Prestressed Concrete Slab Research Articles

Study on Bending Performance of High-Ductility Composite Slab Floor with Composite Ribs

In order to solve the problems of high production cost and complex control of the inverted arch of an unsupported prestressed concrete composite slab, a flange truss high-ductility concrete composite slab floor is proposed to change the structure and pouring material to meet the requirements of no support during construction. The crack distribution and bending performance of the flange truss high-ductile concrete composite slab floor (CRHDCS) under different structures are clarified through the test and numerical analysis of four different rib plate structure floors. According to the analysis results, the calculation formulas of the cracking moment and short-term stiffness before cracking are modified, and the equivalent short-term stiffness formula of a single web member of the “V” truss to this kind of bottom plate is established. The results show that, unlike the short-term stiffness-change law of typical concrete composite slabs after cracking, the short-term stiffness of the designed bottom plate in this paper includes a short-term increase stage. The numerical simulation results are the same as the experimental ones; the maximum error is 10%. The maximum errors between the modified cracking moment and the short-term stiffness calculation formula are 6% and 8%, respectively. The influence rates of removing flange plate, truss-inverted binding, and adding rib plate on the cracking bending moment of foundation structure are −81.5%, 11.0%, and 22.2% respectively, and the influence rates on short-term stiffness are −87.6%, −1.5%, and 37.5% respectively.

Second life for pre-stressed concrete hollow core slabs – time to act

The construction sector contributes to approximately 50% of global carbon dioxide emissions and natural resource consumption, along with generating a significant amount of landfill waste. Thus, there is an urgent need to actively involve our professional community in fostering real environmental change. Embracing circularity in construction presents significant opportunities for decarbonization, particularly in the context of prestressed precast concrete structures. This paper explores the potential for reusing prestressed hollow core slabs already built-in, as well as the principles of designing for future dismantling and reassembly. A second life for hollow core slabs is possible, as has already been confirmed by practical realisations in the Netherlands, Sweden and Finland.

Evaluation of Maximum Shear Strength of Prestressed Concrete (PSC) Hollow Core Slab (HCS)

In this study, four-point load tests were conducted to evaluate the shear performance of factory-produced precast prestressed concrete hollow core slabs (HCS) assembled on-site. The test specimens were fabricated using compression molding and comprised six samples, with variables being the presence or absence of topping concrete and the shear reinforcement. According to the experimental variables, experiments were conducted using simple support beams to evaluate the shear performance and ultimate strength of HCSs. The results showed that HCSs, regardless of whether they included topping concrete or not, exhibited average values of shear strength more than 10% higher than the factored shear strength specified by concrete structure standards, confirming that these materials satisfy existing design standards. According to current standards, the overall reinforcement length should be increased to meet the minimum shear rebar placement requirements. However, the nominal shear strength of PS concrete hollow slabs exceeded the hollow design, with the ratio of experimental results ranging from 1.26 to 1.87 on average, satisfying the required performance.

Behavior of unbonded prestressed concrete slabs subjected to low-velocity impact loading

This study examines the structural performance of unbonded prestressed concrete slabs subjected to low-velocity impact loading. The experiment involved impact loading tests on reinforced concrete (RC) slabs and prestressed concrete (PC) slabs using a drop hammer impact test system. The prestressing force was monitored using intelligent steel strands before the PC slabs were subjected to impact testing. The failure mode, impact force, and displacement response of the specimens were recorded. The study investigated the effects of impact energy, prestress level, and boundary conditions on dynamic damage and response of the specimens. Results showed that RC slabs and unidirectional simply supported PC (PCU) slabs exhibited typical flexural failure modes, while bidirectional supported PC (PCB) slabs experienced a combination of flexural and shear failure modes. Furthermore, PC slabs demonstrated superior impact resistance. A finite element (FE) model was developed to predict the impact behavior of RC and PC slabs and was validated using the failure modes, impact forces, and displacements obtained from the experimental results. The impact process and energy dissipation were also analyzed using the FE model.

Dynamic response of bidirectional bonded prestressed concrete slabs subject to low velocity impact: Impact energy and prestress degree

Bidirectional bonded prestressed concrete (PS) structures have been widely used in energy engineering. However, the systematic studies on the failure mechanism and dynamic response of this structure suffering from impact load are still inadequate. This paper has carried out nine drop hammer impact tests and corresponding numerical models. The results reveal that overall flexure and local punching co-occur in the bidirectional PS slabs under the impact, with the local punching failure as the failure mode. The dynamic response of the slab includes: inertia loading stage, load holding stage and rebound unloading stage. Due to the influence of the membrane force enhancing effect and specimen damage weakening effect, the impact force in the load holding stage may present three conditions. The compressive prestress applied to concrete can provide in-plane constraint and limit the appearance and development of cracks, resulting in decreasing the plastic damage of the specimen and the drop hammer displacement, while improving the bearing capacity and stiffness of the specimen. For impact energy of 5.48 kJ, when the prestress degree increase from 0% to 11.6%, the equivalent impact force increases 95%, the peak drop hammer displacement, equivalent spalling and scabbing diameter decrease 40%, 22.6% and 8.6%, respectively.

