LESSLOSS Sub Project 7 Techniques and Methods for

LESSLOSS Sub Project 7 Techniques and Methods for Vulnerability Reduction Analysis of precast RC structures with dissipative connections Nicolas Hausoul Barcelona 18 th May 07 – Lisbon 24 th May 07 LESSLOSS Dissemination Meeting 1

Post-earthquake surveys Typical damage caused by earthquake on precast reinforced concrete structure: beams fall down from their support, due to lack of resistance and energy dissipation capacity at the beam-column connections. Example: Adana earthquake An industrial building collapses Causes : - under design of the dowel connections between beams and columns - bad implementation of the grouted mortar around these dowels. 2

Reference precast concrete portal frames structure • 17 meters length beam (L x w x h: 17 m x 30 cm x 40/80 cm) • 6 meters height column (L x w x h: 17 m x 40 cm) 3

The most used beam-to-column connections : - simple dowel connections - bolted dowel connections 4

Behaviour of frames with beam-to-column dowel connections 1. Simple equivalent analytical model • Aim: determine structure conditions that cause maximum axial force in the beam (and thus transmits in the beam-column connection) → Allows to design dowel connection → 5

Behaviour of frames with beam-to-column dowel connections 1. Simple equivalent analytical model • Results: the beam axial force and column fixed end moment, in the model, are maximum when the difference of stiffness of the “column-support” system Ksyst-i between the 2 columns constituting the frame is maximum. 6

Behaviour of frames with beam-to-column dowel connections 2. Dynamic non linear analysis (time history) of the structure with dowel connections • Dowel connection non-linear law modelled by springs • Includes difference of stiffness of the column supports fixed partially fixed 7

Behaviour of frames with beam-to-column dowel connections 2. Dynamic non linear analysis (time history) of the structure with dowel connection Results: • Relative beam-column displacement • Moment at column base function of the second moment of area of the dowel connection 8

Behaviour of frames with beam-to-column dowel connections 2. Dynamic non linear analysis (time history) of the structure with dowel connections Analysis of results: • Dowel connection is not a dissipative connection system (no reduction of moment at column base) • Failure of the dowels before any dissipation of energy • 2 dowels with d = 14 mm can resist to a accelogram with a PGA = 0. 4 g if resistance and adherence of grouted mortar around dowels are OK • No great relative displacement: d < 2 mm • MSd, max = MRd, column = 190 k. N. m for a PGA = 0. 15 g ►Yielding of columns at their bases ►Failure of the structure related to plastic rotation capacity of columns 9

Bracings using INERD Pin connections in precast concrete portal frames 10

Pushover analysis: objective To evaluate the effectiveness of bracings using INERD Pin Connections in precast concrete portal frames. Study of 2 structures: a) Reference structure b) Structure with bracings using INERD Pin connection 11

Pushover analysis: Assumptions Plastic hinges at column bases • 3 plastic rotation capacity of columns at their bases in the 2 considered structures a) and b) Design of INERD Pin Connection • One INERD Pin connections law in structure b) With the dimensions indicated on the figure: Pu. d = MRd, connection 12

Pushover analysis: Assumptions Design method of INERD Pin Connection exist (contribution of Callado – IST Lisbon) 13

Pushover analysis: Load – Displacement curves • Reference structure • Structure with bracings using INERD Pin connection 14

Pushover analysis: Analysis of results • Under PGA ag ≤ 0. 2 g low seismic area => no failure, even in low ductility structures. Bracings with INERD Pin connections - only bring rigidity to the structure - reduce rotation and displacement (SLS state). - For ULS , bracings with INERD Pin connections are not needed in precast concrete structures. • For PGA ag > 0. 2 g high seismic area Bracings with INERD Pin connections - effective, especially for low plastic rotation capacity at column base. - ensure stability (ULS) - reduce deformations of the structure (SLS). 15

Pushover analysis: Analysis of results • Comparison of pushover curves for structure with and without INERD Pin Connections at same level of ductility : => Deformation capacity and rigidity are increased => Yielding of column base occur for greater horizontal force => Bracings with INERD Pin connection also reduce damage of the structure 16

Pushover analysis: Analysis of results • The first part of the curve • • • represents the formation of plastic hinges at the base of columns. The second part of pushover curves represents the behaviour of the INERD Pin Connection. By modifying INERD Pin Connection characteristics, the behaviour of the structure, rigidity, ductility, rotation capacity and strength can be modified. Results are confirmed by dynamic non linear analysis. 17

General Conclusions • Globally, the study has • • • demonstrated the possibility to reduce the vulnerability of existing precast concrete portal frames by means of added bracings. These bracings must be dissipative. Using INERD Pin Connections is one practical solution which has the advantage of putting the designer in real control of plastic capacity. The system is applicable to new design as well as to retrofit of existing structures. 18