Prestress Level Research Articles

Improving seismic behaviors of precast segmental piers with bonded prestressed tendons

Precast segmental bridge piers attract engineers due to the strengths of accelerated construction, reduced traffic disturbance and enhanced quality control. However, their widely applications in high-seismicity areas are hindered, for the insufficient capacities of energy dissipation. In this study, precast segmental piers’ seismic behaviors were investigated, focusing on the connection of ‘grouted sleeves/bonded tendons’. To this end, four piers were cyclically loaded, of one cast-in-place pier, one precast segmental pier, and two prestressed precast segmental piers. Among them, Benefits of bonded tendons were evidenced, in terms of lateral strength, ductility, energy dissipation capacity and residual drift. Of particular, bonded tendons prevented the shear-induced slip between the shaft and footing segments. Enlightened from observations, cyclic dowel-friction effect is proposed and implemented within a zero-thickness sliding spring in the finite element model, capable of capturing the shear-induced joint slip. Furthermore, seismic vulnerability assessments of the bridge piers are obtained in terms of fragility curves, by performing incremental dynamic analyses. In addition, the effects of bonded or unbounded tendons are also discussed. Two criteria are adopted to define the limit states, namely displacement ductility and residual drift. It is suggested that bonded tendons could significantly ameliorate the fragility curves of precast segmental piers. HIGHLIGHTS Four bridge piers were cyclically loaded, with various prestressing levels. A reliable fiber-based model was constructed, considering shear-induced slip at the segmental joint for the first time. Seismic vulnerability assessments were performed to quantify the piers’ behaviors.

Design, fabrication and analysis of a bio-based tensegrity structure using non-destructive testing

In this work, an experimental and numerical study of the behavior of a tensegrity structure constructed with natural materials is presented. Firstly, it is shown the concept of tensegrity structures, highlighting its emergence, current context, and applications within Civil Engineering. The design of a bio-based tensegrity structural module is investigated as object of study. Initially, a prototype of a single module of the structure is built in 1:25 scale. Subsequently, a prototype on a 1:5.65 scale is built using Phyllostachys aurea bamboo culms for the struts and sisal (Agave sisalana) ropes for the cable nets. Both non-destructive static and dynamic testing were performed on the module to investigate the level of prestress right after assembly of the structure and also considering the relaxation of the cable networks under laboratory conditions. The results obtained from the experimental tests are compared with the numerical predictions by means of a relative error parameter regarding the static stresses and the natural frequencies. Thus, it was possible to indirectly determine the level of prestress applied in the sisal ropes of the tensegrity module. The prestress level was equal to 15% in both static and dynamic approaches, which indicates a good agreement between them and points to the robustness of the proposed methodology. The use of bamboo as a suitable material for strut-cord joints is proposed to avoid metal components and consider the end-of-life biodegradability of the structure in the design of joints. The study deploys bio-based materials for tensegrity structures and the kit of parts as a whole, contributing to the development of extremely lightweight and sustainable structural systems.

Dynamic response and damage mechanism of parallel wire cables under contact explosion

With the global threat of terrorism on the rise, the protection of important infrastructure such as cable-stayed bridges from terrorist assaults has become a major concern. In cable-stayed bridge designs, the cables are crucial load-carrying components, and their failure could result in the progressive collapse of the bridge with catastrophic results. However, there is very limited understanding of the blast effects on cables. This paper presents a study on the blast performance of parallel wire cables under contact explosions. Field blast tests were conducted on four identical parallel wire cable specimens with varying charge weights and prestress levels. Arbitrary-Lagrangian-Eulerian (ALE) algorithm is utilized to develop the numerical model in LS-DYNA. The numerical model is then validated and further used to investigate the damage mechanism of the cable under contact explosions. The results indicate that the damage process of cables under contact blasts can be divided into three stages: Compression, divergence, and stretching. The wires arranged in angular points facing the detonation are particularly vulnerable, and high-density polyethylene (HDPE) is prone to be pelted off by explosive pressure. Parametric analyses were carried out to investigate the influences of charge weight and prestressing force on the damage degree of cables. The relationship between the TNT equivalent and the number of fracture wires is derived from the parametric analysis results. Furthermore, the prestress is found to have a considerable impact on the degree of cable damage induced by contact explosions. Taking prestress into account, a damage evaluation method for blast-damaged cables is proposed.

