Hall construction with prefabricated concrete elements

PRECAST CONCRETE ELEMENTS

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Up to now, criteria for utilising steel reinforced precast ele-ments have revolved exclusively around load-bearing ca-pacity. In future, other properties will also have to be takeninto account in design engineering. Besides its great load-bearing capacity, steel reinforced concrete possesses out-standing potential as a material for storing thermal energyand then releasing it in delayed action to the surroundings.This property is known by the term: “Building ComponentActivation” (BCA). An increasing number of building tech-nical service components will in future be built into con-struction components in conjunction with this property.Prefabrication is virtually predestined for the successful im-plementation of these new challenges. However, it is im-portant to plan holistically and be aware of mutual influ-ences under these boundary conditions. It means thatstructural details should be designed whilst taking diverseinserted components into account. These can, in turn, exertan influence on computations. In the following, correlationsin multi-functional construction work will be illustrated

using the example of a hall structure made from prefabri-cated concrete elements. In this case, properties, such asload-bearing capacity, thermal energy storage and energydistribution, should be coordinated in over-arching plan-ning.

Load-bearing concrete elements for utilisation as heat storage units

Warehouse halls constructed out of concrete offer the oppor-tunity of designing both building structure and façade. Froman energy viewpoint, these concrete halls can ideally serve asan energy storage unit – available at no extra cost. It is wellknown that concrete possesses great thermal storage capac-ity as a material. Such a storage unit can be optimally ex-ploited for room climate control in conjunction with the massof the load-bearing concrete structure. This storage unit canbe both passively managed without any additional pipelinesand also actively managed by integrating pipe grids.

Hall construction with prefabricated concreteelements – outstanding accomplishments with the load-bearing structure and integratedbuilding technical services

New approaches in planning precast concrete components

� Thomas Friedrich, Innogration GmbH, Bernkastel-Kues, Germany

Hall floor plan with dimensions Thermo-wall set-up

06a-precast_132-151_us_Layout 1 09.11.17 16:09 Seite 136

NETWORKED PLANNING

knowhowexperience

250,000 m2


In terms of over-arching energy management, greater signifi-cance will be ascribed in future to buildings with this appro-priate mass, as many small units are capable of storing surplusenergy on a short or long term basis and then of releasing itwhen needed. The discussion about this issue was just re-cently rekindled due to the utilisation of renewable energy.The more seasonal offer of energy from sun and wind is notnecessarily congruent with consumers’ actual demands. As aconsequence, there has to be intermediate storage points forrenewable energy. And this can be achieved optimally withstructures made from concrete. Hall structures designed withlightweight materials, such as steel or wood, cannot provide

the appropriate mass and are thus unsuitable for energy stor-age.

The specific construction project involves a hall structure witha 20.0 x 30.0 m floor plan. Two storeys are envisaged withinthe total height of 10.34 m. The external walls have beenmade as “thermo-walls”. Its layered cross-sectional set-up ex-

� Dipl.-Eng. Thomas Friedrich, Innogration GmbH, Bernkastel-Kues, Germany studied civil engineering at RWTH Aachen Uni-versity and at ETH Zurich with a scholarship from The German National Academic Foundation. His activities have included: proj-ect engineer at Stahlton/BBR, a prestressing company in Zurich;managing director of Domostatik, an engineering company he

founded in 1988. From 2003 onwards, he has been engaged in developing anew type of prefabricated floor system with integrated technical building serv-ices. Proprietor of numerous patents for newly developed products in the con-struction sector, he founded Innogration GmbH in 2010 for the advanced devel-opment and marketing of this new multi-functional floor system; he is manag-ing partner of Innogration GmbH. He has been lecturer at the special depart-ment of solid construction at Kaiserslautern University of Technology since 2008.

[email protected]

Thermo-wall with bearing support recesses for installing the TT slabs




hibits an outer concrete shell, an insulating layer, the load-bearing core concrete and an inner shell also of concrete. Theprefabricated sandwich structure is composed of the twoouter shells and the insulation. This set-up at the same timefurnishes the formwork for the concrete of the core that willbe poured on site. This construction method offers the advan-tage of smooth concrete surfaces on both sides and protec-tion for the insulation inside. With this, the prerequisites havebeen fulfilled for sufficient insulation with a mass that can beutilised at the same time.

Both the intermediate and upper floors were designed to befree of supports. Only a floor slab with a resolved (TT) cross-section and prestressed reinforcement can come into consid-eration for a 20.0 m span width. A ribbed floor fulfils these re-quirements in terms of slender design (L/d= 29) and lowdeadweight. The weight of a precast slab with ribbed cross-section corresponds to a rectangular cross-section with aheight of 25 cm. The deadweight amounts to 6.20 KN/m2. Pre-

stressed TT slabs were utilised. Single floor elements of 2.50m in width were produced in accordance with the arrange-ment of the façade.

