Bulletin of the New Zealand Society for Earthquake Engineering

The significance of polarisation in near-fault ground motions – A case study of February 2023 Kahramanmaras M7.7 earthquake

2024-12-01T18:16:19+13:00

This article presents a comprehensive study on directivity effects and impulsive signals in near-fault ground motions, focusing on the case of the Kahramanmaraş earthquake in February 2023. The study investigates the impact of polarisation on pulse-type and non-pulse-type ground motions by computing spectral acceleration values for 180-degree rotated components. The results demonstrate that pulse-type ground motions exhibit higher spectral acceleration values and higher levels of polarisation, particularly in the period ranges close to the pulse period. The findings highlight the significance of directivity effects in seismic hazard analyses and emphasise the need for accurate assessment of directivity effects in seismic design procedures.

Prediction model for earthquake death toll based on PCA-BAS-ELM in mainland China

2024-12-01T18:16:04+13:00

In recent years, China has experienced frequent catastrophic earthquakes, causing huge casualties. If the death toll can be quickly predicted after a disaster, then relief supplies can be delivered in a timely and reasonable manner, and the death toll and property losses can be minimized. Therefore, rapid and effective prediction of earthquake deaths plays a key role in guiding post-earthquake emergency rescue. However, there are many factors affecting the number of deaths in an earthquake. Aimed at this issue, a prediction model for earthquake deaths based on extreme learning machine (ELM) optimized by principal component analysis (PCA) and beetle antennae search (BAS) algorithm has been proposed in this study. Firstly, this study selected sample data of destructive earthquakes in mainland China in the past 50 years, then PCA was used to reduce the dimensionality of the factors affecting earthquake deaths, the principal components with lower contribution rates were removed, and the principal components with higher contribution rates were used as the input variables of ELM. Meanwhile, the earthquake deaths were used as the output variable, and the connection weights and thresholds of ELM was optimized using BAS. Finally, the prediction model for earthquake deaths based on PCA-BAS-ELM was established. The established model was used to predict the test samples. The results showed that the prediction results of PCA-BAS-ELM model had a higher fit with the actual values, and its mean square error, mean absolute percentage error and root mean square error were 2.433, 2.756% and 5.443, respectively, which suggested higher prediction accuracy.

Earthquake design pressures from soil interaction on building basement walls

2024-12-01T18:15:48+13:00

Free-standing retaining walls supporting a cohesionless soil backfill are usually designed for earthquake induced soil pressures using the Mononobe-Okabe limit state analysis (Mononobe and Matsuo [1]). This method assumes the development of a failure wedge in the backfill soil leading to active soil pressures on the wall. Building basement walls are usually relatively stiff or restrained from relative displacement so the active pressure state is unlikely to arise. In addition, two components of dynamic pressure that develop on the wall need to be considered. The first of these is due the shear deformations in the soil generated by the earthquake waves. The second results from the inertia forces of the building above ground level generating movements of the wall against the soil.

Two-dimensional elastic finite element analyses were undertaken in the present study to determine the earthquake induced pressure force and its distribution on simplified basement wall structures. The parameters investigated included the width and stiffness of the basement, the depth of the soil layer and the distribution of the soil shear modulus with depth.

Because of the wide range of basement geometries and foundation types it is not possible to develop a simple empirical method that is widely applicable. However, the elastic finite element analyses identified the influence of the most important parameters and the results can be used to decide whether more detailed analyses are necessary for large buildings.

Impact of seismic demand on construction costs for buildings up to 8 storeys high

2024-12-02T18:15:59+13:00

The legally binding earthquake performance requirements in New Zealand's Building Act and Building Code emphasise building collapse prevention, allowing for a certain degree of damage to resist the seismic load. However, societal expectations demand that buildings remain operational after an earthquake. This research aims to understand the true cost of up to 8 storeys high building structures that remain operational after an earthquake. Our assumptions are: 1) higher seismic demand is expected to have a limited impact in overall construction costs, and quite minimal impact on total development costs, and 2) the influence of seismic resilience on construction costs is different depending on the structural system. An extensive construction costs database was developed including the most typical structural and foundation systems. The main conclusions are that 1) the effect of location and floor type on construction costs is not critical, 2) the impact of a higher seismic demand on construction costs depends on the structural system, and 3) foundation type has a large influence on construction costs but seismic demand does not. Engineers should prioritise stiff lateral systems because the cost implications of having a stiffer structural system are minimal, especially when considering the development costs. The cost implications of having more resilient buildings that can be readily occupied after an earthquake are negligible, and New Zealand should move towards stiff, damage resisting structures using well understood structural systems like RC walls. Society expects this from our buildings, our engineers are trained and capable to design them, and the extra cost is minuscule.