New glulam timber structures in CroatiaHaiman, Miljenko1 and Baljkas, Boris2

SUMMARY

The paper presents some new Glulam structures built in Croatia between 1997. and 2000. This structures are: Tennis hallin Rovinj, Multipurpose hall in Djakovo, Renewed pedestrian bridge at Plitvice lakes, Road bridge in Zagreb, Church gridroof structure near Sisak and New swimming pool in Zagreb. Except several photos here are given structural numericalmodels and results of static, buckling and frequency analysis done by using COSMOS/M 2.0, STAAD III and M-STRUDL software.

INTRODUCTION

The Glulam timber structures have many advantages interesting and attractive to architects and structural engineers in lastyears in Croatia. The advantages are very good mechanical characteristics of Glulam wood, high engineering technologyand full production control, very nice aesthetic view and finally, enough durability for long period of years. It gives thepossibility of making many free forms of plane and space structures. Besides that the Glulam structures have very highfire resistance better than steel or concrete structures. But the starting cost of this kind of structures is few percents higherthen the cost of steel or concrete structures. These facts are not decisive in investment decisions and the Glulam structuresare today more used for sport hall structures, pedestrian bridges, markets, swimming pools, churches etc.

TENNIS HALL IN ROVINJ, 1997.

The timber tennis hall structure in Rovinj (Istra, Croatia) was built for roofing four tennis courts. The ground plandimensions of the hall are 36 m span and 64 m in length. The roof structure of the hall is made from lightweight glulamtimber lamella mesh cylinder formed structure supported on reinforced concrete foundations. The axis radius of cylinderstructure is 23.31 m, with a rise of 9.3 m. Isometricscheme of the hall structure is shown in thebeginning of the next page.

Roofing material is trevira PVC 700 gr/m2 fabricsupported by steel plates connected to all structurejoints. In the middle of the hall there are three tree-like pipe steel columns. Their top ends at 650 cmlevel are forked into six 12/12 cm timber members.The connections are made with steel forks and M-16 bolts. Elements of these timber tree-like forkedcolumns are connected to the joints of the lamellanet structure. The main reason to build thesecolumns is the uplift wind loading. In this loadingcase the steel columns with the concretefoundations are working as weight ballast. In thestructural analysis the wind loading was taken as1.1 kN/m2. The structural dimensions aredeterminated according to wind and dead loadcombination. The structure is in the zone of veryhigh wind intensity at the Adriatic coast. The

1 Mr.sc.Civ.Str.Eng., Assistant Lecturer, Depatment of Civli Engineering Zagreb, Croatia2 Civ.Str.Eng., Senior Lecturer, Department of Civil Engineering Zagreb, Croatia

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vertical live load is 0.35 kN/m2 only, because the ice and snow load are very rare.

The structural analysis was done by use of two different types of software. The linear static analyses were done by FEAprogram M-STRUDL, and the FE control analysis was done by use of the FEA program COSMOS/M 1.65A at theFaculty of Civil Engineering Zagreb. The buckling analysis for symmetrical and unsymme-trical loading was done withCOSMOS/M too. All of the inside mesh joints are able to take bending moments, normal and shearing forces as well asare connections to the glulam gable arch. Connections to the reinforced foundations are all with released bendingmoments.

The basic rhombic net of the timber lamella structure is of glulam conifer wood elements about 280 cm long and 8/38 cmcross-section. The joint connect-ions are made with steel cross connectors, which are holding the timber elements on thetop and the bottom side. The upper and bottom steel crosses are connected with 2 M-14 presstresed bolts to each timberelement in the joint. Each element has two notches 45 and 30 mm deep and 10 mm width. In these notches the steel platesform crosses are plugged in, to carry all member forces. The required and obtained construction precision was ±0.5 mm.In the middle of the crosses the M-16 bolts, are 10 cm longer to the exterior side, supporting small 80 mm dia. circularsteel plates, which holds the PVC trevira fabric clamped between rubber rings. It gives the possibility of stretching thePVC trevira fabric. The vertical gable columns are spaced at 450 cm and connected to the gable glulam arch by steel jointconnections. Cross-section dimensions of the columns are 12/30 to 12/40 cm depending on the columns high. Buckling ofthe columns is prevented by the horizontal glulam timber structure with cross section of 14/20 cm, and diagonal glulamtimber elements of the same dimensions.

On the top of the structure a 30 cm elevated timber structure is built on to prevent the PVC flexible trevira roofing fromsagging and ponding. In this way the occurrence of unexpected water loading is avoided. The supports to the reinforcedconcrete foundations are done by standard steel welded plates and connected by four M-16 bolts in each connection.

Photo 1. Photo 2.

