<p>This paper presents an experimental and numerical study of the behavior of steel wide flange sections subjected to loads causing compression buckling in the web. This research includes experimental investigation of the effects of load width and duration on web compression buckling. This data is then used to calibrate numerical models. Experimental investigations were conducted on specimens with load widths of approximately 2.5, 1.75, and 1.5 times their section depth. Loads sustained on the specimens had a magnitude of about 85% of the expected buckling strength to investigate creep effects near failure. Results of these experiments were used to calibrate numerical models for a parametric study.</p><p>The numerical parametric study examined 60 specimens of four wide flange sections, investigating the effects of loaded width and angle of load application on web compression buckling. The numerical models accounted for initial imperfections in the specimens by applying imperfections with a magnitude of 0.13*<i>t_w</i> to the first mode shape obtained from a linear perturbation analysis. This value of imperfection was chosen because it is the average imperfection measured in the experimental specimens and is likely a good representation of a typical wide flange section.</p><p>A prediction method is provided based on the data obtained from the numerical parametric study. This prediction method is derived from rectangular plate buckling solutions and considers the cases where the width of the concentrated load is a function of the section depth, and when the applied load is not orthogonal to the specimen. The current AISC 360-16 provisions do not directly address the influence of load width on the calculation of web compression buckling strength and refer to the design of compression members when the loaded width is greater than or equal to the section depth. The AISC approach was also evaluated and deemed conservative for design.</p><br>

Vid dimensionering av en byggnad är det viktigt att stabiliteten kan garanteras. För att kunna garantera stabiliteten så måste de krafter som en byggnad kan förväntas utsättas för kännas till. För horisontella laster syftar innebär det till lastfördelningen krafter i det horisontalstabiliserande systemet. Syftet med arbetet var att undersöka om FEM-design fördelar vindlast likt traditionella handberäkningar. Detta genom att jämföra resultaten av lastfördelning för de båda beräkningsmetoderna på ett referenshus. Referenshuset betraktas i fyra olika utföranden där dem varierar beroende på styvheten i skjuvväggar och bjälklag. Det för att beakta olika dimensioneringssituationer. Lastfördelningen för de olika utförandena har klarlagts genom att beräkna reaktionskrafter i grunden samt tvärkrafter i väggar. Styvhetsförhållande mellan skjuvväggar och bjälklag kontrollerades för att undersöka hur lastfördelningen till väggarna skulle ske. För två av referenshusets utföranden var bjälklaget vekt i förhållande till skjuvväggarna, för vilket fall litteraturen föreslår att lasten fördelas som för en kontinuerlig balk på fasta stöd. Vid jämförelse av handberäkningar och FEM-design så visade det sig att dem inte överensstämde speciellt bra. FEM-design gav en jämnare lastfördelning vilket istället påminner om ett utförande som litteraturen föreslår för en konstruktion med samma styvhet i väggar som i bjälklaget. Vidare utredning visar att det sannolikt beror på de olika metodernas sätt att beräkna styvhet för KL-trä. Baserat på de analyser som har gjorts i arbetet så kan det konstateras att lastfördelningen för byggnader bestående av styvt bjälklag med samma styvhet i skjuvväggarna överensstämmer för de olika beräkningsmetoderna. För utförandet med styvt bjälklag och olika styvheter i väggar så avviker resultaten. Sannolikt beroende på de olika metodernas sätt att beräkna styvhet för KL-trä. / The stability of the structure must be ensured when designing a building. To ensure the stability, the forces which a building can be exposed for must be known. In case of wind loads it means forces in the horizontal stabilizing system. The purpose with this project was to examine if FEM-design distribute wind loads like traditional hand calculations. This by comparing the results of load distribution for both calculation methods on a reference building. The reference building is designed in four different versions where the stiffness in the walls and the floor is what separate them. That to observe different design situations. The load distribution has been clarified by calculating reaction forces in the ground and shear forces in the walls. The stiffness ratio between the walls and the floor has been calculated to examine the load distribution on the walls. Calculations showed that the floor was weak in relation to the walls for two of the building’s versions. A ratio which the literature suggests that the load distributes like a continuous beam on fixed support. When hand calculations where compared to FEM-design the results did not agree very well. FEM-design gave a more uniform distribution of the loads, which reminds of a design the literature suggests for a structure with the same stiffness in the walls as in the floor. Further research indicates that it probably due to the different methods way of calculating stiffness for CLT. Based on the research done in this project it can be stated that load distribution for buildings with stiff floors and walls with the same stiffness correspond for the different calculation methods. For buildings with stiff floors and different stiffness in the walls the results do not agree. Probably due to the different methods of calculating stiffness for CLT.

