New Zealand Society for Earthquake Engineering
http://https://repo.nzsee.org.nz:8080
The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.2024-11-04T11:16:40ZFinite Element Method Analysis of Reinforced Concrete Exterior Beam-Column Joint Structures Subjected to High Varying Axial Forces
https://repo.nzsee.org.nz/xmlui/handle/nzsee/2774
Finite Element Method Analysis of Reinforced Concrete Exterior Beam-Column Joint Structures Subjected to High Varying Axial Forces
Zhao, Neng; Suzuki, Yusuke; Shegay, Alex; Maeda, Masaki; Taniguchi, Yoshiya
Large variation of axial forces in columns in the lower stories of a high-rise reinforced concrete buildings during a severe earthquake can cause significant changes in the column-to-beam strength ratio in the exterior beam-column joints. When a column is subjected to high tensile axial forces, the column-to-beam strength ratio becomes small, leading to joint yielding and concrete damage in the joint panel zone. It has been reported that if this damage become significant, axial failure may occur in the joints when it is subjected to high compressive axial forces upon load reversal. It is important to understand this mechanism of the axial failure because it can lead to building collapse. Maeda et al. conducted experiments on exterior beam-column joints subjected to high fluctuations in axial force. They proposed a compressive strut strength equation in the joint panel after joint yielding has occurred. In this model, it is assumed that joint axial failure occurs when the compressive axial force acting on the concrete strut in the joint exceeds the estimated strut strength. However, it is concluded that further study is needed to understand the mechanism of this failure mode. To investigate the axial failure phenomenon, a 3D nonlinear FEM analysis is undertaken, referring to a previous experimental study on exterior beam-column joint specimens subjected to high varying axial forces. The results demonstrate that the analytical model closely reproduced the experimental load-deformation relationships, failure modes, and joint shear deformation angles. It showed the ability of the model to simulate the experimental outcomes.
2024-04-09T00:00:00ZComparison between weld sizing methods included in steel structure standards
https://repo.nzsee.org.nz/xmlui/handle/nzsee/2773
Comparison between weld sizing methods included in steel structure standards
Taheri, Hafez; Karpenko, Michail; Clifton, G. Charles; Ramhormozian, Shahab; Dong, Pingsha; Lim, James B. P.; Roy, Krishanu; Fang, Zhiyuan
Although the weld sizing methods given in standards look simple, the actual stress distribution in most welds is complex. Some simplifications are assumed to make designing welds easier for design engineers in different steel design codes. However, the validity of some assumptions made in the sizing method for welds can be questioned. There are concerns that the current design procedures included in NZS 3404, AS 4100 and AS/NZS 5100.6 standards may lead to oversized welds compared to the same welds designed to other standards. This paper investigates the weld sizing method in the above steel design codes of New Zealand and Australia. It examines the weld sizing criteria of structural steel standards as EN 1993-1-8 and ANSI/AISC 360 and compares it with the weld design philosophy in Australasian standards. The paper makes references to the experimental tests performed under HERA’s Seismic Research Programme, in cooperation with partner universities UoA, AUT and UoW, to examine the difference between theoretical and empirical weld capacity. The results reveal that the current fillet weld sizing criterion included in NZS 3404 is conservative. This paper provides the rationale for the introduction of the “equivalent complete penetration butt welds” for T-butt joints to the draft NZS 3404:2024. The equivalent fillet and/or partial penetration compound welds offer the same capacity as complete penetration butt welds but at significantly lower fabrication costs.
2024-04-09T00:00:00ZSimple Three-layer Pagoda Analysis
https://repo.nzsee.org.nz/xmlui/handle/nzsee/2769
Simple Three-layer Pagoda Analysis
Liang, Haoyu; Chen, Jian; MacRae, Gregory; Jia, Liang-Jiu; Li, Minghao
This paper describes the construction of a simplified three-storey pagoda and its behaviour. The following are developed: (i) a 1/20 scale 3-D printed overall structure model, (ii) a 1/10 scale 3-D printed model of one dougong joint, (iii) a numerical model which is subjected to a lateral force distribution and an earthquake record, (iv) element free-body forces, (v) element capacities considering material properties expected for old Chinese structures, wood grain direction, and the different failure modes, and (vi) a comparison between element demands and capacities.
The 3-D printed models enabled an understanding of the construction methods, without special fasteners, and the force carrying mechanisms. The structure numerical model developed using SAP2000 had a period of 0.49s. For an inverted triangular force distribution, uplift occurred between the first and second stories at a roof displacement of 6 mm when the base shear coefficient was 0.66 and the drift ratio was 1%. At an uplift of 10 mm the base shear coefficient and roof drift ratio were 1.26 and 2% respectively. Time history analysis, with a record scaled so that the spectral acceleration at that period is the same as that expected for a 500-year event in Christchurch structure assuming soil class D and 5% damping gave maximum storey drift, roof drift, and uplift displacement of 1.11%, 0.58%, and 6.8mm respectively. Considering the different components and modes, the maximum force demand capacity ratio was 0.21 in the second-storey lower beam considering the compression failure mode.
2024-04-09T00:00:00ZMachine Learning Correction of Overpredicted Liquefaction Manifestation using Liquefaction Severity Number
https://repo.nzsee.org.nz/xmlui/handle/nzsee/2771
Machine Learning Correction of Overpredicted Liquefaction Manifestation using Liquefaction Severity Number
McDougall, Nathan; van Ballegooy, Sjoerd; Kennerley, Ben; Russell, James; Lacrosse, Virginie; Jacka, Mike
Many of state-of-practice methods for predicting liquefaction manifestation, such as the Liquefaction Severity Number (LSN) of van Ballegooy et al. (2014) are known to suffer from significant overprediction in regions characterized by complex soil profiles comprising interbedded sands, silts, and clays (Beyzaei et al., 2018). These methods typically analyse discrete soil layers, and sum results layer-by-layer, which does not properly account for system effects.
We demonstrate that machine learning techniques can be used to identify cases where LSN values give overestimated surficial liquefaction manifestation. Specifically, we have developed a convolutional neural network model. With the aim of properly accounting for system effects, the model uses all the data in a CPT profile simultaneously to capture system effects of soil profiles such as interbedding, rather than process and then aggregate information in discrete layers.
A database of 110,000 historical CPT case histories was used for training and model evaluation, spanning ten New Zealand earthquakes. Special techniques have been used to address sampling bias and class imbalance. Finally, an adjustment procedure is proposed, which uses the machine learning model to improve the accuracy of LSN for specific site categories, resulting in significant accuracy improvements.
This research has been funded by Toka Tū Ake to advance liquefaction science, and support a range of applications in New Zealand, including local government planning, public engagement and education, and loss modelling.
2024-04-09T00:00:00Z