Assessment on the deflection amplification factor of steel buckling-restrained bracing frames

Researchers in the field of earthquake engineering are always looking for new ways to improve the seismic behavior of structures. The buckling-restrained brace (BRB) is one of these exciting innovations that are employed to increase the ductility capacity of traditional steel braced frames. Understanding the nonlinear response of these novel systems in estimating maximum displacements due to an earthquake has been of significant importance for structural designers. Accordingly, this research is carried out to study of deflection amplification factor ( C d) in BRBs, which have recently been presented in seismic design provisions as one of the seismic lateral-resisting systems. To this end, five 3-, 5-, 7-, 10-, and 15-story BRBs are modeled in the software framework of OpenSees. Ground motion simulation is performed by selecting several scaled earthquake records, and the values of elastic and ultimate displacements of structural systems are computed through pushover and nonlinear time-history analyses. The results showed that the deflection amplification factor suggested within famous building codes (such as ASCE-7-16) compared to the obtained values is, in some cases, for certainty; conversely, it is underestimated under some conditions. In fact, the findings indicate that the magnitude of C d in these systems is strongly related to the height of the building.

Comparison of analysis techniques for the seismic evaluation of an 88-storey concrete building

This thesis presents the comparison of results for an 88-storey reinforced concrete building subjected to static and dynamic analyses. Similar to a building designed in a moderate seismic zone, the structure is designed and detailed according to the ACI 318M (2002) Code provisions and the seismic provisions of the UBC (1997). The building is modeled according to structural drawings and element design specifications are used in describing members' deformation characteristics. Resistance to dynamic motion is provided through boxed core-wall assemblies acting as cantilevers walls in one direction and linked with coupling beams at storey levels in the orthogonal direction. The equivalent static, dynamic modal spectrum, linear time-history and nonlinear time-history analyses are employed and a comparison of maximum inter-storey drift response is provided. The results of the analyses show that the linear time-history analysis is the most appropriate method in capturing the behavior of this particular building under dynamic loading.

Comparison of analysis techniques for the seismic evaluation of an 88-storey concrete building

This thesis presents the comparison of results for an 88-storey reinforced concrete building subjected to static and dynamic analyses. Similar to a building designed in a moderate seismic zone, the structure is designed and detailed according to the ACI 318M (2002) Code provisions and the seismic provisions of the UBC (1997). The building is modeled according to structural drawings and element design specifications are used in describing members' deformation characteristics. Resistance to dynamic motion is provided through boxed core-wall assemblies acting as cantilevers walls in one direction and linked with coupling beams at storey levels in the orthogonal direction. The equivalent static, dynamic modal spectrum, linear time-history and nonlinear time-history analyses are employed and a comparison of maximum inter-storey drift response is provided. The results of the analyses show that the linear time-history analysis is the most appropriate method in capturing the behavior of this particular building under dynamic loading.

Seismic Performance of a Green Roof Structure

Sustainability addresses the need to reduce the structure’s impact on the environment but does not reduce the environment’s impact on the structure. To explore this relationship, this study focuses on quantifying the impact of green roofs or vegetated roofs on seismic responses such as story displacements, interstory drifts, and floor level accelerations. Using an archetype three-story steel moment frame, nonlinear time history analyses are conducted in OpenSees for a shallow and deep green roof using a suite of ground motions from various distances from the fault to identify key trends and sensitivities in response.

Comparison of Novel Seismic Protection Devices to Attenuate the Earthquake Induced Energy

This study addresses an alternative use of viscous dampers (VDs) associated with buckling restrained braces (BRBs) as innovative seismic protection devices. For this purpose, 4-, 8- and 12-story steel bare frames were designed with 6.5 m equal span length and 4 m story height. Thereafter, they were seismically improved by mounting the VDs and BRBs in three patterns, namely outer bays, inner bays, and all bays over the frame heights. The structures were modeled using SAP 2000 software and evaluated by the nonlinear time history analyses subjected to the six natural ground motions. The seismic responses of the structures were investigated for the lateral displacement, interstory drift, absolute acceleration, maximum base shear, and time history of roof displacement. The results clearly indicated that the VDs and BRBs reduced seismic demands significantly compared to the bare frame. Moreover, the all-bay pattern performed better than the others.

A Wavelet-based Approach for Truncating Pulse-like Records

The seismic performance assessment of structures using truncated pulse-like ground motion records is discussed. It is shown that it is possible to truncate pulse-like signals using a novel wavelet-based definition that identifies the duration of the predominant velocity pulse. The truncated time history can efficiently reproduce the increased seismic demand that near-field records typically produce. Substituting the original ground motion with the truncated signal, significantly accelerates structural analysis and design. The truncated signal is the part of the original accelerogram that coincides with the duration of the predominant pulse, which is identified using a wavelet-based procedure, previously proposed by the authors. Elastic and inelastic response spectra and nonlinear time history analyses for SDOF (single-degree-of-freedom) systems are first studied. Subsequently a nine-storey steel frame is examined in order to demonstrate the performance of the proposed approach on a multiple-degree-of-freedom system. The proposed approach is found very efficient for pulse-like ground motions, while it is also sufficient for many records that are not characterized as such.

Assessment of the Seismic Performance for a Low-Code RC Shear Walls Structure in Bucharest (Romania)

Background: Low-code RC shear walls structures house a significant proportion (over 20%) of the inhabitants of Bucharest. Objective: In this research, the seismic performance of a low-code reinforced concrete shear walls structure located in various sites in Bucharest (Romania) is assessed. Methods: The seismic performance is assessed using both static and dynamic nonlinear time-history analyses, as well as detailed sectional analysis of the RC shear walls. Results: The results show that the structure has significant capacity differences in the two principal directions. Moreover, it has been observed that the maximum top displacements obtained from nonlinear time history analyses are larger in the transversal direction. Conclusion: Considering the behaviour of such structures during the 1977 Vrancea earthquake, the fact that these structures are already 40 – 50 years old and given the results of some of the analyses shown in this study, it can be concluded that immediate seismic rehabilitation measures are needed in order to correct, at least partially the structural issues of this section type.