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No description available.

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No description available.

Load and Resistance Factor Design is a set of specifications for the design of steel structures. It is based on a consistent probability of failure and the concept of limit states. The main difference between LRFD and the traditional Allowable Stress Design method is the use of load and resistance factors, which account for the variability of parameters affecting the design. The purpose of this study is to compare both design methods. To do so, a computer program for the design of steel frames according to LRFD criteria is created. Three frame structures are designed using this program, then compared to the same structures designed according to the ASD procedures. The results indicated that LRFD criteria yield a structure similar to that designed according to ASD, with a moderate saving in steel weight. Both methods were found to be similar in terms of complexity and effort to complete calculations. An advantage found in using LRFD was that engineers can develop a better understanding of the behavior of material and structures under the influence of different load conditions. / M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by David Matthew DeLonga; Ensign, USN. / M.S.

A36 steel is a commonly used material in civil engineering structures where fatigue damage can lead to catastrophic failure. In this research, nonlinear Rayleigh surface waves are used to characterize damage in A36 steel specimens caused by monotonic tension and low cycle fatigue. Fatigue damage produces the increased acoustic nonlinearity that leads to the generation of measurable higher harmonics in an initially monochromatic Rayleigh wave signal. One specimen is subjected to static tension and four specimens are used for low cycle fatigue tests in the tension-tension mode with a constant stress amplitude. The fatigue tests are interrupted at different numbers of cycles for the nonlinear ultrasonic measurements. Tone burst Rayleigh wave signals are generated and detected using a pair of oil coupled wedge transducers. The amplitudes of the first and second harmonic are measured at varying propagation distances to obtain the nonlinearity parameter for a given damage state. The experimental results show an increase of acoustic nonlinearity in the early stages of fatigue life. Furthermore, a close relationship between plastic deformation and the acoustic nonlinearity is found, which indicates that the acoustic nonlinearity is indeed a measure of microplasticity in this material.

The mechanical and material properties of structural steel at elevated temperatures play an important role in structural fire design. The South African 350W and S355 structural steels are common in building structures with S355 slowly replacing the older 350W. The cost and feasibility of full scale fire tests are some of the causes for the lack of experimental data on the behaviour of steel structures when exposed to fire. Therefore excessively conservative design codes based on isolated laboratory experiments are used in practice which leads to increased material costs. Another area of concern with respect to building safety is the reusability of structural steels post fire exposure, which is not effectively addressed within these codes. This study aims to establish greater insight into structural fire design and simulation on which further research can be built. Experimental programs on the temperature dependent behaviour of these steel members loaded axially are conducted and compared with theory and the Eurocode 3 standard [1]. The reusability of steel exposed to fire and after being cooled down is investigated and compared to the findings by Outinen [2]. Further testing on material to determine the relationship between remaining life and hardness degradation after cooling down was conducted. Experimental data from various external studies are used to develop novel computer models using the finite element analysis software, SimXpert [3]. These are verified against the original data and compared to existing design codes. A parametric approach is used with these models to demonstrate the advantages of computer simulations in structural fire design. Different cross sections and slenderness ratios are evaluated for their susceptibility to buckling at elevated temperatures. The results of this study show that as temperature and exposure time increase the integrity of steel members decrease. The current design codes accurately predict the behaviour of isolated specimens but lack data on real situations where the specimen is part of a complex structure. It was found that steel members can be reused if their exposure temperature does not exceed 700°C, after which their strength can reduce to 90%. This temperature dependant behaviour was successfully modelled using basic computer simulations and then demonstrated the ease in which they can be used in place of experimental regimes. The parametric advantages of these simulations were demonstrated by predicting the effects of slenderness ratios and geometry cross sections on the buckling behaviour. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2012.