Should Torroja’s prestressed concrete Alloz aqueduct be thought of as a beam or a shell?

This paper examines the structural action of Eduardo Torroja’s Alloz aqueduct, completed in 1939, to see whether we should think of it as acting as a beam or a shell. This is of interest regarding the Alloz aqueduct itself, but also in the design of similar structures in the future, where we must have a simple conceptual understanding of how we want it to work.We apply two alternative approaches available at that time, before computers. Firstly, the membrane theory of shells, effectively assuming the aqueduct walls are infinitely flexible in bending, and secondly, the Euler–Bernoulli ‘plane sections remain plane’ elementary beam theory. We also review Torroja’s calculations which were based on an elaboration of the Euler–Bernoulli beam theory know as the Griffith–Taylor theory for the bending of cantilevers, although we are uncertain as to why he decided to use the Griffith–Taylor theory for a thin walled structure.Both the membrane shell and Euler–Bernoulli beam theory require a prestress to be applied along the longitudinal edges of the channel. However, the level of prestress in the Alloz aqueduct is consistent with the beam theory, which seams the most appropriate approach.Whether or not a structure of this type acts as a shell depends upon the thickness of the wall. The thinner the wall, the more it act as a shell. The wall thickness of the Alloz aqueduct is sufficient for it to act mainly as a beam.

Mechanical performance evolution and life prediction of prestressed CFRP plate exposed to hygrothermal and freeze-thaw environments

The long-term prestressed loss of anchorage system and mechanical property evolution play the significant role for the steel/concrete structures strengthened with prestressed CFRP plates. In the present study, a wedge-extrusion bond anchorage system was applied to provide the reliable anchorage load-bearing capacity for CFRP plate. A new prestressed tension device was put forward to realize the coupling exposure of elevated temperature (20 °C, 60 °C and −20 to 30 °C), distilled water and sustained loading (20%, 40% and 60%). The mechanical and thermal properties of CFRP plate were conducted to obtain the long-term evolution exposed to the above environments. The mechanical analysis and tensile tests of anchorage system showed the tensile failure modes under the static and cyclic loads were the CFRP burst, and there was no debonding occurring in the anchor. The higher anchorage capacity was attributed to the uniform stress distribution of CFRP plate parallel to the greatest dimension of cross section in the anchor. The new prestressed tension device can realize the maximum prestressed level (∼70%) with an allowable prestressed loss (∼300 με). Meanwhile, the prestressed loss of CFRP plate exposed at the maximum temperature (60 °C) and longest time (90 days) was found to be ∼300 με. Immersed at higher temperature and prestressed level brought about an additional degradation rate of tensile strength (5%∼10%). The minimum strength retention of CFRP plate was found at the freeze-thaw exposure for 90 days. The long-term life prediction showed the residual tensile strength retentions of CFRP plates were more than 50% for the maximum prestressed level (60%) for the service life of 30 years in civil engineering structures.

Flexural behavior of RC beams strengthened with fully or partially prestressed near-surface mounted FRP strips: An experimental investigation

