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PRECAST CONCRETE ELEMENTS

The main mission of the company is to satis-fy the demanding technical requirements inthe structural, thermal and acoustic fields bypushing the boundaries of the most innova-tive and efficient production technologies.With this company vision, Esse Solai hasincreased its range of production types,starting from hollow core slab production,to now well over twenty types of elementsranging between twin wall systems, ribbedretaining walls and high bearing capacityfloors including the production of Top Sol®

and Top Bridge® precast elements manu-

factured using Nordimpianti technology.Nordimpianti and Esse Solai first startedworking together in 2000 when Nord -impianti supplied a complete line for theproduction of hollow core slabs. This con-sisted of five steel production beds, each150 m long, two slipformers (one for ele-ments up to 250 mm high, the other for ele-ments up to 500 mm high), one transversalsaw, lifting beams and various other acces-sories. In the subsequent years, the partnershipstrengthened and the two companies

worked closely together to produce ele-ments that had previously never been man-ufactured using slipformer technology. Oneproject in particular saw the developmentof a special machine capable of producingprecast elements used in the infrastructuresector with a U section and up to 1 m high.The Infrastructure sector is a significant pro-portion of the construction business and thetechnical requirements are particularlydemanding. Nordimpianti responded tothese challenges by its focus and develop-ment of the vibro-compaction technology

Precast concrete bridge elements produced

with slipformer technology

Nordimpianti System Srl, 66100 Chieti (CH), Italy

For over 40 years, Nordimpianti has designed and built equipment for the production of prestressed concrete elements that does not requirethe use of fixed formworks. It has created strong technical and commercial links with all its clients giving Nordimpianti an excellent reputa-tion for reliability and expert knowledge within mechanical and civil engineering. An important partner of Nordimpianti is Esse Solai compa-ny, located in Vicenza. Esse Solai is a “state of the art” company with 30 years experience of producing prestressed and non-prestressedslabs. Recently Esse Solai, as a parent company of Esse Team, has acquired two plants in Northern Italy, one in Parma and another in Udine.

Esse Solai, based in Vicenza, is a highly respected company in Northern Italy producing both pre-stressed hollow core slabs and other precastconcrete elements.

A Nordimpianti slipformer for the production of prefabricated elements for infrastructure use with U-shaped sections up to 1 meter high.

Nordimpianti’s slipformer during the casting phase. Note the simultaneous use of prestressing wires and steel mesh reinforcement.

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PRECAST CONCRETE ELEMENTS

(slipformer technology). This research led tothe creation of a dedicated slipformermachine to produce structural elements upto 1 m high with the possibility to use threedifferent forming inserts to meet the techni-cal parameters of bridge elements and in -dustrial decks capable of withstandingheavy loads.

The first forming insert from Nordimpianti,developed for Esse Solai created a ribbedslab with a U cross section that can be alsois completed on site with transversal bridgeslabs, usually precast slabs with exposedlattice works, and a completion concretetopping. The overall composite deck sec-tion is a boxed section with high torsionalstiffness suitable for the construction ofbridges and floors in which the transversaldistribution of the concentrated load is ofprimary importance. In cases of long spanelements, it is possible to install the elementsclose to each other obtaining a deep longi-tudinal shear key that reduces the transver-sal stresses of the top (cast in-situ) slabbecause of the external side profile (Fig. 1).

The biggest challenge has been the inser-tion of the normal reinforcement, together

with prestressing wires, inside the precastelement using the slipformer technology. Bysolving the problems around the presenceof steel mesh and of the protruding stirrupsfrom the top of the element, it has been pos-sible to fulfil the requirements of EN 15050(European code for bridge elements) whichdoesn’t allow to take into account the shearfriction between precast and cast in-situconcrete. The composite sections havebeen optimized considering the phases oflife of each part improving flexibility of useand the overall economy of the projects.

To complete the box section, there is a vari-ant whereby EPS blocks are positionedwithin the U or the lattice ribs thus exploit-ing the greater control of the materials andprocesses offered by factory production.

Another forming insert that can be used onthe Nordimpianti slipformer allows for theproduction of a hollow core section withthree hole voids and a low self-weight. Thiselement has very high torsional stiffness thatallows for its use in all cases where a reli-able transfer load distribution is requiredand also where there is no structural cast in-situ topping (Fig. 2).

Use of EPS blocks positioned within the U section.

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The third forming insert from the Nordimpianti slipformer has beendesigned to produce inverted double T beams. This cross sectionallows for great flexibility. In fact it can be used for logistic andindustrial building roofs using lightweight transparent panels withoutcast in-situ topping or for bridges using transversal filigree slabscompleted on site with structural grout. This cross section hasremarkable shear strength due to the two large vertical ribs that canbe further increased by grouting, on site, the space between the ribs(Fig. 3).

With the last two forming inserts it is possible to easily obtain widthsub dimensions. In particular it is possible to have two hollow coreslabs with 600 mm widths and an inverted double T beams with an800 mm wide bottom flange instead of 1200 mm wide. This is a bigadvantage because it means great flexibility in covering large decksand reducing the preparation of dedicated customized moulds onsite.As briefly mentioned before, for all configurations, the prestressingsteel, welded wire reinforcement, normal rebar and all requirements

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PRECAST CONCRETE ELEMENTS

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The forming insert mounted on the Nordimpianti slipformer producing hollow core slabs with three holes, giving considerableweight savings.

