Report - PEER - University of California, Berkeley

The minimal scope of structural seismic tests would be to check the performanceof a model when subjected to the loading considered in its design and to check also itsultimate capacity in order to evaluate safety margins. In fact, the present limit-statebased design codes explicitly consider one or two limit-states (safety andserviceability) and implicitly assume that the structure should be able to withstand(without collapse but with important/severe damage) earthquake intensities muchhigher than the design ones, which is achieved through capacity design (preferentialstabledissipation mechanisms) and requirements on ductility capacity. Explicitquantification of the seismic intensities associated to limit states other than safety isnot given, nor performance is required to be checked. Therefore, one relies onprescriptive design procedures and on intended performances, which requireverification and/or calibration. This has been the main scope of most of the testsperformed at ELSA on structures designed according to the Eurocodes. Building andbridge models were tested and the results were used by the European researchcommunity and code-makers, to calibrate models, to refine some parts of the code(e.g., ductility classes, behavior factors), to introduce new design rules (e.g.,structures with infill panels) and analysis methods, to introduce new materials (e.g.,composite structures) and to introduce new technologies (base-isolation anddistributed passive dissipation systems).Two examples of the tests performed at ELSA in support of Eurocode 8 are givenbelow. One is concerned with new structures and the corresponding tests were carriedout for earthquake intensities corresponding to serviceability life-safety and ultimatecapacity. The other is concerned with the assessment of existing structures, for whicha test protocol tailored for life-safety and for ultimate capacity was adopted.4.1 Testing of a Full-Scale 4-Storey RC Frame Building Designed According tothe EurocodesThe first experiments performed at ELSA in support of the European Codes consistedon a series of tests on a full-scale 4-storey RC frame building designed according toEurocodes 2 and 8 (see Fig. 2). This was the first ‘Eurocode structure’, built andseismically tested for two different earthquake input motion intensities correspondingto serviceability and life-safety limit states. The structure was subsequently subjectedto a displacement controlled cyclic test up to collapse in order to check its ultimatecapacity. Earthquake intensities corresponding to 40% and 150% of the ‘designearthquake’(DE) were used in the PSD tests. Illustrative results are given in Fig. 2.Detailed description of the research programme, test results and analysis can be foundelsewhere (Negro, 1996). It is however important to note that the low-level testcaused only minor cracking in the structure and apparent low damage was sustainedin the high-level test, with cracks remaining open only in the critical parts of thebeams. Yielding of rebars took place in the beams plastic hinge zones and at the baseof the ground floor columns, but neither spalling of concrete (only slight indication ofspalling at the base of the 1 st storey columns) nor buckling of rebars were observed.286