A noniterative design procedure for supplemental brace-damper systems in single-degree-of-freedom systems

SUMMARY: In this paper, a method for designing supplemental brace-damper systems in single-degree-of-freedom (SDOF) structures is presented. We include the effects of the supporting brace stiffness in the dynamic response by using a viscoelastic Maxwell model. On the basis of the study of an SDOF under ground excitation, we propose a noniterative design procedure for simultaneously specifying both the damper and the brace while assuring a desired structural performance. It is shown that to increase the damper size beyond the value delivered by the proposed criteria will not provide any improvement but actually worsen the structural response. The design method presented here shows excellent agreement with the FEMA 273 design approach but offers solutions closer to optimality. © 2013 John Wiley & Sons, Ltd

Optimum strength distribution for seismic design of tall buildings

This paper examines the effects of strength distribution pattern on seismic response of tall buildings. It is shown that in general for an MDOF structure there exists a specific pattern for height-wise distribution of strength and stiffness that results in a better seismic performance in comparison with all other feasible patterns. This paper presents a new optimization technique for optimum seismic design of structures. In this approach, the structural properties are modified so that inefficient material is gradually shifted from strong to weak areas of a structure. This process is continued until a state of uniform deformation is achieved. It is shown that the seismic performance of such a structure is optimal, and behaves generally better than those designed by conventional methods. The optimization algorithm is then conducted on shear building models with various dynamic characteristics subjected to a group of severe earthquakes. Based on the results, a new load pattern is proposed for seismic design of tall buildings that is a function of fundamental period of the structure and the target ductility demand. The optimization method presented in this paper could be useful in the conceptual design phase and in improving basic understanding of seismic behavior of tall buildings

Application of Surface wave methods for seismic site characterization

Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages. Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this topic

Influence of foundation type on seismic response of low-rise structures in liquefiable soil

The 2010-2011 Canterbury Earthquake Sequence (CES) caused extensive damage to low-rise structures in the city of Christchurch, New Zealand, mainly due to liquefaction-induced effects including settlement and angular distortion. This paper will present the results of dynamic centrifuge tests comparing the effects of liquefaction on the seismic performance of isolated structures with different types of shallow foundations (strips or a raft), and the effect of being situated adjacent to a heavier neighbouring structure of the same foundation type (i.e. considering structure-soilstructure interaction, SSSI). Performance will be evaluated under a sequence of successive earthquakes from the 2010-2011 CES and 2011 Tohoku Earthquake, Japan, to permit study under ground motions and aftershocks generating full liquefaction either extensively or to only a limited depth below ground level. The results show firstly that lower intensity ground shaking occurs at the ground surface when liquefaction occurs and that this can be estimated as a function of the degree of liquefaction using a simple estimation method. When subjected to these ground motions, using strip foundations for isolated structures can result in a reduction in structural demand, especially when the soil is extensively liquefied. When a neighbouring structure with the same foundation type is present, the effects of SSSI within liquefied soil result in changes to natural period and damping such that raft-founded structures exhibited lower structural demands. In either case (isolated or adjacent), a reduction in structural demand is accompanied by an increase in post-earthquake permanent foundation deformation