Prestress loss of post-tensioned clay diaphragm and fin brickwork

Unlike calcium silicate and concrete block masonry which undergo shrinkage with time, clay brickwork has been known to expand instead. Expansion of brick units in prestressed masonry will cause an increase in the prestressing force instead of prestress loss. However, not all clay brickwork expand with time; higher strength clay units tend to undergo shrinkage with time. The main objective of this paper is to present experimental data obtained for prestress loss in post-tensioned high strength clay diaphragm and fin brickwork. The main objective of this paper is to present experimental data obtained for prestress loss in posttensioned high strength clay diaphragm and fin brickwork. The brickwork were built from clmisB clay engineering brick with compressive strength of 103 MPa with designation (ii) mortar. The tests which involve monitoring prestress loss, creep and shrinkage of clay sections were carried out over a period of 120 days. Usiog the 120-day experimental data, the predicted long-term prestress loss is 20

Prestress Loss Distributions along Simply Supported Pretensioned Concrete Beams

ABSTRACT: The prestressing forces in prestressed tendons undergo a process of reduction over a period of time. A common assumption is that prestress loss is constantly distributed throughout the span of a simply supported pretensioned concrete beam. The purpose of this work is to investigate the accuracy of this assumption. The types of prestressed concrete beams investigated in this work include the following three typical types of tendon profile: (I) straight strands, (II) single-point depressed, and (III) two-point depressed. The major findings derived from this work are: (1) The total prestress loss is not constantly distributed throughout the span of a simply supported pretensioned concrete beam with any of the three types of tendon profiles, (2) The variation of prestress loss along the span of a pretensioned beam caused by elastic shortening of concrete or creep of concrete is much more significant than that caused by shrinkage of concrete or relaxation of tendons, and (3) The type of tendon profile in a simply supported pretensioned concrete beam has significant effects on the pattern of prestress loss distribution along the beam

Long-Term Performance Evaluation Of NUdeck In Kearney East Bypass

The Kearney East Bypass bridge is the first project that implements the newly developed precast concrete deck system (known as 2nd generation NUDECK). The new system consists of full-depth full-width precast prestressed concrete deck panels that are 12 ft (3.66 m) long each. The panels have covered shear pockets at 4 ft (1.22 m) spacing on each girder line to host clustered shear connectors that are adjustable in height. Narrow unreinforced transverse joints are used to eliminate the need for deck overlay. Also, deck panels are post-tensioned in the longitudinal direction using a new post-tensioning system that eliminates the need for post- tensioning ducts, strand threading, and grouting operations. The project has twin bridges: a southbound bridge with cast-in-place (CIP) concrete deck, and northbound bridge with the new precast concrete (PC) deck system. The two bridges were completed in the fall of 2015 and opened to traffic in the fall of 2016. Due to the unique features of the new PC deck system, this research project was initiated to monitor short-term performance using live load test and long-term performance under traffic loads to evaluate the system performance. Both CIP concrete deck and PC deck bridges were instrumented and tested during the summer of 2016 to compare the performance of their superstructures. Also, finite element analysis (FEA) was conducted to predict the performance of the new PC deck system. The results of both analytical and experimental investigations indicated that the PC deck system performs as predicted and very comparable to the conventional CIP concrete deck

Testing and Development of Pre-Stressed CFRP Retrofit Strategies for Controlling Fatigue Cracking in Steel Waterway Lock Gate Structures

Steel waterway lock gates across the national inland waterway transportation network are reaching and exceeding their intended service life, often experiencing component failures that lead to service interruptions. Unscheduled maintenance and repair of lock gates can be expensive and cause economic ripples throughout the entire inland waterway network. These lock gate component failures are often caused by fatigue cracking from repeated loading during operation. This thesis develops and tests a prestressed carbon fiber reinforced polymer (CFRP) fatigue retrofit for controlling fatigue demands within lock gate components. The study expands upon a recent analytical work by Lozano (2017) by experimentally investigating prestressing strategies, bonding mechanisms, prestress creep/relaxation performance, and large-scale experimental fatigue testing. A total of seven large-scale cyclic tests were conducted on lock gate components (with and without applied retrofits) to gauge the effectiveness of the developed prestressing strategies. All gate specimens tested were artificially notched to create a local stress concentration and worsened fatigue condition. Results indicate that the addition of the prestressed CFRP retrofit increases the fatigue life of the retrofitted gate component despite the prestress loss due to epoxy adhesive debonding following rapid cyclic loading. The retrofitted specimen experienced a fatigue life increase of nearly 3 times over the un-retrofitted specimen. Additionally, load shedding into the CFRP, even without significant prestress applied, contributes to a reduction in the component notch stress. The applied CFRP clamping force is able to provide enough force transfer to the CFRP to reduce the notch local stresses

Nanoscale resolution interrogation scheme for simultaneous static and dynamic fiber Bragg grating strain sensing

A combined interrogation and signal processing technique which facilitates high-speed simultaneous static and dynamic strain demodulation of multiplexed fiber Bragg grating sensors is described. The scheme integrates passive, interferometric wavelength-demodulation and fast optical switching between wavelength division multiplexer channels with signal extraction via a software lock-in amplifier and fast Fourier transform. Static and dynamic strain measurements with noise floors of 1 nanostrain and 10 nanostrain/sqrt(Hz), between 5 mHz and 2 kHz were obtained. An inverse analysis applied to a cantilever beam set up was used to characterise and verify strain measurements using finite element modeling. By providing distributed measurements of both ultahigh-resolution static and dynamic strain, the proposed scheme will facilitate advanced structural health monitoring

