Prestressed concrete construction relies on the application of compressive stresses to concrete elements. The prestressing force is typically applied through the tensioning of strands that react against the concrete and induce compression in the concrete. Loss of prestress is the decrease of this pre-applied stress. The conservative estimation of the prestress losses is imperative to prevent undesired cracking of the prestressed element under service loads. A large fraction of the prestress losses is a consequence of concrete deformations. This fraction of the losses can be identified as strain-related losses, and these occur due to instantaneous elastic shortening, and time-dependent creep and shrinkage. Creep and shrinkage of concrete depend on many factors that are extremely variable within concrete structures. The time-dependent behavior of concrete is not well-understood, but recent findings in the topics of concrete creep and shrinkage provide a better understanding of the underlying mechanisms affecting the nature of these two phenomena. However, current design practices and prestress loss estimation methods do not reflect the state-of-the-art knowledge regarding creep and shrinkage. The main objective of this dissertation was the study and estimation of strain-related prestress losses in simply supported pretensioned bridge girders. Simply supported pretensioned girders are widely designed, produced and frequently used in bridge construction. Due to this common use, pretensioned concrete bridge girders has become fairly standardized elements, which results in a reduced variability in the behavior of pretensioned bridge girders, as compare to that of less standardized concrete structures. Hence, a simplified method was calibrated to estimate prestress losses within pretensioned girders to an adequate level of accuracy. To achieve an acceptable accuracy experimental data from the monitoring of pretensioned simply supported girders was used for the calibration of the method. The accuracy of this simplified method is comparable to that achievable using more elaborate methods developed for generic concrete structures. / text

The infrastructure of today is getting older and problems caused by deterioration over time is affecting the service life of these structures. In Sweden most of the existing bridges were constructed 60 to 70 years ago, rising the need to determine the state of health of the bridges as the maintenance costs will increase heavily. Part of the above-mentioned cut of the bridges owned by Trafikverket (The Swedish Transport Administration) that was constructed 60 – 70 years ago are pre-stressed concrete bridges. Pre-stressing of concrete structures is today a commonly used technology that utilizes the beneficial characteristic of concrete, the compressive strength, to a further extent than reinforced concrete.     This report will focus on the problems with pre-stressed concrete bridges and particularly on the thermal effects on the Abiskojokk railway bridge located in the northern part of Sweden. The pre-stressed box girder bridge spans in total 86 m in three lengths of 30 m, 35 m respectively 21 m starting from the east abutment and is part of the Iron-Ore Line starting in Kiruna and ending in Narvik, Norway. In an ocular(särskild) inspection of the bridge carried out the 18th of August in 2016 several crack patterns were mapped on the inside of the box girder along with some cracks about the top of the first column support starting from the east abutment. This thesis is focusing on the cracks that was mapped along the tendon positions on the inside of the box girder in the first span starting from the east abutment. The hypothesis is that the cracks are caused by temperature loads and normal forces obtained from the tendons at the thickening of the cross-sections. The research questions are; what the monitoring program shows and if it is possible to prove the hypothesis by using of a FE-model considering the gravity loads, temperature loads and the pre-stressing.     In order to determine the cause of the cracks on the inside of the box girder and investigate the behaviour of the bridge a monitoring program was installed, measuring the crack development over time along with the acceleration and temperatures of the bridge. Example data from the program were later used to analyse the behaviour of the bridge.     The results from the temperature data shows that the bridge has a slowness to temperature changes outside. This gives rise to temperature gradient acting over the bridge parts that may contribute to crack propagation. It also showed that the temperature correlates well with the strain of the cracks. The LVDT’s showed that the largest crack openings during train loading occurred in the second span of the bridge. The data also showed relatively large and unexpected negative peaks during the train loads. The strain gauges also show that the largest strain is occurring in the second span of the bridge. The crack envelopment during a train loads are more expected here and may prove that the negative peaks from the LVDT’s and accelerometers are caused by vibrations. The accelerometers showed that the largest transversal accelerations take place in the first and third span. This may be due to more restricted supports conditions at the column supports than the abutments. The accelerometer also showed correlating negative peaks with the LVDT’s that may be caused by vibrations in the bridge.     The conclusion from the monitoring program so far is that is not possible to prove the cause of the cracks so far, but it may be in the future.     The results from the non-linear FE-model showed that the thermal action of the Eurocode gradient was not enough to crack the concrete along with the pre-stressing load. However, the effects of the hypothesis were proven right.

This research embodied a three-prong approach for directly determining the residual prestress force of prestressed concrete bridge girders. For bridges that have yet to be constructed, outfitting girders with instrumentation is a highly effective means of determining residual prestress force in prestressed concrete bridge girders. This constitutes the first prong. Still, many bridges are constructed without such instrumentation. For these bridges, a destructive technique can be used to directly determine the residual prestress in a prestressed concrete bridge girder. This implies that the girder(s) being tested have already been taken out of service. This constitutes the second prong. For bridges that are anticipated to remain in service that are lacking embedded instrumentation, the development of a non-destructive technique used to estimate the remaining force in the tendons of prestressed bridge girders is extremely important. This constitutes the third prong used to directly determine residual prestress force. The flexural capacity was also determined from field tests and compared to analytical estimates. By design, the code estimates are meant to be conservative. Alternatively, the residual prestress force for in-service members can be determined directly through the non-destructive technique presented in this research. As such, bridge service capacities can be determined directly and do not need to be conservatively estimated. (231 pages)

Diploma thesis is focused on design of road bridge bearing structure over a D1 highway. Structure is continuous slab with 4 fields beared by local supports. It is prestressed in longitudinal direction. Internal forces are calculated in Scia Engineer software. Reference is made according to valid standarts.

The subject of this thesis is to design a new slab structure instead of the steel concrete slab. The structure of the new load bearing structure is post-stressed cast-in-situ slab with continuous slab structure consisting of three spans. The slab is pre-stressed by monostrands. The load bearing structure is evaluated for first and second limit state too. The construction is modeled in software named Scia Engineer 2011.

The subject of this diploma thesis is the preparation for the implementation of a prestressed bridge in the village of Hnojník. This thesis contains a technical report, coordination situation of the construction with broader relations to transport routes, phases time shedule, a feasibility study of the main technological phases, project of construction site equipment, a suggested list of the main construction vehicles and building mechanisation, time shedule of main construction, shedule of transport of fresh concrete mixture, technological regulation of concreting bridge deck, technological regulation of additional prestressing bridge deck, control and test plan, health and safety at work on bridge construction, The annexes contain drawings of concept of load-bearing falsework, drawing of the construction site equipment, drawing of coordination situation of the construction with broader relations to transport routes , itemized budget, graph of workers and machines needs, phases time shedule and delivery shedule of fresh concrete mixture.

The thesis deals with a design of the river Labe bridging in the city Hradec Kralove. In order to make option for cyclists and pedistrians to cross between shores. There were made three design variants. For detailed solution curved twin-arm arched structure was chosen. The aim of the thesis was design and assessment of Bering strucutre of the footbridge according ultimate limit states and serviceability limit state given by valid Eurocodes.