Prestressed Structures Research Articles

Study on the influence of guardrails on the mechanical properties of pre-stressed hollow plate beam bridges structure

In order to improve the design level of pre-stressed hollow slab bridge beams, the airport 1# bridge was taken as the research object to study on the influence of guardrails on the mechanical properties of pre-stressed hollow plate beam bridges. On the basis of conducting overall structural verification, a solid model was established to analyze the influence of bridge deck guardrails on the mechanical behavior of cast-in-place joints in hollow slab bridges. Research shows that the maximum deflection and the maximum bending moment internal force decreases by 40 % and 14.5 %, respectively when taking into account the stiffness of the guardrail. However, the maximum shear force of the hollow slab edge joint and middle joint increases by 75 % and 14.5 %, respectively. The maximum shear force increases by 35.62 % when the height of the guardrail increases from 0.5 m to 2 m. The results indicate that the influence of bridge deck guardrails on the shear performance of slab hinge joints should be considered during the preliminary design stage of such bridges. The research results can provide reference for such structures.

An adaptive suspended-dome structure: Static control methods based on minimum strain energy

The suspended-dome structure is a rigid-flexible and pre-stressed space structure composed of grid shells, cable and struts. It is widely used in large-span space structures for its efficient mechanical properties. The emergence of adaptive structure enables the structure to change its shape and stiffness according to the change of external environment, realizing light weight, high efficiency and intelligence of the structure. The concept of adaptivity is introduced into the traditional suspended-dome structure, presenting an Adaptive Suspended-Dome Structure (ASDS) where actuators replace the struts. A static control method utilizing a multi-population gradient genetic algorithm based on a strain energy optimization control model is proposed and developed in terms of control model research, control algorithm theory, and control effects. Specifically, an ASDS control optimization model is established with the adjustment values of the actuators as control variables and the strain energy of the upper grid shell as the objective function. The multi-population gradient genetic algorithm is improved to overcome the premature convergence problem of traditional genetic algorithms, further enhancing the search speed. A numerical simulation of a suspended-dome structure model with a span of 12 m, an aspect ratio of 10, and equipped with 16 actuator struts is featured. The overall strain energy of the controlled structure is reduced by about 40 % at maximum and the sum of squared displacements is reduced by nearly 41 % at maximum, which verifies the adaptability of ASDS to loads and the effectiveness of the control method. The suspended-dome structure of Jinan Olympic Sports Center Gymnasium is selected for data simulation to verify the effectiveness and application value of ASDS in engineering. The research methodology and conclusions provide valuable references for the design and control of adaptive structures.

A novel multi-step superposition model for the dispersion analysis of multiaxial prestressed plate-like structures

Understanding the dispersion characteristics of multi-axial prestressed plate-like structures is crucial for the engineering application of guided wave non-destructive testing. However, existing analytical and semi-analytical models neglect both constitutive and geometric nonlinearities induced by the prestress and require tedious theoretical derivation and coding, which may not achieve accurate predictions. To address these issues, a convenient model based on the multi-step superposition analysis was proposed to investigate the effects of an arbitrary multiaxial prestress on the dispersion characteristics of plate-like structures. The core idea of this model involves introducing an initial configuration to describe the static pre-deformation between undeformed and final states; then, the dynamic wave motion was superimposed on the initial pre-deformation for the eigenfrequency analysis. Additionally, the strain energy density of the hyperelastic material was implanted and set as the relevant variable between the two steps by the inheritance of the solution. This model significantly improved the accuracy compared to the conventional method, as validated through biaxial acoustoelastic experiments. Subsequently, the acoustoelastic responses of the multiaxial prestressed 6061-T6 aluminum plate were investigated. The results reveal that the non-uniform in-plane prestress leads to the coupling of guided wave modes propagating along non-principal directions. Furthermore, the effects induced by multiaxial prestress in the frequency bands with low dispersion could be decomposed into the sum of the effects induced by three uniaxial prestresses with a very small deviation. This work provides new insights into the acoustoelastic behavior and a theoretical basis to optimize the guided wave mode and frequency.

Reliability modeling of pre-stressed composite structures subject to interlayer slip failure under multi-axial random impact and vibration loads

A time-dependent reliability model for pre-stressed metal/polymer/metal composite structures subject to interlayer slip failure is developed in this study, allowing for predicting the probability of failure of the whole structure under multi-axial random multi-peak impact loads and transport vibration. A multi-Gaussian envelope model with uniform modulations is proposed to model random multi-peak impact loads, and the inverse sampling method is employed to model random transport vibration. An interlayer slip physics model is developed based on the contact surface friction mechanism under multi-axial vibration load and the stress-relaxation constitutive model. By implementing the interlayer slip physics model in the finite element method framework via the user-material routine, the geometry effect of the structure can be dealt with, and the reliabilities at an arbitrary location of the structure can be obtained. The proposed method is demonstrated using engineering examples. The results show that the proposed reliability assessment method provides a viable and systematical procedure of computing the time-dependent reliability of composite structures as a whole under multi-axial impact loads and vibrations.

