deformed bars of high-tensile steel. Wires and bars are anchored at the points of support and in the steel junction units at mid-span.

The tendons are post-tensioned by jacks. The bars. as a rule, are tensioned by the electro- thermal method with the prestress force carried by the steel forms before the concrete hardens.

At present many factories are beginning to use beds for manufacturing concrete structures prestressed with wire. Therefore the trusses are frequently made without dividing them into

parts. The bot ton~ chord of the truss with prestressed high-tensile steel wires is made separately. For better connection of the upper chord and the lattice at the bottom chord, prestressing steel projections are provided. After the bottom chord has been concreted and steam-cured and has gained the required strength, it is removed from the bed and delivered to the site, where the upper chord and lattice are concreted to the bottom chord.

Complete trusses up to 24 n~ long are delivered by railway and truck. Special low-loading trailers have been designed for highway transportation so that the trusses do not touch tram and trolleybus cables.

Rafters are of I-section and are also prestressed with high-tensile steel wire. For obtaining

Fig. 2. Building with reinforced concrete colcimns and crane girciers of lattice type witli 30-m reinforced concrete trusses. In the background may be seen the erection of a shell 45 i 45 m in plan.

Fig. 3. Lonstructioii of a multi-bay building with Iiorizontal roof, the colurnn grid being 24 , 12 m.

light structures with a thin web (thickness of 6 cm) the rafters are cast horizontally by compacting the concrete. When it is required to increase the outpiit of the bed the rafters are sometimes concreted vertically. In this case a thick web is inade, which results in excessive consumption of concrete and requires two-sided sliuttering for each rafter.

Taking into account tlie mass production of units at precast reinforced concrete factories in the USSR, the sliuttering is inade of steel, which simultaneously increases the accuracy of manufacturing structures.

The columns for one-storey buildings of low height are niade of rectang~ilar section, and those for high buildings consist of two separate posts of small cross-section connected by horizontal tie members. Each of these posts is located directly under the crane girder, improving the conditions for transfer of crane loads.

I-columns are scarcely iised at preseiit foi- industrial buildings because of the considerable manpower needed for their manufacture.

Precast foundations for columns of buildings and structures are beiiig widely used. For small-sized foundations they are coinpletely pi-efabricated. Heavy foundations are divided into blocks connected by itl situ casting. If cranes of high lifting capacity are available,

Fig. 4. Constr~iction of a garüge with 40 40 rn shells assembled irom flat slabs.

foundations of a still larger size are used, their weight reaching 25 tons and more. The use of precast foundations increases tlie rate of construction, which is very important for winter jobs, for soft soils, for restricted construction sites, etc.

Generally, prestressed concrete crane girders are used for overhead cranes of a lifting capacity of up to 50 tons. The girders are, as a rule, of I-section with a widened upper 17ange for fastening the crane rails.

Crane girders for cranes of much higher lifting capacity (100-125 tons) have also been used. In this case lattice beams proved to be very good.

Technical and economic analysis has shown that the use of prestressed concrete for such girders was not economical in comparison with steel girders. Primarily, this relates to girders supporting cranes of low lifting capacity and to heavy-duty cranes.

Alongside the wide iise of flat precast reinforced concrete structures in the USSR, a large experimental construction is being carried out of industrial buildings with three-dimensional composite structures to evaluate their technical and economic properties. Long and short barrel-vault shells, double curvatiire shells, as well as hyperbolic paraboloid shells, suspend- ed roofs, varioiis types of thin-walled ferro-concrete structures and others are being inves- tigated.

Miilti-storey industrial biiildings, as mentioned above, are being built on a small scale. Many workshops that were previously located in multi-storey buildings are being re-de- signed ; we use for theni standard one-storey buildings of larger Spans and heights made of

standardized mass-produced structures. Any technological equipinent required in these buildings rests on special demountable franie supports or directly on the foundations. This malces it possible to locate the equipiiient at different levels without transfer of its weight to the main structures of the building.

For rn~ilti-storey industrial buildings the loadbearing struct ures are designed as trans- Verse fraines with rigid joints. The joints are formed by welding the inserts and the reinforce- inent ends projected from the colui-iins and horizoiital niembers with subsequent in situ casting. The strength of the weld joints is calculated either for transfer of all forces induced at the joint or for transfer of forces induced by the weight of the precast structures erected before concreting the joints.

The fioors are assenibled of standard large-sized slabs welded to the horizontal meinbers of the fi-aine. For this purpose special steel inserts are embedded in these and in the slabs.

Special attention in such buildings should be paid to ensuriiig their rigidity in the direc- tion perpendicular to tlie franie plane. For this purpose special stiffening members are

E'ig. 5. Multi-storey framed building for chemical industry with walls of large-sized panels.

provided along tlie rows of posts. The headers and floor slabs may have ordinary or pre- stressetl steel reinforcement.