The strengthening technique based on prestressed near-surface mounted (NSM) strips made of fiber-reinforced polymers (FRPs) is well known as an effective means to restore or enhance the flexural performance of reinforced concrete (RC) beams, notably in bridges. To better understand the mechanical behavior of RC beams strengthened with prestressed NSM FRP strips, 18 beams were tested under either static loading (15 specimens) or fatigue loading (3 specimens), with the focus on the failure mode, load-displacement response, stiffness, ductility, and fatigue life. The effects of the prestress level and bond length of the FRP strips were studied as well. The test results show that the bond length plays a major role in the flexural performance of the strengthened beams, since the greater the bond length, the higher the ultimate load, stiffness, and ductility. A strengthening method based on the partial prestressing of NSM FRP strips is proposed as well to reduce the bond stresses around the extremities of the strips and to increase the ultimate load of the beams by delaying the failure due to end debonding. According to the proposed method, the strengthening strips are prestressed along most of their length, but the segments close to the end sections are nonprestressed, because they are bonded to the concrete after prestressing has been released. Compared to the beams with fully prestressed NSM-FRP strips, partially prestressed strips improve the bearing capacity, ductility, and fatigue life of the strengthened beams. The role of the length of the nonprestressed segments is also discussed. Finally, a few strength models available in the literature, aimed at predicting the bearing capacity at the onset of beam failure (because of the separation of the concrete cover at the extremities of the strengthening strips), are applied to the beams tested in this project to check the reliability of the models vs. the test results.

EXPERIMENTAL STUDIES OF SELF-STRESSED CONCRETE

The paper considers the test results self-stressed concrete.In previous studies, it was noted that if the required level of pre-stress of concrete is provided,that is, at the level of a certain effective value, which depends on the structural and strengthparameters of the structural element, then in the limit state it is possible to fully use the strengthproperties of steel, and the concrete core operates in a three-axis stress state under compression withextreme values of longitudinal and radial stress. Therefore, it is necessary to study differentcompositions of self-stressed concrete. To achieve this goal, five series of prisms with differentcompositions were manufactured and tested. According to the results of experimental studies, it wasfound that the first, fourth and fifth series of prisms corresponds to the self-stress brand Sp 1.2 andis self-stressed concrete the second series of prisms does not correspond to any of the self-stressbrands due to the high content of Portland cement, the third series of prisms corresponds to the selfstress brand Sp 0.6 and is non-shrinkable concrete. Since the selected concrete is planned to be usedas the core of a steel concrete column it is advisable to check the ph metric of the given components.At the next stage of the study, the cement of the selected components was tested for ph-metry.For this purpose, aqueous solutions of cement additives and suspensions of selected components weretested for pH and EMF. As a result, possible inhibition of metal corrosion is also confirmed by highpH values of the liquid phase at the level of 8.25 1 13.85 (which is significantly higher than neutralpH = 7) in the presence of both individual additives and cement suspensions containing additives.Therefore, the use of self-stressed concrete with these additives is advisable.

Flexural behaviour of seawater–sea sand concrete beams reinforced with GFRP bars: Effects of the reinforcement ratio, stirrup ratio, shear span ratio and prestress level

Glass fibre-reinforced polymer (GFRP) bar-reinforced seawater–sea sand concrete (SWSSC) has been widely regarded as a new structural material with great potential due to its environmental friendliness. To safely and economically utilize seawater and sea sand to cast GFRP bar-reinforced flexural members in coastal areas, an experimental study was conducted to investigate the flexural behaviour of 12 GFRP bar-reinforced SWSSC beams. The various considered parameters included the (1) reinforcement ratio, (2) stirrup ratio, (3) prestress level, and (4) shear span ratio. The experimental results for the GFRP bar-reinforced SWSSC beams were verified via a comparison to the calculation models of GB 50608-20 and ACI 440.1R-15 for FRP bar-reinforced normal concrete (NC) beams. The results indicated that the prestress level is the main factor controlling the cracking load of the GFRP bar-reinforced SWSSC beams, and the cracking load of prestressed beams was 81% higher than that of nonprestressed beams. The ultimate load of the GFRP bar-reinforced SWSSC beams was strongly correlated with the reinforcement and shear span ratios (the higher the reinforcement ratio or the lower the shear span ratio was, the higher the ultimate load). Under the influence of the reinforcement and stirrup ratios, the failure mode of the GFRP bar-reinforced SWSSC beams could be transformed from GFRP bar rupturing into concrete crushing. Moreover, the calculation model of ACI 440.1R-15 overestimated the ultimate flexural capacity of the nonprestressed beams, while the calculation model of GB 50608-20 yielded conservative estimation values for the nonprestressed specimens and overestimated values for the prestressed beams. To ensure safety, the calculation model of GB 50608-20 for FRP bar-reinforced NC beams can be adopted when designing nonprestressed GFRP bar-reinforced SWSSC beams. In contrast, a prediction model for prestressed GFRP bar-reinforced SWSSC beams should be further investigated.