Concrete and reliability of existing prestressed bridge structures

A large number of post-tensioned concrete bridges were built in the second half of the last century. They have often been insufficiently maintained during their lifetime (usually around 50 years). Nowadays, these structures exhibit significant deterioration, mainly due to leakages and also due to various other deficiencies such as a small concrete cover. Their load-bearing capacity needs to be verified. This paper focuses on estimating the load-bearing capacity calculation of existing post-tensioned concrete bridges. In the engineering practice, this is carried out using the partial factor method according to the currently valid standards (Czech standards ČSN and the Eurocodes), which often impose more stringent requirements than the original standards. The partial factor method then often leads to low load-bearing capacities. This study deals with the bridge for which a very low load-bearing capacity has been determined. For this reason, a comparative probabilistic analysis was performed, allowing for a better description of the uncertainties in the resistance and load effect variables. The probabilistic approach appears to be less conservative and yields a higher load-bearing capacity.

Effects of compressive stress on wave Love waves propagation in a piezoelectric semiconductor ZnO/Diamond: A screening effect

The issue of applied stress in hetero-structures is a persistent problem in materials science and technology. Significant efforts have been made from both numerical and experimental points of view to gain a better understanding of how to address this issue in various engineering industrial applications. In this paper, we numerically calculate the effects of compressive stress on Love waves propagation in a pre-stressed piezoelectric semiconductor ZnO/Diamond. The p-type semiconductor is explicitly taken into account, where the concentrations of holes and electrons are p0 = 1 × 1024m−3and n0 = 1 × 1023m−3, respectively. Numerical results show that the phase velocities of Love waves decrease with uniaxial stress equal to -100 MPa. In addition, this uniaxial compressive stress contributes to a decrease in the magnitude of the electric potential and the concentrations of holes and electrons. In the meantime, the “Screening effect” remains similar for both the unstressed and the pre-stressed structures.

Pre-stress evaluation for steel strand based on energy leakage ratio of ultrasonic guided wave

Accurate prediction of the effective pre-stress in steel strands is of great importance for service performance assessment in pre-stressed structures. In this study, a new parameter for characterizing the pre-stress in steel strand is proposed, named energy leakage ratio (αEL) of ultrasonic guided wave (UGW). Firstly, the propagation of UGW between wires of the strand was theoretically analyzed. Then, finite element (FE) models of steel strand were established and laboratory experiments were conducted to verify the effectiveness and accuracy of the proposed αEL-based pre-stress evaluation approach. Results show that αEL increases linearly with inter-wire contact width. αEL can be taken as a new parameter for strand pre-stress identification, it shows a high linear correlation with pre-stress level, no matter whether the excitation position is located in core or helical wire. In terms of numerical and experimental results, the αEL-based pre-stress evaluation errors are within 3% and 4% respectively. Compared with the acoustoelastic effect based and nonlinear ultrasonic based approaches, the αEL-based approach showed the advantage in pre-stress identification accuracy.

Effects of pretension loads on bending behaviors of CFRP tendons

Carbon fiber reinforced polymer (CFRP) tendons have a high potential to replace steel ones in bridge structures. However, concerns have been raised about their poor transverse properties, particularly when CFRP tendons experience combined tensile and bending loads, as in externally pre-stressed structures. This paper aims to understand and predict the bending behaviors of CFRP tendons with a pretension load. The experiment investigated the static bending behaviors of the CFRP tendon with pretension ratios ranging from 0 to 0.6. The pretension load stiffens the bending behavior of CFRP tendons, and a lower pretension ratio leads to an obvious increase in both the maximum bending load and energy dissipation. An analytical model was proposed to predict the load-deflection relationship and threshold pretension ratio of CFRP tendons under combined tensile and bending loads. The proposed model is in good agreement with the experimental results.