Vid stabilisering av betongstommar är det komplicerat att välja en korrekt elasticitetsmodul. Detta då stommens laster verkar under både kort och lång tid. I detta examensarbete utförs en noggrann kryptalsberäkning för varje plans vertikala element, där hänsyn tas till den varierande byggtiden. Utifrån det analyseras kort- och långtidslaster med respektive elasticitetsmodul för att erhålla en ekvivalent elasticitetsmodul som tar hänsyn till de olika belastningstiderna. Denna elasticitetsmodul bestäms efter förhållandet mellan stommens knäcksäkerhet, snedställning och den vindlast som verkar på byggnaden. Den ekvivalenta elasticitetsmodulen ligger till grund för mer noggrann indata än tidigare vid stabilitetsberäkningar och redovisas i diagram som sedan kan användas i det praktiska ingenjörsarbetet. Där inget annat anges utförs beräkningar enligt Eurokod 2.Där inget annat anges är figurerna ritade av författarna. / When considering stabilization of concrete structures it is difficult to assign a correct modulus of elasticity to the structure. This is due to the presence of both short- and long-term loads. In this thesis a detailed calculation of each vertical elements creep coefficient is performed, which takes into account the varying construction time. Furthermore short and long term loads with respective modulus of elasticity are analyzed to obtain an equivalent modulus of elasticity corresponding to the two previously mentioned. The equivalent modulus of elasticity is determined by the relationship between the buckling resistance of the structure, initial imperfections and the wind load acting on the building. The equivalent modulus of elasticity is the basis for a more accurate input for stability calculations and is presented in graphs that can be used in the practice of engineering. Unless otherwise stated, calculations are performed according to Eurocode 2.Unless otherwise stated, the figures are drawn by the authors.

The object of this thesis is to assess the structural stability of heterogeneous weld joint, which consists of two different base materials (16,537 steel and 16,236 steel) and weld metal NiCrMo2.5-IG with buttering layer P24-IG. All these materials belong to the group of low-alloyed creep-resistant steels that are to be used mainly in the power industry. The weld joint was made by application of the TIG hot wire welding method. Structural stability of this joint was evaluated by carbon redistribution and microstructural changes after annealing in temperature 300 °C and 400 °C during 500 hours. For modelling the phase composition of particular steels was used the ThermoCalc software. All gained results should be employed to appraise whether the heterogeneous weld joint of the steam turbine´s rotor is eligible for long-term operation in hard working conditions.

Heterogeneous welded joints – type ferrite/austenite is inseparable part of structure for energy industry. Welding conditions and post weld heat treatment have a significant impact on the structural stability of welded joint. The structure determines resulting mechanical properties that determine lifetime of these joints. At the same time in microstructure changes in heat affected zone of the base material is diffusion of carbon through the weld interface. This work is focused on the analysis of structural stability of heterogeneous weld carbon/austenitic steel, which was formed carbon steel 22K (base material) and austenitic buttering layer EA 395/9 with a higher content of nickel. Evaluation of the structure was focused on the structure of weld metal (Böhler FOX SAS 2) and structure of the heat affected zone of base material. Metallographic evaluation was performed on the light microscope and scanning electron microscope equipped with the energy and wave dispersive analysis, which identified the contents of substitutional elements and carbon on the interface of carbon/austenitic steel. The results of metallographic analysis were compared with measurements of Vickers hardness and microhardness and calculations using Thermo-Calc software and software SVARY. The description and evaluation of the stability of the weld joints was determined by carbon content of the course interface using wave dispersive spectroscopy. The results of energy dispersive analysis were used to determine the type of carbides present at the interface of carbon/austenitic steel.