FRICTION TEST AND PARAMETER ANALYSIS OF PRESTRESSED CONCRETE CONTINUOUS BEAM BRIDGE

The prestressed ducts of prestressed concrete continuous girder bridges are usually three-dimensionally distributed and long in length. The control of prestress loss during construction is very important. In order to ensure the effect of prestress tensioning, the test and analysis of friction parameters of prestressed ducts are particularly important. Based on the tension process of a prestressed concrete continuous beam bridge, the initial tension stress, loading time and channel friction parameters of the prestressed concrete continuous beam bridge are tested by field tests. Combined with the measured friction parameters, the finite element software Midas / Civil is used to analyse the influence of friction parameters on the mechanical properties of prestressed concrete continuous beam bridge. The results show that when the prestressed steel with bending angle not more than 40° and length not more than 70 m is stretched, the initial tension stress is suggested to be set as 20 % of the tension control force and the loading time is 5 min. The measured tunnel friction parameters are larger than the standard value, and the tension control force should be adjusted during the formal tension construction；The deflection of the key section of the main beam increases with the increase of the friction parameters, and the roof stress decreases with the increase of the friction parameters. The change of channel deviation coefficient has a greater impact on the deflection and roof stress than the change of friction coefficient

Experiment of the monitoring prestress loss of prestressed concrete beams with damages under static loading

In this paper, based on the feasible method and sensors for the full-scale prestressed monitor, the novel optical fiber sensors and the traditional monitoring sensors will be set up into two prestressed concrete beams with the same geometrical dimensions, material properties, and construction conditions, etc. to investigate the working state of the novel sensors and obtain the evolution law of prestress loss of the prestressed feature component under the static load. The results show that the evolution law of prestress loss of the loaded beam under the condition of no damage state and initial crack is the same as the non-loaded one; however, the prestress loss increases with the increase of time under the situation with the limit crack. The total loss of the prestressed beam with the limit crack is 36.4% without damage. The prestress loss of the prestressed beam under the static load increase with the development of the crack (injury)

Behavior of Prestressed Concrete Bridge Girders

For this research, prestress losses were monitored in six HPC bridge girders. These measured losses were compared to predicted losses according to four sources. Prestress loss predictive methods considered for this research were: 1- AASHTO LRFD 2004, 2- AASHTO LRFD 2004 Refined, 3- AASHTO LRFD 2007, and 4- AASHTO LRFD Lump Sum method. On the other hand, the camber prediction methods used in the present research were: 1- Time dependent method described in NCHRP Report 496, 2- PCI multiplier method, and 3- Improved PCI Multiplier method. For the purpose of this research, long-term prestress losses were monitored in select girders from Bridge 669 located near Farmington, Utah. Bridge 669 is a three-span prestress concrete girder bridge. The three spans have lengths of 132.2, 108.5, and 82.2 feet long, respectively. Eleven AASHTO Type VI precast prestressed girders were used to support the deck in each span. The deflection of several girders from a three-span, prestressed, precast concrete girder bridge was monitored for 3 years. Fifteen bridge girders were fabricated for the three span-bridge. Ten girders from the exterior spans had span length of 80 feet, and five girders from the middle span had span length of 137 feet. From the results of this research, in both the 82- and 132-foot-long, the AASHTO LRFD 2004 Refined Method does a better job predicting the prestress loss and it can be concluded that all the prediction methods do a better job predicting the loss for the larger girders. The Lump Sum method predicted very accurately the long term prestress loss for the 132-foot-long girders

Prestress loss of high-strength calcium silicate element masonry with thin-layer mortar

At Eindhoven University of Technology, the behaviour of post-tensioned shear walls of high-strength calcium silicate element (CASIEL) masonry with thin-layer mortar (TLM) is investigated. As a part of this research, prestress losses due to creep and shrinkage of such masonry were monitored for 250 days. Experiments were conducted in a climate-controlled environment and all specimens were conditioned to the same moisture content. The specimens measured 175 x 175 x 1100 mm3 and contained one bed joint of TLM. High-strength CASIELs from two manufacturers were used, having similar compressive strength, but different dry density and Young’s modulus. Test setups for creep and prestress loss were developed and shrinkage was measured on unloaded control specimens. It is concluded that time-dependent deformations and prestress loss of high-strength CASIEL-TLM masonry are low compared to other kinds of masonry. Therefore, this type of masonry is very suitable for post-tensioning

Modelization of the Thermo-Mechanical Structure of the LHC Main Dipole and Influence on Field Quality

The mechanical structure of the main LHC dipole is analysed. A finite element model is used to estimate the loads and the deformations at cryogenic temperature. The correct setting of the model parameters is crucial to obtain a reliable model to forecast the influence of design and tolerances on field quality. We discuss how the prestress loss from room to cryogenic temperature experimentally observed in the prototypes can be predicted using the finite element model. An estimate of the influence on field quality of deformations and tolerances due to manufacturing is given