Research Proposal

Measurement of tensile loads

 of cables

 in tensile roof structures

Matt Walker

February 6, 2013

 Summary statement of proposed project:

The proposed research is to provide scientific data to measure and quantify tensile forces in the cables using vibration technique.

Purpose:

The purpose of this research is to provide test data from vibration tests that could be used by industry to determine in-situ tensile forces in cable for tensile roof structures. The importance of knowing this is crucial in determining the safety of the structure and its durability. 

Goals and objectives:

The end results of this research will be an established procedure for determination of tensile loads on cables in tensile roof structures. The goal of this research is to provide a means to determine the safety of a structure and its estimated lifespan.

Methodology & analytical approach:

To perform this test a scale model of a mast and cable system will be constructed.  A tri-axial accelerometer will be attached to the cable and the cable will be struck with a hammer. Reverberations will be sent through the cable and collected with the accelerometer.  The frequency data will be used to determine the tension in that cable. The principal formula under which this experiment will be conducted is the Taut String Theory commonly used in engineering and physics to determine tension based on frequency.

This test will be conducted in a similar manner as tuning a guitar. When a string is strum vibrations are sent through the string creating a harmonious frequency. This frequency is compared to a reference pitch to determine if the string must be tightened or loosened.

Similarly the frequencies collected by the accelerometer will be used to determine if the cable is under too much or too little tension. Either one of these conditions will result in an undesirable outcome for the structure.    This test is designed to collect data in the form of wave lengths and hence it can be increased in scale and magnitude without skewing the results. The test performed on the scale model will as effective as a test performed on the actual structure.
This test will be performed under various conditions such different combinations of lengths, diameters, forces, and related vibration behaviour. The data collected from the accelerometer and will be compiled on a computer and saved to the hard drive as well as an external disk. This data will be compared to the safe working conditions of a cable predetermined by an engineer. From this data it will be possible to determine if the cable is within its safe working loads.

Below is a chronological breakdown of this research:

April:  Collect measuring instruments and construction materials for scale model of cable and mast.

May: Assemble scale model, begin testing and create photo diary of research to disseminate to blog.

June: Compile findings from scale tests, disseminate to blog and forward findings to related parties, such as Dr. James Gu to seek comments for further work if necessary.

July: Request access to tensile roof structures in Vancouver and Calgary to do some site measurement. Some large scale projects such as Canada Place, BC Place, Brentwood mall and Talisman Center are under consideration.

August: Upon permission of access travel to site and conduct large scale tests.  Compile collected data and disseminate. 

Previous studies:

There have been various published articles on tensile roof structures and the behaviors of their materials under different conditions. Most of these studies have focused on the integrity of the membrane and not the supporting structure.  Similar tests have been used to determine the tension of cables in cable stay bridges with success. But there is no evidence that these procedures are being used in tensile roof structures.

Plans for dissemination of work:

The work shall be disseminated through a blog that is required to be created in the ARET 2220 course. The final report will be submitted to related instructors and hopefully later it will be published in construction/engineering articles and magazines. This research will be presented at the undergraduate conference and will be available through private consultation.

Contribution of project to overall goals:

In the past I have worked directly with the tensile roofing industry and have participated in the installation of roofs at Canada Place and BC Place. During these projects I worked for RAC International in conjunction with Birdair Inc. and Hightex as a rope access technician. This gives me inside knowledge to this industry and is a stepping off point for my research. My role in implementing this research will be constructing a scale model of a mast and cable. Based on this model, data will be collected, compiled and recoded. The Findings will then be progressed on to large scale tests.

My overall educational goals are to complete:

·       Architectural Engineering Technology

·       Bachelors of Building Science

·       Masters of Project Management in construction industry

My career goal is to become a project manager hopefully within the tensile roofing industry. The research I will conduct now and throughout my education will make me a valuable consultant.

Budget:

To complete this research materials will need to be purchased to construct the scale mast and cable system and a tri-axial accelerometer similar to a Kistler 8202Awill need to be borrowed.

At the end of the research a trip to Vancouver or Calgary is under consideration to test real structures. For the onsite tests the researcher intends to use rope access techniques to access the cables, install sensors and cause reverberations. The researcher is a fully certified rope access technician and owns his own equipment but will need to hire an assistant because it is protocol to have two technicians working on any one site. Liability insurance will also be required and will be purchased before any operation is undertaken. 

Below is a breakdown of these costs.

 Price breakdown

Tri-Axial Accelerometer & accessories @ $80/month                   $320.00

Construction materials=                                                             $300.00

Vehicle travel =                                                                         $200.00

Accommodation @ $90/night=                                                  $180.00

                                                                                               --------------

Totals:                                                                                     $1000.00