This thesis presents the results of a theoretical and experimental study of the lateral buckling of straight beams of rectangular cross-section resting on columns, a type of structure commonly found in the roofing system of multi-bayed buildings. The structure is analyzed as a simply supported beam, uniformly loaded, restrained at one end against longitudinal torsion and resting near the other end on a flexible column which may provide various torsional and lateral restraints. Beyond the column is a cantilevered projection of various lengths and loads. The entire top edge of the beam is considered as fastened to a continuous decking which restrains it against horizontal displacement but permits free rotation about this edge. The method of solution of the theoretical lateral buckling load is by using a computer program to calculate the structure stiffness matrix's determinant at increasing load levels, and a plot of the determinant versus load level yields the critical load (at determinant equals zero). This theoretical approach is verified by model experiments in the laboratory. Design curves and equations are produced incorporating the usual flexural beam and axially loaded column strength concepts, with lateral buckling considerations. Recommended design code procedures are forwarded based on these curves which would permit more economical use of deep beams. Included in the thesis is the computer program listing used in the solution technique. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

Green roofs have become an important urban mitigation technology due to their ability to address multiple environmental issues. One of the most common benefits attributed to green roofs is the reduction in heating and cooling loads in buildings by dissipating heat through evaporation. This study focuses on evaluating the effect that evaporative cooling has on the thermal performance of green roofs. Sponge and floral foam were used as porous media for their ability to retain water inside its body, transport it to the surface, evaporate it at a constant rate and for their different pore sizes. Test trays containing sponge or floral foam saturated with water were tested in a low speed wind tunnel equipped to measure weight, temperature and heat flux. Two types of experiments were conducted: one with evaporation at the surface, and the other with evaporation blocked by an impervious layer. The testing conditions for all tests were kept constant except for the ability of evaporation to happen. Evaporation rate for floral foam was 0.14 kg/m2hr and 0.29 kg/m2hr for sponge. Results of tests with evaporation show a decrease of 45-49% in heat conducted through the roof when compared to the tests without evaporation. For optimal thermal performance of green roofs, a material that enhances water transport and thus evaporation at the surface is necessary with large pores and low field capacity. Surface temperatures on test with evaporation were found to be between 3-7°C lower than those without evaporation. Applying a 2 sample t-test to the data, the relationship between heat flux and evaporation was found to be statistically significant.

This study focuses on how green roof thermal performance is affected by the soil moisture in summer condition. It aims to determine whether moist soil is a better insulator during the summer months than dry soil. A soil model is developed to predict simultaneous conduction, convection, and surface evaporation for a layer of moist soil representing a green roof. It used to analyze evaporation process and its affect on the soil resistance. The model considers only bare soil without vegetation on the roof. The model predicts the soil surface temperature as it is affected by soil moisture content, which can then be used to calculate heat transfer through the soil layer. An experimental dry out test was conducted to measure the soil moisture and soil temperature histories. Comparison of the predicted and measured sol surface temperature shows that the model reasonably captures the actual behavior. The evaporative cooling effectively reduces the soil surface temperature and heat flux in moist soil and can be used as an effective way to insulate the roof.

Recent proposed rafter slenderness limits, to prevent snap-through of plastically designed pitched-roof portal frames, incorporate the elastic snap-through buckling load of such frames. It has been suggested that the elastic snap-through buckling load used in the proposals is over-estimated making these slenderness limits unconservative. This is supported by a more rigorous elastic analysis. To test the proposals, model frames lying on or close to the slenderness limits were tested to failure in the laboratory. Frame dimensions were chosen so that the frames were only susceptible to snap-through instability. Failure loads far lower than the expected plastic collapse loads were measured, showing that the elastic snap-through buckling load is over -estimated . Since plastic analysis is easily applied to portal frames, these slenderness limits are best replaced by a similar limit incorporating a more accurate elastic snap-through buckling load. A new limit is outlined which must still be tested by further research

The urban heat island (UHI) effect is a phenomenon that results in cities being warmer than the surrounding rural areas, due to a large amount of impervious surfaces. The purpose of this study is to evaluate the effectiveness of green roofs to mitigate the effects of solar energy on a building in the southern United States. In order to test the green roofs, temperatures were monitored inside and on top of unconditioned model buildings with green and with traditional roofs. Over the course of the study, the data collected showed that green roofs provided a significant benefit for the buildings by reducing daily high temperatures during summer and daily low temperatures during winter, while also reducing temperature fluctuation. The findings of this study suggest that a green roof will reduce indoor temperature and rooftop temperature, while providing several other benefits for city inhabitants such as reduced air temperature.

