Journal of Seismology and Earthquake Engineering
Volume:5 Issue: 1, spring 2003

Major damage was observed mostly in the older bridge structures in the Northridge (1994), Kobe (1995) and Taiwan (1999) earthquakes. The most extensive damage included flexural/shear failure of substructure members and superstructure unseating at simple supports or expansion joints. In general, similar types of damages demonstrate a similar nature in view of the seismic behavior of older bridge design in all three earthquakes. As modern bridges have not been significantly affected during the recent ground motions, no reliable judgment could be made on the seismic performance of modern bridges structures.The seismic performance of Evin-Valley Bridge, a newly built slab-on-girder bridge is investigated analytically at the damage control limit state. A 3-D model of the bridge was built in DRAIN 3DX computer programme using a fiber-section beam-column element to represent inelastic behavior of RC substructure members. Elastomeric bearing pads, shear keys, expansion joints and the abutment backwalls were included in modeling of cyclic behavior of each component. The superstructure girder-beams were assumed to remain elastic and compressive elastic springs were used to represent the soil effect. A free vibration analysis of the multiple-part structure, assuming open gaps and expansion joints, showed the combined influence of a broad number of modes of vibration in dynamic response of the bridge. However, since the gaps are predicted to frequently close and reopen under earthquake forces, such results should not be relied on predicting of the seismic response. The results obtained from dynamic analyses using the Naghan (1977), the Northridge (1994) and the Kobe (1995) acceleration records show that the seismic demand values in the substructure elements are much less than the existing member capacities. The results also indicate that the dynamic response values are not comparable with the earthquake demands obtained from the equivalent static method and a large difference is observed between the results of two methods.

A Markov method of analysis is presented for obtaining the seismic response of suspension bridges to nonstationary random ground motion. A uniformly modulated nonstationary model of the random ground motion is assumed which is specified by the evolutionary r.m.s ground acceleration. Both vertical and horizontal components of the ground motion are considered to act simultaneously at the bridge supports. The analysis duly takes into account the angle of incidence of earthquake, the spatial correlation of ground motion and the quasi-static excitation. A suspension bridge is analysed under a set of parametric variations in order to study the nonstationary response of the bridge, The results of the numerical study indicate that (i) frequency domain spectral analysis with peak r.m.s acceleration as input could provide more r.m.s response than the peak r.m.s response obtained by the nonstationary analysis; (ii) longitudinal component of the ground motion significantly influences the vertical vibration of the bridge; and (iii) the angle of incidence of earthquake has considerable influence on the deck response.

Airport Traffic Control Towers (ATCT''s) are among the most critical structures in an airport that are expected to keep their level of serviceability during and after severe disasters like strong earthquakes. Seismic vulnerability of these structures is the matter of great importance during immense ground motions due to their high sensitiveness to structural and non-structural damage. On the other hand, few of these towers are constructed using special structural systems compared to the ordinary residential and industrial structures, because of their uncommon topology and expected function. Therefore analysis and design of these structures cannot be performed using common building codes and methods, but needs a detailed investigation on the seismic behavior of the structure based on the geotechnical characteristics of its site. The control tower under the study is a reinforced concrete structure consisting of four symmetric flexural flanges connected with floor slabs in twelve elevations. The dynamic analysis of the structure is performed by ANSYS finite element program. The lateral forces are estimated performing spectral analysis. The ultimate strength of the structure and the cracking patterns are revealed through a nonlinear static push-over analysis