The construction of the tennis hall was completely produced and erected in 4-month time. The timber volume includingthe timber gable columns and arches is about 0.05 m3/m2 of the ground plan, and the structural steel is about 7 kg/m2. Thewhole building was erected with three mobile scaffoldings. After mounting of the first gable structure and the part of thetimber elements of net shell structure the scaffoldings are needed only for temporary supporting of the structure elementsand for the geometric control. The structure is selfstanding when built from foundations to the top of the structure. Testingcontrol of the structure was done by Institute of the Faculty for Civil Engineering, Zagreb and has shown that the realdeformations are about 25 % higher then the calculated ones. The results show that the yielding of the bolts in jointconnection is very significant.

The design, organization and contracting of the hall and roofing were done by authors and the Haiman-Baljkas Co.Ltd.Zagreb.

MULTIPURPOSE HALL IN DJAKOVO CITY, 1999.

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The hall is located in the center of Djakovo City near to the famous Djakovo cathedral. The hall is designed asmultipurpose one, primarily as secondary school gymnasium but it may be used for some sports and cultural events ofperformances. The roof area covers 36.0 x 52.0 m. Inside it is provided with two lateral reinforced concrete stands with aseating capacity of 700 spectators. The concrete stands act as supports to the main girders, simple span trusses. The roofcovering is aluminum composite panel placed directly to main girders without secondary structure (purlines). Thestructural system consists of seven simple span trusses spanning 35,7 m and spaced at 6.49m (8 x 6.49). The structure iscombined from the glue laminated timber (top chord, wind bracing verticals in roof area and the diagonals and horizontalsin the gable walls, columns) and steel elements (bottom chord, horizontal and vertical bracing's). The truss is 7 m deepwith double Glulam top chord 2 x 14/60 with 14 cm spacing. The roof - top chord slope is 15°. The bottom chord andstruts are steel pipes. The truss diagonals, lateral and wind bracing's diagonals are steel bars.

Photo 3. Photo 4.

Structural design: The structure is designed by using computer program STAAD for static analysis and COSMOS/M forbuckling analysis (Fig. 1). Loadings are taken according to HRN technical codes and standards (Croatian standards).

gable main girder gable

Erection: The erection has been done by the use of thesimple light scaffolding supporting the top of the truss andlight-capacity crane (Photo 3.). Based on appropriateconstruction sequence the erection started with the firsttwo main girders connected with all roof and verticalbracing. The lifting of the structure has been achieved bythe central lower chord field connection designed as twosteel plates fastened in the field with high strength bolts.

isometric scheme

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Fig. 1. 3D model, result of buckling analysis with COSMOS/M 2.0

Structural design: Boris Baljkas and Miljenko HaimanMain contractor: HAIMAN-BALJKAS, d.o.o.Materials: glulam 98,3 m3 (0,05 m3/m2)

steel members 19.800,0 kg (10,5 kg/m2)

RENEWED PEDESTRIAN TIMBER BRIDGE AT PLITVCE LAKES, 1998.

Old pedestrian bridge over the main road Zagreb-Split was built in 1981. After five years of war occupation of thisterritory from Serbian terrorists the bridge was neglected and the glulam girders were decomposed with yielded contactglue blends. Croatian government decided to renew the bridge. New bridge was built and placed on concrete foundationsin summer 1998 with a completely new Glulam structure protected on the outside of the girders with waterproof plywood.

The main span of the bridge is 31,60 m.The width of the bridge at top hinge is2,0 m. At the support hinge the width ofthe bridge is 2,5 m. Steps and pedestriansurface are made of glulam boards withwaterproof plywood covering. Thethickness of the whole board is 6 cm.All steel elements on the bridge aregalvanized. Isometric FE schema fromCOSMOS/M analysis of the wholebridge is presented on next figure 2. Inaddition there are two photos (5, 6): onthe first is shown one part of the oldbridge and on the second the finishednew bridge. Erection was done in onenight in which period the old bridge wasremoved, and new was placed on thesame place.

Fig. 2. 3D model of the bridge for FE analysis with COSMOS/M 2.0

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Photo 5. Photo 6.

The design aim was to increase the durability of the exposed timber. To achieve that all distances between pedestrianboards and girders have been designed about 5 mm. Main reason for this is to give possibility for atmospheric activity(rain, snow) to run faster down from the exposed pedestrian surfaces. Also this way of solving contacts between thehorizontal and vertical surfaces enables faster drying too. We expect that these structure details will extend the durabilityof the bridge. The specialists for timber structures must control maintenance of the bridge structure during the wholefuture period.

ROAD BRIDGE IN ZAGREB, 2000.

The road bridge over the brook in Zagreb will be erected this year. Main span of the bridge is 17,0 m. Width of the bridgeis 5,9 m. The bridge has four main glulam girders with cross-section 18/100 cm. The main girders are spaced 180 cm. Thesecondary glulam girders have cross-section of 14/50 cm spaced at 212,5 cm. On this main glulam timber grid structureperpendicularly presstressed driving glulam deck plate 16 cm thick, are placed. This road deck plate is made of fiveglulam girder plates with cross-section 16/118 cm. In this girder plates the holes Ø 36 mm for Ø 24 mm presstressing HTsteel bars are drilled equidistantly. The final bridge layer will be asphalt. Glulam girders are made of European kind ofspruce and fir wood. Fence on the bridge is made of oak timber. All steel elements are galvanized protected. Two photos(7, 8) show the erected bridge near by temporary location. When the concrete footing of the bridge will be finished, thebridge will be transported from this location to the final place.