Common Defects of Prefabricated Prestressed Elements for Industrial Construction

This manuscript attempts to classify typical errors occurring during the design, production, and use of prefabricated and prestressed concrete girders and slabs manufactured in Poland for industrial buildings since the 1950s. Although the cases discussed concern Poland, most of them have a universal character, and as such are also found in other countries. The defects and errors are illustrated with examples and the causes of their occurrence are also discussed. A method of classifying flaws based on the period of their occurrence was proposed. Most of the examples discussed were encountered by the authors during their professional work. In most of the presented cases, repair was possible, enabling further safe operation. This paper shows how important it is to periodically check the technical condition of prestressed structures and how common and at the same time trivial mistakes may be made by designers and contractors of this type of structure, despite the experience of over 70 years of their mass use. The quality of modern prestressed structures is undoubtedly higher. Using the experience of previous generations, designers and contractors abandoned the less durable post-tensioned concrete lattice girders. Errors, if they appear, are most often at the stage of implementing new products or are the result of poor workmanship or disregard for unfavorable weather conditions.

Dynamic and uncertainty-based assessment of the progressive collapse probability of prestressed concrete frame structures with infill walls

Since progressive collapse usually has serious consequences, the problem of progressive collapse resistance has gradually become a topical issue in recent years. However, most of the existing studies have been conducted on common reinforced concrete (RC) structures. The methodologies used in the studies are also mostly static and deterministic. There is a lack of research that considers the dynamic effects and uncertainties of pre-stressed structures with infill walls. In this paper, the assessment of progressive collapse probability considering dynamic effect and uncertainties is performed for prestressed concrete frame with infill walls (IW-PC frame) structures. The finite element software OpenSEES is chosen as the analysis platform. By introducing uncertainties in material, geometry and load, five limit states and their quantitative indicators are identified. Based on the nonlinear incremental dynamic analysis (IDA) method, the vulnerability analysis of the IW-PC frame is performed under different working conditions. The vulnerability analysis indicates that the five levels of limit states can visually evaluate the degree of structural damage. Additionally, the resistance relationships of the four structural forms are as follows: IW-PC frame > reinforced concrete frame with infill walls (IW-RC frame) > prestressed concrete frame (PC frame) > RC frame. The load carrying capacity of the frames is significantly increased by the coupling effect of the infill walls and the prestressed strands. Moreover, the prestressed strands can reduce the probability of light and moderate damage, while infill walls have an excellent preventive effect on severe damage. The reliability of the four structures is evaluated using the Zhao-Ono moment method. The results indicate that IW-PC is the safest, followed by IW-RC, PC, and RC.

A PZT active sensing method for monitoring prestressing force based on the ultrasonic reflection coefficient

Prestress monitoring is key to ensuring the safety and longevity of post-tensioned prestressed structures. A new method of prestress monitoring, based on piezoceramic transducers, is proposed. Compared to traditional ultrasonic detection, we utilize piezoelectric (PZT) active sensing monitoring, eliminating the need for a specialized ultrasonic probe. First, a relationship model between the signal received energy and loading force is established based on the principle of ultrasonic reflection coefficient at the contact interface. On this basis, we overcome the low signal-to-noise ratio issue associated with the traditional method by employing the time reversal (TR) method. Next, the model parameters were fitted using experimental data. The values of the fitting evaluation metrics, SSE and RMSE, tend to be close to 0, while the R-squared value tends to be close to 1. This indicates the reliability of the model. Finally, the prestressing force validation tests are conducted through unloading tests. The average relative error between the measured and actual values across different paths ranges from 6.85% at the minimum to 15.61% at the maximum. Since the method is related to the proximity of the interface contact, it can be applied in other areas of civil engineering, such as assessing the adhesive strength of composite structures, crack development, and detecting axial stress.

A PZT-Based Smart Anchor Washer for Monitoring Prestressing Force Based on the Wavelet Packet Analysis Method

Prestressed steel strands in prestressed structures offset or reduce the tensile stress caused by external loads, making them the primary load-bearing components. Great concerns have been raised about prestress monitoring due to the growing use of structural health monitoring (SHM). Piezoceramic (PZT) active sensing methods are commonly used in this field. However, there appears to be a problem of “energy saturation” in the utilization of piezoceramic active sensing methods. In this study, a smart anchor washer with semi-cylinders was developed to alleviate the saturation problem. An intelligent monitoring system is formed by combining the upper and lower annular cylinders with two piezoelectric patches. The piezoelectric patch on the upper annular cylinder is used as an actuator to emit signals through the contact interface of the smart anchor washer, which are then received by the piezoelectric patch on the lower annular cylinder. Based on wavelet packet decomposition, we investigate the correlation between the energy of the received signal and the applied tension force. Finally, a prestressing force index is developed for monitoring prestressing force using Shannon entropy. It is found that the index decreases with the increase in tension. The proposed design and index are also sensitive to early monitoring of prestressing force and can be used to monitor the entire prestressing process of steel strands.

