Nonlinear Pushover Analysis of Concrete Infilled Frames

[[abstract]]Six reinforced concrete frames with or without masonry infi lls were constructed and tested under horizontal cyclic loads. All six frames had identical details in which the transverse reinforcement in columns was provided by rectangular hoops that did not meet current ACI specifi cations for ductile frames. For comparison purposes, the columns in three of these frames were jacketed by carbon-fi ber-reinforced-polymer (CFRP) sheets to avoid possible shear failure. A nonlinear pushover analysis, in which the force-deformation relationships of individual elements were developed based on ACI 318, FEMA 356, and Chen’s model, was carried out for these frames and compared to test results. Both the failure mechanisms and impact of infills on the behaviors of these frames were examined in the study. Conclusions from the present analysis provide structural engineers with valuable information for evaluation and design of infi lled concrete frame building structures.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]EI[[incitationindex]]SCI[[booktype]]紙本[[countrycodes]]US

Characterization of the dynamic response of structures to damaging pulse-type near-fault ground motions

The presence of long-period pulses in near-fault records can be considered as an important factor in causing damage due to the transmission of large amounts of energy to the structures in a very short time. Under such circumstances high-energy dissipation demands usually occur, which are likely to concentrate in the weakest parts of the structure. The maximum nonlinear response or collapse often happens at the onset of directivity pulse and fling, and this time is not predicted by the natural structural vibration periods. Nonlinear response leading to collapse may in most cases occur only during one large amplitude pulse of displacement. From the study of the response of both linear and nonlinear SDOF systems, the effects of these distinctive long-period pulses have been assessed by means of : (i) synthetic parameters directly derived from the strong ground motion records, and (ii) elastic and inelastic spectra of both conventional and energy-based seismic demand parameters. SDOF systems have first been subjected to records obtained during recent earthquakes in near-fault areas in forward directivity conditions. The results indicate that long duration pulses strongly affect the inelastic response, with very high energy and displacement demands which may be several times larger than the limit values specified by the majority of codes. In addition, from the recognition of the fundamental importance of velocity and energy-based parameters in the characterization of near-fault signals, idealized pulses equivalent to near-fault signals have been defined on account of such parameters. Equivalent pulses are capable of representing the salient observed features of the response to near-fault recorded ground motions