Buckling of cylindrical concrete tanks and silos due to prestressing — nonlinear approach

The buckling of concrete cylindrical tanks and silos is associated mainly with prestressing, which influences the meridional critical force. Higher compression produces a lower meridional critical force. For three-dimensional structures subjected to biaxial or triaxial loading, the simplified methods of stability analysis proposed in Eurocode standard for concrete structures are inappropriate. The authors try to answer which procedure may be helpful for the assessment of buckling possibility, which results from prestressing of cylindrical structures. The numerical analyses are performed with the use of “Simulia Abaqus system”, which allows the nonlinear stability analysis adopting the plasticity-based damage material model and assuming initial imperfections. Two variants of load distribution (constant and hydrostatic external prestress) and two variants of wall-foundation connection are considered. The results are presented with the use of two parameters. The first one constitutes the ratio of lateral pressure to vertical pressure on the upper edge. The second one describes the ratio of current vertical force – corresponding to real load – to the initial test value of the iterative process. The obtained relationships of critical vertical force and the level of external prestress for cylindrical tank of height twice the diameter can be the guideline for engineers in designing process.

Long-term mechanical behaviors of uncracked concrete beams prestressed with external basalt fiber-reinforced polymer tendons

In this study, an experiment was conducted on four uncracked concrete beams prestressed with external basalt fiber-reinforced polymer (BFRP) tendons or stress-relieved strands subjected to 300-day sustained loads. The experimental variables included tendon type, prestress level (40 kN and 50 kN), and concrete strength grade (C40 and C60). The effects of these variables on the long-term deformation and prestress loss of the beams were discussed and analyzed. Based on an existing approach using an age-adjusted effective modulus method (AEMM), a modified model was proposed for predicting the long-term deformation and prestress loss of concrete beams prestressed with external BFRP tendons. The results indicated that the prestress level had significant effects on the long-term deformation and prestress loss. The concrete strength grade significantly affected the long-term deformation, but had no effect on the prestress loss. The stress-relieved strands exhibited a prestress loss that was 16% greater than that of the BFRP tendons. The theoretical results based on the modified model were consistent with the experimental results. The results of this study contribute to the design and prediction of the long-term behaviors of concrete beams prestressed with external BFRP tendons.

Fatigue behavior of RC slabs flexurally strengthened with prestressed NSM CFRP laminates

AbstractSome reinforced concrete (RC) structures requiring strengthening intervention are subjected to cyclic loads during their lifetime. To evaluate the effect of this kind of loading on the behavior of flexurally strengthened RC slabs with prestressed near‐surface mounted (NSM) carbon fiber reinforced polymer (CFRP) laminates, an experimental program formed by 10 RC slabs was carried out. Four specimens were submitted to monotonic loading and the remaining were submitted to 1 million cycles at a frequency of 1 Hz. Two levels of fatigue loading were applied and, for each one, three prestress levels for the CFRP were tested (0%, 20%, and 40%). Failure during the fatigue loading was occurred only in one specimen (at 752,000 cycles) with a maximum fatigue stress level of 92% (percentage of the maximum load carrying capacity of the equivalent slab tested up the failure under monotonic static loading). The other specimens, submitted to a maximum fatigue stress level between 46% and 82%, did not fail during the fatigue loading process. After 1 million cycles, the NSM strengthened slabs with 0%, 20%, and 40% of prestress presented an increase of 20%, 18%, and 25%, respectively in mid‐span deflection. In general, the strains in the CFRP laminates marginally increased during the fatigue loading. The results of the postfatigue monotonic tests until failure showed that the damage accumulation due the fatigue cycles neither affected the ultimate load capacity of the strengthened NSM CFRP slabs nor the failure mode in which the CFRP rupture.