For some branches of industry cliaracterized by heavy service loads (coal and mining) or by tlie preseiice of harmfiil chemical effects (clien-iical), use is made of special structures rarely used in other branches of construction. These structures have either large cross- sections or a thicker protective layer for the reinforcenient.

Considerable increase of the coefficient of prefabrication of buildings and of the con- struction rates is achieved by replacing brick and large-block walls by walls of large-sized multi-layer panels of heavy concrete with highly efficient heat insulation or by walls of one- layer panels made of cellular and lightweight concretes. The length of the wall panels is equal to the column spacing of 6 and 12 in, wliile the height is a multiple of the enlarged module of 0.6, 1.2, 1.8 and 2.4 ni.

For heat ins~ilation of reinforced concrete panels, wide use is made of local efficient materials such as mineral felt, expanded clay concrete, perlite concrete, cellular concretes made with local fly-ashes, slate, etc.

Special attention should be paid to the use of precast reinforced concrete for the construc- tion of large thermal power stations with a n output reaching 2,400,000 kW.

Because there are frequently no plants producing precast reinforced concrete a t the construction sites of power stations, the structures for their erection are made a t factories located at a long distance from the construction site. Precast structures up to 25 m long, weighing up to 25 tons, are transported by railway for distances of 600-1,000 km.

The main building of the power statioii has coluniiis 40-45 m high, and trusses spanning 36 in and over. These structures are assembled, at the construction site, from prefabricated ineinbers, placed into position by cranes of high lifting capacities. The hopper and de- aerator frame supports are made entirely of precast reinforced concrete.

The walls of the power-station buildings are made of large-sized panels. The application of welded joints, requiriiig in situ concreting only in certain cases so as

to ensure the required strength, allows the erection of buildings independent of season. T11is is of particular importance for the USSR, with its severe climate.

The development of standard structures and their mass production require a very strict approach to the solution of this probleni. It is in no case admissible that individual parts of the structure have insufficient strength (as tliis might lead to inass failure of structures), or excessive strengt11 (as tliis leads to excessive consumption of material, repeated thousands of tiines). Therefore, in the USSR, a standard full-scale structure, before being approved, is tested to failure in order to check all its parts.

New designs of buildings and structures are, before their introduction into practice, checlted in experimental consti-uction, the scale of wliich is in some cases very large.

P R E C A S T R E I N F O R C E D C O N C R E T E I N I N D U S T R I A L

S T R U C T U R E S

Precast reinforced concrete is also successfully used for tlie coiistruction of various indus- trial structures such as transport galleries, trestles for pipeliiies, service tunnels and ducts, lioppers, silos, coal towers, retaining walls, water cooling towers, tanks, etc.

Fig. 6. Blast-furnace hopper trestle erected by means of a gantry crane.

Of special iniportance are large structures, such as reinforced concrete hopper trestles for blast furnaces, which were previously made of monolithic reinforced concrete or of steel. The first trestle of this type was erected in the USSR in 1954, using members of a lengtl-i iip to 25 n ~ , weighing up to 45 tons.

The replacement of steel hopper trestles by precast reinforced concrete ones leads to a reduc- tion of steel consumption by 35-45 per cent, the cost being tl-ie saine. Simultaneously, labour consumption in manufacturing and erecting the struct~ires is decreased by 10-1 5 per cent.

Precast reinforced concrete hopper trestles have great advantages in comparison with those niade of monolithic rcinforced concrete, especially in relation to the reduction of labour consumption and the increase of tlie rates of construction. Usually these trestles

Fig. 7. Prefabricated coal tower at a coke by-product factory.

are erected at restricted construction sites. Because of this the manufacture of all precast inembers (including the foundations) away froin the construction site greatly siinplifies all construction operations.

The use of precast reinforced concrete for the charging platfornis of the blast furnace casting yards should also be noted. Usually it took 45 days to erect this in situ reinforced concrete platform, and this involved a large ainount of tin-iber, used because of a lack of structures of similar type and because of the iiecessity of providing individual shuttering for each member.

The charging platforiii of precast reinforced concrete str~ictures is erected in 7-8 days, saving timber by a factor of 5-6 tinies.

Particularly advantageous is tlie use of precast reinforced concrete for industrial struc- tures of great height and small area in plan. Such structures include coal towers of coke furnaces, water-cooling towers and others.

The erection of such structures of monolithic reinforced concrete requirss the installation of scaffolding and shuttering of a height of 45-50 m and over, having a high loadbearing capacity and rigidity. The severe climatic conditions of the USSR inake it difficult to erect such structures. Because of these difficulties the erection of high structures is delayed in relation to the construction of all other structures and is, for comparatively small aniounts of werk, the cause of delays in putting tlie entire project into operation.

Fig. 8. Construction of thernial power station o f precast reinforced concrete structures

Change-over to the construction O E such structures of precast reinforced concrete with welded joints which are covered with concrete inade in situ with rapid-liardening cement allows the erection of such structures in a considerably shorter time, independent of season.

