Vulnerability Reduction Techniques for Precast RC Structures with Dissipative Connections

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

2. 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.

3. 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 x 40 cm)

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

5. 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 →

6. Behaviour of frames with beam-to-column dowel connections • 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.

7. 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

8. 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 function of the second moment of area of the dowel connection • Moment at column base function of the second moment of area of the dowel connection

9. 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 kN.m for a PGA = 0.15 g • ►Yielding of columns at their bases • ►Failure of the structure related • to plastic rotation capacity of columns

10. Bracings using INERD Pin connections in precast concrete portal frames

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

12. 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

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

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

15. 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).

16. 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

17. 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.

18. 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.