Monitoring fish welfare using heart rate bio-loggers in farmed Atlantic salmon (Salmo salar L.): An insight into the surgical recovery

Atlantic salmon are one of most studied cultured species, still continuous fish welfare monitoring is a challenge during commercial farming operations. Although, mortality is the terminal indicator of fish welfare, but without further explanation, this parameter is of limited use. Fish welfare on-site can be monitored by using implantable DST milli-HRT bio-loggers that record heart rate, electrocardiography and temperature. These heart rate loggers gave us the opportunity to monitor fish welfare under common farm handlings in free-swimming farmed Atlantic salmon (~1 kg). Three different stress tests such as crowding (test 1), grading (test 2) & vaccination (test 3) were performed on three separate fish groups three weeks post-surgery. Heart rate and biochemical parameters (blood plasma and mucous) including cortisol were measured and compared in pre-stressed (T0), stressed (T1) and post-stressed (T48) fish. A modified loggers anchoring technique was used where two separate thin sutures were threaded at front hole of the logger and knot them through the skin/muscle for anchoring as it improved the fish welfare during surgery. Surgical wound showed complete skin/peritoneal apposition with regenerated skeletal muscle, fibrosis, lymphocyte-like cells and vascularization at the site three weeks post-surgery. Following surgery, heart rate (fH) was elevated (˃70 beats min−1) which stabilized 3 days post-surgery in tests 1 & 3. However, it took at least 10 days to stabilize fH in case of test 2. All three stress tests inflicted tachycardia suggesting aquaculture practices incur stress in farmed Atlantic salmon. Heart rate was raised at stress (range 62–78 beats min−1) as compared to pre-stress levels (range 44–48 beats min−1) that corresponds to 42–77% elevation in all three tests. Cortisol levels were upregulated following tests but only significantly different in test 3. This study reveals that physiological responses (heart rate) should be combined with histological evaluation of surgical healing before utilizing the heart rate (fH) data. Upon handling, fish should be given enough time (˃48 h) to stabilize fH levels before commencing to other tests/handlings. In conclusion, heart rate can be used for continuous fish welfare monitoring under farming conditions.

Progressive damage in pretensioned and reinforced concrete plates against repeated impacts

This study is planned to explore the performance of pretensioned concrete (PC) plates under multiple impacts. A detailed investigation has been carried out on pretensioned concrete plates (0.8 × 0.8 m2) against drop impact. The plates prepared using Mix-40 and Mix-60 grade concrete have been induced with two different levels of initial prestress, that is, 1/10 and 1/5 (i.e. level-1 and level-2) times the strength of the concrete. The PC plates have been impacted by a falling impactor (2382 N) dropped from 0.5 m height. The response of those plates has been obtained and compared with the reference RC plates. The post-impact performance of the damaged plates has been further discovered by subsequently dropping the impactor multiple times from the identical height. The FE simulations of the problem have been carried out using Johnson-Holmquist-2 and metal-plasticity constitutive models for concrete and steel, respectively. The models have been initially verified with the experimental results available in literature, and subsequently the simulations for drop impact have been carried out. The simulation results are also compared with the results of drop impact experimentations performed. In general, both the pretensioned and reinforced concrete have witnessed flexural cracks at the beginning, such that pretensioned concrete witnessed lesser cracks compared to reinforced concrete. As the number of drops increased, one major splitting crack developed only in pretensioned concrete, whereas the reinforced concrete exhibited additional punching cracks. For a given concrete grade, the pretensioned concrete level-2 witnessed the smallest damage, minimal cracks, and also minimal spalling followed by the pretensioned concrete level-1 and reinforced concrete. The reinforced concrete absorbed the minimal impact energy followed by the pretensioned concrete level-1 and level-2 under the multiple impacts. The FE simulations predicted the impact force and reaction within 11.9 and 9.9% variation, respectively, with the corresponding experimental results.

