Arthur C. Heidebrecht

Engineering implication of ground motion A/V ratio

Abstract An earthquake data set consisting of 45 strong motion records was analyzed to investigate the significance of the peak ground acceleration-to-velocity (A/V) ratio as a parameter to indicate the dynamic characteristics of earthquake ground motions. It was found that the A/V ratio of ground motions is a viable indicator of the M (magnitude)-R (epicentral distance) relationships associated with the motions. Due to its tacit correlation with the M-R relationship, the A/V ratio provides useful information regarding the relative frequency content and duration of strong shaking for ground motions resulting from different seismic environments. In light of these observations, the implications of seismic ground motions having different A/V ratios on engineering design were discussed, and an example to incorporate this ratio into the specification of seismic design forces for building structures was illustrated.

Approximate analysis of asymmetric wall-frame structures

Abstract An approximate hand method is proposed for lateral force analysis of asymmetric wall-frame structures having constant properties along the height. The coupled torsion-bending differential equations of equilibrium are decoupled using an orthogonal transformation. The deformations and stress resultants in the wall and frame assemblies are obtained by linearly combining the respective coefficients of each of the solved decoupled equations, stresses in members being obtained by simple force distribution formulae. Non-dimensional coefficients for deflection and stress resultants are given for a practical range of system parameters. The method is illustrated by a numerical example.

ENGINEERING PERSPECTIVE FOR THE SEISMIC SITE RESPONSE OF ALLUVIAL VALLEYS

SUMMARYThe seismic site response of alluvial valleys with limited width is evaluated using three engineering models. The modelsare based on the one-dimensional, two-dimensional and the frame model approaches. The objective is to analyse thee⁄ects of the main parameters governing surface motions and provide engineering guidance for predicting them. Thelimitations on the use of the one-dimensional model in site response evaluation in valleys are pointed out. The framemodel, which accounts for the limited width of valley, gives response results that are in good agreement with thetwo-dimensional model results. It is found that the e⁄ect of the two-dimensional ampliÞcation is signiÞcant overadistancefromthevalleyedgesbeyondwhichtheresponsemaybeadequatelyrepresentedbyone-dimensionalanalysis.ThesoilampliÞcationvariesdependingon the soil type,site locationrelativeto the valley and the dominantperiod andamplitude of input rock record. ( 1997 by John Wiley & Sons, Ltd. KEY WORDS: earthquake; site response; dynamic analysis; valley; soil conditions

A simple engineering model for the seismic site response of alluvial valleys

Abstract The seismic site response of alluvial valleys with limited width is studied. The intent of this investigation is to integrate the seismological and engineering perspectives to gain physical insight into the dynamic behaviour of alluvial valleys. A simplified engineering model (frame model) is developed to predict the nonlinear seismic response of symmetrical valleys. The proposed model is one-dimensional and accounts for the limited width of the valley. The frame model identifies the significant vibration modes and their variation in the horizontal and vertical directions. Sensitivity analyses are performed on the valley response to evaluate the effect of the uncertainty in establishing the dynamic soil properties. Response results from the frame model are compared with those calculated using one-dimensional and two-dimensional finite-element models. The proposed frame model response shows good agreement with finite-element model results.

Effect of normal frames on shear walls

Abstract An approximate method is presented to study the interacting effect of normal frames on uniform shear walls and the shear lag effect in the normal frames. Based on the axial deformation distribution among columns, a reasonable assumption is further introduced to simplify the method. An example is included to illustrate the application of the proposed method and the accuracy of the simplified method. Based on the simplified method design curves are presented for rapid determination of maximum deflection, wall moment and column axial stress of a uniform structure subjected to point load at top, uniform and triangular load distribution.