1000 mm high lightweight hollow core slabs in the storage area.

Forming insert installed on the Nordimpiantislipformer producing inverted double T floorbeams: such a section allows great flexibilityof use.

Box section highway underpass at the A4-A13 intersection in Padua, Italy.

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Fig. 2 Fig. 3

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Reconstruction of a bridge deck destroyed by a landslide in Serina,Italy.

have been adopted in order to fulfil the requirements of generalEuropean norms (such as En1992-1:1, EN206, etc.) and special-ized ones (i.e. EN13369, EN15050, EN13224, etc.).

It must be noted also that, for all configurations, it’s possible to raisethe slipformer by 30 mm in order to increase the fire resistance ofthe precast elements allowing them to reach a fire rating of up tofour hours.

The slipformer technology, used in the cases mentioned above, pres-ents advantages for different reasons.

First of all the flexibility of use: all configurations described abovecan be practicably obtained by one machine, changing only theforming inserts, while with traditional formworks to reach the samelevel of efficiency and flexibility would require a much bigger invest-ment.

Secondly, the quality and grade of concrete that is possible toachieve is very important. The type of concrete required for thesemachines is a semi-dry mix and the water/cement ratio is very low(ranging between 0.35 and 0.40): this gives the optimum benefit interms of the final strength of concrete and for the production costs.The workability of this concrete is practically zero when using tradi-tional methods whereas the Nordimpianti slipformer, processing rel-atively less concrete than formwork methods gives the optimumdegree of compaction and quality.

Nordimpianti’s slipformer performs uniquely in its field by subjectingthe concrete to a combination of simultaneous mechanical actions,in particular compression from the shaped vibrating plates, and thelongitudinal oscillation of the forming tubes and internal moulds.

The quality of the finished elements, in particular the surface finishof the exposed parts, is of a high level because of the oscillating for-mers. Moreover the parts that will be in contact with the cast in-situgrouts have a surface roughness that enhances the aggregate inter-lock and, by consequence, the reliability of the composite sectionbehaviour.A third consideration is that the productivity of machines that oper-ate on casting production lines is higher than with traditional form-

works. The time for setting up the machineand the time required for concrete curingare minimised and allow for high produc-tion volumes. Below are some of the appli-cations from Esse Solai company showingexamples of the performance and flexibilityof the elements produced with machinesfrom Nordimpianti.

Boxed sections for a highway underpass(highway of Padova, Italy):Project surface is around 800 m2, and itconsists of a first category bridge with slabspositioned side by side creating a massiveboxed section. The perfect alignment andthe possibility to create elements with skewheads allow for the correct construction ofthe curved parts of the bridge. The overalldepth of the deck is 900 mm (600 mm pre-cast element and 300 mm cast in-situ struc-tural screed) and the U shape is suitable inorder to have continuity between the headsof two contiguous spans or with the retain-ing walls giving also improvement in sup-porting the soil lateral load.

Reconstruction of a bridge destroyed by a landslide (Serina town, Bergamo, Italy):The bridge, accessible to vehicles, has aspan of 16 m and the overall thickness is850 mm (600+250 mm) and beam spacesup to 1200 mm. Existing head supportshave been reused. The construction systemadopted for the deck is Top Bridge.Through slipformer technology, it was pos-sible to design, build and carry out theinstallation within two weeks from when theoverall project was approved.

First category Bridge with 22 m span(Noceto town, Parma, Italy):The U section construction system is suitablefor first category bridge types. In particular

the overall depth of the deck is 1100 mm(900+200 mm) but the required thickness-es are very small when compared with thesolution of using precast I beams (Fig. 4).

High bearing capacity deck (Sant’Anna di Alfaedo town, Verona, Italy):It happens more and more often that Archi -tectural design becomes more demandingfrom the structural point of view. This appli-cation perfectly represents this point. In factthe conceptual design requires that twofloors of the building are supported bycolumns resting on the basement instead ofthe normal foundation. The basement hasbeen built with the Top Bridge system withan overall depth of 800 mm (600+200mm) with solid zones located at columnbases.

Esse Solai is at the forefront of respondingto the market requirements of constructionend users. This makes for a perfect fit withNordimpianti’s own constant mission tobuild strong relationships with its clients.Nordimpianti invests heavily in the techni-cal professionalism of its staff who, not onlyhave great experience of the design andoptimisation of specialist machinery butalso have the skill and in-depth knowledgeto advise customers on all aspects of theproduction, transport and installation ofprecast elements manufactured by its equip-ment. �

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PRECAST CONCRETE ELEMENTS

1st Category bridge type with 22 m span in Noceto, Italy. High bearing capacity deck (Sant’Anna di Alfaedo town, Verona)Italy.

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FURTHER INFORMATION

NORDIMPIANTI SYSTEM SRLVia Erasmo Piaggio, 19/A66100 Chieti (CH), ItalyT +39 0871 540222F +39 0871 562408info@nordimpianti.comwww.nordimpianti.com

ESSE SOLAI SRLStrada delle Fornaci, 1336031 Vivaro di Dueville (VI), ItalyT +39 0444 986440F +39 0444 986558info@essesolai.itwww.essesolai.com

Fig. 4