Lateral collapse is a failure mode of wood pallets which most frequently occurs during transportation and handling. The study objective was to develop a simplified procedure for making relative comparisons in the lateral collapse potential of competing pallet designs. A theoretical model was developed to predict the maximum horizontal force a pallet can sustain. A simple equilibrium of forces approach including joint rigidity was used. A lateral load test machine was built which induces and measures the amount of horizontal force required to collapse a pallet. After testing, the model was shown to be accurate when no upper deckboard bending occurred and inaccurate when bending occurred. To account for bending, two multiple regression equations were developed to predict modification factors using a matrix structural analysis program. predicts K-factors for two stringer A closed form solution designs. These K-factors are used to modify the resisting moments generated by the fastened joints. The modified model was shown to slightly overpredict maximum collapse load but did accurately discern differences in relative lateral collapse potential. The ratio of the maximum horizontal load to the vertical load on the pallet provides a means of ranking the potential for lateral collapse. Those designs whose ratios fall between 0.0 and 0.6 are at high risk, from 0.6 but less then 1.0 are at medium risk, and from 1.0 to infinity are at low risk of lateral collapse. These ratios have been calibrated against documented cases of lateral collapse. The factors that influence the lateral collapse potential of a design are stringer aspect ratio, joint characteristics, unit load, and upper deck flexural rigidity. / M.S.

The probabilistic stability of a laminated composite plate is investigated. Three different models are considered in this study, namely, the classical laminated plate theory, a first-order shear deformation theory, and a higher-order shear deformation theory. The probabilistic characteristics, such as the probability density and cumulative distribution functions for the resistance to buckling of the plate are obtained by employing the first-order second-moment method of reliability analysis. Uncertainties associated with material mechanical properties and fiber orientations of individual layers are modeled as statistically independent random variables. Numerical results are presented for rectangular simply-supported laminates, showing the effects of thickness ratio, stacking sequence, and number of layers on the probabilistic stability of the plates. / Master of Science

The objective of this study is to apply the combined linear buckling and nonlinear analysis to the stability investigations of the plane and space frame structures. A comparative study of the combined analysis and the nonlinear analysis is conducted with ABAQUS to demonstrate the applicability and effectiveness of the combined analysis for the critical load predictions. Several test problems and a glulam dome cap are analyzed, and the critical load prediction curves and the nonlinear equilibrium paths are presented. It is verified that the B33 finite element in ABAQUS is capable of modeling the curved beam. The modeling procedure of the dome cap model is discussed. Finally, conclusions and recommendations are made for future studies. / Master of Science

Several design equations for predicting the capacity of a single-headed anchor bolt embedded in plain concrete have been recommended in the United States. The capacities computed by these different recommendations, in some cases, differ significantly. The existing differences in current design criteria for anchor bolts subjected to tensile or shear loading is discussed with emphasis on the ACI, the PCI and the proposed Load and Resistance Factor Design (LRFD) equations. Available data from test results on the anchor bolts and welded studs were analyzed. Then, based on the analysis of these data and statistical information on basic design variables, a reliability analysis was performed. Using the advanced first-order second-moment reliability analysis method, risk levels implied in these design equations were computed for a dead and maximum live load combination. It was found that there are inconsistencies in the levels of safety implied by both the ACI and the PCI design equations, and that the level of safety depends on the loading and the failure mode under consideration. By comparing reliability indices for these design equations, it is thus possible to make an objective evaluation of current design criteria. / Master of Science

One of the major problems with surface-mounted or embedded induced strain actuator (ISA) patches are the considerably high stress gradients introduced at the edges of the actuator patches when an electric field is applied. These excessive stress gradients initiate debonding of the actuators from the substrate, thus affecting the mechanical reliability of the structure. This thesis is begun by investigating existing theoretical models of induced strain actuated structures, and will later use these to compare with the finite element analysis. The finite element analysis is used to explore the stress concentrations located at the edges of the actuators and begins by refining the mesh areas of the same structure focusing in on the ends of the ISA’s. This preliminary analysis is conducted on a structural configuration with a perfectly bonded actuator and proceeds to one with a finite bonding layer. After completion of the mesh refinement investigation several modifications in the design and implementation of the induced strain actuators are examined to reduce the stress concentrations at the edges of the actuators. In the finite element analysis two separate modeling considerations are examined: 1) The actuator is perfectly-bonded to the substrate. 2) A finite adhesive layer is incorporated between the actuator and the substrate. With each modeling consideration several design modifications are considered in this thesis including employing partial electrodes on the induced strain actuator surface regions instead of fully electroded surfaces, examining an actuator with a chamfered end, and using caps to reduce the stress concentrations and possibly increase the performance of the structure by allowing the induced strain actuators to utilize their piezoelectric strain coefficient in the thickness direction, d₃₃. The design modifications and different modeling techniques help to alleviate the critical stresses in the structure while gaining a better understanding of causes them. / Master of Science