Prestressed hollow-core slabs performance at high temperatures- A review

Pre-stressed concrete hollow core slabs (HCS) are now progressively usedin commercial, industrial, and residential buildings due to their sustainability,affordability, and adaptability. The performance of HCS units subjected to fire isparticularly difficult and is attributable to their unusual cross-section, whichfeatures voids. Numerous investigations were executed on HCS at hightemperatures concerning the crucial temperature and failure mechanisms of bothconcrete and prestressing steel. Fire performance is influenced by a number ofvariables, including support condition, concrete aggregate type, slab thickness, fireinsulation and cover thickness for reinforcement, spalling accessibility, void coresand size, and firing methodology. While a number of these variables have receivedextensive research, some have been noted as potential contributory reasons forfailure, while others have received relatively little attention. This paper summarisesnumerous experimental, numerical, and analytical studies about the attitude of HCSvulnerable to fire in addition the building standards limitations to provide a valuablereference for future researchers

Multi-objective green design model for prestressed concrete slabs in long-span buildings

ABSTRACT Prestressed concrete (PC) slab using tendons is one of the most frequently used slab systems in the construction of buildings with long-span slabs. To simultaneously minimize the construction cost and the environmental impact, a green design model for PC slabs in long-span structures is necessary. In this paper, a multi-objective green design model for prestressed concrete slabs (MGDPCS) was developed to minimize both CO2 emissions and the construction costs of PC slabs. MGDPCS provides the optimized PC slab thickness, diameter and yield strength of the rebar, size and yield strength of the tendon using the Non-dominated Sorting Genetic Algorithm (NSGA-II) for the input PC slab size and load. Furthermore, the effects of changes in the long- and short-side of span and tendons of PC slabs on construction costs and environmental impact are analyzed using the proposed model. Accordingly, we developed two indicators, that is, the environmental and economic scores and the eco-friendly coefficient, to evaluate the performance of the practical green designs using MGDPCS. To verify the applicability of MGDPCS, the model was applied used to analyze the designs of PC slabs in an actual six-story industrial building with a slab span of 10 m × 10 m. The results showed that the optimal designs obtained from MGDPCS outperformed existing slab designs for buildings by 8.12% and 13.62% based on the reductions in CO2 emissions and costs, respectively.

Experiment Study on Residual Flexural Capacity of Prestressed Concrete Deck Slab Under Fatigue Loading

The deterioration of a concrete deck damaged by repeated traffic loads could directly affect its performance. Two full-scale specimens modified from a precast, prestressed concrete (PC) deck slab on a 12.65-m-wide composite bridge with twin I-girders spaced at 7.05 m were tested to study the degradation of mechanical performance of the slabs under fatigue loading. The depth of the slabs was 30 cm at the midspan and 40 cm at the two supports. One specimen was 3.0 m wide and conducted a three-stage fatigue loading before the static destructive loading, the other was 1.5 m wide and performed a static load test to failure only. The ultimate strength of specimens was obtained, and the variation of deflection, reinforcing strain, and cracks were discussed. The test results showed that the failure mode of the PC slabs was flexure subjected to static load. Fatigue loading significantly degenerated the stiffness of the slab, and the maximum stiffness reduction was about 35.2 %. The distribution scale of cracks was expanded about twice as much at the same load level under the fatigue loading. It could be deduced that the fatigue loading could enlarge the crack width, by comparing the measured results of concrete crack widths of the two specimens, however, the design provisions did not take this into account. A comparison between the transformed flexural capacity of the two specimens showed the residual flexural capacity was reduced by 7.8 %. Moreover, an analysis model was developed to predict the residual flexural capacity of PC slabs.

