This thesis aims to find a new weld sizing criterion for the steel construction industry in New Zealand. Current standards, such as NZS 3404, ANSI/AISC 360-16, and Eurocode 3 use a factor of 0.6 to calculate weld capacity from the weld metal’s ultimate tensile strength (UTS). This difference between weld capacity and UTS is thought to have arisen from the need for a large factor of safety to ensure welds perform correctly during an earthquake. The events in Christchurch proved that this criterion was able to work as intended. Several papers have been published by P. Dong from University of Michigan, and alongside other researchers, they investigate a new definition of weld shear strength by using a traction stress-based method. This new method not only allows realistic angles of weld fracture to be investigated, but also different weld geometries such as partial penetration butt welds. Ongoing research at HERA is showing how this welding technique is a more economical option than larger fillet welds with similar performance. For this thesis a range of sample types were statically tested until failure. UTS of several weld metals was found and then compared with transverse shear results to see if 0.6 is indeed correct. It was found that if the results from the standardized transverse shear samples was used, this ratio could be increased to 1.0. But if the results from cruciform joint samples was used, which still load the weld in a transverse direction but with a higher stress concentration, required the ratio to be 0.8 for welds that could be welded with a single pass, and decreased further to 0.75 for large welds with 3 passes. Two types of partial penetration butt weld (PPBW) geometries were compared to a comparatively sized fillet weld. These tests showed the PPBWs were the best performers, with all PPBWs surviving testing compared to only 33% of fillet welds.
Damage distribution maps from strong earthquakes and recorded data from field experiments have repeatedly shown that the ground surface topography and subsurface stratigraphy play a decisive role in shaping the ground motion characteristics at a site. Published theoretical studies qualitatively agree with observations from past seismic events and experiments; quantitatively, however, they systematically underestimate the absolute level of topographic amplification up to an order of magnitude or more in some cases. We have hypothesized in previous work that this discrepancy stems from idealizations of the geometry, material properties, and incident motion characteristics that most theoretical studies make. In this study, we perform numerical simulations of seismic wave propagation in heterogeneous media with arbitrary ground surface geometry, and compare results with high quality field recordings from a site with strong surface topography. Our goal is to explore whether high-fidelity simulations and realistic numerical models can – contrary to theoretical models – capture quantitatively the frequency and amplitude characteristics of topographic effects. For validation, we use field data from a linear array of nine portable seismometers that we deployed on Mount Pleasant and Heathcote Valley, Christchurch, New Zealand, and we compute empirical standard spectral ratios (SSR) and single-station horizontal-to-vertical spectral ratios (HVSR). The instruments recorded ambient vibrations and remote earthquakes for a period of two months (March-April 2017). We next perform two-dimensional wave propagation simulations using the explicit finite difference code FLAC. We construct our numerical model using a high-resolution (8m) Digital Elevation Map (DEM) available for the site, an estimated subsurface stratigraphy consistent with the geomorphology of the site, and soil properties estimated from in-situ and non-destructive tests. We subject the model to in-plane and out-of-plane incident motions that span a broadband frequency range (0.1-20Hz). Numerical and empirical spectral ratios from our blind prediction are found in very good quantitative agreement for stations on the slope of Mount Pleasant and on the surface of Heathcote Valley, across a wide range of frequencies that reveal the role of topography, soil amplification and basin edge focusing on the distribution of ground surface motion.
