The design of structural members subjected to seismic activity has progressed in recent years but does not yet include the effects of cold temperatures. In areas such as Alaska, the Midwest, East Coast, and even in some parts of the West Coast, this approach introduces a real deficiency as it is likely that an earthquake will occur during winter months. The current research program was initiated to address this deficiency by developing a section analysis tool program capable of defining the moment-curvature response in either warm or low temperatures. As part of this investigation, the stress-strain behavior of A706 Grade 60 mild steel reinforcement was studied under low temperatures (20.C to -40.C) to ensure that the effects of temperature is accurately accounted for in the newly developed analysis tool. In addition to mild steel, the effects of cold temperatures on the behavior of soil, unconfined concrete, and confined concrete are currently being examined by other researchers at Iowa State University.
The Versatile Section Analysis Tool (VSAT) was developed to reduce the general limitations found in other programs. Amongst these limitations are limited available material models, lack of commonly used section shapes, and the exclusion of soil and low temperature effects. VSAT was constructed with many different features to provide versatility in how the user wishes to establish material properties for a particular analysis. VSAT includes the following features: permitting different cross-sections, defining normal strength or UHPC material properties, defining simplistic or sophisticated mild steel or prestressing steel material properties, allowing the addition of soil pressure, including a steel shell circular section, and accounting for low temperature effects on material behavior.
The testing of mild steel reinforcement at low temperatures showed a quadratic increase in the yield and ultimate strengths of 5.1 and 6.3 percent, respectively, when lowering specimen temperatures from 20.C to -40.C. It was also found that the modulus of elasticity, ultimate strain, and strain hardening strain were insignificantly affected under the same conditions. Assumptions for the behavioral changes of concrete under low temperatures to be used in VSAT have been compiled from previous research until current testing can be completed. These assumptions will then be replaced with experimental data collected by this project’s partner researcher, Aaron Shelman.
As portions of VSAT were completed, the program was continually verified to be functioning correctly. First, previously known material models were verified to coincide with those presented in this thesis by hand and within the newly developed program. Second, as shown in the verification section of this thesis, non-prestressed rectangular and circular sections were compared with King’s Program to ensure accuracy. UHPC H-shaped sections were also examined based upon the work and experimentation of Vande Voort et al. (2008). Unique features, where a comparison is impossible (i.e. temperature effects on the stress-strain behavior of mild steel reinforcement), have been carefully added to VSAT. The effects of these features have been checked, by hand, to ensure that the program is functioning properly.
The development of VSAT has been successfully initiated and the results for particular sections have proven to be comparable with previously created section analysis programs. Further expansion of the program is possible as additional desired features become apparent. Due to time constraints and the scope of this project, any addition features and continual testing of the program was left for a successor to complete.