An experimental study on the seismic response of cold-formed steel tubular members functioning as bracing members in concentrically braced frames is described. A number of shake table tests were carried out to examine member and storey performance under earthquake loads. Three different square and rectangular hollow cross-sections were utilised for the bracing members. It is shown that maximum brace tensile forces can be over 30% higher than those estimated using the actual yield strength, due to strain hardening and strain rate effects. Moreover, the experimental storey shear can exceed that predicted by design procedures by more than 50%. The tests also indicate that the ductility demand under seismic loading can be estimated reasonably well for the frame models using a conventional equal-energy idealisation. In addition, the results illustrate generally satisfactory performance for braces with member slenderness exceeding typical limits in seismic codes.
To provide quantitative information on the ground acceleration necessary to break speleothems, laboratory measurements on samples of stalagmite have been performed to study their failure in bending. Due to their high natural frequencies, speleothems can be considered as rigid bodies to seismic strong ground motion. Using this simple hypothesis and the determined mechanical properties (a minimum value of 0.4 MPa for the tensile failure stress has been considered), modelling indicates that horizontal acceleration ranging from 0.3 m/s2 to 100 m/s2 (0.03 to 10g) are necessary to break 35 broken speleothems of the Hotton cave for which the geometrical parameters have been determined. Thus, at the present time, a strong discrepancy exists between the peak accelerations observed during earthquakes and most of the calculated values necessary to break speleothems. One of the future research efforts will be to understand the reasons of the defined behaviour. It appears fundamental to perform measurements on in situ speleothems.
In this study, the seismic design and performance of composite steel-concrete frames are studied. The new Eurocode 4 and Eurocode 8, which are in a preliminary stage at the moment, are employed for the design of six composite steel-concrete frames. The deficiencies of the codes and the clauses that cause difficulties to the designer are discussed. The inelastic static pushover analysis is employed for obtaining the response of the frames and the overstrength factors. The evaluation of the response modification factor takes place by performing incremental time-history analysis up to the satisfaction of the yield and collapse limit states in order to investigate the conservatism of the code. The last purpose of this study is to investigate if elastically designed structures can behave in a dissipative mode.
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