Structural Window Design for In-plane Seismic Strengthening

Abstract

In recent decades, gas production has caused numerous human-induced shallow earthquakes in the province of Groningen, The Netherlands. The buildings in this area were not designed for these unexpected earthquake loads and have shown to be vulnerable. However, current strengthening measures are considered to be time-consuming, expensive, and a great hindrance to the residents. Consequently, the question rises whether unconventional strengthening measures can offer relatively simple and quick-to-implement alternatives. This thesis researches if replacing existing windows by structural windows could provide an effective strengthening alternative. The structural window design aims to increase the in-plane seismic force capacity of an existing masonry structure by utilising the glass pane as a structural element. The structural window is designed to be composed of a timber frame, a semi-rigid adhesive, and a double glazing unit. The structural layer of the double glazing unit has a thickness of 20mm and is composed of two laminated annealed glass panes with equal thickness.

The potential of the structural window is investigated in various numerical studies, using DIANA FEA 10.2. The numerical studies are split into validation studies and seismic strengthening predictions. In the validation studies, results from numerical models are compared to and validated against experimental results reported in literature. Subsequently, the potential of the structural window is assessed by seismic strengthening predictions that combine and extrapolate the validation studies. A mass proportional one-directional monotonic pushover loading scheme is adopted. The seismic strengthening predictions address masonry walls and one type of terraced house (Dutch: “Rijtjeshuis") with two rigid floors, masonry spandrels, and two large windows in the front façade wall.

The numerical strengthening predictions of the masonry walls and the terraced house indicate that a structural window improves the in-plane seismic performance significantly. It is found that strengthening not only greatly increases the seismic force capacity, but also reduces the expected damage. For example, the strengthened terraced house with openable window sections reaches 205% of the seismic force capacity of the unstrengthened terraced house. Furthermore, it is found that the stress levels in the glass pane are expected to remain well below the stress levels at the onset of glass cracking. The numerical strengthening predictions are promising. Therefore, it is recommended to validate these numerical predictions with an experimental testing campaign.