Effects of foundation rocking and uplifting on displacement amplification factor

Prediction of displacement demand to assess seismic performance of structures is a necessary step where nonlinear static procedures are followed.While such predictions have been well established in literature for fixed-base structures,fewer bodies of researches have been carried out on the effect of rocking and uplifting of shallow foundations supported by soil,on such prediction.This paper aimed to investigate the effect of soil structure interaction on displacement amplification factor C1 using the beam on nonlinear Winkler foundation concept.A practical range of natural period,force reduction factors,and wide range of anticipated behavior from rocking,uplifting and hinging are considered and using thousands nonlinear time history analysis,displacement amplification factors are evaluated.The results indicate that the suggested equations in current rehabilitation documents underestimate displacement demands in the presence of foundation rocking and uplift.Finally,using regression analyses,new equations are proposed to estimate mean values of C1.

Inelastic displacement ratio of low-to mid-rise BRBFs designed under variable levels of seismicity

Buckling-restrained braces(BRBs)have shown their capability to provide building structures with stiffness,strength,and ductility.Estimating the seismic drifts of buckling-restrained braced frames(BRBFs)is an important design step to control structural and non-structural damage.In current practice of seismic design,the estimation of seismic drifts of BRBFs is performed by using empirical calculations that are independent upon either the type of the structural system or the design level of seismicity.In these empirical calculations,the seismic drifts are estimated by amplifying the reduced elastic drifts obtained under design lateral loading with a displacement amplification factor(DAF).The value of DAF is considered equal to the product of the response modification factor R and the inelastic displacement ratioρ.The goal of the current research is to assess the value ofρfor low-to mid-rise BRBFs designed under low and high levels of seismicity.This goal has been achieved by conducting a series of elastic and inelastic time-history analyses pertaining to an ensemble of earthquake records on 3-,6-and 9-story BRBFs.The results indicate that theρ-ratio increases with an increase in design seismic intensity and an increase in experienced inelasticity.The range ofρfor low seismicity designs ranges from 0.63 to 0.9,while for high seismicity designs this range stretches from 0.83 to 1.29.It has been found that the consideration of a generalρ-ratio of 1.0 is a reasonable estimation for the design of the BRBFs considered in this study.