An alternative method to reduce process-induced deformation of CFRP by introducing prestresses

Process-induced deformation is an important limiting factor to the application of high performance composite structures. An alternative method to reduce process-induced deformation is proposed by introducing prestress to a single layer or part of the layers instead of all the applicable layers. In this method, the necessary prestress level that applied to the single layer was in the reasonable range. Two kinds of unsymmetric laminates are manufactured at varying prestress levels. The experimental results described that the curing deformation is changed rapidly with the growing prestress level and flipped after a certain prestress level. Moreover, there is a good linear relationship between prestress level and final curing deformation, which gives a convenient way to calculate the prestress level that can fully counteract the curing deformation. The numerical model to predict the curing deformation was built. A good agreement between the numerical and the experimental results shows the effectiveness of the numerical model. To predict the prestress level that can fully counteract the curing deformation, an analytical model is also proposed. Theoretically, the prestress method can fully counteract the curing deformation of the specimens, while the experimental results show that the prestressing layer reduces more than 80% of the curing deformation.

The in-plane expansion of fractured thermally pre-stressed glass panes: -An equivalent temperature difference model for engineering glass design

The present paper is concerned with deriving simplified design equations and charts for modelling in-plane expansion of fractured thermally pre-stressed soda-lime-silica glass panes using the method of equivalent temperature differences (ETD) together with a thermal expansion analogy for strains. The starting point is a theoretical method based on linear elastic fracture mechanics merged with approaches from stochastic geometry to predict the 2D-macro-scale fragmentation of glass. The approach is based on two influencing parameters of glass: (i) fragment particle size, δ, and (ii) fracture particle intensity, λ, which are related to the pre-stress induced strain energy density, UD, before fracture. Further Finite Element (FE) analysis of single cylindrical glass particles allow for establishing functional relations of the glass fragment particle dimensions, the pre-stress level and the resulting maximum in-plane deformation. Combining the two parts of two-parameter fracture pattern modelling and FE results on fragment expansion, formulas and engineering design charts for quantifying the in-plane expansion of thermally pre-stressed glass panes due to fracturing via an ETD approach is derived and provided within this paper. Two examples from engineering practice serve as demonstrators on how to use our ETD approach to compute the equivalent temperature difference and resulting internal forces as well as deformations. This approach serves furthermore as a basis to estimate secondary effects (such as fracture-expansion-induced deformations or stresses) on support structures or remaining parts of glass laminates in form of handy ETD load cases within analytical as well as FE analysis.

Durability of GFRP bars embedded in seawater sea-sand concrete: A coupling effect of prestress and immersion in seawater

Using prestressed glass fibre-reinforced polymer (GFRP) bars for seawater sea-sand concrete (SSC) structures in offshore engineering is of particular interest for improving the utilisation of GFRP and natural resources. However, limited information is available on the effects of prestressing on the durability of GFRP. Therefore, the durability of SSC-coated GFRP bars was investigated under the coupling effect of prestressing and immersion in seawater at room temperature, 40 °C, and 60 °C, with prestress levels set at 20% and 40% of the ultimate tensile strength (%fu) of GFRP. The tensile properties, interlaminar shear strength, transverse shear strength degradation after 0 d, 30 d, 60 d and 120 d, and the prestress loss of GFRP within 70 d were studied. The results showed that SSC wrapping was not conducive to the long-term performance of GFRP bars due to the alkaline environment, and the prestress further accelerated the tensile strength degradation, with the tensile strength decreasing almost to zero for the specimens (with 40% fu prestress level) immersed in seawater after 120 days at 40 °C and 60 °C. However, the interlaminar shear strength and transverse shear strength retention were 37.1% and 52.2% for 60 °C immersion under the same conditions, respectively. These findings suggest that the shear properties degenerated more slowly than the tensile properties of the prestressed GFRP bars embedded in SCC under seawater environment, which also evidences that the glass fibres were damaged more heavily than the epoxy vinyl resin under the prestressing.