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Fig. 3. FE 3 D model of the bridge for COSMOS/M 2.0 analyze

Photo 7. Photo 8.

The whole isometric model is shown on the figure 3. Structural analysis of the bridge was done for loading with one truckof maximal 16 t weight. So according our Croatian standards for loading, bridge was calculated to pedestrian load of 5,0kN/m2. On the next figure 4 we show one of the results of the first mode of frequency analysis.

Static, frequency and buckling analysis of the whole bridge structure was done with COSMOS/M 2.0 software.

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Fig. 4. First frequency mode

Main designer of the bridge is Miljenko Haiman. Haiman-Baljkas Co.Ltd from Zagreb did contracting of the bridge.Materials: 32,5 m3 of Glulam

1,6 m3 of oak timberAbout 2500 kg of steel elements

THE CHURCH ROOF STRUCTURE NEAR SISAK, 1998.

Main glulam grid structure was designed on the truncated rhombic plan view with spans 15,1 x 17,35 m. Secondaryglulam elements 16/50 cm are placed in the half-height of the roof. Over this structure are placed conifer spars spaced at85 cm. Spars are supported on the main glulam grid and the ridges of 14/24 and 14/30 cm. The slope of the roof surfaceschanges between 35o and 43o degree. The main glulam girders were done with circular curved intrados of 650 cm radius.Cross section of the girders is 14/90 cm. Structure is supported on sixth neoprene supports. The two parallel glulamgirders have built in steel presstresed cable between supports to prevent big displacements. Cables are from HT qualitysteel Ø 30 mm . The isometric view of the structure for FE COSMOS/M 2.0 analysis is shown on the figure 5.

The continuity of the Glulam grid is achieved by steel plates in tension and compression zone and with steel dowels.Galvanizing protects the steel elements, and two azure coatings protect the wood. On the photos (9,10) we want to showthe outside view on the church, and the inside view of the timber glulam grid structure.

Design was done by Miljenko Haiman. The structurewas built in 1998. FE model of the structure wascompletely done by COSMOS/M 2.0 including allstatic, frequency and buckling analysis. Any otheranalysis could be performed with COSMOS/M, whichgives the possibility to analyze any known physicalproblem. There are a lot of possibilities to create a realFE model of the structure and to get real results thatcan be controlled through several types of FE analysis.Main capability of COSMOS/M is to analyze thestructures that are made from orthotropic materials incombination with isotropic or anisotropic materials.

Fig. 5

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Photo 9. Photo 10.

NEW TOWN SWIMMING POOL IN ZAGREB

The structure covers the area 37.0 x 80.0 m (2960 m2). The roof is a cylindrical space structure forming some kind ofspace vaulted timber shell. The main vaulted girders are obliquely located in the ground plan. All girders in roof plane areof laminated timber girders: main and secondary vaults, longitudinal purlines and lateral bracings. All other structuralmembers positioned out of the roof plane are steel construction: main vaults pyramids - steel pipes, tension members -steel cables and columns - steel pipes.

Structural design: The structure is designed by using program STAAD for static analysis and COSMOS/M for bucklinganalysis. Loadings are taken according to HRN codes and standards (Croatian standards).

grnd. plan characteristic part of the structure isometric scheme

The following drawings show the characteristic structure sections (ground plan, structure segment, isometric scheme) andswimming pool cross section.

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Structure design: Boris Baljkas and Tanja BaljkasDesigned: April - August 1999.The building project is in progress.The expecting building time 2000. - 2002.

LITERATURE

1. Natterer, J.: HOLZBAU ATLAS Zwei, Holzwirtschaftlicher Verlag der Arbeitsgemeinschaft Holz Düsseldorf, 1990.

2. Žagar Z.: Proračunavanje konstrukcija računalom, Zagreb, 1993.

3. Neuhaus, H.: Lehrbuch des Ingenieurholzbaus; Stuttgart: Teubner, 1994.

4. Informationsdienst HOLZ, Holzbauwerke EC5, Step 1-5, Düsseldorf, 1995.

5. Caironi, M.; Bonera, L.: Il legno lamellare il calcolo, Edolo, 1989.

6. COSMOS/M ver 2.5, priručnici, SRAC Los Angeles, California, 1999.

7. STAAD III priručnik, R.E.I. California USA,1996.

8. Nevada M.A.R.; Diseno Estructural en Madera, AITIM (Asociacion de Investigacion Tecnica de las Industrias de laMadera y el Chorco) i KHITARIS SL., Madrid, 1999.