Elisa Lumantarna

Inelastic Displacement Demand of Strength-Degraded Structures

This article presents findings from parametric studies involving nonlinear time-history analyses of inelastic systems with and without strength degradation. Results showed that estimates based on the equal-displacement and equal-energy propositions can be exceeded significantly by the inelastic displacement demands in the acceleration and velocity-sensitive regions of the response spectrum. The displacement demand behaviour is sensitive to the strength degradation and the frequency properties of the ground shaking. With a modest strength reduction factor of 2, the inelastic displacement demand would typically be constrained by the Peak Displacement Demand as indicated on the elastic displacement response spectrum for 5% damping.

Displacement-Controlled Behavior of Asymmetrical Single-Story Building Models

Displacement controlled behavior is a feature of low to moderate seismicity areas where the peak displacement demand on structures could be limited despite significant structural strength and stiffness degradation. In this article, the extension of the displacement controlled phenomenon to torsionally unbalanced framing systems is investigated. It is shown that the displacement demand of critical elements within a building can be insensitive to changes in eccentricity and torsional stiffness properties. While torsional actions is a well-researched topic, the incorporation of displacement controlled phenomenon into the analysis is original and represents a new development.

Plastic Hinge Length for Lightly Reinforced Rectangular Concrete Walls

ABSTRACT This research investigates the plastic hinge length in lightly reinforced rectangular walls typically found in regions of low-to-moderate seismicity. Poor performance has been exhibited by lightly reinforced concrete walls in past earthquake events. A series of finite element analyses have been carried out which demonstrate that if the longitudinal reinforcement ratio in the wall is below a certain threshold value, there will not be sufficient reinforcement to cause secondary cracking, and instead fracture of the longitudinal reinforcement at a single crack could occur. A plastic hinge length equation has been derived based on the results from the numerical simulations.

Drift Demand Predictions in Low to Moderate Seismicity Regions

Abstract This paper presents results obtained from a recent study that is aimed at assessing the drift demand on buildings for a range of projected earthquake scenarios in Australia. Parameters considered that may affect the response of buildings included building height, structural systems, and mass and stiffness distributions. It has been found that, for the range of buildings studied, the maximum angle of drift is 2.6–4.4 times the maximum response spectral displacement of the earthquake divided by the building height. This can be checked against the limiting drift capacity of the building to enable various levels of damage to be predicted for given earthquake scenarios.

Plastic Hinge Length for Lightly Reinforced C-Shaped Concrete Walls

ABSTRACT This research investigates the equivalent plastic hinge length of reinforced concrete C-shaped walls with reinforcement detailing typically found in low-to-moderate seismic regions. Reinforced concrete walls in these regions commonly have low amounts of longitudinal reinforcement and unconfined boundary regions, which have been shown to perform poorly in recent earthquake events. A series of state-of-the-art finite element analyses are undertaken to find the longitudinal strain distributions of low-rise, mid-rise, and high-rise C-shaped walls. The results of the equivalent plastic hinge lengths from the numerical investigation are shown to compare poorly to the predictions from some of the equations that currently exist in the literature. Subsequently, expressions are derived for the equivalent plastic hinge length for these types of walls and for the different modes of bending. The expressions derived from this research intend to improve the displacement capacity for these types of walls when using plastic hinge analyses.

Soil amplification in low-to-moderate seismic regions

The results of a study that investigates potential revisions of the spectral shape factors used in standards in regions of low-to-moderate seismicity are presented here. Using an equivalent linear analysis, the investigation particularly focuses on the effects of seismic intensity associated with rare and very rare intraplate earthquake events on site response. The Pacific Earthquake Engineering Research Center ground motion database (PEER) is used in selecting appropriate acceleration-time histories for the intraplate region. The results are normalised for comparison with the current spectral shape factors given in the Australian Standards for Earthquake Actions AS 1170.4:2007, with some differences being observed. The dependency of site amplification on seismic intensity was only observed for soil classes Ce, De and Ee. The rock site of class Be had considerably higher response in the short period range relative to class Ee. The records from the PEER ground motion database were also used for comparison with the results from this study, using a modified normalisation approach. The results from this study correlate well with the records from PEER.

Fragility Functions for RC Shear Wall Buildings in Australia

This research investigates the development of analytical fragility functions for reinforced concrete shear wall buildings in Australia. A building stock for the city of Melbourne is used in conducting an assessment of these types of structures. The assessment uses the best information available for selecting the building parameters applicable to the low-to-moderate seismic region, site soil class, expected earthquake ground motions, and site response. The capacity spectrum method is used to derive vulnerability functions for low-, mid-, and high-rise reinforced concrete shear wall buildings. Although there is a paucity of earthquake damage data available in Australia, some comparisons are made using the results from the fragility functions derived here to the damage data from the Newcastle earthquake in 1989.

Plastic hinge analysis for lightly reinforced and unconfined concrete structural walls

Poor performance of lightly reinforced and unconfined concrete structural walls have been observed in recent earthquake events. This research investigates the displacement capacity of such walls by comparing the results of a series of state-of-the-art finite element analyses for a range of different structural walls to that estimated using plastic hinge analyses. The common expressions used in estimating the yield curvature, yield displacement and plastic displacement are scrutinised for these types of walls. Some recommendations are given to improve the prediction of the displacement capacity of lightly reinforced and unconfined rectangular and C-shaped walls for flexural actions using a plastic hinge analysis. Importantly, a parameter has been recommended to be used in a “modified” approach for estimating the nominal yield displacement of lightly reinforced concrete walls. Different expressions are also recommended depending on the amount of longitudinal reinforcement used in the wall in comparison to that required to initiate secondary cracking. This is important for providing better estimations of the displacement capacity of RC structural wall buildings in low-to-moderate seismic regions such that vulnerability studies can be conducted.

Seismic Site Response Analysis Leading to Revised Design Response Spectra for Australia

This study explores the effects of local site conditions on seismic site response and investigates the validity of the site classification system and the response spectra in codes, with a focus on the Australian earthquake loading standard. The results show that the averaging process used to derive the design spectra in existing codes has led, in general, to an underestimation of the site response. A new systematic method is proposed for obtaining the displacement response spectra based on the correlations between the initial and degraded fundamental natural site period and amplification factors. Modifications to the site classification system are also recommended.

Effects of Interior Partition Walls on Natural Period of High Rise Buildings

In regions of low to moderate seismicity, serviceability limits states such as inter-story drift under wind load govern the design of the lateral load resisting structural systems of high rise buildings. The key objective in this regard is to provide adequate lateral stiffness to control lateral deflections and inter-story drifts. Current design practice assumes that the structural system alone provides lateral resistance against wind, the dominant load considered for countries like Australia. The contribution of nonstructural components (NSCs) such as interior partition walls on lateral stiffness is generally disregarded in the analysis of the buildings, even though it is commonly acknowledged that the NSCs play a significant role on the lateral stiffness of buildings. This technical note presents the results of a parametric study on the effects of NSCs, in particular, the effects of masonry interior partition walls on the fundamental period of buildings. The parameters considered in this study include: the number and length of walls, their material properties, the number of parallel moment resisting frames and the height of buildings. The results of this study indicate that interior walls can have significant effects on the lateral stiffness of buildings.