RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY

Transcription

1 RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY Zvonimir Perić, Davor Banić, Tomislav Brozović Summary Reconstruction projects of old existing buildings where material degradation has occurred and where the repurpose of their functions is required, in most cases requiring changes to the static system, represent one of the most complex tasks for the designer engineer. This article shall describe one such RC structure reconstruction and upgrading project of a building that is part of the Zagreb brewery industrial premises. The investor required that a part of the existing building, built in the 1960 s, where beer tanks were formerly located, to be converted to storage area. The said requirements necessitated increase in the rigidity of the RC structure system and intervention regarding the advanced material degradation. Keywords: reconstruction, numerical modelling, construction systems, durability, corrosion 1 Structure description and design criteria Topic of this article is the reconstruction project of the industrial building in Zagreb brewery complex. The building was built in 1967, and its previous purpose was storage of beer in big tanks and production of beer (beer fermentation). In plain view, building has rectangular shape with dimensions 17.5 x 21.3 m and it is 37 m high. First 5 floors have average high of 4 m, while the last floor is 15 m high. The purpose of the space between 1 st and 5 th floor was storage of 50 horizontally placed tanks (each weighing 93 t), while on the 6 th floor 25 vertical placed tanks that were used for beer fermentation were stored (each weighing 88.5 t). The structure system of the first five floors is a space frame structure. In transverse direction frame columns are on disposition of 7.1 m and in longitudinal direction 2.5 m. Frames are based on line foundation placed in transverse direction and connected between each other with foundation plate. Whole structure is made from concrete with strength class C16/20 and reinforced with smooth S220 reinforcement bars. 253

2 A B C D E F Perić, Banić & Brozović: RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY +33,45 Fig. 1 Brewery building with structure section cut ,50 +29,60 +27,52 +26,85 +19,10 +17,80 +13,80 +11,25 +9,80 +7,25 +5,80 +3,25 +1,80-1,50-2,20-2,70-3,10 The structure system of the first five floors is a space frame structure. In transverse direction frame columns are on disposition of 7.1 m and in longitudinal direction 2.5 m.frames are based on line foundation placed in transverse direction and connected between each other with foundation plate. Whole structure is made from concrete with strength class C16/20 and reinforced with smooth S220 reinforcement bars. Upper part of structure was made of columns which are continued to the lateral frame columns. On the top, columns are connected with beams. Roof vault structure was made from masonry elements and their thrust was hosted with cables. Investor s design criteria required redevelopment of the 1 st five floors. Instead of the previous horizontal beer tanks, space is reorganized to enable new industrial section of beer cant filling and their storage. In terms of structure, that means that we need to cut frame beams on two levels. ±29.40 ±29.40 ±19.00 ±19.00 ±0.00 ±0.00 Fig. 2 Project task scheme 254

3 Perić, Banić & Brozović: RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY 2 Structure damage analysis in terms of durability Before we start to analyze and design the new structure static system which will satisfy all project task design criteria, structure examination is required. The purpose of the structure examination is to determinate structure s durability, that is, to determine the material characteristics (concrete degradation) taking into account aggressive environment (acid industry), during the last 45 years. Fig. 3 Reinforcement corrosion and lack of protective concrete layer Examination works include visual structure inspection, taking boring samples from the characteristic structure elements and determination of disposition and condition of reinforcement bars in structure elements cross sections. To evaluate structure elements bearing capacity, concrete and re-bars strength was analyzed. To determinate structure elements durability, concrete ph, density and gas permeability were analyzed. Concrete strength, density and carbonation process were analyzed using the boring samples taken from the structure elements. Fig. 4 Concrete boring sample sprayed with fenolftalein 255

4 Perić, Banić & Brozović: RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY Tab. 1 Boring samples in construction P-1 Boring samples in columns VG-3 Boring samples in beams VT-7 Boring samples in plates Reinforcement examination Fig. 5 Boring samples extraction places in structure elements 3 Structure strengthening design The primary goal of the brewery building reconstruction is to redesign the building space so it could serve a new purpose. From designer s point of view, reconstruction process means, primarily, to examine the existing structure s bearing capacity and, after that, eventually to design and calculate structure strengthening in order to upgrade structure rigidity. Structure system must be rigid enough to resist the gravitation forces (self weight and permanent load) and inertial forces caused by earthquake. In this case, the building is high with great mass concentration on the last flour (25 vertical placed tanks x 88.5 t), so the earthquake inertial forces are dominant. Considering that we have to cut all the frame beams on the 2 nd and 4 th flour, the existing frame system is weakened and it won t be rigid enough to resist the lateral forces, so it needs to be strengthened. There are few solutions how to strength the structure. One of them predicts increasing the rigidity of structure elements by enhancing the cross section dimensions. The second solution is the steel type of reconstruction (Fig. 6). Both solutions are acceptable, but from technological and financal point of view, they are complex and expensive solutions. The third solution, which has been chosen as a final, is to strengthen the excisting space frame structure with shear walls by setting them along building perimeter. This solution is cheaper and, from a tehnological point of view, much easyer to built. 256

5 Perić, Banić & Brozović: RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY Fig. 6 Steel reconstruction Fig. 7 FE model with first 3 modes Walls posses shear rigidity and, becouse of that, they are able to strengthen the exsisting space frame structure through mutual interaction. At the same time, we must accent that the system will not work propertly if the floor structures aren t built. In this case, floor structure (RC plates) also functions as a diaphragm, so it can dissipate floor shear force to the walls. Considering that the upper part is much more flexible than the rest of the building (first five foors), this upper part was separately analyzed and designed. FE model showed that the columns do not posses enough rigidity, so they have to be strengthened. Because the industrial manufacturing plant is in operation all the time, steel prefabricated solution has an advantage over the concrete one. In this case concrete columns are strengthened with steel braces. 257

6 Perić, Banić & Brozović: RECONSTRUCTION OF THE RC INDUSTRIAL BUILDING IN ZAGREB BREWERY Fig. 8 Structure strengthening with braces 4 Conclusion Reconstruction projects of old concrete (industrial) buildings and facilities, which, regarding durability, do not meet the modern standards and also require intervention in the structure static system, represent a truly great challenge for the structure engineers. Very old buildings require an investigation to evaluate the material characteristic and their degradation due to aggressive environment during the years of exploitation. This is the first step of the design process, and only after that, when the material and structural parameters are known, structure bearing capacity can be determined. Structure elements bearing capacity represents crucial data and together with elements internal forces resulting from the predicted loads and design load combinations, conclusion can be made whether that structure satisfies the standards or whether it should be strengthened. References [1] Institut IGH d.d., (2012): Projekt rekonstrukcije zgrade Zagrebačke pivovare [2] Eurocode 8: Design of structures for earthquake resistance Part 3: Assessment and retrofitting of buildings, CEN, 2005 B. Sc. Zvonimir Perić, C.E. M. Sc. Davor Banić, C.E. B. Sc. Tomislav Brozović, C.E. Institute IGH Janka Rakuše, br Zagreb, Croatia tomislav.brozovic@igh.hr URL 258