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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 83
Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Paper 250

Seismic Design of Pre-Cast Reinforced Concrete Structures Using Additional Viscous Dampers

C. Ceccoli, T. Trombetti, S. Silvestri and G. Gasparini

Department of Civil Engineering, DISTART, University of Bologna, Italy

Full Bibliographic Reference for this paper
C. Ceccoli, T. Trombetti, S. Silvestri, G. Gasparini, "Seismic Design of Pre-Cast Reinforced Concrete Structures Using Additional Viscous Dampers", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Eighth International Conference on Computational Structures Technology", Civil-Comp Press, Stirlingshire, UK, Paper 250, 2006. doi:10.4203/ccp.83.250
Keywords: pre-cast concrete structures, seismic performances, traditional bracing systems, insertion of viscous dampers, damper design.

Pre-cast concrete structures are commonly assembled on construction sites so the structural systems obtained are not capable of transmitting bending moments at joints. Such structural systems show a relatively large flexibility with respect to lateral seismic loads. This characteristic often hampers the satisfaction of the interstorey drift limitations imposed by most of the seismic codes. In this paper, the use of added viscous dampers is compared with the use of traditional lateral-resisting bracing systems in order to provide such structures with the necessary lateral stiffness and resistance. The comparison is here developed with reference to the executive design of a shopping mall building in Rimini, Italy.

The total surface of the "Le Befane" shopping mall is about 40,000 m2 (two floors of about 20,000 squared meters each). From a structural point of view the building is divided in 6 different structures separated by appropriately-sized seismic joints. This paper focuses on the description of the seismic design of Building 1. It has a rectangular plan (of about 55x67 m2) and a maximum height of about 10.50 m (it is composed of a ground floor at 0.00 m, a first floor at 4.55 m and roof at 10.50 m). Overall, the total floor area of Building 1 is about 8000 m2. The floors are built to bear live loads (in addition to self weights and dead loads) of 700 kg/m2 (at the ground and the first floors) and of 130 kg/m2 (at the roof floor), depending on the different use of allocations. The maximum deformations of the floors, due to live loads only, turn out to be (in compliance with the regulation) lower than 1/1000 of the floor span.

The columns and the beams are realized with precast reinforced concrete elements (concrete of class Rck 550 kg/cm2 and steel bars of type FeB44K weldable) which are dry assembled without any casting "in situ". This structural typology is therefore characterized by not moment-resisting frames.

More in detail, the columns are monolithic elements (characterized, in general, by cross-section equal to 80x80 cm2) from which appropriate cantilevers stand out. The prestressed concrete beams lean on these cantilevers and, in turn, support the floors which are realized with prestressed concrete -shaped load-bearing tiles filled with a 6 cm thick cast-in-situ concrete slab. The connections between columns and beams, those between beams and slab and those between slab and -shaped load-bearing tiles are adequately dimensioned in order to ensure effective and safe transmission of the earthquake-induced actions. Also the 6 cm thick cast-in-situ concrete slab is characterized by the presence of an adequate additional steel reinforcement capable of ensuring effective transmission of the earthquake-induced actions to the beams below. All the connections between columns and beams are realized by means of the insertion of appropriate steel pins (which are drowned in the beams and in the cantilevers standing out from the columns and filled with adequate high-resistance mixtures) capable of transmitting shears forces, but not bending moments, to the columns.

It is then clear that, with reference to the horizontal seismic actions, the columns act like cantilever elements. It is therefore hard to successfully complete all structural verifications required by the seismic code either with respect to the strength (in terms of bending moment and shear at the base) or to the deformability (in terms of interstorey drifts).

Due to architectonical and distributive reasons, the necessary earthquake-resistant bracing systems cannot be spread over the whole building plan, but they can be placed in about ten bays at the most. Insofar as it is consistent with architectural requirements, the choice of the bracing system positions has been studied in such a way as to optimize their plan disposal in order to minimize the torsional effects on the structure

Four distinct structural solutions have been taken into consideration during the design phase:

  • precast structure with no bracing (called the "original" solution);
  • precast structure with steel bracing (called the "SB" solution);
  • precast structure with dampers placed so that they connect each floor to the ground (called the "MPD" solution);
  • precast structure with dampers placed between adjacent storeys (called the "SPD" solution).

The results of the numerical time-history simulations show that traditional bracing systems (made up using steel elements, "SB" solution) are capable of satisfying the deformability requirements at the expense of large forces both in the bracing system and upon the foundation. On the other hand, the insertion of viscous dampers (following the more efficient MPD scheme or the usual SPD one) allows at the same time to limit the drifts of the structure and to keep the forces in the bracing system at acceptable levels.

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