Building component activation for the slab with a ribbed cross-section

The walls represent the passive mass for heat storage. How-ever, the floor structure has to be both actively and thermallyexploited in order to control the rooms’ air conditioning. Tothis end, pipe grids have to be set into the slab, the ribs andthe entire cross-section. Since the ribs compose approxi-mately 43% of the overall cross-sectional volume, suitableamounts of pipelines have to be set into both the slab andthe narrow ribs as well. These pipelines are usually fastenedto the load-bearing reinforcement for reasons of economy.Meshes are employed for this purpose with flat constructioncomponents like slabs. By the same token, stirrup meshes areutilised for fastening with rib installations. However, the two

Thermo-walls in their assembled state Comparison of cross-sections with similar volume

TT slab cross-section with data concerning reinforcementand pipelines

Thermal performance for a comparable rectangular cross-section

Thermal performance for the resolved geometry of the TT slab (100 % more output than with the rectangular cross-section)


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sections of the pipeline system have to be installed separatelyand then finally connected up to form a continuous grid. Leak-age tests can then be performed on the connected pipe gridsystem.

Provision has been made for two individual grids on one slabwith a view to creating the most flexible management possi-

ble at a later point in time for differing zones and to limit thelength of the pipelines in any one grid. Individual grids withan area of 2.50 x 10.0 m = 25.0 m2 are joined up to a distrib-utor, which allows their output to be regulated individually.The individual grid connections terminate in a defined con-nection on the floor’s underside. The extension – to be com-pleted on site – from the individual grids to the distributorbeam is carried through inside the floor cavity between theribs or else through the openings in the ribs. The distributorbeams are also fastened in the floor cavity and are accessiblefrom the floor underside.

Structural prerequisites for setting the pipelines into the ribs

The open space inside the ribs should be kept as free as pos-sible from bulky elements in order to provide the necessaryfree space for setting in the pipelines. This can mostly beachieved if the number of reinforcing elements (in particularnon-stressed rebar) is kept to a minimum. In fact, this onlyhappens if the load-bearing reinforcement is solely made upof prestressing tendons. Non-stressed longitudinal reinforce-ment can be entirely eliminated if there is sufficient pre-stressed reinforcement. The cross-sectional area needed forprestressed reinforcement is related to the state of load-bear-

Pipeline layout in the upper floor slab layer




ing capacity. It must be borne in mind when utilising this pro-cedure that a part of the prestressing tendons can also bereckoned against the minimum reinforcement. This procedurewith flexural reinforcement consisting solely of prestressingsteel is basically feasible according to [1]. This option facili-tates a simplified production process at precast componentproduction facilities and offers the additional possibility of thenon-conflicting installation of pipelines for thermal activation. However, the choice of a large proportion of prestressingsteel necessitates a reduction in the pre-tensioning possibleespecially in order to keep any initial deformations of the con-struction component to within prescribed boundaries. Themaximum approved initial steel prestressing according tostandard can thus not be exploited. Nonetheless, the break-age stress of the prestressing steel in its ultimate limit statecan be attained as the admissible strain states permit greatstrains in the tensile zone. The amount of initial prestressing (pre-tensioning) for individ-ual tendons is solely related to the intended deformation of

the construction component in its constructed state. The initialactions of deadweight and prestressing should not lead toany uncontrollable deformation – especially upwards. The in-tended elongation and curvature of the cross-section and thecorresponding deformation of the construction componentare influenced by the following measures:

- Amount of initial steel prestressing of the tendons in theprestressed tensile zone

- Amount of tendons and their prestressing force in thecompressive zone

- The partially unbonded arrangement of the tendons inthe support area

Any deformation possible with a construction component inits constructed state will have been influenced by these threeadjusting factors. Successful optimisation leads to only minordeformations upwards in the constructed state. In its finalstate, this deformation will have almost ebbed away and thefloor exhibits no sagging even under constant actions. For theconstruction project described here, the deformation was setat a value of 1.0 cm upwards; this had practically disappearedin the final state.

Pipeline connection from the crosspiece

Pipeline connection between the crosspiece and floor slab



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Optimised radiant performance thanks to ribbedcross-section – greatest thermal output

The ribbed cross-section exhibits an appreciably larger sur-face than a rectangular cross-section of similar volume. In thisspecific case, the surface was enlarged by 84% in order to re-lease thermal energy. The total transfer of heat from the cross-section into the room is increased by approx.50%. This pro-cedure is well-known by the term of “cooling fins” – of smallor large dimensions. More thermal output is generated by en-larging the surface.