The objective of this thesis is to verify the "base test method" for uplift loading of C- and Z-purlin supported, standing seam metal building roof systems. To achieve this end, eight sets of full-scale roof system tests were conducted. Each test set consisted of a single span base test and a three-span, multi-purlin line, confirming test. The base test method for uplift loading, in its present form, did not prove to be an effective method for determining the failure load of a multispan, multi-purlin line, standing seam roof system. Suggestions are made for possible modifications to the method. / Master of Science

The Base Test Method has been shown to be a viable means to predict the capacity of gravity loaded standing seam roof systems. However, for uplift loaded standing seam roof systems, the base test method is still being investigated. Previous tests conducted at Virginia Tech in 1990 and 1991 have led to the belief that scatter is inherent in the results of the base test method for uplift. It was found in this research that scatter does exist in the base test method for uplift loading. Tests were also conducted to determine if purlin size and span could be eliminated from a manufacturer's testing program. It could not be shown in this research that a relationship exists between the percentage of through-fastened capacity, 'R', and the constrained bending capacity of a purlin. / Master of Science

The objective of this thesis is to further investigate the base test method and to develop an analytical model which can accurately predict the failure of an uplift-loaded standing seam roof system. Four sets of full-scale tests were conducted and their results were analyzed along with previous results (Anderson 1991). It was found that by normalizing the data, a reduction factor could be established for each test set configuration. This reduction factor applies to both the base test and confirming multi-span test in each test set. Three analytical models were applied to predict the failure of the purlin. It was found that only the LaBoube Method accurately predicted the yield stress for only the simple span tests. It was determined that a variance exists in the failure loads of uplift-loaded standing seam roof systems which need to be investigated through testing. / Master of Science

The objectives of this research were to determine the required net lateral restraining force to brace j-webs or j-chords braced by one or more continuous lateral braces (CLB's), and to develop a methodology for permanent bracing design using a combination of lateral and diagonal braces. SAP2000 (CSI, 1995), a finite element analysis program, was used to analyze structural analogs for three sets of truss chords braced by n-CLB's and one or two diagonals, one web braced by one and two CLB's, and j-truss chords braced by n-CLB's. System analogs used to model five eight-foot truss chords braced by three CLB's and one diagonal, six twenty-foot truss chords braced by nine CLB's and two diagonals, and eleven twenty-foot truss chords braced by nine CLB's and two diagonals were analyzed. For each of the three cases analyzed, the chord lumber was assumed to be 2x4 No. 2 Southern Pine (S. Pine) braced by 2x4 STUD Spruce-Pine-Fir (SPF). Chord load levels of 10% to 50% of the allowable compression load parallel-to-grain assuming le/d of 16 were studied. All wood-to-wood brace connections were assumed to be made with 2-16d Common nails. A nonlinear load-displacement function was used to model the behavior of the nail connections. Single member analogs were analyzed that represented web members varying in length from four-feet to twelve-feet braced by one and two CLB's. The web and CLB's were assumed to be 2x4 STUD SPF. The web members were also analyzed assuming 2x6 STUD SPF. Single member analogs were analyzed that represented chord members varying in length from four-feet to forty-feet braced by n-CLB's spaced twenty-four inches on-center. The truss chord was assumed to be No. 2 Southern Pine and the CLB's were assumed to be STUD SPF. The chord size was varied from 2x4 to 2x12 and connections were assumed to consist of 2-16d Common nails. The system analog analysis results were compared to the single member chord analysis results based on the number of truss chords and the diagonal brace configuration. For the three cases studied involving multiple 2x4 chords braced as a unit (and believed to be representative of typical truss construction), the bracing force from the single member analog analysis was a conservative estimate for bracing design purposes. It was concluded that the single member analysis analog yields approximate bracing forces for chords larger than 2x4 and for typical constructions beyond the three cases studied in this research. For analysis and design purposes, a ratio R was defined as the net lateral restraining force per web or chord divided by the axial compressive load in the web or chord. For both 2x4 and 2x6 webs braced with one CLB, the R-value was 2.3% for all web lengths studied. For both 2x4 and 2x6 webs braced with two CLB's, the R-value was 2.8% for all web lengths studied. The web and CLB lumber species did not affect the R-values for the braced webs. Calculated R-values for truss chords, 2x4 up to 2x12, braced by n-CLB's assumed to be spaced two feet on-center for chords four to twelve feet in length ranged from 2.2% to 3.0%, respectively. For chords from sixteen to forty feet in length, R ranged from 3.1% to 2.6%, respectively. The lumber species and grade assumed for the chord and CLB did not affect the R-values for the truss chords. Step-by-step design procedure was developed for determining the net lateral restraining force required for bracing j-chords based on the results of the single member analogs studied. The required total lateral restraining force for j-compression members in a row can be calculated based on the R-value for or the number of CLB's installed at 2 feet on-center, the design axial compression load in the chord, and number of trusses to be braced. / Master of Science