Seismic performance of confined prestressed hollow core wall panels part II: Numerical simulation and analysis

In Part I of this research, confined prestressed hollow core wall structures were proposed and experimental tests of 19 specimens were conducted to study its mechanical behaviors. In this part, a detailed finite element model was developed in ANSYS to provide a tool for further investigating the seismic behaviors of confined prestressed hollow core wall structures. Contact elements were applied to simulate the interaction between material interfaces. Techniques in ANSYS including coupling of degrees of freedom (CP) of overlapped nodes and deactivation of concrete elements (EKILL) were adopted, along with restart analysis (REST) to simulate nonlinear mechanical behaviors of the structural system. The developed modeling method was verified by the experimental test results and was shown to accurately predict the global and local behaviors such as failure modes and load bearing capacities of precast hollow core walls. Parametric analysis on shear span ratio, axial load ratio, rigidity of floor systems as well as strength of vertical wall-wall joints was conducted, and relevant design recommendations were provided for prestressed hollow core wall structures. Results show that for a ductile prestressed hollow core wall structure, the axial load ratio is recommended to be smaller than 0.06 and the story number less than 5. Influence of rigidity of floor systems requires further study with dynamic tests, but low-strength vertical wall-wall joint is highly recommended for this system. Two analytical mechanisms that are shear-flexural mechanism and truss mechanism were proposed for calculation of load bearing capacities. These two mechanisms provide good predictions for an upper bound and a lower bound for load bearing capacities of prestressed hollow core walls, respectively. From Part I and II of this research, the mechanical behaviors of prestressed hollow core wall structures are verified experimentally, numerically, and theoretically, and it is concluded that they can be used as a potential choice for low-rise buildings in rural areas.

A new PZT-enabled device for monitoring prestress loss in post-tensioned prestressed structures

ABSTRACT Anchorage performance monitoring plays an important role in ensuring the safety of prestressed structures. Over the past decades, traditional structural health monitoring (SHM) methods, such as vibration, magnetoelastic, and acoustoelastic methods, have been plagued by low sensitivity and high susceptibility to environmental and temperature interference. Lead-Zirconate-Titanate (PZT)-enabled active sensing method has proven its effectiveness in prestress monitoring. The main contribution of this paper is the development of a new device that utilises the relationship between energy transfer and contact stress at the interface. This device addresses the existing problem of signal saturation and offers higher sensitivity for practical implementation. First, the time reversal (TR) method was used to overcome the problem of low signal-to-noise ratio (SNR) in traditional methods. Based on this, the empirical mode decomposition (EMD) method was employed to process the acquired signals, thereby improving the stability of the data. A quantitative index for monitoring prestress loss was proposed by normalising the peak value of the reconstructed signals. Finally, several repeated experiments were conducted to verify the accuracy of the proposed method.

ДОСЛІДЖЕННЯ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ЗАЛІЗОБЕТОННОЇ МОНОЛІТНОЇ ПОПЕРЕДНЬО НАПРУЖЕНОЇ ПРОГОНОВОЇ БУДОВИ ШЛЯХОПРОВОДУ

Introduction. The experience of operation of reinforced concrete span structures of bridges from the time of their use shows the need for their constant improvement. Due to the use of pre-tensioning of reinforcement in reinforced concrete span structures of bridges, it was possible to increase the crack resistance of such structures and operational reliability. This is especially relevant when it is necessary to increase the length of spans of reinforced concrete span structures. Problems Statement. The use of monolithic prestressed span structures with tension on concrete (post-tensioned systems) is the newest for Ukraine. They have many advantages compared to prefabricated prestressed reinforced concrete. But it is necessary to solve a number of problems in the design and construction of such structures in order to achieve the efficiency of structures that would serve the designed term, using all their advantages. Therefore, the study of such structures, assessment of their stress-strain state will allow in the future to find solutions for their improvement, development of appropriate calculation recommendations, construction of such structures. Purpose. Study of the stress-strain state of the structure of the monolithic non-separated prestressed span structure of the overpass with tension on concrete (post-tensioned system) in the city of Kherson.