Precast reinforced concrete is also being used in mine construction for vertical shafts and horizontal drifts. In 1960 precast reinforced concrete was used in only 6.5 per cent of coal tnines, while in 1965 tliis figure is expected to be 19 per cent.

Reinforced concrete supports are made of various types: arch hinged, framed (of hollow units in the shape of tubings) and others. Mining supports are niass produced at specialized factories.

P R E C A S T R E I N F O R C E D C O N C R E T E P R O D U C T S

Besides precast reinforced concrete structural ~inits widely used for the erection of industrial buildings and structures, various other reinforced concrete products are also used (rein- forced concrete pressure pipes, railway sleepers, poles for transmission lines, posts for contact cables for electric transport, etc.). However, these products are not being widely used as yet.

Until recently mainly reinforced concrete non-pressure pipes have been manufactured in the USSR. Tliougli the technology of manufacturing prestressed concrete pressure pipes was developed and mastered in the USSR a long time ago, the first factories for their production were put into operation only 4 or 5 years ago. At present, new types of machine have been designed, now being successfully used at various factories. However, the quantity of pressuse pipes supplied by factories does not yet meet the demand.

Reinforced concrete poles for electric transmission and contact cables for electric trans- Port are being widely used. These poles are manufactured both of ordinary reinforced and prestressed concrete. Prestressed concrete poles are made either round or of I-section with a smaller cross-section at the top and with reinforcement of high-tensile steel wire.

The inanufacture of such products and their use in industrial construction is constantly increasing,.

E C O N O M I C S O F A P P L I C A T I O N O F P R E C A S T R E J N F O R C E D

C O N C R E T E S T R U C T U R E S

Many factors should be taken into account when determining the efficiency of the use of precast reinforced concrete structures as compared with others and, primarily, with steel structures.

Calculations show that because of local conditions the iinportance of some factors changes, not only within the country but in some cases even for different structures at the Same construction site. Therefore it is possible to review only general considerations concerning the economy of precast reinforced concrete.

Taking into account the rapid development of all kinds of machine-building, using immense yuantities of steel, one of the most important factors when clioosing the materials for construction is the problem of saving steel. In the erection of industrial buildings, the replacement of steel structures by precast reinforced coiicrete ones leads to the following saving of the steel used :

In columns, trusses and trussed rafters by a factor of 2-3; In roofs (when replacing steel purlins with small slabs by large-sized ribbed slabs) by a

factor of 2.5-3.5 ; In high external walls (when replacing brickwork reinforced with steel frameworks by

large-sized panels) by a factor of 2.5-3.0. Data 011 saving steel in individual structures are as yet insufficient for obtaining a general

picture. In view of this two experimental designs have been made of a four-bay building with a column grid of 24 x 12 m, area of 1,152 m%nd height, up to the craneway railheads, of 8 111 with cranes of a lifting capacity of 20 tons. The comparison of these designs has shown that, taking into account all structures, the consumption of steel per square metre of production area in a building with precast reinforced concrete structures is reduced by a factor of two.

Generally, the replacement of in situ reinforced concrete by precast reinforced concrete (for similar structures) reduces the consumption of reinforced concrete by 15-25 per cent and in some cases by as much as 40 per cent. One ton of steel structure is replaced by 2.1 m3 of precast reinforced concrete. Taking into account the consumption of reinforcement, the use of 1 m b f precast reinforced concrete saves up to 300 kg of steel.

The use of reinforced concrete instead of steel significantly increases the durability of loadbearing structures and reduces by 2-3 times the maintenance expenses for open-air structures and for buildings with unfavourable internal working conditions (chemical industry, non-ferrous metallurgy, etc.).

The replacement of brick walls with steel frameworks by walls made of large-sized panels reduces their weigl~t by 2.5 times and the labour consumption involved in erection by 1.5-1.8 tirnes.

To ascertain the saving achieved over the entire country by using various materials and structures, it is necessary to take into account the investrnents in various branches of industry. Thus, for exarnple, to widen the use of steel structures it is necessary to develop the coal industry, mining, iron and steel works and factories manufacturing steel structures. To widen the use of precast reinforced concrete structures the iron and steel industry must be developed to a much smaller degree, but it will require the expansion of the production of cement, quarrying operations and factories producing precast reinforced concrete.

It is impossible to discuss these problems in a short report since they should be dealt with a t length in a special Paper.

C O N C L U S I O N

Industrial construction in the USSR is based on a wide use of standard mass-produced precast reinforced concrete structures. Standard structures make it possible successfully to design and erect standardized industrial buildings providing workshops for various branches of industry.

Factory production of precast structures makes it possible to perforrn merely the erection of buildings and structures at the construction site and to carry out construction work all year round, not lowering the rate of construction even during severe winter conditions.

At present in the USSR there are various and very economical designs of standard rein- forced concrete structures for one-storey and multi-storey industrial buildings and struc- tures. As a result most of the members of the framework and enclosing structures of indus- trial buildings are made of precast reinforced concrete.