No abstract

No abstract

This paper addresses the issue of horizontal overstrength in modern code‐designed reinforced‐concrete (RC) buildings. The relationship between the lateral capacity, the design force reduction factor, the ductility level and the overstrength factor are investigated. The lateral capacity and the overstrength factor are estimated by means of inelastic static pushover as well as time‐history collapse analysis for 12 buildings of various characteristics representing a wide range of contemporary RC buildings. The importance of employing the elongated periods of structures to obtain the design forces is emphasized. Predicting this period from free vibration analysis by employing ‘effective’ flexural stiffnesses is investigated. A direct relationship between the force reduction factor used in design and the lateral capacity of structures is confirmed in this study. Moreover, conservative overstrength of medium and low period RC buildings designed according to Eurocode 8 is proposed. Finally, the implication of the force reduction factor on the commonly utilized overstrength definition is highlighted. Advantages of using an additional measure of response alongside the overstrength factor are emphasized. This is the ratio between the overstrength factor and the force reduction factor and is termed the inherent overstrength (Ω i). The suggested measure provides more meaningful results of reserve strength and structural response than overstrength and force reduction factors. Copyright © 2002 John Wiley & Sons, Ltd.

Many sites around the world may be subjected to severe distant earthquakes alongside moderate-size, short sourceto-site distance events. The two scenarios have different impacts on high-rise buildings and should be therefore investigated. Dubai, a region with an exceptionally high rate of development, is vulnerable to the aforementioned earthquake hazard scenarios. The region represents one of the most rapidly growing in construction of tall buildings worldwide. It was therefore selected for the investigation described in the paper. A hazard study for the construction site of a 187 m high reinforced concrete tower is conducted. Seismicity of the region is outlined and a hazard assessment is carried out to evaluate peak ground accelerations and uniform hazard spectra for different probabilities of exceedance. A number of natural and synthetic records are selected to represent different seismic assessment scenarios at the site. The RC tower is then modeled and analyzed using state-of-the art analytical platforms. Three-dimensional elastic, inelastic pushover and response history analyses are carried out to verify the dynamic characteristic and estimate the capacity to compare it with the predicted demand. The significance of including severe distant earthquakes in design and assessment of high-rise buildings is confirmed. Records representing the latter scenario amplify the fundamental mode that may be overlooked in design using short sourceto-site earthquakes. A proposal is made for scaling the results from inelastic dynamic analysis to arrive at a safe and economical design level. The study not only presents comprehensive hazard and vulnerability study for the selected test case, but also gives conclusions that generically apply to the class of long-period buildings subjected to large-distant and small-close earthquakes.• Select a typical high-rise RC structure in an appropriate region for this investigation. An actual 54story high-strength RC building from Dubai was selected. 392 A. MWAFY ET AL.It is observed that the values shown in Table 1 are lower than the finding of GSHAP (2004). The latter maps indicate values for Dubai in the range of 0·24-0·33 g. However, it has been pointed out (GSHAP, 2004) that some of the assumptions made in the latter study might be conservative. Also, it should be pointed out that faults, like the Dibba fault and the fault on the west coast of the UAE, were not included in the GSHAP study. A recent seismic hazard assessment study for UAE (Abdallah and Al-Homoud, 2004) showed that the design horizontal peak ground acceleration in Greater Dubai, Sharjah and Ajman area is between 0·10 g and 0·20 g, with an average of 0·15 g. The highest PGA in the latter study (0·2 g) is assigned to Fujaira. These values are consistent with the finding of the current study and confirm the over-conservatism of the values suggested by GSHAP.The uniform hazard spectra for the site for 10%, 5% and 2% probability of exceedance in 50 years are shown on Figure 6. No smoothing has been performed on the respon...

No abstract