No description available.

Construction with composite materials has become increasingly popular in contemporary structural design for multi-storey residential, commercial, and industrial buildings. As a composite structure, pre-stressed heavy timber buildings offer sustainable, environmentally-friendly advantages over competing construction technologies utilising structural steel and concrete components. Research at the University of Canterbury is continually investigating the performance and behaviour of this composite heavy timber construction assembly. The following research report provides a fire resistance analysis for pre-stressed heavy timber structures that includes: • A comprehensive literature review detailing the fire resistance for pre-stressed heavy timber structural components and typical connections; and • A four-phase series of experiments with epoxy grouted steel threaded rods and proprietary mechanical fasteners to determine the fire resistance properties of steel to wood connections. Laboratory experimentation includes cold testing to determine connection performance at ambient temperature, oven testing to evaluate heating effects on steel to wood connections, cooled testing to determine the residual strength of connections in minor fires and, finally, furnace testing to generate fire resistance design and analysis equations to be utilised for steel to wood connections. Recommendations for the fire performance of connections in pre-stressed heavy timber structures are included in the report.

No description available.

The major cause of cracking in bridge decks, concrete pavements, as well as slabs on grade, is restrained shrinkage of the concrete. The resulting steel corrosion problem causes tremendous increase of maintenance and replacement cost. Shrinkage-compensating concrete (SHCC) and fiber-reinforced polymer (FRP) are explored to develop a hybrid slab system as one possible method of delaying the cracking and eliminating corrosion. To achieve the objective, a hybrid FRP reinforced SHCC structural system was developmed, and short-term and long-term behavior of this hybrid FRP-SHCC beams were investigated in this dissertation. In the first-stage development, a series of “coffee can” tests were carried out to measure and compare the expansion of SHCC from two candidate materials which were ettringite-system SHCC and lime-system SHCC. The selected SHCC candidate mix was then optimized to get the maximum expansion as well as a reasonable concrete strength. The optimized SHCC mix was used to make FRP-SHCC beams. The expansion of the concrete was measured through strain gauges on the FRP composite sheets during curing. Both glass FRP (GFRP) composite sheets and carbon FRP (CFRP) composite sheets were used for comparison. A series of third-point loading experiments were conducted to study the behavior of the proposed hybrid FRP-SHCC beams. In the second-stage development, long term prestress loss and static structural test of the proposed beams are investigated. Test results were evaluated based on maximum expansion strain, cracking load, crack width, load-deflection and ultimate load.The results indicate that the proposed system is promising in terms of its ability to develop a residual pre-stressing effect. Tests also show that the pre-stressing effect from the expansion of SHCC increases as the axial stiffness of the FRP reinforcement increases. A lime-system SHCC structural system shows higher prestress strain and less prestress loss than an ettringite-system SHCC system over the long term.

Standing support is often used in conjunction with underground retreat mining. Knowledge of the load-displacement behavior of a standing support and loading induced by the mine opening is critical proper support selection. The NIOSH STOP database contains load-displacement laboratory test data for most commonly used standing supports. Hydraulic load cells currently used to measure in-situ loading of standing supports have exhibited leakage under load, producing irregularities within the dataset. An improved hydraulic load cell eliminates leakage and produces more consistent data. / Master of Science / In retreat mining of a traditional room and pillar or longwall mining operation standing support is utilized. The standing support is comprised over various types of systems, wood timbers, wood cribs, pumpable supports and metal supports. These standing supports help aid in the recovery of the reserves and/or maintain ventilation through the mining excavation. National Institute for Occupational Safety and Health (NIOSH) Support Technology Optimization Program (STOP) has a database of laboratory testing on load displacement used on various standing supports. To relate this laboratory testing to in-situ load of standing support hydraulic load cells have been introduced. The hydraulic load cells design is a thin metal bladder filled with fluid that is placed on the top or bottom of the standing support. These hydraulic load cells have exhibited inconsistencies due to leakage under load, producing irregularities within the dataset. To achieve a reliable dataset on active standing supports it is vital that current load-measuring devices needs to be re-evaluated and redesigned.

M. Tech. (Department of Mechanical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / A project investigating the behaviour of an assembled preloaded rotor was performed for an M-Tech qualification in the Mechanical Engineering Department. Pre-Stressing of mechanical structures is widely applied to improve their performance, and in this project the behaviour of an assembled preloaded rotor was investigated. An Impact Test was done on the structure to see if induced stresses originated by a set of bolts which keep the discs system together, would influence the natural dynamic response or the rotor. Tendencies in the natural response were investigated. Analytical models like the Finite Element Beam model and the Solid Finite Element model were studied in order to find a represntative description of this particular structure's dynamic behaviour after pre-tension. From the experimental results it was apparent that the slenderness of the pre-tensioned sector influences the natural frequency. The solid finite element model appears to be the most applicable model to present the assembled rotor-disk system as a continuous shaft. Furthermore, modelling and predictions for a typical rotor and similar assembled structures can be generated from the findings.