Utilising this type of cross-section in conjunction with energy-efficient building component activation can be especiallybeneficial in buildings requiring great thermal output. As ac-tivation of the concrete core is known to be limited in thermaloutput due to its large, inert mass, this output can only be im-proved by a special design and setting in the pipelines closeto the surface.

Manufacturing process

Individual slab elements are manufactured in standard form-work for TT slabs. Reinforcement work is reduced to a mini-mum by eliminating the non-stressed longitudinal reinforce-ment in the ribs. The stirrup reinforcement is installed as a pre-fabricated reinforcing cage; the tendons are subsequently setin and prestressed to the required level. The free space abovethe prestressed tendons can now be utilised for installingpipelines as well as for installing the formwork for the ribopenings. The position of the pipelines is given by the geo-metric harmonisation of all inserted components inside theribs. The pipelines are fastened to the stirrup legs. Two

pipelines are fixed one above the other onto the stirrup legson each side of the rib. The pipelines inside the upper floorlayer are set in precisely using a template, as with pure slabelements, and fastened to the reinforcing mesh.

The pipelines in the ribs and those in the floor have to be setin separately for process engineering reasons. At the end,however, a continuous system has to be made out of bothsections. As press connectors are used to join up the pipelineends, they have to be brought together at the same place.The connection for the flow and return now only has to be laiddown for this communal pipeline system. This is made insidethe upper slab with an outflow downwards consisting of abend with internal threading. The connection for the exten-sion of the grid to the distributor will be installed later at thispoint. Pressure testing is also carried out at these connectionpoints before concreting.

Record accomplishments as regards transportationand assembly as well

Slab elements with a ribbed cross-section are particularly suit-able for large span widths and big areas. The base area of oneprecast component covers 50 m2. This size is advantageousin assembly work, as a large area can be set in place with onehoist. However, it also results in heavy weights, which all haveto be mastered in loading, transport and assembly. One sin-gle element weighs approximately 24 tonnes. With the aim ofoptimising transportation, two elements with a total weight of48 tonnes were brought each time with a single transport unitfrom the factory to the construction site. Such lengths andweights for construction components are not commonplaceand require special transport vehicles and hoisting units.

Connection points for flow and return (to be prolonged to the distributor)

Floor underside – connection of individual grids with a prolongation of the pipelines to a distributor inside the floor cavity




The slabs’ rigid steel reinforced concrete structure was advan-tageous during transportation as they could be supported ateach end on two points. The connection – resistant to bothtensile and compressive pressures – from the tractor unit’sturntable to the bogie is maintained solely by the prestressedfloor slabs. In a similar way to long timber transporters, thebogie is steerable so that it can accommodate even narrowbends and driving backwards.

These rigid, low deformation floor elements need only a fewrows of support yokes in their constructed state. One yoke ateach bearing support and two additional ones set up uni-formly along its length are sufficient. Both middle rows ofyokes mainly serve the purpose of compensating for possibletolerances in the deformations of individual floor slabs. Theyokes are adjusted once the slabs have been set in place.

Only 12 elements were needed for an approx. 600 m2 floorplan. Six transport units delivered the slab components inshort time intervals during the morning. Once the mobilecrane had been positioned correctly, it was possible to set theslabs in place during a time period of 5.5 hours. Such a goodperformance is also unusual for floor slabs during assemblywork.

Conclusion

The planning and execution of the above-mentioned floorslabs broke new ground in many respects: - Slender floor slabs with low deadweight - Integration of thermal activation with uniform distribu-

tion over the entire mass - Adaptation of reinforcement in view of the pipelines

needing to be installed for the thermal activation - Enlargement of the heat transfer area with the ribbed

cross-section to attain very great thermal output

Transport unit for two slab sections (2 x 24 = 48 t)

Slab end illustrating the reinforcement elements

Storing completed slabs in the production facility



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These planning achievements could only be attained thanksto extensive expertise both in the area of structural design en-gineering and technical building services. The reinforcementchosen and the installation of the pipelines were harmonisedwith each other and designed accordingly. The type and di-mensions of the reinforcement governed the installationneeded for the pipelines. It is impossible to plan and success-fully execute any cost-effective, functioning construction com-ponent without any knowledge of the possibilities with theseinserted components. �

Bibliography

[1] Konrad Zilch, Gerhard Zehetmaier: Bemessung im konstruktiven Be-tonbau; 2. Auflage 2010 Springer Verlag, Berlin

One slab element being assembled (notice the reinforce-ment at the slab end and the bearing support recesses forthe slab cross-section in the thermo-wall)

Hoisting individual slabs from the transport vehicle to theirfinal position

Installing slabs on their bearing supports Interior view of the finished hall

Innogration GmbHCusanusstraße 23, 54470 Bernkastel-Kues, GermanyT +49 6531 [email protected], www.innogration.de

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Hall construction with prefabricated concrete elements