Damage Detection in Prestressed Concrete Slabs Using Wavelet Analysis of Vibration Responses in the Time Domain

Detection of damages in structures during their service life is of vital importance and under attention of researchers. In this paper, it is attempted to identify damages in prestressed concrete slabs using vibration responses obtained from modal testing in the time domain. For this purpose, first some damage scenarios with various geometric shapes and at different locations of numerical models, corresponding to a prestressed concrete slab, were created. Next, the impact hammer force in the modal test was simulated and the accelerations time histories at different degrees of freedom corresponding to the numerical models per two states of damaged and undamaged structure were selected as the inputs for a number of damage indices to identify the damage locations. Some of these damage scenarios have been located at the middle of prestressed concrete slabs and some at the corners. The proposed damage indices in this research are obtained based on the area under the diagram of acceleration time histories, maximum and also the area under diagram of detail coefficients of the wavelet transform using the three wavelet families of Daubechies, Biorthogonal and Reverse Biorthogonal. The results showed that using damage index obtained from the area under diagram of detail coefficients of wavelet transform with the mother wavelet db2 could detect the damage scenarios at the middle and corners of the slab with a well precision. Furthermore, the damage scenarios at the corners of numerical models could be detected properly by using the mother wavelet rbio2.2 in the proposed damage index.

Numerical study on the ballistic performance of prestressed concrete slabs subjected to hard missile impact

Prestressed concrete (PC) structure has been extensively used in civil engineering like nuclear and protective structures. But systematic studies on its ballistic performance are still inadequate, hindering its ballistic design and applications. In this paper, the ballistic performance of PC slabs subjected to hard missile impact is numerically investigated through finite element (FE) modeling. The method to introduce prestressing force is specially investigated and the feasibility of the established models is verified against existing experimental results. The models are then employed to conduct a comparative study between PC and reinforced concrete (RC) slabs, in which the influences of the prestress and prestressing bars are decoupled. The variations of concrete tensile strain and energy dissipation capacities of PC slabs with different failure modes are analyzed to understand the mechanism of the ballistic resistance. It is revealed that the prestress is the main reason for the enhancement of ballistic resistance of PC slabs, while the increase of reinforcement ratio due to prestressing bars is the secondary reason. It is also proved that the confinement effect applied to the concrete is the major reason for the increase in ballistic resistance. Based on the mechanism, by using mechanical and regression analysis, a semi-empirical formula for the critical perforation velocity of the PC slabs is proposed, which gives better predictions compared to existing formulas. The proposed formula also allows a straightforward parametric study, the results of which could be used for simplified estimations in the ballistic design of PC slabs.

Distinguished punching shear behaviour of unbonded post-tensioned concrete slab – CFT column vs reinforced concrete slab – CFT column connections

This article evaluates and compares the punching shear behaviour of unbonded prestressed concrete (UPC) slab - concrete-filled steel tube (CFT) column connections/joints with that of reinforced concrete (RC) slab connection – CFT column connections. The experimental program was carried out on five large-sized samples, including three UPC slab - CFT column samples and two RC slab - CFT column samples. Steel plate connection details were utilised to increase the bond between the concrete slab and the CFT column. The experimental results showed that the prestressing tendons significantly increased the pre and post-cracking stiffness of the slab-column connections, thereby, greatly reducing the deflection of the UPC slab - CFT column samples than that of the RC slab - CFT column samples, especially during the serviceability phase (by up to 58%). However, the use of tendons resulted in a significant decrease in the ductility and energy absorption index of the UPC slab - CFT column samples compared to that of the RC slab - CFT column samples (by up to 44% and 41%, respectively). Using prestressing tendons slightly increased the punching shear capacity, and significantly reduced the strain of the connection details such as the vertical ribs and the horizontal bearing plate. At the same time, the tendons helped greatly reduce the strain of the longitudinal rebars in the UPC slabs.
 Keywords: Unbonded post-tensioned concrete (UPC); connection/joint; CFT column; flat slab; connection details; punching shear; experiment.

Experimental and numerical study on seismic behavior of prestressed concrete composite shear wall

In this study, a novel type of prestressed concrete composite shear wall is proposed. The proposed shear wall consists of two precast prestressed concrete slabs with steel trusses and in-filled concrete. The thickness of this precast slab was reduced to 35 mm, and the weight was correspondingly reduced. The prestressed steel in the precast slab acted as horizontal steel in the composite shear wall, thereby improving the shear resistance of the composite shear wall. Four prestressed concrete composite shear walls and one cast-in-situ shear wall were tested under cyclic loading to study the seismic behavior. The seismic behaviors, including failure modes, hysteretic curves, stiffness degradation, and energy dissipation, are analyzed and compared. The effect of the type of boundary element on the composite shear wall was also examined. The test results revealed that the composite shear walls had almost the same seismic performance as the cast-in-situ shear wall. Compared with the cast-in-situ shear wall, the energy dissipation capacity of the composite shear wall was enhanced. The horizontal prestressed steel in the composite shear wall reduced diagonal crack propagation. Among the prestressed concrete composite shear walls, specimen PW1, whose boundary elements were completely cast-in-situ, exhibited better seismic performance. To investigate the effects of the axial compression ratio and initial prestress level on the seismic performance of the composite shear wall, a finite element model was established for the cast-in-situ shear wall and prestressed concrete composite shear wall. The analysis results indicated that under a high axial compression ratio, the bearing capacity and ductility of the composite shear wall were higher than those of the cast-in-situ shear wall. Under a higher axial compression ratio, the ductility of the composite shear wall improved as the initial prestress increased. Above all, the proposed prestressed concrete composite shear wall is suitable for practical projects.