No description available.

The purpose of the thesis is to suggest a span enlargement of steel Modular footbridge ML36 for pedestrian and cycling transport. The aim is to preserve as many elements of the original construction as possible. In the thesis, three variants are discussed with the detailed focus on one of them. The chosen variant is made up by elongated original footbridge ML36, which is supported by prestressed structure. From the static point of view, it is a simply supported truss. The span of the footbridge is 39-45. The main material of the structural elements is steel S355, S460 and S520.

Implementing pre-stressing cables is a viable option aiming at controlling deformation and cracking of concrete flat slabs in serviceability limit state. The pre-stressing cables also contribute to punching shear capacity of the slab when they are located in vicinity of the column. The positive influence of pre-stressing cables on punching capacity of the concrete slabs is mainly due to the vertical component of inclined cables, compressive in-plane stresses and counter acting bending moments near the support region. The method presented in Eurocode 2 to determine the punching capacity of the pre-stressed concrete flat slabs considers the in-plane compressive stresses but totally neglects the effect of counter acting moments. The effect of vertical forces introduced by inclined cables is only considered when they are within the distance 2d from the face of the column. This area is called basic control area in the Eurocode 2. In this master thesis nonlinear finite element analysis is carried out to study the effect of pre-stressing cables on punching shear capacity of concrete slabs respecting the distance of cables from the face of the column. To attain this objective, the concrete damage plasticity model is implemented to model the concrete. The results indicate that until the distance of 6d from the face of the column the contribution of pre-stressing cables in punching shear capacity of slabs is significant. Furthermore, comparing the numerical results with the punching shear capacity of slabs predicted by Eurocode 2 reveals that Eurocode tremendously underestimates the punching shear capacity when the cables are located outside the basic control area.

Irradiation of a reactor pressure vessel (RPV) causes a shift of the ductile to brittle transition region towards higher temperature regions. In the event of a pressurized thermal shock (PTS), where the temperature drops drastically, the ductile to brittle transition region might be entered for irradiated ferritic steel. Hence, there is a risk of brittle cleavage fracture. Cleavage fracture is a transgranular unstable fracture initiated by cracked second phase particles and rapidly propagated over grain boundaries. The warm pre-stressing (WPS) effect can be helpful as it increases the apparent fracture toughness of ferritic steel pre-loaded in the ductile temperature region, which is the case for a PTS. This effect has been proven effective for virgin material, but the impact of residual stress fields on the WPS effect have not been investigated thoroughly. Utilizing a finite element model of notched three-point bending specimens and a non-local probabilistic model for fracture prediction the effect of residual stresses on the WPS effect was investigated in this thesis. Regarding the crack tip state, expressed as J, the probability of fracture was alike for both material with and without residual stresses, however a significant loss of load bearing capacity was found comparing them two. The magnitude of this loss depends on pre-load level as well as specimen size. This loss however, was also found when not considering the WPS effect. / Bestrålning av ferritiska reaktortankar orakar en förskjutning av den duktil-spröda omslagstemperaturen till högre temperaturer. Vid en trycksatt termisk shock (TTS) sjunker temperaturen drastiskt i reaktorn och omslagstemperaturen kan nås. Därför uppstår en risk för klyvbrott. Klyvbrott är en transgranulär ostabil spricktillväxt initierad av sprickor i sekundärfaspartiklar som propagerar över korngränserna om spänningstillståndet är gynnsamt. Varm förbelastning, eller warm pre-stressing (WPS) kan vara fördelaktig eftersom den höjer den effektiva brottsegheten hos ferritiskt stål som förbelstats i den duktila temperaturregionen, som är fallet för TTS. Den här effekten har visats effektiv för material utan restspänningar, men för fallet med restspäninningar saknas utförliga undersökningar av WPS-effekten. Med hjälp av en finita element model av tre-punkt böjprovstavar och en icke-lokal sannolikhetsmodell för prediktion av brott så undersöktes vilken effekt restspänningar har på WPS-effekten. Brottsannolikheten visade sig vara lika för både material med och utan restspännigar om man syftar på sprickspetstillståndet, uttryckt som J. Däremot syns en tydlig förlust i lastbärande förmåga mellan de två fallen. Storleksordningen på förlustern beror både på förbelastningsnivå och provstavsstorlek. Den förlusten kunde dock finnas även för fall utan någon WPS effekt.