Selection of optimal vector-valued seismic intensity measures for fragility analysis of self-centering prestressed RC structures

Selection of optimal vector-valued seismic intensity measures for fragility analysis of self-centering prestressed RC structures

An enhanced ultrasonic method for monitoring and predicting stress loss in multi-layer structures via vibro-acoustic modulation

A sensitivity and reliability enhanced ultrasonic method for monitoring and predicting stress loss in pre-stressed multi-layer structures is developed in this study. The enhancement is based on the idea of leveraging the potential breathing effect of porous cushion materials in the structures to increase the sensitivity of the signal feature to stress loss, and is achieved via vibro-acoustic modulation by mixing a low-frequency pumping wave and an ultrasonic probing wave. A mathematical model correlating the stress state with the relative change in velocity of the coda portion of the received wave is derived. A pre-stressed five-layer mockup structure made of three materials with vastly different properties is manufactured and used for experimental investigation. Different stress states are simulated by bolting the structure with prescribed torques. Data are acquired for model calibration and verification. Independent data are further acquired to validate the prediction performance of the proposed method using the calibrated model. A thorough comparison between the proposed method and the conventional method is made. Results show that the proposed method offers improved accuracy, reliability, and sensitivity to stress change.

Research on Temperature Field of Controllable Bonded Prestressed Structure Based on Electrothermal Method.

Controllable bonded prestress represents an innovative advancement stemming from retard-bonded prestress systems, distinguished by its intrinsic controllability in bonding. The controllable bonded binder can be artificially heated and cured rapidly through DC heating after the completion of prestressed tension, allowing for enhanced control over the process. FLUENT simulates controllable bonded prestressed structure's temperature field, yielding a 1.73% max error validated against measured data. Based on the theory of heat transfer, the maximum error of the calculated temperature field of the controllable bonded test beam under DC heating using the Stehfest numerical algorithm is 1.28%, which exhibits a strong alignment with both simulated and measured results. The parameter analysis identifies current, binder thickness, and steel-strand diameter as key temperature distribution influencers. The relationship between the current and heating time follows a quadratic inverse pattern. Increasing the heating current can significantly reduce the duration of heating. Under identical heating conditions, the temperature of the controllable binder is directly proportional to its thickness. A higher thickness results in a higher temperature. Additionally, larger diameters of steel-stranded wire lead to a lower heating efficiency.

Impedance-based Identification of Strand Looseness in Multi-strand Anchorage under Temperature Effects

In this study, strand looseness in a multi-strand anchorage is identified using measured impedance features of the PZT (Lead zirconate titanate) interface array under temperature effects. Firstly, a PZT-interface method for impedance monitoring in prestressed structures is briefly described. Secondly, a finite element model of multi-strand anchorage equipped with a PZT array is established to analyze the effects of prestress loss and temperature changes in impedance features. Thirdly, variations in simulated impedance signals are quantified using statistical damage metrics for damage detection in the analyzed structure. Last, a test on real-scale multi-strand anchorage is conducted to measure impedance signatures of the PZT interface under temperature fluctuation and prestress loss. The measured signals are then quantified using damage metrics for prestress looseness monitoring. The result reveals that environmental changes cause significant changes in PZT interfaces’ impedance features and affect strand looseness monitoring results.

Study on vibration characteristics of fine breccia soil subgrade reinforced with a new prestressed structure under train cyclic loading

Train cyclic loading generally results in significant dynamic responses of the breccia soil subgrade, resulting in a series of subgrade problems. A new prestressed reinforcement structure (PRS) is proposed to reinforce subgrade structures. However, characteristics of the prestressed subgrade under dynamic loading have not been investigated. This study investigates the vibration characteristics of a new prestressed subgrade structure under train cyclic loading. The acceleration responses of the subgrade surface under different train axle loads and prestress levels are measured and discussed by developing a 1:5 scale dynamic model test on a prestressed fine breccia soil subgrade structure. Subsequently, a three-dimensional dynamic finite element model of the prestressed subgrade is constructed for an in-depth analysis of the internal acceleration of the prestressed subgrade. The results showed that a periodic acceleration response of the subgrade should be observed, and its mean crest and mean trough are used to characterize the long-term vibration degree of the subgrade. The peak vertical acceleration of the subgrade is significantly affected by the prestress level, and the dynamic response of the subgrade around the lateral pressure plate (LPP) is reduced more obviously by the prestress than that of the subgrade’s inner region. The peak vertical acceleration at the subgrade shoulder presents linear increase and exponential attenuation with the rise in the train axle load and prestress level, respectively. In addition, an empirical model describing the relationships among the peak acceleration, train axle load, and prestress is proposed. The vertical dynamic displacement and dynamic stress decrease with the increase of the prestress. The average elastic deformation and peak dynamic stress of the subgrade under a prestress level of 100 kPa are found to be 95.8% and 87.22–90.07% of that with the absence of prestress, respectively. The vertical vibration of the prestressed subgrade structure can be reduced by taking measures such as adjusting the prestress magnitude and increasing the subgrade slope ratio, thereby achieving an effective prestress reinforcement effect.