Long-term behavior of CFRP plates under sustained loads

This paper studies the long-term behavior of carbon fiber–reinforced polymer (CFRP) plates under sustained loads. Two typical loading conditions, CFRP plate loading controlled by displacement constraints and force constraints, are studied. The first section investigates the prestress loss of the CFRP plate when it is loaded via displacement constraints, which serves as a prestressed system applied for prestressed structures. Short- and long-term measurements show that the prestress loss of CFRP is caused by material creep, temperature change, and CFRP and anchorage slippage. When the CFRP prestress level is 5.0%–12.3%, the average prestress loss after 42 days is 5.1%. The second section investigates the permanent deformation of the CFRP plate with curved anchorages caused by creep under a certain sustained load (i.e., controlled by force constraints), which serves as a suspension bar or cable applied for determinate structures. The creep strain-to-time relationship, creep rate, and residual strength were obtained. The creep strain-to-time relationship strongly depends on the stress level applied; the creep coefficient is less than 10.94% and the residual strength is greater than 80% of the initial tensile strength after 1000 h. The findings show the effectiveness and reliability of these two typical cases of CFRP plates under long-term sustained loads.

Experimental study on the cutting compensation of PTFE-coated fabric membrane structures

As a flexible structure, the membrane structure is tensioned to generate prestress and produce corresponding stiffness. The prestress level is controlled by scaling the cutting pattern according to the cutting compensation. In this paper, the cutting compensation of the PTFE-coated fabric membrane is taken as the research object, and different test schemes are carried out to simulate the actual stress of the membrane structure. The test scheme is divided into four stages according to the construction process and external loads condition of membrane structures: initial tension, load-bearing, creep, and elastic recovery. Then the combination schemes of different loading modes are conducted to explore the influence of loading factors on the cutting compensation. Through the simulation analysis of the construction process and stress relaxation of an HP-type example, the feasibility study of the cutting compensation under different test schemes is performed. Finally, a proper test scheme of cutting compensation is put forward, which provides the theoretical basis and scientific demonstration for guiding engineering practice.

Fatigue performance of CFRP reinforced pretensioned prestressed beams

This study presents an experimental investigation on the fatigue performance of CFRP reinforced pretensioned prestressed beams. A total of 10 specimens were designed and tested under monotonic or fatigue conditions. The investigated variables included the prestressing level, fatigue load range, and the absence or presence of novel additional aluminum alloy ribs (ARs) anchorage. Specimens using a high prestressing level or subjected to a low fatigue load range would have a reduced deflection and crack width development compared to those in their counterparts. In addition, the fatigue loading was found to cause cumulative bond damage of pretensioned FRP bar to concrete and finally led to an uncontrollable slippage failure of the beam. Such bond issue was demonstrated to have been avoided by using the ARs anchorage at beam ends. The applicability of three theoretical models proposed for steel reinforced beams to predicting the deflection of CFRP reinforced pretensioned prestressed beams under fatigue loading were evaluated, and CEB-FIP model was found to be the most suitable one to describe the deflection development of the tested specimens.

Theoretical and Numerical Study on the Three-Edge Bearing Capacity of Prestressed Concrete Cylinder Pipe

Prestressed Concrete Cylinder Pipe (PCCP) is a composite pipe structure commonly subjected to earth pressure, internal pressure, and ground loads. To confirm the bearing capacity of PCCP by using the in-direct design method, one of the most important experiments is the Three-Edge Bearing (TEB) test. A rational theoretical analysis method and Finite Element Analysis (FEA) are developed in this study because the TEB test is costly and difficult to conduct. The proposed theoretical analysis method and Finite Element (FE) method can be used to calculate the internal force, the displacement, the cracking load, and the bearing capacity of PCCP under the TEB load. In addition, a parametric study is carried out by using the validated theoretical analysis and FEA method. It is found that the concrete strength, the prestressing level, and the radius-to-thickness ratio of the steel cylinder affects the bearing capacity of PCCP under the TEB load. Furthermore, the proposed theoretical analysis method can be used to calculate the bearing capacity of other kinds of rigid pipes under the three-edge bearing load.