Numerical simulation on the dynamic response of bonded unidirectional prestressed concrete slabs subjected to low-velocity impact

In this study, the dynamic response of bonded unidirectional prestressed concrete slabs subjected to low-velocity drop hammer impact is numerically investigated by using finite element software LS-DYNA. The feasibility of the finite element models is verified using experimental results available in the literature. With the verified FE models, the dynamic response of bonded unidirectional prestressed concrete slabs is analyzed in terms of the impact force, displacement, energy dissipation, and failure modes by changing the parameters of prestressing degree, drop hammer weight, and impact velocity. The results show that the response of the prestressed concrete slab under the impact of the drop hammer can be divided into five stages, which are the initial impact stage, the inertial loading stage, the inertial unloading stage, the secondary loading stage, and the impact unloading stage. The deformations of the slabs consist of global deformation and local deformation. Impact kinetic energy is the key parameter that determines the dynamic response of the specimen, which could be used to derive the calculation formula of the specimen. With the increase of the impact kinetic energy, the main response of the specimen is changed from global response to local response. The concrete dissipates most of the impact energy under the impact of the drop hammer, which is above 67%, and the dissipation effect of the prestress bars is neglectable, which is less than 5%. The increase of unidirectional prestress can improve the impact stiffness and the penetration resistance of the slabs, and increase the proportion of local response in the specimen.

EVALUATION OF PUNCHING SHEAR STRENGTH OF PRESTRESSED CONCRETE SLABS

PC床版はRC床版に比較して高いせん断耐力を有することが知られているが，設計に用いることができる押抜きせん断強度の算定式は現在の国内基準に反映されていない．また，軽量骨材を用いたPC床版に関しては，プレストレスの効果について具体的に検討された研究事例が少ない．そこで本研究では，PC床版に関する押抜きせん断実験の結果をもとに，既存算定式の適用性について検討した．次に，PC床版の押抜きせん断破壊挙動に与える影響要因を明らかにすることを目的に，床版内部の応力状態を確認できるFEM解析を用いて検討した．これらの結果より，普通骨材および軽量骨材を用いたPC床版の押抜きせん断強度算定式を，土木学会のPCはり式と同様の形式により導いた．

Punching Shear Capacity of Prestressed Concrete Slabs Made of Lightweight Concrete Mixed with Short Fibers

The purpose of this study is to examine means of creating light and very strong prestressed concrete slabs made of lightweight aggregate concrete mixed with short fibers. The experiments reported in this paper demonstrated that the ratio of short fibers in the mix must be kept to 0.5 vol% or less, in order to obtain the same strength as that demonstrated by lightweight aggregate concrete designed to a standard strength of 50 N/mm2. In addition, the results of load testing various slabs confirmed that lightweight PC slabs mixed with 0.5 vol% of short PVA fibers had the same punching shear capacity as PC slabs made from normal weight concrete. The results led to the conclusion that the increase in the shear capacity of lightweight PC slabs mixed with short fibers was caused by the suppression of the progress of cracks in the RC direction and an accompanying tide arch formation in the PC direction.This paper is the English translation of the authors’ previous work [Kitano, Y., Ito, H. and Suzuki, S., (2020). “Study on lightweight and high strength prestressed concrete slab by using lightweight concrete mixed with short fibers.” Journal of Japan Society of Civil Engineers, Ser. E2 (Materials and Concrete Structures), 76(3), 239-254. (in Japanese)].

A strength and deformation model for prestressed lightweight concrete slabs under two-way shear

Prestressed concrete slabs (PCS) are one of the top choices in many applications, which is due to their significantly improved performance compared to conventional normal-weight concrete slabs (NCS). However, very limited models exist for the two-way shear behavior of PCS, in particular, lightweight ones (PLCS). In this study, a two-way shear mechanical behavior model is developed for PCS, that accounts for all effective parameters and capable of predicting both strength and deformation. An experimental database of PCS was compiled from the literature with emphasis on lightweight concrete. A mechanical model developed by the author for lightweight concrete slabs (LCS) was adapted and modified in order to include the effect of prestressing in terms of the following components: (1) the membrane compression stress; (2) the prestressing eccentricity; and (3) the prestressing vertical component. The extended model was used to predict the behavior of PLCS and prestressed normal-weight concrete slabs (PNCS), which was compared to that using selected design codes and models. The model predicted the rotation accurately and consistently compared to the experimentally measured rotation. The strength predicted using the proposed model was better than existing ones concerning experimentally measured strength, yet it was found to be reasonably safe. However, conclusions are limited to the experimental database.

