Assessment of seismic drift of structural walls designed according to SANS 10160 - Part 4

[摘要] ENGLISH ABSTRACT: Reinforced concrete structures, designed according to proper capacity design guidelines, can deforminelastically without loss of strength. Therefore, such structures need not be designed for full elasticseismic demand, but could be designed for a reduced demand. In codified design procedures thisreduced demand is obtained by dividing the full elastic seismic demand by a code-defined behaviourfactor. There is however not any consensus in the international community regarding the appropriatevalue to be assigned to the behaviour factor. This is evident in the wide range of behaviour factorvalues specified by international design codes.The purpose of this study is to assess the seismic drift of reinforced concrete structural walls in orderto evaluate the current value of the behaviour factor prescribed by SANS 10160-4 (2009). This isdone by comparing displacement demand to displacement capacity for a series of structural walls.Displacement demand is calculated according to equivalency principles (equal displacement principleand equal energy principle) and verified by means of a series of inelastic time history analyses (ITHA).In the application of the equivalency rules the fundamental periods of the structural walls were basedon cracked sectional stiffness from moment-curvature analyses.Displacement capacity is defined by seismic design codes in terms of inter storey drift limits, with thepurpose of preventing non-structural damage in building structures. In this study both thedisplacement demand and displacement capacity were converted to ductility to enable comparison.The first step in seismic force-based design is the estimation of the fundamental period of thestructure. The influence of this first crucial step is investigated in this study by considering two periodestimation methods. Firstly, the fundamental period may be calculated from an equation provided bythe design code which depends on the height of the building. This equation is known to overestimateacceleration demand, and underestimate displacement demand. The second period estimationmethod involves an iterative procedure where the stiffness of the structure is based on the crackedsectional stiffness obtained from moment-curvature analysis. This method provides a more realisticestimate of the fundamental period of structures, but due to its iterative nature it is not often applied indesign practice.It was found that, regardless of the design method, the current behaviour factor value prescribed inSANS 10160-4 (2010) is adequate to ensure that inter storey drift of structural walls would not exceedcode-defined drift limits. Negligible difference between the equivalency principles and ITHA wasobserved.

[发布机构] Stellenbosch University