EcoHouse Research

Tom Partington (MEng, 2013)

 

This project aims to design a rig to assess the seismic resistance of building designs, and perform testing on initial designs of a low cost, sustainable housing solution for use across South and Latin America. The structures tested consisted of variations on a basic timber frame structure, which was designed using the International Association for Earthquake Engineering design guide for timber housing.

 

The main constraint on any structure is the safety of use. For a timber housing solution being considered for construction near Quito, Ecuador, the main safety constraints are earthquake resistance, fire resistance and landslide resistance. The overall design was based on the guide “Normas De Arquitectura Y Urbanismo”, with detailed design being based on the International Association for Earthquake Engineering design guide for timber housing.

Quito is in a region of high seismic activity. Data from the USGS indicates that there is a 10% chance of an earthquake producing a peak ground acceleration greater than 4m/s² every 50 years. For this project a design ground acceleration of 5m/s² (approximately 0.5g) will be used. This value was selected due to its convenience for use in design and the conservative designs it will generate compared to the anticipated earthquake loading the structure is likely to experience.

 

Another major hazard faced near Quito is from landslides. Quito is in a mountainous region with moderate rainfall. This combination of steep slopes, wet or saturated ground and seismic activity makes the probability of landslides large. It is difficult to design a building to resist landslide loads due to the very large forces which can be imposed. As such this risk will be avoided by constructing outside of high-risk areas. This work is being done by the Urban

 

Planning team within the EcoHouse Initiative, and will not be considered further in this project.

An un-weighted merit index selection process was used to select an appropriate design, with designs being rated from 1 to 5 (1 being poor, 5 being excellent) on speed of construction, complexity of construction, quality control, ease of manufacture, cost of manufacture, cost of construction, embodied energy, operational energy use, social acceptance, earthquake resistance and long term resilience. These ratings were summed to find an optimal design. A timber frame with plywood cladding emerged as the highest rated design.

 

Static testing was performed by fixing the platform and then applying a lateral load to the top centre of the frame through the use of a crane and pulley. The force applied was measured using a spring balance graduated in pounds (lbs), while the displacement was measured by fixing paper to the wall section and marking on this the location of a fiducial marker, which was fixed to the supporting frame, at each increment of applied load. The fiducial markers consisted of lengths of 16mm diameter studding on each of the end returns of the wall, and a length of 2mm diameter string hung over the top of the wall between each end of the supporting frame to measure deflections at the centre of the cross beam.

 

Dynamic testing was performed in two main stages: One set of testing was performed to calibrate and establish the capabilities of the testing rig, the other was performed to test the response of a wall section to an applied seismic loading.

 

This report shows that the rig used to test wall sections is suitable for the single storey designs being considered by the EcoHouse Initiative. The underlying assumption that resonant effects are not of significance to low rise buildings is supported by the frequency analysis performed, while the rig is capable of applying accelerations with a similar frequency content to that of real earthquakes and at a magnitude up to and beyond those experienced in real earthquakes. However, the monitoring provided during the dynamic testing could be improved upon, particularly regarding measuring the displacement at the top of the wall sections. Either more accurate accelerometers at more locations should be provided or another method of monitoring, such as using Demec gauges to directly measure displacement, should be used. It was also found that noise during accelerometer readings can lead to significant errors when the double integration is performed. This could be avoided by measuring displacement directly rather than using accelerometers. The deflection should also be monitored at more locations, particularly at both ends of the wall section.

 

The report also shows that the timber framed design produced originally is more than capable of withstanding a typical earthquake loading, and is able to withstand ground accelerations more than 8 times as large as those which are expected in the Quito region of Ecuador.