Static and dynamic camber behavior of uniaxial and biaxial post-tensioned fully, limited, and partially unbonded pre-stressed concrete slab

Pre-stressed members in various structures are gaining popularity among engineers in many parts of the world because pre-stressed strands offer better stability, serviceability, economy, aesthetics, and structural efficiency. The profile of the strand greatly influences the tensile strength of concrete. The force exerted by the strand on the concrete counterbalances internal tensile forces. A construction engineer’s principal goal is to build an excellent strength structure without sacrificing agility and cost-effectiveness. This study’s main objective is to model numerically different pre-stressed concrete slabs to understand and predict the upward deflection (camber) behavior of uniaxial and biaxial pre-stressing of unbonded concrete strands in the static and dynamic behavior and the maximum moments of pre-stressed concrete members by considering previous experimental work as a benchmark for validation. Particular emphasis was placed on the unbonded post-tensioned pre-stressed slab parameters that influence the mid-span upward deflections and internal moments in linear and nonlinear crack analysis. This study also investigated the effect of strand profiles, strand areas, number of strands, strand eccentricities, loading types, and level. It looked into full and partial pre-stressing with uniaxial and biaxial pre-stressing directions. The numerical dynamic characteristics in terms of members’ natural frequency with such parameters were found. This study used a finite element numerical model for the analysis of linear and cracked sections and concluded that the upward deflection (camber) of uniaxial and biaxial one-way and two-way partially unbounded pre-stressed concrete slabs is affected by the strand’s profile, area, and number and eccentricity; the loading type and value; and the pre-stressing level in static and dynamic analyses.

3D Nonlinear Analysis of Precast Prestressed Hollow Core Slab

In the last decades, precast prestressed hollow core slabs have gradually increased their market presence in many countries due to their excellent structural performance at room temperature. Longitudinal voids through the one way prestressed (or reinforced) concrete slabs are very important for reducing the self-weight of the structure. Although the hollow core precast concrete is larger than on-site placement concrete, when viewing the entire construction of the building as a whole, the use of hollow core precast concrete contributes more to the reduction of energy consumption than half-precast concrete or on-site placement concrete. Precast prestressed hollow core slabs are among to the more advanced structural floor systems for all kinds of buildings. This paper presents results from nonlinear numerical analysis of precast prestressed concrete hollow core slabs with dimensions 13,9m length, 1,19m width and 300mm thickness. Material properties obtained from testing of concrete (concrete cube strength) and 7 wire pre-stressing strands (yield strength) were used as input data for nonlinear simulation. The ATENA 3D FEM software was used for nonlinear numerical modelling. The results from numerical are compared with data from experimental investigation of a total 7 hollow core slabs.

Static loading test and analysis of prestressed concrete bridge

In order to test the structural performance for the bridge of Linxi 9th road project, the static test of precast prestressed concrete bridge hollow slab was carried out by four stage static loading method. Under the condition of elastic working, the flexural bearing capacity, crack propagation and relative residual displacement of the main control sections of the hollow slab are mainly investigated. The results of static loading test show that, when the efficiency of static loading test is 97%, the structural calibration coefficient, residual displacement of main measuring points and crack propagation meet the requirements.

Characterization of damage on precast pre-stressed concrete composite slabs under static loading based on acoustic emission parameters

Precast pre-stressed concrete composite slabs have been widely used in recent years owing to excellent mechanical properties and cost savings. The low accuracy of visual observation and the complexity of actual measurement make the determination of the precise information of structural safety difficult. This article presents an acoustic emission study on the precast pre-stressed concrete composite slab under static loading. First, the correlation between acoustic emission hits (or energy) and crack width (or deflection) was obtained and compared in detail. Second, the stiffness of this composite slab was predicted using the acoustic emission amplitude. Third, a novel analysis method for damage fracture classification is proposed, which is based on the traditional parameter and fuzzy C-means clustering. This method can be used to determine visual crack emerging, rebar yielding, and eventual failure mode by an acoustic emission parametric analysis without involving visual inspection or mechanical measurement. It can be effectively used for fracture characterization and health monitoring of composite slabs.